全文获取类型
收费全文 | 86490篇 |
免费 | 11809篇 |
国内免费 | 9332篇 |
专业分类
化学 | 59449篇 |
晶体学 | 919篇 |
力学 | 5361篇 |
综合类 | 772篇 |
数学 | 10318篇 |
物理学 | 30812篇 |
出版年
2024年 | 251篇 |
2023年 | 1529篇 |
2022年 | 2629篇 |
2021年 | 2793篇 |
2020年 | 2928篇 |
2019年 | 2878篇 |
2018年 | 2564篇 |
2017年 | 2312篇 |
2016年 | 3558篇 |
2015年 | 3729篇 |
2014年 | 4444篇 |
2013年 | 6011篇 |
2012年 | 7174篇 |
2011年 | 7363篇 |
2010年 | 5112篇 |
2009年 | 5041篇 |
2008年 | 5439篇 |
2007年 | 4941篇 |
2006年 | 4647篇 |
2005年 | 3966篇 |
2004年 | 3307篇 |
2003年 | 2647篇 |
2002年 | 2561篇 |
2001年 | 2224篇 |
2000年 | 1957篇 |
1999年 | 1969篇 |
1998年 | 1584篇 |
1997年 | 1422篇 |
1996年 | 1432篇 |
1995年 | 1260篇 |
1994年 | 1178篇 |
1993年 | 1028篇 |
1992年 | 911篇 |
1991年 | 765篇 |
1990年 | 654篇 |
1989年 | 560篇 |
1988年 | 409篇 |
1987年 | 396篇 |
1986年 | 337篇 |
1985年 | 333篇 |
1984年 | 226篇 |
1983年 | 193篇 |
1982年 | 157篇 |
1981年 | 126篇 |
1980年 | 92篇 |
1978年 | 67篇 |
1977年 | 59篇 |
1976年 | 57篇 |
1975年 | 62篇 |
1973年 | 63篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
43.
For a ? R\alpha \in \mathbf{R}, the class of a-\alpha -order spherical harmonic functions in an open set W í\Omega \subseteq Sn-1\mathbf{S}^{n-1}, Ha(W)H^{\alpha }(\Omega ) is defined as the C2-C^{2}-solutions of Dau=0\Delta _{\alpha }u=0; where Da=Ds+a(n+a-2)\Delta _{\alpha }=\Delta _{s}+\alpha (n+\alpha -2) is the spherical Laplace--Beltrami operator of order a\alpha and Ds\Delta _{s} is the radially independent part of the Laplace operator. We obtain a Green's integral formula for the functions in Ha(W)H^{\alpha }(\Omega ) with kernel expressed as a Gegenbauer function. As generalizations, higher order spherical iterated Dirac operators are defined in a polynomial form. Integral representations of the null solutions to these operators and an intertwining formula relating these operators on the sphere and their analogues in Euclidean space are presented. 相似文献
44.
45.
A Modified Quasi-Newton Method for Structured Optimization with Partial Information on the Hessian 总被引:2,自引:0,他引:2
This paper develops a modified quasi-Newton method for structured unconstrained optimization with partial information on the
Hessian, based on a better approximation to the Hessian in current search direction. The new approximation is decided by both
function values and gradients at the last two iterations unlike the original one which only uses the gradients at the last
two iterations. The modified method owns local and superlinear convergence. Numerical experiments show that the proposed method
is encouraging comparing with the methods proposed in [4] for structured unconstrained optimization
Presented at the 6th International Conference on Optimization: Techniques and Applications, Ballarat, Australia, December
9–11, 2004 相似文献
46.
The rate constants k1 for the reaction of CF3CF2CF2CF2CF2CHF2 with OH radicals were determined by using both absolute and relative rate methods. The absolute rate constants were measured at 250–430 K using the flash photolysis–laser‐induced fluorescence (FP‐LIF) technique and the laser photolysis–laser‐induced fluorescence (LP‐LIF) technique to monitor the OH radical concentration. The relative rate constants were measured at 253–328 K in an 11.5‐dm3 reaction chamber with either CHF2Cl or CH2FCF3 as a reference compound. OH radicals were produced by UV photolysis of an O3–H2O–He mixture at an initial pressure of 200 Torr. Ozone was continuously introduced into the reaction chamber during the UV irradiation. The k1 (298 K) values determined by the absolute method were (1.69 ± 0.07) × 10?15 cm3 molecule?1 s?1 (FP‐LIF method) and (1.72 ± 0.07) × 10?15 cm3 molecule?1 s?1 (LP‐LIF method), whereas the K1 (298 K) values determined by the relative method were (1.87 ± 0.11) × 10?15 cm3 molecule?1 s?1 (CHF2Cl reference) and (2.12 ± 0.11) × 10?15 cm3 molecule?1 s?1 (CH2FCF3 reference). These data are in agreement with each other within the estimated experimental uncertainties. The Arrhenius rate constant determined from the kinetic data was K1 = (4.71 ± 0.94) × 10?13 exp[?(1630 ± 80)/T] cm3 molecule?1 s?1. Using kinetic data for the reaction of tropospheric CH3CCl3 with OH radicals [k1 (272 K) = 6.0 × 10?15 cm3 molecule?1 s?1, tropospheric lifetime of CH3CCl3 = 6.0 years], we estimated the tropospheric lifetime of CF3CF2CF2CF2CF2CHF2 through reaction with OH radicals to be 31 years. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 36: 26–33, 2004 相似文献
47.
Various 2-substituted indoles were prepared by heteroannulation of o-iodoanilines and terminal alkynes in a one-pot reaction with a Pd(II)-NaY zeolite catalyst. The product formation largely depended on the solvent, base, and reaction temperature. The recycled catalyst showed good reusability in the heteroannulation reaction. 相似文献
48.
49.
The semi‐iterative method (SIM) is applied to the hyper‐power (HP) iteration, and necessary and sufficient conditions are given for the convergence of the semi‐iterative–hyper‐power (SIM–HP) iteration. The root convergence rate is computed for both the HP and SIM–HP methods, and the quotient convergence rate is given for the HP iteration. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
50.