首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   51280篇
  免费   4090篇
  国内免费   3446篇
  2024年   88篇
  2023年   518篇
  2022年   1251篇
  2021年   2249篇
  2020年   1531篇
  2019年   1940篇
  2018年   2075篇
  2017年   1703篇
  2016年   2207篇
  2015年   2566篇
  2014年   3290篇
  2013年   3595篇
  2012年   4101篇
  2011年   3857篇
  2010年   2708篇
  2009年   2397篇
  2008年   2760篇
  2007年   2506篇
  2006年   2193篇
  2005年   1837篇
  2004年   1732篇
  2003年   1627篇
  2002年   1349篇
  2001年   1077篇
  2000年   935篇
  1999年   693篇
  1998年   427篇
  1997年   361篇
  1996年   345篇
  1995年   369篇
  1994年   335篇
  1993年   260篇
  1992年   352篇
  1991年   328篇
  1990年   248篇
  1989年   243篇
  1988年   180篇
  1987年   223篇
  1986年   193篇
  1985年   190篇
  1984年   157篇
  1983年   153篇
  1982年   139篇
  1981年   117篇
  1980年   92篇
  1979年   107篇
  1978年   103篇
  1977年   84篇
  1976年   92篇
  1973年   107篇
排序方式: 共有10000条查询结果,搜索用时 491 毫秒
31.
32.
This paper presents an algorithm for determining the content of oil products in remediated soil that is safe for plants and microorganisms. The algorithm includes laboratory modeling of the remediation of soil samples that contain different amounts of soil products, determination of the biological parameters that provide the integral characterization of the soil state in these samples, and analysis of the results on the basis of odds-ratio statistics, which allows one to determine the content of oil products, starting from which the state of an oil-contaminated soil has no significant difference from a control soil.  相似文献   
33.
DC‐UbP/UBTD2 is a ubiquitin (Ub) domain‐containing protein first identified from dendritic cells, and is implicated in ubiquitination pathway. The solution structure and backbone dynamics of the C‐terminal Ub‐like (UbL) domain were elucidated in our previous work. To further understand the biological function of DC‐UbP, we then solved the solution structure of the N‐terminal domain of DC‐UbP (DC‐UbP_N) and studied its Ub binding properties by NMR techniques. The results show that DC‐UbP_N holds a novel structural fold and acts as a Ub‐binding domain (UBD) but with low affinity. This implies that the DC‐UbP protein, composing of a combination of both UbL and UBD domains, might play an important role in regulating protein ubiquitination and delivery of ubiquitinated substrates in eukaryotic cells.  相似文献   
34.
35.
New olean-18(19)-ene triterpenoids were effectively synthesized by the interaction of allobetulin or its acetate with phosphorous oxychloride in refluxing pyridine. The structures of the synthesized 17-chloromethyloleane-18(19)-enes were confirmed by NMR spectroscopy and X-ray analysis.  相似文献   
36.
37.
We studied intraspecific features of the main enzymes of metabolism and detoxication of xenobiotics on mice (eight inbred lines) and rats (five lines) for estimation of possible variants of complete or incomplete metabolic equality. Significant genetically determined intraspecific differences for activities of the enzymes of metabolism and detoxication of xenobiotics were described. Generalized criteria for comparison of the metabolic status were proposed on the basis of activities of the main enzymes: cytochrome P-450 (hydroxylation and epoxidation), epoxyhydrolase, glutathione-S-transferase, UDP-glucuronosyl transferase, and sulfotransferase. The proposed criteria for estimation of the metabolic parameters of an individual can serve as a basis of metabolic portraiting.  相似文献   
38.
39.
Accumulation of hyperphosphorylated tau in the entorhinal cortex (EC) is one of the earliest pathological hallmarks in patients with Alzheimer’s disease (AD). It can occur before significant Aβ deposition and appears to “spread” into anatomically connected brain regions. To determine whether this early-stage pathology is sufficient to cause disease progression and cognitive decline in experimental models, we overexpressed mutant human tau (hTauP301L) predominantly in layer II/III neurons of the mouse EC. Cognitive functions remained normal in mice at 4, 8, 12 and 16 months of age, despite early and extensive tau accumulation in the EC. Perforant path (PP) axon terminals within the dentate gyrus (DG) contained abnormal conformations of tau even in young EC-hTau mice, and phosphorylated tau increased with age in both the EC and PP. In old mice, ultrastructural alterations in presynaptic terminals were observed at PP-to-granule cell synapses. Phosphorylated tau was more abundant in presynaptic than postsynaptic elements. Human and pathological tau was also detected within hippocampal neurons of this mouse model. Thus, hTauP301L accumulation predominantly in the EC and related presynaptic pathology in hippocampal circuits was not sufficient to cause robust cognitive deficits within the age range analyzed here.  相似文献   
40.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号