全文获取类型
收费全文 | 120128篇 |
免费 | 21663篇 |
国内免费 | 5987篇 |
出版年
2024年 | 107篇 |
2023年 | 1054篇 |
2022年 | 1354篇 |
2021年 | 5062篇 |
2020年 | 4986篇 |
2019年 | 7114篇 |
2018年 | 7201篇 |
2017年 | 6507篇 |
2016年 | 7762篇 |
2015年 | 9669篇 |
2014年 | 10239篇 |
2013年 | 11221篇 |
2012年 | 10369篇 |
2011年 | 9215篇 |
2010年 | 7618篇 |
2009年 | 5946篇 |
2008年 | 5535篇 |
2007年 | 4736篇 |
2006年 | 4151篇 |
2005年 | 3595篇 |
2004年 | 3120篇 |
2003年 | 2716篇 |
2002年 | 2383篇 |
2001年 | 2125篇 |
2000年 | 1997篇 |
1999年 | 1787篇 |
1998年 | 893篇 |
1997年 | 886篇 |
1996年 | 878篇 |
1995年 | 792篇 |
1994年 | 720篇 |
1993年 | 490篇 |
1992年 | 798篇 |
1991年 | 658篇 |
1990年 | 575篇 |
1989年 | 433篇 |
1988年 | 371篇 |
1987年 | 371篇 |
1986年 | 280篇 |
1985年 | 314篇 |
1984年 | 190篇 |
1983年 | 182篇 |
1982年 | 137篇 |
1981年 | 109篇 |
1980年 | 90篇 |
1979年 | 130篇 |
1978年 | 90篇 |
1977年 | 98篇 |
1976年 | 86篇 |
1974年 | 106篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
61.
62.
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
63.
64.
Yitao Luo Chengqiang Zhang Li Ma Yuxiao Zhang Zhengyuan Liu Li Chen Rui Wang Yujing Luan Yulan Rao 《Journal of lipid research》2022,63(6):100228
7-dehydrocholesterol (7-DHC) and cholesterol (CHOL) are biomarkers of Smith-Lemli-Opitz Syndrome (SLOS), a congenital autosomal recessive disorder characterized by elevated 7-DHC level in patients. Hair samples have been shown to have great diagnostic and research value, which has long been neglected in the SLOS field. In this study, we sought to investigate the feasibility of using hair for SLOS diagnosis. In the presence of antioxidants (2,6-ditert-butyl-4-methylphenol and triphenylphosphine), hair samples were completely pulverized and extracted by micro-pulverized extraction in alkaline solution or in n-hexane. After microwave-assisted derivatization with N,O-Bis(trimethylsilyl)trifluoroacetamide, the analytes were measured by GC-MS. We found that the limits of determination for 7-DHC and CHOL were 10 ng/mg and 8 ng/mg, respectively. In addition, good linearity was obtained in the range of 50–4000 ng/mg and 30–6000 ng/mg for 7-DHC and CHOL, respectively, which fully meets the requirement for SLOS diagnosis and related research. Finally, by applying the proposed method to real hair samples collected from 14 healthy infants and two suspected SLOS patients, we confirmed the feasibility of hair analysis as a diagnostic tool for SLOS. In conclusion, we present an optimized and validated analytical method for the simultaneous determination of two SLOS biomarkers using human hair. 相似文献
65.
66.
67.
To clarify the mechanisms of Nosema ceranae parasitism, we deep-sequenced both honey bee host and parasite mRNAs throughout a complete 6-day infection cycle. By time-series analysis, 1122 parasite genes were significantly differently expressed during the reproduction cycle, clustering into 4 expression patterns. We found reactive mitochondrial oxygen species modulator 1 of the host to be significantly down regulated during the entire infection period. Our data support the hypothesis that apoptosis of honey bee cells was suppressed during infection. We further analyzed genome-wide genetic diversity of this parasite by comparing samples collected from the same site in 2007 and 2013. The number of SNP positions per gene and the proportion of non-synonymous substitutions per gene were significantly reduced over this time period, suggesting purifying selection on the parasite genome and supporting the hypothesis that a subset of N. ceranae strains might be dominating infection. 相似文献
68.
Late Quaternary climate change,relict populations and present‐day refugia in the northern Atacama Desert: a case study from Quebrada La Higuera (18° S) 下载免费PDF全文
69.
70.