全文获取类型
收费全文 | 7785篇 |
免费 | 886篇 |
国内免费 | 728篇 |
专业分类
化学 | 1281篇 |
晶体学 | 120篇 |
力学 | 742篇 |
综合类 | 149篇 |
数学 | 5200篇 |
物理学 | 1907篇 |
出版年
2024年 | 9篇 |
2023年 | 83篇 |
2022年 | 102篇 |
2021年 | 126篇 |
2020年 | 216篇 |
2019年 | 239篇 |
2018年 | 206篇 |
2017年 | 247篇 |
2016年 | 283篇 |
2015年 | 218篇 |
2014年 | 386篇 |
2013年 | 664篇 |
2012年 | 371篇 |
2011年 | 477篇 |
2010年 | 400篇 |
2009年 | 432篇 |
2008年 | 474篇 |
2007年 | 484篇 |
2006年 | 423篇 |
2005年 | 404篇 |
2004年 | 348篇 |
2003年 | 321篇 |
2002年 | 341篇 |
2001年 | 303篇 |
2000年 | 309篇 |
1999年 | 254篇 |
1998年 | 222篇 |
1997年 | 206篇 |
1996年 | 144篇 |
1995年 | 102篇 |
1994年 | 84篇 |
1993年 | 58篇 |
1992年 | 50篇 |
1991年 | 57篇 |
1990年 | 33篇 |
1989年 | 39篇 |
1988年 | 40篇 |
1987年 | 28篇 |
1986年 | 17篇 |
1985年 | 32篇 |
1984年 | 30篇 |
1983年 | 17篇 |
1982年 | 21篇 |
1981年 | 16篇 |
1980年 | 13篇 |
1979年 | 19篇 |
1978年 | 16篇 |
1977年 | 7篇 |
1976年 | 8篇 |
1974年 | 4篇 |
排序方式: 共有9399条查询结果,搜索用时 15 毫秒
991.
992.
谢凤艳 《浙江大学学报(理学版)》1959,46(6):656-659
设G是有限群,X是G的一个非空子集,子群H称为在G中X-ss-半置换,若H在G中有补充子群T,对于T的任意Sylowp-子群P,只要(p,|H|)=1,就存在x∈X使得HPx=PxH。通过对p2-阶子群的X-ss-半置换性研究,得到了p-幂零群的新判断。 相似文献
993.
Let N points be arbitrarily chosen on the circle with unit circumference, and order them clockwise. The uniform mth order spacings are then defined as the clockwise distances between any pair of points having m − 1 other points in between. A Glivenko-Cantelli theorem and nonlinear almost sure bounds for the empirical distribution function based on these uniform spacings are derived. The parameter m is allowed to increase with N to infinity. Applications to linear combinations of functions of mth order spacings are given. 相似文献
994.
Shan-Huo Chen 《Fuzzy Sets and Systems》1985,17(2):113-129
Up to now, these are five methods of ranking n fuzzy numbers in order, but these methods contain some confusions and occasionally conflict with intuition. This paper introduces the concept of maximizing set and minimizing set to decide the ordering value of each fuzzy number and uses these values to determine the order of the n fuzzy numbers. In addition, we give a method for calculating the ordering value of each fuzzy number with triangular, trapezoidal, and two-sided drum-like shaped membership functions. 相似文献
995.
It is proved that the correlation coefficient between the elements of the order statistics is maximal for a rectangularly (uniformly) distributed population. 相似文献
996.
Kenneth S. Kaminsky Lennart S. Rhodin 《Annals of the Institute of Statistical Mathematics》1985,37(1):507-517
The principle of maximum likelihood is applied to the joint prediction and estimation of a future random variable and an unknown
parameter. We assume dependence between present and future, and the approach is non-Bayesian. Our principal application is
to the prediction of higher order statistics from lower ones in Type II censored random samples. Some simple criteria for
existence and uniqueness of the predictor are given for this situation and the methods are illustrated with several examples. 相似文献
997.
Q. F. Xiao E. Brück Z. D. Zhang F. R. de Boer K. H. J. Buschow 《Journal of magnetism and magnetic materials》2004,280(2-3):381-390
We have investigated the ordering transformation and magnetic properties of Fe59.75Pt39.5Nb0.75 bulk alloys in detail by using different high-temperature homogenization treatments, different cooling rates and different low-temperature annealing treatments to obtain samples with different microstructure and different atomically ordered states. The quenching rate after the high-temperature homogenization treatment was chosen much lower than in previous investigations. In this way, we were able to obtain nanostructured bulk alloys consisting exclusively of the hard-magnetic face-centered-tetragonal phase. A high remanence ratio was obtained by profiting from the nanocomposite exchange coupling between nearest-neighbor-ordered regions. The present results are compared with results of previous investigations in which much higher cooling rates were applied. We also discussed why the present alloy systems are less suitable for the attainment of exchange spring behavior. 相似文献
998.
The phase transition behaviour of an amplifier with positive feedback is experimentally studied. The results are interpreted
using catastrophe theory language. Zero (in Gilmore’s classification), first and second-order transitions are demonstrated
by driving the system along appropriate trajectories in control parameter space and the cusp and the spinodal are mapped.
The fluctuations of the order parameter are investigated and their relationship to system response time established. Quench
experiments analogous to those familiar in condensed matter have also been performed and with similar results. 相似文献
999.
L.J. Ratliff 《Journal of Pure and Applied Algebra》1978,12(2):159-175
A chain condition intermediate to the catenary property and the chain condition for prime ideals (c.c.) is studied. Like the c.c., the condition is inherited from a semi-local domain R by integral extension domains, by local quotient domains, and by factor domains, and a semi-local ring that satisfies the condition is catenary. (Unlike the c.c., none of these statements is true when R is not semi-local.) A number of characterizations of a semi-local domain that satisfies the condition are given in terms of: integral (respectively, algebraic, transcendental) extension domains, Henselizations, completions, Rees rings, associated graded rings and certain discrete valuation over-rings. Then four of the catenary chain conjectures are characterized in terms of this condition. 相似文献
1000.
The crystallization process of the thermoplastic polyimide derived from 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) and 2,2-dimethyl-1,3,-(4-aminophenoxy) propane (DMDA) is studied at the molecular level by utilizing infrared spectroscopy's sensitivity to local molecular environment. Assignments of the unique spectral features appearing upon crystallization are made with additional verification from crystalline model imide compounds. A direct comparison of an annealed polyimide film studied by both infrared spectroscopy and x-ray diffraction shows fairly close agreement in the amount of crystallinity obtained. The unique crystalline infrared spectral features provide insight into the molecular mechanism involved with the crystallization process. Spectral shifts occurring upon crystallization reflect intramolecular rotations toward increased coplanarity as well as intermolecular chain packing of certain molecular groups at specific sites of the chain backbone. The site specific information is then used to study the relative kinetic behavior of the intramolecular and intermolecular effects occurring during crystallization. © 1994 John Wiley & Sons, Inc. 相似文献