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   260956篇
  免费   1988篇
  国内免费   534篇
化学   134275篇
晶体学   4243篇
力学   13046篇
综合类   11篇
数学   28943篇
物理学   82960篇
  2021年   2552篇
  2020年   2676篇
  2019年   3274篇
  2018年   4712篇
  2017年   4750篇
  2016年   6265篇
  2015年   3091篇
  2014年   5519篇
  2013年   11057篇
  2012年   8985篇
  2011年   10488篇
  2010年   8347篇
  2009年   8550篇
  2008年   9868篇
  2007年   9721篇
  2006年   8765篇
  2005年   7714篇
  2004年   7311篇
  2003年   6712篇
  2002年   6707篇
  2001年   7273篇
  2000年   5392篇
  1999年   4118篇
  1998年   3612篇
  1997年   3576篇
  1996年   3261篇
  1995年   2863篇
  1994年   2941篇
  1993年   2870篇
  1992年   3182篇
  1991年   3350篇
  1990年   3189篇
  1989年   3320篇
  1988年   3148篇
  1987年   3104篇
  1986年   2973篇
  1985年   3690篇
  1984年   3857篇
  1983年   3223篇
  1982年   3243篇
  1981年   3117篇
  1980年   2900篇
  1979年   3289篇
  1978年   3401篇
  1977年   3580篇
  1976年   3483篇
  1975年   3234篇
  1974年   3216篇
  1973年   3302篇
  1972年   2510篇
排序方式: 共有10000条查询结果,搜索用时 343 毫秒
911.
Electron beam processing of poly(ethylene terephthalate) (PET) films is found to promote significant changes in the melting heat, intrinsic viscosity and polymer film-liquid (water, isooctane and toluene) boundary surface tension. These properties are featured with several maximums depending on the absorbed dose and correlating with the modification of PET surface functionality. Studies using adsorption of acid-base indicators and IR-spectroscopy revealed that the increase of PET surface hydrophilicity is determined by the oxidation of methylene and methyne groups. Electron beam treatment of PET films on the surface of N-vinylpyrrolidone aqueous solution provided graft copolymerization with this comonomer at optimum process parameters (energy 700 keV, current 1 mA, absorbed dose 50 kGy).  相似文献   
912.
Effect of annealing on the soft magnetic properties of Fe73.5Si13.5B9Nb3Au1 amorphous ribbon has been investigated by means of structure examination, magnetoimpedance ratio (MIR) and incremental permeability ratio (PR) spectra measured in the frequency range of 1–10 MHz at a fixed current of 10 mA X-ray diffraction analysis showed that the as-cast sample was amorphous and it became nanocrystalline under a proper heat treatment. When annealing amorphous alloy at 530 °C for 30, 60, 90 min, soft magnetic properties have been improved drastically. Among the samples investigated, the sample annealed at 530 °C for 90 min showed the softest magnetic behavior. The MIR and PR curves revealed the desirable changes in anisotropy field depending upon annealing.  相似文献   
913.
High-energy X-ray photoelectron spectroscopy (XPS) is of particular importance for minimizing the effects of surface contamination by increasing photoelectron escape depths. In this study high-resolution high-energy Cu Kα1 and soft Al Kα1 XPS and Auger electron spectroscopy were used to compare the electronic structure of Ti in TiO2 powder and Ti metal. The Ti 1s in TiO2 XPS line is narrower and more symmetric than in Ti metal. A comparison of the relative intensities of the L23M23M45 and L23M23M23 Auger transitions in Ti metal and TiO2 is consistent with the expected transfer of Ti 3d electrons away from the Ti site in the oxide. The satellites accompanying the Ti 1s XPS line excited by Cu Kα1 X-rays occur at the same energies as the satellites accompanying the Ti 2s and 2p XPS lines excited by Al Kα1 X-rays indicating that they do not depend on the core-level, the experimental resolution or inelastic scattering processes.  相似文献   
914.
We report on the status of the LPCTrap experiment, devoted to measure the β–ν angular correlation in the pure Gamow–Teller decay of 6He. This measurement is motivated by the search for the presence of tensor type contributions to the weak interaction. The 6He ions are confined in a novel transparent Paul trap. The β particles and the recoil ions are detected in coincidence to deduce the angular correlation parameter. The commissioning run performed in 2005 has given the proof of principle of this experiment. Up to 105 coincidences were recorded during a second run in 2006.  相似文献   
915.
This paper considers efforts to improve in-patient flows, a particularly urgent issue in the National Health Service (NHS). The context is described and related to reasons why OR has been making relatively little contribution. The paper argues that large complex models may often be unnecessary and even get in the way of providing clear insight and guidance for problem owners. The importance of understanding the generic working of systems to lead to improvement, and the limitations of simply describing them, is stressed. It is demonstrated that some very simple models can be of significant practical value in understanding and managing complex systems, changing mindsets and driving collection and use of operationally valuable data. Recommendations for more effective engagement with the NHS are offered.  相似文献   
916.
917.
918.
919.
920.
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