全文获取类型
收费全文 | 142560篇 |
免费 | 21070篇 |
国内免费 | 16288篇 |
专业分类
化学 | 76673篇 |
晶体学 | 1249篇 |
力学 | 6092篇 |
综合类 | 770篇 |
数学 | 13573篇 |
物理学 | 40528篇 |
无线电 | 41033篇 |
出版年
2024年 | 359篇 |
2023年 | 3210篇 |
2022年 | 3763篇 |
2021年 | 5207篇 |
2020年 | 5402篇 |
2019年 | 4928篇 |
2018年 | 4523篇 |
2017年 | 4295篇 |
2016年 | 6026篇 |
2015年 | 6445篇 |
2014年 | 7923篇 |
2013年 | 10140篇 |
2012年 | 11990篇 |
2011年 | 12349篇 |
2010年 | 9252篇 |
2009年 | 9213篇 |
2008年 | 9505篇 |
2007年 | 8620篇 |
2006年 | 8164篇 |
2005年 | 7135篇 |
2004年 | 5205篇 |
2003年 | 4324篇 |
2002年 | 3884篇 |
2001年 | 3316篇 |
2000年 | 2969篇 |
1999年 | 3093篇 |
1998年 | 2635篇 |
1997年 | 2274篇 |
1996年 | 2264篇 |
1995年 | 2007篇 |
1994年 | 1712篇 |
1993年 | 1424篇 |
1992年 | 1248篇 |
1991年 | 1048篇 |
1990年 | 863篇 |
1989年 | 619篇 |
1988年 | 491篇 |
1987年 | 395篇 |
1986年 | 400篇 |
1985年 | 316篇 |
1984年 | 230篇 |
1983年 | 199篇 |
1982年 | 143篇 |
1981年 | 88篇 |
1980年 | 66篇 |
1979年 | 27篇 |
1978年 | 28篇 |
1976年 | 24篇 |
1975年 | 23篇 |
1957年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
871.
872.
In this paper, we study the growth of solutions of a first order linear differential equation. From this we verify that a
conjecture given by Brück is true under the restriction of the hyper order less than 1/2, and obtain some uniqueness theorems
of a nonconstant entire function and its first derivative sharing a nonzero constant CM. The results in this paper also improve
some known results. Some examples show that the results in this paper are best possible.
Project supported by the NSFC (NO. A0324617) and the RFDP (NO. 20060422049).
Received: 20 April 2006 Revised: 4 February 2007 相似文献
873.
利用富铈混合稀土改善工业纯铝中富铁相形貌的研究 总被引:1,自引:0,他引:1
利用金相分析方法研究了富Ce混合稀土变质对含不同Fe量的工业纯铝的组织和其中富铁相形貌的影响。试验结果表明,随着Fe含量的增加,富铁相由弥散细小的颗粒状向短棒状、长针状转变;富Ce混合稀土变质使铝中的富铁相由长针状变为弥散细小的颗粒状。随着稀土含量的增加,-αAl晶粒逐渐细化,富铁相尺寸及数量逐渐减小。添加0.5%稀土时,-αAl晶粒细化效果最佳,而且富铁相呈细小颗粒状均匀分布在-αAl基体的晶界处。本文还对稀土改善富铁相的机制进行了分析。 相似文献
874.
A number of generalized metric spaces have been defined or characterized in terms of g-functions. Symmetric g-functions are discussed by C. Good, D. Jennings and A. M. Mohamad. In this paper, some questions about symmetric g-functions are answered, particularly it is shown that every sym-wg-space is expandable.
The project is supported by the NNSF (10571151) and NSF (2006J0397) of Fujian Province of China. 相似文献
875.
A delayed stage-structured predator–prey model with non-monotone functional responses is proposed. It is assumed that immature individuals and mature individuals of the predator are divided by a fixed age, and that immature predators do not have the ability to attack prey. Some new and interesting sufficient conditions are obtained for the global existence of multiple positive periodic solutions of the stage-structured predator–prey model. Our method is based on Mawhin’s coincidence degree and novel estimation techniques for the a priori bounds of unknown solutions to Lx = λNx. An example is given to illustrate the feasibility of our main result. 相似文献
876.
Cai-yun Jin Cao-zong Cheng Yong-tao Jin Jing Li 《应用数学学报(英文版)》2006,22(4):607-614
Two two-function minimax theorems are proved.The concavity-convexity conditions of the twofunctions involve strictly monotone transformations and mixing of the values of the two functions,and aredescribed by the inequalities as upward and weakly downward conditions. 相似文献
877.
878.
Xin Tao YE Chong LI 《数学学报(英文版)》2007,23(1):65-76
The BCQ and the Abadie CQ for infinite systems of convex inequalities in Banach spaces are characterized in terms of the upper semi-continuity of the convex cones generated by the subdifferentials of active convex functions. Some relationships with other constraint qualifications such as the CPLV and the Slate condition are also studied. Applications in best approximation theory are provided. 相似文献
879.
A single-picosecond GaAs photoconductive switch is used to pulse excite a microwave resonant cavity, thus generating a variety of RF (radiofrequency) waveforms with picosecond synchronization. The length of the transmission line that connects the photoconductive switch and the cavity and the strength of input/output cavity coupling elements provide for continuous variation of the frequency distribution of the generated RF power. The generation of greater than 7-kW broadband microwave bursts is demonstrated 相似文献
880.