全文获取类型
收费全文 | 181801篇 |
免费 | 843篇 |
国内免费 | 275篇 |
专业分类
化学 | 91083篇 |
晶体学 | 2652篇 |
力学 | 9424篇 |
综合类 | 7篇 |
数学 | 21207篇 |
物理学 | 58546篇 |
出版年
2020年 | 1894篇 |
2019年 | 2346篇 |
2018年 | 3452篇 |
2017年 | 3583篇 |
2016年 | 4244篇 |
2015年 | 1925篇 |
2014年 | 3650篇 |
2013年 | 7159篇 |
2012年 | 5666篇 |
2011年 | 6782篇 |
2010年 | 5618篇 |
2009年 | 5729篇 |
2008年 | 6487篇 |
2007年 | 6459篇 |
2006年 | 5799篇 |
2005年 | 5124篇 |
2004年 | 4912篇 |
2003年 | 4446篇 |
2002年 | 4593篇 |
2001年 | 5032篇 |
2000年 | 3723篇 |
1999年 | 2846篇 |
1998年 | 2617篇 |
1997年 | 2475篇 |
1996年 | 2271篇 |
1995年 | 2056篇 |
1994年 | 2014篇 |
1993年 | 2049篇 |
1992年 | 2081篇 |
1991年 | 2387篇 |
1990年 | 2318篇 |
1989年 | 2384篇 |
1988年 | 2265篇 |
1987年 | 2295篇 |
1986年 | 2125篇 |
1985年 | 2657篇 |
1984年 | 2672篇 |
1983年 | 2316篇 |
1982年 | 2371篇 |
1981年 | 2276篇 |
1980年 | 2079篇 |
1979年 | 2395篇 |
1978年 | 2548篇 |
1977年 | 2640篇 |
1976年 | 2729篇 |
1975年 | 2536篇 |
1974年 | 2467篇 |
1973年 | 2634篇 |
1972年 | 2153篇 |
1971年 | 1973篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Monoclinic (N2H6)3Zr2F13·F crystallizes in space group P21-C
2
2
(No. 4) with unit cell dimensionsa=5.670(1),b=10.984(2),c=10.601(2) Å,=93.88(1)°,V=658.7(4) Å3 andZ=2. Two different types of N2H6
2+ ions are present. One is involved in strong H-bonds to F– ions in infinite chains running along the a axis (the shortest N-F distance is 2.437(5) Å), and the other links the structure through weaker bi- and trifurcated H-bonds to fluorine ligands of the Zr2F13
5– ions. The N-N bond lengths range from 1.430(5) to 1.446(5) Å with apparently no meaningful correlation to the type of N2H2
2+ ions. The Zr2F13
5– ions have very nearly C2 point symmetry and are formed by joining two distorted bicapped trigonal prisms of ZrF8-units through a common face. Distances of Zr-F terminal bonds range from 2.015(2) to 2.112(2) Å and of bridging bonds from 2.133(2) to 2.212(2) Å. (N2H6)3Hf2F13·F is isomorphous. The vibrational spectra of the two compounds are nearly identical, with the exception of a strong infrared band, which is assigned to a stretching mode with the moving central atom within the anion. The anion part of the spectrum is simple, showing broad unresolved bands. The cation part shows two types of N2H6
– ions. H-Bonding is strongly present in the spectra, but no simple correlations with the H-bond strength is evident. 相似文献
992.
In this paper, assuming a certain set-theoretic hypothesis, a positive answer is given to a question of H. Kraljevi, namely it is shown that there exists a Lebesgue measurable subsetA of the real line such that the set {c R: A + cA contains an interval} is nonmeasurable. Here the setA + cA = {a + ca: a, a A}. Two other results about sets of the formA + cA are presented. 相似文献
993.
This short study reports an application of the Shapley value axioms to a new concept of two-stage games. In these games, the formation of a coalition in the first stage entitles its members to play a prespecified cooperative game at the second stage. The original Shapley axioms have natural equivalents in the new framework, and we show the existence of (non-unique) values and semivalues for two stage games, analogous to those defined by the corresponding axioms for the conventional (one-stage) games. However, we also prove that all semivalues (hence, perforce, all values) must give patently unacceptable solutions for some two-stage majority games (where the members of a majority coalition play a conventional majority game). Our reservations about these prescribed values are related to Roth's (1980) criticism of Shapley's -transfer value for non-transferable utility (NTU) games. But our analysis has wider scope than Roth's example, and the argument that it offers appears to be more conclusive. The study also indicates how the values and semivalues for two-stage games can be naturally generalized to apply for multi-stage games.Earlier versions of this study were presented at the International Conference on Game Theory and its Applications, organized by Ohio State University in 1987, and at the Workshop on Mathematical Economics and Game Theory at Tel Aviv Unversity. We gratefully acknowledge the valuable comments received on both occasions, especially those of Robert J. Aumann, Roy Gardner, Sergiu Hart, Ehud Kalai, Michael Maschler, Alvin E. Roth, and Lloyd S. Shapley, and also those ofIJGT's anonymous referees. Of course, all responsibility lies with us. 相似文献
994.
This paper describes a numerical realization of an extended continuous Newton method defined by Diener. It traces a connected set of locally one-dimensional trajectories which contains all critical points of a smooth functionf:
n
. The results show that the method is effectively applicable.The authors would like to thank L. C. W. Dixon for pointing out some errors in the original version of this paper and for several suggestions of improvements. 相似文献
995.
Yu. M. Berezanskii B. Ya. Levin V. A. Marchenko Yu. A. Mitropol''skii I. V. Ostrovskii 《Functional Analysis and Its Applications》1990,24(2):85-85
Obituary
Mark Grigor'evich Krein 相似文献996.
A. I. Stepanets 《Ukrainian Mathematical Journal》1990,42(1):93-102
We introduce classes
of functions defined on the real line which in the periodic case become the classes
defined by multipliers (·) and translations with respect to the argument equal to . We study the simplest properties of these classes needed for the study of their approximation characteristics which will be discussed in the second part of the paper.Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 42, No. 1, pp. 102–112, January, 1990. 相似文献
997.
Ordinary differential equations with impulse action are considered at fixed moments of time when finite limits points are admitted to the set of moments of the shocks. The topological structure of this set is clarified: it must be resolvable, in particular nowhere dense in R.Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 42, No. 3, pp. 378–383, March, 1990. 相似文献
998.
Yu. I. Volkov 《Ukrainian Mathematical Journal》1990,42(7):785-796
The concept of the deformation of positive linear operators of type B is introduced, in particular, that of a linear deformation of operators. These concepts are applied to the solving of operator equations of type B. One solves completely the problems of the determination of all positive linear operators of type B for which the covariance of the operators is 1) a polynomial of degrees 3; 2) any power function; 3) an exponential function. In addition, one finds; two families of positive linear operators of type B for which the covariance is a polynomial of degree four.Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 42, No. 7, pp. 888–900, July, 1990. 相似文献
999.
For eachd1 there is a constantc
d>0 such that any finite setXR
d contains a subsetYX, |Y|[1/4d(d+3)]+1 having the following property: ifEY is an ellipsoid, then |E X|c
d |X|.On leave from the Mathematical Institute of the Hungarian Academy of Sciences, 1364 Budapest, P.O. Box 127, Hungary. Supported by a research fellowship from the Science and Engineering Research Council, U.K., and by Hungarian National Foundation for Scientific Research Grant No. 1812. 相似文献
1000.
Oleg G. Filippov 《Annals of Global Analysis and Geometry》1990,8(2):113-126
A decomposition of any pseudodifferential operator (D) onR
n
with almost periodic symbol as 113-1 1 is obtained in the paper, where
A
(D) is a pseudodifferential operator over a certainC
*-algebraA acting on sections of a vector bundle over a torusT
n whose fibre isA. The coincidence of spectra sp (D) = sp
A
(D) is proved for all (D) either bounded or elliptic. 相似文献