全文获取类型
收费全文 | 90871篇 |
免费 | 18808篇 |
国内免费 | 9171篇 |
专业分类
化学 | 78763篇 |
晶体学 | 1303篇 |
力学 | 4095篇 |
综合类 | 654篇 |
数学 | 8595篇 |
物理学 | 25440篇 |
出版年
2024年 | 210篇 |
2023年 | 1117篇 |
2022年 | 1913篇 |
2021年 | 2178篇 |
2020年 | 3321篇 |
2019年 | 4534篇 |
2018年 | 2875篇 |
2017年 | 2527篇 |
2016年 | 5746篇 |
2015年 | 6003篇 |
2014年 | 6488篇 |
2013年 | 7959篇 |
2012年 | 7891篇 |
2011年 | 7277篇 |
2010年 | 6502篇 |
2009年 | 6440篇 |
2008年 | 6293篇 |
2007年 | 5219篇 |
2006年 | 4826篇 |
2005年 | 4365篇 |
2004年 | 3622篇 |
2003年 | 3096篇 |
2002年 | 3727篇 |
2001年 | 2755篇 |
2000年 | 2602篇 |
1999年 | 1574篇 |
1998年 | 1025篇 |
1997年 | 900篇 |
1996年 | 864篇 |
1995年 | 780篇 |
1994年 | 707篇 |
1993年 | 567篇 |
1992年 | 508篇 |
1991年 | 433篇 |
1990年 | 373篇 |
1989年 | 286篇 |
1988年 | 254篇 |
1987年 | 201篇 |
1986年 | 181篇 |
1985年 | 195篇 |
1984年 | 126篇 |
1983年 | 91篇 |
1982年 | 78篇 |
1981年 | 53篇 |
1980年 | 26篇 |
1979年 | 26篇 |
1978年 | 11篇 |
1977年 | 15篇 |
1975年 | 12篇 |
1972年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
This paper gives some global and uniform convergence estimates for a class of subspace correction (based on space decomposition) iterative methods applied to some unconstrained convex optimization problems. Some multigrid and domain decomposition methods are also discussed as special examples for solving some nonlinear elliptic boundary value problems.
62.
A nonlinear, compressible, non-isothermal gravity wave model that involves photochemistry is used to study the effects of gravity wave on atmospheric chemical species distributions in this paper. The changes in the distributions of oxygen compound and hydrogen compound density induced by gravity wave propagation are simulated. The results indicate that when a gravity wave propagates through a mesopause region, even if it does not break, it can influence the background distributions of chemical species. The effect of gravity wave on chemical species at night is larger than in daytime. 相似文献
63.
Bingxin LiuYoshio Tatamitani Jun ShimadaTeruhiko Ogata 《Journal of Molecular Spectroscopy》2002,211(1):99-106
The microwave spectrum of the 35Cl and 37Cl isotopic species of 1-chloro-1,1,2-trifluoroethane (HCFC-133b) has been investigated in the frequency region 10 to 50 GHz using a Stark modulation microwave spectrometer. A pulsed jet Fourier transform microwave spectrometer was also used for the measurement of hyperfine splittings. A least-squares analysis of the observed b-type Q- and R-branch transition frequencies gave rotational and centrifugal distortion constants and components of the chlorine nuclear quadrupole coupling constant tensors in the principal axes system as follows: A=4625.161 (3) MHz, B=2004.127 (2) MHz, C=1875.813 (2) MHz, ΔJ=0.144 (9) kHz, ΔJK=1.0748 (8) kHz, ΔK=1.57 (1) kHz, δJ=0.01376 (4) kHz, δK=−0.146 (4) kHz, χaa=−57.958 (10) MHz, χbb=21.231 (11) MHz, and χcc=36.727 (11) MHz for 35ClCF2CH2F species, and A=4607.684 (6) MHz, B=1960.565 (2) MHz, C=1834.823 (2) MHz, ΔJ=0.106 (7) kHz, ΔJK=1.022 (3) kHz, ΔK=1.48 (1) kHz, δJ=0.0142 (2) kHz, δK=−0.18 (2) kHz, χaa=−46.268 (11) MHz, χbb=17.319 (13) MHz, and χcc=28.950 (13) MHz for 37ClCF2CH2F species. The structural parameters are calculated from the observed six rotational constants by assuming the partial structure of ab initio calculation. The electronic properties of the C-Cl bond are evaluated from the observed nuclear quadrupole constants of chlorine. These molecular properties are compared with those of other related molecules. 相似文献
64.
65.
The fuzzification of convex sets in median algebras is considered, and some of their properties are investigated. A characterization of finite valued fuzzy convex set is given. 相似文献
66.
Soliton interaction under the influence of higher-order effects 总被引:6,自引:0,他引:6
In this paper, we present exact N-soliton solution by employing simple, straightforward Darboux transformation based on the Lax pair for Hirota equation, a higher-order nonlinear Schrödinger (HNLS) equation. As examples, one- and two-soliton solutions in explicit forms are given and their properties are also analyzed. A bound solution without interaction will be theoretically predicted if one can adjust frequency shift for each soliton appropriately. Further, we obtain the approximate eigenvalues by employing two-soliton solution and discuss analytically the interaction between neighboring solitons under the influence of the higher-order effects. It is shown that the combined effects of the higher-order effects can restrain the interaction between neighboring solitons to some extent. The results are proved by directly solving HNLS equation numerically. 相似文献
67.
Jong Chan Lee Jin Young Park So Young Yoon Yong Hun Bae Seung Jun Lee 《Tetrahedron letters》2004,45(1):191-193
A novel and direct method for the synthesis of α-halocarbonyl compounds using sequential treatment of carbonyl compounds with [hydroxy(tosyloxy)iodo]benzene followed by magnesium halides under solvent-free microwave irradiation conditions is described. 相似文献
68.
69.
A graph G is N2‐locally connected if for every vertex ν in G, the edges not incident with ν but having at least one end adjacent to ν in G induce a connected graph. In 1990, Ryjá?ek conjectured that every 3‐connected N2‐locally connected claw‐free graph is Hamiltonian. This conjecture is proved in this note. © 2004 Wiley Periodicals, Inc. J Graph Theory 48: 142–146, 2005 相似文献
70.
The Iyengar Type Inequalities with Exact Estimations and the Chebyshev Central Algorithms of Integrals 总被引:3,自引:0,他引:3
Xing Hua WANG Shi Jun YANG 《数学学报(英文版)》2005,21(6):1361-1376
In this paper, both low order and high order extensions of the Iyengar type inequality are obtained. Such extensions are the best possible in the same sense as that of the Iyengar inequality. hzrthermore, the Chebyshev central algorithms of integrals for some function classes and some related problems are also considered and investigated. 相似文献