全文获取类型
收费全文 | 17315篇 |
免费 | 1907篇 |
国内免费 | 1622篇 |
专业分类
化学 | 8431篇 |
晶体学 | 149篇 |
力学 | 909篇 |
综合类 | 105篇 |
数学 | 1494篇 |
物理学 | 4633篇 |
综合类 | 5123篇 |
出版年
2024年 | 59篇 |
2023年 | 218篇 |
2022年 | 373篇 |
2021年 | 420篇 |
2020年 | 451篇 |
2019年 | 391篇 |
2018年 | 359篇 |
2017年 | 359篇 |
2016年 | 533篇 |
2015年 | 536篇 |
2014年 | 746篇 |
2013年 | 968篇 |
2012年 | 1057篇 |
2011年 | 1162篇 |
2010年 | 793篇 |
2009年 | 870篇 |
2008年 | 960篇 |
2007年 | 925篇 |
2006年 | 843篇 |
2005年 | 819篇 |
2004年 | 648篇 |
2003年 | 518篇 |
2002年 | 498篇 |
2001年 | 473篇 |
2000年 | 432篇 |
1999年 | 612篇 |
1998年 | 596篇 |
1997年 | 558篇 |
1996年 | 527篇 |
1995年 | 460篇 |
1994年 | 472篇 |
1993年 | 332篇 |
1992年 | 296篇 |
1991年 | 266篇 |
1990年 | 295篇 |
1989年 | 204篇 |
1988年 | 180篇 |
1987年 | 158篇 |
1986年 | 123篇 |
1985年 | 82篇 |
1984年 | 52篇 |
1983年 | 36篇 |
1982年 | 37篇 |
1981年 | 29篇 |
1980年 | 21篇 |
1979年 | 17篇 |
1978年 | 16篇 |
1976年 | 8篇 |
1973年 | 10篇 |
1970年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
5‐Methylene‐2‐oxazolidinone (1) and 5‐methylene‐1,3‐thiazolidine‐2‐thione (4) react with various isocyanates to give the corresponding urethanes 3 and 5 in high yields in the presence of palladium(0) or palladium(II) catalyst under mild reaction conditions. A mechanism is proposed. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
32.
Yu Zanping Zhou Zheyan School of Math.and Computer Science Fujian Normal University Fuzhou ) Shen Jianhe 《Annals of Differential Equations》2007,23(3):365-372
The paper aims to obtain existence and uniqueness of the solution as well as asymptotic estimate of the solution for singularly perturbed nonlinear third- order Robin boundary value problem with a turning point.In order to achieve this aim,existence and uniqueness of the solution for third-order nonlinear Robin boundary value problem is derived first based on the upper and lower solutions method under relatively weaker conditions.In this manner,the goal of this paper is gained by applying the existence and uniqueness results mentioned above. 相似文献
33.
超软X射线流气式正比计数管 总被引:2,自引:0,他引:2
介绍了一种用于测量183~933eV超软X射线的圆柱形、侧窗式、流气式正比计数管,工作气体是0.11MPa的P-10气体或氦气-丙烷混合气体。计数管内径为φ25mm,直径为φ0.3mm的入射窗是由厚度80~90μgcm~2聚乙烯甲醛制成的。该计数管的特点:(1)薄窗,对软X射线透过率高。(2)流气式,工作寿命长。(3)能量分辨率好。(4)计数率高(1×10~(14)个/s)。(5)可测能区宽(0.183~10keV)。(6)可以方便更换窗膜材料、厚度及窗口直径。近几年来该计数管已经为高强度低能X光源提供较好监测。 相似文献
34.
本文论述应用光学薄膜技术对汽车窗口玻璃和塑料的若干性能进行改进的技术发展水平,这些性能包括塑料表面的硬化,红外区的反射,紫外区的吸收,偏振化作用,双折射,憎水性以及光学角度选择性等,评论等离子体处理和物理蒸汽淀积薄膜工艺近来应用的一些例子。对于物理蒸汽淀积薄膜所提供的异常功能连同实际使用中它们的耐久性作了特殊的强调。 相似文献
35.
本文对某一型号的一类轴流通风机的出口紊流流场进行了测量,得出了风机出口流场紊流度的变化特性和紊流流场的波形图,根据实验结果的分析,指出了该类通风机的空气动力噪声源。 相似文献
36.
本文在系统阐述当代跨国经营战略调整与发展趋势的基础上,简要剖析了现阶段我国企业跨国经营的主要问题,重点探讨了我国跨国企业发展战略的基本构想。 相似文献
37.
38.
39.
T. Ramanathan S. Stankovich D. A. Dikin H. Liu H. Shen S. T. Nguyen L. C. Brinson 《Journal of Polymer Science.Polymer Physics》2007,45(15):2097-2112
Mechanical, thermal, and electrical properties of graphite/PMMA composites have been evaluated as functions of particle size and dispersion of the graphitic nanofiller components via the use of three different graphitic nanofillers: “as received graphite” (ARG), “expanded graphite,” (EG) and “graphite nanoplatelets” (GNPs) EG, a graphitic materials with much lower density than ARG, was prepared from ARG flakes via an acid intercalation and thermal expansion. Subsequent sonication of EG in a liquid yielded GNPs as thin stacks of graphitic platelets with thicknesses of ~10 nm. Solution‐based processing was used to prepare PMMA composites with these three fillers. Dynamic mechanical analysis, thermal analysis, and electrical impedance measurements were carried out on the resulting composites, demonstrating that reduced particle size, high surface area, and increased surface roughness can significantly alter the graphite/polymer interface and enhance the mechanical, thermal, and electrical properties of the polymer matrix. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2097–2112, 2007 相似文献
40.
Crosslinking behaviors of acrylonitrile butadiene rubber (NBR)/poly (vinyl chloride) (PVC) alloy, filled with anhydrous copper sulfate (CuSO4) particles, were investigated for the first time by dynamic mechanical analysis (DMA) under hetero and isothermal modes, respectively. In the heterothermal testing, (NBR/PVC)/CuSO4 compound showed two marked increases in the storage modulus (E′), corresponding to coordination crosslinking of NBR-CuSO4 and self-crosslinking of NBR and PVC respectively. During the isothermal testing, a dramatic increase in E′ was found at the initial stage while that of original NBR/PVC alloy was not detected. The marked increase in E′ of (NBR/PVC)/CuSO4 compound was mainly due to the crosslinking induced by coordination between CN and Cu2+. The increasing extent of E′ increased with the rise of CuSO4 content, suggesting the formation of a greater number of crosslinks. Moreover, the activation energy (Ea) of crosslinking process was about 139 kJ/mol. In this work, fourier transform infrared spectrum (FT-IR) and equilibrium swelling method were also performed for the characterization of the compound. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 41–51, 2007 相似文献