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   4962篇
  免费   98篇
  国内免费   91篇
化学   609篇
晶体学   9篇
力学   77篇
数学   4127篇
物理学   329篇
  2023年   26篇
  2022年   26篇
  2021年   35篇
  2020年   32篇
  2019年   60篇
  2018年   70篇
  2017年   65篇
  2016年   64篇
  2015年   58篇
  2014年   77篇
  2013年   294篇
  2012年   129篇
  2011年   194篇
  2010年   114篇
  2009年   301篇
  2008年   378篇
  2007年   407篇
  2006年   305篇
  2005年   240篇
  2004年   207篇
  2003年   148篇
  2002年   66篇
  2001年   93篇
  2000年   85篇
  1999年   97篇
  1998年   102篇
  1997年   70篇
  1996年   95篇
  1995年   114篇
  1994年   103篇
  1993年   79篇
  1992年   84篇
  1991年   40篇
  1990年   59篇
  1989年   47篇
  1988年   48篇
  1987年   67篇
  1986年   60篇
  1985年   81篇
  1984年   48篇
  1983年   48篇
  1982年   91篇
  1981年   68篇
  1980年   62篇
  1979年   31篇
  1978年   57篇
  1977年   57篇
  1976年   57篇
  1975年   7篇
  1974年   4篇
排序方式: 共有5151条查询结果,搜索用时 0 毫秒
81.
Epi-derivatives have many applications in optimization as approached through nonsmooth analysis. In particular, second-order epi-derivatives can be used to obtain optimality conditions and carry out sensitivity analysis. Therefore the existence of second-order epi-derivatives for various classes of functions is a topic of considerable interest. A broad class of composite functions on n called fully amenable functions (which include general penalty functions composed withC 2 mappings, possibly under a constraint qualification) are now known to be twice epi-differentiable. Integral functionals appear widely in problems in infinite-dimensional optimization, yet to date, only integral functionals defined by convex integrands have been shown to be twice epi-differentiable, provided that the integrands are twice epi-differentiable. Here it is shown that integral functionals are twice epi-differentiable even without convexity, provided only that their defining integrands are twice epi-differentiable and satisfy a uniform lower boundedness condition. In particular, integral functionals defined by fully amenable integrands are twice epi-differentiable under mild conditions on the behavior of the integrands.This work was supported in part by the National Science Foundation under grant DMS-9200303.  相似文献   
82.
The Banach algebra generated by one-dimensional linear singular integral operators with matrix valued piecewise continuous coefficients in the spaceL p (,) with an arbitrary weight is studied. The contour consists of a finite number of closed curves and open arcs with satisfy the Carleson condition. The contour may have a finite number of points of selfintersection. The symbol calculus in this algebra is the main result of the paper.  相似文献   
83.
聚苯胺导电复合物二次掺杂的基材效应   总被引:1,自引:0,他引:1  
对十二烷基苯磺酸掺杂的聚苯胺与氯磺化聚乙烯或苯乙烯-丁二烯-苯乙烯三嵌段共聚物形成的复合物的二次掺杂进行了研究。二次掺杂的复合膜经反掺杂后的UV-Vis吸收光谱在580 ̄800nm处呈现宽的吸收,证实了二次掺杂后PAn主链的展开,同时表明PAn在CSPE中的展开较在SBS中更充分,ESR动态测试表明二次掺杂诱导主链的载流子间相互作用有2种方式;PAn/CSPE中的单极化子转变为双极化子;PAn/S  相似文献   
84.
It is widely believed that order of exactness is a good measure of the quality of an algorithm for numerical quadrature. We show that this is not the case, by exhibiting a situation in which the optimal algorithm does not even integrate constants exactly. We also show that there are situations in which the penalty for using equidistant nodes is unbounded. Finally, we show that the complexity of obtaining an -approximation can be an arbitrary function of , i.e., there is no hardest quadrature problem.  相似文献   
85.
Given a finite setX of vectors from the unit ball of the max norm in the twodimensional space whose sum is zero, it is always possible to writeX = {x1, , xn} in such a way that the first coordinates of each partial sum lie in [–1, 1] and the second coordinates lie in [–C, C] whereC is a universal constant.  相似文献   
86.
87.
The surface chemical composition of raw unscoured cotton was successfully investigated by the surface analytical techniques X-ray Photoelectron Spectroscopy (XPS) and Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS). The presence of non-cellulosic material at the fibre surface was established and determined to be a complex mixture of fatty acids, alcohols, alkanes, esters and glycerides. The effect of scouring and bleaching was to reduce the surface concentration of these materials but even after aqueous processing some non-cellulosic material residue was still detected at the fibre surface.  相似文献   
88.
1,4-Disubstituted 1,2,3-triazoles are obtained in excellent yields via a three-component coupling of secondary alcohols, alkynes and trimethylsilyl azide (TMSN3). This one-pot reaction occurs through in situ generation of an azide from the alcohol and TMSN3, followed by 1,3-dipolar cycloaddition of the terminal alkyne to afford the corresponding disubstituted triazoles.  相似文献   
89.
Yu-Wu Zhong  Guo-Qiang Lin 《Tetrahedron》2004,60(40):8861-8868
Some new pyridyl alcohols with the cis-bicyclo[3.3.0]octane scaffold were synthesized and used as chiral ligands for the enantioselective addition of diethylzinc to aldehydes. Ligands 4 were found to be far superior to the C2-symmetric ligands 2 in terms of enantioselectivities. Quantitative yields and enantiomeric excesses of up to 92% were obtained when the ligand 4 was used. The carbonyl function in 4 proved to be beneficial for the high enantioselectivities in the addition of diethylzinc to aldehydes. Conversion of the carbonyl group into oxime or oxime ether group led to a sort of more active ligands, which catalyzed the same reaction with rate acceleration.  相似文献   
90.
A set is amorphous, if it is not a union of two disjoint infinite subsets. The following variants of the Tychonoff product theorem are investigated in the hierarchy of weak choice principles. TA1: An amorphous power of a compactT 2 space is compact. TA2: An amorphous power of a compactT 2 space which as a set is wellorderable is compact. In ZF0TA1 is equivalent to the assertion, that amorphous sets are finite. RT is Ramsey's theorem, that every finite colouring of the set ofn-element subsets of an infinite set has an infinite homogeneous subset and PW is Rubin's axiom, that the power set of an ordinal is wellorderable. In ZF0RT+PW implies TA2. Since RT+PW is compatible with the existence of infinite amorphous sets, TA2 does not imply TA1 in ZF0. But TA2 cannot be proved in ZF0 alone. As an application, we prove a theorem of Stone, using a weak wellordering axiomD 3 (a set is wellorderable, if each of its infinite subsets is structured) together with RT.
Diese Arbeit ist Teil der Habilitationsschrift des Verfassers im Fachgebiet Mathematische Analysis an der Technischen Universität Wien.  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