全文获取类型
收费全文 | 11663篇 |
免费 | 2083篇 |
国内免费 | 1576篇 |
专业分类
化学 | 7349篇 |
晶体学 | 230篇 |
力学 | 680篇 |
综合类 | 91篇 |
数学 | 1045篇 |
物理学 | 5927篇 |
出版年
2024年 | 19篇 |
2023年 | 136篇 |
2022年 | 270篇 |
2021年 | 356篇 |
2020年 | 465篇 |
2019年 | 426篇 |
2018年 | 406篇 |
2017年 | 400篇 |
2016年 | 529篇 |
2015年 | 477篇 |
2014年 | 549篇 |
2013年 | 1376篇 |
2012年 | 689篇 |
2011年 | 757篇 |
2010年 | 574篇 |
2009年 | 721篇 |
2008年 | 697篇 |
2007年 | 640篇 |
2006年 | 682篇 |
2005年 | 596篇 |
2004年 | 557篇 |
2003年 | 515篇 |
2002年 | 459篇 |
2001年 | 351篇 |
2000年 | 394篇 |
1999年 | 315篇 |
1998年 | 248篇 |
1997年 | 228篇 |
1996年 | 185篇 |
1995年 | 160篇 |
1994年 | 177篇 |
1993年 | 144篇 |
1992年 | 125篇 |
1991年 | 106篇 |
1990年 | 85篇 |
1989年 | 79篇 |
1988年 | 55篇 |
1987年 | 39篇 |
1986年 | 51篇 |
1985年 | 47篇 |
1984年 | 50篇 |
1983年 | 15篇 |
1982年 | 31篇 |
1981年 | 25篇 |
1980年 | 18篇 |
1979年 | 18篇 |
1978年 | 12篇 |
1977年 | 10篇 |
1976年 | 8篇 |
1973年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Iwao Omae 《应用有机金属化学》2009,23(3):91-107
Group 9 metal compounds in organic synthesis have two characteristic reactions. The first occurs because the group 9 metals have a high affinity to carbon–carbon or carbon–nitrogen π‐bonds. The first type of characteristic reactions in these group 9 metal compounds includes Pauson–Khand reactions, the Pauson–Khand‐type reactions ([2 + 2 + 1] cyclization), the other cyclizations and coupling reactions. The second occurs because the group 9 metals have a high affinity to carbonyl groups. The second type of characteristic reactions includes carbonylations such as hydroformylations, the carbonylations of methanol, amidocarbonylations and other carbonylations. The first characteristic reactions are applied for the synthesis of fine chemicals such as pharmaceuticals and agrochemicals. However, the second characteristic reactions are utilized not only for fine chemicals but also for important bulk commodity chemicals such as aldehydes, carboxylic acids and alcohols. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
992.
V.M. Shabaev A.N. Artemyev O.M. Zherebtsov V.A. Yerokhin G. Plunien G. Soff 《Hyperfine Interactions》2000,127(1-4):279-286
The present status of calculations of the hyperfine splitting and the transition probability between the hyperfine splitting
components in hydrogen and lithium like ions is discussed. The results of the calculations are compared with recent experimental
data. A special attention is focused on the hyperfine splitting in hydrogen like lead and lithium like bismuth. It is shown
that the theoretical prediction for the ground state hyperfine splitting in lead based on the single particle nuclear model
for the Bohr-Weisskopf effect is in fair agreement with experiment. The theoretical prediction for the ground state hyperfine
splitting in lithium like bismuth is improved due to more accurate calculations of the interelectronic interaction, QED, and
nuclear corrections.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
993.
Taining Liang Xiaozhen Yang Xiangyu Zhang 《Journal of Polymer Science.Polymer Physics》2001,39(19):2243-2251
The prediction of chemical structures that possess higher glass‐transition temperatures (Tg's) is crucial for designing polyimides. Because of a lack of suitable parameters, several estimation methods cannot be used for this purpose. In this study, therefore, we used molecular dynamic simulation with the DREIDING II force field to predict Tg's for polyimides. Simulated results indicated a good agreement with experimental observations. A barrier analysis of the bridging bonds between moieties along the main‐chain backbone showed a correlation between Tg and the barrier height. This proved to be helpful in a preliminary selection before the molecular dynamic simulation for accelerating the process of research and development on new polyimides. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2243–2251, 2001 相似文献
994.
We consider the permeability estimation problem in two-phase porous media flow. We try to identify the permeability field by utilizing both the production data from wells as well as inverted seismic data. The permeability field is assumed to be piecewise constant, or can be approximated well by a piecewise constant function. A variant of the level set method, called Piecewise Constant Level Set Method is used to represent the interfaces between the regions with different permeability levels. The inverse problem is solved by minimizing a functional, and TV norm regularization is used to deal with the ill-posedness. We also use the operator-splitting technique to decompose the constraint term from the fidelity term. This gives us more flexibility to deal with the constraint and helps to stabilize the algorithm. 相似文献
995.
Let F= F(X) be a free group of rand n, A be a finite subset of F(X) and x∈X be a generator. The theorem states that x can be denoted as a rotation-inserting word of A if x is in the normal closure of A in F(X). Finally, an application of the theorem in Heegaard splitting of 3manifolds is given. 相似文献
996.
M. Fukuyama 《Journal of statistical physics》2000,98(5-6):1049-1061
Georgii's theorem ensures that, restricted to two-dimensional planes, a single ocean (i.e., infinite connected component) of a ground state and islands (i.e., finite connected components) are observed in lattice spin systems at sufficiently low temperature. This paper extends his results for higher dimensional hyperplanes. Our proof is mainly based on a kind of Peierls argument and is different from Georgii's, which relies on the percolation method. 相似文献
997.
M. M. A. Imran D. Bhandari N. S. Saxena 《Journal of Thermal Analysis and Calorimetry》2001,65(1):257-274
Results of phase transformations, enthalpy released and specific heat of Ge22Se78–xBix(x=0, 4 and 8) chalcogenide glasses, using differential scanning calorimetry (DSC), under non-isothermal condition have been reported and discussed. The glass transition temperature, T
g, is found to increase with an average coordination number and heating rates. Following Gibbs—Dimarzio equation, the calculated values of T
g (i.e. 462.7, 469.7 and 484.4 K) and the experimental values (i.e. 463.1, 467.3 and 484.5 K) increase with Bi concentration. Both values of T
g, at a heating rate of 5 K min–1, are found to be in good agreement. The glass transition activation energy increases i.e. 102±2, 109±3 and 115±8 kJ mol–1 with Bi concentration. The demand for thermal stability has been ensured through the temperature difference T
c–T
g and the enthalpy released during the crystallization process. Below T
g, specific heat has been observed to be temperature independent but highly compositional dependent. The growth kinetic has been investigated using the Kissinger, Ozawa, Matusita and modified JMA equations. Results indicate that the crystallization ability is enhanced, the activation energy of crystallization increases with increasing the Bi content and the crystal growth of these glasses occur in 3 dimensions.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
998.
Stephen R. Elliott C. N. R. Rao John M. Thomas 《Angewandte Chemie (International ed. in English)》1986,25(1):31-46
This article sets out to describe and account for the chemical and physical consequences of the presence of gross disorder in solids. Knowledge of the structure of such disordered materials is an obvious prerequisite to a further understanding of other properties and behavior, and our current knowledge of the structure of various noncrystalline systems is discussed together with the experimental techniques which need to be employed in order to obtain such information. The so-called glass transition, which takes place as a liquid is supercooled below the crystallization temperature, is discussed in terms of the various models which have been proposed to account for this phenomenon. The effect of noncrystallinity on electronic properties is also discussed, and we highlight new developments in the understanding of electron localization and transport processes. Finally, two applications of amorphous solids are considered in some detail: optical fibers for use in communication networks and “superionic” glasses for possible use in solid-state batteries. 相似文献
999.
本文利用分子动力学方法研究了KCl晶体在ρ=ρ0时的温度相变。面心立方(fcc)和体心立方(bcc)两种结构的径向分布函数随温度的变化的情况说明,在高压下,发生着bcc结构相fcc结构的转变,bcc结构是不稳定的。为了选取合理的势参数,利用了分子动力学程序在T=0时的性质,计算了NaCl和KCl晶体的零温状态方程,研究了它们在压力作用下发生的多形性相变。计算表明,NaCl和KCl晶体将分别于18.8 GPa和5.9 GPa发生从fcc到bcc的多形性相变,这些值相当接近实验结果。着说明本文选用的势参数势有一定精度的。 相似文献
1000.
Summary We have studied the scattering of electrons by a structured target in the presence of a quantizing static magnetic field,
under the assumption that the presence of the field does not affect the behaviour of the massive target nuclei, but it influences
only the motion of the incident electrons. In this case, the electron motion in the plane perpendicular to the magnetic field
is confined within a typical distance given by the cyclotron radius ρ0=(cℏ/|e|B)1/2, that for particular values of the intensity of the magnetic field can be comparable with the distance between two scattering
centres. The known field-free interference conditions are modified, depending both on the energy of the incident particle
and on the intensity and the direction of the magnetic field. The general case of a three-dimensional scattering array has
been derived in detail. Numerical results are given for the case of two scattering centres in perpendicular geometry.
To speed up publication, the authors of this paper have agreed to not receive the proofs for correction. 相似文献