全文获取类型
收费全文 | 109460篇 |
免费 | 18239篇 |
国内免费 | 9533篇 |
学科分类
数理化 | 137232篇 |
出版年
2024年 | 260篇 |
2023年 | 1512篇 |
2022年 | 2515篇 |
2021年 | 2793篇 |
2020年 | 3819篇 |
2019年 | 4898篇 |
2018年 | 3341篇 |
2017年 | 2786篇 |
2016年 | 6266篇 |
2015年 | 6536篇 |
2014年 | 7106篇 |
2013年 | 8979篇 |
2012年 | 9054篇 |
2011年 | 8499篇 |
2010年 | 7140篇 |
2009年 | 7044篇 |
2008年 | 6807篇 |
2007年 | 5793篇 |
2006年 | 5292篇 |
2005年 | 4894篇 |
2004年 | 4075篇 |
2003年 | 3343篇 |
2002年 | 3933篇 |
2001年 | 3104篇 |
2000年 | 2854篇 |
1999年 | 2095篇 |
1998年 | 1489篇 |
1997年 | 1264篇 |
1996年 | 1318篇 |
1995年 | 1162篇 |
1994年 | 1061篇 |
1993年 | 925篇 |
1992年 | 816篇 |
1991年 | 715篇 |
1990年 | 596篇 |
1989年 | 501篇 |
1988年 | 383篇 |
1987年 | 367篇 |
1986年 | 308篇 |
1985年 | 310篇 |
1984年 | 204篇 |
1983年 | 177篇 |
1982年 | 147篇 |
1981年 | 114篇 |
1980年 | 83篇 |
1979年 | 53篇 |
1978年 | 56篇 |
1977年 | 55篇 |
1975年 | 57篇 |
1973年 | 57篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
We reveal that for a realistic system, interference effects are obtained such as the suppression of central line and inner sidebands and the narrowing of the outer fluorescence sidebands. For this purpose, we consider a spontaneous decay from an excited state to a metastable state when the excited and metastable states are resonantly coupled to an auxiliary metastable state by a laser field and a microwave field, respectively. The fluorescence spectrum evolves from a five-peaked structure into a doublet of ultrasharp lines as the ratio of the laser field Rabi frequency to the microwave Rabi frequency is decreased. The physical origin is presented in terms of dressed states. 相似文献
22.
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
23.
本文主要研究的是相函数为齐次椭圆多项式的自由高阶Schrodinger方程.通过相函数等值面的几何性质,得到了解算子的Strichartz加权估计和极大算子加权估计. 相似文献
24.
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
25.
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
26.
27.
28.
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
29.
Compact, time‐harmonic, acoustic sources produce waves that decay too slowly to be square‐integrable on a line away from the sources. We introduce an inner product, arising directly from Green's second theorem, to form a Hilbert space of these waves and present examples of its computation.1 © 2005 Wiley Periodicals, Inc. 相似文献
30.
Existence, Multiplicity and Infinite Solvability of Positive Solutions for One-Dimensional p-Laplacian 总被引:5,自引:0,他引:5
Qing Liu YAO 《数学学报(英文版)》2005,21(4):691-698
The existence, multiplicity and infinite solvability of positive solutions are established for some two-point boundary value problems of one-dimensional p-Laplacian. In this paper, by multiplicity we mean the existence of m solutions, where m is an arbitrary natural number. 相似文献