全文获取类型
收费全文 | 17971篇 |
免费 | 1563篇 |
国内免费 | 612篇 |
专业分类
化学 | 5319篇 |
晶体学 | 24篇 |
力学 | 1516篇 |
综合类 | 106篇 |
数学 | 7655篇 |
物理学 | 5526篇 |
出版年
2024年 | 27篇 |
2023年 | 176篇 |
2022年 | 311篇 |
2021年 | 426篇 |
2020年 | 474篇 |
2019年 | 498篇 |
2018年 | 338篇 |
2017年 | 439篇 |
2016年 | 661篇 |
2015年 | 542篇 |
2014年 | 852篇 |
2013年 | 1375篇 |
2012年 | 779篇 |
2011年 | 910篇 |
2010年 | 765篇 |
2009年 | 1054篇 |
2008年 | 1227篇 |
2007年 | 1231篇 |
2006年 | 1004篇 |
2005年 | 738篇 |
2004年 | 637篇 |
2003年 | 671篇 |
2002年 | 656篇 |
2001年 | 497篇 |
2000年 | 520篇 |
1999年 | 454篇 |
1998年 | 415篇 |
1997年 | 301篇 |
1996年 | 240篇 |
1995年 | 213篇 |
1994年 | 201篇 |
1993年 | 181篇 |
1992年 | 162篇 |
1991年 | 111篇 |
1990年 | 107篇 |
1989年 | 101篇 |
1988年 | 123篇 |
1987年 | 85篇 |
1986年 | 81篇 |
1985年 | 111篇 |
1984年 | 88篇 |
1983年 | 27篇 |
1982年 | 53篇 |
1981年 | 50篇 |
1980年 | 51篇 |
1979年 | 40篇 |
1978年 | 35篇 |
1977年 | 38篇 |
1976年 | 32篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
L. A. Sakhnovich 《Functional Analysis and Its Applications》2002,36(3):205-211
The conjecture according to which the mean energy of an equilibrium system in quantum theory exceeds the mean energy of the corresponding classical system is considered. It is rigorously proved that the conjecture holds for the potential well. The estimates for the mean energy of the potential well at high and low temperatures are of special interest. 相似文献
32.
An effective residual interaction between particles and holes for shell model calculations around 208Pb, derived from the interaction between free nucleons, is compared with the measured properties of proton-hole neutron states
in 208Tl and the interaction between proton holes is adjusted to newly measured level energies in 206Hg. These interaction elements are particularly relevant for neutron-rich nuclei. The adjustment of two mixing elements reproduces
the known γ-decay data in 208Tl.
Received: 2 April 2002 / Accepted: 2 May 2002 相似文献
33.
Coulomb systems in which the particles interact through thed-dimensional Coulomb potential but are confined in a flat manifold of dimensiond–1 are considered. The actual Coulomb potential acting is defined by particular boundary conditions involving a characteristic macroscopic distanceW in the direction perpendicular to the manifold: either it is periodic of periodW in that direction, or it vanishes on one ideal conductor wall parallel to the manifold at a distanceW from it, or it vanishes on two parallel walls at a distanceW from each other with the manifold equidistant from them. Under the assumptions that classical equilibrium statistical mechanics is applicable and that the system has the macroscopic properties of a conductor, it is shown that the suitably smoothed charge correlation function is universal, and that the free energy and the grand potential have universal dependences onW (universal means independent of the microscopic detail). The casesd=2 are discussed in detail, and the generic results are checked on an exactly solvable model. The cased=3 of a plane parallel to an ideal conductor is also explicitly worked out.Laboratoire associé au Centre National de la Recherche Scientifique-URA D0063. 相似文献
34.
F. Rubio F. García H. D. Burrows A. A. C. C. Pais A. J. M. Valente M. J. Tapia J. M. García 《Journal of polymer science. Part A, Polymer chemistry》2007,45(9):1788-1799
The interaction between trivalent lanthanide ions and poly(1,4,7,10,13‐pentaoxacyclopentadecan‐2‐yl‐methyl methacrylate), PCR5, in aqueous solution and in the solid state have been studied. In aqueous solution, evidence of a weak interaction between the lanthanides and PCR5 comes from the small red shift of the Ce(III) emission spectra and the slight broadening of the Gd(III) EPR spectra. From the Tb(III) lifetimes in the presence of H2O and D2O the loss of one or two water coordinated molecules is confirmed when Tb(III) is bound to PCR5. An association constant of the order of 200 M?1 was obtained for a 1:1 (lanthanide:15‐crown‐5) complex from the shift of the polymer NMR signals induced by Tb(III). A similar association constant is obtained from the differences of the molar conductivity of Ce(III) solution at various concentrations in presence and absence of PCR5. When Tb(III) is adsorbed on PCR5 membranes, lifetime experiments in H2O and D2O confirm the loss of 5 or 6 water coordinated molecules indicating that in solid state the lanthanide(III)‐PCR5 interaction is stronger than in solution. The adsorption of Ce(III) in PCR5 membranes shows a Langmuir type isotherm, from which an equilibrium constant of 39 M?1 has been calculated. SEM shows that the membrane morphology is not much affected by lanthanide adsorption. Support for lanthanide ion–crown interactions comes from ab initio calculations on 15‐crown‐5/La(III) complex. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1788–1799, 2007 相似文献
35.
P Rabindra Reddy P R Prasad Reddy M Harilatha Reddy 《Journal of Chemical Sciences》1987,99(5-6):297-303
Studies on interaction of La(III), Pr(III), Nd(III), Sm(III), Gd(III), Dy(III) and Er(III) with inosine and xanthosine in
a 1:1 ratio have been carried out by potentiometric equilibrium measurements at 35±0·1°C and 0·1 M (KNO3) ionic strength. Investigations were also made for the interaction of these metal ions and nucleosides with the biologically
important secondary ligands glycine and histidine. These investigations were undertaken with a view to assess the influence
of charge on the structure and stability of 1:1 metal-inosine/xanthosine systems.
DBT/India overseas Fellow at Harvard University (1986–88). 相似文献
36.
The complete and incomplete aggregation-annihilation processes are investigated with the method of generating function, and the scale exponents are obtained exactly. We find that the scale exponents of incomplete aggregation-annihilation process are different from the previous exponents obtained by different methods. The time dependence of the total number of clusters and the total mass of clusters are analytically obtained. 相似文献
37.
The current state of using expert system (ES) techniques for statistics is expounded through the difficulties of defining the notion of statistical expert system (SES) and through several well-known examples. The main characteristics of statistical expertise, and particularly the important concept of strategy are emphasized. The current state of SESs is seen in the context of the global trend of the evolution of ES, i.e. within the growth of second generation expert system (SGESs). The knowledge base of these ESs represent an attempt to represent not only experts' knowledge but also the way experts acquire their expertise, thanks to the existence of an underlying model. We show through many examples how far SESs are and/or will be able to be SGESs. 相似文献
38.
在非线性项满足全局Lipschitz条件下,本文研究了一类It型非线性时滞关联随机大系统的分散鲁棒控制问题.系统的时滞是关于状态和控制输入的.基于Lyapunov泛函及线性矩阵不等式(LMI)的分析方法,得到了无记忆状态反馈控制器使整个时滞关联随机大系统可镇定的充分条件. 相似文献
39.
Characterizations of the containment of a convex set either in an arbitrary convex set or in the complement of a finite union
of convex sets (i.e., the set, described by reverse-convex inequalities) are given. These characterizations provide ways of
verifying the containments either by comparing their corresponding dual cones or by checking the consistency of suitable associated
systems. The convex sets considered in this paper are the solution sets of an arbitrary number of convex inequalities, which
can be either weak or strict inequalities. Particular cases of dual characterizations of set containments have played key
roles in solving large scale knowledge-based data classification problems where they are used to describe the containments
as inequality constraints in optimization problems. The idea of evenly convex set (intersection of open half spaces), which
was introduced by W. Fenchel in 1952, is used to derive the dual conditions, characterizing the set containments. 相似文献
40.
Daniel Pa?ca 《Journal of Mathematical Analysis and Applications》2007,325(1):90-100
Some existence results are obtained for periodic solutions of nonautonomous second-order differential inclusions systems with p-Laplacian. 相似文献