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   70023篇
  免费   5056篇
  国内免费   6495篇
化学   25927篇
晶体学   285篇
力学   6301篇
综合类   1244篇
数学   27091篇
物理学   20726篇
  2023年   544篇
  2022年   1020篇
  2021年   1172篇
  2020年   1313篇
  2019年   1565篇
  2018年   1297篇
  2017年   1551篇
  2016年   1770篇
  2015年   1593篇
  2014年   2306篇
  2013年   4490篇
  2012年   2667篇
  2011年   3093篇
  2010年   2679篇
  2009年   3828篇
  2008年   4282篇
  2007年   4471篇
  2006年   4173篇
  2005年   3535篇
  2004年   3246篇
  2003年   3333篇
  2002年   3051篇
  2001年   2586篇
  2000年   2529篇
  1999年   2268篇
  1998年   2122篇
  1997年   1755篇
  1996年   1551篇
  1995年   1397篇
  1994年   1289篇
  1993年   1099篇
  1992年   1066篇
  1991年   827篇
  1990年   685篇
  1989年   599篇
  1988年   542篇
  1987年   433篇
  1986年   368篇
  1985年   433篇
  1984年   428篇
  1983年   209篇
  1982年   341篇
  1981年   402篇
  1980年   302篇
  1979年   290篇
  1978年   222篇
  1977年   206篇
  1976年   154篇
  1974年   110篇
  1973年   104篇
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
991.
利用精炼的C语言进行程序设计,定量模拟狭义相结论的运动时钟变慢,并对处于两种不同时空观的时钟运行进行对比,使得时间膨胀效应变得直观。  相似文献   
992.
We give a short proof of the inner product conjecture for the symmetric Macdonald polynomials of type An-1. As a special case, the corresponding constant term conjecture is also proved.  相似文献   
993.
A pulsed field gradient version of the sensitivity-enhanced 2D TOCSY experiment is proposed which yields high-quality spectra with improved sensitivity and a minimum of two scans pert1increment. For rapid acquisition of 1D TOCSY spectra, the 1D DPFGSE–TOCSY experiment was modified to include phase-encoded multiple-selective excitation followed by a simple spectral editing. Combination of these two building blocks is used in a sensitivity-enhanced 2D analog of the 3D TOCSY–TOCSY experiment which provides an efficient tool for resolving severely overlapped signals of oligomers in short experimental time.  相似文献   
994.
为进一步提高大学物理实验的教学质量,本文就实验课的预习、操作、实验报告的撰写及考核方法进行了探讨。  相似文献   
995.
本文考察了以微波等离子体炬(MPT)为光源,电热钽丝环进样时,溶液中共存元素对发射信号的影响。  相似文献   
996.
We construct a series of pairs of domains in the plane and pairs of surfaces with boundary that are isospectral but not isometric. The construction is based on the existence of finite transformation groups that are spectrally equivalent but not isomorphic. Translated fromMatematicheskie Zametki, Vol. 63, No. 5, pp. 660–664, May, 1998. This research was partially supported by the Russian Foundation for Basic Research and by INTAS under joint grant No. 96-01-00043.  相似文献   
997.
The viscosity-dependent retarding effect of a polymeric solvent on the rotation of small solute molecules is investigated by13C NMR relaxation measurements. It is found that the relaxation data of 1,3-dibromoadamantane in highly viscous polymeric chlorotrifluoroethene can be explained neither by isotropic nor by realistic anisotropic tumbling in a single environment. The experimental data are rationalized in terms of fast exchange between at least two environments with correlation times differing by up to two orders of magnitude. The study shows that a uniform retardation of molecular tumbling by a polymeric solvent, desirable for shifting the NMR observation window in studies of intramolecular mobility, is not always feasible.  相似文献   
998.
We propose a formulation of the term structure of interest rates in which the forward curve is seen as the deformation of a string. We derive the general condition that the partial differential equations governing the motion of such string must obey in order to account for the condition of absence of arbitrage opportunities. This condition takes a form similar to a fluctuation-dissipation theorem, albeit on the same quantity (the forward rate), linking the bias to the covariance of variation fluctuations. We provide the general structure of the models that obey this constraint in the framework of stochastic partial (possibly non-linear) differential equations. We derive the general solution for the pricing and hedging of interest rate derivatives within this framework, albeit for the linear case (we also provide in the appendix a simple and intuitive derivation of the standard European option problem). We also show how the “string” formulation simplifies into a standard N-factor model under a Galerkin approximation. Received: 30 January 1998 / Revised: 12 February 1998 / Accepted: 16 February 1998  相似文献   
999.
    
The solvent extraction of cobalt(II), nickel(II) and copper(II) using 2,4-pent-dione (Hacac) and 4-phenyl-2, 4-but-dione (Hbzac) is carried out by varying the reagent concentration and pH of the aqueous phase. Each of these metals is quantitatively separated (≈ 98%) from their binary mixtures with monovalent (Ag), divalent (Mn, Zn, Cd, Hg, Mg, Sn, Pb) and trivalent (Cr, Fe) metals. The extraction constants are calculated from the metal distribution data using linear regression analysis. The extracted species is MA2 in each case. A most significant result is separation of copper(II) from iron(III) which otherwise interferes when extracted from the acidic medium.  相似文献   
1000.
本文在Menser概率赋范空间中引入了(Φ,Δ)型概率收缩的概念,研究了Menger概率赋范空间中具有这类概率收缩的非线性算子方程的解的存在性与唯一性.发展和改进了引文[1]、[4~8]的相应结果.  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