全文获取类型
收费全文 | 825篇 |
免费 | 6篇 |
国内免费 | 1篇 |
专业分类
化学 | 631篇 |
晶体学 | 4篇 |
力学 | 11篇 |
数学 | 88篇 |
物理学 | 98篇 |
出版年
2022年 | 13篇 |
2021年 | 11篇 |
2020年 | 14篇 |
2019年 | 10篇 |
2018年 | 8篇 |
2017年 | 10篇 |
2016年 | 20篇 |
2015年 | 16篇 |
2014年 | 16篇 |
2013年 | 33篇 |
2012年 | 47篇 |
2011年 | 46篇 |
2010年 | 22篇 |
2009年 | 30篇 |
2008年 | 41篇 |
2007年 | 31篇 |
2006年 | 18篇 |
2005年 | 19篇 |
2004年 | 14篇 |
2003年 | 15篇 |
2002年 | 9篇 |
2001年 | 6篇 |
2000年 | 8篇 |
1999年 | 7篇 |
1997年 | 15篇 |
1996年 | 7篇 |
1994年 | 9篇 |
1993年 | 7篇 |
1991年 | 7篇 |
1990年 | 6篇 |
1989年 | 12篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 15篇 |
1985年 | 12篇 |
1984年 | 10篇 |
1983年 | 10篇 |
1982年 | 16篇 |
1981年 | 12篇 |
1980年 | 12篇 |
1979年 | 12篇 |
1978年 | 15篇 |
1977年 | 15篇 |
1976年 | 14篇 |
1975年 | 8篇 |
1974年 | 22篇 |
1973年 | 15篇 |
1972年 | 15篇 |
1970年 | 12篇 |
1957年 | 6篇 |
排序方式: 共有832条查询结果,搜索用时 15 毫秒
91.
This paper considers the inversion of experimental field data collected with light receiving systems designed to meet operational requirements. Such operational requirements include system deployment in free drifting configurations and a limited number of acoustic receivers. A well-known consequence of a reduced spatial coverage is a poor sampling of the vertical structure of the acoustic field, leading to a severe ill-conditioning of the inverse problem and data to model cost function with a massive sidelobe structure having many local extrema. This causes difficulties to meta-heuristic global search methods, such as genetic algorithms, to converge to the true model parameters. In order to cope with this difficulty, broadband high-resolution processors are proposed for their ability to significantly attenuate sidelobes, as a contribution for improving convergence. A comparative study on simulated data shows that high-resolution methods did not outperform the conventional Bartlett processor for pinpointing the true environmental parameter when using exhaustive search. However, when a meta-heuristic technique is applied for exploring a large multidimensional search space, high-resolution methods clearly improved convergence, therefore reducing the inherent uncertainty on the final estimate. These findings are supported by the results obtained on experimental field data obtained during the Maritime Rapid Environmental Assessment 2003 sea trial. 相似文献
92.
We study a coarsening process of one-dimensional cell complexes. We show that if cell boundaries move with velocities proportional to the difference in size of neighboring cells, then the average cell size grows at a prescribed exponential rate and the Poisson distribution is precisely invariant for the distribution of the whole process, rescaled in space by its average growth rate. We present numerical evidence toward the following universality conjecture: starting from any finite mean stationary renewal process, the system when rescaled by e ?2t converges to a Poisson point process. For a limited case, this makes precise what has been observed previously in experiments and simulations, and lays the foundation for a theory of universal asymptotic states of dynamical cell complexes. 相似文献
93.
In this study, affinity capillary electrophoresis (ACE) and quantum mechanical density functional theory (DFT) calculations were combined to investigate non-covalent binding interactions between the hexaarylbenzene-based receptor (R) and alkali metal ions, Rb(+) and Cs(+) , in methanol. The apparent binding (stability) constants (K(b) ) of the complexes of receptor R with alkali metal ions in the methanolic medium were determined by ACE from the dependence of effective electrophoretic mobility of the receptor R on the concentration of Rb(+) and Cs(+) ions in the BGE using a non-linear regression analysis. The receptor R formed relatively strong complexes both with rubidium (log K(b) =4.04±0.21) and cesium ions (log K(b) =3.72±0.22). The structural characteristics of the above alkali metal ion complexes with the receptor R were described by ab initio density functional theory calculations. These calculations have shown that the studied cations bind to the receptor R because they synergistically interact with the polar ethereal fence and with the central benzene ring via cation-π interaction. 相似文献
94.
95.
The development of a new platform for the direct and selective detection of nitrates is described. Two thioether-based chemosensors and the corresponding sulfoxides and sulfones were prepared, and their photophysical properties were evaluated. Upon selective sulfoxidation of these thioethers with nitrates via an oxygen-transfer reaction promoted by a bioinspired Mo-Cu system, significant fluorescence shifts were measured. A selective response of these systems, discriminating between nitrate salts and H(2)O(2), was also shown. 相似文献
96.
Molecular dynamics simulations with atomistic detail of the gel phase and melting transitions of dipalmitoyl phosphatidylcholine bilayers in water reveal the dependency of many thermodynamic and structural parameters on the initial system ordering. We quantitatively compare different methods to create a gel phase system and we observe that a very high ordering of the gel phase starting system is necessary to observe behavior which reproduces experimental data. We performed heating scans with speeds down to 0.5 K/ns and could observe sharp first order phase transitions. Also, we investigated the transition enthalpy as the natural intrinsic parameter of first order phase transitions, and obtained a quantitative match with experimental values. Furthermore, we performed systematic investigations of the statistical distribution and heating rate dependency of the microscopic phase transition temperature. 相似文献
97.
98.
Yanyuan Ma Marc G. Genton Emanuel Parzen 《Annals of the Institute of Statistical Mathematics》2011,63(2):227-243
The asymptotic distribution of sample quantiles in the classical definition is well-known to be normal for absolutely continuous
distributions. However, this is no longer true for discrete distributions or samples with ties. We show that the definition
of sample quantiles based on mid-distribution functions resolves this issue and provides a unified framework for asymptotic
properties of sample quantiles from absolutely continuous and from discrete distributions. We demonstrate that the same asymptotic
normal distribution result as for the classical sample quantiles holds at differentiable points, whereas a more general form
arises for distributions whose cumulative distribution function has only one-sided differentiability. For discrete distributions
with finite support, the same type of asymptotics holds and the sample quantiles based on mid-distribution functions either
follow a normal or a two-piece normal distribution. We also calculate the exact distribution of these sample quantiles for
the binomial and Poisson distributions. We illustrate the asymptotic results with simulations. 相似文献
99.
Given an isotropic random vector X with log-concave density in Euclidean space
\mathbbRn{\mathbb{R}^n} , we study the concentration properties of |X| on all scales, both above and below its expectation. We show in particular that
l \mathbbP( | |X| - ?n | 3 t?n ) £ C exp ( -cn1/2 min(t3, t) ) "t 3 0, \begin{array}{l} \mathbb{P}\left ( \left | |X| - \sqrt{n} \right | \geq t\sqrt{n} \right ) \leq C \, {\rm exp} \left ( -cn^{1/2} {\rm min}(t^{3}, t) \right) \; \forall t \geq 0, \end{array} 相似文献
100.
|