全文获取类型
收费全文 | 132867篇 |
免费 | 12947篇 |
国内免费 | 8796篇 |
专业分类
化学 | 47949篇 |
晶体学 | 1992篇 |
力学 | 7056篇 |
综合类 | 1571篇 |
数学 | 35683篇 |
物理学 | 60359篇 |
出版年
2023年 | 679篇 |
2022年 | 2703篇 |
2021年 | 2550篇 |
2020年 | 1956篇 |
2019年 | 2122篇 |
2018年 | 1948篇 |
2017年 | 1960篇 |
2016年 | 2145篇 |
2015年 | 1999篇 |
2014年 | 3420篇 |
2013年 | 5226篇 |
2012年 | 3710篇 |
2011年 | 4603篇 |
2010年 | 4981篇 |
2009年 | 9809篇 |
2008年 | 11059篇 |
2007年 | 9645篇 |
2006年 | 8374篇 |
2005年 | 6136篇 |
2004年 | 5835篇 |
2003年 | 5731篇 |
2002年 | 8746篇 |
2001年 | 5256篇 |
2000年 | 4736篇 |
1999年 | 4441篇 |
1998年 | 3757篇 |
1997年 | 2854篇 |
1996年 | 2587篇 |
1995年 | 2960篇 |
1994年 | 2782篇 |
1993年 | 2262篇 |
1992年 | 1742篇 |
1991年 | 1333篇 |
1990年 | 1087篇 |
1989年 | 928篇 |
1988年 | 940篇 |
1987年 | 657篇 |
1986年 | 449篇 |
1985年 | 1302篇 |
1984年 | 879篇 |
1983年 | 655篇 |
1982年 | 933篇 |
1981年 | 1090篇 |
1980年 | 977篇 |
1979年 | 861篇 |
1978年 | 767篇 |
1977年 | 653篇 |
1976年 | 626篇 |
1974年 | 416篇 |
1973年 | 562篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
自由电子激光的预群聚 总被引:1,自引:0,他引:1
研究了自由电子激光预群聚产生的辐射,表明预群聚不仅可以提高效率而且使低增益得到增强,从而在理论上解释了由射频直线加速器驱动的自由电子激光预群聚器(prebuncher)的作用。同时还指出,预群聚有在不增加电子束能量情况下缩短激光波长和降低对电子束质量要求等作用。 相似文献
52.
C. Fallnich B. Ruffing Th. Herrmann A. Nebel R. Beigang R. Wallenstein 《Applied physics. B, Lasers and optics》1995,60(5):427-436
We report on a cw mode-locked non-critically phase matched KTP optical parametric oscillator synchronously pumped by a picosecond Ti:Sapphire laser. High average signal output power of up to 950 mW over a large tuning range has been achieved. For this OPO the influence of resonator-length detuning on the output power, pulse duration and spectral bandwidth has been investigated. The measured data are in good agreement with the results of a numerical simulation using a split-step Fourier method which considers the group-velocity mismatch, the group-velocity dispersion and the self-phase modulation. The numerical simulation also describes the measured strong pump depletion and its influence on the OPO output and efficiency. 相似文献
53.
54.
An M/G/1 retrial queueing system with additional phase of service and possible preemptive resume service discipline is considered. For an arbitrarily distributed retrial time distribution, the necessary and sufficient condition for the system stability is obtained, assuming that only the customer at the head of the orbit has priority access to the server. The steady-state distributions of the server state and the number of customers in the orbit are obtained along with other performance measures. The effects of various parameters on the system performance are analysed numerically. A general decomposition law for this retrial queueing system is established. 相似文献
55.
56.
HIRONOBU Ishihara 《Geometriae Dedicata》1997,67(3):309-336
Several classification results for ample vector bundles of rank 2 on Hirzebruch surfaces, and on Del Pezzo surfaces, are obtained. In particular, we classify rank 2 ample vector bundles with c2 less than seven on Hirzebruch surfaces, and with c2 less than four on Del Pezzo surfaces. 相似文献
57.
We investigate congruence classes and direct congruence classes of m-tuples in the complex projective space ℂP
n
. For direct congruence one allows only isometries which are induced by linear (instead of semilinear) mappings. We establish
a canonical bijection between the set of direct congruence classes of m-tuples of points in ℂP
n
and the set of equivalence classes of positive semidefinite Hermitean m×m-matrices of rank at most n+1 with 1's on the diagonal. As a corollary we get that the direct congruence class of an m-tuple is uniquely determined by the direct congruence classes of all of its triangles, provided that no pair of points of
the m-tuple has distance π/2. Examples show that the situation changes drastically if one replaces direct congruence classes by
congruence classes or if distances π/2 are allowed. Finally we do the same
kind of investigation also for the complex hyperbolic space ℂH
n
. Most of the results are completely analogous, however, there are also some interesting differences.
Received: 15 January 1996 相似文献
58.
Summary. We generalise and apply a refinement indicator of the type originally designed by Mackenzie, Süli and Warnecke in [15] and
[16] for linear Friedrichs systems to the Euler equations of inviscid, compressible fluid flow. The Euler equations are symmetrized
by means of entropy variables and locally linearized about a constant state to obtain a symmetric hyperbolic system to which
an a posteriori error analysis of the type introduced in [15] can be applied. We discuss the details of the implementation of the refinement
indicator into the DLR--Code which is based on a finite volume method of box type on an unstructured grid and present numerical results.
Received May 15, 1995 / Revised version received April 17, 1996 相似文献
60.
对由一类非线性抛物型变分不等方程所描述的无穷维动力系统,给出了存在全局吸引子及弱近似惯性流形的充分条件. 相似文献