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   439207篇
  免费   4994篇
  国内免费   1255篇
化学   235922篇
晶体学   6509篇
力学   18902篇
综合类   13篇
数学   50518篇
物理学   133592篇
  2021年   3868篇
  2020年   4261篇
  2019年   4620篇
  2018年   5947篇
  2017年   5817篇
  2016年   8989篇
  2015年   5661篇
  2014年   8703篇
  2013年   20486篇
  2012年   15839篇
  2011年   19471篇
  2010年   13641篇
  2009年   13482篇
  2008年   17788篇
  2007年   17673篇
  2006年   16387篇
  2005年   14657篇
  2004年   13624篇
  2003年   11981篇
  2002年   11817篇
  2001年   13476篇
  2000年   10144篇
  1999年   7953篇
  1998年   6591篇
  1997年   6344篇
  1996年   6100篇
  1995年   5495篇
  1994年   5411篇
  1993年   5215篇
  1992年   5850篇
  1991年   5934篇
  1990年   5672篇
  1989年   5496篇
  1988年   5504篇
  1987年   5380篇
  1986年   5101篇
  1985年   6582篇
  1984年   6713篇
  1983年   5312篇
  1982年   5408篇
  1981年   5385篇
  1980年   4970篇
  1979年   5366篇
  1978年   5502篇
  1977年   5392篇
  1976年   5334篇
  1975年   4925篇
  1974年   4891篇
  1973年   4886篇
  1972年   3456篇
排序方式: 共有10000条查询结果,搜索用时 3 毫秒
181.
182.
183.
The behavior of the intensity of anomalous and galactic cosmic rays in the outer heliosphere is compared. The previous hypothesis, according to which the lowest energy galactic cosmic rays affected by large-scale electric fields far beyond the termination shock wave of the solar wind may contribute to the behavior of the anomalous component intensity, is analyzed.  相似文献   
184.
We exhibit a family of homogeneous hypersurfaces in affine space, one in each dimension, that generalize the Cayley surface.  相似文献   
185.
We investigate the dependence of the relaxation time of the current flowing in a nematic cell submitted to an external dc voltage on the physical properties of the substrate. We show that previously presented analyses of the same problem are not very useful for practical applications. We compare our theoretical predictions with experimental data, and show that the agreement is rather good. The influence of the adsorption-desorption phenomenon on the relaxation time is also discussed.  相似文献   
186.
187.
188.
Electron spin resonance (ESR) spectra of poly(acrylic acid) (PAA) γ-irradiated in air at room temperature and recorded at room temperature and at liquid-nitrogen temperature have been studied to identify the radiation products. The ESR spectra are composed of eight lines with hyperfine splittings of 23 ± 1 G and 11 ± 1 G. The method of least-squares total curve fitting, employing the Lorentzian line shape function, to the observed spectra enabled the assignment of the spectra. Computed spectra obtained by the superposition of a singlet and the spectra due to chain radicals are considered to give the best fits to the observed ESR spectra. The singlet is assigned to the radicals COOH, and the component 10-line spectra are assigned to the chain radicals CH3? CH? CH2 ~ and/or ~ CH2? CH? CH2 ~. The observed change in line shape with temperature of the ESR spectra is attributed to the hindered oscillations of the methyl groups about the Cα? Cβ bond axis of the chain radicals. The existence of the methyl groups is confirmed by the measurement of infrared absorption.  相似文献   
189.
The partition coefficient of strontium upon its extraction from the aqueous solutions of picric acid into chloroform containing DC-18-crown-6, B-15-crown-5 after their exposition to gamma radiation has been studied. A significant decrease of the partition coefficient in the studied range of doses 10–70 kGy was observed. This effect can be attributed to the radiolytic products of chloroform. The radiation destruction as well as dehydrogenation of crown ethers were not observed.  相似文献   
190.
Causal realists maintain that the causal relation consists in “something more” than its relata. Specifying this relation in nonreductive terms is however notoriously difficult. Michael Tooley has advanced a plausible account avoiding some of the relation’s most obvious difficulties, particularly where these concern the notion of a cross-temporal “connection.” His account distinguishes discrete from nondiscrete causation, where the latter is suitable to the continuity of cross-temporal causation. I argue, however, that such accounts face conceptual difficulties dating from Zeno’s time. A Bergsonian resolution of these difficulties appears to entail that, for the causal realist, there can be no indirect causal relations of the sort envisioned by Tooley. A consequence of this discussion is that the causal realist must conceive all causal relations as ultimately direct.  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