全文获取类型
收费全文 | 30472篇 |
免费 | 4873篇 |
国内免费 | 4257篇 |
专业分类
化学 | 22434篇 |
晶体学 | 475篇 |
力学 | 2047篇 |
综合类 | 348篇 |
数学 | 3656篇 |
物理学 | 10642篇 |
出版年
2024年 | 54篇 |
2023年 | 477篇 |
2022年 | 915篇 |
2021年 | 935篇 |
2020年 | 1041篇 |
2019年 | 1145篇 |
2018年 | 943篇 |
2017年 | 1009篇 |
2016年 | 1346篇 |
2015年 | 1407篇 |
2014年 | 1675篇 |
2013年 | 2144篇 |
2012年 | 2669篇 |
2011年 | 2743篇 |
2010年 | 1951篇 |
2009年 | 1893篇 |
2008年 | 2118篇 |
2007年 | 1939篇 |
2006年 | 1902篇 |
2005年 | 1520篇 |
2004年 | 1253篇 |
2003年 | 1098篇 |
2002年 | 1213篇 |
2001年 | 1041篇 |
2000年 | 742篇 |
1999年 | 670篇 |
1998年 | 493篇 |
1997年 | 393篇 |
1996年 | 418篇 |
1995年 | 338篇 |
1994年 | 284篇 |
1993年 | 245篇 |
1992年 | 215篇 |
1991年 | 215篇 |
1990年 | 169篇 |
1989年 | 162篇 |
1988年 | 105篇 |
1987年 | 90篇 |
1986年 | 99篇 |
1985年 | 77篇 |
1984年 | 60篇 |
1983年 | 48篇 |
1982年 | 34篇 |
1981年 | 34篇 |
1980年 | 31篇 |
1979年 | 21篇 |
1978年 | 24篇 |
1977年 | 25篇 |
1976年 | 23篇 |
1973年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
111.
The single-longitudinal-mode Nd:GdVO4/RTiOPO4 (RTP) solid-state Green laser operation of a laser-diode (LD) end-pumped laser is realized by multi-cavities and a Brewster plate. The LD-pumped single-frequency green laser has been demonstrated by optimizing several parameters and a cavity length, with precise temperature controlling of Nd:GdV04, RTP and laser diode. When the incident pump power is 2 W at 808.4 nm, a single-frequency cw green laser at 532nm with output 210 m W is obtained, the optical-to-optical conversion efficiency is up to 10.5%. 相似文献
112.
本文用AES研究了P-InP/TiPdAu热处理前后的界面特性,结果表明:TiPd层对Au的内扩散和In的扩散有阻挡作用。以TiPdAu作InGaAsP/InP双异质结发光管的p面电极、镀Au作热沉,采用In焊料,研究了器件的可靠性问题,在室温大气气氛中;70℃存储,70~80℃带电老化,三种条件下长时间考核结果表明:器件的I-V特性正常,末见正向压降明显变化。还比较了Au-Zn材料作p面电极用TiPdAu作肖脱基势垒限制层制成的器件和用TiPdAu作电极材料制成的深Zn扩散型器件在老化过程中的特性变化,后二种结构的器件,在长期老化过程中,有源区中有大面积DSD生长和增殖。 相似文献
113.
This work proposes and demonstrates the feasibility of gray image encryption using multiple polarization encoding, in which
the cascaded twisted nematic liquid crystal devices sandwiched between a crossed polarizer pair are used to implement exclusive
OR (XOR) logical encryption and decryption. The polarization encoding scheme provides a multichannel XOR logic operation to
secure bit-plane images derived from a gray image, according to the adiabatic following properties of twisted nematic liquid
crystal devices. Experimental data reveal that the multiple polarization encoding schemes for gray image encryption and decryption
are performed with acceptable image quality by selecting appropriate polarization orientation and modulation conditions. Both
analytic and experimental results are presented and discussed. 相似文献
114.
On Polynomial Functions over Finite Commutative Rings 总被引:1,自引:0,他引:1
Jian Jun JIANG Guo Hua PENG Qi SUN Qi Fan ZHANG 《数学学报(英文版)》2006,22(4):1047-1050
Let R be an arbitrary finite commutative local ring. In this paper, we obtain a necessary and sufficient condition for a function over R to be a polynomial function. Before this paper, necessary and sufficient conditions for a function to be a polynomial function over some special finite commutative local rings were obtained. 相似文献
115.
Jian Ming ZHAN Bijan DAVVAZ K. P. SHUM 《数学学报(英文版)》2007,23(8):1345-1356
We describe the relationship between the fuzzy sets and the algebraic hyperstructures. In fact, this paper is a continuation of the ideas presented by Davvaz in (Fuzzy Sets Syst., 117: 477- 484, 2001) and Bhakat and Das in (Fuzzy Sets Syst., 80: 359-368, 1996). The concept of the quasicoincidence of a fuzzy interval value with an interval-valued fuzzy set is introduced and this is a natural generalization of the quasi-coincidence of a fuzzy point in fuzzy sets. By using this new idea, the concept of interval-valued (α,β)-fuzzy sub-hypermodules of a hypermodule is defined. This newly defined interval-valued (α,β)-fuzzy sub-hypermodule is a We shall study such fuzzy sub-hypermodules and sub-hypermodules of a hypermodule. generalization of the usual fuzzy sub-hypermodule. consider the implication-based interval-valued fuzzy 相似文献
116.
In the present paper, a Lotka–Volterra type mutualism system with several delays is studied. Some new and interesting sufficient conditions are obtained for the global existence of positive periodic solutions of the mutualism system. Our method is based on Mawhin’s coincidence degree and novel estimation techniques for the a priori bounds of unknown solutions. Our results are different from the existing ones such as those in of Yang et al. [F. Yang, D. Jiang, A. Ying, Existence of positive solution of multidelays facultative mutualism system, J. Eng. Math. 3 (2002) 64–68] and Chen et al. [F. Chen, J. Shi, X. Chen, Periodicity in a Lotka–Volterra facultative mutualism system with several delays, J. Eng. Math. 21 (3) (2004) 403–409]. 相似文献
117.
超子中子星性质的温度效应 总被引:2,自引:0,他引:2
从相对论平均场理论出发,考虑核子、超子和介子的相互作用,研究了温度对中子星组成粒子、状态方程和中子星质量等的影响.发现温度越高,超子在中子星内部出现时的重子数密度越低.当密度较高时,中子星的核心区主要由超子组成,即中子星转变成以奇异粒子为主要成分的超子星,并且这种转变受到温度的影响,温度越高,转变密度越低.由于超子的出现,中子星核心高密度区域的状态方程,对于不同温度,差别不大,所以有限温度中子星的最大质量都在1.8M⊙附近.这与观测结果相符. 相似文献
118.
Based on solving the couple mode equation numerically, the characterization of the signal power on the gate power was analyzed. And the relationship of the tolerance of the grating period and the bulk temperature on the interaction length was analyzed. 相似文献
119.
120.