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   247796篇
  免费   2901篇
  国内免费   911篇
化学   134081篇
晶体学   3748篇
力学   10030篇
综合类   2篇
数学   27724篇
物理学   76023篇
  2020年   1828篇
  2019年   2113篇
  2018年   2525篇
  2017年   2443篇
  2016年   3929篇
  2015年   2682篇
  2014年   3989篇
  2013年   11402篇
  2012年   8371篇
  2011年   10369篇
  2010年   6753篇
  2009年   6631篇
  2008年   9315篇
  2007年   9495篇
  2006年   8747篇
  2005年   8197篇
  2004年   7318篇
  2003年   6461篇
  2002年   6382篇
  2001年   7281篇
  2000年   5426篇
  1999年   4279篇
  1998年   3614篇
  1997年   3625篇
  1996年   3358篇
  1995年   3191篇
  1994年   2999篇
  1993年   3043篇
  1992年   3338篇
  1991年   3371篇
  1990年   3183篇
  1989年   3136篇
  1988年   3195篇
  1987年   3062篇
  1986年   2960篇
  1985年   4040篇
  1984年   4190篇
  1983年   3442篇
  1982年   3792篇
  1981年   3692篇
  1980年   3554篇
  1979年   3593篇
  1978年   3823篇
  1977年   3650篇
  1976年   3853篇
  1975年   3414篇
  1974年   3542篇
  1973年   3838篇
  1972年   2333篇
  1971年   1790篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The convergent iterative procedure for solving the groundstate Schr?dinger equation is extended to derive the excitation energy and the wavefunction of the low-lying excited states. The method is applied to the one-dimensional quartic potential problem. The results show that the iterative solution converges rapidly when the coupling g is not too small.  相似文献   
992.
CrCl2-mediated condensation of γ-chloro-gem-trichloroalkanes with aldehyde generates homoallylic alcohols through a hydride rearrangement followed by a Nozaki-Hiyama allylation.  相似文献   
993.
994.
A para-sexiphenyl monolayer of near up-right standing molecules (nominal thickness of 30 Å) is investigated in-situ by X-ray diffraction using synchrotron radiation and ex-situ by atomic force microscopy. A terrace like morphology is observed, the step height between the terraces is approximately one molecular length. The monolayer terraces, larger than 20 μm in size, are extended along the [0 0 1] direction of the TiO2(1 1 0) substrate i.e. along the Ti-O rows of the reconstructed substrate surface. The structure of the monolayer and its epitaxial relationship to the substrate is determined by grazing incidence X-ray diffraction. Extremely sharp diffraction peaks reveal high crystalline order within the monolayer, which was found to have the bulk structure of sexiphenyl. The monolayer terraces are epitaxially oriented with the (0 0 1) plane parallel to the substrate surface (out-of-plane order). Four epitaxial relationships are observed. This in-plane alignment is determined by the arrangement of the terminal phenyl rings of the sexiphenyl molecules parallel to the oxygen rows of the substrate.  相似文献   
995.
We explore the magnetic heat capacity in exchange-biased ferromagnet/antiferromagnet bilayers theoretically. We show that changes in the antiferromagnetic structure due to the reversal of the ferromagnet layer can be detected by distinct features in the heat capacity. This offers a method for probing antiferromagnetic domains in exchange-biased systems.  相似文献   
996.
We construct division algebras with involution containing a Baer ordering with noninvariant order ring. This gives a negative answer to a question of Holland, whether the order ring is always invariant under inner automorphisms. Furthermore, we give examples of any index. Previously, the only known examples of division algebras containing Baer orderings were of index 2 n or of indexp forp a prime of the form 4m + 3. Supported in part by the National Science Foundation.  相似文献   
997.
Summary We report on neutron emission in palladium and titanium electrolitically charged with deuterium. The detection of neutrons is observed after thermal treatment of the electrode. In the hypothesis that neutrons came from cold fusion processes, we estimate a fusion rate as high as 1.3·10−21 fusions/deuteron pair/second.  相似文献   
998.
We consider equations of motion for some massiveN=1 supermultiplets of fields, using superfields and their superderivatives. The formalism is based on the superprojectors.  相似文献   
999.
A comparison of results of indirect and direct electrochemical fluorosulfation of nonsaturated fluorocarbons shows that the main or the only product in potentiostatic conditions is vicinal fluorosulfates. Owing to a high rate of the electrochemical step, which exceeds the rate of desorption of intermediate radicals from the electrode surface into solution, it is possible to improve the process selectivity by increasing the contribution of the ionic reaction route.  相似文献   
1000.
The interaction of Ag and In with a thin film of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) was studied by near-edge X-ray absorption fine structure (NEXAFS). Upon Ag deposition on a PTCDA film of 20 nm thickness the relative intensities and lineshapes, as well as the angular dependence of the spectra remains unchanged, illustrating the formation of a chemically unreactive Ag/PTCDA interface. On the other hand, the adsorption of 0.3 nm In strongly decreases the intensity of the π* resonances in C and O K-edge NEXAFS spectra. This is attributed to a strong charge transfer between In and PTCDA, leading to a redistribution of the charge in the molecule. However, the absence of a strong shift or new features and negligible dependence of peak intensities corresponding to π* resonances on the In thickness indicate that the interaction between In and PTCDA is not accompanied by a covalent bond formation.  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