全文获取类型
收费全文 | 152639篇 |
免费 | 10343篇 |
国内免费 | 22320篇 |
专业分类
化学 | 125960篇 |
晶体学 | 3046篇 |
力学 | 3215篇 |
综合类 | 1375篇 |
数学 | 16915篇 |
物理学 | 34791篇 |
出版年
2024年 | 291篇 |
2023年 | 1703篇 |
2022年 | 3818篇 |
2021年 | 3679篇 |
2020年 | 4142篇 |
2019年 | 5076篇 |
2018年 | 3599篇 |
2017年 | 5605篇 |
2016年 | 5077篇 |
2015年 | 4388篇 |
2014年 | 5892篇 |
2013年 | 11686篇 |
2012年 | 9826篇 |
2011年 | 9022篇 |
2010年 | 7521篇 |
2009年 | 9530篇 |
2008年 | 9848篇 |
2007年 | 10127篇 |
2006年 | 9277篇 |
2005年 | 7992篇 |
2004年 | 7551篇 |
2003年 | 6219篇 |
2002年 | 7080篇 |
2001年 | 4637篇 |
2000年 | 4905篇 |
1999年 | 4150篇 |
1998年 | 3732篇 |
1997年 | 2711篇 |
1996年 | 2334篇 |
1995年 | 2189篇 |
1994年 | 1848篇 |
1993年 | 1525篇 |
1992年 | 1432篇 |
1991年 | 1010篇 |
1990年 | 798篇 |
1989年 | 736篇 |
1988年 | 587篇 |
1987年 | 446篇 |
1986年 | 381篇 |
1985年 | 369篇 |
1984年 | 353篇 |
1983年 | 183篇 |
1982年 | 285篇 |
1981年 | 289篇 |
1980年 | 277篇 |
1979年 | 283篇 |
1978年 | 237篇 |
1977年 | 178篇 |
1976年 | 146篇 |
1973年 | 99篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
We obtain upper bounds for the tail distribution of the first nonnegative sum of a random walk and for the moments of the overshoot over an arbitrary nonnegative level if the expectation of jumps is positive and close to zero. In addition, we find an estimate for the expectation of the first ladder epoch. 相似文献
62.
The breakthrough and stoichiometric SO2 adsorption efficiencies of a biomass supported Na2CO3 system (80 wt %Na2CO3/straw) have reached 48.9% and 80.6% respectively at a desulfurization temperature of 80℃. 相似文献
63.
64.
Kasper K. Berthelsen Jesper Møller 《Bulletin of the Brazilian Mathematical Society》2002,33(3):351-367
This primer provides a self-contained exposition of the case where spatial birth-and-death processes are used for perfect
simulation of locally stable point processes. Particularly, a simple dominating coupling from the past (CFTP) algorithm and
the CFTP algorithms introduced in [13], [14], and [5] are studied. Some empirical results for the algorithms are discussed.
Received: 30 June 2002 相似文献
65.
66.
Let G=(V(G),E(G)) be a graph. A (n,G, λ)‐GD is a partition of the edges of λKn into subgraphs (G‐blocks), each of which is isomorphic to G. The (n,G,λ)‐GD is named as graph design for G or G‐decomposition. The large set of (n,G,λ)‐GD is denoted by (n,G,λ)‐LGD. In this work, we obtain the existence spectrum of (n,P3,λ)‐LGD. © 2002 Wiley Periodicals, Inc. J Combin Designs 10: 151–159, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/jcd.10008 相似文献
67.
A design of diode-pumped high-efficiency Nd:YVO4/LBO red laser is reported. Using critical phase-matching (CPM) LBO, 671 nm red laser was obtained from 1342 nm light by intracavity frequency doubling. With an incident pump laser of 800 mW, using type-I and type-II CPM LBO, 97 and 52 mWTEM00 mode red laser outputs were obtained, with optical-to-optical conversion efficiencies of up to 12.1% and 6.5%, respectively. 相似文献
68.
K. Batra V. Prasad M. Mohan 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(2):191-198
The scattering of heavy ion with a multilevel Rydberg atom in the presence of an electromagnetic field is studied. The interaction
of Rydberg atom and the e.m field is explored using non-perturbative quasi-energy technique. Although the results are presented
for selected excitations but in actual calculations we have included many levels of the atom. The effect of various parameters
are shown on collisional excitation process. As an illustration detailed calculations are performed for the inelastic proton-Na
Rydberg atom collision accompanied by the transfer of photons and the effects of dressing due to the field are considered.
The emphasis of the present work is on collision induced transitions especially the case that involves change of orbital as
well as principal quantum number.
Received 26 December 2001 / Received in final form 8 April 2002 Published online 19 July 2002 相似文献
69.
用全实加关联方法计算了类锂V20+离子1s23d-1s2nf的跃迁能和偶极振子强度.依据量子亏损理论, 确定了1s2nf系列的量子数亏损,用这些作为能量的缓变函数的量子亏损,实现对该Rydberg系列任意高激发态(n≥10)的能量的可靠预言.将这些分立态振子强度与量子亏损理论相结合,得到在电离域附近束缚态间的偶极跃迁振子强度以及束缚态-连续态跃迁的振子强度密度,从而将V20+离子的这一重要光谱特性的理论预言外推到整个能域. 相似文献
70.
非傍轴平顶高斯光束M2因子两种定义的比较研究 总被引:3,自引:2,他引:1
基于功率密度的二阶矩方法,推导出了非傍轴平顶高斯(FG)光束束宽和远场发散角的解析表达式·研究表明,当w0/λ→0时,远场发散角趋于渐近值θmax=63.435°,与阶数无关·使用非傍轴高斯光束代替傍轴高斯光束作为理想光束,研究了非傍轴FG光束的M2因子,并与传统定义的M2因子作了比较·在非傍轴范畴,非傍轴FG光束的M2因子不仅与阶数N有关,而且与w0/λ有关·按照定义,当w0/λ→0时,非傍轴FG光束的M2因子不等于0,对阶数N=1,2,3时,M2因子分别趋于0.913,0.882和0.886·当N→∞时,M2因子取最小值M2min=0.816· 相似文献