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   585888篇
  免费   2880篇
  国内免费   1404篇
化学   284030篇
晶体学   11004篇
力学   28472篇
综合类   14篇
数学   86293篇
物理学   180359篇
  2021年   4751篇
  2020年   5448篇
  2019年   5948篇
  2018年   16762篇
  2017年   16635篇
  2016年   16097篇
  2015年   7365篇
  2014年   10246篇
  2013年   22909篇
  2012年   21219篇
  2011年   31306篇
  2010年   20751篇
  2009年   21016篇
  2008年   25981篇
  2007年   27572篇
  2006年   18529篇
  2005年   17509篇
  2004年   16736篇
  2003年   15493篇
  2002年   14786篇
  2001年   15695篇
  2000年   11948篇
  1999年   9494篇
  1998年   7903篇
  1997年   7570篇
  1996年   7217篇
  1995年   6551篇
  1994年   6428篇
  1993年   6205篇
  1992年   6865篇
  1991年   7007篇
  1990年   6718篇
  1989年   6652篇
  1988年   6566篇
  1987年   6342篇
  1986年   6079篇
  1985年   7669篇
  1984年   7860篇
  1983年   6345篇
  1982年   6457篇
  1981年   6381篇
  1980年   5974篇
  1979年   6372篇
  1978年   6598篇
  1977年   6539篇
  1976年   6359篇
  1975年   5930篇
  1974年   5890篇
  1973年   5867篇
  1972年   4240篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
Water vapor diffusion coefficient (WVDC) and thermal diffusivity (alpha) were determined in gelatin-starch films through photothermal techniques. The effect of different variables in the elaboration of these films, such as starch and glycerol concentrations and pH, were evaluated through the response surface methodology. The results indicated that an increase in the glycerol concentration and pH favored the WVDC of the films. On the other hand, alpha was influenced principally by the starch content and pH of the film-forming solution. The minimum alpha value was 4.5 x 10(-4) cm2/s, which is compared with alpha values reported for commercial synthetic polymers.  相似文献   
122.
123.
124.
This paper investigates algorithms of motion planning for a six-legged walking machine over complex terrain. Application of the Rodrigues-Hamilton parameters for describing the orientation of the body enables one to develop algorithms of motion planning for the body and legs in an absolute coordinate frame with automatic adaptation to the surface. Experiments with a laboratory scale walking machine have demonstrated the efficiency of proposed algorithms. __________ Translated from Fundamentalnaya i Prikladnaya Matematika, Vol. 11, No. 7, pp. 197–206, 2005.  相似文献   
125.
The adsorption of nonionic surfactant Triton X-100 on quartz sand and methylated quartz sand from water and toluene was investigated by means of spectrophotometry, the radiotracer technique, and wetting angle measurements.  相似文献   
126.
127.
128.
Phytochemical investigation of the aerial parts of three Baccharis species (Asteraceae family) was performed using HPLC and chemometric methods, with the objective of distinguishing between three morphologically very similar species: Baccharis genistelloides Persoon var. trimera (Less.) DC, B. milleflora (Less.) DC and B. articulata (Lam.) Persoon. With the help of Principal Component Analysis (PCA) and variance weights, it was possible to characterize the chromatographic profiles of the alcoholic extracts of the three species. Application of Soft Independent Modeling of Class Analogy (SIMCA) and K-Nearest Neighbor (KNN) methods on a training set of 74 extracts resulted in models that correctly classified all eight samples in an independent test set.  相似文献   
129.
130.
For the NO molecule, modelled as a Morse oscillator, time-dependent (TD) nuclear Schr?dinger equation has been numerically solved for the multiphoton vibrational dynamics of the molecule under a far-infrared laser of wavelength 10503 nm, and four different intensities,I = 1 × 108, 1 × 1013, 5 × 1016, and 5 × 1018 W cm−2 respectively. Starting from the vibrational ground state at zero time, various TD quantities such as the norm, dissociation probability, potential energy curve and dipole moment are examined. Rich high-harmonics generation (HHG) spectra and above-threshold dissociation (ATD) spectra, due to the multiphoton interaction of vibrational motions with the laser field, and consequent elevation to the vibrational continuum, have been obtained and analysed. Dedicated to Professor C N R Rao on his 70th birthday An erratum to this article is available at .  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