全文获取类型
收费全文 | 10838篇 |
免费 | 973篇 |
国内免费 | 1339篇 |
专业分类
化学 | 723篇 |
晶体学 | 16篇 |
力学 | 636篇 |
综合类 | 285篇 |
数学 | 9471篇 |
物理学 | 2019篇 |
出版年
2024年 | 17篇 |
2023年 | 123篇 |
2022年 | 139篇 |
2021年 | 182篇 |
2020年 | 212篇 |
2019年 | 265篇 |
2018年 | 249篇 |
2017年 | 282篇 |
2016年 | 309篇 |
2015年 | 249篇 |
2014年 | 479篇 |
2013年 | 715篇 |
2012年 | 433篇 |
2011年 | 628篇 |
2010年 | 586篇 |
2009年 | 769篇 |
2008年 | 837篇 |
2007年 | 888篇 |
2006年 | 712篇 |
2005年 | 662篇 |
2004年 | 498篇 |
2003年 | 572篇 |
2002年 | 485篇 |
2001年 | 389篇 |
2000年 | 443篇 |
1999年 | 389篇 |
1998年 | 363篇 |
1997年 | 292篇 |
1996年 | 214篇 |
1995年 | 114篇 |
1994年 | 123篇 |
1993年 | 75篇 |
1992年 | 56篇 |
1991年 | 52篇 |
1990年 | 41篇 |
1989年 | 26篇 |
1988年 | 31篇 |
1987年 | 16篇 |
1986年 | 14篇 |
1985年 | 36篇 |
1984年 | 32篇 |
1983年 | 13篇 |
1982年 | 28篇 |
1981年 | 15篇 |
1980年 | 19篇 |
1979年 | 19篇 |
1978年 | 12篇 |
1977年 | 11篇 |
1976年 | 8篇 |
1936年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
141.
A family of of open subsets of the real line is called an ω-cover of a set X iff every finite subset of X is contained in an element of . A set of reals X is a γ-set iff for every ω-cover of X there exists such that In this paper we show that assuming Martin's axiom there is a γ-set X of cardinality the continuum. 相似文献
142.
Two sufficient criteria for the convergence of the Rayleigh-Ritz Method (RRM) with respect to the eigenvalues (E-convergence) of non-relativistic electronic Hamiltonians of molecules are discussed and compared. Moreover, a necessary and sufficient criterion is given. By example (Sect. 9) it is shown that the L
2-completeness of the basis is not sufficient to guarantee E-convergence. The convergence of the wave functions in different norms (-convergence) is also investigated. In particular, sufficient conditions for the one-particle basis functions (orbitals) are given, such that a CI calculation in this basis is both E- and -convergent. 相似文献
143.
CHEN Wen-Tong GUO Guo-Cong ZENG Xi-Rui LI Xin-Fa FANG Xiao-Niu KUANG Han-Mao LIU Dong-Sheng LIU Li-Min 《结构化学》2007,26(10)
The title compound (4,4'-H2bipy)[CdBr4]·H2O 1 has been synthesized via hydrothermal reaction and characterized by X-ray diffraction. The crystal belongs to monoelinic,space group P21/c with a=8.260(3), b=23.926(7), c=9.774(2) (A), β=106.777(9)°,C10H12Br4CdN2O, Mr=608.26, V=1849.4(9)(A)3, Z=4, Dc=2.185 g/cm3, S=1.005, μ(MoKα)=9.814 mm-1, F(000)=1128, R=0.0646 and wR=0.0989. The crystal structure analysis of 1reveals that the title compound features an isolated structure, based on discrete 4,4'-H2bipy moieties and lattice water molecules which are linked by hydrogen bonds together with tetrahedral cadmium atoms terminally coordinated by four bromine atoms. 相似文献
144.
Kaupp M Patrakov A Reviakine R Malkina OL 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(9):2773-2782
The characteristic dependence of J(31P,31P) spin-spin coupling constants of alkali metal tetraphosphane-1,4-diides on structure and composition has been analyzed by density functional methods. The computations confirm that the structure of the contact ion pairs is conserved in solution. Calculations on model systems M2P4H4, on naked P4H4(2-) anions, and on models including point charges, show that the role of the cations is mainly structural and to a smaller extent electrostatic. Three of the four J(P,P) coupling constants depend characteristically on the conformation of the anion, which in turn is determined by the substituents R and by cation-anion interactions. Several couplings exhibit a large through-space component and are thus strongly dependent on the relative orientation of nonbonding electron pairs on the phosphorus atoms involved. This is shown by visualization of coupling pathways using the recently introduced coupling energy density (CED), in combination with the electron localization function (ELF). 相似文献
145.
146.
The kinetics of the diffusion-limited decay reaction A + B B was simulated by the Monte—Carlo method on a two-dimensional square lattice with defects presented by randomly distributed sites. The cases were considered where [B] [A] at the random initial distribution (quenching reaction) and [B] = [A] with the initial distribution of the A and B particles on neighboring sites (geminate recombination). The kinetic curves were approximated by the simplest analytical equation [A]/[A]0 = (1 – )exp[–(kt)1–h
] + (where k and are constants). The plots of the heterogeneity parameter (h) and time-averaged first-order rate constant vs. concentration of defects (p) or B particles (in the case of quenching) were obtained and compared with similar correlations obtained earlier by the experimental study of the kinetics of forward (quenching reaction) and backward (geminate recombination) electron phototransfer on the surface of different porous silica gels. The experimental plots of h vs. silica gel porosity are in satisfactory agreement with the plots of h vs. p in the model space, if the fraction of volume inaccessible for reactants, calculated from the free silica gel volume, is chosen as the p parameter for silica gel.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1536–1541, August, 2004. 相似文献
147.
El-B. Yallaoui 《Periodica Mathematica Hungarica》1991,23(2):109-120
Let X be an abstract set and L a lattice of subsets of X. To each lattice regular measure µ, we associate two induced measures
and
on suitable lattices of the Wallman space IR(L) and another measure µ on the spaceIR(L). We will investigate the reflection of smoothness properties of p onto
,
and µ; and try to set some new criterion for repleteness and measure repleteness. 相似文献
148.
We give a necessary and sufficient condition for the uniformly non-l
n
(1)
property of Musielak-Orlicz sequence spacesl
Φ generated by a sequence Φ=(ϕn:n⩾l) of finite Orlicz functions such that
for eachn∈ℕ. As a result, forn
0⩾2, there exist spacesl
Φ which are only uniformly non-l
n
(1)
forn⩾n
0. Moreover we obtain a characterization of uniformly non-l
n
(1)
and reflexive Orlicz sequence spaces over a wide class of purely atomic measures and of uniformly non-l
n
(1)
Nakano sequence spaces. This extends a result of Luxemburg in [19].
Submitted in memory of Professor W. Orlicz 相似文献
149.
We study wild embeddings of S
1 in S
n which are tame in a sense introduced by Quinn. We show that if is a finitely presented group with H
1()=H
2()=0, then any finiteness obstruction K
0() can be realized on the complement of such an embedded S
1. We also realize trivially symmetric K
–1() obstructions on the complements of such embeddings. For trivially symmetric , the embeddings constructed are shown to be isotopy homogeneous. 相似文献
150.
Michel Talagrand 《Journal of Theoretical Probability》1992,5(2):327-331