全文获取类型
收费全文 | 713559篇 |
免费 | 6489篇 |
国内免费 | 1696篇 |
专业分类
化学 | 323620篇 |
晶体学 | 9445篇 |
力学 | 31977篇 |
综合类 | 16篇 |
数学 | 85052篇 |
物理学 | 198505篇 |
无线电 | 73129篇 |
出版年
2021年 | 6341篇 |
2020年 | 7121篇 |
2019年 | 7993篇 |
2018年 | 10806篇 |
2017年 | 10680篇 |
2016年 | 15143篇 |
2015年 | 8351篇 |
2014年 | 14234篇 |
2013年 | 30292篇 |
2012年 | 23616篇 |
2011年 | 28500篇 |
2010年 | 21758篇 |
2009年 | 22722篇 |
2008年 | 28341篇 |
2007年 | 28509篇 |
2006年 | 26351篇 |
2005年 | 23622篇 |
2004年 | 22188篇 |
2003年 | 20095篇 |
2002年 | 20025篇 |
2001年 | 21332篇 |
2000年 | 17066篇 |
1999年 | 13562篇 |
1998年 | 12004篇 |
1997年 | 11553篇 |
1996年 | 10827篇 |
1995年 | 9830篇 |
1994年 | 9778篇 |
1993年 | 9353篇 |
1992年 | 9906篇 |
1991年 | 10255篇 |
1990年 | 9944篇 |
1989年 | 9623篇 |
1988年 | 9200篇 |
1987年 | 8621篇 |
1986年 | 8068篇 |
1985年 | 10026篇 |
1984年 | 10202篇 |
1983年 | 8338篇 |
1982年 | 8475篇 |
1981年 | 8198篇 |
1980年 | 7653篇 |
1979年 | 8267篇 |
1978年 | 8472篇 |
1977年 | 8457篇 |
1976年 | 8395篇 |
1975年 | 7766篇 |
1974年 | 7616篇 |
1973年 | 7746篇 |
1972年 | 5917篇 |
排序方式: 共有10000条查询结果,搜索用时 7 毫秒
981.
M.A.R. Alves 《Microelectronics Journal》2005,36(1):51-54
We developed a process to obtain sharper silicon tips by employing anisotropic etching in a KOH solution followed by SF6 plasma etch. The tips were further sharpened using the established thermal oxidation technique to decrease the cone angle and, therefore, obtain smaller curvature radii. We have analyzed the impact of such changes in geometry on a figure of merit associated with the field emission characteristics. An increase in the figure of merit by a factor of three was found in relation to the tips before sharpening. 相似文献
982.
Ophir J. McWhirt R. E. Maklad N. F. Jaeger P. M. 《IEEE transactions on bio-medical engineering》1985,(3):205-212
The principles of a narrowband technique for pulse echo attenuation measurements are presented. Experiments are described which compare the attenuation in tissue-mimicking phantoms, measured by known methods, to the attenuation measured by the present technique. The effects of various experimental parameters on the results are investigated. The attenuation in spleens of canine models and in livers of human volunteers is presented. 相似文献
983.
984.
985.
S.T.V. Parthasaradhi R. Derakhshani L.A. Hornak S.A.C. Schuckers 《IEEE transactions on systems, man and cybernetics. Part C, Applications and reviews》2005,35(3):335-343
Fingerprint scanners may be susceptible to spoofing using artificial materials, or in the worst case, dismembered fingers. An anti-spoofing method based on liveness detection has been developed for use in fingerprint scanners. This method quantifies a specific temporal perspiration pattern present in fingerprints acquired from live claimants. The enhanced perspiration detection algorithm presented here improves our previous work by including other fingerprint scanner technologies; using a larger, more diverse data set; and a shorter time window. Several classification methods were tested in order to separate live and spoof fingerprint images. The dataset included fingerprint images from 33 live subjects, 33 spoofs created with dental material and Play-Doh, and fourteen cadaver fingers. Each method had a different performance with respect to each scanner and time window. However, all the classifiers achieved approximately 90% classification rate for all scanners, using the reduced time window and the more comprehensive training and test sets. 相似文献
986.
987.
988.
A. M. Samoilenko 《Ukrainian Mathematical Journal》1991,43(10):1195-1208
Expanded text of paper read by the author to a meeting of the Kiev Mathematical Society, February 26, 1991. 相似文献
989.
A particle imaging technique has been used to collect droplet displacement statistics in a round turbulent jet of air. Droplets are injected on the jet axis, and a laser sheet and position-sensitive photomultiplier tube are used to track their radial displacement and time-of-flight. Dispersion statistics can be computed which are Lagrangian or Eulerian in nature. The experiments have been simulated numerically using a second-order closure scheme for the jet and a stochastic simulation for the particle trajectories. Results are presented for non-vaporizing droplets of sizes from 35 to 160 μm. The simulations have underscored the importance of initial conditions and early droplet displacement history on the droplet trajectory for droplets with large inertia relative to the turbulence. Estimates of initial conditions have been made and their effect on dispersion is quantified. 相似文献
990.