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   266423篇
  免费   2296篇
  国内免费   899篇
化学   116993篇
晶体学   3998篇
力学   10759篇
综合类   1篇
数学   25513篇
物理学   78802篇
无线电   33552篇
  2020年   2048篇
  2019年   2293篇
  2018年   3030篇
  2017年   2923篇
  2016年   4306篇
  2015年   2533篇
  2014年   4366篇
  2013年   10752篇
  2012年   7993篇
  2011年   9923篇
  2010年   7242篇
  2009年   7575篇
  2008年   9924篇
  2007年   10286篇
  2006年   9750篇
  2005年   8940篇
  2004年   8358篇
  2003年   7413篇
  2002年   7308篇
  2001年   8392篇
  2000年   6680篇
  1999年   5424篇
  1998年   4740篇
  1997年   4587篇
  1996年   4289篇
  1995年   4000篇
  1994年   3891篇
  1993年   3984篇
  1992年   3999篇
  1991年   4174篇
  1990年   3917篇
  1989年   3755篇
  1988年   3718篇
  1987年   3312篇
  1986年   3183篇
  1985年   4163篇
  1984年   4379篇
  1983年   3535篇
  1982年   3659篇
  1981年   3603篇
  1980年   3481篇
  1979年   3521篇
  1978年   3614篇
  1977年   3555篇
  1976年   3626篇
  1975年   3320篇
  1974年   3313篇
  1973年   3371篇
  1972年   2373篇
  1971年   1967篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
92.
We have simultaneously used adsorption isotherm volumetry and Fourier transform infrared spectroscopy in order to take the investigations on amorphous ice structure a step further, especially concerning porosity and annealing-induced modifications. We have studied surface reorganization during annealing and found that the number of surface sites decreases before crystallization, their relative ratios being different for amorphous and crystalline ice. We also present results confirming that ice can have a large specific surface area and nevertheless be non-microporous.  相似文献   
93.
单光子态的产生与测量   总被引:1,自引:0,他引:1  
报道了通过自发参量下转换产生单光子态的实验研究,使用中心波长425 nm的飞秒脉冲泵浦Ⅰ类非共线相位匹配的BBO晶体,在实验上得到单光子计数率为2.978×10-4,并分析了实验中的相关问题.  相似文献   
94.
Silica@copper (SiO2@Cu) core–shell nanoparticles were synthesized and well characterized by XRD, TEM, AFM, XPS, UV/Vis, TGA–MS, and ICP–AES techniques. The synthesized SiO2@Cu core–shell nanoparticles were employed as catalysts for the conjugate addition of amines to α,β‐unsaturated compounds in water to obtain β‐amino carbonyl compounds in excellent yields in shorter reaction times. Furthermore, the catalyst works well for hetero‐Michael addition reactions of heteroatom nucleophiles such as thiols to α,β‐unsaturated compounds. As the reaction is performed in water, it allows for easy recycling of the catalyst with consistent activity.  相似文献   
95.
96.
The growth of the isolated (100) face of a KDP crystal at exposure of the phase boundary to the initial ultrasound field and a standing acoustic wave has been investigated. A significant growth response of this face, exposed to sound normally along the acoustic axis in the near zone of a piston-like half-wave vibrator with f = 20 kHz and tangentially in the pulsed two-frequency (f = 600 and 900 kHz) standing-wave mode, has been revealed. It is shown that the mechanisms of mass exchange enhancement in these acoustic modes are different. The results obtained show a fundamental possibility of controlling crystal growth and dissolution by varying the parameters of inhomogeneous acoustic field.  相似文献   
97.
The features of doping of KDP crystals with cerium ions and organocerium complexes with alizarin complexon and arsenazo III have been investigated. It is established that “direct” doping by introducing cerium salts into the initial solution cannot be implemented. The effect of organometallic complexes of cerium on the crystal growth has been studied. Organocerium complexes predominantly enter the prismatic or pyramidal growth sectors. It is shown that the complex arsenazo III + Ce blocks the growth of the prismatic sector. Cerium-doped KDP crystals exhibit a photoluminescence band peaking at the wavelength λmax= 350 nm.  相似文献   
98.
Our model for light-induced defect creation in hydrogenated amorphous silicon is applied to its kinetics, i.e., the growing curve of light-induced dangling bond density as a function of illumination time, which is fitted to a stretched exponential function. Two parameters β and τ involved in the function are estimated as functions of saturated dangling bond density in terms of our model. These are compared with two experimental results, i.e., our results obtained from ESR measurements and Shimakawa et al.’s results obtained from photoconductivity measurements. The saturated dangling bond density is also measured as a function of the generation rate of free carriers. The experimental results are compared with calculated results and discussed.  相似文献   
99.
100.
在拥有了多年大权在握、呼风唤雨的经历之后。相当一部分企业领导人很难从容地放弃权力。这时。董事会必须采取行动,不仅要帮助退休领导人选择和培养好接班人。更要积极参与管理层交接班的全过程。  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