全文获取类型
收费全文 | 20119篇 |
免费 | 488篇 |
国内免费 | 443篇 |
专业分类
化学 | 3993篇 |
晶体学 | 973篇 |
力学 | 385篇 |
综合类 | 44篇 |
数学 | 11942篇 |
物理学 | 3713篇 |
出版年
2023年 | 59篇 |
2022年 | 185篇 |
2021年 | 153篇 |
2020年 | 187篇 |
2019年 | 371篇 |
2018年 | 394篇 |
2017年 | 271篇 |
2016年 | 332篇 |
2015年 | 324篇 |
2014年 | 600篇 |
2013年 | 1361篇 |
2012年 | 526篇 |
2011年 | 1581篇 |
2010年 | 1388篇 |
2009年 | 1281篇 |
2008年 | 1384篇 |
2007年 | 1360篇 |
2006年 | 1022篇 |
2005年 | 904篇 |
2004年 | 796篇 |
2003年 | 608篇 |
2002年 | 632篇 |
2001年 | 419篇 |
2000年 | 399篇 |
1999年 | 371篇 |
1998年 | 382篇 |
1997年 | 293篇 |
1996年 | 334篇 |
1995年 | 336篇 |
1994年 | 318篇 |
1993年 | 244篇 |
1992年 | 248篇 |
1991年 | 173篇 |
1990年 | 183篇 |
1989年 | 172篇 |
1988年 | 106篇 |
1987年 | 124篇 |
1986年 | 89篇 |
1985年 | 158篇 |
1984年 | 114篇 |
1983年 | 68篇 |
1982年 | 91篇 |
1981年 | 121篇 |
1980年 | 107篇 |
1979年 | 61篇 |
1978年 | 108篇 |
1977年 | 91篇 |
1976年 | 90篇 |
1975年 | 39篇 |
1974年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
172.
This work is supported in part by the fund OTKA (No. 5-134). 相似文献
173.
A simple microscopic model of charge ordering in the NaxCoO2 system is presented. The model takes into account the interplane interactions between the ordered Na ions and d electrons from the CoO2 layers as well as the nearest-neighbor intraplane Coulomb interactions between d electrons. It is shown that a driving force of charge ordering in the CoO2 layers is the interplane interaction that alone is able to describe various types of inhomogeneous charge ordering (e.g., the striped phases) as well as to predict correctly the conducting properties of the system. 相似文献
174.
Low-temperature property investigation of the lead indium-niobate-lead nickel-niobate solid solution
Edward F AlbertaAmar S Bhalla 《Journal of Physics and Chemistry of Solids》2002,63(9):1759-1769
The complex perovskite solid solution (1−x) Pb(In1/2Nb1/2)O3-(x) Pb(Ni1/3Nb2/3)O3 has been successfully prepared by the Columbite precursor method. The temperature dependencies of the dielectric constant and pyroelectric coefficient were measured between −261 and 200 °C. Relaxor ferroelectric behavior has been noticed in all compositions across the solid solution. The room-temperature electrostrictive coefficient, Q33, was 1.83×10−2 C2/m4 for x=0.10. No room-temperature piezoelectric activity was detected; however, upon cooling to −261 °C the maximum coupling coefficients kp=29%, kt=11%, and k33=31% were observed for the composition x=1.00. 相似文献
175.
Global Existence and Exponential Stability of Smooth Solutions to a Full Hydrodynamic Model to Semiconductors 总被引:1,自引:0,他引:1
We study a full hydrodynamic semiconductor model in multi-space dimension. The global existence of smooth solutions is established
and the exponential stability of the solutions as is investigated.
Received November 14, 2000; in revised form March 25, 2002 Published online August 5, 2002 相似文献
176.
The spectral structure of two parameter unbounded operator pencils of waveguide type is studied. Theorems on discreteness
of the spectrum for a fixed parameter are proved. Variational principles for real eigenvalues in some parts of the root zones
are established. In the case of n = 1 (quadratic pencils) domains containing the spectrum are described (see Fig. 1–3). Conditions in the definition of the
pencils of waveguide type arise naturally from physical problems and each of them has a physical meaning. In particular a
connection between the energetic stability condition and a perturbation problem for the coefficients is given. 相似文献
177.
LIU Biao BAO Yong-li WEI Zhuang WU Yin MENG Xiang-ying LI Yu-xin YIN Wei-tian 《高等学校化学研究》2006,22(2):217-220
Introduction Activinisamemberofthetransforminggrowth factor(TGF)βsuperfamilyofextracellularsignaling proteins.Themembersofthisfamilyplayacriticalrole duringembryogenesisandinmaintainingtissuehomeo stasisinadultlife[1—3].DeregulatedTGFfamilysigna lingisi… 相似文献
178.
Gianluigi Luppi Rodrigo J. Corrêa Angelo C. Pinto Quirinus B. Broxterman Claudia Tomasini 《Tetrahedron》2006,62(51):12017-12024
The first total synthesis of (R)-convolutamydine A has been achieved by the organocatalytic addition of acetone to 4,6-dibromoisatin. The absolute configuration was determined by single crystal X-ray diffraction. DFT studies were used to model the transition states for the aldol reaction and equilibrium geometries of the post-aldol reaction intermediates. The DFT study revealed that the aldol bond forming reaction was considerably endothermic. 相似文献
179.
Common fixed-point results are established for a new class of noncommuting selfmaps. We apply them to obtain several invariant approximation results which unify, extend, and complement well-known results. 相似文献
180.
Nicola Fusco Michele Gori Francesco Maggi 《NoDEA : Nonlinear Differential Equations and Applications》2006,13(4):425-433
An approximation theorem for families of weakly coercive convex functions by means of countably many smooth families of convex
functions is proved. As a consequence, the classical “three-fold” lower semicontinuity theorem for integral functionals of
the Calculus of Variations by James Serrin is unified in one single statement. 相似文献