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   396020篇
  免费   3563篇
  国内免费   1193篇
化学   201221篇
晶体学   6579篇
力学   19523篇
综合类   11篇
数学   45222篇
物理学   128220篇
  2020年   3454篇
  2019年   4109篇
  2018年   5651篇
  2017年   5593篇
  2016年   7802篇
  2015年   4332篇
  2014年   7452篇
  2013年   17175篇
  2012年   13079篇
  2011年   15855篇
  2010年   11855篇
  2009年   11963篇
  2008年   14831篇
  2007年   14755篇
  2006年   13528篇
  2005年   12074篇
  2004年   11450篇
  2003年   10237篇
  2002年   10138篇
  2001年   11510篇
  2000年   8721篇
  1999年   6743篇
  1998年   5687篇
  1997年   5700篇
  1996年   5350篇
  1995年   4822篇
  1994年   4857篇
  1993年   4814篇
  1992年   5227篇
  1991年   5424篇
  1990年   5146篇
  1989年   5163篇
  1988年   5110篇
  1987年   4990篇
  1986年   4778篇
  1985年   6292篇
  1984年   6553篇
  1983年   5308篇
  1982年   5526篇
  1981年   5407篇
  1980年   5165篇
  1979年   5552篇
  1978年   5590篇
  1977年   5664篇
  1976年   5758篇
  1975年   5287篇
  1974年   5257篇
  1973年   5386篇
  1972年   3934篇
  1971年   3426篇
排序方式: 共有10000条查询结果,搜索用时 951 毫秒
961.
A short-term load-forecasting system has been developed to predictload demand for the Irish Electricity Supply Board from 1 to10 days in advance. Model output is acceptably accurate at mosttimes, but special days such as public holidays and the Easterweekend etc. require individual treatment. The basic model usedin everyday load forecasting is presented first, and specialdays when this model fails in accuracy are then examined andtreated separately using rule-based procedures. These proceduresare based on identified relationships between weather conditionsand prevailing daily load shapes. Comparisons are made betweenthe forecasts for these special days as given by the standardmodel and the ruled-based procedures.  相似文献   
962.
963.
The possibilities and the limitations of 2D NMR for the structural characterization of paramagnetic metalloproteins are reviewed. We survey the general strategies for 2D1H NMR investigations of hyperfine shifted signals. Careful adaptation of classical 2D NMR experiments to fast relaxing systems results in the detection of previously not observed scalar and dipolar connectivities, thus leading to the specific assignment of selected resonances. The approach is of general applicability for paramagnetic metalloproteins. We report here on the application of the application of the method to an iron sulfur protein and a heme protein. In both cases specific assignment of several hyperfine shifted signals, corresponding to active site protons, were obtained; this allowed significant insight into the structure-function relationships of these metalloproteins.  相似文献   
964.
An assembly of cation receptor 1 and anion receptor 2 via the hydrogen bonding melamine-barbiturate structural motif complexes sodium thiocyanate, sodium iodide, and sodium azide in apolar solvents.  相似文献   
965.
T. Shevchenko Kiev University, 252022 Kiev, Pr. Akad. Glushakova, 6, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 62, No. 3, pp. 192–196, May–June, 1995.  相似文献   
966.
967.
Methods are proposed for determining the diffusion coefficients of adsorbed molecules and the adsorption isotherms from given concentrations of the solutes in the external solution. The methods are based on a comparison of experimental data with the numerical results produced by a mathematical model of internal-diffusion kinetics of adsorption from a constant bounded volume.Translated from Vychislitel'naya i Prikladnaya Matematika, No. 66, pp. 41–46, 1988.  相似文献   
968.
969.
970.
The magnified cross-section of the LDV probe volume fringe field created on a far screen (image plane) with an imaging lens is examined both analytically and experimentally. It is shown that measurements of the image plane fringe field can be used to quantitatively determine the fringe field existing within the probe volume. Because the fringe spacing in the magnified image is more accessible experimentally, both longitudinal- and lateral-coordinate variations in fringe spacing can be determined, permitting a complete mapping of the fringe field. The detailed knowledge of the fringe field thus obtained allows beam quality, alignment, and fringe uniformity to be evaluated with greater precision than is possible with other techniques.The authors would like to acknowledge C. F. Edwards and R. L. Schmitt for the loan of the beam profiler and for many helpful discussions. This work was performed at the Combustion Research Facility, Sandia National Laboratories, and was supported by the U.S. Department of Energy, Office of Industrial Technologies, Advanced Industrial Concepts Division.  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