全文获取类型
收费全文 | 22222篇 |
免费 | 2186篇 |
国内免费 | 1915篇 |
专业分类
化学 | 5987篇 |
晶体学 | 211篇 |
力学 | 1211篇 |
综合类 | 263篇 |
数学 | 7711篇 |
物理学 | 4742篇 |
无线电 | 6198篇 |
出版年
2024年 | 34篇 |
2023年 | 191篇 |
2022年 | 325篇 |
2021年 | 423篇 |
2020年 | 581篇 |
2019年 | 528篇 |
2018年 | 507篇 |
2017年 | 595篇 |
2016年 | 722篇 |
2015年 | 707篇 |
2014年 | 1063篇 |
2013年 | 1442篇 |
2012年 | 1102篇 |
2011年 | 1273篇 |
2010年 | 1063篇 |
2009年 | 1279篇 |
2008年 | 1370篇 |
2007年 | 1539篇 |
2006年 | 1321篇 |
2005年 | 1159篇 |
2004年 | 973篇 |
2003年 | 1042篇 |
2002年 | 992篇 |
2001年 | 774篇 |
2000年 | 665篇 |
1999年 | 579篇 |
1998年 | 560篇 |
1997年 | 434篇 |
1996年 | 468篇 |
1995年 | 412篇 |
1994年 | 329篇 |
1993年 | 270篇 |
1992年 | 238篇 |
1991年 | 195篇 |
1990年 | 174篇 |
1989年 | 128篇 |
1988年 | 129篇 |
1987年 | 87篇 |
1986年 | 69篇 |
1985年 | 91篇 |
1984年 | 71篇 |
1983年 | 42篇 |
1982年 | 73篇 |
1981年 | 66篇 |
1980年 | 34篇 |
1979年 | 54篇 |
1978年 | 38篇 |
1977年 | 29篇 |
1976年 | 31篇 |
1973年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
51.
52.
Most of the novel highly potent drugs, developed on the basis of modern molecular medicine, taking into account cell surface recognition techniques, show poor water solubility. A chemical modification of the drug substance enhancing the solubility often decreases the pharmacological activity. Thus, as an alternative an increase of the solubility can be obtained by the reduction of the size of the drug particles. Unfortunately, it is often difficult to obtain micro or nanosized drug particles by classical or more advanced crystallization using supercritical gases or by milling techniques. In addition, nanosized particles are often not physically stable and need to be stabilized in an appropriate matrix. Thus, it may be of interest to manufacture directly nanosized drug particles stabilized in an inert hydrophilic matrix, i.e. nanostructured and nanocomposite systems. Solid solutions and solid dispersions represent nanostructured and nanocomposite systems. In this context, the use of the vacuum-fluidized-bed technique for the spray-drying of a low water soluble drug cosolubilized with a hydrophilic excipient in a polar organic solvent is discussed. In order to avoid the use of organic solvents, a special spray-freeze-drying technique working at atmospheric pressure is presented. This process is very suitable for temperature and otherwise sensitive drugs such as pharmaproteins. 相似文献
53.
ZHANG Shibin ZHANG Xinsheng & SUN Shuguang School of Management Fudan University Shanghai China Department of Mathematics Shanghai Maritime University Shanghai China 《中国科学A辑(英文版)》2006,49(9):1231-1257
The stationary Gamma-OU processes are recommended to be the volatility of the financial assets. A parametric estimation for the Gamma-OU processes based on the discrete observations is considered in this paper. The estimator of an intensity parameter A and its convergence result are given, and the simulations show that the estimation is quite accurate. Assuming that the parameter A is estimated, the maximum likelihood estimation of shape parameter c and scale parameter a, whose likelihood function is not explicitly computable, is considered. By means of the Gaver-Stehfest algorithm, we construct an explicit sequence of approximations to the likelihood function and show that it converges the true (but unkown) one. Maximizing the sequence results in an estimator that converges to the true maximum likelihood estimator and the approximation shares the asymptotic properties of the true maximum likelihood estimator. Some simulation experiments reveal that this method is still quite accurate in most of rational situations for the background of volatility. 相似文献
54.
We obtain upper bounds for the tail distribution of the first nonnegative sum of a random walk and for the moments of the overshoot over an arbitrary nonnegative level if the expectation of jumps is positive and close to zero. In addition, we find an estimate for the expectation of the first ladder epoch. 相似文献
55.
Kasper K. Berthelsen Jesper Møller 《Bulletin of the Brazilian Mathematical Society》2002,33(3):351-367
This primer provides a self-contained exposition of the case where spatial birth-and-death processes are used for perfect
simulation of locally stable point processes. Particularly, a simple dominating coupling from the past (CFTP) algorithm and
the CFTP algorithms introduced in [13], [14], and [5] are studied. Some empirical results for the algorithms are discussed.
Received: 30 June 2002 相似文献
56.
设珮犠(狋):犚犖+ →犚犱是犖指标犱维广义Wiener过程,对任意紧集犈1,…,犈犿犚犖> ,该文研究了犿项代数和珮犠(犈1)…珮犠(犈犿)的Hausdorff维数,Packing维数和正的Lebesgue测度及内点的存在性. 其结果包含并推广了布朗单的结果. 相似文献
57.
曾六川 《数学物理学报(A辑)》2002,22(1):99-106
该文研究Banach空间中一类强增生型变分包含解的存在性及其具误差的Ishikawa迭代程序的收敛性问题.该文结果是几位作者早期与最近的相应结果的改进和推广. 相似文献
58.
A simple simulation scheme that simultaneously describes the growth kinetics of SiO2 films at the nanometer scale and the SiOx/Si interface dynamics (its extent, and spatial/temporal evolution) is presented. The simulation successfully applies to experimental data in the region above and below 10 nm, reproduces the Deal and Grove linear-parabolic law and the oxide growth rate enhancement in the very thin film regime (the so-called anomalous region). According to the simulation, the oxidation is governed mainly by two processes: (a) the formation of a transition suboxide layer and (b) its subsequent drift towards the silicon bulk. We found that it is the superposition of these two processes that produces the crossover from the anomalous oxidation region behavior to the linear-parabolic law. 相似文献
59.
Mariano J. Valderrama 《商业与工业应用随机模型》1991,7(1):93-106
Alternative procedures for representing a stochastic signal as a denumerable series with uncorrelated terms are developed. The study includes considerations about parametric rescaling and its repercussions on the orthogonal expansion, as well as numerical techniques for approaching such an expansion. In addition, applications to the Gaussian characterization of stochastic signals, filtering and stochastic modelling are treated. 相似文献
60.
Piotr Garbaczewski 《Journal of statistical physics》2006,123(2):315-355
We analyze the functioning of Gibbs-type entropy functionals in the time domain, with emphasis on Shannon and Kullback-Leibler entropies of time-dependent continuous probability distributions. The Shannon entropy validity is extended to probability distributions inferred from L
2(R
n
) quantum wave packets. In contrast to the von Neumann entropy which simply vanishes on pure states, the differential entropy quantifies the degree of probability (de)localization and its time development. The associated dynamics of the Fisher information functional quantifies nontrivial power transfer processes in the mean, both in dissipative and quantum mechanical cases.
PACS NUMBERS: 05.45.+b, 02.50.-r, 03.65.Ta, 03.67.-a 相似文献