全文获取类型
收费全文 | 1069篇 |
免费 | 23篇 |
国内免费 | 31篇 |
专业分类
化学 | 245篇 |
力学 | 67篇 |
综合类 | 5篇 |
数学 | 321篇 |
物理学 | 485篇 |
出版年
2023年 | 7篇 |
2022年 | 6篇 |
2021年 | 16篇 |
2020年 | 16篇 |
2019年 | 17篇 |
2018年 | 17篇 |
2017年 | 11篇 |
2016年 | 28篇 |
2015年 | 17篇 |
2014年 | 48篇 |
2013年 | 88篇 |
2012年 | 41篇 |
2011年 | 56篇 |
2010年 | 47篇 |
2009年 | 76篇 |
2008年 | 66篇 |
2007年 | 72篇 |
2006年 | 46篇 |
2005年 | 58篇 |
2004年 | 42篇 |
2003年 | 36篇 |
2002年 | 28篇 |
2001年 | 25篇 |
2000年 | 30篇 |
1999年 | 26篇 |
1998年 | 49篇 |
1997年 | 13篇 |
1996年 | 15篇 |
1995年 | 13篇 |
1994年 | 17篇 |
1993年 | 8篇 |
1992年 | 4篇 |
1991年 | 7篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 5篇 |
1987年 | 13篇 |
1986年 | 5篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1978年 | 3篇 |
1977年 | 5篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1973年 | 4篇 |
1972年 | 2篇 |
1969年 | 2篇 |
排序方式: 共有1123条查询结果,搜索用时 687 毫秒
51.
K. Broderix M. Weigt A. Zippelius 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(3):441-455
We consider the gelation of particles which are permanently connected by random crosslinks, drawn from an ensemble of finite-dimensional
continuum percolation. To average over the randomness, we apply the replica trick, and interpret the replicated and crosslink-averaged
model as an effective molecular fluid. A Mayer-cluster expansion for moments of the local static density fluctuations is set
up. The simplest non-trivial contribution to this series leads back to mean-field theory. The central quantity of mean-field
theory is the distribution of localization lengths, which we compute for all connectivities. The highly crosslinked gel is
characterized by a one-to-one correspondence of connectivity and localization length. Taking into account higher contributions
in the Mayer-cluster expansion, systematic corrections to mean-field can be included. The sol-gel transition shifts to a higher
number of crosslinks per particle, as more compact structures are favored. The critical behavior of the model remains unchanged
as long as finite truncations of the cluster expansion are considered. To complete the picture, we also discuss various geometrical
properties of the crosslink network, e.g. connectivity correlations, and relate the studied crosslink ensemble to a wider class of ensembles, including the Deam-Edwards
distribution.
Received on 24 April 2002 Published online 14 October 2002
RID="a"
ID="a"deceased
RID="b"
ID="b"e-mail: weigt@theorie.physik.uni-goettingen.de 相似文献
52.
53.
John S. Delaney 《Molecular diversity》1996,1(4):217-222
Summary A method for assessing the biological discriminating power of chemical similarity measures is presented. The main concern of this work was to develop an objective way of evaluating different similarity measures in terms of how well they distinguished between active and inactive compounds. In addition, we have explored the level of similarity required for optimal separation and commented on its implications for work in the field of chemical diversity studies. The results for one simple similarity measure showed that statistically significant separation could be achieved, and indicated a reasonable similarity value for future work. 相似文献
54.
Cardiac elastography is a useful diagnostic technique for detection of heart function abnormalities, based on analysis of echocardiograms. The analysis of the regional heart motion allows assessing the extent of myocardial ischemia and infarction. In this paper, a new two-stage algorithm for cardiac motion estimation is proposed, where the data is taken from a sequence of 2D echocardiograms. The method combines the advantages of block-matching and optical flow techniques. The first stage employs a standard block-matching algorithm (sum of absolute differences) to provide a displacement estimate with accuracy of up to one pixel. At the second stage, this estimate is corrected by estimating the parameters of a local image transform within a test window. The parameters of the image transform are estimated in the least-square sense. In order to account for typical heart motions, like contraction/expansion, translation and rotation, a local affine model is assumed within the test window. The accuracy of the new algorithm is evaluated using a sequence of 500 grayscale B-mode images, which are generated as distorted, but known copies of an original ROI, taken from a real echocardiogram. The accuracy of the motion estimation is expressed in terms of errors: maximum absolute error, root-mean-square error, average error and standard deviation. The errors of the proposed algorithm are compared with these of the known block-matching technique with cross-correlation and interpolation in the sub-pixel space. Statistical analysis of the errors shows that the proposed algorithm provides more accurate estimates of the heart motion than the cross-correlation technique with interpolation in the sub-pixel space. 相似文献
55.
We address the problem of finding the worst possible traffic a
user of a telecommunications network can send.
We take worst to mean having the highest effective
bandwidth, a concept that arises in the Large Deviation theory of
queueing networks.
The traffic is assumed to be stationary and to satisfy leaky bucket
constraints, which represent the a priori knowledge the network
operator has concerning the traffic.
Firstly, we show that this optimization problem may be reduced to an
optimization over periodic traffic sources.
Then, using convexity methods, we show that the realizations of a
worst case source must have the following properties:
at each instant the transmission rate must be either zero,
the peak rate, or the leaky bucket rate; it may only be the latter when
the leaky bucket is empty or full;
each burst of activity must either start with the leaky
bucket empty or end with it full. 相似文献
56.
高功率激光系统中随机相位屏的统计模型出发,分析了其相位噪声及梯度的一阶和二阶统计性质。研究了完全相干光与部分相干光通过随机相位屏后的传输性质,推导得出部分相干光在经过随机相位屏后,其交叉谱密度的期望等于随机相位屏透过率函数的期望与入射光交叉谱密度的乘积。对该模型下的远场分布进行了数值模拟。结果显示,能量对称分布的完全相干光通过相位干屏后,只有通过随机相位屏透过率函数期望的远场分布是对称的;部分相干光在传输通过随机相位屏后,其谢尔模光束性质不会改变,但光强分布不再具有对称性,且强度明显降低。 相似文献
57.
J. C. Li J. Zhu Z. J. Peng 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(2):325-330
We study analytically and numerically the properties of one-dimensional
chain of cold ions placed in a periodic potential of optical lattice
and global harmonic potential of a trap.
In close similarity with the Frenkel-Kontorova model, a transition from
sliding to pinned phase takes place with the increase of
the optical lattice potential for the density of ions
incommensurate with the lattice period. We show that at zero temperature the quantum
fluctuations lead to a quantum phase transition
and melting of pinned instanton glass phase at large values of dimensional Planck constant.
After melting the ion chain can slide in an optical lattice.
The obtained results are also relevant for a Wigner crystal placed
in a periodic potential. 相似文献
58.
59.
60.
JavaStatSoft, implemented using Java, is an open-source software for performing statistics. The current features of JavaStatSoft
are described. Several well-known patterns the software used are introduced. In addition, based on these patterns and the
experience in developing the software, a new framework, referred to as Data Analysis Module, is proposed to help programmers
develop a user-friendly software for data analysis. 相似文献