全文获取类型
收费全文 | 15518篇 |
免费 | 2609篇 |
国内免费 | 1675篇 |
专业分类
化学 | 7901篇 |
晶体学 | 163篇 |
力学 | 804篇 |
综合类 | 105篇 |
数学 | 1250篇 |
物理学 | 4719篇 |
无线电 | 4860篇 |
出版年
2024年 | 39篇 |
2023年 | 442篇 |
2022年 | 496篇 |
2021年 | 699篇 |
2020年 | 636篇 |
2019年 | 604篇 |
2018年 | 517篇 |
2017年 | 504篇 |
2016年 | 723篇 |
2015年 | 742篇 |
2014年 | 865篇 |
2013年 | 1080篇 |
2012年 | 1329篇 |
2011年 | 1296篇 |
2010年 | 999篇 |
2009年 | 985篇 |
2008年 | 962篇 |
2007年 | 877篇 |
2006年 | 871篇 |
2005年 | 757篇 |
2004年 | 484篇 |
2003年 | 427篇 |
2002年 | 422篇 |
2001年 | 312篇 |
2000年 | 297篇 |
1999年 | 317篇 |
1998年 | 277篇 |
1997年 | 263篇 |
1996年 | 272篇 |
1995年 | 225篇 |
1994年 | 195篇 |
1993年 | 132篇 |
1992年 | 127篇 |
1991年 | 111篇 |
1990年 | 104篇 |
1989年 | 85篇 |
1988年 | 68篇 |
1987年 | 33篇 |
1986年 | 48篇 |
1985年 | 32篇 |
1984年 | 22篇 |
1983年 | 20篇 |
1982年 | 17篇 |
1981年 | 8篇 |
1980年 | 11篇 |
1975年 | 8篇 |
1973年 | 5篇 |
1972年 | 7篇 |
1965年 | 6篇 |
1964年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 134 毫秒
111.
本文在集值优化的框架下提出了一个二层多目标规划模型(BLMOP).利用集值映射的相依导数和相依上导数,给出了几个有关(BLMOP)的弱有效解的必要或充分最优性条件. 相似文献
112.
113.
研究了油/水界面电解的示差半微分循环伏安行为。在0.01mol/L LiCl(w)-0.01mol/L TBATCIPB(nb)体系“电位窗”比TBATPB(nb)向正方向扩展约50mV,残余电流基本消除,使“电位窗”内的平台向左右拓宽约50mV。算得界面电容约为16μF/cm~2。考察了琥珀酰胆碱离子在w/nb界面的传递伏安特性,结果与一般半微分循环伏安法相似。但峰形改善,检测限降低一个数量级(1×10~(-6)mol/L),相对标准偏差在5%以内,可用于定量测定琥珀酰胆碱。 相似文献
114.
Mai Lu Paul J. Leonard Duo-Wang Fan Fu-Yong Xu 《Journal of Infrared, Millimeter and Terahertz Waves》2004,25(10):1469-1479
In this paper, the cutoff characteristic of rectangular-shaped microshield transmission line has been analysed by edge element method. Dependence of cutoff wavelengths on the thickness of metallic signal strip, dielectric constant of dielectric substrate and the width of the rectangular-shaped ground conductor are presented in tabular form. Numerical results in this paper have important values in design of rectangular-shaped microshield lines in microwave and millimeter wave integrated circuits. 相似文献
115.
范进军 《Annals of Differential Equations》2004,20(1):21-29
In this paper, by using Lyapunov function and weak noncompactness conditions, we give an existence theorem of generalized weakly solutions of Cauchy problem of differential equations in product spaces. 相似文献
116.
For improved mechanical and water‐swelling properties of chitosan films, a series of transparent films were prepared with dialdehyde starch as a crosslinking agent. Fourier transform infrared and X‐ray analysis results demonstrated that the formation of Schiff's base disturbed the crystallization of chitosan. The mechanical properties and water‐swelling properties of the films were significantly improved. The best values of the tensile strength and breaking elongation were 113.1 MPa and 27.0%, respectively, when the dialdehyde starch content was 5%. All the crosslinked films still retained obvious antimicrobial effects toward S. aureus and E. coli, and they showed potential for biomedical applications. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 993–997, 2003 相似文献
117.
Xia Yin Weiguang Zhang Qijiao Zhang Jun Fan Chian Sing Lai Edward R. T. Tiekink 《应用有机金属化学》2004,18(3):139-140
The centrosymmetric structure of {Cd[S2CN(CH2Ph)2]2}2 features both bridging and chelating dithiocarbamate ligands so that a square pyramidal S5 coordination geometry results. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
118.
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
119.
120.
H. Fan A. Wright J. Gabaldon A. Rodriguez C.J. Brinker Y.‐B. Jiang 《Advanced functional materials》2006,16(7)
The synthesis of three‐dimensionally ordered, transparent gold‐nanocrystal (NC)/silica superlattice thin films using the self‐assembly (by spin‐coating) of water‐soluble gold nanocrystal micelles and soluble silica is reported by Fan and co‐workers on p. 891. The robust, 3D NC/silica superlattice films are of interest for the development of collective optical and electronic phenomena, and, importantly, for the integration of NC arrays into device architectures. Nanocrystals and their ordered arrays hold many important applications in fields such as catalysis, surface‐enhanced Raman spectroscopy based sensors, memory storage, and electronic and optical nanodevices. Herein, a simple and general method to synthesize ordered, three‐dimensional, transparent gold nanocrystal/silica superlattice thin films by self‐assembly of gold nanocrystal micelles with silica or organosilsesquioxane by spin‐coating is reported. The self‐assembly process is conducted under acidic sol–gel conditions (ca. pH 2), ensuring spin‐solution homogeneity and stability and facilitating the formation of ordered and transparent gold nanocrystal/silica films. The monodisperse nanocrystals are organized within inorganic host matrices as a face‐centered cubic mesostructure, and characterized by transmission electron spectroscopy and X‐ray diffraction. 相似文献