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   100913篇
  免费   603篇
  国内免费   478篇
化学   36031篇
晶体学   1235篇
力学   7416篇
综合类   7篇
数学   34119篇
物理学   23186篇
  2020年   206篇
  2019年   237篇
  2018年   10635篇
  2017年   10466篇
  2016年   6427篇
  2015年   1108篇
  2014年   701篇
  2013年   1535篇
  2012年   4499篇
  2011年   11287篇
  2010年   6196篇
  2009年   6618篇
  2008年   7365篇
  2007年   9545篇
  2006年   954篇
  2005年   1951篇
  2004年   2077篇
  2003年   2496篇
  2002年   1518篇
  2001年   962篇
  2000年   828篇
  1999年   592篇
  1998年   556篇
  1997年   490篇
  1996年   518篇
  1995年   502篇
  1994年   432篇
  1993年   424篇
  1992年   411篇
  1991年   457篇
  1990年   420篇
  1989年   433篇
  1988年   397篇
  1987年   398篇
  1986年   391篇
  1985年   459篇
  1984年   484篇
  1983年   357篇
  1982年   369篇
  1981年   394篇
  1980年   379篇
  1979年   385篇
  1978年   373篇
  1977年   336篇
  1976年   350篇
  1975年   311篇
  1974年   300篇
  1973年   325篇
  1967年   347篇
  1966年   301篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
871.
872.
The production of the neutralK ? (892) resonances by 200 GeVK ? andπ ? has been studied over the kinematic range 0.0<x f<1.0 andp t 2 <5.0 GeV2. Longitudinal and transverse momentum distributions are presented. In addition the decay angular distributions inK ? fragmentation to \(\bar K^{0*} \) have been investigated.  相似文献   
873.
From hyperfine interaction studles on free single electron16O(3) ions. in a time differential mode using the recoil distance technique. It is shown that these ions are polarized when emerging from magnetized thin layers of Fe. The observed degree of polarization , however, is smaller than expected from transient field measurements.  相似文献   
874.
This paper is concerned with a combined production-transportation scheduling problem. The problem comprises a simple, two-machine, automated manufacturing cell, which either stands alone or is a subunit of a complete flexible manufacturing system. The cell consists of two machines in series with a dedicated part-handling device such as a crane or robotic arm for transferring parts from the first machine to the second. The loading of a new piece on the first machine and the ejection of a finished piece from the second machine are performed by dedicated automated mechanisms. The introduction of parts into the system is done n at a time, whereby the parts are reshuffled into a sequence that minimizes completion time. All processing and transfer times are considered deterministic—a reasonable assumption for a cell comprising a robotic transfer device and two CNC machining units. What complicates the problem is the assumption of a non-negligible time for the transfer device to return (empty) from the second machine to the first. The operation is a generalization of a two-machine flowshop problem, and is formulated as a specially structured, asymmetric travelling salesman problem. An approximate polynomial time 0(n log n) algorithm is proffered. The procedure incorporates a lower bound using the Gilmore–Gomory algorithm for the no-wait, two-machine flowshop problem.  相似文献   
875.
A simple argument is presented by which one can show that the critical inverse temperature c of a two-dimensional Coulomb gas (standard or hard-core) with activityz satisfies , where in the low-activity limit. Previous results yield .  相似文献   
876.
We investigate representations of classical noncompact Lie groups induced by representations of the maximal parabolic subgroup. Formulas are obtained for 5O0(2p, 2q)/U(p, q) and U(2p, 2q) Sp(p, q).Translated from Ukrainskii Mathematicheskii Zhurnal, Vol. 42, No. 1, pp. 128–131, January, 1990.  相似文献   
877.
Au/Pt(111) has been studied by spin-, angle- and energy-resolved photoemission with normal incident circularly polarized synchrotron radiation of BESSY and normal photoelectron emission for different Au coverages. The prepared layers were characterized by LEED and Augerelectron spectroscopy and turned out to grow up two dimensional and epitaxially. In the photoemission experiments the development of the 3-dimensional bandstructure in the -direction could be observed. For a coverage of 2.6 layers the highest occupied spin-orbit split bands are located at about 0.6 eV lower binding energy than the corresponding bands for a 3D-Au crystal and show dispersion which is, however, weaker than in a 3D-Au crystal. A 5 layer Au adsorbate was found to have already the same dispersion and energetic location as a Au(111)-crystal. For thick gold layers, which behave in photoemission like Au(111)-crystals, we find structures that cannot be due to direct transitions into a free electron like final band. The coverage dependence and spin polarization of these structures show that some of them are due to surface resonances, while the origin of one strong peak could not yet be explained conclusively. In addition we find strong hybridization and two avoided crossings in the occupied part of the bandstructure.  相似文献   
878.
The spin content of the proton is investigated by studying the flavor singlet axial structure of the nucleon in a non-topological chiral soliton model. In order to construct a nucleon state we used the generator coordinate projection method as well as a coherent state for the meson wave function. Using a standard set of parameters we found the value g A 0 ? 0.44 for the flavor singlet axial vector coupling constant. This result is not far from that of a typical valence quark model.  相似文献   
879.
The influence of impurity scattering is studied theoretically in a two-layer model for the high-T c superconductor Y1Ba2Cu3O7– with intra- and inter-layer pairing. Two types of impurities are considered: (I) impurities which conserve the reflection symmetry of the two layers and (II) impurities which break it. Impurities of type (I) have no influence on the critical temperature. Type (II) impurities have strong influence onT c as well as onH c2 if there is a pairing interaction between carriers of different layers. The treatment of type (II) impurities is generalized to a periodic layer model appropriate for La2–x Ba x CuO4. Available experiments on impurities in Y1Ba2Cu3O7– and La2–x Ba x CuO4 are interpreted with our theory.  相似文献   
880.
We first demonstrate that mixed strategies are relevant in decision analysis for a maximin decision-maker quite apart from any game-theory considerations. This rectifies the apparent misconception that results from MS/OR textbooks which discuss mixed strategies only in the game-theory setting. Next we show an example of an implementable mixed strategy, by which we mean a mixed decision strategy which does not require randomization for its implementation. This application is to portfolio construction.  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