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   2764篇
  免费   109篇
  国内免费   15篇
化学   2167篇
晶体学   32篇
力学   38篇
数学   101篇
物理学   550篇
  2023年   13篇
  2022年   13篇
  2021年   30篇
  2020年   39篇
  2019年   42篇
  2018年   33篇
  2017年   25篇
  2016年   66篇
  2015年   61篇
  2014年   71篇
  2013年   130篇
  2012年   141篇
  2011年   196篇
  2010年   90篇
  2009年   113篇
  2008年   194篇
  2007年   195篇
  2006年   178篇
  2005年   149篇
  2004年   150篇
  2003年   123篇
  2002年   107篇
  2001年   48篇
  2000年   40篇
  1999年   48篇
  1998年   27篇
  1997年   30篇
  1996年   32篇
  1995年   19篇
  1994年   28篇
  1993年   26篇
  1992年   26篇
  1991年   16篇
  1990年   23篇
  1989年   18篇
  1988年   14篇
  1987年   24篇
  1986年   16篇
  1985年   34篇
  1984年   35篇
  1983年   24篇
  1982年   30篇
  1981年   22篇
  1980年   11篇
  1979年   24篇
  1978年   18篇
  1977年   11篇
  1976年   13篇
  1975年   15篇
  1973年   22篇
排序方式: 共有2888条查询结果,搜索用时 15 毫秒
11.
For Belavin's elliptic quantum R-matrix, we construct an L-operator as a set of difference operators acting on functions on the type A weight space. According to the fundamental relation RLL=LLR, taking the trace of the L-operator gives a set of commuting difference operators. We show that for the above mentioned L-operator this approach gives Macdonald type operators with elliptic theta function coefficient, actually equivalent to Ruijsenaars' operators. The relationship between the difference L-operator and Krichever's Lax matrix is given, and an explicit formula for elliptic commuting differential operators is derived. We also study the invariant subspace for the system which is spanned by symmetric theta functions on the weight space. Received: 27 December 1995 / Accepted: 11 November 1996  相似文献   
12.
Embeddings of the CAR (canonical anticommutation relations) algebra of fermions into the Cuntz algebra ?2 (or ?2 d more generally) are presented by using recursive constructions. As a typical example, an embedding of CAR onto the U(1)-invariant subalgebra of ?2 is constructed explicitly. Generalizing this construction to the case of ?2 p , an embedding of CAR onto the U(1)-invariant subalgebra of ?2 p is obtained. Restricting a permutation representation of the Cuntz algebra, we obtain the Fock representation of CAR. We apply the results to embed the algebra of parafermions of order p into ?2 p according to Green's ansatz. Received: 3 September 2001 / Accepted: 19 January 2002  相似文献   
13.
Abstract— Irradiation of near-UV light in the presence of FeCl3 caused oxidation of adenosine with concomitant reduction of Fe(III) under either aerobic or anaerobic atmosphere. Major photoproducts were adenine and adenosine-5'-aldehyde, showing that oxidation took place mostly at the ribose moiety of adenosine. Detailed study showed that the reaction proceeded by the light absorption due to Fe(III) at 300-350 nm.  相似文献   
14.
A simple and rapid method for the analysis of trace amounts of gold(III), palladium(II), and platinum(IV) by the combined use of graphite furnace atomic absorption spectrometry and anion-exchange separation was proposed, and successfully applied to the rapid determination of metals in industrial waste solutions obtained from the final process of noble-metal recovery factories, because noble metals can be selectively and quantitatively separated to a high degree by using a small column containing only a 0.7 g-portion of a common anion-exchange resin and a dilute thiourea solution.  相似文献   
15.
Copper(II) is determined by non-extractive spectrophotometry as a complex of butylene dithiocarbamate formed in situ by reaction between carbon disulfide and pyrrolidine in aqueous Triton X-100 medium. This method is similar to that with butylene dithiocarbamate as starting material in the sense of simplicity, sensitivity, precision and accuracy. Pyrrolidine is the best of seven secondary amines tested in this way for copper determinations.  相似文献   
16.
Temperature stability of the threshold current and the lasing wavelength is investigated in a 1.3-μm GaInNAs/ GaAs single quantum-well laser. The measured characteristic-temperature was 88 K. The small wavelength shift per change in temperature of 0.35 nm/°C was obtained, indicating the superior lasing-wavelength stability. Therefore, it is shown experimentally that GaInNAs is very promising material for the fabrication of light source with excellent high-temperature performance for optical fiber communications.  相似文献   
17.
Tetraethoxysilane (TEOS) and polyethoxysiloxanes (PEOSs; prepared by the acid‐catalyzed hydrolytic polycondensation of TEOS) were subjected to the sol–gel process in the presence of cetyltrimethylammonium bromide (CTAB), respectively. The PEOSs with Mw 700–26,000, as prepared by sol–gel coating of TEOS and PEOS under various conditions, were used. Uniform and crack‐free thin films of thickness 276–613 nm were prepared by spin‐coating of a PEOS solution containing CTAB. When the coating films were sintered at 400 °C, the combustion of ethoxy groups and CTAB took place to provide porous silica thin films. The structure of the thin films was found to be dependent on the molecular weight of PEOS and the molar ratio of CTAB/Si: lamellar or hexagonal phase was observed for Mw less than 15,000 and for CTAB/Si molar ratios greater than 0.10. Honeycomb structures were observed for Mw less than 5000 and for CTAB/Si molar ratios of 0.15. The honeycomb structure was also observed by atomic force microscopy and transmission electron microscope. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2542–2550, 2006  相似文献   
18.
19.
20.
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