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   357940篇
  免费   2290篇
  国内免费   744篇
化学   174574篇
晶体学   5234篇
力学   17639篇
综合类   7篇
数学   52543篇
物理学   110977篇
  2021年   2390篇
  2020年   2666篇
  2019年   3070篇
  2018年   11380篇
  2017年   12021篇
  2016年   9237篇
  2015年   3787篇
  2014年   5252篇
  2013年   11956篇
  2012年   12788篇
  2011年   21435篇
  2010年   13943篇
  2009年   13969篇
  2008年   19367篇
  2007年   22420篇
  2006年   9922篇
  2005年   14148篇
  2004年   10709篇
  2003年   10288篇
  2002年   8442篇
  2001年   7869篇
  2000年   6288篇
  1999年   4528篇
  1998年   3973篇
  1997年   3884篇
  1996年   3713篇
  1995年   3127篇
  1994年   3187篇
  1993年   3214篇
  1992年   3397篇
  1991年   3498篇
  1990年   3331篇
  1989年   3358篇
  1988年   3227篇
  1987年   3147篇
  1986年   3012篇
  1985年   3854篇
  1984年   4095篇
  1983年   3331篇
  1982年   3631篇
  1981年   3412篇
  1980年   3175篇
  1979年   3452篇
  1978年   3704篇
  1977年   3653篇
  1976年   3580篇
  1975年   3398篇
  1974年   3384篇
  1973年   3534篇
  1972年   2393篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
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   
102.
The density functional theory calculation of 1H and 13C NMR chemical shifts in a series of ten 10 classically known Strychnos alkaloids with a strychnine skeleton was performed at the PBE0/pcSseg-2//pcseg-2 level. It was found that calculated 1H and 13C NMR chemical shifts provided a markedly good correlation with experiment characterized by a mean absolute error of 0.08 ppm in the range of 7 ppm for protons and 1.67 ppm in the range of 150 ppm for carbons, so that a mean absolute percentage error was as small as ~1% in both cases.  相似文献   
103.
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   
104.
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   
105.
Sukhorukova  O. S.  Tarasenko  A. S.  Tarasenko  S. V.  Shavrov  V. G. 《JETP Letters》2020,112(7):420-427
JETP Letters - At the resonant passage of a plane elastic shear wave through an acoustically continuous heterostructure consisting of magnetic and nonmagnetic layers in a symmetric nonmagnetic...  相似文献   
106.
Optics and Spectroscopy - Scattering of light by disordered structures is normally detrimental to their applicability in many optoelectronic devices. However, some micro and nanostructures are...  相似文献   
107.
108.
Optics and Spectroscopy - 10.1134/S0030400X17050095  相似文献   
109.
Optics and Spectroscopy - The transmission of intrinsic, antimony-doped, and gallium-doped Ge single crystals in the THz spectral range have been experimentally investigated. It is shown that the...  相似文献   
110.
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