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   6061篇
  免费   267篇
  国内免费   24篇
化学   3958篇
晶体学   35篇
力学   153篇
数学   1129篇
物理学   1077篇
  2023年   51篇
  2022年   77篇
  2021年   118篇
  2020年   104篇
  2019年   127篇
  2018年   108篇
  2017年   121篇
  2016年   246篇
  2015年   172篇
  2014年   236篇
  2013年   399篇
  2012年   451篇
  2011年   497篇
  2010年   285篇
  2009年   299篇
  2008年   384篇
  2007年   348篇
  2006年   298篇
  2005年   300篇
  2004年   253篇
  2003年   203篇
  2002年   176篇
  2001年   61篇
  2000年   66篇
  1999年   50篇
  1998年   53篇
  1997年   52篇
  1996年   51篇
  1995年   27篇
  1994年   37篇
  1993年   40篇
  1992年   39篇
  1991年   31篇
  1990年   38篇
  1989年   30篇
  1988年   33篇
  1987年   24篇
  1986年   30篇
  1985年   34篇
  1984年   49篇
  1983年   24篇
  1982年   24篇
  1981年   30篇
  1980年   27篇
  1979年   24篇
  1978年   25篇
  1977年   28篇
  1976年   15篇
  1975年   18篇
  1974年   20篇
排序方式: 共有6352条查询结果,搜索用时 15 毫秒
111.
112.
113.
114.
Let (X,l,) be a measure space, letW be a cylindrical Hilbert-Wiener process, and let be an anticipating integrable process-valued function onX. We prove, under natural assumptions on, that there exists a measurable version Yx,x X, of the anticipating integral of(x) such that the integral x Yx(dx) is a version of the anticipating integral of X (x)(dx). We apply this anticipating Fubini theorem to study solutions of a class of stochastic evolution equations in Hilbert space.  相似文献   
115.
116.
Ab initio molecular dynamics simulation of a room temperature ionic liquid   总被引:1,自引:0,他引:1  
Ab initio molecular dynamics simulations have been performed for the first time on the room-temperature organic ionic liquid dimethyl imidazolium chloride [DMIM][Cl] using density functional theory. The aim is to compare the local liquid structure with both that obtained from two different classical force fields and from neutron scattering experiments. The local structure around the cation shows significant differences compared to both the classical calculations and the neutron results. In particular, and unlike in the gas-phase ion pair, chloride ions tend to be located near a ring C-H proton in a position suggesting hydrogen bonding. The results are used to suggest ways in which the classical potentials may be improved.  相似文献   
117.
[reaction: see text] Chiral beta-syn-alkoxyhomoallylic alcohols derived from alkoxyallylboration of aldehydes upon oxidation provided the corresponding chiral ketones. Chelation-controlled nucleophilic addition to these ketones occurred in a highly stereoselective manner to afford anti-homoallylic tertiary alcohols. This methodology has been applied for the synthesis of the C(1)-C(11) subunit of C(8)-epi-fostriecin.  相似文献   
118.
The inclusion complexes of β-cyclodextrin (β-CD) with naphthalene and some of its derivatives in the solid state have been studied by infrared spectroscopy. Digital subtraction, deconvolution and curve fitting have been used to investigate the interactions between the naphthalene derivatives andβ-CD. Several preparation methods for the solid dispersions have been tested, using FTIR as an effective tool to evaluate the interactions at the molecular level. The effects of temperature and humidity on the spectra have been also analyzed. A carbonyl moiety in the guest molecule can increase the stability of the complex by establishing specific interactions with the hydroxyl groups of the CD cavity rims. The stability of the complexes is higher for 2-naphthylacetate than that for 1-naphthyl acetate, andso is the degree of association of its carbonyl groups. On the other hand, 2-acetylnaphthaleneforms very stable inclusioncomplexes although its carbonyl groups appear to be significantly less associated.  相似文献   
119.
[reaction: see text] A highly versatile approach to the enantioselective synthesis of securinega alkaloids is presented. Crucial steps are a palladium-catalyzed enantioselective imide alkylation, a vinylogous Mannich reaction, and a ring-closing metathesis process. Through this strategy, the synthesis of (-)-norsecurinine has been accomplished in nine steps and 11% overall yield.  相似文献   
120.
The tautomeric properties of isoguanine (also named 2-oxoadenine or 2-hydroxyadenine) have been studied in the gas phase, in different pure solvents, and in the DNA environment using state of the art theoretical methods. Our results show that isoguanine constitutes an unique example of how tautomerism can be modulated by the environment. Compared to the tautomeric preference in the gas phase, both polar solvents and the DNA microenvironment dramatically change the intrinsic tautomeric properties of isoguanine. Tautomers which are important in physiological conditions are less than 1/10(5) of the total population of isoguanine in the gas phase. The impact of the present findings in the understanding of spontaneous mutations and in the design of new nucleobases with multiple recognition properties is discussed.  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