全文获取类型
收费全文 | 7592篇 |
免费 | 563篇 |
国内免费 | 1334篇 |
专业分类
化学 | 4305篇 |
晶体学 | 55篇 |
力学 | 537篇 |
综合类 | 221篇 |
数学 | 1298篇 |
物理学 | 3073篇 |
出版年
2024年 | 8篇 |
2023年 | 53篇 |
2022年 | 100篇 |
2021年 | 88篇 |
2020年 | 122篇 |
2019年 | 91篇 |
2018年 | 102篇 |
2017年 | 94篇 |
2016年 | 138篇 |
2015年 | 148篇 |
2014年 | 160篇 |
2013年 | 230篇 |
2012年 | 270篇 |
2011年 | 1158篇 |
2010年 | 660篇 |
2009年 | 669篇 |
2008年 | 225篇 |
2007年 | 230篇 |
2006年 | 233篇 |
2005年 | 409篇 |
2004年 | 1037篇 |
2003年 | 610篇 |
2002年 | 487篇 |
2001年 | 400篇 |
2000年 | 147篇 |
1999年 | 137篇 |
1998年 | 161篇 |
1997年 | 108篇 |
1996年 | 87篇 |
1995年 | 58篇 |
1994年 | 58篇 |
1993年 | 229篇 |
1992年 | 210篇 |
1991年 | 125篇 |
1990年 | 116篇 |
1989年 | 112篇 |
1988年 | 91篇 |
1987年 | 7篇 |
1986年 | 69篇 |
1985年 | 12篇 |
1984年 | 26篇 |
1983年 | 7篇 |
1982年 | 3篇 |
1979年 | 2篇 |
1936年 | 2篇 |
排序方式: 共有9489条查询结果,搜索用时 187 毫秒
961.
双周期圆截面纤维复合材料平面问题的解析法 总被引:4,自引:0,他引:4
结合双准周期Riemann边值问题理论与Eshelby等效夹杂原理,为双周期圆截面纤维复合材
料平面问题发展了一个实用有效的解析方法,获得了问题的全场级数解并与有限元结果进行
了比较. 该方法为非均匀材料的力学性质分析和复合材料等新材料的微结构设计提供了
一个有效的计算工具,也可用来评估有限元等数值与近似方法的精度. 相似文献
962.
963.
Ruoyu Hong * Jianmin Ding Guoliang Zheng College of Chemistry Chemical Engineering Soochow University Suzhou P. R. China Institute of Process Engineering Chinese Academy of Sciences Beijing P. R. China IBM HYDA/- C Highway North Rochester MN USA *Author to whom correspondence should be addressed. E-mail: rhong@suda.edu.cn 《中国颗粒学报》2004,2(5):207-214
1. Introduction1.1 Silica nanoparticles and synthesis methods Silica (SiO2) nanoparticles are widely used in industry asan active filler for polymer reinforcement, a rheologicaladditive in fluids, a free flow agent in powders, and anagent for chemical mechanical polishing during IC (inte-grated circuit) fabrication (Sniegowski & de Boer, 2000).Silica powder is also used for producing silicon carbide(Koc & Cattamanchi, 1998) or opaque silica aerosols (Leeet al., 1995). Many methods can … 相似文献
964.
力学可以为农业现代化作贡献 总被引:10,自引:0,他引:10
农业现代化提出了许多与力学各个分支都有密切关系的问题.从农田耕作、农业物料性质、农产品烘干、水果和蔬菜生产、农业生物环境、节水灌溉、农业水土资源合理利用和作物生长等方面,介绍了有关的力学问题和目前的研究进展. 相似文献
965.
Jiang Mingxiao Zhu Weiqiu Zhejiang University Hangzhou P. R. China 《Acta Mechanica Solida Sinica》1996,9(2):169-178
Two stochastic models of fatigue crack growth under constant amplitude cyclic loadingare proposed and studied by using the stochastic averaging method and total probability theorem to ac-count for high frequency component and low frequency component, respectively, of the irregular na-ture of fatigue crack growth observed in Virkler's experiment. Particular attention is paid to the predic-tion performance of the models under a change in the initial crack length. It is shown that the modelsproposed in the present paper yields better agreement with experimental data than other models avail-able in literature. 相似文献
966.
数值研究激波与旋涡的相互作用 总被引:4,自引:1,他引:4
从非定常形式的Euler方程出发,数值模拟了运动激波与旋涡相互作用的非定常流动过程。为保证激波具有较高的分辨率,采用对称型TVD格式进行了数值计算。结果表明。这样可以有效地模拟流场中一些复杂的流动现象,如激波变形、激波分叉和三波点的形成,以及旋涡结构的变化过程等,并与已有的实验流动显示相符良好。同时,也是对TVD格式求解这类问题的一次初步尝试。 相似文献
967.
968.
Cuprous Oxide Catalyzed Oxidative CC Bond Cleavage for CN Bond Formation: Synthesis of Cyclic Imides from Ketones and Amines
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Min Wang Dr. Jianmin Lu Dr. Jiping Ma Zhe Zhang Prof. Feng Wang 《Angewandte Chemie (International ed. in English)》2015,54(47):14061-14065
Selective oxidative cleavage of a C? C bond offers a straightforward method to functionalize organic skeletons. Reported herein is the oxidative C? C bond cleavage of ketone for C? N bond formation over a cuprous oxide catalyst with molecular oxygen as the oxidant. A wide range of ketones and amines are converted into cyclic imides with moderate to excellent yields. In‐depth studies show that both α‐C? H and β‐C? H bonds adjacent to the carbonyl groups are indispensable for the C? C bond cleavage. DFT calculations indicate the reaction is initiated with the oxidation of the α‐C? H bond. Amines lower the activation energy of the C? C bond cleavage, and thus promote the reaction. New insight into the C? C bond cleavage mechanism is presented. 相似文献
969.
Effect of polyethylene glycol on the crystallization and impact properties of polylactide‐based blends
下载免费PDF全文
![点击此处可从《先进技术聚合物》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Polylactide (PLA) was plasticized by polyethylene glycols (PEGs) with five different molecular weights (Mw = 200–20,000 g/mol). The effects of content and molecular weight of PEG on the crystallization and impact properties of PLA were studied by wide‐angle X‐ray diffraction, differential scanning calorimetry, scanning electron microscopy, transmission electron microscopy, and V‐notched impact tests, respectively. The results revealed that PEG‐10,000 could significantly improve the crystallization capacity and impact toughness of PLA. When the PEG‐10,000 content ranged from 0 to 20 wt%, the increases in both V‐notched Izod and Charpy impact strengths of PLA/PEG‐10,000 blends were 206.10% and 137.25%, respectively. Meanwhile, the crystallinity of PLA/PEG‐10,000 blends increased from 3.95% to 43.42%. For 10 wt% PEG content, the crystallization and impact properties of PLA/PEG blends mainly depended upon PEG molecular weight. With increasing the Mw of PEG, the crystallinity and impact strength of PLA/PEG blends first decreased and then increased. The introduction of PEG reduced the intermolecular force and enhanced the mobility of PLA chains, thus improving the crystallization capacity and flexibility of PLA. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
970.
Zhe Sun Parantap Sarkar Takuya Suenaga Sota Sato Hiroyuki Isobe 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2015,127(43):12991-12995
The recent development of cyclo‐para‐phenylenes has demonstrated the feasibility of radial π systems in nanohoop structures, especially in the crystalline state. However, in contrast to macrocyclic molecules with benzene units, which have a several‐decades‐long history, macrocycles composed solely of naphthylene units (the smallest acene) have been much less explored. Although two examples of cyclonaphthylenes have been reported to date, neither possesses a radial π system. We herein report the first example of belt‐shaped cyclonaphthylenes with curved π systems. The molecule, [8]cyclo‐amphi‐naphthylene, is linked at the 2,6‐positions of the naphthylene units, thus affording belt‐shaped molecules. Although the molecular structures are flexible, which allows for rotation of the naphthylene units in solution, they can be rigidified with the aid of methylene bridges to afford persistent molecular structures in solution. 相似文献