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   381717篇
  免费   2603篇
  国内免费   1179篇
化学   163114篇
晶体学   5605篇
力学   22210篇
综合类   1篇
数学   74907篇
物理学   119662篇
  2020年   1806篇
  2019年   2066篇
  2018年   18852篇
  2017年   19321篇
  2016年   12284篇
  2015年   3857篇
  2014年   4361篇
  2013年   10487篇
  2012年   14265篇
  2011年   28540篇
  2010年   17522篇
  2009年   17904篇
  2008年   23272篇
  2007年   28100篇
  2006年   8635篇
  2005年   14724篇
  2004年   11226篇
  2003年   10886篇
  2002年   8211篇
  2001年   7437篇
  2000年   5901篇
  1999年   4404篇
  1998年   3776篇
  1997年   3618篇
  1996年   3591篇
  1995年   3199篇
  1994年   3097篇
  1993年   3196篇
  1992年   3264篇
  1991年   3453篇
  1990年   3190篇
  1989年   3145篇
  1988年   3203篇
  1987年   3083篇
  1986年   2918篇
  1985年   3933篇
  1984年   4138篇
  1983年   3319篇
  1982年   3530篇
  1981年   3450篇
  1980年   3354篇
  1979年   3468篇
  1978年   3553篇
  1977年   3371篇
  1976年   3499篇
  1975年   3168篇
  1974年   3174篇
  1973年   3267篇
  1972年   2267篇
  1971年   1865篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
Russian standards in training conventional graduates and bachelors are considered. These standards determine the status and volume of analytical chemistry courses at different higher educational institutions. An analysis of the educational standards, standard curricula, and the aims of teaching analytical chemistry suggests the advisability of changing the content of the course, particularly at industrial (branch) higher educational institutions. The provision of the analytical chemistry course with special literature (manuals, textbooks), equipment, and computer software is considered.  相似文献   
982.
Ultracold molecules have been produced by photoassociation of Cs atoms trapped in a mirror magneto-optical trap. The molecules were detected by resonantly enhanced multi-photon ionization followed by time-of-flight mass spectroscopy. The time-of-flight ofatomic and molecular ions was investigated in the presence of a dc bias voltageapplied to the conducting mirror. This technique provides a new tool for determining the distance between the cold molecules and the mirror surface. This revised version was published online in August 2005 with a corrected cover date.  相似文献   
983.
The results of the elemental analysis of blood serum are often used for the diagnosis of different diseases associated with derangements of mineral metabolism. In this work, we studied the main sources of a systematic error in the atomic-emission spectrometric (AES) analysis of blood serum and developed a procedure for the AES determination of Ca, Cu, Fe, Mg, P, and Zn in the human blood serum. The repeatability relative standard deviations of determinations varied from 10 to 24%.  相似文献   
984.
Electron transport in a three-dimensional quantum wire is analyzed by taking into account electron scattering by a single point impurity. It is shown that the magnetoconductance plotted versus chemical potential μ has narrow peaks and closely located peaks separated by a dip when the scattering length is positive and negative, respectively. The peaks lie near the conductance steps. The thermopower plotted versus μ has narrow peaks and closely located peaks separated by a dip when the scattering length is positive and negative, respectively.  相似文献   
985.
986.
In view of the growing interest for non-destructive tests of materials, geodynamical monitoring and in general remote sensing, there is a great effort to bring practical optical sensors from research labs to industrial and environmental applications. In this paper, we employ digital holographic technique as an efficient tool for evaluating the strain measurement capability of fiber Bragg gratings (FBG). A cantilever beam has been employed as a test structure under loading test. The strain measurements results obtained by fiber-based sensors have been compared to those obtained by using full-field digital holographic technique and point-wise strain gauge sensors glued on the same cantilever beam. A simple theoretical model is also presented to interpret and compare the experimental results coming from different techniques.  相似文献   
987.
The modified Gross–Pitaevskii equation was derived and solved to obtain the 1D solution in the zero-energy limit. This stationary solution could account for the dominated contributions due to the kinetic effect as well as the chemical potential in inhomogeneous Bose gases.  相似文献   
988.
A new approach to identify the independent amplitudes along with their partial wave multipole expansions, for photo-and electro-production is suggested, which is generally applicable to mesons with arbitrary spin-parity. These amplitudes facilitate direct identification of different resonance contributions.   相似文献   
989.
We present the results of a spectroscopic study of a nonequilibrium plasma in a Hall accelerator, in particular for such an important parameter as the electron temperature. For the studied conditions, we used the semicoronal equilibrium model, which relates the intensity ratios for two successive ionization steps for the same element. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 1, pp. 93–96, January–February, 2007.  相似文献   
990.
X-ray diffraction (XRD), Mössbauer spectrometry (MS), secondary ions mass spectroscopy (SIMS) and laser-ablation microprobe–inductively coupled plasma–mass spectrometry (LAM–ICP–MS) were used to study mineral samples of Colombian auriferous ores collected from the “El Diamante” mine, located in the municipality of Guachavez-Nariño, in Colombia. The samples were prepared as polished thin sections and polished sections. From XRD data, quartz, sphalerite and pyrite were detected and their respective cell parameters were estimated. From MS analyses, pyrite, arsenopyrite and chalcopyrite were identified; their respective hyperfine parameters and respective texture were deduced. Multiple regions of approximately 200 × 200 μm in each sample were analyzed with SIMS; the occurrence of “invisible gold” associated mainly with pyrite and secondarily with arsenopyrite could thus be assigned. It was also found that pyrite is of the arsenious type. Spots from 30 to 40 μm in diameter were analyzed with LAM–ICP–MS for pyrite, arsenopyrite and sphalerite; Au is “homogeneously” distributed inside the structure of the arsenious pyrite and the arsenopyrite (not as inclusions); the chemical composition indicates similarities of this “invisible gold”, forming a solid solution with arsenious pyrite and arsenopyrite. One hundred nineteen and 62 ppm of ‘invisible gold’ was quantified in 21 spots analyzed on pyrite and in 14 spots on arsenopyrite, respectively.  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