全文获取类型
收费全文 | 4136篇 |
免费 | 347篇 |
国内免费 | 98篇 |
专业分类
化学 | 758篇 |
晶体学 | 33篇 |
力学 | 131篇 |
综合类 | 84篇 |
数学 | 261篇 |
物理学 | 892篇 |
无线电 | 2422篇 |
出版年
2024年 | 2篇 |
2023年 | 13篇 |
2022年 | 31篇 |
2021年 | 104篇 |
2020年 | 114篇 |
2019年 | 29篇 |
2018年 | 37篇 |
2017年 | 109篇 |
2016年 | 136篇 |
2015年 | 140篇 |
2014年 | 193篇 |
2013年 | 252篇 |
2012年 | 181篇 |
2011年 | 175篇 |
2010年 | 153篇 |
2009年 | 155篇 |
2008年 | 221篇 |
2007年 | 242篇 |
2006年 | 220篇 |
2005年 | 235篇 |
2004年 | 238篇 |
2003年 | 240篇 |
2002年 | 204篇 |
2001年 | 179篇 |
2000年 | 158篇 |
1999年 | 107篇 |
1998年 | 124篇 |
1997年 | 102篇 |
1996年 | 109篇 |
1995年 | 74篇 |
1994年 | 72篇 |
1993年 | 44篇 |
1992年 | 26篇 |
1991年 | 28篇 |
1990年 | 17篇 |
1989年 | 14篇 |
1988年 | 12篇 |
1987年 | 12篇 |
1986年 | 18篇 |
1985年 | 18篇 |
1984年 | 16篇 |
1983年 | 6篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1976年 | 4篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1967年 | 2篇 |
1966年 | 1篇 |
排序方式: 共有4581条查询结果,搜索用时 31 毫秒
101.
102.
103.
研究了客体模型FTO的闪光照相系统X光输运过程,给出了直穿照射量、散射照射量、直散比、直穿照射量能谱、散射照射量能谱、直穿X光通量能谱和散射X光通量能谱在记录平面的空间分布。结果表明:后锥是照射量散射成分的主要来源,后锥照射量占总散射量97%;后锥也是造成散射的空间分布不均匀的主要器件,这一不均匀性高达58%。照相系统的最小直散比非常小,表明锥造成的散射已经严重地淹没了直穿(轫致辐射)信号。计算中使用高空间分辨率记录法进行分点,合成图像对吸收系数的复原结果与国外报道的结果相符。 相似文献
104.
《Journal of Polymer Science.Polymer Physics》2018,56(3):255-264
The influence of monomer functionality on the mechanical properties of epoxies is studied using molecular dynamics (MD) with the Reax Force Field (ReaxFF). From deformation simulations, the Young's modulus, yield point, and Poisson's ratio are calculated and analyzed. Comparison between the network structures of distinct epoxies is further advanced by the monomeric degree index (MDI). Experimental validation demonstrates the MD results correctly predict the relationship in Young's moduli. Therefore, ReaxFF is confirmed to be a useful tool for studying the mechanical behavior of epoxies. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 255–264 相似文献
105.
Multiaxial mechanical behavior of aramid fibers and identification of skin/core structure from single fiber transverse compression testing
下载免费PDF全文
![点击此处可从《Journal of Polymer Science.Polymer Physics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Judith Wollbrett‐Blitz Sébastien Joannès Rémi Bruant Christophe Le Clerc Marc Romero De La Osa Anthony Bunsell Alba Marcellan 《Journal of Polymer Science.Polymer Physics》2016,54(3):374-384
The transverse and longitudinal mechanical properties of aramid fibers like Kevlar? 29 (K29) fibers are strongly linked to their highly oriented structure. Mechanical characterization at the single fiber scale is challenging especially when the diameter is as small as 15 µm. Longitudinal tensile tests on single K29 fibers and single fiber transverse compression test (SFTCT) have been developed. Our approach consists of coupling morphological observations and mechanical experiments with SFTCT analysis by comparing analytical solutions and finite element modeling. New insights on the analysis of the transverse direction response are highlighted. Systematic loading/unloading compression tests enable to experimentally determine a transverse elastic limit. Taking account of the strong anisotropy of the fiber, the transverse mechanical response sheds light on a skin/core architecture. More importantly, results suggest that the skin of the fiber, typically representing a shell of one micrometer in thickness, has a transverse apparent modulus of 0.2 GPa. That is around more than fifteen times lower than the transverse modulus of 3.0 GPa in the core. By comparison, the measured longitudinal modulus is about 84 GPa. The stress distribution in the fiber is explored and the critical areas for damage initiation are discussed. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 374–384 相似文献
106.
F. L. Vook 《辐射效应与固体损伤》2013,168(3-4):155-160
This paper was given as the opening address at the 1970 Albany International Conference on Radiation Effects in Semiconductors, and it attempts to establish a general overview of the field by concentrating on recent research developments and important unanswered questions. The continuing importance of impurity-defect interactions, of microscopic defect identification, and of the necessity for more theoretical calculations are emphasized. The rapid development of the field of ion implantation and its close relationship with radiation effects studies are pointed out. It is predicted that research in compound semiconductors will increase rapidly with close beneficial interaction with ion implantation studies. 相似文献
107.
易经是中华民族宝贵文化遗产,它包含上古时期人们对自然宇宙和人生社会的思想认识、哲学理念和辩证法,代表了先民哲学地把握宇宙的思维成果.现代科学的许多重大发现和突破,如二进制、原子结构、生物遗传DNA等学科理论,都可以从八卦和六十四卦模型中发现与之对应的形态和哲学思维.计算机体系结构设计原理(PPCAD)应是易经这种形态和思维的一种自然现象和映射对象,利用八卦和六十四卦哲学思维和策略,提供PPCAD的思路和策略是本文的目标.本文依据PPCAD中的基本推演理念,提炼出4对基本对立统一推演关系,根据4对基本关系构造了新的易经八卦及六十四卦.同时,结合体系结构设计中的层次模型方法,指出了易经层次模型的特点及动态性.为了便于对PPCAD易经模型的理解,我们选择了10个新卦的例子加以说明和表达,同时也给出了一些PPCAD原则和策略的新观察.我们想指出,我们的新易经模型方法不但可用于计算机体系结构的设计,也可尝试用于其他复杂系统的设计原理.最后,对全文进行了总结,并对下一步的研究进行了展望. 相似文献
108.
In this paper, we establish new sufficient conditions for the infected equilibrium of a nonresident computer virus model to be globally asymptotically stable. Our results extend two kind of known results in recent literature. 相似文献
109.
网络时代计算机通信与控制技术应用在各行各业之中,在获得这项技术带来的便利之时,其可靠性也受到人们的关注,并成为计算机发展的重要研究课题。本文首先对其可靠性理论进行了探讨,并重点分析了影响其可靠性的因素,从而提出了提升计算机通信与控制系统的策略。 相似文献
110.
Molecular dynamics simulation of poly(3‐hexylthiophene) helical structure In Vacuo and in amorphous polymer surrounding
下载免费PDF全文
![点击此处可从《Journal of Polymer Science.Polymer Physics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Natalia I. Borzdun Sergey V. Larin Stanislav G. Falkovich Victor M. Nazarychev Igor V. Volgin Alexander V. Yakimansky Alexey V. Lyulin Vikas Negi Peter A. Bobbert Sergey V. Lyulin 《Journal of Polymer Science.Polymer Physics》2016,54(23):2448-2456
The stability of poly(3‐hexylthiophene) (P3HT) helical structure has been investigated in vacuo and in amorphous polymer surrounding via molecular dynamics‐based simulations at temperatures below and above the P3HT melting point. The results show that the helical chain remains stable at room temperature both in vacuo and in amorphous surrounding, and promptly loses its structure at elevated temperatures. However, the amorphous surrounding inhibits the destruction of the helix at higher temperatures. In addition, it is shown that the electrostatic interactions do not significantly affect the stability of the helical structure. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2448–2456 相似文献