全文获取类型
收费全文 | 602134篇 |
免费 | 8051篇 |
国内免费 | 1948篇 |
专业分类
电工技术 | 11317篇 |
综合类 | 657篇 |
化学工业 | 89690篇 |
金属工艺 | 21795篇 |
机械仪表 | 17979篇 |
建筑科学 | 15925篇 |
矿业工程 | 1810篇 |
能源动力 | 15699篇 |
轻工业 | 57931篇 |
水利工程 | 5208篇 |
石油天然气 | 5497篇 |
武器工业 | 81篇 |
无线电 | 78114篇 |
一般工业技术 | 112272篇 |
冶金工业 | 112410篇 |
原子能技术 | 9684篇 |
自动化技术 | 56064篇 |
出版年
2021年 | 4309篇 |
2019年 | 4084篇 |
2018年 | 6611篇 |
2017年 | 6759篇 |
2016年 | 7188篇 |
2015年 | 5235篇 |
2014年 | 8761篇 |
2013年 | 27620篇 |
2012年 | 14956篇 |
2011年 | 20994篇 |
2010年 | 16344篇 |
2009年 | 18617篇 |
2008年 | 19954篇 |
2007年 | 20257篇 |
2006年 | 18244篇 |
2005年 | 16774篇 |
2004年 | 16277篇 |
2003年 | 15815篇 |
2002年 | 15345篇 |
2001年 | 15316篇 |
2000年 | 14394篇 |
1999年 | 15072篇 |
1998年 | 34584篇 |
1997年 | 25098篇 |
1996年 | 19822篇 |
1995年 | 15485篇 |
1994年 | 13779篇 |
1993年 | 13310篇 |
1992年 | 10238篇 |
1991年 | 9696篇 |
1990年 | 9149篇 |
1989年 | 8761篇 |
1988年 | 8381篇 |
1987年 | 7253篇 |
1986年 | 7106篇 |
1985年 | 8575篇 |
1984年 | 8004篇 |
1983年 | 7100篇 |
1982年 | 6601篇 |
1981年 | 6663篇 |
1980年 | 6250篇 |
1979年 | 6047篇 |
1978年 | 5674篇 |
1977年 | 6831篇 |
1976年 | 8911篇 |
1975年 | 4928篇 |
1974年 | 4804篇 |
1973年 | 4730篇 |
1972年 | 3772篇 |
1971年 | 3405篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Eric P. Kvam Ph.D. Srikanth B. Samavedam B.Tech. 《JOM Journal of the Minerals, Metals and Materials Society》1994,46(3):47-51
The Ge-Si on Si epilayer system, besides being an interesting technological system in its own right, is a superb model for strained-layer studies. The point defect and symmetry defect structures associated with compound semiconductors can be avoided, allowing a focus on the mechanics of the system. Dislocation sources, glide behavior, and performance effects have been examined for strained-layer systems. Surprises have appeared along the way, but these materials are now becoming characterized well enough for industrial device applications. 相似文献
992.
E. A. Ivanova D. F. Kasatkin L. A. Akishina E. V. Nepomnyashchaya 《Chemistry and Technology of Fuels and Oils》1992,28(5):241-243
Translated from Khimiya i Tekhnologiya Topliv i Masel, No. 5, pp. 2–3, May, 1992. 相似文献
993.
S. I. Glinchak Yu. A. Egorov R. R. Aliev E. D. Radchenko B. K. Nefedov N. A. Grigor'ev 《Chemistry and Technology of Fuels and Oils》1992,28(3):175-177
Translated from Khimiya i Tekhonologiy Topliv i Masel, No. 3, pp. 33–34, March, 1992. 相似文献
994.
The kinetics of spherulite radial growth and the morphology of the compatible system PEO/PVC have been studied by optical microscopy. The usual spherulite radial growth behaviour has been found for compatible blends with PEO content higher than 70%. For lower composition, distortion of the usual spherulite morphology has been observed; the anomalies have been attributed to partial miscibility of the components. 相似文献
995.
Chen L.R. Benjamin S.D. Smith P.W.E. Sipe J.E. 《Quantum Electronics, IEEE Journal of》1998,34(11):2117-2129
We discuss theoretical and experimental studies on the propagation of ultrashort pulses through fiber Bragg gratings. We also consider several applications in optical communications to be found by combining ultrashort pulses and fiber Bragg gratings: a multiwavelength source for wavelength-division-multiplexed systems and a means for implementing optical code-division multiple access 相似文献
996.
Low-temperature-grown GaAs (LT-GaAs) is a promising material for all-optical switching devices due to its outstanding optical characteristics. In this paper, we outline a simplified model we have developed to describe the dynamics of the carriers in this material. We also report the results of a series of measurements that we have performed to characterize the optical properties of the material. Specifically, we present the first measurements of the two-photon absorption coefficient and the refractive index changes as a function of the growth and annealing temperatures in LT-GaAs. Finally, we show how our model can be used to optimize the material for applications in all-optical switching 相似文献
997.
998.
Dotarizine is a new diphenylmethylpiperazine derivative with Ca2+ channel blocking properties and inhibitory effects on 5-HT2A and 5-HT2C receptors. Previous pilot studies in healthy volunteers demonstrated a good tolerability after single and multiple dosing. Dotarizine appeared to be rapidly and extensively metabolized to an active compound (FI-6020). We aimed to study the physiologic, subjective and psychomotor acute effects of oral dotarizine after single dose administration, to evaluate the tolerability and safety after multiple dosing over 2 weeks, and to study the pharmacokinetic parameters and linearity after single and multiple administration. Two different studies were carried out in 2 groups of 8 healthy male volunteers. Oral single doses of dotarizine 50, 100 and 200 mg were administered in a randomized, double-blind, crossover, placebo-controlled trial. Oral doses of 50 mg twice daily were administered in an open trial over 14 days. Drug effect assessments included vital signs, collection of adverse events, ECG and blood and urine safety evaluations, subjective effects, psychomotor performance tasks and blood sampling. Dotarizine and its metabolite were determined by gas chromatography with N-P detector. The results showed a good tolerability of dotarizine after single oral doses as well as multiple oral doses over 14 days. No clinically relevant adverse events were reported during the study. The highest single dose (200 mg) produced a slight increase in sedation-related symptoms as well as a slight impairment in psychomotor performance tasks. Dotarizine and its major metabolite proved linear kinetics at single doses. The administration of oral doses of dotarizine 50 mg b.i.d. reached the steady state after the 7th day of treatment. The pharmacokinetic parameters remained similar from day 7 to day 14. The terminal elimination half-life of dotarizine and its metabolite appeared to be between 7 and 12 h. 相似文献
999.
P. Kristiansson C. M. Nilsson H. Busk L. Malmqvist M. Elfman K. G. Malmqvist J. Pallon K. A. Sj land R. J. Utui C. Yang 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》1997,130(1-4):303-307
A technique for measuring optical dot gain, i.e. the relative difference between the actual screen dot and the optically perceived one, is presented. By combining measurements from the non-optical nuclear microprobe with data from image analyzing technique the optical dot gain can be determined. The procedure to reach pixel by pixel correlation on a micrometer scale is discussed. In the newsprint sample studied in this investigation a typical optical dot gain between 15 and 20% was deduced. The variation in the optical dot gain was correlated with other characteristic parameters of the print and newsprint and especially a positive correlation to the mass density of the newsprint was observed. 相似文献
1000.