全文获取类型
收费全文 | 144407篇 |
免费 | 23891篇 |
国内免费 | 14456篇 |
专业分类
化学 | 97198篇 |
晶体学 | 1434篇 |
力学 | 9679篇 |
综合类 | 993篇 |
数学 | 17982篇 |
物理学 | 55468篇 |
出版年
2024年 | 332篇 |
2023年 | 2851篇 |
2022年 | 4115篇 |
2021年 | 4808篇 |
2020年 | 5611篇 |
2019年 | 5187篇 |
2018年 | 4697篇 |
2017年 | 4191篇 |
2016年 | 6589篇 |
2015年 | 6378篇 |
2014年 | 7785篇 |
2013年 | 10283篇 |
2012年 | 12646篇 |
2011年 | 13254篇 |
2010年 | 8841篇 |
2009年 | 8681篇 |
2008年 | 9169篇 |
2007年 | 8195篇 |
2006年 | 7752篇 |
2005年 | 6436篇 |
2004年 | 5043篇 |
2003年 | 3923篇 |
2002年 | 3579篇 |
2001年 | 3122篇 |
2000年 | 2811篇 |
1999年 | 3184篇 |
1998年 | 2771篇 |
1997年 | 2595篇 |
1996年 | 2644篇 |
1995年 | 2273篇 |
1994年 | 2049篇 |
1993年 | 1786篇 |
1992年 | 1560篇 |
1991年 | 1387篇 |
1990年 | 1141篇 |
1989年 | 940篇 |
1988年 | 703篇 |
1987年 | 619篇 |
1986年 | 584篇 |
1985年 | 531篇 |
1984年 | 337篇 |
1983年 | 282篇 |
1982年 | 233篇 |
1981年 | 165篇 |
1980年 | 118篇 |
1979年 | 56篇 |
1978年 | 57篇 |
1977年 | 52篇 |
1975年 | 57篇 |
1973年 | 57篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
991.
992.
Effects of barium on the nonlinear electrical characteristics and dielectric properties of SnO2-based varistors
下载免费PDF全文
![点击此处可从《中国物理》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The effects of barium on electrical and dielectric properties of the SnO_2·Co_2O_3·Ta_2O_5 varistor system sintered at 1250℃ for 60min were investigated. It is found that barium significantly improves the nonlinear properties. The breakdown electrical field increases from 378.0 to 2834.5V/mm, relative dielectric constant (at 1kHz) falls from 1206 to 161 and the resistivity (at 1kHz) rises from 60.3 to 1146.5kΩ·cm with an increase of BaCO_3 concentration from 0mol% to 1.00mol%. The sample with 1.00mol% barium has the best nonlinear electrical property and the highest nonlinear coefficient (α=29.2). A modified defect barrier model is introduced to illustrate the grain-boundary barrier formation of barium-doped SnO_{2}-based varistors. 相似文献
993.
Low-threshold, high-efficiency, high-repetition-rate optical parametric generator based on periodically poled LiNbO3
下载免费PDF全文
![点击此处可从《中国物理》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We report a high-repetition-rate optical parametric generator (OPG) with a periodically poled lithium niobate (PPLN) crystal pumped by an acousto-optically Q-switched CW-diode-end-pumped Nd:YVO_4 laser. For the maximum 1064nm pump power of 970mW, the maximum conversion efficiency is 32.9% under the conditions of 250℃, 1064nm pulse repetition rate of 22.6kHz and pulse width of 12ns, and the PPLN OPG threshold in the collinear case is less than 23.7μJ. The output power increases with the increase of the crystal temperature. The 1485-1553nm signal wave and 3383-3754nm idler wave are obtained by changing the temperature and the angle of the PPLN crystal. 相似文献
994.
Xicheng Zhang 《Bulletin des Sciences Mathématiques》2004,128(5):333-340
In this paper we give a representation formula for the heat semigroup on adapted vector fields by the horizontal lift of Ornstein-Uhlenbeck process over Riemannian path space. 相似文献
995.
Y.-D Feng Y.-S. Wang Z.-M. Zhang 《Archive of Applied Mechanics (Ingenieur Archiv)》2003,73(5-6):337-347
Summary A 2D time-domain Boundary Element Method (BEM) is applied to solve the problem of transient scattering of plane waves by an inclusion with a unilateral smooth contact interface. The incident wave is assumed strong enough so that localized separations take place along the interface. The present problem is indeed a nonlinear boundary value problem since the mixed boundary conditions involve unknown intervals (separation and contact regions). In order to determine the unknown intervals, an iterative technique is developed. As an example, we consider the scattering of plane waves by the cross section of a circular cylinder embedded in an infinite solid. Numerical results for the near field solutions are presented. The distortion of the response waves and the variation of the interface states are discussed.
The financial support by the China National Natural Science Foundation under Grant No. 19872001 and No. 59878004 is gratefully acknowledged. The second author is also grateful to the support of the National Science Fund for Distinguished Young Scholars under Grant No. 10025211. 相似文献
996.
Ke-Zhi Li Jian Wei He-Jun Li Yu-Lei Zhang Chuang Wang Dang-She Hou 《Applied Surface Science》2007,253(18):7365-7368
Well-aligned carbon nanotubes (CNTs) of high quality were synthesized by pyrolysis of phenolic resin at 800 °C in anodic alumina oxide (AAO) pores under argon protection. The innocuous source materials and safe operational conditions permit this method to synthesize well-aligned CNTs in large-scale and low cost. The formation mechanism of the synthesized CNTs is also proposed in this work by a series of visual sketches and is proved with obvious evidence. Firstly, phenolic resin nanotubes form in the template pores through the evaporation of solvent. Heat treatment then transfers these tubes into CNTs. 相似文献
997.
998.
Peng Ping Wenshou Wang Xuesi Chen Xiabin Jing 《Journal of Polymer Science.Polymer Physics》2007,45(5):557-570
Poly(ε‐caprolactone)‐based segmented polyurethanes (PCLUs) were prepared from poly(ε‐caprolactone) diol, diisocyanates (DI), and 1,4‐butanediol. The DIs used were 4,4′‐diphenylmethane diisocyanate (MDI), 2,4‐toluenediisocyanate (TDI), isophorone diisocyanate (IPDI), and hexamethylene diisocyanate (HDI). Differential scanning calorimetry, small‐angle X‐ray scattering, and dynamic mechanical analysis were employed to characterize the two‐phase structures of all PCLUs. It was found that HDI‐ and MDI‐based PCLUs had higher degree of microphase separation than did IPDI‐ and TDI‐based PCLUs, which was primarily due to the crystallization of HDI‐ and MDI‐based hard‐segments. As a result, the HDI‐based PCLU exhibited the highest recovery force up to 6 MPa and slowest stress relaxation with increasing temperature. Besides, it was found that the partial damage in hard‐segment domains during the sample deformation was responsible for the incomplete shape‐recovery of PCLUs after the first deformation, but the damage did not develop during the subsequent deformation. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 557–570, 2007 相似文献
999.
Nanosized ZnOs were synthesized on the surface of α brass coated a film of nickel catalyst at 500-700 °C under atmosphere of O2 and CH4 gases. The nanosized ZnOs have shapes including pillar, leaf, sheet and rod, which were determined by the synthesis temperature and the flow rates of O2 and CH4 gases. The nanosized ZnOs were characterized by electron microscopy including transmission electron microscope for crystal structure, morphology and high resolution images, both field emission scanning electron microscope and scanning electron microscope for morphology, and energy dispersive X-ray spectroscope equipped in electron microscope for chemical composition. A mechanism was proposed for the growth of nanosized ZnO obtained in this work. 相似文献
1000.
Photoinitiated cationic polymerization of cycloaliphatic epoxide with siloxane or alkoxysilane functionalized polyol coatings 总被引:1,自引:0,他引:1
Jianxia Chen 《European Polymer Journal》2003,39(3):505-520
Polyols were reacted with tetraethyl orthosilicate (TEOS) or 3-isocyanatopropyltriethoxysilane (IPTES) to form siloxane functionalized polyols. The UV-reactivity of these siloxane functionalized polyols were investigated using real-time FT-IR spectroscopy. The reactivity of TEOS modified polyols was dependent on the relative humidity. However, for the IPTES functionalized polyols the effect of relative humidity was dependent on the degree of IPTES functionalization. When the polyols were only partially functionalized with IPTES, the effect of relative humidity was minimal. However, when polyols were fully functionalized with IPTES, the curing was dependent on relative humidity. The siloxane functionalized polyols were formulated with a cycloaliphatic epoxide and cationic photoinitiator. The photo-induced curing kinetics of these cycloaliphatic epoxide/siloxane functionalized polyol coatings were also investigated. Unlike the TEOS functionalized polyols, the addition of IPTES functionalized polyols into the formulation inhibited the curing speed. This inhibition was attributed to the basicity nitrogen of the urethane linkage. The effect of relative humidity on the UV-curing reaction of cycloaliphatic epoxide coatings was lowered by the incorporation of the TEOS functionalized polyols. 相似文献