全文获取类型
收费全文 | 143498篇 |
免费 | 13781篇 |
国内免费 | 10295篇 |
专业分类
化学 | 54312篇 |
晶体学 | 2091篇 |
力学 | 9242篇 |
综合类 | 1717篇 |
数学 | 40561篇 |
物理学 | 59651篇 |
出版年
2023年 | 755篇 |
2022年 | 2646篇 |
2021年 | 2594篇 |
2020年 | 2324篇 |
2019年 | 2481篇 |
2018年 | 2302篇 |
2017年 | 2436篇 |
2016年 | 2635篇 |
2015年 | 2326篇 |
2014年 | 3949篇 |
2013年 | 6458篇 |
2012年 | 4386篇 |
2011年 | 5208篇 |
2010年 | 5508篇 |
2009年 | 10470篇 |
2008年 | 11685篇 |
2007年 | 10303篇 |
2006年 | 8963篇 |
2005年 | 6639篇 |
2004年 | 6317篇 |
2003年 | 6097篇 |
2002年 | 9095篇 |
2001年 | 5595篇 |
2000年 | 5046篇 |
1999年 | 4748篇 |
1998年 | 4022篇 |
1997年 | 3039篇 |
1996年 | 2758篇 |
1995年 | 3157篇 |
1994年 | 2940篇 |
1993年 | 2413篇 |
1992年 | 1853篇 |
1991年 | 1446篇 |
1990年 | 1174篇 |
1989年 | 979篇 |
1988年 | 974篇 |
1987年 | 693篇 |
1986年 | 484篇 |
1985年 | 1323篇 |
1984年 | 904篇 |
1983年 | 676篇 |
1982年 | 951篇 |
1981年 | 1110篇 |
1980年 | 992篇 |
1979年 | 876篇 |
1978年 | 778篇 |
1977年 | 666篇 |
1976年 | 630篇 |
1974年 | 415篇 |
1973年 | 559篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
采用DIS数字信息化系统,对不同浓度的蓝墨水溶液在激光光源照射下的透射平均照度及照度分布图像进行实验研究,得到了平均照度值随溶液浓度变化的规律。对不同颜色塑料膜片对白炽灯光源透过照度值及照度分布图像进行实验研究得到及其相关之规律。 相似文献
52.
In view of immense importance of silylenes and the fact that their properties undergo significant changes on substitution with halogens, here, we have used B3LYP/6-311++G** level of theory to access the effects of 1–4 halogens (X = F, Cl, Br, and I) on four unprecedented sets of cyclopentasilylene-2,4-dienes; with the following formulas: SiC4H3X ( 1 X ), SiC4H2X2 ( 2 X ), SiC4HX3 ( 3 X ), and SiC4X4 ( 4 X ). In going down from F to I, the singlet (s)-triplet (t) energy gap (ΔEs-t, a possible indication of stability), and band gap (ΔEH-L) decrease while nucleophilicity (N), chemical potential (μ), and proton affinity (PA) increase. The overall order of N, μ, and PA for each X is 2 X > 1 X > 3 X > 4 X . Precedence of 2 X over 1 X is attributed to the symmetric cross conjugation in the former. The highest and lowest N are shown by 2 I and 4 F . The trend of divalent angle () for each X is 4 X > 1 X > 3 X > 2 X . The results show that in going from electron withdrawing groups (EWGs) to electron donating groups (EDGs), the ΔEs-t and ΔEH-L decrease while N, μ, and PA increase. Also, rather high N of our scrutinized silylenes may suggest new promising ligands in organometallic chemistry. 相似文献
53.
In this work, the variation of the magnetic moments of the Ni/Pt multilayers are studied using the linearized augmented plane waves (LAPW) method in the framework of the density functional theory (DFT) implemented in the version of WIEN2K program. The systems have been modeled by seven layers slab separated in z direction by a vacuum region of four substrate layers. We present the results of the dependence of the magnetic properties with respect to the thickness variation of the different multilayers. The modeling of these systems finds an important empirical support. Experiment and theory show the same trends for the magnetic moments: hybridization effects between Ni and Pt are mostly localized at the interface. 相似文献
54.
Single-crystalline gallium nitride nanobelts have been synthesized through the reaction of gallium vapor with flowing ammonia using nickel as a catalyst. The as-synthesized products were characterized using X-ray powder diffraction (XRD), scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and selected-area electron diffraction (SAED). XRD and SAED results revealed that the products are pure, single-crystalline GaN with hexagonal structure. The widths and thickness of the nanobelts ranged from 80 to 200 nm, and 10 to 30 nm, respectively. The lengths were up to several tens of micrometers. The nanobelts had smooth surface with no amorphous sheath, and a sharp-tip end. The growth mechanism of nanobelts was discussed. 相似文献
55.
M.A. Tawhid 《Journal of Optimization Theory and Applications》2002,113(1):149-164
In this paper, we give some sufficient conditions for the local uniqueness of solutions to nonsmooth variational inequalities where the underlying functions are H-differentiable and the underlying set is a closed convex set/polyhedral set/box/polyhedral cone. We show how the solution of a linearized variational inequality is related to the solution of the variational inequality. These results extend/unify various similar results proved for C
1 and locally Lipschitzian variational inequality problems. When specialized to the nonlinear complementarity problem, our results extend/unify those of C
2 and C
1 nonlinear complementarity problems. 相似文献
56.
58.
Inner derivations and norm equality 总被引:3,自引:0,他引:3
Mohamed Barraa Mohamed Boumazgour 《Proceedings of the American Mathematical Society》2002,130(2):471-476
We characterize when the norm of the sum of two bounded operators on a Hilbert space is equal to the sum of their norms.
59.
本文证明了Heisenberg群上Laplace算子的Dirichlet特征值的存在性,给出了特征值的估计 相似文献
60.