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   833904篇
  免费   8305篇
  国内免费   3241篇
化学   425839篇
晶体学   12055篇
力学   41327篇
综合类   81篇
数学   113709篇
物理学   252439篇
  2021年   7211篇
  2020年   7849篇
  2019年   8713篇
  2018年   11540篇
  2017年   11785篇
  2016年   16673篇
  2015年   9811篇
  2014年   15789篇
  2013年   37713篇
  2012年   29314篇
  2011年   35196篇
  2010年   25858篇
  2009年   25651篇
  2008年   32823篇
  2007年   32565篇
  2006年   30063篇
  2005年   26851篇
  2004年   24699篇
  2003年   22016篇
  2002年   21888篇
  2001年   23865篇
  2000年   18309篇
  1999年   14285篇
  1998年   12146篇
  1997年   11894篇
  1996年   11297篇
  1995年   10079篇
  1994年   10061篇
  1993年   9698篇
  1992年   10463篇
  1991年   10891篇
  1990年   10345篇
  1989年   10204篇
  1988年   9800篇
  1987年   9650篇
  1986年   9309篇
  1985年   12087篇
  1984年   12503篇
  1983年   10484篇
  1982年   10864篇
  1981年   10227篇
  1980年   9851篇
  1979年   10487篇
  1978年   10837篇
  1977年   10682篇
  1976年   10652篇
  1975年   10142篇
  1974年   10041篇
  1973年   10392篇
  1972年   7537篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
12.
We find logarithmic small ball asymptotics for the L2-norm with respect to self-similar measures for a certain class of Gaussian processes including Brownian motion, Ornstein-Uhlenbeck process, and their integrated counterparts. Bibliography: 46 titles. __________ Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 311, 2004, pp. 190–213.  相似文献   
13.
A new solvent-free sample preparation method using silver trifluoroacetate (AgTFA) was developed for the analysis of low molecular weight paraffins and microcrystalline waxes by laser desorption/ionization time-of-flight mass spectrometry (LDI-TOFMS). Experiments show that spectral quality can be enhanced by dispersing AgTFA directly in liquid paraffins without the use of additional solvents. This preparation mixture is applied directly to the MALDI probe. Solid waxes could be examined by melting prior to analysis. The method also provides sufficiently reproducible spectra that peak area ratios between mono- and bicyclic alkane peaks indicated variations in the cycloalkane content of paraffin samples. Dehydrogenation of hydrocarbons observed during the desorption/ionization process was studied by analysis of alkane standards.  相似文献   
14.
The excitation of eigen surface waves by tubular electron beams in cylindrical discharge devices is studied. The influence of the wave‐field azimuthal structure on the excitation efficiency and nonlinear stage of the plasmabeam instability is investigated both numerically and analytically. Analytical expressions for the saturation amplitude and excitation efficiency of the wave under study are derived. They are found to agree well with results obtained by numerical modelling of the plasma‐beam interaction presented in this paper. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   
15.
Time‐dependent differential equations can be solved using the concept of method of lines (MOL) together with the boundary element (BE) representation for the spatial linear part of the equation. The BE method alleviates the need for spatial discretization and casts the problem in an integral format. Hence errors associated with the numerical approximation of the spatial derivatives are totally eliminated. An element level local cubic approximation is used for the variable at each time step to facilitate the time marching and the nonlinear terms are represented in a semi‐implicit manner by a local linearization at each time step. The accuracy of the method has been illustrated on a number of test problems of engineering significance. © 2005 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 2006  相似文献   
16.
17.
18.
In developing travel demand models it is generally assumed that the base-year data used in developing the parameters, as well as the forecasted data to be used as independent variables for the design year, are of acceptable quality. The purpose of this paper is to present the application of error propagation theory in assesing the predictive quality of one type of travel demand forecasting model (multinomial logit models) and to demonstrate how error considerations can be used as a tool for identifying the optimal model. The general conclusions of this study are that: (1) it is indeed possible to quantify errors in dependent variables in logit models as a consequence of errors in independent variables; and (2) error consideration can be used as a tool for identifying the optimal model from a set of candidate models. Further research is recommended to develop better insights into the phenomenon of error propagation so that the consideration of errors can be a factor in decisions on model selection.  相似文献   
19.
V. A. Steklov Mathematics Institute, USSR Academy of Sciences. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 79, No. 3, pp. 347–358, June, 1989.  相似文献   
20.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 1, pp. 46–50, January, 1991.  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