全文获取类型
收费全文 | 4990篇 |
免费 | 567篇 |
国内免费 | 404篇 |
专业分类
化学 | 3050篇 |
晶体学 | 91篇 |
力学 | 762篇 |
综合类 | 63篇 |
数学 | 574篇 |
物理学 | 1421篇 |
出版年
2024年 | 23篇 |
2023年 | 71篇 |
2022年 | 184篇 |
2021年 | 193篇 |
2020年 | 263篇 |
2019年 | 243篇 |
2018年 | 192篇 |
2017年 | 257篇 |
2016年 | 307篇 |
2015年 | 225篇 |
2014年 | 238篇 |
2013年 | 622篇 |
2012年 | 214篇 |
2011年 | 218篇 |
2010年 | 204篇 |
2009年 | 210篇 |
2008年 | 208篇 |
2007年 | 239篇 |
2006年 | 225篇 |
2005年 | 217篇 |
2004年 | 198篇 |
2003年 | 181篇 |
2002年 | 154篇 |
2001年 | 127篇 |
2000年 | 105篇 |
1999年 | 100篇 |
1998年 | 79篇 |
1997年 | 72篇 |
1996年 | 47篇 |
1995年 | 71篇 |
1994年 | 50篇 |
1993年 | 31篇 |
1992年 | 40篇 |
1991年 | 18篇 |
1990年 | 17篇 |
1989年 | 16篇 |
1988年 | 12篇 |
1987年 | 6篇 |
1986年 | 25篇 |
1985年 | 9篇 |
1984年 | 8篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 12篇 |
1978年 | 3篇 |
1976年 | 2篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1971年 | 6篇 |
排序方式: 共有5961条查询结果,搜索用时 15 毫秒
1.
Nanocomposite hydrogel consisting of Na‐montmorillonite with enhanced mechanical properties 下载免费PDF全文
Ting Li Shuangfei Xiang Piming Ma Huiyu Bai Weifu Dong Mingqing Chen 《Journal of Polymer Science.Polymer Physics》2015,53(14):1020-1026
A new kind of nanocomposite (NC) hydrogel with Na‐montmorillonite (MMT) is presented in this article. The NC hydrogels were synthesized by free radical copolymerization of acrylamide and (3‐acrylamidopropyl) trimethylammonium chloride (ATC) in the presence of MMT and N,N′‐methylene‐bis‐acrylamide used as chemical cross‐linker. Due to the cation‐exchange reaction between MMT and ATC (cationic monomer) during the synthesis of NC hydrogels, MMT platelets were considered chemical “plane” cross‐linkers, different from “point” cross‐linkers. With increasing amount of MMT, the crosslinking degree enhanced, causing a decrease of the swelling degree at equilibrium. Investigations of mechanical properties indicated that NC hydrogels exhibited enhanced strength and toughness, which resulted from chemical interaction between exfoliated MMT platelets and polymer chains in hydrogels. Dynamic shear measurements showed that both storage modulus and loss modulus increased with increasing MMT content. The idea described here provided a new route to prepare hydrogels with high mechanical properties by using alternative natural Na‐MMT. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1020–1026 相似文献
2.
3.
Maria Kordaki Athanasia Balomenou 《International Journal of Computers for Mathematical Learning》2006,11(1):99-135
This study focuses on the constructions in terms of area and perimeter in equivalent triangles developed by students aged 12–15 years-old, using the tools provided by Cabri-Geometry II [Labore (1990). Cabri-Geometry (software), Université de Grenoble]. Twenty-five students participated in a learning experiment where they were asked to construct: (a) pairs of equivalent triangles “in as many ways as possible” and to study their area and their perimeter using any of the tools provided and (b) “any possible sequence of modifications of an original triangle into other equivalent ones”. As regards the concept of area and in contrast to a paper and pencil environment, Cabri provided students with different and potential opportunities in terms of: (a) means of construction, (b) control, (c) variety of representations and (d) linking representations, by exploiting its capability for continuous modifications. By exploiting these opportunities in the context of the given open tasks, students were helped by the tools provided to develop a broader view of the concept of area than the typical view they would construct in a typical paper and pencil environment. 相似文献
4.
论大学物理实验体系建设与教学改革 总被引:3,自引:1,他引:2
传统的物理实验是按普通物理、电子线路和近代物理等内容进行划分,这种体系突出了学科的系统性,但忽视了学科之间的兼容互补性,各学科相互独立,限制了学生跨学科思维能力和创新能力的培养,建立现代物理实验教学新体系是大学物理实验教学改革的必然趋势.新的物理实验体系应依照训练层次,划分为引导性实验、基本实验、综合性实验、设计性实验、研究性实验.并需要注重时代性和先进性,改革和更新大学物理实验教学内容,改革实验教学与管理模式,形成新的运行机制,从而达到学生素质和能力的提高. 相似文献
5.
6.
复合体系方法测量液体力学谱 总被引:2,自引:0,他引:2
本文介绍了采用复合体系,测量得到凝聚态物质从固态到液态连续变化力学谱的一种新的实验方法。以簧振动为例,给出了解析的计算公式,以及应用条件。通过进一步综合分析,得到具有更广应用范围的近似公式,可以近似应用于其他不同的振动模式,如低频扭摆。应用新的测量方法,给出了典型小分子玻璃材料甘油和碳酸丙稀从玻璃态到液态的力学谱,观察到甘油和碳酸丙稀玻璃化转变、碳酸丙稀的再结晶、熔化和挥发的过程;测量得到挥发过程中水的质量随时间精确变化的曲线。最后,本文给出了新方法的一些应用展望。 相似文献
7.
The effect of the amount of desorbed water on the mechanical properties of composites based on low-density polyethylene and linen yarn production waste (LW) is analyzed by statistical methods. It is shown that the amount of absorbed water decreases during the desorption process at room temperature both for specimens modified and unmodified with diphenylmethane diisocyanate (DIC.) The most sensitive to the action of water is the elastic modulus, which decreases considerably under the effect of water and is fully restored in the desorption process. The tensile strain also increases with the amount of absorbed water. It is found that the elastic modulus of the unmodified composite correlates linearly with the amount of desorbed water. Between the amount of desorbed water and the tensile strain, as well the specific work of deformation, a negative linear correlation is revealed. After water desorption, all strength and deformation characteristics of both the modified and unmodified composites are fully recovered.__________Translated from Mekhanika Kompozitnykh Materialov, Vol. 41, No. 4, pp. 515–524, July–August, 2005. 相似文献
8.
9.
两部美国大学物理教材对我们教学改革的启示 总被引:9,自引:1,他引:8
介绍了美国两部大学物理教材的特点,分析了美国教材在教学内容、教学方法、教学手段现代化方面的特色,为我们的教学改革提供一些可供借鉴的经验。 相似文献
10.
J. M. Martínez‐Burgos R. Benavente E. Prez M. L. Cerrada 《Journal of Polymer Science.Polymer Physics》2003,41(11):1244-1255
Several composites were prepared on the basis of an ethylene homopolymer and different copolymers of ethylene and 1‐hexene, synthesized with a metallocene catalyst, as matrices and a content of a 5 wt % of short glass fiber. The effect of the fiber incorporation on the structure and mechanical and viscoelastic behaviors was analyzed for the different samples. The glass fibers induced a slightly higher crystallinity, and the crystallite morphology significantly changed (long spacings and crystal orientation). The incorporation of fibers did not reinforce the different matrices under study at this low content; consequently, the mechanical parameters, such as Young's modulus, yielding stress, and microhardness, were lower in the composites as compared with those values found in the neat polyolefins. The location and apparent activation energies of distinct relaxation processes are also discussed. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1244–1255, 2003 相似文献