首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   5730篇
  免费   161篇
  国内免费   43篇
化学   3782篇
晶体学   34篇
力学   177篇
综合类   1篇
数学   986篇
物理学   954篇
  2023年   39篇
  2022年   144篇
  2021年   155篇
  2020年   116篇
  2019年   108篇
  2018年   122篇
  2017年   94篇
  2016年   186篇
  2015年   163篇
  2014年   204篇
  2013年   346篇
  2012年   382篇
  2011年   436篇
  2010年   266篇
  2009年   258篇
  2008年   396篇
  2007年   345篇
  2006年   336篇
  2005年   264篇
  2004年   230篇
  2003年   189篇
  2002年   186篇
  2001年   68篇
  2000年   68篇
  1999年   53篇
  1998年   46篇
  1997年   36篇
  1996年   65篇
  1995年   50篇
  1994年   41篇
  1993年   44篇
  1992年   27篇
  1991年   24篇
  1990年   34篇
  1989年   34篇
  1988年   32篇
  1987年   24篇
  1986年   25篇
  1985年   29篇
  1984年   31篇
  1983年   24篇
  1982年   22篇
  1981年   21篇
  1980年   20篇
  1979年   22篇
  1978年   24篇
  1977年   13篇
  1976年   12篇
  1975年   12篇
  1974年   14篇
排序方式: 共有5934条查询结果,搜索用时 15 毫秒
21.
In this work, thermoanalytical, diffractometry, and microscopy measurements have been performed in order to characterize the effect of high energy milling on a drug active in the migraine prophylaxis and smoke cessation. We can assert that the mechanical treatment induces only a partial amorphisation of the solid phase, in particular it reduces the crystal order by producing lattice defects which propagate from the surface to the bulk crystal. For this reason, the DSC is able to detect the presence of ordered solid, while the powder X-ray diffractometry, because of its low penetration depth, does not reach the crystalline core of the particles.  相似文献   
22.
23.
24.
25.
We present a simplified correlation for calculating the dissolved gas moles in a pendant drop during the diffusion time, for several drop shapes. After this correlation is determined, the Yang and Gu (Ind Eng Chem Res 44:4474–4483, 2005) dynamic pendant drop volume analysis (DPDVA) method for calculation of mass diffusivity from the pendant drop volume variation against time can be used. We solved the differential equation in cylindrical coordinates for the mass transfer model of the gas diffusion into the liquid inside the pendant drop, using a different characteristic length (LC), instead of the outer radius of the syringe needle (rn) used in Yang and Gu (Ind Eng Chem Res 44:4474–4483, 2005) for defining the dimensionless variables. LC is the relationship between the pendant drop volume and its mass transfer surface area at the initial conditions. The generalized correlation saves time, simplifies the method application and the deviations in the diffusion coefficient calculation respect to the complete Yang and Gu model are below 6%.  相似文献   
26.
We use a quite concrete and simple realization of sl q (2, ) involving finite difference operators. We interpret them as derivations (in the noncommutative sense) on a suitable graded algebra, which gives rise to the noncommutative scheme 1 II 1* as the counterpart of the standard 1 = Sl(2, )/B.  相似文献   
27.
This article reviews different kinds of models for the electric power grid that can be used to understand the modern power system, the smart grid. From the physical network to abstract energy markets, we identify in the literature different aspects that co-determine the spatio-temporal multilayer dynamics of power system. We start our review by showing how the generation, transmission and distribution characteristics of the traditional power grids are already subject to complex behaviour appearing as a result of the the interplay between dynamics of the nodes and topology, namely synchronisation and cascade effects. When dealing with smart grids, the system complexity increases even more: on top of the physical network of power lines and controllable sources of electricity, the modernisation brings information networks, renewable intermittent generation, market liberalisation, prosumers, among other aspects. In this case, we forecast a dynamical co-evolution of the smart grid and other kind of networked systems that cannot be understood isolated. This review compiles recent results that model electric power grids as complex systems, going beyond pure technological aspects. From this perspective, we then indicate possible ways to incorporate the diverse co-evolving systems into the smart grid model using, for example, network theory and multi-agent simulation.  相似文献   
28.
We predict the existence of surface waves in layered superconductors in the THz frequency range, below the Josephson plasma frequency omega J. This wave propagates along the vacuum-superconductor interface and dampens in both transverse directions out of the surface (i.e., towards the superconductor and towards the vacuum). This is the first prediction of propagating surface waves in any superconductor. These predicted surface Josephson plasma waves are important for different phenomena, including the complete suppression of the specular reflection from a sample (Wood's anomalies) and a huge enhancement of the wave absorption (which can be used as a THz detector).  相似文献   
29.
30.
We demonstrate a high-power, narrowband pulsed source at 390 nm by two stages of frequency doubling in periodically poled MgO:LiNbO(3) and periodically poled KTiOPO(4) of an amplified, passively mode-locked fiber laser. With a frequency quadrupling efficiency of 5.5% and a 0.1 nm bandwidth, the 250 mW ultraviolet source is a suitable compact pump source for many entanglement-based quantum information processing tasks.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号