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   170761篇
  免费   2300篇
  国内免费   716篇
化学   91961篇
晶体学   2461篇
力学   7604篇
综合类   7篇
数学   17708篇
物理学   54036篇
  2021年   992篇
  2020年   1114篇
  2019年   1127篇
  2018年   1155篇
  2017年   1167篇
  2016年   2330篇
  2015年   1909篇
  2014年   2485篇
  2013年   7688篇
  2012年   6269篇
  2011年   7936篇
  2010年   4883篇
  2009年   5032篇
  2008年   7301篇
  2007年   7284篇
  2006年   7007篇
  2005年   6534篇
  2004年   5855篇
  2003年   5045篇
  2002年   4954篇
  2001年   6027篇
  2000年   4559篇
  1999年   3474篇
  1998年   2625篇
  1997年   2617篇
  1996年   2567篇
  1995年   2275篇
  1994年   2161篇
  1993年   2026篇
  1992年   2343篇
  1991年   2309篇
  1990年   2022篇
  1989年   2005篇
  1988年   2028篇
  1987年   1961篇
  1986年   1871篇
  1985年   2774篇
  1984年   2752篇
  1983年   2206篇
  1982年   2391篇
  1981年   2272篇
  1980年   2226篇
  1979年   2173篇
  1978年   2243篇
  1977年   2199篇
  1976年   2129篇
  1975年   2118篇
  1974年   2023篇
  1973年   2105篇
  1972年   1199篇
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
891.
Results from a systematic experiment on isolated perfused rat heart and isolated myocytes of adult rat showed that the mechanism of calcium influx during myocardial ischemia-reperfusion is due to the development of intracellular sodium overload during ischemic period; on reperfusion, the high intracellular Na+ content activated the reverse direction of Na(+)-Ca2+ exchange over myocardial sarcolemma (SL), thus a large quantity of extracellular Ca2+ fluxed over the SL to the intracellular space, forming a condition of intracellular Ca2+ overload, which leads to irreversible damage of the myocardium.  相似文献   
892.
893.
Hyperfine Interactions - Sm2(Co1?x Fe x )17 alloys form the basis of a new class of permanent magnets. We have investigated these materials with57Fe Mössbauer spectroscopy. Alloys...  相似文献   
894.
A new apparatus for measuring the magnetic properties of metal clusters has been constructed. The technique involves the conventional Stern-Gerlach deflection scheme together with modern pulsed laser vaporization source technology and time of flight mass spectrometry. High field seeking monodirectional deflections have been measured for cobalt clusters containing between 40 and 400 atoms. The measured magnetic moments per atom are found to be lower than the known values for the bulk. Special attention has been given to velocity measurements of the metal clusters and the carrier gas atoms in the beam. The residence time of the particles in the source cavity has been measured.  相似文献   
895.
Feng Liu  C. T. Salling  M. G. Lagally   《Surface science》1997,370(2-3):L213-L218
The edge structure and stability of monolayer-high islands fabricated on Si(001) surfaces by scanning tunneling microscopy have been analyzed theoretically. In contrast to the edges of similar islands grown by depositing Si, the properties of edges of fabricated islands are determined by the length of the trench of dimers that are removed to create the island. We demonstrate the possibility of controlling the edge structure, and thus the stability, through a selective process of atom removal.  相似文献   
896.
We give an overview of current methods for the detection of point mutations as well as small insertions and deletions in clinical diagnostics. For each method, the following characteristics are specified: (a) principle, (b) major modifications, (c) maximum fragment size that can be analyzed, (d) ratio and type of mutations that can be detected (e) minimum ratio of mutant to wild-type alleles at which mutations can be detected, and (j) detection methods. Special attention is paid to the possibilities of quality assessment and the potential for standardization and automation.  相似文献   
897.
898.
Preparation of Papers   总被引:8,自引:0,他引:8  
We motivate the study of a vector variational inequality by a practical flow equilibrium problem on a network, namely a generalization of the well-known Wardrop equilibrium principle. Both weak and strong forms of the vector variational inequality are discussed and their relationships to a vector optimization problem are established under various convexity assumptions.  相似文献   
899.
We classify smooth subvarieties of codimension twoXP n , 4≤n≤5, which are arithmetically Cohen-Macaulay and of non general type. By the way we exhibit some classes of non extendable subvarieties. Then we give new proofs of the classification of scrolls inP 4; finally we consider smooth surfaces of non general type inP 4 arising from rank three vector bundles.
Sunto Classifichiamo le sottovarietà lisce di codimensione dueXP n , 4≤n≤5, aritmeticamente Cohen-Macaulay e non di tipo generale. Nel contempo descriviamo alcune classi di sottovarietà non estendibili. Diamo poi due nuove dimostrazioni della classificazione degli scrolls inP 4; infine consideriamo superfici lisce inP 4, non di tipo generale, associate a fibrati di rango tre.
  相似文献   
900.
LetB1: n× N1m1,B2: n× N2m2andQ: m2m1be bilinear forms which are related as follows: ifμandνsatisfyB1(ξ, μ)=0 andB2(ξ, ν)=0 for someξ≠0, thenμτ=0. Supposep−1+q−1=1. Coifman, Lions, Meyer and Semmes proved that, ifuLp( n) andvLq( n), and the first order systemsB1(D, u)=0,B2(D, v)=0 hold, thenuτQvbelongs to the Hardy spaceH1( n), provided that both (i)p=q=2, and (ii) the ranks of the linear mapsBj(ξ, ·) : Njm1are constant. We apply the theory of paracommutators to show that this result remains valid when only one of the hypotheses (i), (ii) is postulated. The removal of the constant-rank condition whenp=q=2 involves the use of a deep result of Lojasiewicz from singularity theory.  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