全文获取类型
收费全文 | 3544篇 |
免费 | 253篇 |
国内免费 | 275篇 |
专业分类
4072篇 |
出版年
2024年 | 8篇 |
2023年 | 42篇 |
2022年 | 109篇 |
2021年 | 199篇 |
2020年 | 126篇 |
2019年 | 154篇 |
2018年 | 161篇 |
2017年 | 104篇 |
2016年 | 137篇 |
2015年 | 194篇 |
2014年 | 268篇 |
2013年 | 264篇 |
2012年 | 348篇 |
2011年 | 294篇 |
2010年 | 165篇 |
2009年 | 144篇 |
2008年 | 189篇 |
2007年 | 143篇 |
2006年 | 136篇 |
2005年 | 107篇 |
2004年 | 84篇 |
2003年 | 97篇 |
2002年 | 78篇 |
2001年 | 41篇 |
2000年 | 58篇 |
1999年 | 62篇 |
1998年 | 34篇 |
1997年 | 30篇 |
1996年 | 23篇 |
1995年 | 30篇 |
1994年 | 26篇 |
1993年 | 22篇 |
1992年 | 32篇 |
1991年 | 24篇 |
1990年 | 23篇 |
1989年 | 19篇 |
1988年 | 15篇 |
1987年 | 14篇 |
1986年 | 9篇 |
1985年 | 9篇 |
1984年 | 7篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1969年 | 3篇 |
1966年 | 2篇 |
1951年 | 2篇 |
排序方式: 共有4072条查询结果,搜索用时 15 毫秒
31.
Idiopathic dilated cardiomyopathy (IDC) has been hypothesized as a multifactorial disorder initiated by an environment trigger
in individuals with predisposing human leukocyte antigen (HLA) alleles. Published data on the association between HLA-DR polymorphism
and IDC risk are inconclusive. To derive a more precise estimation of the relationship, a meta-analysis was performed. A total
of 19 case–control studies including 1,378 cases and 10,383 controls provided data on the association between HLA-DR polymorphism
and genetic susceptibility to IDC. Overall, statistically elevated frequencies of HLA-DR4 (OR 1.58; 95% CI 1.21–2.07; P = 0.0009) and HLA-DR5 (OR 1.35; 95% CI 1.05–1.73; P = 0.02) alleles were found in patients with IDC compared with controls. Individuals with HLA-DR3 antigen have a protective
effect against IDC (OR 0.72; 95% CI 0.58–0.90; P = 0.004). In summary, this meta-analysis indicated that certain HLA-DR alleles may be genetic markers for susceptibility
and resistance to IDC. 相似文献
32.
The type VI secretion systems (T6SS) have emerging roles in interspecies competition. In order to have an advantage in defense against other organisms, this system in Pseudomonas aeruginosa delivers a peptidoglycan amidase (Tse1) to the periplasmic space of a competitor. An immune protein (Tsi1) is also produced by the bacterium to protect itself from damage caused by Tse1. Tsi1 directly interacts with Tse1. We report that the crystal structure of Tse1 displays a common CHAP protein fold. Strikingly, our structures showed that the third residue in the catalytic triad may be novel as this residue type has not been observed previously. 相似文献
33.
应用ELISA直接双抗体夹心法检查轮状病毒抗原,24份仔猪和29份犊牛的腹泻粪样,分别有12和16份阳性。用病毒RNA电泳分析检查阳性粪样,各出现两种病毒RNA电泳型,用中和试验检查17份成年牛和16份成年猪血清,分别有16和15份病毒抗体阳性。将其与ELISA间接法和结合法进行了比较。 相似文献
34.
Xiaodan Ni Joseph H. Davis Nikhil Jain Aida Razi Samir Benlekbir Andrew G. McArthur John L. Rubinstein Robert A. Britton James R. Williamson Joaquin Ortega 《Nucleic acids research》2016,44(17):8442-8455
YphC and YsxC are GTPases in Bacillus subtilis that facilitate the assembly of the 50S ribosomal subunit, however their roles in this process are still uncharacterized. To explore their function, we used strains in which the only copy of the yphC or ysxC genes were under the control of an inducible promoter. Under depletion conditions, they accumulated incomplete ribosomal subunits that we named 45SYphC and 44.5SYsxC particles. Quantitative mass spectrometry analysis and the 5–6 Å resolution cryo-EM maps of the 45SYphC and 44.5SYsxC particles revealed that the two GTPases participate in the maturation of the central protuberance, GTPase associated region and key RNA helices in the A, P and E functional sites of the 50S subunit. We observed that YphC and YsxC bind specifically to the two immature particles, suggesting that they represent either on-pathway intermediates or that their structure has not significantly diverged from that of the actual substrate. These results describe the nature of these immature particles, a widely used tool to study the assembly process of the ribosome. They also provide the first insights into the function of YphC and YsxC in 50S subunit assembly and are consistent with this process occurring through multiple parallel pathways, as it has been described for the 30S subunit. 相似文献
35.
36.
37.
38.
MeiSheng Yi Ni Hong ZhenDong Li Yan Yan DanKe Wang HaoBin Zhao YunHan Hong 《中国科学:生命科学英文版》2010,53(4):426-434
Stem cells are present in developing embryos and adult tissues of multicellular organisms. Owing to their unique features, stem cells provide excellent opportunities for experimental analyses of basic developmental processes such as pluripotency control and cell fate decision and for regenerative medicine by stem cell-based therapy. Stem cell cultures have been best studied in 3 vertebrate organisms. These are the mouse, human and a small laboratory fish called medaka. Specifically, medaka has given rise to... 相似文献
39.
利用大型环境生长箱研究了两种幼龄沙地优势灌木柠条 (Caraganaintermedia) 和羊柴 (Hedysarummon golicum) 对CO2 浓度倍增和土壤干旱交互作用的响应。CO2 浓度倍增并没有改善两种沙生灌木叶片的水分状况, 而土壤干旱使叶片的相对含水量 (RWC) 显著降低。在土壤水分充足条件下, CO2 浓度倍增促进两种沙生灌木植株生长, 在干旱条件下则主要促进根的生长, 提高根冠比。土壤干旱显著减少了植株生物量, 但相对促进了根的生长, 特别是显著提高了羊柴的根冠比。CO2 倍增使稳定性碳同位素组分 (δ13 C) 降低, 但土壤干旱使之增加。两种沙生灌木叶片与根部的δ13 C值呈极显著线性关系, 羊柴的斜率大于柠条的, 表明前者叶片与根部在光合产物分配上具有较高的生态可塑性, 这和干旱条件下羊柴的根冠比增加相关联。羊柴的“源库”调节特性反映了对土壤水分胁迫具有较高的耐性。 相似文献