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   111557篇
  免费   7680篇
  国内免费   6888篇
化学   65533篇
晶体学   1508篇
力学   6355篇
综合类   555篇
数学   13764篇
物理学   38410篇
  2023年   858篇
  2022年   1565篇
  2021年   2288篇
  2020年   2689篇
  2019年   2940篇
  2018年   3267篇
  2017年   3217篇
  2016年   4056篇
  2015年   2986篇
  2014年   4263篇
  2013年   5890篇
  2012年   6121篇
  2011年   6617篇
  2010年   5241篇
  2009年   5295篇
  2008年   5598篇
  2007年   5205篇
  2006年   4790篇
  2005年   4234篇
  2004年   3724篇
  2003年   3254篇
  2002年   3506篇
  2001年   3031篇
  2000年   2392篇
  1999年   1874篇
  1998年   1716篇
  1997年   1467篇
  1996年   1416篇
  1995年   1163篇
  1994年   1233篇
  1993年   1152篇
  1992年   1116篇
  1991年   1170篇
  1990年   1155篇
  1989年   1078篇
  1988年   953篇
  1987年   933篇
  1986年   896篇
  1985年   939篇
  1984年   922篇
  1983年   829篇
  1982年   804篇
  1979年   802篇
  1978年   823篇
  1977年   808篇
  1976年   921篇
  1975年   812篇
  1974年   841篇
  1973年   844篇
  1972年   752篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
A novel algorithm, alternatively minimizing coupled vector (COV) resolution error and PARAFAC error algorithm, is proposed in this paper. This algorithm can overcome the problem of slow convergence and is insensitive to the estimation of component number, such problems are unavoidable while using the traditional parallel factors analysis (PARAFAC) algorithm. In other words, this algorithm is capable of improving the computing speed and providing accurate resolutions provided that the number of factors used in the computation is no less than that of the actual underlying ones. The characteristic performances were demonstrated with a novel fluorescence data array.  相似文献   
972.
卟啉及其配合物在分析化学中应用进展   总被引:7,自引:0,他引:7  
综述了卟啉及配合物在分析化学中的应用研究进展。重点介绍了其在光度分析、电化学、分子识别、探针等方面的应用。  相似文献   
973.
The action of illumination on the conducting and dielectric properties of lead magnoniobate was investigated. The photostimulated currents were examined and the spectral dependence of photoconductivity in the region of diffuse phase transition was obtained. It was found that the illumination affects the dielectric properties and that its action is memorized at temperatures below room temperature. The role of defect states in the formation of relaxor properties is discussed on the basis of the obtained data.  相似文献   
974.
975.
We develop a general method for the construction of a probability structure on the space F of random sets in ℝ. For this purpose, by using the introduced notion of c-system, we prove a theorem on the unique extension of a finite measure from a c-system to the minimal c-algebra. The obtained structure of measurability enables one to determine probability distributions of the c-algebra of random events sufficient, e.g., for the so-called fractal dimensionality of random realizations to be considered as a measurable functional on F.__________Translated from Ukrains’kyi Matematychnyi Zhurnal, Vol. 56, No. 11, pp. 1467–1483, November, 2004.  相似文献   
976.
Combining color imaging with phase shifting, a technique named five-step color phase shifting is presented to determine the whole-field isoclinic parameter. Relevant theory is derived and explicit conditions for directly determining the isoclinic parameter in the range of [0,π/2] are given. The unloaded light intensity of the model is systematically studied. A color camera recorded five isoclinic images coupled with isochromatics from a plane polariscope with five different settings, respectively. Experiments have been carried out with a circular disk under diametral compression and errors have been analyzed and estimated. This technique utilizes white light, which avoids undefined isoclinics near the locations where the isochromatics exist and will have active effect on experimental stress analysis and structural strength design.  相似文献   
977.
We have used potentiometric titration with tetrabutylammonium hydroxide to determine the acid center content on the outer surface of dealuminated natural and synthetic mordenites. We have established a symbatic relationship between the 2,2-dimethylbutane content in the hydroisomerization products of n-hexane on dealuminated palladium-containing mordenites and the number of their external acid centers. We have studied the possibility of partial deactivation of such centers during ion-exchange deposition of palladium on the catalysts, using a tetraammine palladium solution.  相似文献   
978.
Two-color photoionization of nickelocene molecules cooled in a supersonic jet is performed using a tunable nanosecond pulsed laser. The first stage of the multiphoton excitation is the transition from the highest occupied molecular orbital of nickelocene to the lowest Rydberg level. Conditions are found under which molecular ions (η 5-C5H5)2Ni+ are the only product of the multiphoton ionization in the one-color experiment. Irradiation of an excited molecule by an intense pulse of another laser increases significantly the yield of molecular ions. The dependence of the yield of (η5-C5H5)2Ni+ ions on the frequency of the second laser makes it possible to determine the adiabatic ionization potential of nickelocene as 6.138±0.012eV.  相似文献   
979.
Statics of elasto-plastic media is stated in terms of eigenstrains acting upon a background elastic problem with fixed (initial) stiffness. In order to minimize the number of unknowns and to provide computationally cheap algorithms plastic multipliers are used as main driving variables. Fixed-point type iterations are suggested for computing plastic multipliers within the load increment. Numerical experiments results are shown to be in good correlation with other software results. A range of problems is outlined where the usage of the proposed algorithms can be advantageous.  相似文献   
980.
本文进一步研究了Bessel框架的性质,给出其稳定性和摄动的几个有意义的结果。  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