全文获取类型
收费全文 | 24457篇 |
免费 | 3769篇 |
国内免费 | 2646篇 |
专业分类
化学 | 16996篇 |
晶体学 | 296篇 |
力学 | 1484篇 |
综合类 | 240篇 |
数学 | 2677篇 |
物理学 | 9179篇 |
出版年
2024年 | 79篇 |
2023年 | 507篇 |
2022年 | 819篇 |
2021年 | 885篇 |
2020年 | 987篇 |
2019年 | 907篇 |
2018年 | 753篇 |
2017年 | 727篇 |
2016年 | 1105篇 |
2015年 | 1040篇 |
2014年 | 1296篇 |
2013年 | 1679篇 |
2012年 | 2081篇 |
2011年 | 2080篇 |
2010年 | 1429篇 |
2009年 | 1370篇 |
2008年 | 1537篇 |
2007年 | 1412篇 |
2006年 | 1346篇 |
2005年 | 1093篇 |
2004年 | 871篇 |
2003年 | 727篇 |
2002年 | 629篇 |
2001年 | 524篇 |
2000年 | 522篇 |
1999年 | 601篇 |
1998年 | 492篇 |
1997年 | 432篇 |
1996年 | 440篇 |
1995年 | 389篇 |
1994年 | 362篇 |
1993年 | 326篇 |
1992年 | 271篇 |
1991年 | 230篇 |
1990年 | 237篇 |
1989年 | 159篇 |
1988年 | 120篇 |
1987年 | 86篇 |
1986年 | 98篇 |
1985年 | 67篇 |
1984年 | 38篇 |
1983年 | 39篇 |
1982年 | 39篇 |
1981年 | 22篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1976年 | 1篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Deming Zhu 《应用数学学报(英文版)》1991,7(2):108-113
The cycle control function is defined and used to estimate the number of limit cycles for some planar autonomous systems. Some sufficient conditions for the existence of no or at most one limit cycle are given. 相似文献
32.
33.
对水热处理后得到的USY沸石作进一步的酸处理以及采用改进的氟硅酸盐溶液骨架富硅工艺,分别得到了经XPS剖面分析证实为铝分布均匀的超稳Y沸石HAY-Ⅰ和HAY-Ⅱ。IR分析表明,在酸处理过程中从USY沸石中去掉的那部分非骨架铝类与3690cm~(-1)处羟基有关,仍残留在HAY-Ⅰ沸石中的那部分非骨架铝类与3670cm~(-1)和3600cm~(-1)处羟基有关。XRD和化学分析表明HAY-Ⅰ沸石仍含有约50%的非骨架铝类,而HAY-Ⅱ沸石则基本上不含非骨架铝类,HAY-Ⅱ沸石还显示更高的结晶保留度。DTA分析表明,HAY-Ⅰ和HAY-Ⅱ两种沸石的热稳定性均高于USY沸石。 相似文献
34.
稳态锁模产生4ps激光脉冲 总被引:1,自引:0,他引:1
首次利用GaAs光电导开关,控制Nd:YLF激光器腔内Q值,实现稳态锁模,获得脉宽和能量稳定性极高的4ps激光脉冲。 相似文献
35.
Q.J. Zhu 《Journal of Mathematical Analysis and Applications》2007,326(1):708-720
Investment systems are studied using a framework that emphasize their profiles (the cumulative probability distribution on all the possible percentage gains of trades) and their log return functions (the expected average return per trade in logarithmic scale as a function of the investment size in terms of the percentage of the available capital). The efficiency index for an investment system, defined as the maximum of the log return function, is proposed as a measure to compare investment systems for their intrinsic merit. This efficiency index can be viewed as a generalization of Shannon's information rate for a communication channel. Applications are illustrated. 相似文献
36.
Wei Mingjun Zhu Wanzhen 《Annals of Differential Equations》2007,23(4):511-518
In this paper we consider the system of classical particles coupled with a Klein-Gordon field in two dimensions.We establish a-priori-bounds on the solutions of this system with initial data satisfying a size restriction derived from conservation of energy.This result,together with the smoothing of"velocity averaging",yields the existence of global weak solutions to the corresponding restricted initial value problem.The size restriction is necessary since energy of the system is indefinite.Finally,we show that the weak solutions preserve the total mass. 相似文献
37.
By using the theory of coincidence degree, we study a kind of periodic solutions to p-Laplacian neutral functional differential equation with multiple deviating arguments, a new result on the existence of periodic solutions is obtained. 相似文献
38.
De Ming ZHU Ying SUN 《数学学报(英文版)》2007,23(8):1495-1504
In this paper, we study the dynamical behavior for a 4-dimensional reversible system near its heteroclinic loop connecting a saddle-focus and a saddle. The existence of infinitely many reversible 1-homoclinic orbits to the saddle and 2-homoclinic orbits to the saddle-focus is shown. And it is also proved that, corresponding to each 1-homoclinic (resp. 2-homoclinic) orbit F, there is a spiral segment such that the associated orbits starting from the segment are all reversible 1-periodic (resp. 2-periodic) and accumulate onto F. Moreover, each 2-homoclinic orbit may be also accumulated by a sequence of reversible 4-homoclinic orbits. 相似文献
39.
X.P. Hu X. Wang Z. Yan H.X. Li J.L. He S.N. Zhu 《Applied physics. B, Lasers and optics》2007,86(2):265-268
High power red light was generated from a periodically-poled stoichiometric LiTaO3 (PPSLT) by single-pass frequency doubling of a diode-side-pumped, Q-switched Nd:YAG laser at 1319 nm. An average power of
2.4 W of the 660 nm red light was obtained at the fundamental power of ∼5.4 W with the conversion efficiency up to 44.4% and
with low fluctuation down to 2%. The high efficiency and stability at the red output indicate that it is a practical method
to construct a reliable compact red laser.
PACS 42.70.Mp; 42.79.Nv; 42.55.Xi 相似文献
40.