全文获取类型
收费全文 | 13185篇 |
免费 | 249篇 |
国内免费 | 58篇 |
专业分类
化学 | 6615篇 |
晶体学 | 92篇 |
力学 | 415篇 |
数学 | 1957篇 |
物理学 | 2870篇 |
无线电 | 1543篇 |
出版年
2021年 | 129篇 |
2020年 | 142篇 |
2019年 | 152篇 |
2018年 | 169篇 |
2017年 | 129篇 |
2016年 | 236篇 |
2015年 | 193篇 |
2014年 | 222篇 |
2013年 | 655篇 |
2012年 | 462篇 |
2011年 | 573篇 |
2010年 | 405篇 |
2009年 | 363篇 |
2008年 | 549篇 |
2007年 | 537篇 |
2006年 | 513篇 |
2005年 | 475篇 |
2004年 | 467篇 |
2003年 | 373篇 |
2002年 | 364篇 |
2001年 | 276篇 |
2000年 | 267篇 |
1999年 | 212篇 |
1998年 | 177篇 |
1997年 | 197篇 |
1996年 | 249篇 |
1995年 | 203篇 |
1994年 | 183篇 |
1993年 | 209篇 |
1992年 | 214篇 |
1991年 | 234篇 |
1990年 | 172篇 |
1989年 | 158篇 |
1988年 | 199篇 |
1987年 | 209篇 |
1986年 | 184篇 |
1985年 | 232篇 |
1984年 | 217篇 |
1983年 | 179篇 |
1982年 | 197篇 |
1981年 | 199篇 |
1980年 | 186篇 |
1979年 | 197篇 |
1978年 | 183篇 |
1977年 | 185篇 |
1976年 | 163篇 |
1975年 | 169篇 |
1974年 | 142篇 |
1973年 | 142篇 |
1972年 | 85篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
101.
W.-H. Steeb M. A. Van Wyk R. Stoop 《International Journal of Theoretical Physics》1998,37(10):2653-2655
We describe a one-dimensional chaotic map wherethe Liapunov exponent is a smooth function of a controlparameter. 相似文献
102.
103.
Hans van den Berg Michel Mandjes Rudesindo Núñez-Queija 《Operations Research Letters》2007,35(3):297-307
We study a processor-sharing model in which users choose between a high- and a low-priority service, based on their utility functions and prices charged by the service provider. The latter aims at revenue maximization. The model is motivated by file transmissions in data networks with distributed congestion control. 相似文献
104.
The generator coordinate approximation is a non-adiabatic theory of molecular systems. Its fundamental outlines were developed during the 1970's. A further analysis and first applications were published during the 1980's. In this paper, we review the present status of the theory. 相似文献
105.
Experimental results on adiabatic coupling into SOI photonic Crystal coupled-cavity waveguides 总被引:1,自引:0,他引:1
P. Sanchis J. Marti W. Bogaerts P. Dumon D. Van Thourhout R. Baets 《Photonics Technology Letters, IEEE》2005,17(6):1199-1201
The experimental implementation of an adiabatic coupling technique for efficient coupling between photonic crystal single-line defect waveguides and coupled-cavity waveguides is reported. The samples were fabricated in a silicon-on-insulator substrate using 248-nm-deep ultraviolet lithography. Experimental results are compared with three-dimensional (3-D) finite-difference time-domain simulations. Furthermore, the discrepancies between two-dimensional and 3-D simulation results are analyzed. 相似文献
106.
A. J. Seebregts L. W. M. M. Rademakers B. A. van den Horn 《Microelectronics Reliability》1995,35(9-10)
Wind turbines are being designed in accordance with deterministic design rules. As wind turbines increase in size and power, these rules may not be adequate to ascertain a safe and well balanced design. Wind turbine industry can take advantage of the safety and reliability practices in e.g. aerospace, nuclear and offshore industry. These practices include System Reliability (such as FMECA, Event Sequence Analysis and Fault Tree Analysis) and Structural Reliability methods. The approach to introduce Probabilistic Safety Assessment (PSA) which incorporates these reliability methods into wind turbine engineering will be described. By means of two recent case studies, the applicability, benefits, and limitations of these methods will be illustrated. 相似文献
107.
Carnel L. Gordon I. Van Gestel D. Vanhaeren D. Eyben P. Beaucarne G. Poortmans J. 《Electron Device Letters, IEEE》2007,28(10):899-901
Thin-film polysilicon solar cells are a promising low-cost alternative for bulk silicon solar cells due to their reduced material thickness. Recently, we showed that the use of an amorphous silicon/polycrystalline silicon heterojunction emitter instead of a diffused homojunction emitter led to a boost in the open-circuit voltage by 90 mV. Now, we present a full evidence that shows that this improvement is related to the absence of dopant smearing along the grain boundaries. By using scanning spreading resistance microscopy, we found an enlargement of the junction area by a factor of five in case of a homojunction. The tips of the dopant spikes represent lowly doped areas with an enhanced recombination. 相似文献
108.
109.
For a real Enriques surface Y we prove that every homology class in H1(Y (R), Z/2) can be represented by a real algebraic curve if and only if all connected components of Y(R) are orientable. Furthermore, we give a characterization of real Enriques surfaces which are Galois-Maximal and/or Z-Galois-Maximal and we determine the Brauer group of any real Enriques surface Y. 相似文献
110.
Tetsuya Okuyama Masaru Nakayama Yoshitsugu Tomokiyo Omer Van Der Biest 《Microscopy and microanalysis》2002,8(1):11-15
Lattice strains around a platelet oxygen precipitate in Si wafer is studied by energy filtering convergent-beam electron diffraction (CBED) and calculations based on the finite element method (FEM). Local lattice strains are measured from CBD patterns obtained with a probe size less than 2 nm in a specimen thicker than 450 nm. Strains measured are compressive along a direction normal to a plate of the precipitation and tensile along a direction parallel to the plate. Two-dimensional stress fields near the precipitate are obtained with FEM computer analyses by fitting the measured strains. It appears that shear stresses are concentrated at the end of the precipitate edge and the maximum shear stress at an interface between the precipitate and the Si-matrix is 1.9 GPa. It is demonstrated that a combination of the energy filtering CBED and FEM is very useful for the study of local strains near interfaces in semiconductor devices, in particular for the study of stress fields that are too steep for application of the conventional CBED technique. 相似文献