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   1936篇
  免费   33篇
  国内免费   23篇
化学   1494篇
晶体学   14篇
力学   15篇
数学   86篇
物理学   299篇
无线电   84篇
  2022年   12篇
  2021年   28篇
  2020年   23篇
  2019年   18篇
  2018年   17篇
  2017年   12篇
  2016年   22篇
  2015年   17篇
  2014年   38篇
  2013年   70篇
  2012年   96篇
  2011年   100篇
  2010年   66篇
  2009年   75篇
  2008年   109篇
  2007年   113篇
  2006年   116篇
  2005年   127篇
  2004年   117篇
  2003年   105篇
  2002年   92篇
  2001年   32篇
  2000年   21篇
  1999年   35篇
  1998年   37篇
  1997年   23篇
  1996年   35篇
  1995年   22篇
  1994年   13篇
  1993年   12篇
  1992年   17篇
  1991年   16篇
  1990年   6篇
  1989年   17篇
  1988年   19篇
  1987年   14篇
  1986年   7篇
  1985年   20篇
  1984年   26篇
  1983年   10篇
  1982年   26篇
  1981年   27篇
  1980年   18篇
  1979年   25篇
  1978年   23篇
  1977年   26篇
  1976年   16篇
  1975年   17篇
  1974年   14篇
  1973年   15篇
排序方式: 共有1992条查询结果,搜索用时 0 毫秒
111.
Microgel polymers containing a series of functional groups have been prepared. These microgels were composed of cross-linked poly(styrene) and were prepared by radical polymerization in solution. The microgel polymers exhibit good solubility in an array of different organic solvents, and in addition, they can be efficiently precipitated by the addition of methanol and isolated by filtration. A nine-member phthalide library was synthesized using an aminomethyl-functionalized microgel 5. To further demonstrate the versatility of these microgel polymers, tris(2-aminoethyl)amino microgel 11 was examined as a scavenger reagent to remove unreacted isocyanate after a urea synthesis. Finally, a microgel-supported ammonium borohydride reagent 14 was successfully prepared and used as a reducing agent. Notable features of these microgels are that in all applications the progress of the reaction could be monitored by standard NMR techniques and their preparation is performed using common glassware and techniques found in all organic laboratories.  相似文献   
112.
[reaction: see text] Radical cascade reaction with various 1,4-dienes and 1,4-enynes using dimethyl 2-(iodomethyl)cyclopropane-1,1-dicarboxylate as a homoallyl radical precursor smoothly proceeds through an iodine atom transfer mechanism to give functionalized bicyclo[3.3.0]octane derivatives in good yields.  相似文献   
113.
[reaction: see text] The stereoselectivity of nucleophilic addition of 2-trimethylsilyloxyfuran to N-gulosyl-C-alkoxymethylnitrones was investigated. It was found that the selectivity was highly dependent on the bulkiness of the C-substituent of the nitrone. The major adducts were elaborated into the key intermediate of polyoxin C.  相似文献   
114.
In inertial confinement fusion research, uniform laser irradiation on a fusion target is a key issue. We propose a new method of beam smoothing in which we use three-directional spectral dispersion to reduce the coherent speckle that is unavoidable in the usual two-directional spectral-dispersion scheme. We have used this smoothing technique in a Nd:glass laser system and have demonstrated that the coherent speckle is reduced by a factor of 2.9 from that in two-directional spectral dispersion.  相似文献   
115.
The objective of this study was to assess the effect of comprehensive exercise program widely accepted as a community-based physical intervention for the prevention of falling in the elderly persons on their controlling standing balance. Twenty-six community-dwelling elderly persons (13 males and females; 69.8 ± 2.8 years old) participated in this study. Daily exercise was comprised of walking for more than 30 min, stretching, muscle strengthening and balance exercise without exercise equipments. The intervention was continued for three months. Indicators of standing balance related to static balance, dynamic balance and postural response were measured before and after the intervention. As an effect of the intervention on static balance, the sway of center of pressure (COP) in the static stance significantly increased. In the dynamic balance, significant improvements were observed in one leg standing time, the 10-m gait time, functional reach. Additionally, the maximal movable length of COP which subjects can move voluntarily to right and left significantly increased. In the postural response, the integrated electromyography (IEMG) induced by postural response for sudden postural perturbation significantly decreased in the lower leg muscles. Since less muscular activities were sufficient to maintain posture, it was suggested that postural response was elicited more efficiently following the intervention. This study suggested that the comprehensive exercise program, which has been widely introduced as community-based interventions for the prevention of falling, have extensive effects on the control of standing balance covering static balance, dynamic balance and postural response in the elderly persons.  相似文献   
116.
Catalytic asymmetric allylation of aldehydes with allylic trimethoxysilanes was achieved with the p-Tol-BINAP small middle dotAgF complex as catalyst [Eq. (a); p-Tol-BINAP=2,2'-bis(di-p-tolylphosphanyl)-1,1'-binaphthyl)]. High anti and enantioselectivities were obtained in the reaction with crotyltrimethoxysilane, irrespective of the configuration at the double bond.  相似文献   
117.
118.
119.
120.
An X-ray topographic method utilizing non-parallel (+,-) setting for measuring lattice mismatches between epitaxial films and substrates is reported. This method gives quantitative as well as topographical information on lattice distortions in a distorted crystal and allows us to study any reflection from various crystals, in which the fractional variation of lattice spacing, δd/d, is of the order of 10-4?10-5. Examples of applications are lattice mismatches between epitaxial magnetic garnet films and (111) gadolinium garnet (GGG) substrates. The spacing of the epitaxial film was slightly larger along the [111] direction than that of the substrate and the apparent crystal symmetry of the epitaxial film is rhombohedral.  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