全文获取类型
收费全文 | 43928篇 |
免费 | 5523篇 |
国内免费 | 2869篇 |
专业分类
化学 | 5454篇 |
晶体学 | 184篇 |
力学 | 6179篇 |
综合类 | 553篇 |
数学 | 26565篇 |
物理学 | 13385篇 |
出版年
2024年 | 81篇 |
2023年 | 381篇 |
2022年 | 510篇 |
2021年 | 662篇 |
2020年 | 1202篇 |
2019年 | 1167篇 |
2018年 | 1105篇 |
2017年 | 1159篇 |
2016年 | 1266篇 |
2015年 | 1039篇 |
2014年 | 1875篇 |
2013年 | 3453篇 |
2012年 | 2026篇 |
2011年 | 2402篇 |
2010年 | 2316篇 |
2009年 | 2598篇 |
2008年 | 2812篇 |
2007年 | 2887篇 |
2006年 | 2494篇 |
2005年 | 2475篇 |
2004年 | 2068篇 |
2003年 | 2078篇 |
2002年 | 1891篇 |
2001年 | 1527篇 |
2000年 | 1422篇 |
1999年 | 1338篇 |
1998年 | 1221篇 |
1997年 | 1038篇 |
1996年 | 828篇 |
1995年 | 724篇 |
1994年 | 567篇 |
1993年 | 483篇 |
1992年 | 420篇 |
1991年 | 404篇 |
1990年 | 308篇 |
1989年 | 190篇 |
1988年 | 206篇 |
1987年 | 189篇 |
1986年 | 186篇 |
1985年 | 198篇 |
1984年 | 167篇 |
1983年 | 88篇 |
1982年 | 153篇 |
1981年 | 154篇 |
1980年 | 99篇 |
1979年 | 117篇 |
1978年 | 97篇 |
1977年 | 69篇 |
1976年 | 54篇 |
1973年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
We obtain a solution of the DGLAP equation for the gluon at low x first by expanding the gluon in a Taylor series and then using the method of characteristics. We test its validity by comparing
it with that of Glück, Reya and Vogt. The convergence criteria of the approximation used are also discussed. We also calculate
εF
2(x,Q)2/ε In Q
2 using its approximate relations with the gluon distribution at low x. The predictions are then compared with the HERA data. 相似文献
62.
63.
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
64.
在保持非负定性不变的前提下,本文对矩阵每一元素容许多大的扰动作了进一步的研究, 将本文的结论和C.R.Johnson提出的部分正定阵的正定完备化进行比较,容易发现对已知的正定矩阵求扰动,本文的结论比用C.R.Johnson的正定完备化计算扰动形式上更简单,同时也给出了不同于C.R.Johnson的部分正定阵的正定完备化表示的另外一个公式,推出了这些正定完备化矩阵应具有的若干性质. 相似文献
65.
66.
A. V. Bobylev 《Journal of statistical physics》2006,124(2-4):371-399
It is well-known that the classical Chapman-Enskog procedure does not work at the level of Burnett equations (the next step after the Navier-Stokes equations). Roughly speaking, the reason is that the solutions of higher equations of hydrodynamics (Burnett's, etc.) become unstable with respect to short-wave perturbations. This problem was recently attacked by several authors who proposed different ways to deal with it. We present in this paper one of possible alternatives. First we deduce a criterion for hyperbolicity of Burnett equations for the general molecular model and show that this criterion is not fulfilled in most typical cases. Then we discuss in more detail the problem of truncation of the Chapman-Enskog expansion and show that the way of truncation is not unique. The general idea of changes of coordinates (based on analogy with the theory of dynamical systems) leads finally to nonlinear Hyperbolic Burnett Equations (HBEs) without using any information beyond the classical Burnett equations. It is proved that HBEs satisfy the linearized H-theorem. The linear version of the problem is studied in more detail, the complete Chapman-Enskog expansion is given for the linear case. A simplified proof of the Slemrod identity for Burnett coefficients is also given. 相似文献
67.
Cai Xiaochun 《Annals of Differential Equations》2006,22(1):1-6
In this paper, we apply a critical point theorem and obtain the condition for the existence of three solutions to two-point boundary value problem of a second order nonlinear difference equation. 相似文献
68.
The molding processes of polymer melts involve geometrically complex dies. Such dies are usually tapered or streamlined to achieve a maximum output rate under conditions of laminar flow. The model of a generalized second-grade fluid of power-law type is used and the results obtained are illustrated by examples of convergent flows in conical and wedge-shaped dies. 相似文献
69.
Benjamin J. K. Evans Susan M. Scott Antony C. Searle 《General Relativity and Gravitation》2002,34(10):1675-1684
We have developed a new tool for numerical work in General Relativity: GRworkbench. We discuss how GRworkbench's implementation of a numerically-amenable analogue to Differential Geometry facilitates the development of robust and chart-independent numerical algorithms. We consider, as an example, geodesic tracing on two charts covering the exterior Schwarzschild space-time. 相似文献
70.
This paper is concerned with the implementation and testing of an algorithm for solving constrained least-squares problems. The algorithm is an adaptation to the least-squares case of sequential quadratic programming (SQP) trust-region methods for solving general constrained optimization problems. At each iteration, our local quadratic subproblem includes the use of the Gauss–Newton approximation but also encompasses a structured secant approximation along with tests of when to use this approximation. This method has been tested on a selection of standard problems. The results indicate that, for least-squares problems, the approach taken here is a viable alternative to standard general optimization methods such as the Byrd–Omojokun trust-region method and the Powell damped BFGS line search method. 相似文献