全文获取类型
收费全文 | 49319篇 |
免费 | 4700篇 |
国内免费 | 21篇 |
出版年
2022年 | 223篇 |
2021年 | 658篇 |
2020年 | 390篇 |
2019年 | 548篇 |
2018年 | 650篇 |
2017年 | 576篇 |
2016年 | 956篇 |
2015年 | 1518篇 |
2014年 | 1757篇 |
2013年 | 2278篇 |
2012年 | 2785篇 |
2011年 | 2838篇 |
2010年 | 1822篇 |
2009年 | 1704篇 |
2008年 | 2596篇 |
2007年 | 2604篇 |
2006年 | 2511篇 |
2005年 | 2605篇 |
2004年 | 2477篇 |
2003年 | 2475篇 |
2002年 | 2425篇 |
2001年 | 592篇 |
2000年 | 412篇 |
1999年 | 619篇 |
1998年 | 716篇 |
1997年 | 486篇 |
1996年 | 517篇 |
1995年 | 449篇 |
1994年 | 483篇 |
1993年 | 448篇 |
1992年 | 445篇 |
1991年 | 410篇 |
1990年 | 431篇 |
1989年 | 366篇 |
1988年 | 400篇 |
1987年 | 383篇 |
1986年 | 354篇 |
1985年 | 472篇 |
1984年 | 580篇 |
1983年 | 481篇 |
1982年 | 539篇 |
1981年 | 602篇 |
1980年 | 601篇 |
1979年 | 379篇 |
1978年 | 386篇 |
1977年 | 396篇 |
1976年 | 361篇 |
1975年 | 291篇 |
1974年 | 357篇 |
1973年 | 317篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
Abstract: The phosphorylcholine concentration of rat brain rises and falls in response to parallel changes in the concentration of circulating choline. A single oral dose of choline chloride (20 mmol/kg) elevated whole-brain concentrations of both choline and phosphorylcholine 5 h after administration; a greater proportion of exogenously administered choline was retained by the brain in its phosphorylated form than as the free arnine. Striatal phosphorylcholine concentrations were elevated within 2 h of choline administration and continued to be significantly greater than control values for up to 34 h after treatment. The response of striatal choline levels to exogenous choline was of shorter duration than that of phosphorylcholine and was correlated with a significant increase in striatal acetylcholine concentrations. The consumption of a choline-free diet for 7 days lowered both serum choline and striatal phosphorylcholine concentrations, but had no effect on striatal choline or acetylcholine. These results suggest that choline kinase is unsaturated by its substrate in vivo and may thus serve to modulate the response of brain choline concentrations to alterations in the supply of circulating choline. 相似文献
23.
24.
25.
Energy-dispersive X-ray microanalysis of membrane-associated inclusions in hydrogenosomes isolated from Trichomonas vaginalis 总被引:1,自引:0,他引:1
Energy-dispersive X-ray microprobe analysis of electron-dense inclusions in hydrogenosomes isolated from the aerotolerant anaerobic protozoal human parasite Trichomonas vaginalis, Bushby strain, indicated the presence of high levels of Mg, P and Ca. This suggested that divalent cation (e.g. Ca2+ or Mg2+) accumulation by hydrogenosomes may be important in the regulation of intracellular ion concentrations. 相似文献
26.
Jin Wei Mia Madel Alfajaro Peter C. DeWeirdt Ruth E. Hanna William J. Lu-Culligan Wesley L. Cai Madison S. Strine Shang-Min Zhang Vincent R. Graziano Cameron O. Schmitz Jennifer S. Chen Madeleine C. Mankowski Renata B. Filler Neal G. Ravindra Victor Gasque Fernando J. de Miguel Ajinkya Patil Huacui Chen Craig B. Wilen 《Cell》2021,184(1):76-91.e13
- Download : Download high-res image (212KB)
- Download : Download full-size image
27.
28.
Published gene frequency data, checked for consistency of allele definitions across laboratories and for comparability of
geographically identical samples, were pooled into a data set containing frequencies at nine loci for each of 20 populations
that encompassed 10 macaque species. Genetic distances were calculated by the methods of Kidd and Cavalli-Sforza (1974). These
distances were used to construct phylogenetic trees and to evaluate the relationships between divergence times and effective
population sizes. Inter-and intraspecific genetic distances and the groupings defined by phenetic tree analyses support Fooden’s
(1976) classification of the genus Macacainto four species groups. A paleozoogeographical model of Asia including the known times of major sea-level changes allows
us to explain Macacainto four species groups. A paleozoogeographical model of Asia including the known times of major sea-level changes allows
us to explain qualitatively the inferred evolutionary relationships among macaque species. Many assumptions are required in
order to estimate the variables necessary in the quantitative prediction of genetic differences for a comparison between any
two populations. Examination of those assumptions demonstrates the need for more accurate genetic as well as paleozoogeographic
information.
An erratum to this article is available at . 相似文献
29.
John A. Schneider Rakhi Dandona Shravani Pasupneti Vemu Lakshmi Chuanhong Liao Vijay Yeldandi Kenneth H. Mayer 《PloS one》2010,5(7)
Studies of HIV prevention interventions such as pre-exposure prophylaxis (PREP) and circumcision in India are limited. The present study sought to investigate Indian truck-drivers initial commitment to PREP and circumcision utilizing the AIDS Risk Reduction Model. Ninety truck-drivers completed an in-depth qualitative interview and provided a blood sample for HIV and HSV-2 testing. Truck-drivers exhibited low levels of initial commitment towards PREP and even lower for circumcision. However, potential leverage points for increasing commitment were realized in fear of infecting family rather than self, self-perceptions of risk, and for PREP focusing on cultural beliefs towards medication and physicians. Cost was a major barrier to both HIV prevention interventions. Despite these barriers, our findings suggest that the ARRM may be useful in identifying several leverage points that may be used by peers, health care providers and public health field workers to enhance initial commitment to novel HIV prevention interventions in India. 相似文献
30.
William Sellar 《BMJ (Clinical research ed.)》2000,321(7271):1297