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   8131篇
  免费   284篇
  国内免费   5篇
化学   4797篇
晶体学   165篇
力学   175篇
数学   1635篇
物理学   1648篇
  2023年   41篇
  2022年   48篇
  2021年   65篇
  2020年   123篇
  2019年   175篇
  2018年   201篇
  2017年   233篇
  2016年   429篇
  2015年   315篇
  2014年   384篇
  2013年   717篇
  2012年   456篇
  2011年   511篇
  2010年   350篇
  2009年   291篇
  2008年   504篇
  2007年   442篇
  2006年   384篇
  2005年   303篇
  2004年   254篇
  2003年   193篇
  2002年   153篇
  2001年   113篇
  2000年   111篇
  1999年   65篇
  1998年   77篇
  1997年   51篇
  1996年   65篇
  1995年   57篇
  1994年   45篇
  1993年   36篇
  1992年   41篇
  1991年   64篇
  1990年   52篇
  1989年   61篇
  1988年   57篇
  1987年   53篇
  1986年   52篇
  1985年   101篇
  1984年   104篇
  1983年   69篇
  1982年   62篇
  1981年   70篇
  1980年   67篇
  1979年   52篇
  1978年   41篇
  1977年   33篇
  1976年   43篇
  1975年   36篇
  1974年   32篇
排序方式: 共有8420条查询结果,搜索用时 31 毫秒
991.
In this paper we study a class of separable Banach spaces which can be approximated by certain special finite-dimensional subspaces. This class is characterized in Theorem 1.1, from which it follows that the space of continuous scalar-valued functions on a compact metric space always belongs to this class, and that every member of this class has a monotone basis. Supported in part by N.S.F. Grant 11-5020. Supported in part by N.S.F. Grant GP-3579.  相似文献   
992.
Glycinehydroxamic acid, C2H6N2O2 (NH2CH2C(O)NHOH), was synthesized and its crystal and molecular structure determined by single-crystal X-ray diffraction methods. The crystals are monoclinic:P2 1/c C 2h 5 , No. 14),a=5.682(2),b=7.133(2),c=9.540(3) Å,=104.38(4)°,Z=4. The structure has been solved by direct phase determination methods, and refined to anR value of 0.042 for 633 nonzero independent amplitudes. The molecule of the title compound exists in the structure as a zwitterion, NH 3 + -CH2-C(O)-N-OH. The hydroxamate group is planar and the N (amino) atom, from the glycine part of the molecule, deviates by 1.43 Å from the best molecular plane defined by O(1), N(1), C(1), and O(2) atoms, respectively.The molecules are held together by a network of N+-HO, N+-H¯N, and O-HO hydrogen bonds.  相似文献   
993.
1H NMR studies of mixed-ligand iron (III) dithiocarbamates have been carried out using the following ligands: N,N-diethyldithiocarbamate, morpholinyl-N-, and piperidyl-N-carbodithioate. The ligand exchange equilibria gave all species of the general formula Fe(dtc)n(dtc′)3?n, where n = 0-3 with nearly random statistical distribution of Fe(Et2dtc)n(morphdtc)3?n complexes. Magnetic moments of the mixed-ligand complexes have been determined. Both the magnetic moment and isotropic shift temperature dependences confirmed the cross-over properties of these mixed-ligand complexes.  相似文献   
994.
In this paper a Fixed-Point Theorem and an application is presented.  相似文献   
995.
In this paper new topological concepts connected with fuzzy multi-valued functions theory-as presented in the first part of this work-are introduced and their properties are investigated. As will be shown in future papers these concepts and properties are indispensable in connection with the analysis of fuzzy economic systems.  相似文献   
996.
The Hermite series estimate of a density f?Lp, p > 1, convergessin the mean square to f (x) for almost all x? |R, ifN (n) → ∞ and N (n) / n2 → ) as n → ∞, where N is the number of the Hermite functions in the estimate while n is the number of observations. Moreover, the mean square and weak consistency are equivalent. For m times differentiable densities, the mean squares convergence rate is O(n?(2m?1)/2m). Results for complete convergence are also given.  相似文献   
997.
Sufficient conditions are obtained which guarantee that all solutions (or all bounded solutions) of a class of second order nonlinear difference equations are nonoscillatory. Oscillation criteria and theorems concerning the growth of solutions are also given.  相似文献   
998.
This paper deals with some problems of the control of fuzzy systems described by means of a relational equation of the type: Xκ + 1 = Uκ ° Xκ ° R. The basic aspects such as mutual identification and control, stabilization control, control with constraints, generation of control rules of a fuzzy logic controller, important from the theoretical and applicational point of view are discussed and illustrated by means of numerical examples.  相似文献   
999.
A quantum-mechanical theory of the magnetic field effect on radiationless transitions in an isolated molecule is presented. The mechanism of this phenomenon is a second-order process relying on the simultaneous radiationless relaxation of an excited electronic state and the interaction of the molecule with a constant uniform magnetic field.  相似文献   
1000.
The crystal and molecular structure of glycinium diphenylphosphate, C14H16NO6P, has been determined by X-ray methods. The crystals are orthorhombic:Pbca (No. 61),a=11.412(3),b=24.624(7),c=10.775(3) Å,Z=8. The structure was solved by direct methods and refined to anR value of 0.043 for 1289 nonzero independent amplitudes. The molecule exists in the structure as+NH3CH2CO2H,(C6H5O)2PO 2 and is planar except for the N atom, which deviates by 0.49 Å from the plane defined by C(1), C(2), O(5), and O(6) atoms, respectively. The conformation of the diphenylphosphate anion isgauche with respect to both P-O ester bonds. There are four crystallographically independent hydrogen bonds, three of the N-HO type and one of the O-HO type.  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