全文获取类型
收费全文 | 2153篇 |
免费 | 665篇 |
国内免费 | 97篇 |
专业分类
化学 | 356篇 |
晶体学 | 9篇 |
力学 | 302篇 |
综合类 | 124篇 |
数学 | 344篇 |
物理学 | 1780篇 |
出版年
2024年 | 5篇 |
2023年 | 18篇 |
2022年 | 69篇 |
2021年 | 54篇 |
2020年 | 52篇 |
2019年 | 36篇 |
2018年 | 51篇 |
2017年 | 106篇 |
2016年 | 114篇 |
2015年 | 78篇 |
2014年 | 178篇 |
2013年 | 151篇 |
2012年 | 163篇 |
2011年 | 165篇 |
2010年 | 128篇 |
2009年 | 124篇 |
2008年 | 136篇 |
2007年 | 169篇 |
2006年 | 147篇 |
2005年 | 137篇 |
2004年 | 96篇 |
2003年 | 112篇 |
2002年 | 102篇 |
2001年 | 98篇 |
2000年 | 69篇 |
1999年 | 64篇 |
1998年 | 57篇 |
1997年 | 37篇 |
1996年 | 32篇 |
1995年 | 28篇 |
1994年 | 25篇 |
1993年 | 14篇 |
1992年 | 14篇 |
1991年 | 10篇 |
1990年 | 16篇 |
1989年 | 12篇 |
1988年 | 10篇 |
1987年 | 9篇 |
1986年 | 7篇 |
1985年 | 10篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1979年 | 1篇 |
排序方式: 共有2915条查询结果,搜索用时 15 毫秒
21.
R. Thomas conjectured, 20 years ago, that the presence of a positive circuit in the interaction graph of a dynamical system is a necessary condition for the presence of several stable states. Recently, E. Remy et al. stated and proved the conjecture for Boolean dynamical systems. Using a similar approach, we generalize the result to discrete dynamical systems, and by focusing on the asynchronous dynamics that R. Thomas used in the course of his analysis of genetic networks, we obtain a more general variant of R. Thomas’ conjecture. In this way, we get a necessary condition for genetic networks to lead to differentiation. 相似文献
22.
高斯光束计算平板波导自由传输区远场分布及其修正 总被引:2,自引:2,他引:0
对近轴近似条件下求解亥姆霍兹方程得到的高斯光束显式传播公式做了分析,同时,基于基尔霍夫衍射理论,在菲涅耳近似的条件下给出了相应的高斯光束在远场的传播公式,在此基础上,对近轴近似条件做出了定量分析,给出了这个近似条件引入的误差,提出了一种计算高斯光束远场分布的修正方法,并采用有限差分-光束传播方法(FD-BPM)来检验各种方法的准确性。把这种修正方法应用到平面光集成波导器件,如阵列波导光栅(AWG)、蚀刻衍射光栅(EDG)等器件的设计和模拟中,可以大大降低工作的复杂性,同时可以得到精确的结果。 相似文献
23.
通过保持非耗散介观LC电路的固有频率不变,而使电路参数作阶跃函数变化,就可将介观LC电路由初始的偶相干态制备到压缩偶相干态;在压缩偶相干态下,介观电路系统不仅有非经典的量子压缩效应,而且有非经典的反聚束效应.
关键词:
介观LC电路
单位阶跃函数
压缩算符
压缩偶相干态 相似文献
24.
Traveling wave Ti:LiNbO3 Mach-Zehnder optical modulators with buried electrodes and etched grooves in the SiO2 buffer layer are analyzed by the finite element method. The tradeoff between the bandwidth BW and the half-wave voltage Vπ is discussed. The value of BW/Vπ is used to weight the total performance of the modulator. Taking a thick buffer layer and etching deep grooves in the buffer layer are demonstrated as two effective methods to improve the performance of the modulator. A 3-dB optical bandwidth of 18 GHz with half-wave voltage 5V at a wavelength of 1.55 pm could be obtained even though the electrode is not very thick. When the requirement of half-wave voltage is not very critical, a bandwidth of more than 100 GHz can be obtained. 相似文献
25.
P.A. Postigo A.R. Alija L.J. Martínez M.L. Dotor D. Golmayo J. Snchez-Dehesa C. Seassal P. Viktorovitch M. Galli A. Politi M. Patrini L.C. Andreani 《Photonics and Nanostructures》2007,5(2-3):79-85
Two-dimensional photonic crystal lasers have been fabricated on III–V semiconductor slabs. Tuning of the spontaneous emission in micro and nanocavities has been achieved by accurate control of the slab thickness. Different structures, some of them of new application to photonic crystal lasers, have been fabricated like the Suzuki-phase or the coupled-cavity ring-like resonators. Laser emission has been obtained by pulsed optical pumping. Optical characterization of the lasing modes have been performed showing one or more laser peaks centred around 1.55 μm. Far field characterization of the emission pattern has been realized showing different patterns depending on the geometrical shape of the structures. These kinds of devices may be used as efficient nanolaser sources for optical communications or optical sensors. 相似文献
26.
提出了一种基于模型驱动的元数据管理方案.方案采用了基于模型的形式化描述方法,统一了专业网管子系统间的元数据模式;通过引入模型驱动技术,从元模型的抽象层次消除了不同专业网管子系统之间存在的“信息孤岛”;方案还对综合网管环境下的元数据理论和交换机制进行了研究,并给出了元数据的管理框架以及元数据交换的Java接口映射. 相似文献
27.
In hardware design, it is necessary to simulate the anticipated behavior of the integrated circuit before it is actually cast in silicon. As simulation procedures are long due to the great number of tests to be performed, optimization of the simulation code is of prime importance. This paper describes two mathematical models for the minimization of the memory access times for a cycle-based simulator.An integrated circuit being viewed as a directed acyclic graph, the problem consists in building a graph order on the vertices, compatible with the relation order induced by the graph, in order to minimize a cost function that represents the memory access time. For both proposed cost functions, we show that the corresponding problems are NP-complete. However, we show that the special cases where the graphs are in-trees or out-trees can be solved in polynomial time. 相似文献
28.
29.
30.