全文获取类型
收费全文 | 13059篇 |
免费 | 1105篇 |
国内免费 | 6篇 |
专业分类
14170篇 |
出版年
2023年 | 76篇 |
2022年 | 205篇 |
2021年 | 305篇 |
2020年 | 168篇 |
2019年 | 300篇 |
2018年 | 338篇 |
2017年 | 295篇 |
2016年 | 437篇 |
2015年 | 694篇 |
2014年 | 711篇 |
2013年 | 903篇 |
2012年 | 1066篇 |
2011年 | 997篇 |
2010年 | 633篇 |
2009年 | 592篇 |
2008年 | 772篇 |
2007年 | 773篇 |
2006年 | 658篇 |
2005年 | 586篇 |
2004年 | 523篇 |
2003年 | 488篇 |
2002年 | 430篇 |
2001年 | 167篇 |
2000年 | 146篇 |
1999年 | 154篇 |
1998年 | 119篇 |
1997年 | 87篇 |
1996年 | 78篇 |
1995年 | 85篇 |
1994年 | 82篇 |
1993年 | 59篇 |
1992年 | 111篇 |
1991年 | 74篇 |
1990年 | 63篇 |
1989年 | 76篇 |
1988年 | 61篇 |
1987年 | 60篇 |
1986年 | 60篇 |
1985年 | 64篇 |
1984年 | 38篇 |
1983年 | 55篇 |
1981年 | 29篇 |
1980年 | 42篇 |
1979年 | 56篇 |
1978年 | 32篇 |
1977年 | 31篇 |
1976年 | 26篇 |
1974年 | 47篇 |
1972年 | 26篇 |
1968年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Molecular mechanisms of ceramide-mediated CD95 clustering. 总被引:2,自引:0,他引:2
H Grassmé H Schwarz E Gulbins 《Biochemical and biophysical research communications》2001,284(4):1016-1030
Receptor clustering has been suggested as a crucial mechanism to initiate receptor signaling. Here we show that ceramide in sphingolipid-rich membrane rafts mediates clustering of CD95. Neutralization of surface ceramide or inhibition of its endogenous generation prevented CD95 clustering. Furthermore, application of ceramide at the cell surface triggered clustering of active but not inactive CD95. Apoptosis was inhibited by neutralization of surface ceramide or inhibition of ceramide release in vitro and in vivo. Thus, we conclude that surface ceramide mediates CD95 clustering, which is required for initiation of apoptosis, at least in some cell types. 相似文献
12.
Antoine Wystrach Sebastian Schwarz Patrick Schultheiss Guy Beugnon Ken Cheng 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2011,197(2):167-179
The Australian desert ant Melophorus bagoti often follows stereotypical routes through a cluttered landscape containing both distant panoramic views and obstacles (plants)
to navigate around. We created an artificial obstacle course for the ants between a feeder and their nest. Landmarks comprised
natural objects in the landscape such as logs, branches, and tussocks. Many ants travelled stereotypical routes home through
the obstacle course in training, threading repeatedly the same gaps in the landmarks. Manipulations altering the relations
between the landmarks and the surrounding panorama, however, affected the routes in two major ways. Both interchanging the
positions of landmarks (transpositions) and displacing the entire landmark set along with the starting position of the ants
(translations) (1) reduced the stereotypicality of the route, and (2) increased turns and meanders during travel. The ants
might have used the entire panorama in view-based travel, or the distal panorama might prime the identification and use of
landmarks en route. Despite the large data set, both options (not mutually exclusive) remain viable. 相似文献
13.
Felix Roosen-Runge Marcus Hennig Tilo Seydel Fajun Zhang Maximilian W.A. Skoda Stefan Zorn Robert M.J. Jacobs Marco Maccarini Peter Fouquet Frank Schreiber 《Biochimica et Biophysica Acta - Proteins and Proteomics》2010,1804(1):68-75
We report on a combined cold neutron backscattering and spin-echo study of the short-range and long-range nanosecond diffusion of the model globular protein bovine serum albumin (BSA) in aqueous solution as a function of protein concentration and NaCl salt concentration. Complementary small angle X-ray scattering data are used to obtain information on the correlations of the proteins in solution. Particular emphasis is put on the effect of crowding, i.e. conditions under which the proteins cannot be considered as objects independent of each other. We thus address the question at which concentration this crowding starts to influence the static and in particular also the dynamical behaviour. We also briefly discuss qualitatively which charge effects, i.e. effects due to the interplay of charged molecules in an electrolyte solution, may be anticipated. Both the issue of crowding as well as that of charge effects are particularly relevant for proteins and their function under physiological conditions, where the protein volume fraction can be up to approximately 40% and salt ions are ubiquitous. The interpretation of the data is put in the context of existing studies on related systems and of existing theoretical models. 相似文献
14.
15.
16.
The signal sequence suffices to direct export of outer membrane protein OmpA of Escherichia coli K-12. 总被引:8,自引:3,他引:5
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We studied whether information required for export is present within the mature form of the Escherichia coli 325-residue outer membrane protein OmpA. We had previously analyzed overlapping internal deletions in the ompA gene, and the results allowed us to conclude that if such information exists it must be present repeatedly within the membrane part of the protein encompassing amino acid residues 1 to 177 (R. Freudl, H. Schwarz, M. Klose, N. R. Movva, and U. Henning, EMBO J. 4:3593-3598, 1985). A deletion which removed the codons for amino acid residues 1 to 229 of the OmpA protein was constructed. In this construct the signal sequence was fused to the periplasmic part of the protein. The resulting protein, designated Pro-OmpA delta 1-229, was processed, and the mature 95-residue protein accumulated in the periplasm. Hence, information required for export does not exist within the OmpA protein. 相似文献
17.
18.
19.
Luca Racca Andrea Villa Lukardis C. M. Wencker Marco Camaiti Hugues-Alexandre Blain Massimo Delfino 《Journal of morphology》2020,281(7):808-833
The skull osteology of Hierophis viridiflavus is here described and figured in detail on the basis of 18 specimens. The sample includes specimens from the ranges of both H. viridiflavus viridiflavus and H. viridiflavus carbonarius as well as specimens not identified at sub-specific level. The main characters that define H. viridiflavus in comparison to the parapatric congeneric species Hierophis gemonensis are wide maxillary diastema, basioccipital crest well distinct in three lobes and basioccipital process well marked. The foramina of the otoccipital and prootic, and the basioccipital process of the basioccipital are among the most ontogenetically variable characters, as indicated by two juvenile specimens included in the sample. A specimen-level phylogenetic analysis including H. gemonensis and other outgroups (overall 6 species, 26 specimens, 64 skull characters) recovered all H. viridiflavus specimens in one clade, indicating the presence of a clear phylogenetic signal in the applied characters. However, the resolution within the H. viridiflavus clade is poor the monophyly of H. viridiflavus carbonarius was retrieved, but not that of Hierophis v. viridiflavus. Probably due to the relatively high variability, the skull morphology does not support the recently proposed specific status of the two subspecies. 相似文献
20.
Sonja Schmidt Birthe Gericke Giulio Fracasso Dunia Ramarli Marco Colombatti Hassan Y. Naim 《PloS one》2013,8(6)
Prostate-specific membrane antigen (PSMA) is a type-II membrane glycoprotein that was initially identified in LNCaP cells. It is expressed at elevated levels in prostate cancer. In view of the correlation between the expression levels of PSMA and disease grade and stage, PSMA is considered to be one of the most promising biomarkers in the diagnosis and treatment of prostate cancer. In LNCaP cells PSMA undergoes internalization via clathrin-coated pits followed by accumulation in the endosomes. PSMA associates with different types of detergent-resistant membranes (DRMs) along the secretory pathway. Its mature form is mainly insoluble in Lubrol WX, but does not associate with Triton X-100-DRMs. To understand the mechanism of PSMA internalization we investigated its association during internalization with DRMs. For this purpose, internalization was induced by antibody cross-linking. We demonstrate at the biochemical and cell biological levels that: [i] exclusively homodimers of PSMA are associated with Lubrol WX-DRMs, [ii] antibody-induced cross-linking of PSMA molecules results in a time-dependent partitioning into another DRMs type, namely Triton X-100-DRMs, and [iii] concomitant with its association with Triton-X-100-DRMs internalization of PSMA occurs along tubulin filaments. In a previous work (Colombatti et al. (2009) PLoS One 4: e4608) we demonstrated that the small GTPases RAS and RAC1 and the MAPKs p38 and ERK1/2 are activated during antibody cross-linking. As downstream effects of this activation we observed a strong induction of NF-kB associated with an increased expression of IL-6 and CCL5 genes and that IL-6 and CCL5 enhanced the proliferative potential of LNCaP cells synergistically. These observations together with findings reported here hypothesize a fundamental role of DRMs during activation of PSMA as platforms for trafficking, endocytosis and signalling. Understanding these mechanisms constitutes an essential prerequisite for utilization of PSMA as a therapeutically suitable target in prostate cancer. 相似文献