全文获取类型
收费全文 | 50232篇 |
免费 | 3717篇 |
国内免费 | 2749篇 |
出版年
2024年 | 89篇 |
2023年 | 831篇 |
2022年 | 1124篇 |
2021年 | 1692篇 |
2020年 | 1673篇 |
2019年 | 2236篇 |
2018年 | 1892篇 |
2017年 | 1347篇 |
2016年 | 1494篇 |
2015年 | 1833篇 |
2014年 | 2783篇 |
2013年 | 3636篇 |
2012年 | 2020篇 |
2011年 | 2505篇 |
2010年 | 1895篇 |
2009年 | 2188篇 |
2008年 | 2271篇 |
2007年 | 2405篇 |
2006年 | 2117篇 |
2005年 | 2026篇 |
2004年 | 1751篇 |
2003年 | 1526篇 |
2002年 | 1472篇 |
2001年 | 1260篇 |
2000年 | 1059篇 |
1999年 | 974篇 |
1998年 | 924篇 |
1997年 | 832篇 |
1996年 | 789篇 |
1995年 | 728篇 |
1994年 | 683篇 |
1993年 | 648篇 |
1992年 | 619篇 |
1991年 | 581篇 |
1990年 | 447篇 |
1989年 | 447篇 |
1988年 | 409篇 |
1987年 | 348篇 |
1986年 | 293篇 |
1985年 | 362篇 |
1984年 | 463篇 |
1983年 | 252篇 |
1982年 | 342篇 |
1981年 | 316篇 |
1980年 | 270篇 |
1979年 | 240篇 |
1978年 | 172篇 |
1977年 | 113篇 |
1976年 | 123篇 |
1973年 | 50篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
21.
22.
Pairs of radioimmunoassays, each of which include a two-dimensional matrix of standards, have been previously employed to resolve specificity problems in steroid immunoassay. In this study the bivariate radioimmunoassay principle has been applied to simultaneous measurement of plasma antidiuretic hormone, arginine vasopressin, and the synthetic antidiuretic agent 1-deamino-8-D-arginine vasopressin (desmopressin), by utilizing two arginine vasopressin antisera which show significantly different cross-reactivities with the synthetic analog. Data processing consists of mathematical representation of two curved dose-response surfaces followed by solution of this pair of nonlinear simultaneous equations for the unknown arginine vasopressin and desmopressin concentrations. Details of numerical procedures are given in the Appendix. The assay appears entirely adequate in terms of sensitivity, accuracy, and precision for measurement of these antidiuretic agents in clinical samples. No evidence of significant covariance in estimated concentrations could be detected but precision of estimation is (not unexpectedly) a function of the concentration of both agents. The plasma disappearance half-time of desmopressin (probably the second of a biphasic disappearance) was estimated as 37 min in one normal subject, which is in good agreement with a previously reported value of 30 min. 相似文献
23.
24.
Satoko Iwahori Daisuke Kohmon Junya Kobayashi Yuhei Tani Takashi Yugawa Kenshi Komatsu 《Cell cycle (Georgetown, Tex.)》2014,13(3):471-481
Ataxia-telangiectasia mutated (ATM) plays crucial roles in DNA damage responses, especially with regard to DNA double-strand breaks (DSBs). However, it appears that ATM can be activated not only by DSB, but also by some changes in chromatin architecture, suggesting potential ATM function in cell cycle control. Here, we found that ATM is involved in timely degradation of Cdt1, a critical replication licensing factor, during the unperturbed S phase. At least in certain cell types, degradation of p27Kip1 was also impaired by ATM inhibition. The novel ATM function for Cdt1 regulation was dependent on its kinase activity and NBS1. Indeed, we found that ATM is moderately phosphorylated at Ser1981 during the S phase. ATM silencing induced partial reduction in levels of Skp2, a component of SCFSkp2 ubiquitin ligase that controls Cdt1 degradation. Furthermore, Skp2 silencing resulted in Cdt1 stabilization like ATM inhibition. In addition, as reported previously, ATM silencing partially prevented Akt phosphorylation at Ser473, indicative of its activation, and Akt inhibition led to modest stabilization of Cdt1. Therefore, the ATM-Akt-SCFSkp2 pathway may partly contribute to the novel ATM function. Finally, ATM inhibition rendered cells hypersensitive to induction of re-replication, indicating importance for maintenance of genome stability. 相似文献
25.
《Cell》2021,184(22):5670-5685.e23
26.
《Cell》2021,184(25):6138-6156.e28
27.
28.
1. Simple mechanical models (random walks and the 'gas model') were used to investigate the movement patterns and intergroup encounter rates of a high- and low-density subpopulation of Grey-Cheeked Mangabeys ( Cercocebus albigena johnstoni, Lydeker) at two sites in the Kibale Forest, Western Uganda.
2. Random walk simulations showed that the presence of conspecific groups could act as 'social barriers' which constrained group movements, and promoted high levels of site attachment to a specific home range area.
3. Encounter rate models showed that in the low-density subpopulation (Kanyawara), intergroup encounters occurred no more frequently than expected if groups were moving randomly and independently of each other. This was in contrast to previous analyses which suggested that Grey-Cheeked Mangabeys employed a social spacing mechanism (mediated by male loud calls) in order to reduce the frequency of encounter to below chance levels.
4. Encounters in the high-density subpopulation (Ngogo) were found to occur less frequently than expected at short range (within 100 m). This was suggested to be due to the operation of a territorial mate defence strategy by males at this site. 相似文献
2. Random walk simulations showed that the presence of conspecific groups could act as 'social barriers' which constrained group movements, and promoted high levels of site attachment to a specific home range area.
3. Encounter rate models showed that in the low-density subpopulation (Kanyawara), intergroup encounters occurred no more frequently than expected if groups were moving randomly and independently of each other. This was in contrast to previous analyses which suggested that Grey-Cheeked Mangabeys employed a social spacing mechanism (mediated by male loud calls) in order to reduce the frequency of encounter to below chance levels.
4. Encounters in the high-density subpopulation (Ngogo) were found to occur less frequently than expected at short range (within 100 m). This was suggested to be due to the operation of a territorial mate defence strategy by males at this site. 相似文献
29.
30.
On the measurement of growth with applications to the modelling and analysis of plant growth 总被引:3,自引:0,他引:3
M. L. Roderick 《Functional ecology》2000,14(2):244-251