全文获取类型
收费全文 | 656篇 |
免费 | 63篇 |
出版年
2021年 | 9篇 |
2018年 | 14篇 |
2017年 | 10篇 |
2016年 | 15篇 |
2015年 | 15篇 |
2014年 | 17篇 |
2013年 | 29篇 |
2012年 | 26篇 |
2011年 | 31篇 |
2010年 | 17篇 |
2009年 | 14篇 |
2008年 | 21篇 |
2007年 | 30篇 |
2006年 | 20篇 |
2005年 | 20篇 |
2004年 | 33篇 |
2003年 | 21篇 |
2002年 | 20篇 |
2001年 | 13篇 |
2000年 | 28篇 |
1999年 | 24篇 |
1998年 | 12篇 |
1997年 | 9篇 |
1996年 | 13篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1993年 | 11篇 |
1992年 | 13篇 |
1991年 | 15篇 |
1990年 | 15篇 |
1989年 | 10篇 |
1988年 | 16篇 |
1987年 | 12篇 |
1986年 | 6篇 |
1985年 | 8篇 |
1984年 | 9篇 |
1983年 | 9篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1978年 | 8篇 |
1977年 | 8篇 |
1976年 | 7篇 |
1975年 | 6篇 |
1974年 | 7篇 |
1973年 | 13篇 |
1972年 | 4篇 |
1971年 | 5篇 |
1970年 | 8篇 |
1969年 | 8篇 |
1968年 | 4篇 |
排序方式: 共有719条查询结果,搜索用时 171 毫秒
101.
102.
Brian H Shilton J Hugh McDowell W Clay Smith Paul A Hargrave 《European journal of biochemistry》2002,269(15):3801-3809
Visual arrestin is converted from a 'basal' state to an 'activated' state by interaction with the phosphorylated C-terminus of photoactivated rhodopsin (R*), but the conformational changes in arrestin that lead to activation are unknown. Small-angle X-ray scattering (SAXS) was used to investigate the solution structure of arrestin and characterize changes attendant upon activation. Wild-type arrestin forms dimers with a dissociation constant of 60 micro m. Small conformational changes, consistent with local movements of loops or the mobile N- or C-termini of arrestin, were observed in the presence of a phosphopeptide corresponding to the C-terminus of rhodopsin, and with an R175Q mutant. Because both the phosphopeptide and the R175Q mutation promote binding to unphosphorylated R*, we conclude that arrestin is activated by subtle conformational changes. Most of the arrestin will be in a dimeric state in vivo. Using the arrestin structure as a guide [Hirsch, J.A., Schubert, C., Gurevich, V.V. & Sigler, P.B. (1999) Cell 97, 257-269], we have identified a model for the arrestin dimer that is consistent with our SAXS data. In this model, dimerization is mediated by the C-terminal domain of arrestin, leaving the N-terminal domains free for interaction with phosphorylated R*. 相似文献
103.
Elizabeth M. McDowell 《Histochemistry and cell biology》1973,34(4):281-291
Summary Using 0.5 thick (i.e., semi-thin) and conventional thin sections, observations have been made on the localization of acid phosphatase in the Golgi apparatus and related structures in the pars recta of rat kidney. In thin sections one or two Golgi cisternae located at the concave (basilar) aspect of the stack had enzymic activity. The periphery of these cisternae may be fenestrated. Coated vesicles were seen apparently free in the cytoplasm and in continuity with both reactive Golgi cisternae and smooth tubular elements. Smooth vesicular profiles with electron-lucent matrices and low enzymic activity were seen, apparently free, in the central Golgi zone. Semi-thin sections demonstrated more fully the extent of the reactive Golgi elements, their architecture and their relationships with other organelles. Within a stack the reactive Golgi cisternae were continuous with one another. A network of anastomosing tubular elements formed the periphery of the cisternae and linked some adjacent cisternae. Tubules extended considerable distances from this network in apical and lateral directions. Vesicular protuberances formed ends to the tubular extensions but free vesicles were not obvious. Apparent continuity was seen between reactive tubules and dense bodies (secondary lysosomes). Vesicular profiles with electron-lucent matrices andlow enzymic activity appeared to be continuous with the periphery of reactive Golgi cisternae and may represent the formation of primary lysosomes. This study demonstrates that semi-thin sections could be used to great advantage in the study of organelle interactions in both normal and pathological states. 相似文献
104.
L M McDowell L A Burzio J H Waite J Schaefer 《The Journal of biological chemistry》1999,274(29):20293-20295
13C2H rotational echo double resonance NMR has been used to provide the first evidence for the formation of quinone-derived cross-links in mussel byssal plaques. Labeling of byssus was achieved by allowing mussels to filter feed from seawater containing L-[phenol-4-13C]tyrosine and L-[ring-d4]tyrosine for 2 days. Plaques and threads were harvested from two groups of mussels over a period of 28 days. One group was maintained in stationary water while the other was exposed to turbulent flow at 20 cm/s. The flow-stressed byssal plaques exhibited significantly enhanced levels of 5, 5'-di-dihydroxyphenylalanine cross-links. The average concentration of di-dihydroxyphenylalanine cross-links in byssal plaques is 1 per 1800 total protein amino acid residues. 相似文献
105.
106.
Francesca Megiorni Giovanni Luca Gravina Simona Camero Simona Ceccarelli Andrea Del Fattore Vincenzo Desiderio Federica Papaccio Heather P. McDowell Rajeev Shukla Antonio Pizzuti Filip Beirinckx Philippe Pujuguet Laurent Saniere Ellen Van der Aar Roberto Maggio Francesca De Felice Cinzia Marchese Carlo Dominici Vincenzo Tombolini Claudio Festuccia Francesco Marampon 《Journal of hematology & oncology》2017,10(1):161
Background
EPH (erythropoietin-producing hepatocellular) receptors are clinically relevant targets in several malignancies. This report describes the effects of GLPG1790, a new potent pan-EPH inhibitor, in human embryonal rhabdomyosarcoma (ERMS) cell lines.Methods
EPH-A2 and Ephrin-A1 mRNA expression was quantified by real-time PCR in 14 ERMS tumour samples and in normal skeletal muscle (NSM). GLPG1790 effects were tested in RD and TE671 cell lines, two in vitro models of ERMS, by performing flow cytometry analysis, Western blotting and immunofluorescence experiments. RNA interfering experiments were performed to assess the role of specific EPH receptors. Radiations were delivered using an x-6 MV photon linear accelerator. GLPG1790 (30 mg/kg) in vivo activity alone or in combination with irradiation (2 Gy) was determined in murine xenografts.Results
Our study showed, for the first time, a significant upregulation of EPH-A2 receptor and Ephrin-A1 ligand in ERMS primary biopsies in comparison to NSM. GLPG1790 in vitro induced G1-growth arrest as demonstrated by Rb, Cyclin A and Cyclin B1 decrease, as well as by p21 and p27 increment. GLPG1790 reduced migratory capacity and clonogenic potential of ERMS cells, prevented rhabdosphere formation and downregulated CD133, CXCR4 and Nanog stem cell markers. Drug treatment committed ERMS cells towards skeletal muscle differentiation by inducing a myogenic-like phenotype and increasing MYOD1, Myogenin and MyHC levels. Furthermore, GLPG1790 significantly radiosensitized ERMS cells by impairing the DNA double-strand break repair pathway. Silencing of both EPH-A2 and EPH-B2, two receptors preferentially targeted by GLPG1790, closely matched the effects of the EPH pharmacological inhibition. GLPG1790 and radiation combined treatments reduced tumour mass by 83% in mouse TE671 xenografts.Conclusions
Taken together, our data suggest that altered EPH signalling plays a key role in ERMS development and that its pharmacological inhibition might represent a potential therapeutic strategy to impair stemness and to rescue myogenic program in ERMS cells.107.
Oslob JD Romanowski MJ Allen DA Baskaran S Bui M Elling RA Flanagan WM Fung AD Hanan EJ Harris S Heumann SA Hoch U Jacobs JW Lam J Lawrence CE McDowell RS Nannini MA Shen W Silverman JA Sopko MM Tangonan BT Teague J Yoburn JC Yu CH Zhong M Zimmerman KM O'Brien T Lew W 《Bioorganic & medicinal chemistry letters》2008,18(17):4880-4884
This communication describes the discovery of a novel series of Aurora kinase inhibitors. Key SAR and critical binding elements are discussed. Some of the more advanced analogues potently inhibit cellular proliferation and induce phenotypes consistent with Aurora kinase inhibition. In particular, compound 21 (SNS-314) is a potent and selective Aurora kinase inhibitor that exhibits significant activity in pre-clinical in vivo tumor models. 相似文献
108.
Studelska DR Mandik-Nayak L Zhou X Pan J Weiser P McDowell LM Lu H Liapis H Allen PM Shih FF Zhang L 《The Journal of biological chemistry》2009,284(4):2354-2362
In the K/BxN mouse model of rheumatoid arthritis, autoantibodies specific for glucose-6-phosphate isomerase (GPI) can transfer joint-specific inflammation to most strains of normal mice. Binding of GPI and autoantibody to the joint surface is a prerequisite for joint-specific inflammation. However, how GPI localizes to the joint remains unclear. We show that glycosaminoglycans (GAGs) are the high affinity (83 nm) joint receptors for GPI. The binding affinity and structural differences between mouse paw/ankle GAGs and elbows/knee GAGs correlated with the distal to proximal disease severity in these joints. We found that cartilage surface GPI binding was greatly reduced by either chondroitinase ABC or beta-glucuronidase treatment. We also identified several inhibitors that inhibit both GPI/GAG interaction and GPI enzymatic activities, which suggests that the GPI GAG-binding domain overlaps with the active site of GPI enzyme. Our studies raise the possibility that GAGs are the receptors for other autoantigens involved in joint-specific inflammatory responses. 相似文献
109.
K.M. Crowley D.M. Prendergast D.A. McDowell J.J. Sheridan 《Journal of applied microbiology》2009,107(5):1542-1550
Aim: To investigate changes in Escherichia coli O157:H7 numbers on excised beef carcass surfaces over 72 h at different temperatures.
Methods and Results: Excised lean meat, fascia and fat were inoculated with E. coli O157:H7 and held in an environmental chamber for 72 h, at air speed 0·5 m s−1 , relative humidity (RH) 90%, and temperatures 4, 8 and 12°C. On lean, pathogen counts increased significantly at 12°C. On fascia, significant reductions in counts occurred at 4 and 8°C. Pathogen numbers were significantly reduced on fat at 4, 8 and 12°C (64 h). Counts on fat were significantly less at all temperatures, compared to lean or fascia and surface water activity, aw , decreased significantly over time on fat at 4°C. Significant decreases in surface pH values were recorded on all meat substrates.
Conclusions: The survival of E. coli O157:H7 varied in relation to the meat substrate and the holding temperature. Reductions in counts on fat surfaces appeared to be related to low surface aw values. No relationship between pathogen survival and surface pH was established.
Significance and Impact of the Study: The use of excised meat pieces in an environmental cabinet offers a more flexible approach to determining the use of different chilling regimes in the production of safe meat. 相似文献
Methods and Results: Excised lean meat, fascia and fat were inoculated with E. coli O157:H7 and held in an environmental chamber for 72 h, at air speed 0·5 m s
Conclusions: The survival of E. coli O157:H7 varied in relation to the meat substrate and the holding temperature. Reductions in counts on fat surfaces appeared to be related to low surface a
Significance and Impact of the Study: The use of excised meat pieces in an environmental cabinet offers a more flexible approach to determining the use of different chilling regimes in the production of safe meat. 相似文献
110.
Biological Nitrogen Fixation in Two Tropical Forests: Ecosystem-Level Patterns and Effects of Nitrogen Fertilization 总被引:1,自引:0,他引:1
Humid tropical forests are often characterized by large nitrogen (N) pools, and are known to have large potential N losses.
Although rarely measured, tropical forests likely maintain considerable biological N fixation (BNF) to balance N losses. We
estimated inputs of N via BNF by free-living microbes for two tropical forests in Puerto Rico, and assessed the response to
increased N availability using an on-going N fertilization experiment. Nitrogenase activity was measured across forest strata,
including the soil, forest floor, mosses, canopy epiphylls, and lichens using acetylene (C2H2) reduction assays. BNF varied significantly among ecosystem compartments in both forests. Mosses had the highest rates of
nitrogenase activity per gram of sample, with 11 ± 6 nmol C2H2 reduced/g dry weight/h (mean ± SE) in a lower elevation forest, and 6 ± 1 nmol C2H2/g/h in an upper elevation forest. We calculated potential N fluxes via BNF to each forest compartment using surveys of standing
stocks. Soils and mosses provided the largest potential inputs of N via BNF to these ecosystems. Summing all components, total
background BNF inputs were 120 ± 29 μg N/m2/h in the lower elevation forest, and 95 ± 15 μg N/m2/h in the upper elevation forest, with added N significantly suppressing BNF in soils and forest floor. Moisture content was
significantly positively correlated with BNF rates for soils and the forest floor. We conclude that BNF is an active biological
process across forest strata for these tropical forests, and is likely to be sensitive to increases in N deposition in tropical
regions. 相似文献