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   57603篇
  免费   1183篇
  国内免费   144篇
化学   31999篇
晶体学   831篇
力学   1969篇
综合类   2篇
数学   7210篇
物理学   16919篇
  2022年   393篇
  2021年   541篇
  2020年   635篇
  2019年   634篇
  2018年   964篇
  2017年   847篇
  2016年   1512篇
  2015年   1036篇
  2014年   1362篇
  2013年   2992篇
  2012年   2862篇
  2011年   3195篇
  2010年   2144篇
  2009年   2074篇
  2008年   2713篇
  2007年   2737篇
  2006年   2476篇
  2005年   2208篇
  2004年   2055篇
  2003年   1682篇
  2002年   1543篇
  2001年   1804篇
  2000年   1386篇
  1999年   1113篇
  1998年   819篇
  1997年   789篇
  1996年   785篇
  1995年   663篇
  1994年   662篇
  1993年   576篇
  1992年   644篇
  1991年   641篇
  1990年   621篇
  1989年   564篇
  1988年   575篇
  1987年   556篇
  1986年   499篇
  1985年   623篇
  1984年   662篇
  1983年   467篇
  1982年   508篇
  1981年   505篇
  1980年   447篇
  1979年   489篇
  1978年   468篇
  1977年   493篇
  1976年   467篇
  1975年   421篇
  1974年   376篇
  1973年   407篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
83.
Crystalline materials that are transparent in the vacuum UV spectral region and currently used have been reviewed. Transmission of crystals of solid solutions with the fluorite structure Ca1?x R xF2+x (R = Sc, Y, La, Yb, Lu) in the UV and vacuum UV spectral regions has been investigated. It is shown that application of different methods of purification of fluorides from some impurities can significantly improve the optical quality of fluoride multicomponent crystals in the short-wavelength spectral region.  相似文献   
84.
Comprehensive studies of X-ray diffraction, oxygen content, superconductivity and Mössbauer effect have been made on FexCu1−xBa2YCu2O7+y superconductors (0.00≤x≤0.70) synthesized by ambient (AM) and high pressure (HP). Results indicate that all the HP-samples have tetragonal structure, smaller lattice parameter c and unit-cell volume than the AM-samples. The studies of oxygen content, and Mössbauer spectroscopy indicate that the HP-samples have higher oxygen content, carrier concentration and average valence of Fe than the AM-samples. Moreover, for the HP-samples more Fe atoms located in CuOx chains have fivefold-oxygen coordination. These are important reasons for the enhancement of Tc in the HP-samples.  相似文献   
85.
In order to study the influence of seeded impurities on ITER like reactor operation the COREDIV code has been extended to include the transport of several sputtered and/or injected impurities. In the COREDIV code the core plasma is treated in the frame of 1D radial transport model whereas in the edge the 2D multifluid code EPIT is used. The EPIT code solves in the slab geometry the MHD equations for densities and velocities for all ions species as well as for electron and ion temperatures. The iteration scheme in the code leads to steady state solution of coupled core and SOL system. The numerical results for Carbon and Nickel plate and seeded impurities Silicon and Neon are presented.  相似文献   
86.
The thermodynamic properties of the Ln2BaO4 phases (Ln = Dy, Ho, Sm) were studied by the electromotive force method with a fluoride electrolyte (890–1180 K), solution calorimetry in 1.07 N hydrochloric acid at 298.15 K, and differential scanning calorimetry (298–860 K). The experimental data were jointly processed, and the thermodynamic functions of the compounds over the temperature range 298–1200 K were calculated.  相似文献   
87.
Mo2Ni3Si/NiSi metal silicide composite coatings with a fine microstructure consisting of Mo2Ni3Si primary dendrites and the interdendritic Mo2Ni3Si/NiSi eutectics were fabricated on austenitic stainless steel AISI 321 by laser cladding process. Small amplitude reciprocating sliding wear resistance of the coatings is evaluated as functions of normal load and slip amplitude and the wear mechanisms were discussed based on worn surface morphology observations. Results showed that the Mo2Ni3Si/NiSi coatings have excellent small amplitude reciprocating sliding wear resistance.  相似文献   
88.
89.
Ohne Zusammenfassung Die mitgeteilten Untersuchungen haben wir mit Unterstützung der Ungarischen wissenschaftlichen „Széchenyi“-Gesellschaft durchgeführt.  相似文献   
90.
In this study, lead sulphide (PbS) was prepared by the chemical bath deposition technique. The sample was characterized by X-ray diffraction (XRD), Energy Dispersive Analysis of X-rays (EDAX) and cyclic voltammetry. EDAX spectrum shows peaks attributable to lead and sulphur. The EDAX analysis also shows that the prepared sample is stoichiometric. Cyclic voltammetry experiments were recorded at 100 mV·s−1 and 400 mV·s−1 scan rates. Results show that the rate controlling electrochemical reaction is electron transfer. The presence of redox waves shows that the lithium intercalation and deintercalation can occur as a result of lattice expansion in PbS. There were no differences in the PbS XRD data before and after the cyclic voltammetry experiments indicating that the PbS structure is not modified upon lithium ion intercalation and deintercalation in PbS. The discharge characteristics for 35 cycles of the cell using the LiCoO2/PbS couple is presented indicating the possible development of such materials as anode in lithium ion cells.  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