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   296564篇
  免费   3436篇
  国内免费   625篇
化学   158664篇
晶体学   4283篇
力学   12571篇
综合类   9篇
数学   34861篇
物理学   90237篇
  2020年   2455篇
  2019年   2549篇
  2018年   3465篇
  2017年   3446篇
  2016年   5286篇
  2015年   3336篇
  2014年   5026篇
  2013年   12340篇
  2012年   9359篇
  2011年   11473篇
  2010年   7879篇
  2009年   7520篇
  2008年   10791篇
  2007年   10942篇
  2006年   10151篇
  2005年   9154篇
  2004年   8287篇
  2003年   7484篇
  2002年   7343篇
  2001年   7865篇
  2000年   6144篇
  1999年   4709篇
  1998年   4159篇
  1997年   4114篇
  1996年   3975篇
  1995年   3676篇
  1994年   3866篇
  1993年   3651篇
  1992年   4042篇
  1991年   3920篇
  1990年   3885篇
  1989年   3686篇
  1988年   3810篇
  1987年   3720篇
  1986年   3522篇
  1985年   4726篇
  1984年   4963篇
  1983年   4180篇
  1982年   4322篇
  1981年   4268篇
  1980年   4194篇
  1979年   4145篇
  1978年   4499篇
  1977年   4380篇
  1976年   4416篇
  1975年   4072篇
  1974年   4090篇
  1973年   4272篇
  1972年   2949篇
  1971年   2480篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
82.
83.
84.
85.
An innovative volatolomic approach employs the detection of biomarkers present in cerumen (earwax) to identify cattle intoxication by Stryphnodendron rotundifolium Mart., Fabaceae (popularly known as barbatimão). S. rotundifolium is a poisonous plant with the toxic compound undefined and widely distributed throughout the Brazilian territory. Cerumen samples from cattle of two local Brazilian breeds (‘Curraleiro Pé-Duro’ and ‘Pantaneiro’) were collected during an experimental intoxication protocol and analyzed using headspace (HS)/GC–MS followed by multivariate analysis (genetic algorithm for a partial least squares, cluster analysis, and classification and regression trees). A total of 106 volatile organic metabolites were identified in the cerumen samples of bovines. The intoxication by S. rotundifolium influenced the cerumen volatolomic profile of the bovines throughout the intoxication protocol. In this way, it was possible to detect biomarkers for cattle intoxication. Among the biomarkers, 2-octyldecanol and 9-tetradecen-1-ol were able to discriminate all samples between intoxicated and nonintoxicated bovines. The cattle intoxication diagnosis by S. rotundifolium was accomplished by applying the cerumen analysis using HS/GC–MS, in an easy, accurate, and noninvasive way. Thus, the proposed bioanalytical chromatography protocol is a useful tool in veterinary applications to determine this kind of intoxication.  相似文献   
86.
Research on Chemical Intermediates - A series of quinoxaline derivatives were efficiently synthesized by convenient and simple procedure in excellent yields using 1 wt.% of titanium silicate (TS-1)...  相似文献   
87.
88.
Galkina  E. G.  Zaspel  C. E.  Ivanov  B. A.  Kulagin  N. E.  Lerman  L. M. 《JETP Letters》2019,110(7):481-486
JETP Letters - The motion of domain walls in GdFeCo-type ferrimagnets near the point of compensation of sublattice spins s1 and s2, when the effects of the exchange increase in the limiting wall...  相似文献   
89.
90.
Prostate cancer is a highly prevalent disease and ranks second among malignant neoplasms that affect men around the world, behind lung cancer alone. Trace elements are very important and are involved in many cellular processes. The X-ray microfluorescence technique is an advanced tool of high spatial resolution, sensitivity, multielemental analysis, and nondestructiveness for trace element study. This study aimed to investigate the elemental distribution in spheroids obtained through the following human prostate cell lines using synchrotron X-ray microfluorescence: tumor cell line androgen independent (DU145), tumor cell line androgen dependent (LNCaP), and normal cell line (RWPE-1). The measurements were performed with a standard geometry of 45° of incidence, excited by a white beam using a pixel of 25 μm and an acquisition time of 300 ms/pixel at the X-ray fluorescence beamline at the Synchrotron Light National Laboratory (Campinas, Brazil). The synchrotron X-ray microfluorescence results showed differences between groups in all elements analyzed and suggested that further studies should be performed to understand the relationship of these trace elements with the progression and development of the disease.  相似文献   
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