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   437518篇
  免费   19385篇
  国内免费   10086篇
化学   220704篇
晶体学   6597篇
力学   24001篇
综合类   515篇
数学   61878篇
物理学   153294篇
  2022年   4643篇
  2021年   5204篇
  2020年   5942篇
  2019年   5777篇
  2018年   14231篇
  2017年   14623篇
  2016年   12638篇
  2015年   7810篇
  2014年   9872篇
  2013年   18142篇
  2012年   20540篇
  2011年   30143篇
  2010年   19662篇
  2009年   19466篇
  2008年   25036篇
  2007年   27554篇
  2006年   14080篇
  2005年   18169篇
  2004年   13624篇
  2003年   12179篇
  2002年   10135篇
  2001年   9916篇
  2000年   7929篇
  1999年   6645篇
  1998年   5600篇
  1997年   5485篇
  1996年   5393篇
  1995年   4780篇
  1994年   4521篇
  1993年   4365篇
  1992年   4417篇
  1991年   4542篇
  1990年   4142篇
  1989年   3939篇
  1988年   3899篇
  1987年   3705篇
  1986年   3505篇
  1985年   4503篇
  1984年   4640篇
  1983年   3664篇
  1982年   3901篇
  1981年   3786篇
  1980年   3612篇
  1979年   3784篇
  1978年   3856篇
  1977年   3712篇
  1976年   3829篇
  1975年   3472篇
  1974年   3460篇
  1973年   3557篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
广义最小偏差法(GLDM)是层次分析中一种重要的排序方法.本文讨论了广义最小偏差法的性质和灵敏度分析问题.  相似文献   
992.
A study of the gas-phase parameters involved in ArF laser induced chemical vapour deposition of silicon-oxide thin films is presented. A complete set of experiments has been performed showing the influence of the concentration of the precursor gases, N2O and SiH4, and their influence on total and partial pressures on film growth and properties. In this paper we demonstrate the ability of this LCVD method to deposit silicon oxide films of different compositions and densities by appropriate control of gas composition and total pressure. Moreover, a material specific calibration plot comprising data obtained using different preparation techniques is presented, allowing determination of the stoichiometry of SiO x films by using FTIR spectroscopy independently of the deposition method. For the range of processing conditions examined, the experimental results suggest that chemical processes governing deposition take place mainly in the gas phase.  相似文献   
993.
Flowing and static gas-phase samples of HNO3 in O2 and N2 were analyzed by long-path ultraviolet/visible (UV/VIS) spectroscopy to reveal the presence of both NO2 and NO3, the concentrations of which were calculated using differential absorption cross sections. NO2 is produced predominantly by the heterogeneous decomposition of HNO3, whereas NO3 is generated in the gas phase by the thermal decomposition of N2O5, a product of the self-disproportionation of liquid HNO3. © 1993 John Wiley & Sons, Inc.  相似文献   
994.
995.
含三正辛胺微胶囊对六价铬的富集   总被引:5,自引:0,他引:5  
本文将对六价铬有效的萃取剂TOA(三正辛胺)微胶囊化,制成填充柱型的酸性体系六价铬的富集分离装置。实验结果表明,微胶囊填充柱中每毫升TOA对六价铬的最大萃取容量为158.0g/mL,为纯TOA液相萃取的4.9倍。微胶囊经碱/水洗涤后,可再生使用。  相似文献   
996.
Elliptic systems of two second-order equations, which can be written as a single equation with complex coefficients and a homogeneous operator, are studied. The necessary and sufficient conditions for the connection of traces of a solution are obtained for an arbitrary bounded domain with a smooth boundary. These conditions are formulated in the form of a certain moment problem on the boundary of a domain; they are applied to the study of boundary-value problems. In particular, it is shown that the Dirichlet problem and the Neumann problem are solvable only together. In the case where the domain is a disk, the indicated moment problem is solved together with the Dirichlet problem and the Neumann problem. The third boundary-value problem in a disk is also investigated.Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 45, No. 11, pp. 1476–1483, November, 1993.  相似文献   
997.
A theoretical model of Dewangan, in which the total scattering wave function is approximated by a distorted wave containing two Coulomb wave functions, is discussed and its relation with the Brauner-Briggs-Klar model for ionization is examined. An important feature of the theory is that it includes a second Born amplitude naturally and in addition, contains, albeit approximately, both real and imaginary parts of all higher order Born terms. The theory is applied to study the 1s→2s excitation of hydrogen by electrons in the energy range 54.4 to 400eV. The differential and integral cross sections predicted by the theory are compared with the results of other theories and experimental data at 54.4eV and a good agreement is found.  相似文献   
998.
Two Convergence Problems for Monotone Sequences   总被引:1,自引:0,他引:1  
Rong Zhang  Li Wang 《Acta Appl Math》1997,47(2):213-220
Eight measures of rate of convergence of monotone sequences of real numbers have been proposed and discussed in a paper by Beyer, Ebanks, and Qualls (Acta Appl. Math. 20 (1990), 267–284). These rates arose in discussions of dynamical systems. In the comparisons of these rates, two problems remained. A complete answer is given to one of the problems and a partial answer is given to the other problem.  相似文献   
999.
We solve the problem of the normal and transverse shear in an anisotropic monolith during the excavation of a stratum of solid mineral. It is shown that the stress perturbation field in the rock is due to the whole extent of the excavated portion of the stratum. We study way in which the friction that arises between the interacting rock of the roof and the floor influences the strain and stress fields as the front of the excavation evolves, and also the influence of the extent of the excavated portion of the rock stratum on the magnitude of the accumulated tangential displacements. Three figures. Translated fromTeoreticheskaya i Prikladnaya Mekhanika, No. 25, 1995, pp. 62–69.  相似文献   
1000.
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