全文获取类型
收费全文 | 3375篇 |
免费 | 195篇 |
专业分类
3570篇 |
出版年
2023年 | 21篇 |
2022年 | 47篇 |
2021年 | 89篇 |
2020年 | 70篇 |
2019年 | 72篇 |
2018年 | 104篇 |
2017年 | 93篇 |
2016年 | 124篇 |
2015年 | 158篇 |
2014年 | 206篇 |
2013年 | 251篇 |
2012年 | 319篇 |
2011年 | 286篇 |
2010年 | 177篇 |
2009年 | 137篇 |
2008年 | 210篇 |
2007年 | 171篇 |
2006年 | 185篇 |
2005年 | 159篇 |
2004年 | 125篇 |
2003年 | 112篇 |
2002年 | 88篇 |
2001年 | 24篇 |
2000年 | 14篇 |
1999年 | 19篇 |
1998年 | 18篇 |
1997年 | 18篇 |
1996年 | 14篇 |
1995年 | 10篇 |
1994年 | 12篇 |
1992年 | 10篇 |
1991年 | 8篇 |
1990年 | 13篇 |
1989年 | 9篇 |
1988年 | 9篇 |
1986年 | 13篇 |
1985年 | 9篇 |
1984年 | 12篇 |
1983年 | 12篇 |
1982年 | 10篇 |
1980年 | 17篇 |
1977年 | 10篇 |
1976年 | 7篇 |
1975年 | 7篇 |
1974年 | 8篇 |
1973年 | 7篇 |
1972年 | 8篇 |
1971年 | 10篇 |
1969年 | 9篇 |
1964年 | 7篇 |
排序方式: 共有3570条查询结果,搜索用时 15 毫秒
41.
Christine App Jana Knop Thomas Huff Heinrich Sticht Ewald Hannappel 《The protein journal》2013,32(6):484-492
Thymosin β4 is the prototype of β-thymosins and is present in almost every mammalian cell. It is regarded to be the main intracellular G-actin sequestering peptide. Thymosin β4 serves as a specific glutaminyl substrate for guinea pig transglutaminase. In the absence of an appropriate additional aminyl donor an ε-amino group of thymosin β4 serves also as an aminyl substrate and an intramolecular bond is formed concomitantly NH3 (17 Da) is lost. The molecular mass of the product is 4,949.6 Da. This is 16.3 Da less than the molecular mass of thymosin β4 (4,965.9 Da). Digestion with endopeptidases and Edman degradation of the fragments identified the exact position of the ring forming isopeptide bond. In spite of 3 glutaminyl and 9 lysyl residues of thymosin β4 only one isopeptide bond between Lys16 and Gln36 was formed (cyclic thymosin β4). These two amino acid residues are conserved in all β-thymosins. Cyclic thymosin β4 still forms a complex with G-actin albeit the stability of the complex is about one fiftieth of the stability of the thymosin β4 × G-actin complex. 相似文献
42.
Modelling of complex psychiatric disorders, e.g., depression and schizophrenia, in animals is a major challenge, since they are characterized by certain disturbances in functions that are absolutely unique to humans. Furthermore, we still have not identified the genetic and neurobiological mechanisms, nor do we know precisely the circuits in the brain that function abnormally in mood and psychotic disorders. Consequently, the pharmacological treatments used are mostly variations on a theme that was started more than 50 years ago. Thus, progress in novel drug development with improved therapeutic efficacy would benefit greatly from improved animal models. Here, we review the available animal models of depression and schizophrenia and focus on the way that they respond to various types of potential candidate molecules, such as novel antidepressant or antipsychotic drugs, as an index of predictive validity. We conclude that the generation of convincing and useful animal models of mental illnesses could be a bridge to success in drug discovery. 相似文献
43.
The hydroid Ectopleura larynx is a common fouling organism on aquaculture nets. To contribute to the development of novel cleaning methods, laboratory and field studies determined the effects of heat (30, 40, 50 and 60°C for immersion times of 1 and 3 s) and acetic acid (0.2 and 2.0% for immersion times of 1, 3 and 10 s, 1 and 5 min) on the settlement of actinulae and the survival of juvenile and adult E. larynx. Laboratory studies showed that, regardless of immersion time, a temperature of 50°C was effective in preventing the settlement of actinulae and the survival of juveniles, while ≤12% of adult hydroids could survive. A temperature of 60°C killed all adult hydroids. For an acetic acid concentration of 0.2%, an immersion time of 1 min substantially reduced the settlement of actinulae and the survival of juvenile and adult hydroids, and none of the juvenile and adult hydroids survived after 5 min. For an acetic acid concentration of 2.0%, all immersion times were effective and reduced the mean settlement of actinulae and the survival of juvenile and adult hydroids to ≤10%. Field studies with fouled net panels exposed to selected heat or acetic acid treatments showed small reductions in mean wet weight and net aperture occlusion of the net panels 2 and 5 days after treatment. Visual inspections of the net panels showed that hydranths of the hydroids were shed, but the dead stolons of the hydroids remained on the treated net panels. Novel cleaning methods and devices may utilise these results to effectively kill E. larynx on aquaculture nets, while further studies are needed to determine the necessity of removing the dead hydroids before further biofouling accumulates on thenets. 相似文献
44.
Abstract The role of surface topography as a defence against fouling in tropical sea stars was investigated. The sea stars Linckia laevigata, Fromia indica, Cryptasterina pentagona and Archaster typicus are not fouled and have paxillae (modified ossicles with a median vertical pillar) on their aboral surfaces, which varied in diameter, height and distance depending on species and position on the aboral surface, providing unique and complex surface microtopographies for each species. The surfaces of the sea stars L. laevigata, F. indica and A. typicus were moderately wettable, with their mean seawater contact angles, calculated from captive bubble measurements, being 60.1°, 70.3° and 57.3°, respectively. The seawater contact angle of C. pentagona could not be measured. To evaluate the effectiveness of the surface microtopographies in deterring the settlement of fouling organisms, field experiments with resin replicas of the four sea star species were conducted at three sites around Townsville, Australia, for 8 weeks during the dry and wet seasons. The fouling community and total fouling cover did not differ significantly between replicas of L. laevigata, F. indica, C. pentagona, A. typicus and control surfaces at any site during the dry season. Significant differences between fouling communities on the replicas of the sea stars and control surfaces were detected at two sites during the wet season. However, these differences were transitory, and the total fouling cover did not differ significantly between replicas of sea stars and control surfaces at two of the three sites. In contrast to recent literature on the effects of biofouling control by natural surfaces in the marine environment, the surface microtopographies of tropical sea stars alone were not effective in deterring the settlement and growth of fouling organisms. 相似文献
45.
46.
Václav Brázda Jana Čechová Jan Coufal Sigrun Rumpel Eva B. Jagelská 《Journal of biomolecular structure & dynamics》2013,31(4):371-378
The 14-3-3 protein family is a highly conserved and widely distributed group of proteins consisting of multiple isoforms in eukaryotes. Ubiquitously expressed, 14-3-3 proteins play key roles in DNA replication, cell cycle regulation, and apoptosis. The function of 14-3-3 proteins is mediated by interaction with a large number of other proteins and with DNA. It has been demonstrated that 14-3-3γ protein binds strongly to cruciform structures and is crucial for initiating replication. In this study, we analyzed DNA binding properties of the 14-3-3γ isoform to linear and supercoiled DNA. We demonstrate that 14-3-3γ protein binds strongly to long DNA targets, as evidenced by electrophoretic mobility shift assay on agarose gels. Binding of 14-3-3γ to DNA target results in the appearance of blurry, retarded DNA bands. Competition experiments with linear and supercoiled DNA on magnetic beads show very strong preference for supercoiled DNA. We also show by confocal microscopy that 14-3-3 protein in the HCT-116 cell line is co-localized with DNA cruciforms. This implies a role for the 14-3-3γ protein in its binding to local DNA structures which are stabilized by DNA supercoiling. 相似文献
47.
Eric Allan Wolfgang W. Weisser Markus Fischer Ernst-Detlef Schulze Alexandra Weigelt Christiane Roscher Jussi Baade Romain L. Barnard Holger Beßler Nina Buchmann Anne Ebeling Nico Eisenhauer Christof Engels Alexander J. F. Fergus Gerd Gleixner Marlén Gubsch Stefan Halle Alexandra M. Klein Ilona Kertscher Annely Kuu Markus Lange Xavier Le Roux Sebastian T. Meyer Varvara D. Migunova Alexandru Milcu Pascal A. Niklaus Yvonne Oelmann Esther Pašalić Jana S. Petermann Franck Poly Tanja Rottstock Alexander C. W. Sabais Christoph Scherber Michael Scherer-Lorenzen Stefan Scheu Sibylle Steinbeiss Guido Schwichtenberg Vicky Temperton Teja Tscharntke Winfried Voigt Wolfgang Wilcke Christian Wirth Bernhard Schmid 《Oecologia》2013,173(1):223-237
In order to predict which ecosystem functions are most at risk from biodiversity loss, meta-analyses have generalised results from biodiversity experiments over different sites and ecosystem types. In contrast, comparing the strength of biodiversity effects across a large number of ecosystem processes measured in a single experiment permits more direct comparisons. Here, we present an analysis of 418 separate measures of 38 ecosystem processes. Overall, 45 % of processes were significantly affected by plant species richness, suggesting that, while diversity affects a large number of processes not all respond to biodiversity. We therefore compared the strength of plant diversity effects between different categories of ecosystem processes, grouping processes according to the year of measurement, their biogeochemical cycle, trophic level and compartment (above- or belowground) and according to whether they were measures of biodiversity or other ecosystem processes, biotic or abiotic and static or dynamic. Overall, and for several individual processes, we found that biodiversity effects became stronger over time. Measures of the carbon cycle were also affected more strongly by plant species richness than were the measures associated with the nitrogen cycle. Further, we found greater plant species richness effects on measures of biodiversity than on other processes. The differential effects of plant diversity on the various types of ecosystem processes indicate that future research and political effort should shift from a general debate about whether biodiversity loss impairs ecosystem functions to focussing on the specific functions of interest and ways to preserve them individually or in combination. 相似文献
48.
A soil enrichment culture of the sulfate-reducers Desulfosporosinus auripigmenti and Citrobacter freundii and of fermentative bacteria from a former uranium-mining site was studied for its metal retention potential by promoting metal sulfide precipitation. The culture could tolerate up to 30 mM Ni and 40 mM Co. XRD and TEM analyses revealed the formation of amorphous NiS together with nanocrystalline, metastable α-NiS, and nanocrystalline cobalt pentlandite. The α-NiS with a grain size of 5 nm shows probably an example of size-dependent phase stability and/or specific biomineralization precipitation paths. Detailed mineralogical characterizations are necessary to correctly assess the mineral inventory and thus metal bioavailability. 相似文献
49.
Susan Ehinger Jana Seifert Andrea Kassahun Lorina Schmalz Nils Hoth Michael Schlömann 《Geomicrobiology journal》2013,30(5):326-338
The microbial communities in sulfate-rich, saline formation fluids of a natural gas reservoir in Lower Saxony, Germany were investigated to enhance the knowledge about microbial communities in potential carbon dioxide sequestration sites. This investigation of the initial state of the deep subsurface microbiota is necessary to predict their influence on the long-term stability and storage capacity of such sites. While the bacterial 16S rDNA gene library was comprised of sequences affiliating with the Firmicutes, the Alphaproteobacteria, the Gammaproteobacteria and the Thermotogales, the archaeal 16S rDNA libraries were simply dominated by two phylotypes related to the genera Methanolobus and Methanoculleus. The monitoring of the archaeal communities in different formation fluid samples by T-RFLP and Real-Time-PCR indicated that these two methanogenic genera dominated at all, whereas the proportion of the two groups varied. Thus, methylotrophic and autotrophic methanogenesis seems to be of importance in the reservoir fluids, dependent on the provided reduction equivalents and substrates and it also may influence the fate of CO2 in the subsurface. 相似文献
50.
Jean‐François Bourzac Karine L'Ériger Jean‐François Larrivée Guillaume Arguin Maude S. Bilodeau Jana Stankova Fernand‐Pierre Gendron 《Journal of cellular physiology》2013,228(1):120-129
With the diabetes epidemic affecting the world population, there is an increasing demand for means to regulate glycemia. Dietary glucose is first absorbed by the intestine before entering the blood stream. Thus, the regulation of glucose absorption by intestinal epithelial cells (IECs) could represent a way to regulate glycemia. Among the molecules involved in glycemia homeostasis, extracellular ATP, a paracrine signaling molecule, was reported to induce insulin secretion from pancreatic β cells by activating P2Y and P2X receptors. In rat's jejunum, P2X7 expression was previously immunolocalized to the apex of villi, where it has been suspected to play a role in apoptosis. However, using an antibody recognizing the receptor extracellular domain and thus most of the P2X7 isoforms, we showed that expression of this receptor is apparent in the top two‐thirds of villi. These data suggest a different role for this receptor in IECs. Using the non‐cancerous IEC‐6 cells and differentiated Caco‐2 cells, glucose transport was reduced by more than 30% following P2X7 stimulation. This effect on glucose transport was not due to P2X7‐induced cell apoptosis, but rather was the consequence of glucose transporter 2 (Glut2)'s internalization. The signaling pathway leading to P2X7‐dependent Glut2 internalization involved the calcium‐independent activation of phospholipase Cγ1 (PLCγ1), PKCδ, and PKD1. Although the complete mechanism regulating Glut2 internalization following P2X7 activation is not fully understood, modulation of P2X7 receptor activation could represent an interesting approach to regulate intestinal glucose absorption. J. Cell. Physiol. 228: 120–129, 2013. © 2012 Wiley Periodicals, Inc. 相似文献