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   41916篇
  免费   507篇
  国内免费   136篇
化学   20958篇
晶体学   707篇
力学   1740篇
综合类   2篇
数学   4889篇
物理学   14263篇
  2021年   364篇
  2020年   351篇
  2019年   358篇
  2018年   648篇
  2017年   569篇
  2016年   890篇
  2015年   539篇
  2014年   887篇
  2013年   2019篇
  2012年   1762篇
  2011年   2204篇
  2010年   1539篇
  2009年   1501篇
  2008年   1836篇
  2007年   1813篇
  2006年   1680篇
  2005年   1407篇
  2004年   1319篇
  2003年   1121篇
  2002年   1061篇
  2001年   1427篇
  2000年   1036篇
  1999年   851篇
  1998年   653篇
  1997年   626篇
  1996年   545篇
  1995年   512篇
  1994年   464篇
  1993年   427篇
  1992年   514篇
  1991年   506篇
  1990年   504篇
  1989年   465篇
  1988年   489篇
  1987年   474篇
  1986年   413篇
  1985年   496篇
  1984年   534篇
  1983年   404篇
  1982年   441篇
  1981年   415篇
  1980年   370篇
  1979年   444篇
  1978年   439篇
  1977年   427篇
  1976年   439篇
  1975年   380篇
  1974年   365篇
  1973年   373篇
  1972年   309篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
81.
In this paper, a model of a linear multilevel programming problem with dominated objective functions (LMPPD(l)) is proposed, where multiple reactions of the lower levels do not lead to any uncertainty in the upper-level decision making. Under the assumption that the constrained set is nonempty and bounded, a necessary optimality condition is obtained. Two types of geometric properties of the solution sets are studied. It is demonstrated that the feasible set of LMPPD(l) is neither necessarily composed of faces of the constrained set nor necessarily connected. These properties are different from the existing theoretical results for linear multilevel programming problems.  相似文献   
82.
83.
In this paper, we prove convergence rates for spherical spline Hermite interpolation on the sphere Sd−1 via an error estimate given in a technical report by Luo and Levesley. The functionals in the Hermite interpolation are either point evaluations of pseudodifferential operators or rotational differential operators, the desirable feature of these operators being that they map polynomials to polynomials. Convergence rates for certain derivatives are given in terms of maximum point separation.  相似文献   
84.
85.
We study condensation of ethanol-hexanol vapour by numerical solution of kinetic equations. The number of droplets formed in unit volume is computed within self-consistent classical model. It is shown that formation of ethanol-rich droplets prevails at the initial stage of nucleation process, but in the stationary state formation of droplets near the saddle point (on cluster formation energy surface) plays the dominant role. Presented at the 6th Joint Seminar “Development of Materials Science in Research and Education”, Karlštejn, Czech Republic, 17–19 September 1996. This work was supported by Grant No. A1010615 of the Grant Agency of the Academy of Sciences of the Czech Republic.  相似文献   
86.
87.
The purpose of this paper is to give the Reid ``Roundabout Theorem' for quadratic functionals with general boundary conditions. In particular, we describe the so-called coupled point and regularity condition introduced in [16] in terms of Riccati equation solutions. Accepted 27 February 1996  相似文献   
88.
The new techniques and ideas in quantum interferometry with neutrons, photons, atoms, electrons, and Bose condensates that fluorished in the last two decades have influenced in a decisive way the thinking and the research in the foundations and interpretation of quantum mechanics. The controversies existing among different schools on the reality of matter waves of quantum theory, the postulates of quantum measurement theory, and the (in)completeness of quantum mechanics have to be approached now in a new way. Our argumentation follows the spirit of the Paris school.  相似文献   
89.
Some of the motivations for as well as the main points of the quantization of the Nappi-Witten string in the light-cone gauge are reviewed.  相似文献   
90.
Unique crystallization and melting behavior in poly(aryl ether ketone ketone) containing alternated terephthalic and isophthalic moieties were studied by time-resolved synchrotron x-ray methods. Recently, this material has been shown to exhibit three polymorphs (forms I, II, and III). In this work, we further investigated their distinctive thermal properties and found that form I is the dominating and the most thermally stable phase while form II is favored by fast nucleation conditions and is the least stable phase. On the other hand, form III represents a minor intermediate phase that usually coexists with form I and can be transferred from form II and to form I. Structural and morphological changes in form I have been followed by simultaneous wide-angle x-ray diffraction (WAXD)/small-angle x-ray scattering (SAXS) measurements during cold- or melt-crystallization and subsequent melting. In all cases, a larger dimensional change was found in the crystallographic a-axis than the b-axis during heating and cooling. This may be due to the greater lateral stress variation with respect to temperature along the a direction of the primary lamellae which is induced by either the formation of secondary lamellae or the preferential chain-folding direction in poly(aryl ether ketone ketone)s. During the phase transitions of form II ← III in the cold-crystallized specimen and form III ← I in the melt-crystallized samples, lamellar variables (long period, lamellar thickness, and invariant) obtained from SAXS remain almost constant. This indicates that the density distribution in the long spacing is independent of the melting in form II or III. For melt-crystallization, the corresponding changes in unit-cell dimensions and lamellar morphology during the annealing-induced low endotherm are most consistent with the argument that these changes are due to the melting of thin lamellar population. © 1995 John Wiley & Sons, Inc.  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