全文获取类型
收费全文 | 883篇 |
免费 | 31篇 |
国内免费 | 3篇 |
专业分类
化学 | 485篇 |
晶体学 | 9篇 |
力学 | 12篇 |
数学 | 85篇 |
物理学 | 191篇 |
无线电 | 135篇 |
出版年
2023年 | 6篇 |
2022年 | 7篇 |
2021年 | 8篇 |
2020年 | 7篇 |
2019年 | 22篇 |
2018年 | 9篇 |
2017年 | 9篇 |
2016年 | 28篇 |
2015年 | 15篇 |
2014年 | 8篇 |
2013年 | 27篇 |
2012年 | 36篇 |
2011年 | 44篇 |
2010年 | 25篇 |
2009年 | 35篇 |
2008年 | 70篇 |
2007年 | 57篇 |
2006年 | 63篇 |
2005年 | 45篇 |
2004年 | 35篇 |
2003年 | 30篇 |
2002年 | 40篇 |
2001年 | 35篇 |
2000年 | 15篇 |
1999年 | 10篇 |
1998年 | 7篇 |
1997年 | 14篇 |
1996年 | 11篇 |
1995年 | 10篇 |
1994年 | 11篇 |
1993年 | 11篇 |
1992年 | 20篇 |
1991年 | 17篇 |
1990年 | 12篇 |
1989年 | 14篇 |
1988年 | 9篇 |
1987年 | 6篇 |
1986年 | 8篇 |
1985年 | 15篇 |
1984年 | 8篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 10篇 |
1978年 | 8篇 |
1977年 | 4篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1971年 | 2篇 |
1930年 | 2篇 |
排序方式: 共有917条查询结果,搜索用时 484 毫秒
101.
del Amo A. Montero J. Fernandez A. Lopez M. Tordesillas J.M. Biging G. 《IEEE transactions on systems, man and cybernetics. Part C, Applications and reviews》2002,32(1):42-48
Geographical information (including remotely sensed data) is usually imprecise, meaning that the boundaries between different phenomena are fuzzy. In fact, many classes in nature show internal gradual differences in species, health, age, moisture, as well other factors. If our classification model does not acknowledge that those classes are heterogeneous, and crisp classes are artificially imposed, a final careful analysis should always search for the consequences of such an unrealistic assumption. We consider the unsupervised algorithm presented by A. del Amo et al. (2000), and its application to a real image in Sevilla province (south Spain). Results are compared with those obtained from the ERDAS ISO-DATA classification program on the same image, showing the accuracy of our fuzzy approach. As a conclusion, it is pointed out that whenever real classes are natural fuzzy classes, with gradual transition between classes, then its fuzzy representation will be more easily understood, and therefore accepted by users 相似文献
102.
103.
In a fingerprinting scheme, marks are embedded in a digital object to protect intellectual property. Dishonest users can collude, change some of the marks and create a new copy. In this case codes with the 'identifiable parent property' or IPP codes [4], provide means of traceability. Here, both a new decoding algorithm for IPP codes and an improvement of earlier algorithms are presented. 相似文献
104.
Hristov H.D. Feick R. Grote W. Fernandez P. 《Antennas and Propagation, IEEE Transactions on》2004,52(4):933-940
A simple inexpensive on-wall Fresnel zone plate (FZP) lens for indoor focusing of microwave signals is studied. It consists of concentric metal rings mounted on the outside of an exterior building wall. In our theoretical and empirical work the on-wall FZP lens is illuminated normally by a plane or spherical wave, of vertical or horizontal polarization, but other, more general incidence situations can be treated by similar means. The scalar quasi-optical focusing theory of the free-space zone plate has been modified and used for design and analysis of one-, two-, and three-ring on-wall FZP lenses. It is found that the presence of the wall does not change the FZP lens focusing efficiency significantly, but it has a strong axial defocusing effect. A 2-GHz FZP lens assembly consisting of three metal rings made out of thin antimosquito mesh has a focusing efficiency of about 15 dB (measured) and 14 dB (calculated), and axial defocusing of about 0.22 m. Some variations of on-wall/on-roof FZP lenses and their feasible applications in the microwave/millimeter-wave communication links are also discussed. 相似文献
105.
Xavier Fernandez Josep Maria Salla Angels Serra Ana Mantecn Xavier Ramis 《Journal of polymer science. Part A, Polymer chemistry》2005,43(15):3421-3432
3,4‐Epoxycyclohexylmethyl 3,4‐epoxycyclohexane carboxylate (ECH) was cured with different proportions of 1,6‐dioxaspiro [4,4]nonane‐2,7‐dione (s(γ‐BL)) using lanthanum triflate as a catalyst. The shrinkage undergone during curing was monitored by means of thermomechanical analysis (TMA) in isothermal experiments. Fourier transform infrared spectroscopy in attenuated‐total‐reflection mode (FTIR/ATR) was used to study the evolution of lactone, epoxide, and intermediate spiroorthoester (SOE) groups to identify the different reactions that take place during the curing process. DSC was used to study the thermal characteristics of the curing process and to assess the glass‐transition temperature (Tg) of the cured material. The dynamic mechanical properties of the cured material were determined based on the data obtained by DMTA. An increase in the proportion of s(γ‐BL) led to a decrease in the gelation time and the shrinkage after gelation. By combining the data obtained by TMA and FTIR/ATR, it was also possible to identify the reactive processes responsible for the shrinkage. It was observed that an increase in the proportion of s(γ‐BL) also increases the speed of the curing process and modifies the structure of the material, thus giving rise to more flexible materials. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3421–3432, 2005 相似文献
106.
Cristina Bazgan W. Fernandez de la Vega Marek Karpinski 《Random Structures and Algorithms》2003,23(1):73-91
It is known that large fragments of the class of dense Minimum Constraint Satisfaction (MIN‐CSP) problems do not have polynomial time approximation schemes (PTASs) contrary to their Maximum Constraint Satisfaction analogs. In this paper we prove, somewhat surprisingly, that the minimum satisfaction of dense instances of kSAT ‐formulas, and linear equations mod 2, Ek‐LIN2, do have PTASs for any k. The MIN‐Ek‐LIN2 problems are equivalent to the k‐ary versions of the Nearest Codeword problem, the problem which is known to be exceedingly hard to approximate on general instances. The method of solution of the above problems depends on the development of a new density sampling technique for k‐uniform hypergraphs which could be of independent interest. © 2003 Wiley Periodicals, Inc. Random Struct. Alg., 23: 73–91, 2003 相似文献
107.
108.
Stefan T. Ochsenbein Dr. Floriana Tuna Dr. Marzio Rancan Rachel S. G. Davies Christopher A. Muryn Dr. Oliver Waldmann Dr. Roland Bircher Dr. Andreas Sieber Dr. Graham Carver Dr. Hannu Mutka Dr. Felix Fernandez‐Alonso Dr. Andrew Podlesnyak Dr. Larry P. Engelhardt Dr. Grigore A. Timco Dr. Hans U. Güdel Prof. Dr. Richard E. P. Winpenny Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(17):5087-5087
109.
G. Fernandez 《Journal of sound and vibration》1984,96(1):37-43
For a submerged cable, the classical equation of a vibrating string must be modified to account for added mass and damping effects. This can be done with the aid of Morison's formulae. The resulting equation is non-linear. It is solved for the case when one end of the string is forced into sinusoidal transverse motion. The first harmonic approximations for both resonant and non-resonant responses are obtained by the method of matched asymptotic expansions under the assumption that the non-dimensional damping coefficient is small. 相似文献
110.
Cvetovic S.R. Fernandez F.A. An Ping Zhao Ettinger R.D. Sewell G. Davies J.B. 《Lightwave Technology, Journal of》1994,12(7):1112-1120
This paper presents a comparison of two- finite-element programs developed for accurate cross-sectional analysis of arbitrary optical and microwave waveguiding structures. Both techniques were developed in response to the growing demand from scientists and engineers for application-specific expert systems, and employ advanced interactive pre- and post-processing facilities. They show good agreement, strongly complement one another, and could form the core of a whole library of similar “intelligent” software for computer-assisted analysis and design, with a wide range of possible applications within both supercomputer and workstation environments 相似文献