全文获取类型
收费全文 | 33928篇 |
免费 | 4425篇 |
国内免费 | 1068篇 |
专业分类
化学 | 8054篇 |
晶体学 | 446篇 |
力学 | 1085篇 |
综合类 | 99篇 |
数学 | 9597篇 |
物理学 | 20140篇 |
出版年
2023年 | 148篇 |
2022年 | 340篇 |
2021年 | 326篇 |
2020年 | 368篇 |
2019年 | 651篇 |
2018年 | 504篇 |
2017年 | 616篇 |
2016年 | 583篇 |
2015年 | 498篇 |
2014年 | 868篇 |
2013年 | 1679篇 |
2012年 | 1207篇 |
2011年 | 1940篇 |
2010年 | 1157篇 |
2009年 | 1579篇 |
2008年 | 1806篇 |
2007年 | 1866篇 |
2006年 | 1728篇 |
2005年 | 1242篇 |
2004年 | 1667篇 |
2003年 | 1703篇 |
2002年 | 2311篇 |
2001年 | 2206篇 |
2000年 | 2087篇 |
1999年 | 2207篇 |
1998年 | 1881篇 |
1997年 | 1206篇 |
1996年 | 714篇 |
1995年 | 454篇 |
1994年 | 387篇 |
1993年 | 247篇 |
1992年 | 245篇 |
1991年 | 200篇 |
1990年 | 262篇 |
1989年 | 224篇 |
1988年 | 149篇 |
1987年 | 137篇 |
1986年 | 156篇 |
1985年 | 207篇 |
1984年 | 200篇 |
1983年 | 81篇 |
1982年 | 147篇 |
1981年 | 254篇 |
1980年 | 238篇 |
1979年 | 111篇 |
1978年 | 168篇 |
1977年 | 104篇 |
1976年 | 74篇 |
1975年 | 83篇 |
1974年 | 78篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
Knut Smoczyk 《Mathematische Zeitschrift》2002,240(4):849-883
We prove that symplectic maps between Riemann surfaces L, M of constant, nonpositive and equal curvature converge to minimal symplectic maps, if the Lagrangian angle for the corresponding Lagrangian submanifold in the cross product space satisfies . If one considers a 4-dimensional K?hler-Einstein manifold of nonpositive scalar curvature that admits two complex structures J, K which commute and assumes that is a compact oriented Lagrangian submanifold w.r.t. J such that the K?hler form w.r.t.K restricted to L is positive and , then L converges under the mean curvature flow to a minimal Lagrangian submanifold which is calibrated w.r.t. .
Received: 11 April 2001 / Published online: 29 April 2002 相似文献
32.
Formalization for problems of multicriteria decision making under uncertainty is constructed in terms of guaranteed and weak
estimates. A relevant definition of the vector maximinimax value is given. Parameterization and approximation of maximum,
minimax, and maximinimax values based on the inverse logical convolution are suggested. An application for multicommodity
networks is considered.
Received: December 13, 2000 / Accepted: August 21, 2001?Published online May 8, 2002 相似文献
33.
超强脉冲激光在低密度等离子体中的相对论自导引效应 总被引:1,自引:1,他引:0
分析了相对论条件下激光超短脉冲在等离子体中的传输特性 ,在傍轴近似和慢变振幅近似条件下 ,推导了折射率、电子密度、静电场以及电子空腔尺度的表达式。当激光功率超过产生自导引阈值功率时 ,激光束斑沿着传输光轴方向振荡。在有质动力产生的压力非常强时 ,聚焦光束中央部分的电子被全部排开形成电子空腔。给出了电子空腔的尺寸以及在出现电子空腔时的处理方法。在超过形成电子空腔的阈值功率 (Pc≈ 2 .5TW )时 ,空腔的尺度几乎与激光功率无关 ,这意味着电子空腔阻止了激光脉冲的进一步聚焦。 相似文献
34.
A new method for controlling the quantum coherence of atom laser by applying input light with strong strength is presented
within the framework of quantum dynamical theory. Unlike the case of rotating wave approximation(RWA), we show that the non-classical
properties, such as sub-Poisson distribution and quadrature squeezed effect, can appear in the output atom laser beam with
time. By choosing suitable initial RF phase, a steady and brighter output of squeezed coherent atom laser is also available. 相似文献
35.
36.
37.
在长距离无线光通信中,接收点光功率密度与光束发散角平方呈反比关系,为了获得小的发散角和大的功率耦合效率,要求准直系统有较大的数值孔径(NA),但数值孔径过大会增加像差,因此合理设计功率耦合效率与准直系统的数值孔径就非常重要。该文对半导体激光器光束准直系统中功率耦合效率进行了研究,给出了半导体激光器光束功率耦合效率与k(孔径半径与孔径处等效光束半径之比)的关系表达式,并结合激光器光束准直系统,给出了半导体激光器光束功率耦合效率与准直系统数值孔径的关系表达式。该研究结论对于半导体激光器光束准直系统设计具有参考作用。 相似文献
38.
V. I. Dashkevich 《Journal of Applied Spectroscopy》2002,69(6):862-870
Based on a semiclassical theory, investigations were made of the dynamics and spectral composition of pulsed generation with self-injection of priming radiation from the active part of a three-mirror linear resonator, the passive part of which contains an active loss modulator and serves as the output reflector of the laser. It is shown that there exists a range of resonator parameters at which pulsed lasing has virtually a single frequency irrespective of the detuning of the frequencies of the priming radiation and of the nearest eigenmode of the composite resonator. Considering graphically the phase conditions of generation, it is established that among pulsed lasers with self-injection of priming radiation which are constructed on the basis of three-mirror linear and branched resonators, the most efficient for creating single-frequency generation are those in which the length of the main resonator, where generation of the pulse occurs, is larger than the length of the additional one intended for forming the priming radiation. With an inverse ratio of the lengths of the resonators, the conditions of single-frequency pulsed generation becomes dependent on the priming radiation frequency. 相似文献
39.
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
40.
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