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   178988篇
  免费   875篇
  国内免费   261篇
化学   89366篇
晶体学   2363篇
力学   9376篇
综合类   7篇
数学   20911篇
物理学   58101篇
  2020年   1848篇
  2019年   2288篇
  2018年   3394篇
  2017年   3523篇
  2016年   4157篇
  2015年   1852篇
  2014年   3586篇
  2013年   7047篇
  2012年   5532篇
  2011年   6586篇
  2010年   5510篇
  2009年   5635篇
  2008年   6360篇
  2007年   6323篇
  2006年   5617篇
  2005年   4980篇
  2004年   4821篇
  2003年   4366篇
  2002年   4521篇
  2001年   4999篇
  2000年   3697篇
  1999年   2823篇
  1998年   2603篇
  1997年   2457篇
  1996年   2253篇
  1995年   2048篇
  1994年   2005篇
  1993年   2038篇
  1992年   2073篇
  1991年   2380篇
  1990年   2314篇
  1989年   2384篇
  1988年   2264篇
  1987年   2294篇
  1986年   2095篇
  1985年   2628篇
  1984年   2629篇
  1983年   2287篇
  1982年   2349篇
  1981年   2253篇
  1980年   2053篇
  1979年   2363篇
  1978年   2528篇
  1977年   2625篇
  1976年   2707篇
  1975年   2518篇
  1974年   2452篇
  1973年   2626篇
  1972年   2136篇
  1971年   1964篇
排序方式: 共有10000条查询结果,搜索用时 165 毫秒
121.
Radiophysics and Quantum Electronics - We consider whether it is possible in principle to retrieve the key parameters of the mixed layer in the upper ocean (its thickness, bulk eddy viscosity and...  相似文献   
122.
Siberian Mathematical Journal - Under study are the right-symmetric algebras over a field  $ F $ which possess a “unital” matrix subalgebra  $...  相似文献   
123.
Methods for phase stabilization of ammonium nitrate were sought for in order to considerably expand the application area of this oxidizing agent in various-purpose self-combustible formulations, including that in a new generation of gas-generating formulations for automobile air bags. New methods for stabilization of ammonium nitrate were studied and, in particular, a search was made for organic compounds that can stabilize ammonium nitrate even at their low content. The mechanism of phase state stabilization of ammonium nitrate by compounds of this kind was examined.  相似文献   
124.
In this work the results of the statistical topometric analysis of fracture surfaces of soda-lime-silica glass with and without ionic exchange treatment are reported. In this case, the mechanism of substitution is K+-Na+. atomic force microscopy (AFM) was employed to record the topometric data from the fracture surface. The roughness exponent (ζ) and the correlation length (ξ) were calculated by the variable bandwidth method. The analysis for both glasses (subjected and non-subjected to ionic exchange) for ζ shows a value ∼0.8, this value agrees well with that reported in the literature for rapid crack propagation in a variety of materials. The correlation length shows different values for each condition. These results, along with those of microhardness indentations suggest that the self-affine correlation length is influenced by the complex interactions of the stress field of microcracks with that resulting from the collective behavior of the point defects introduced by the strengthening mechanism of ionic exchange.  相似文献   
125.
Experimental data on the effect of thallium and sodium impurities on the lattice heat conductivity of PbTe at room temperature are reported. Because the lattice of lead chalcogenides is strongly polarized near charged impurities, the effect of impurities on the lattice heat conductivity depends substantially on their charge state. This property of the material has been used to determine the charge state of the thallium impurity in PbTe. The results obtained argue for a model of quasi-local thallium-impurity states which assumes low electron-correlation energy at an impurity center. Fiz. Tverd. Tela (St. Petersburg) 40, 1206–1208 (July 1998)  相似文献   
126.
We use the eikonal approximation to develop a general formula for the cross sections of inelastic collisions of multicharged fast ions (including relativistic ions) with atoms that is applicable within a broad range of collision energies, has the standard nonrelativistic limit, and becomes, in the ultrarelativistic case, the well-known result that follows from the exact solution of the Dirac equation. As an example we study the excitation and ionization of a hydrogenlike atom, the single and double excitation and ionization of a heliumlike atom, and multiple (up to the eighth order) ionization of the neon atom and (up to eighteenth order) ionization of the argon atom. We derive simple analytical expressions for the inelastic cross sections and establish recurrence relations linking the cross sections of ionization of different orders. Finally, we compare our results with the experimental data. Zh. éksp. Teor. Fiz. 114, 1646–1660 (November 1998)  相似文献   
127.
128.
The dependence of distribution functions of quarks, antiquarks, diquarks and their fragmentation into hadrons on the transverse momentumk t is discussed in the frame of the quark-gluon string model. We then discuss the division ofk t between 2n-quark-antiquark chains, orn-pomeron showers. Hadron and hadron-nuclear processesp?p,p?A,K +?p,K +?A are analysed. A strong dependence of the observed values on the numbern is derived by this method, which is of special importance for the analysis of hadron-nucleus collisions. Our method is compared with the regulark t division method.  相似文献   
129.
A theory is developed for the density profile of low temperature plasmas confined by applied magnetic field and an experiment of the electron-cyclotron-resonance (ECR) plasma is conducted to compare the theoretical prediction and experimental measurements. Due to a large electron mobility along the magnetic field, electrons move quickly out of the system, leaving ions behind and building a space charge potential, which leads to the ambipolar diffusion of ions. In a steady-state condition, the plasma generation by ionization of neutral molecules is in balance with plasma loss due to the diffusion, leading to the electron temperature equation, which is expressed in terms of the plasma size, chamber pressure, and the ionization energy and cross section of neutrals. The power balance condition leads to the plasma density equation, which is also expressed in terms of the electron temperature, the input microwave power and the chamber pressure. It is shown that the plasma density increases, reaches its peak and decreases, as the chamber pressure increases from a small value (0.1 mTorr). These simple expressions of electron temperature and density provide a scaling law of ECR plasma in terms of system parameters. After carrying out an experimental observation, it is concluded that the theoretical predictions of the electron temperature and plasma density agree remarkably well with experimental data  相似文献   
130.
Experimental results are presented on acoustic probing of electric fields in solid insulators. An experimental apparatus and methods are described for acoustic measurements of the bulk space charge density and electric field strength in solid insulators. The sensitivity and spatial resolution of the acoustic probe technique are determined.Institute of Introscopy Research, Polytechnical University, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 62–67, September, 1993.  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