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   735709篇
  免费   8350篇
  国内免费   2356篇
化学   397073篇
晶体学   10357篇
力学   32295篇
综合类   23篇
数学   90637篇
物理学   216030篇
  2021年   5512篇
  2020年   6225篇
  2019年   6596篇
  2018年   8067篇
  2017年   7858篇
  2016年   12851篇
  2015年   8660篇
  2014年   12839篇
  2013年   33569篇
  2012年   25315篇
  2011年   31310篇
  2010年   21267篇
  2009年   20985篇
  2008年   28538篇
  2007年   28775篇
  2006年   27053篇
  2005年   24457篇
  2004年   22332篇
  2003年   19877篇
  2002年   19538篇
  2001年   21345篇
  2000年   16358篇
  1999年   12996篇
  1998年   10890篇
  1997年   10523篇
  1996年   10382篇
  1995年   9342篇
  1994年   9119篇
  1993年   8775篇
  1992年   9843篇
  1991年   9784篇
  1990年   9325篇
  1989年   9083篇
  1988年   9226篇
  1987年   8927篇
  1986年   8535篇
  1985年   11437篇
  1984年   11709篇
  1983年   9540篇
  1982年   9996篇
  1981年   9930篇
  1980年   9408篇
  1979年   9997篇
  1978年   10197篇
  1977年   10085篇
  1976年   9976篇
  1975年   9512篇
  1974年   9447篇
  1973年   9532篇
  1972年   6377篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
Phase Relations and Sodium Ion Conductivity within the Quasi-binary System Na2SiF6/Na2AIF6 . The phase diagram of the Na2SiF6/Na3AlF6 system has been determined by means of x-ray powder diffraction, thermal analysis and conductivity measurements in the sub-solidus region. Na3AlF6 accomodates up to 73 mol.-% Na2SiF6 maintaining the crystal structure type. The sodium ion conductivity increases by about five orders of magnitude upon doping Na3AlF6 with Na2SiF6.  相似文献   
63.
Oxidation of the title compounds yields, besides the reported isoimides 3 and/or the amides 4 , also the imides 5 . The observed product dichotomy is considered as the result of an intramolecular nucleophilic attack on the aroyl group, of the pressumed zwitterionic intermediate 2 , by O or N present in the ambident N-aroylimine site of 2 . The results of AM1 calculations agree with the product studies and both permit the formulation of a set of rules correlating structure and selectivity.  相似文献   
64.
We develop an approach to the solution of the spinless Bethe-Salpeter equation for the different-mass case. Although the calculations are developed for spinzero particles in any arbitratry spherically symmetric potential, the non-Coulombic effective power-law potential is used as a kernel to produce the spin-averaged bound states of the non-self-conjugate mesons. The analytical formulas are also applicable to the self-conjugate mesons in the equal-mass case. The flavor-independent case is investigated in this work. The calculations are carried out to the third-order correction of the energy series. Results are consistent with those obtained before.  相似文献   
65.
66.
This paper reports on the first experimental observation of quantum-well states and sp-type resonances in thin single-crystal gold, silver, and copper layers formed on single-crystal W(110) surfaces, which result from spatial localization of Bloch-type electronic wave functions in a quantum well with potential barriers at the vacuum/metal and metal/W(110) interfaces. The quantization of the valence-band electronic structure in Au/W(110), Ag/W(110), and Cu/W(110) systems was studied experimentally using angle-resolved photoelectron spectroscopy.  相似文献   
67.
The problem of the vector and axial-vector dominance of weak interactions within the framework of the quark model of superconductivity type is discussed.  相似文献   
68.
69.
Physics and Mathematics Division with Computational Center of the Bashkir Branch of the USSR Academy of Sciences. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 80, No. 3, pp. 470–473, September, 1989.  相似文献   
70.
This paper presents an alternative to the beta continuous probability distribution for risk analysis. Particular attention has been given to two major applications of distributions, namely project management risk and critical path analysis (PERT). In conjunction with the beta, the triangular and normal distributions are frequently employed in order to give sufficient robustness to risk analysis. The beta distribution, as used in PERT, has a major theoretical implementation flaw. The new distribution was developed to give a possible alternative method of assessing risk. It is shown that the requirement to estimate the most pessimistic variate may be replaced by the probability to exceed the mode. Proposals for other simplifications in risk analysis are discussed. Practical means to validate the most appropriate distributions for risk analysis are outlined, and a cost-data case study is included.  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