全文获取类型
收费全文 | 3655篇 |
免费 | 372篇 |
出版年
2021年 | 47篇 |
2019年 | 36篇 |
2018年 | 48篇 |
2017年 | 41篇 |
2016年 | 75篇 |
2015年 | 111篇 |
2014年 | 123篇 |
2013年 | 164篇 |
2012年 | 220篇 |
2011年 | 214篇 |
2010年 | 171篇 |
2009年 | 112篇 |
2008年 | 203篇 |
2007年 | 172篇 |
2006年 | 173篇 |
2005年 | 182篇 |
2004年 | 196篇 |
2003年 | 181篇 |
2002年 | 146篇 |
2001年 | 75篇 |
2000年 | 61篇 |
1999年 | 69篇 |
1998年 | 52篇 |
1997年 | 38篇 |
1996年 | 40篇 |
1995年 | 52篇 |
1994年 | 43篇 |
1993年 | 36篇 |
1992年 | 54篇 |
1991年 | 40篇 |
1990年 | 51篇 |
1989年 | 48篇 |
1988年 | 30篇 |
1987年 | 26篇 |
1986年 | 40篇 |
1985年 | 29篇 |
1984年 | 44篇 |
1983年 | 35篇 |
1982年 | 41篇 |
1981年 | 26篇 |
1980年 | 31篇 |
1979年 | 37篇 |
1978年 | 33篇 |
1977年 | 35篇 |
1976年 | 25篇 |
1975年 | 39篇 |
1974年 | 27篇 |
1973年 | 32篇 |
1972年 | 30篇 |
1971年 | 19篇 |
排序方式: 共有4027条查询结果,搜索用时 31 毫秒
971.
Simeon Bowers Gary D. Probst Anh P. Truong Roy K. Hom Andrei W. Konradi Hing L. Sham Albert W. Garofalo Karina Wong Erich Goldbach Kevin P. Quinn John-Michael Sauer William Wallace Lan Nguyen Susanna S. Hemphill Michael P. Bova Guriqbal S. Basi 《Bioorganic & medicinal chemistry letters》2009,19(24):6952-6956
The structural modification of a series of [3.3.1] bicyclic sulfonamide based γ-secretase inhibitors is described. Appropriate substitution on the bicyclic scaffold provides a significant increase in the metabolic stability of the compounds resulting in an improved in vivo metabolic profile. 相似文献
972.
Daniel V. Bax Ursula R. Rodgers Marcela M. M. Bilek Anthony S. Weiss 《The Journal of biological chemistry》2009,284(42):28616-28623
Elastin fibers are predominantly composed of the secreted monomer tropoelastin. This protein assembly confers elasticity to all vertebrate elastic tissues including arteries, lung, skin, vocal folds, and elastic cartilage. In this study we examined the mechanism of cell interactions with recombinant human tropoelastin. Cell adhesion to human tropoelastin was divalent cation-dependent, and the inhibitory anti-integrin αVβ3 antibody LM609 inhibited cell spreading on tropoelastin, identifying integrin αVβ3 as the major fibroblast cell surface receptor for human tropoelastin. Cell adhesion was unaffected by lactose and heparin sulfate, indicating that the elastin-binding protein and cell surface glycosaminoglycans are not involved. The C-terminal GRKRK motif of tropoelastin can bind to cells in a divalent cation-dependent manner, identifying this as an integrin binding motif required for cell adhesion.Cellular interactions with extracellular matrix proteins are vital for cell survival and tissue maintenance. The attachment of cells to their extracellular matrix (ECM)3 is often mediated by cell surface integrins. As such, integrins are involved in many biological functions such cell migration and proliferation, tissue organization, wound repair, development, and host immune responses. In addition to roles under normal physiological conditions, integrins are involved in the pathogenesis of diseases such as arthritis, cardiovascular disease, inflammation, microbial and parasitic infection, and cancer. Integrins are a family of heterodimeric transmembrane receptors containing one α subunit and one β subunit (1). Often integrins bind to ECM proteins via short RGD motifs within the matrix protein (2). In addition to an RGD motif, fibronectin also contains an upstream PHSRN synergy sequence, which is required for full integrin binding activity (3).Elastin confers elasticity on all vertebrate elastic tissues including arteries, lung, skin, vocal fold, and elastic cartilage (4). Elastin comprises ∼90% of the elastic fiber and is intermingled with fibrillin-rich microfibrils (5). There is a single human tropoelastin gene in which alternative splicing can result in the loss of domains 22, 23, 24, 26A, 30, 32, and 33 (4). Elastin is made from the secreted monomer tropoelastin, which is a 60–72-kDa protein containing repeating hydrophobic and cross-linking domains. Hydrophobic domains are rich in GVGVP, GGVP, and GVGVAP repeats, which can associate by coacervation (6). This association results in structural changes and increased α-helical content (7). The cross-linking domains are lysine-rich. Occasionally these residues are modified to allysine through the activity of members of the family of lysyl oxidase (LOX) and four LOX-like enzymes. During coacervation the allysine and other allysines or specific lysine side chains come into close proximity, allowing nonenzymatic condensation reactions to occur, forming desmosine or isodesmosine cross-links (4). This process gives a highly stable cross-linked elastin matrix which has a half-life of ∼70 years. Members of the serine, aspartate, cysteine, and matrix metalloproteinase families of proteases can degrade elastin (8). The resulting elastin peptides have effects on ECM synthesis and cell attachment, migration, and proliferation (9).The consequences of mutated or hemizygous elastin in the hereditary, connective tissue disorders cutis laxa, supravalvular aortic stenosis, and Williams-Beuren syndrome highlight the elastins essential role in elastic tissue function (10). Elastin is the major protein in large elastic blood vessels such as the aorta, where it is likely to inhibit the proliferation of vascular smooth muscle cells and so preventing vessel occlusion (11), which is a major cause of death in developed countries. Previous studies have shown that human and bovine tropoelastin can bind directly to a variety of cell types directly through a number of cell surface receptors (12–14) and also bind indirectly to cells through ECM proteins such as fibulin-5 (15, 16).A mechanism by which elastin binds to cells is via the 67-kDa elastin-binding protein (EBP), which is a peripheral membrane splice variant of β-galactosidase. The EBP forms a complex with the integral membrane proteins carboxypeptidase A and sialidase, forming a transmembrane elastin receptor (12). The binding site for the EBP has been mapped to the consensus sequence XGXXPG within elastin and in particular to VGVAPG within exon 24 (17). The binding of elastin to the EBP results in cell morphological changes (18, 19), chemotaxis (20), decreased cell proliferation (21), and angiogenesis (22). Knockouts of β-galactosidase, which remove the EBP, display correctly deposited elastin (27). Additionally tropoelastin actively promotes cell adhesion, whereas VGVAPG does not. These observations imply that receptors other than EBP can interact with elastin.Other studies have proposed a second mechanism involving the necessity of cell surface heparan and chondroitin sulfate-containing glycosaminoglycans for bovine chondrocyte interaction with bovine tropoelastin (14). Peptide binding analysis implicated the last 17 amino acids at the C terminus of bovine tropoelastin in this cell adhesive activity, with higher binding requiring the C-terminal 25 amino acids. This region is of interest, as in humans a mutation of Gly-773 to Asp in exon 33 results in blocked elastin network assembly and modulates cell binding to a peptide corresponding to exons 33 and 36 of human tropoelastin (28). Indeed Broekelmann et al. (14) have shown that synthetic peptides containing the C-terminal 29 amino acids of bovine tropoelastin possess cell adhesive activity; however, when the G773D mutation was incorporated into the peptide, it prevented cell adhesion to that peptide.Although tropoelastin does not contain an RGD motif, other data identified a third mechanism involving direct interaction between integrin αvβ3 and human tropoelastin (13, 29). This interaction was also localized to the C-terminal domains of tropoelastin.More recent data has shown that human umbilical vein endothelial cells can adhere to recombinant fragments of human tropoelastin (30, 31). In contrast to other data, regions encoded by the N-terminal exons (1–18), the central exons (18–27), and the C-terminal exons (18–36) all supported human umbilical vein endothelial cell attachment.Although a previous study has shown a direct interaction between purified integrin αvβ3 and human tropoelastin (13), the integrin dependence of cell adhesion to tropoelastin had not been demonstrated. Here we demonstrate that human dermal fibroblasts adhere to recombinant human tropoelastin and that inhibitors of the elastin-binding protein and cell surface heparan sulfate have no effect on cell adhesion. In contrast, cell adhesion was dependent upon the presence of divalent cations, indicating integrin dependence. Inhibitory monoclonal antibodies identified integrin αVβ3 as the major receptor necessary for fibroblast adherence and spreading onto human tropoelastin. The binding motif for integrin-mediated cell adhesion is unknown; therefore, through the use of synthetic peptides, the adhesive activity was localized to the extreme C-terminal GRKRK motif of tropoelastin. This data present a novel mechanism for cell adhesion to human tropoelastin and identify a novel integrin binding motif within tropoelastin. 相似文献
973.
Christophe Lechauve Latifa Bouzhir-Sima Taku Yamashita Michael C. Marden Marten H. Vos Ursula Liebl Laurent Kiger 《The Journal of biological chemistry》2009,284(52):36146-36159
Dos from Escherichia coli is a bacterial gas sensor protein comprising a heme-containing gas sensor domain and a phosphodiesterase catalytic domain. Using a combination of static light scattering and gel filtration experiments, we established that, as are many other sensor proteins, the full-length protein is dimeric. The full-length dimer (association constant <10 nm) is more stable than the dimeric heme domain (association constant ∼1 μm), and the dimer interface presumably includes both sensor and catalytic domains. Ultrafast spectroscopic studies showed little influence of the catalytic domain on kinetic processes in the direct vicinity of the heme. By contrast, the properties of ligand (CO and O2) binding to the heme in the sensor domain, occurring on a microsecond to second time scale, were found to be influenced by (i) the presence of the catalytic domain, (ii) the dimerization state, and in dimers, (iii) the ligation state of the other subunit. These results imply allosteric interactions within dimers. Steady-state titrations demonstrated marked cooperativity in oxygen binding to both the full-length protein and the isolated heme domain, a feature not reported to date for any dimeric sensor protein. Analysis of a variety of time-resolved experiments showed that Met-95 plays a major role in the intradimer interactions. The intrinsic binding and dissociation rates of Met-95 to the heme were modulated ∼10-fold by intradimer and sensor-catalytic domain interactions. Dimerization effects were also observed for cyanide binding to the ferric heme domains, suggesting a similar role for Met-95 in ferric proteins. 相似文献
974.
Plasmin-mediated Proteolysis Is Required for Hepatocyte Growth Factor
Activation during Liver
Repair
Kumar Shanmukhappa Ursula Matte Jay L. Degen Jorge A. Bezerra 《The Journal of biological chemistry》2009,284(19):12917-12923
The physiological relevance of the activation of hepatocyte growth factor
(Hgf) by the plasminogen (Plg) system of proteases and its contribution to
tissue repair are largely undefined. Here, we investigated whether the
defective liver repair in mice lacking Plg is due to impaired activation of
Hgf. Loss of Plg in vivo suppressed Hgf activation and signaling
through its Met tyrosine kinase receptor. Without Plg, hepatocytes were
unresponsive to Hgf-induced proliferation and migration, with a more
pronounced impairment in hepatocyte movement within the hepatic environment.
Most notably, circumventing the defect in proteolytic activation of Hgf by the
downstream expression of an activated Met receptor corrected the functional
deficits and improved liver repair in Plg-deficient mice. These findings
support a fibrinolysis-unrelated role for Plg in modulating cell proliferation
and migration by activation of Hgf.Tissue repair requires a prompt proliferative response in concert with the
timely reorganization of the extracellular matrix. Each one of these processes
can be disrupted by the loss of individual growth factors or proteases, but
the precise regulatory relationship between these molecules in supporting
tissue repair is not fully understood. Multiple in vitro studies have
inferred that proteases in the plasminogen
(Plg)2 activation
system may be important in the proteolytic activation of the hepatocyte growth
factor (Hgf)
(1–4),
the ligand for the Met tyrosine kinase receptor that exerts potent mitogenic
and motogenic properties to mesenchymal and epithelial cells. This concept is
made even more attractive by the fact that Hgf is structurally related to Plg,
with multiple kringle domains and a catalytically inactive serine
protease-like domain. However, the physiological relevance of Plg to Hgf
activation and Hgf-related reparative processes are controversial and
effectively unexplored in vivo.We previously reported that a genetically imposed loss of circulating Plg
severely impairs clearance of necrotic cells and the repopulation of injured
zones by newly formed cells but without compromising the general hepatic
proliferative response (5).
Despite the indisputable role of Plg in fibrin clearance
(6), complementary studies in
mice with no capacity for fibrin deposition have shown that the loss of
fibrinolytic function alone in Plg-deficient mice cannot account for the
impediment in tissue repair
(5). Multiple nonfibrin targets
of plasmin-mediated proteolysis are known (e.g. serine and
metalloprotease zymogens, and extracellular matrix glycoproteins, latent
growth factors), and it is feasible that they may contribute to the focal
clearance of necrotic tissue. However, based on recent findings pointing to a
strikingly similar defect in hepatic repair in mice lacking Plg or a
conditional loss of Met (7), an
attractive hypothesis emerged that the Plg activation system supports
physiological liver repair by activation of the Met ligand, Hgf. Testing this
hypothesis, we found that the loss of Plg impairs Hgf activation, suppresses
Met phosphorylation and signaling, and prevents Hgf-induced migration of
hepatocytes. Most notably, consistent with a physiologically relevant
contribution of Plg to Hgf-Met signaling, the expression of an
autophosphorylated Met largely corrected the defective repair in Plg-deficient
livers. 相似文献
975.
Gangishetti U Breitenbach S Zander M Saheb SK Müller U Schwarz H Moussian B 《European journal of cell biology》2009,88(3):167-180
Chitin is an essential constituent of the insect exoskeleton, the cuticle, which is an extracellular matrix (ECM) covering the animal. It is produced by the glycosyltransferase chitin synthase at the apical plasma membrane of epidermal and tracheal cells. To fulfil its role in cuticle elasticity and stiffness it associates with proteins, thereby adopting a stereotypic arrangement of helicoidally stacked sheets, which run parallel to the surface of the animal. One approach to understand the mechanisms of chitin synthesis and organisation is to dissect these processes genetically. However, since only a few genes coding for factors involved in chitin synthesis and organisation have been identified to date using the model arthropod Drosophila melanogaster insight arising from mutant analysis is rather limited. To collect new data on the role of chitin during insect cuticle differentiation, we have analysed the effects of chitin synthesis inhibitors on Drosophila embryogenesis. For this purpose, we have chosen the benzoylphenylurea diflubenzuron and lufenuron that are widely used as insect growth regulators. Our data allow mainly two important conclusions. First, correct organisation of chitin seems to directly depend on the amount of chitin synthesised. Second, chitin synthesis and organisation are cell-autonomous processes as insecticide-treated larvae display a mosaic of cuticle defects. As benzoylphenylurea are used not only as insecticides but also as anti-diabetic drugs, the study of their impact on Drosophila cuticle differentiation may be fruitful for understanding their mode of action on a cellular pathway that is seemingly conserved between vertebrates and invertebrates. 相似文献
976.
Bacteria growing in biofilms can become up to 1000-fold more resistant to antibiotics and biocides as compared to their planktonic counterparts. As a result of this increased resistance, biofilms and biofilm-related infections cannot be effectively treated with conventional antibiotic therapy. The goal of this study was to determine the efficacy of three neutral pH, super-oxidised solutions (nSOSs, OIS-80, OIS-125, OIS-200, Microcyn Technology) varying in oxychlorine concentration (80, 125 and 200 ppm) against P. aeruginosa grown planktonically and as biofilms. Exposure for 20 s of exponential phase cells to any of the three solutions was sufficient to reduce viability by more than five logs. However, only exposure for 10 min to OIS-125 and OIS-200 for 10 min was sufficient to eradicate stationary phase P. aeruginosa cells. The efficacy of nSOSs on P. aeruginosa biofilms, grown to maturity in continuous flow tube reactors, was determined upon treatment up to 60 min. Viability pre- and post-treatment was determined by CFU counts. The effect of these solutions on P. aeruginosa biofilms and biofilm architecture was further visualised by confocal scanning laser microscopy and quantitatively analysed by COMSTAT. Under these experimental conditions, only OIS-125 and OIS-200 achieved a >3-log reduction and biofilm disaggregation within 30 min of exposure. Because OIS-125 and OIS-200 enhance the disaggregation of biofilms, their use in the treatment of surface-related biofilm infections deserves further investigation. 相似文献
977.
Ursula Eberhardt Henry J. Beker Jan Vesterholt Rena Gadjieva 《Mycological Research》2009,113(1):153-162
The genus Hebeloma has a number of species highly specific to Cistus and others that occur with several host genera. This paper discusses the species of Hebeloma that appear to be ectomycorrhizal with Cistus, judging from their occurrence when Cistus is the only available host. The previously unknown species H. plesiocistum spec. nov. is described. We also provide a key to the known Hebeloma associates of Cistus. Molecular analyses based on ITS sequence data further illustrate the distinctness of the newly described species and difficulties in the species delimitation with view to H. erumpens. Specific associations with Cistus may have evolved more than once within the genus Hebeloma. 相似文献
978.
Siegel G Rodríguez M Sauer F Abletshauser C de Mey C Schötz K Ringstad L Malmsten M Schäfer P 《Biosensors & bioelectronics》2009,24(5):1512-1517
A proteoheparan sulfate coated, hydrophobic silica surface serves as lipoprotein receptor at which the Ca(2+)-driven arteriosclerotic nanoplaque formation can be pursued by laser-based ellipsometry. Any lipoprotein from human blood can be very sensitively tested for its atherogenic properties. From the same blood sample, it is possible to determine the concentration and activity of a series of interacting biomarker molecules which, through a pattern analysis, allow to assess the state of health with respect to cardiovascular diseases. These two interlinked and complementary biosensors make a prospective cardio-cerebro-vascular risk stratification feasible, especially the sequelae of an underlying arteriosclerotic disease. Based on these diagnostic tools, an optimized therapy decision for the patient can be taken and the necessary preventive measures for the still healthy person. 相似文献
979.
The site of Isernia La Pineta (Molise, Italie) is characterized by the presence of a rich faunal assemblage related to a very abundant lithic industry in several archaeosurfaces dated between 600,000 and 700,000 BP. A specific archaeozoological study has been carried out on Bison schoetensacki specimens that are the most represented taxon in each archaeological level, followed by rhinoceros, elephant, bear and cervid. The quantitative et qualitative analysis of the faunal remains, the age profiles and the identification of anthropic modifications have allowed to better understand the exploitation strategies adopted by humans in the site and to underline a selective hunting of population of bison, related to the age of the individuals. 相似文献
980.