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   49039篇
  免费   1654篇
  国内免费   203篇
化学   31627篇
晶体学   370篇
力学   945篇
综合类   4篇
数学   8857篇
物理学   9093篇
  2023年   291篇
  2022年   411篇
  2021年   754篇
  2020年   784篇
  2019年   851篇
  2018年   960篇
  2017年   869篇
  2016年   1679篇
  2015年   1400篇
  2014年   1475篇
  2013年   3017篇
  2012年   3052篇
  2011年   3285篇
  2010年   2071篇
  2009年   1939篇
  2008年   2838篇
  2007年   2760篇
  2006年   2554篇
  2005年   2342篇
  2004年   1980篇
  2003年   1635篇
  2002年   1388篇
  2001年   1023篇
  2000年   899篇
  1999年   708篇
  1998年   537篇
  1997年   513篇
  1996年   632篇
  1995年   462篇
  1994年   511篇
  1993年   431篇
  1992年   434篇
  1991年   400篇
  1990年   380篇
  1989年   317篇
  1988年   300篇
  1987年   284篇
  1986年   277篇
  1985年   378篇
  1984年   397篇
  1983年   255篇
  1982年   292篇
  1981年   283篇
  1980年   281篇
  1979年   204篇
  1978年   196篇
  1977年   209篇
  1976年   181篇
  1975年   168篇
  1973年   164篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
The rational and sustainable exploitation of nature resources is one of the priority objectives of our society. In this article a method is proposed to evaluate and exploit the energetic resources contained in different forest formations. This method is based on the use of a combustion bomb calorimeter to determine the calorific values of the different samples studied. These results were complemented with chemical analysis of the samples and with environmental and geomorphological studies of the zones were samples were taken. The results obtained during the last 3 years for the residual biomass originated from the forest formations existing in Galicia ensure the reliability and usefulness of the method that can be extended to any forest formation all over the world.  相似文献   
72.
Sauer, Shelah, Vapnik and Chervonenkis proved that if a set system on n vertices contains many sets, then the set system has full trace on a large set. Although the restriction on the size of the groundset cannot be lifted, Frankl and Pach found a trace structure that is guaranteed to occur in uniform set systems even if we do not bound the size of the groundset. In this note we shall give three sequences of structures such that every set system consisting of sufficiently many sets contains at least one of these structures with many sets.  相似文献   
73.
The distribution of mono- poly- and unlabelled protein molecules in the radiolabelling mixture was calculated from probability point of view as a function of the radioiodine/protein ratio.  相似文献   
74.
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   
75.
We predict ultraslow collapse of “tubular image states” (TIS) on material surfaces. TIS are bound Rydberg-like electronic states formed at large distances (∼30 nm) from the surfaces of suspended circularly-symmetric nanowires, such as metallic C nanotubes. The states are formed in potential wells, resulting from a combination of the TIS-electron attraction to image charges in the nanotube and its centrifugal repulsion, caused by spinning around the tube. We demonstrate that TIS can collapse on the tube surface by passing their angular momentum l to circularly polarized flexural phonons excited in the tube. Our analysis shows that for highly detached TIS with l ? 6 the relaxation lifetimes are of the order of 10 ns-1 μs, while for l < 6 these lifetimes are reduced by several orders of magnitude.  相似文献   
76.
77.
Summary Studies performed by the Brazilian Nuclear Corporation (NUCLEBRAS), in collaboration with the Geological Survey Company of Brazil (CPRM), identified high levels of natural uranium in the districts of Pedra and Venturosa, in the rural region of the state of Pernambuco (PE) - Brazil, where the maximum value found in rocks was 22,000 mg.  相似文献   
78.
Ohne Zusammenfassung Die mitgeteilten Untersuchungen haben wir mit Unterstützung der Ungarischen wissenschaftlichen „Széchenyi“-Gesellschaft durchgeführt.  相似文献   
79.
80.
    
Ohne Zusammenfassung  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