全文获取类型
收费全文 | 157792篇 |
免费 | 7442篇 |
国内免费 | 4944篇 |
专业分类
170178篇 |
出版年
2023年 | 1044篇 |
2022年 | 2404篇 |
2021年 | 4093篇 |
2020年 | 2669篇 |
2019年 | 3253篇 |
2018年 | 4021篇 |
2017年 | 3331篇 |
2016年 | 5983篇 |
2015年 | 10851篇 |
2014年 | 11167篇 |
2013年 | 11345篇 |
2012年 | 11537篇 |
2011年 | 7971篇 |
2010年 | 5682篇 |
2009年 | 5277篇 |
2008年 | 4183篇 |
2007年 | 3766篇 |
2006年 | 3365篇 |
2005年 | 8849篇 |
2004年 | 7140篇 |
2003年 | 5090篇 |
2002年 | 2436篇 |
2001年 | 2299篇 |
2000年 | 1523篇 |
1999年 | 2570篇 |
1998年 | 978篇 |
1997年 | 819篇 |
1996年 | 766篇 |
1995年 | 764篇 |
1992年 | 2482篇 |
1991年 | 2442篇 |
1990年 | 2475篇 |
1989年 | 2279篇 |
1988年 | 2193篇 |
1987年 | 2042篇 |
1986年 | 1788篇 |
1985年 | 1844篇 |
1984年 | 1195篇 |
1983年 | 949篇 |
1979年 | 1134篇 |
1978年 | 786篇 |
1975年 | 897篇 |
1974年 | 1032篇 |
1973年 | 1039篇 |
1972年 | 983篇 |
1971年 | 951篇 |
1970年 | 834篇 |
1969年 | 847篇 |
1968年 | 744篇 |
1967年 | 766篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Mandy L. Roberts-Crowley Tora Mitra-Ganguli Liwang Liu Ann R. Rittenhouse 《Cell calcium》2009,45(6):589-601
Great skepticism has surrounded the question of whether modulation of voltage-gated Ca2+ channels (VGCCs) by the polyunsaturated free fatty acid arachidonic acid (AA) has any physiological basis. Here we synthesize findings from studies of both native and recombinant channels where micromolar concentrations of AA consistently inhibit both native and recombinant activity by stabilizing VGCCs in one or more closed states. Structural requirements for these inhibitory actions include a chain length of at least 18 carbons and multiple double bonds located near the fatty acid's carboxy terminus. Acting at a second site, AA increases the rate of VGCC activation kinetics, and in CaV2.2 channels, increases current amplitude. We present evidence that phosphatidylinositol 4,5-bisphosphate (PIP2), a palmitoylated accessory subunit (β2a) of VGCCs and AA appear to have overlapping sites of action giving rise to complex channel behavior. Their actions converge in a physiologically relevant manner during muscarinic modulation of VGCCs. We speculate that M1 muscarinic receptors may stimulate multiple lipases to break down the PIP2 associated with VGCCs and leave PIP2's freed fatty acid tails bound to the channels to confer modulation. This unexpectedly simple scheme gives rise to unanticipated predictions and redirects thinking about lipid regulation of VGCCs. 相似文献
92.
Simultaneous Display of Multiple Foreign Peptides in the FliD Capping and FliC Filament Proteins of the Escherichia coli Flagellum 下载免费PDF全文
Katariina Majander Timo K. Korhonen Benita Westerlund-Wikstr?m 《Applied microbiology》2005,71(8):4263-4268
The bacterial flagellum is composed of more than 20 different proteins. The filament, which constitutes the major extracellular part of the flagellum, is built up of approximately 20,000 FliC molecules that assemble at the growing distal end of the filament. A capping structure composed of five FliD molecules located at the tip of the filament promotes polymerization of FliC. Lack of FliD leads to release of the subunits into the growth medium. We show here that FliD can be successfully used in bacterial surface display. We tested various insertion sites in the capping protein, and the optimal region for display was at the variable region in FliD. Deletion and/or insertion at other sites resulted in decreased formation of flagella. We further developed the technique into a multihybrid display system in which three foreign peptides are simultaneously expressed within the same flagellum, i.e., D repeats of FnBPA from Staphylococcus aureus at the tip and fragments of YadA from Yersinia enterocolitica as well as SlpA from Lactobacillus crispatus along the filament. This technology can have biotechnological applications, e.g., in simultaneous delivery of several effector molecules. 相似文献
93.
L V Loskutova M A Gilinski? 《Zhurnal vysshe? nervno? deiatelnosti imeni I P Pavlova》1987,37(6):1070-1074
Character of conditioned reaction of passive avoidance was analyzed in Wistar line male rats after neurochemical destruction of terminal dopaminergic fields of the amygdalar complex. 6-hydroxydopamine was bilaterally administered to the central nucleus of the amygdalar complex after preliminary treating with desmethylimipramine for selective destruction of dopaminergic terminals. Lowering of dopamine level in the amygdalar complex led to a weakening of reproduction and to prolongation of spontaneous extinction of conditioned reaction. Features of conditioned reaction are highly similar to the effect of latent inhibition connected with attention deficit. It is suggested that activity of terminal fields of the amygdalar complex is one of the mechanisms providing for attention and intensifying selection of information in learning. 相似文献
94.
95.
96.
97.
98.
99.
100.
Substance P-like immunoreactive nerve fibers in the pars distalis of the anterior pituitary in the dog 总被引:1,自引:0,他引:1
Summary The pars distalis of the anterior pituitary is known to be regulated by hypothalamic hormones. Recently, we have discovered the presence of substance P-like immunoreactive nerve fibers in the pars distalis of the monkeys. Substance P-like immunoreactivity in the pars distalis of the dog was investigated in this study. A substantial amount of substance P-like immunoreactive nerve fibers with a large amount of varicosities were found. They were widely distributed in the gland, more abundant along its periphery. Most of them were closely related to the glandular tissue, some were located on vascular walls. Substance P-like immunoreactive nerve fibers were also found in the meningeal sheath of the anterior pituitary. They could be followed into the parenchyma of the gland. 相似文献