全文获取类型
收费全文 | 98654篇 |
免费 | 6765篇 |
国内免费 | 12455篇 |
专业分类
化学 | 72885篇 |
晶体学 | 1215篇 |
力学 | 3107篇 |
综合类 | 906篇 |
数学 | 13484篇 |
物理学 | 26277篇 |
出版年
2024年 | 127篇 |
2023年 | 729篇 |
2022年 | 2068篇 |
2021年 | 2005篇 |
2020年 | 2424篇 |
2019年 | 2302篇 |
2018年 | 2071篇 |
2017年 | 3048篇 |
2016年 | 3193篇 |
2015年 | 2707篇 |
2014年 | 3898篇 |
2013年 | 7264篇 |
2012年 | 6702篇 |
2011年 | 5552篇 |
2010年 | 4630篇 |
2009年 | 6399篇 |
2008年 | 6605篇 |
2007年 | 6793篇 |
2006年 | 6126篇 |
2005年 | 5211篇 |
2004年 | 4865篇 |
2003年 | 4022篇 |
2002年 | 5197篇 |
2001年 | 3075篇 |
2000年 | 2865篇 |
1999年 | 2654篇 |
1998年 | 2303篇 |
1997年 | 1845篇 |
1996年 | 1550篇 |
1995年 | 1474篇 |
1994年 | 1280篇 |
1993年 | 1054篇 |
1992年 | 1007篇 |
1991年 | 686篇 |
1990年 | 568篇 |
1989年 | 546篇 |
1988年 | 391篇 |
1987年 | 311篇 |
1986年 | 288篇 |
1985年 | 231篇 |
1984年 | 247篇 |
1983年 | 144篇 |
1982年 | 213篇 |
1981年 | 180篇 |
1980年 | 197篇 |
1979年 | 184篇 |
1978年 | 171篇 |
1977年 | 123篇 |
1976年 | 109篇 |
1973年 | 67篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
We analyze diffusion from a periodic array of hemispherical droplets through a membrane. We find that the multiple sources do not interact strongly, even when the droplets are closely spaced, so that the flux through the membrane appears nearly additive. 相似文献
52.
考虑电子的反冲并利用康普顿散射,研究了激光同步辐射光源(LSS)辐射的光子波长、光子能量。结果表明,对于不同的γ,LSS辐射的光子波长和能量有不同的近似公式。当γ<<λ1/4λe时,LSS辐射的光子波长λ2≈λ1/4γ2,能量(εc2≈4γ2εc1;当γ>>λ1/4λe时,LSS辐射的光子波长λ2≈λe/γ,能量cε2≈m0γc2;结果表明,LSS辐射的条件是种子激光的波长λ1大于电子的物质波波长λm;LSS辐射的极值波长是λ2m ax=h/m0γv,极值能量是cε2m ax=βeε;本文后半部分提出了利用北京正负电子对撞机的强流高亮度电子束与激光的康普顿背散射产生单色γ射线的建议。 相似文献
53.
meso-Tetra(n-hexyloxycarbonyl)porphyrin was found to be converted into porphine, the mother compound of porphyrins, in a 77% yield when heated in aqueous sulfuric acid at 180 °C over 30 min under an inert atmosphere. The observation demonstrates that the substituted porphyrin serves as a novel and useful precursor for porphine. 相似文献
54.
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
55.
56.
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
57.
58.
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
59.
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
60.
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