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   7479篇
  免费   382篇
  国内免费   111篇
化学   5726篇
晶体学   40篇
力学   396篇
数学   738篇
物理学   1072篇
  2024年   17篇
  2023年   57篇
  2022年   288篇
  2021年   371篇
  2020年   374篇
  2019年   375篇
  2018年   376篇
  2017年   362篇
  2016年   494篇
  2015年   349篇
  2014年   458篇
  2013年   841篇
  2012年   636篇
  2011年   559篇
  2010年   360篇
  2009年   348篇
  2008年   349篇
  2007年   298篇
  2006年   205篇
  2005年   174篇
  2004年   119篇
  2003年   118篇
  2002年   96篇
  2001年   33篇
  2000年   17篇
  1999年   26篇
  1998年   18篇
  1997年   21篇
  1996年   21篇
  1995年   10篇
  1994年   14篇
  1993年   10篇
  1992年   13篇
  1991年   10篇
  1990年   9篇
  1989年   7篇
  1988年   5篇
  1987年   15篇
  1986年   5篇
  1985年   12篇
  1984年   13篇
  1982年   14篇
  1981年   7篇
  1980年   14篇
  1979年   6篇
  1978年   11篇
  1977年   5篇
  1976年   5篇
  1971年   3篇
  1968年   6篇
排序方式: 共有7972条查询结果,搜索用时 15 毫秒
141.
This study deals with the problem of controlling a class of uncertain nonlinear systems in the presence of external disturbances. To achieve this goal, a new Optimal Type-2 Fuzzy Sliding Mode Controller (OT2FSMC) is introduced. In the proposed controller, a novel heuristic algorithm, namely particle swarm optimization with random inertia weight (RNW–PSO), is employed. To achieve an optimal performance, the parameters of the proposed controller as well as the input and output membership functions are optimized simultaneously by RNW–PSO. The globally asymptotic stability of the closed-loop system is mathematically proved. Finally, this method of control is applied to the inverted pendulum system as a case study. Simulation results show the system performance is desirable.  相似文献   
142.
143.
144.
In recent years, gold nanoparticles (Au‐NPs) have been taken into consideration in nanomedicine due to their excellent biocompatibility, chemical stability and promising optical properties. In this research, podophyllotoxin conjugated with gold nanoparticles (Au‐NPs‐POT) was synthesized and the conjugation of POT with Au‐NPs was confirmed using scanning electron microscopy, mass spectrometry and Fourier transform infrared spectroscopy. The anticancer effects of the product on preclinical models of lung, colon and breast cancers were investigated using MTT test. The analyses showed a direct dose–response relationship. It was found that higher concentrations of POT have more positive effects on the inhibition of cancer cell growth. At POT concentrations of 1, 2.5, 5, 7.5, 10, 15 and 20 ng ml?1, approximately 50% of the growth of colorectal, lung and breast cancer cell lines was inhibited, while similar results were obtained in the presence of 1, 2, 3, 4 and 5 μg ml?1 Au‐NPs‐POT. Au‐NPs‐POT exhibited the lowest cytotoxicity due to the presence of POT. The anticancer feature of Au‐NPs‐POT proved the potential to develop better anticancer therapeutics and to open new avenues for treatment of cancers.  相似文献   
145.
146.
Void swelling is an important phenomenon observed in both nuclear fuels and cladding materials in operating nuclear reactors. In this work we develop a phase-field model to simulate void evolution and void volume change in irradiated materials. Important material processes, including the generation of defects such as vacancies and self-interstitials, their diffusion and annihilation, and void nucleation and evolution, have been taken into account in this model. The thermodynamic and kinetic properties, such...  相似文献   
147.
148.
149.
We propose that spectral intensity of superconductor based random lasers can be made tunable by changing temperature. The two fluid model and wavelength dependent dispersion formula have been employed to describe the optical response of the superconducting materials. Random laser characteristics have been calculated using the one dimensional FDTD method. Our simulation results reveal that the emission spectrum can be manipulated through the ambient temperature of the system. It is observed that transition from metal phase to pure superconducting phase leads to the enhancement of the laser emission. Furthermore, spatial distribution of the fields in one dimensional disordered media is very sensitive to the system temperature.  相似文献   
150.
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