全文获取类型
收费全文 | 7186篇 |
免费 | 713篇 |
国内免费 | 874篇 |
专业分类
化学 | 2279篇 |
晶体学 | 39篇 |
力学 | 453篇 |
综合类 | 57篇 |
数学 | 602篇 |
物理学 | 1636篇 |
综合类 | 3707篇 |
出版年
2024年 | 45篇 |
2023年 | 99篇 |
2022年 | 243篇 |
2021年 | 248篇 |
2020年 | 298篇 |
2019年 | 219篇 |
2018年 | 223篇 |
2017年 | 237篇 |
2016年 | 281篇 |
2015年 | 258篇 |
2014年 | 400篇 |
2013年 | 448篇 |
2012年 | 415篇 |
2011年 | 453篇 |
2010年 | 298篇 |
2009年 | 395篇 |
2008年 | 361篇 |
2007年 | 482篇 |
2006年 | 448篇 |
2005年 | 406篇 |
2004年 | 349篇 |
2003年 | 279篇 |
2002年 | 253篇 |
2001年 | 248篇 |
2000年 | 179篇 |
1999年 | 174篇 |
1998年 | 147篇 |
1997年 | 110篇 |
1996年 | 133篇 |
1995年 | 99篇 |
1994年 | 86篇 |
1993年 | 69篇 |
1992年 | 66篇 |
1991年 | 45篇 |
1990年 | 64篇 |
1989年 | 45篇 |
1988年 | 42篇 |
1987年 | 39篇 |
1986年 | 25篇 |
1985年 | 14篇 |
1984年 | 12篇 |
1982年 | 11篇 |
1981年 | 8篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1976年 | 3篇 |
1971年 | 3篇 |
1955年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有8773条查询结果,搜索用时 31 毫秒
1.
2.
3.
给出2005年全国部分高校研究生数学建模竞赛D题的研究背景,对参赛论文作了简要评注,并提供了一种参考解答. 相似文献
4.
5.
6.
A.J.?Lpez-Moreno 《Acta Mathematica Hungarica》2005,106(4):343-354
Summary We obtain preservation inequalities for Lipschitz constants of higher order in simultaneous approximation processes by Bernstein type operators. From such inequalities we derive the preservation of the corresponding Lipschitz spaces. 相似文献
7.
详细介绍了双光头同步控制原理.对采集的伺服模块聚焦误差跟踪信号及共焦模块读写光头的聚焦线圈驱动信号进行了频域分析,并以此两路信号作为系统输入输出,分别对三种参数模型进行参数优化.根据3种模型的频率响应及阶跃响应,选择双光头同步控制过程的参数模型为[450]阶的ARX模型.实测曲线与模型仿真结果符合度(fit)为78.0259%. 相似文献
8.
In this paper, we use weighted modules ω(?)(f,t)w to study the pointwise approximation on Szasz-type operators, and obtain the direct and converse theorem, as well as characterizations of the pointwise approximation of Jacobi-weighted Szasz-type operators. 相似文献
9.
Ecaterina Stela Dragan Simona Schwarz 《Journal of polymer science. Part A, Polymer chemistry》2004,42(10):2495-2505
The formation and characterization of some interpolyelectrolyte complex (IPEC) nanoparticles based on poly(sodium 2‐acrylamido‐2‐methylpropanesulfonate) (NaPAMPS), as a function of the polycation structure, polyanion molar mass, and polyion concentration, were followed in this work. Poly(diallyldimethylammonium chloride) and two polycations (PCs) containing (N,N‐dimethyl‐2‐hydroxypropyleneammonium chloride) units in the backbone (PCA5 and PCA5D1) were used as starting polyions. The complex stoichiometry, (n?/n+)iso, was pointed out by optical density at 500 nm (OD500), polyelectrolyte titration, and dynamic light scattering. IPEC nanoparticle sizes were influenced by the polycation structure and polyanion molar mass only before the complex stoichiometry, which was higher for the more hydrophilic polycations (PCA5 and PCA5D1) and for a higher NaPAMPS molar mass, and were almost independent of these factors after that, at a flow rate of the added polyion of about 0.28 mL × (mL PC)?1 × h?1. The IPEC nanoparticle sizes remained almost constant for more than 2 weeks, both before and after the complex stoichiometry, at low concentrations of polyions. NIPECs as stable colloidal dispersions with positive charges in excess were prepared at a ratio between charges (n?/n+) of 0.7, and their storage colloidal stability, as a function of the polycation structure and polyion concentration (from 0.8 to ca. 7.8 mmol/L), was demonstrated. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2495–2505, 2004 相似文献
10.
Hiroaki Miyagawa Michael J. Rich Lawrence T. Drzal 《Journal of Polymer Science.Polymer Physics》2004,42(23):4391-4400
The thermophysical and mechanical properties of a nanocomposite material composed of amine‐cured diglycidyl ether of bisphenol A (DGEBA) reinforced with organomontmorillonite clay are reported. The storage modulus at 100 °C, which was above the glass‐transition temperature (Tg), increased approximately 350% with the addition of 10 wt % (6.0 vol %) of clay. Below the Tg, the storage modulus at 30 °C increased 50% relative to the value of unfilled epoxy. It was determined that the Tg linearly increased as a function of clay volume percent. The tensile modulus of epoxy at room temperature increased approximately 50% with the addition of 10 wt % of clay. The reinforcing effect of the organoclay nanoplatelets is discussed with respect to the Tandon–Weng and Halpin–Tsai models. A pseudoinclusion model is proposed to describe the behavior of randomly oriented, uniformly dispersed platelets in nanocomposite materials. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4391–4400, 2004 相似文献