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   666123篇
  免费   6755篇
  国内免费   2041篇
化学   358334篇
晶体学   9867篇
力学   29244篇
综合类   22篇
数学   79671篇
物理学   197781篇
  2021年   5421篇
  2020年   6075篇
  2019年   6638篇
  2018年   8628篇
  2017年   8510篇
  2016年   12763篇
  2015年   7997篇
  2014年   12265篇
  2013年   30120篇
  2012年   22813篇
  2011年   27932篇
  2010年   19804篇
  2009年   19619篇
  2008年   25972篇
  2007年   25902篇
  2006年   24237篇
  2005年   21831篇
  2004年   19953篇
  2003年   17839篇
  2002年   17625篇
  2001年   19803篇
  2000年   15147篇
  1999年   11832篇
  1998年   9766篇
  1997年   9579篇
  1996年   9245篇
  1995年   8172篇
  1994年   8112篇
  1993年   7825篇
  1992年   8826篇
  1991年   9021篇
  1990年   8589篇
  1989年   8370篇
  1988年   8399篇
  1987年   8258篇
  1986年   7720篇
  1985年   10113篇
  1984年   10433篇
  1983年   8273篇
  1982年   8570篇
  1981年   8340篇
  1980年   7853篇
  1979年   8552篇
  1978年   8909篇
  1977年   8727篇
  1976年   8661篇
  1975年   8050篇
  1974年   8058篇
  1973年   8202篇
  1972年   5676篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
901.
902.
Myerson (1977) derived an efficient value for games in partition function form. In this paper, we present a set of axioms which characterize a different efficient value for such games. This latter value assigns value 0 to dummies and assigns nonnegative values to players in monotone simple games.  相似文献   
903.
We give an almost complete classification of ergodicity and transience conditions for a general multi-queue system with the following features: arrivals form Poisson streams and there are various routing schemes for allocating arrivals to queues; the servers can be configured in a variety of ways; completed jobs can feed back into the system; the exponential service times and feedback probabilities depend upon the configuration of the servers (this model includes some types of multi-class queueing system); switching between service regimes is instantaneous. Several different levels of control of the service regimes are considered. Our results for the N-queue system require randomisation of service configurations but we have studied the two queue system in situations where there is less control. We use the semi-martingale methods described in Fayolle, Malyshev and Menshikov [3] and our results generalise Kurkova [8] and complement Foley and McDonald [4] and [5]. AMS 2000 subject classification: Primary: 90B22; Secondary: 60J10 90B15  相似文献   
904.
905.
Spatio temporal dynamics of the positive column of a dc neon glow discharge is studied and investigated experimentally and theoretically. Spatio temporal analysis by means of biorthogonal decomposition method (BOD) gives insights into the mechanism of irregularity and can be employed for characterization of spatio‐ temporal complexity. In the weak nonlinear region, the wave dynamics is approximated by an amplitude equation of the Ginzburg‐Landau equation (CGLE) with complex coefficients and an additional integral term based on a fluid model. In the present work we deal with irregular spatio‐temporal data. A comparison between the numerical analysis of the experimental data and simulation results are studied. A good agreement between the dynamical behaviour for experimental space‐time data and theoretical simulation space‐time results was obtained. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   
906.
We consider a two-echelon inventory system with a number of non-identical, independent ‘retailers’ at the lower echelon and a single ‘supplier’ at the upper echelon. Each retailer experiences Poisson demand and operates a base stock policy with backorders. The supplier manufactures to order and holds no stock. Orders are produced, in first-come first-served sequence, with a fixed production time. The supplier therefore functions as an M/D/1 queue. We are interested in the performance characteristics (average inventory, average backorder level) at each retailer. By finding the distribution of order lead time and hence the distribution of demand during order lead time, we find the steady state inventory and backorder levels based on the assumption that order lead times are independent of demand during order lead time at a retailer. We also propose two alternative approximation procedures based on assumed forms for the order lead time distribution. Finally we provide a derivation of the steady state inventory and backorder levels which will be exact as long as there is no transportation time on orders between the supplier and retailers. A numerical comparison is made between the exact and approximate measures. We conclude by recommending an approach which is intuitive and computationally straightforward.  相似文献   
907.
Modification of shungite with polyamines, followed by corss-linking with epoxy compounds, yielded chemically and thermally stable polyfunctional anion exchangers. The effect of the nature of a polyamine and epoxy compounds and of the carbon content of shungites and the process conditions on the ion-exchange properties of the samples obtained was studied.  相似文献   
908.
Eight emission spectra of pure N2O and N2O + N2 + He mixtures excited by a radio frequency discharge were recorded by Fourier Transform Spectroscopy at a resolution of 0.005 and 0.004 cm−1 in the 4.5 μm region. Results (wavenumbers, band centers, and spectroscopic constants) concerning nine new vibrational transitions which have not been observed before, and which occur between highly excited levels of the bending mode are reported. The derived spectroscopic parameters allow us to reproduce the experimental wavenumbers with an RMS error lower than 4.5 × 10−4 cm−1.  相似文献   
909.
We survey recent progress achieved in understanding the impact of inelastic processes on coherent backscattering of light from cold atoms that are saturated by a powerful laser field.  相似文献   
910.
We explored phase separation and self‐assembly of perfluoroalkyl segments at the surface of polymer films obtained from latices of semifluorinated acrylate copolymers and the corresponding latex blends of nonfluorinated and semifluorinated polyacrylates. With laser‐induced secondary mass spectrometry the fluorine distribution was measured after annealing above the minimum film‐forming temperature of the polymers up to a depth of several micrometers. Depth profiles of a semifluorinated acrylate homopolymer and latex blends thereof with fluorine‐free alkylacrylates with 25, 50, and 75 mol % semifluorinated acrylate as well as a copolymer comprised of alkyl acrylate and semifluorinated acrylate (50/50 mol %) were investigated. In the case of latex blends containing both semifluorinated polyacrylates and fluorine‐free or low‐fluorine polymers, self‐assembly accounted for enrichment of the perfluoroalkyl segments at the surface. Coatings exhibiting low surface energy and having a substantially reduced total fluorine content were obtained. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 360–367, 2003  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