全文获取类型
收费全文 | 1015篇 |
免费 | 122篇 |
国内免费 | 254篇 |
专业分类
化学 | 745篇 |
晶体学 | 22篇 |
力学 | 87篇 |
综合类 | 12篇 |
数学 | 157篇 |
物理学 | 368篇 |
出版年
2024年 | 5篇 |
2023年 | 11篇 |
2022年 | 35篇 |
2021年 | 35篇 |
2020年 | 41篇 |
2019年 | 24篇 |
2018年 | 39篇 |
2017年 | 37篇 |
2016年 | 37篇 |
2015年 | 47篇 |
2014年 | 51篇 |
2013年 | 65篇 |
2012年 | 101篇 |
2011年 | 91篇 |
2010年 | 69篇 |
2009年 | 68篇 |
2008年 | 105篇 |
2007年 | 71篇 |
2006年 | 79篇 |
2005年 | 65篇 |
2004年 | 59篇 |
2003年 | 34篇 |
2002年 | 32篇 |
2001年 | 34篇 |
2000年 | 21篇 |
1999年 | 36篇 |
1998年 | 23篇 |
1997年 | 12篇 |
1996年 | 6篇 |
1995年 | 10篇 |
1994年 | 6篇 |
1993年 | 5篇 |
1992年 | 7篇 |
1991年 | 6篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1980年 | 1篇 |
1964年 | 2篇 |
排序方式: 共有1391条查询结果,搜索用时 15 毫秒
1.
We propose a system of time-division multiplexing(TDM) and spatial frequency-division multiplexing(SFDM). Extrinsic Fabry–Perot interferometric sensors are applied to detect weak acoustic signals. The broadband source is employed, the light from it is modulated by a pulse signal sequence and is efficiently amplified by semiconductor optical amplifiers. Experimental results show that the equivalent noise pressure spectrum level is-97.2 d B re 1 rad/√Hz below 1250 Hz, and the cross talk between two sensors in one TDM channel is-32.7 d B with a cavity length difference of 60 μm. The number of sensors in this multiplexing system can theoretically reach 160. 相似文献
2.
3.
Y. KAGAWAT. FUJITANI Y. FUJITAL. CHAI N. WAKATSUKIT. TSUCHIYA 《Journal of sound and vibration》2002,255(2):323-335
The application of the discrete Huygens' modelling has been discussed for acoustic wave propagation problems, in which the scalar wave field problems have been focused. The present paper extends the application of the modelling to the elastic wave propagation in a homogeneous elastic medium in which two types of waves, the longitudinal wave and the shear wave, are independent except at the boundary. Each wave can be treated like a scalar wave until the two waves reach the boundary where they couple so as to satisfy the displacement or stress boundary condition. We propose the approach confining ourselves to the two-dimensional field. Some examples are demonstrated, whose solutions are compared with the vectorial wave modelling and finite difference modelling solutions whenever they are available. 相似文献
4.
A Promising MoO_x-based Catalyst for n-Heptane Isomerization 总被引:1,自引:0,他引:1
Song Hai CHAI Xin Ping WANG* Ying Jun WANG Tian Xi CAI State Key Laboratory of Fine Chemicals Dalian University of Technology Dalian 《中国化学快报》2003,14(7)
The increasing demand for higher-octane gasoline and the regulations limiting the amount of aromatics in the fuel motivate the interest in catalytic isomerization of n-alkanes. In the last ten years, transition metal oxides or oxycarbides based on molybdenum or tungstate have attracted much attention due to their high activity and isomerization selectivity compared to the conventional bifunctional supported platinum catalyst and high resistance to sulphur and nitrogen catalyst poisons1-5. Ma… 相似文献
5.
6.
Anti-BZ-Structure in Effect Algebras 总被引:1,自引:0,他引:1
The definitions of sharply approximating effect algebras, anti-BZ-effect algebras, central approximating effect algebras, and S-anti-BZ-effect algebras are given, the relationships between sharply approximating effect algebras and anti-BZ-effect algebras, between central approximating effect algebras and anti-BZ-effect algebras are established, and the set of anti-BZ-sharp elements in S-anti-BZ-effect algebras is proved to be an orthomodular lattice. 相似文献
7.
关于《一类奇异边值问题的正解》的注记 总被引:3,自引:0,他引:3
文[4]通过构造反例断言文[1]中定理的必要性证明有误,本文首先指出文[4] 的这个断言不正确,然后对文[4]中定理2.1作了本质性的改进. 相似文献
8.
氩气介质阻挡放电的发光特性 总被引:1,自引:0,他引:1
本文使用水电极介质阻挡放电装置,采用光学方法测量了氩气介质阻挡放电的发光特性。发现在驱动电压处于一定的范围内时,放电处于丝极模式,在驱动电压的每半周期内,无论是放电的总光还是单个微通道的放电发光均只有一次脉冲,单个微放电的时间为2μs,而总放电时间为2.4μs,这表明在氩气的丝极模式中,各单丝产生与熄灭的时间极其接近,各个放电丝之间有着很好的时间相关性。最后将本文的结果与空气中介质阻挡放电丝极模式的发光特性相比较,空气放电在每半周内的总光信号由多个脉冲组成,而每一个脉冲对应多个放电丝,因而氩气中各个放电微通道之间的时间相关性远强于空气的情况。 相似文献
9.
10.
Complete Surjections and Complete Epimorphisms over Completely Distributive Lattices 总被引:1,自引:0,他引:1
Generators and lattice properties of the poset of complete homomorphisic images of a completely distributive lattice are exploited via the localic methods. Some intrinsic and extrinsic conditions about this poset to be a completely distributive lattice are given. It is shown that the category of completely distributive lattices is co-well-powered,and complete epimorphisms on completely distributive lattice are not necessary to be surjections. Finally, some conditions about complete epimorphisms to be surjections are given. 相似文献