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   620篇
  免费   17篇
  国内免费   36篇
化学   73篇
力学   7篇
综合类   2篇
数学   527篇
物理学   64篇
  2023年   6篇
  2022年   6篇
  2021年   11篇
  2020年   9篇
  2019年   8篇
  2018年   9篇
  2017年   4篇
  2016年   11篇
  2015年   8篇
  2014年   20篇
  2013年   55篇
  2012年   24篇
  2011年   35篇
  2010年   40篇
  2009年   46篇
  2008年   65篇
  2007年   51篇
  2006年   45篇
  2005年   32篇
  2004年   22篇
  2003年   26篇
  2002年   11篇
  2001年   9篇
  2000年   13篇
  1999年   16篇
  1998年   6篇
  1997年   9篇
  1996年   7篇
  1995年   12篇
  1994年   12篇
  1993年   4篇
  1992年   5篇
  1991年   2篇
  1990年   5篇
  1989年   4篇
  1988年   3篇
  1986年   1篇
  1985年   3篇
  1984年   2篇
  1983年   1篇
  1982年   2篇
  1981年   1篇
  1980年   4篇
  1979年   1篇
  1978年   1篇
  1976年   5篇
  1974年   1篇
排序方式: 共有673条查询结果,搜索用时 93 毫秒
51.
Novel temperature-responsive copolymers of N-isopropylacrylamide and monoaza-tetrathioether derivative, were synthesized for the selective extraction of soft metal ions such as silver(I), copper(I), gold(III) and palladium(II) ion. The ratio between N-isopropylacrylamide group and monoaza-tetrathioether group in the copolymer was determined. The ratio between N-isopropylacrylamide group and monoaza-tetrathioether group varied in the range of 66:1–187:1. Each lower critical solution temperature (LCST) of the polymer solution was determined spectrophotometrically by the relative absorbance change at 750 nm via temperature of the polymer solution. Metal ion extraction using the copolymer with appropriate counter anions such as picrate ion, nitrate or perchlorate ion was examined. Soft metal ions such as silver(I), copper(I), gold(III) and palladium(II) ion were extracted selectively into the solid polymer phase. The extraction efficiency of a metal ion such as silver ion increased as the increase of the ratio of the monoaza-tetrathioether group to N-isopropylacrylamide group in the polymer. The quantitative extraction of class b metal ions as well as the liquid–liquid extraction of metal ions with monoaza-tetrathioether molecule was performed.  相似文献   
52.
Upper bounds for the security of coherent-one-way (COW) quantum key distribution protocols have been analyzed by considering the one-pulse-attack [Branciard C, Gisin N and Scarani V (BGS) New J.Phys. (2008) 10 013031]. However, their security analysis was based on long distance case, and the typical value of the transmission distance is larger than 50 km. Applying the sharp continuity for the von Neumann entropy and some basic inequalities, we provide lower bounds for the security of modified coherent-one-way quantum key distribution protocol against the most general one-pulse-attack by only considering photon number resolved detectors that will be used in the receiver's side. Comparing with BGS's security analysis, our security analysis can be satisfied with arbitrary distance case.  相似文献   
53.
The weighted graphs, where the edge weights are positive numbers, are considered. The authors obtain some lower bounds on the spectral radius and the Laplacian spectral radius of weighted graphs, and characterize the graphs for which the bounds are attained. Moreover, some known lower bounds on the spectral radius and the Laplacian spectral radius of unweighted graphs can be deduced from the bounds.  相似文献   
54.
Recently Kamran extended the result of Mizoguchi and Takahashi for closed multi-valued mappings and proved a fixed point theorem. In this paper we further extend the result concluded by Kamran and prove a common fixed point theorem by using the concept of lower semi-continuity.  相似文献   
55.
56.
In this paper, the lower semicontinuity of solution mapping to parametric generalized strong vector equilibrium problems without the assumptions of monotonicity and compactness is established by using a new proof method which is different from the ones used in the literature.  相似文献   
57.
In this paper matching upper and lower bounds for broadcast on general purpose parallel computation models that exploit network locality are proven. These models try to capture both the general purpose properties of models like the PRAM or BSP on the one hand, and to exploit network locality of special purpose models like meshes, hypercubes, etc., on the other hand. They do so by charging a cost l(|ij|) for a communication between processors i and j, where l is a suitably chosen latency function.An upper bound T(p)=∑i=0loglogp2i·l(p1/2i) on the runtime of a broadcast on a p processor H-PRAM is given, for an arbitrary latency function l(k).The main contribution of the paper is a matching lower bound, holding for all latency functions in the range from l(k)=Ω(logk/loglogk) to l(k)=O(log2k). This is not a severe restriction since for latency functions l(k)=O(logk/log1+log(k)) with arbitrary >0, the runtime of the algorithm matches the trivial lower bound Ω(logp) and for l(k)=Θ(log1+k) or l(k)=Θ(k), the runtime matches the other trivial lower bound Ω(l(p)). Both upper and lower bounds apply for other parallel locality models like Y-PRAM, D-BSP and E-BSP, too.  相似文献   
58.
主要研究方程f"(z)+A(z)f'(z)+B(z)f(z)=0(A(z)),B(z)为整函数)的解、解的多项式或微分多项式这些具有无穷下级的整函数的Julia集的径向分布问题.  相似文献   
59.
In this paper the concept of lower and upper solutions combined with the fixed point theorem of Bohnnenblust–Karlin is used to investigate the existence of solutions for a class of the initial value problem for impulsive differential inclusions involving the Caputo fractional derivative.  相似文献   
60.
A two-dimensional, flow-enhanced gradient echo pulse sequence for nuclear magnetic resonance angiography is described. It employs interleaved, presaturated slices to acquire data efficiently on imagers which favor interleaved acquisition over sequential acquisition for multislice imaging. It is useful on any imager when the effective TR is extended to enhance the sensitivity to slow flow. The technique was applied to the region from aortic bifurcation to the iliac bifurcations of three normal volunteers. The right and left common iliac arteries and veins, the separation of the external and internal iliac arteries, and secondary branches were clearly depicted.  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