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   155133篇
  免费   845篇
  国内免费   488篇
化学   65126篇
晶体学   2054篇
力学   10004篇
综合类   1篇
数学   39568篇
物理学   39713篇
  2022年   632篇
  2021年   878篇
  2020年   973篇
  2019年   1107篇
  2018年   11933篇
  2017年   11856篇
  2016年   8145篇
  2015年   1854篇
  2014年   2011篇
  2013年   3574篇
  2012年   6627篇
  2011年   13693篇
  2010年   8220篇
  2009年   8605篇
  2008年   9523篇
  2007年   11541篇
  2006年   2981篇
  2005年   3727篇
  2004年   3752篇
  2003年   4035篇
  2002年   3134篇
  2001年   2480篇
  2000年   1921篇
  1999年   1413篇
  1998年   1320篇
  1997年   1187篇
  1996年   1094篇
  1995年   954篇
  1994年   894篇
  1993年   921篇
  1992年   923篇
  1991年   1007篇
  1990年   932篇
  1989年   970篇
  1988年   883篇
  1987年   831篇
  1986年   798篇
  1985年   915篇
  1984年   1012篇
  1983年   858篇
  1982年   883篇
  1981年   790篇
  1980年   758篇
  1979年   814篇
  1978年   931篇
  1977年   932篇
  1976年   827篇
  1975年   791篇
  1974年   806篇
  1973年   791篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
The results of studying the formation of the three-dimensional micromechanical structure of an integral tensoconverter are presented. The technological restrictions on contact photolithography over the relief structure formed on the device layer of the silicon-on-insulator wafer are analyzed. The effect of the design parameters (the frame height and the width of the frame slit) are described.  相似文献   
992.
993.

The 3-acyl tetramic acids constitute a growing class of natural products displaying a range of biological activities. The g , g ' tricarbonyl moiety present in the 3-acyl tetramic acid provides a suitable site for bidentate complexation to a metal, which increases the biological activity. For the dielectric study of N-acetyl-3-butanoyl tetramic acid and a series of its complexes with Cu(II) and Co(II) in symmetric and asymmetric forms, we used the Thermally Stimulated Depolarization Currents (TSDC) technique. The drastic decrease of the intensity of the TSDC peaks of the symmetric and asymmetric complexes, compared to the above mentioned ligand, suggested that the polarizability of the side groups is considerably reduced. This result enhances the proposed complexation mode of the ligand through oxygen next to carbons 3 and 4 of the 5-member ring.  相似文献   
994.
The morphological evolution of pyramids, developed on bombarded copper surfaces, as a function of consecutive doses of 12 keV Kr—ions from 2.4 × 1016 up to 3 × 1016 ions/cm2, has been studied. In disagreement with many previous studies, apparently based on a limited choice of doses which were sometimes not in sequence, we found that the pyramids disappeared at high enough doses. Pyramids are therefore not an equilibrium structure.  相似文献   
995.
This work reports on the photoluminescent properties of three new lanthanide complexes with acetoacetanilide (aaa), a β-diketonate ligand. The complexes have the general molecular formulae [RE(aaa)3(H2O)], they are soluble in organic solvents such as ethanol and chloroform and insoluble in water. The energy of the triplet state was determined at about 4,700 cm?1 higher than the 5D4 emitting level of the Tb(III) ion, leading to an absolute quantum yield of 22 % for the [Tb(aaa)3(H2O)] complex. The photoluminescent properties were studied and the luminescence parameters of the [Eu(aaa)3(H2O)] complex were experimentally determined. The photostabilities of the complexes under continuous UV irradiation were measured and the data indicate low stability of the [Tb(aaa)3(H2O)] complex when the system is excited at the band attributed to energy transfer from the ligand to terbium(III) ion. However, its photostability is significantly improved under inert atmosphere.  相似文献   
996.
MnSb layers are deposited on GaAs(100) via the laser ablation of Mn and Sb targets. The magnetic field dependences of the transverse Kerr effect display magnetic anisotropy and magnetization jumps. Measurements of the Hall effect reveal a hysteresis loop at temperatures of up to 300 K.  相似文献   
997.
The elemental composition of four species of the genus Pentaphylloides Hill is determined by means of synchrotron radiation X-ray fluorescence analysis (SRXRF). Each of the studied species is characterized by specific concentrations of elements that are typical of it and can be used in a comparative analysis of other species and be included in a corresponding database. In the case of P. fruticosa and P. x mandshurica, a high content of microelements is observed in all organs that distinguishes them from other species.  相似文献   
998.
On the basis of low-energy QCD theorems, the bulk viscosity ζ(T, µ, H) is expressed in terms of basic thermodynamic quantities that characterizes quark-gluon matter at finite temperature and a finite baryon density in a magnetic field. Various limiting cases are considered.  相似文献   
999.
A holistic study of the lepton sector is fulfilled in the framework of rigorous restrictions by five input suppositions. All leptons are divided into three classes on the structure of their equations. They are singlets, doublets and quartets. The quartet states are the most interesting among them from the point of view of their properties and possible physical interpretations.  相似文献   
1000.
Results of studying the specific features of formation of the crystal structure and distribution of iron cations over the sites in the DyFeTi2O7 compound have been presented and the comparison with the GdGaTi2O7 isostructural compound has been performed. The atomic disorder in the distribution of the Fe3+ ions over structural sites in the DyFeTi2O7 compound is confirmed by the Mössbauer spectroscopy and X-ray diffractometry. The results of magnetic measurements in the low-temperature region have revealed an inflection point in the temperature dependence of the magnetic moment and its dependence on the magnetic prehistory of the sample. The obtained experimental data suggest that there is a spin glass state with freezing point T f = 6 K in the DyFeTi2O7 compound.  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