全文获取类型
收费全文 | 92734篇 |
免费 | 4955篇 |
国内免费 | 11616篇 |
专业分类
化学 | 70977篇 |
晶体学 | 1164篇 |
力学 | 2415篇 |
综合类 | 897篇 |
数学 | 14592篇 |
物理学 | 19260篇 |
出版年
2024年 | 115篇 |
2023年 | 683篇 |
2022年 | 1983篇 |
2021年 | 1865篇 |
2020年 | 2242篇 |
2019年 | 2217篇 |
2018年 | 1939篇 |
2017年 | 2729篇 |
2016年 | 2840篇 |
2015年 | 2412篇 |
2014年 | 3363篇 |
2013年 | 6618篇 |
2012年 | 6266篇 |
2011年 | 5101篇 |
2010年 | 4368篇 |
2009年 | 5912篇 |
2008年 | 6104篇 |
2007年 | 6352篇 |
2006年 | 5763篇 |
2005年 | 4824篇 |
2004年 | 4498篇 |
2003年 | 3714篇 |
2002年 | 4895篇 |
2001年 | 2810篇 |
2000年 | 2641篇 |
1999年 | 2454篇 |
1998年 | 2142篇 |
1997年 | 1688篇 |
1996年 | 1410篇 |
1995年 | 1349篇 |
1994年 | 1220篇 |
1993年 | 1048篇 |
1992年 | 981篇 |
1991年 | 648篇 |
1990年 | 550篇 |
1989年 | 527篇 |
1988年 | 387篇 |
1987年 | 319篇 |
1986年 | 283篇 |
1985年 | 234篇 |
1984年 | 247篇 |
1983年 | 144篇 |
1982年 | 215篇 |
1981年 | 180篇 |
1980年 | 196篇 |
1979年 | 183篇 |
1978年 | 172篇 |
1977年 | 127篇 |
1976年 | 108篇 |
1973年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Let T and S be invertible measure preserving transformations of a probability measure space (X, ℬ, μ). We prove that if the group generated by T and S is nilpotent, then exists in L
2-norm for any u, v∈L
∞(X, ℬ, μ). We also show that for A∈ℬ with μ(A)>0 one has . By the way of contrast, we bring examples showing that if measure preserving transformations T, S generate a solvable group, then (i) the above limits do not have to exist; (ii) the double recurrence property fails, that
is, for some A∈ℬ, μ(A)>0, one may have μ(A∩T
-n
A∩S
-
n
A)=0 for all n∈ℕ. Finally, we show that when T and S generate a nilpotent group of class ≤c, in L
2(X) for all u, v∈L
∞(X) if and only if T×S is ergodic on X×X and the group generated by T
-1
S, T
-2
S
2,..., T
-c
S
c
acts ergodically on X.
Oblatum 19-V-2000 & 5-VII-2001?Published online: 12 October 2001 相似文献
42.
Balázs Szendröi 《Mathematische Zeitschrift》2002,240(2):233-241
This note shows that a certain toric quotient of the quintic Calabi-Yau threefold in provides a counterexample to a recent conjecture of Cox and Katz concerning nef cones of toric hypersurfaces.
Received: 8 February 2001; in final form: 17 September 2001 / Published online: 1 February 2002 相似文献
43.
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
44.
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
45.
46.
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
47.
48.
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
49.
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
50.
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