全文获取类型
收费全文 | 10236篇 |
免费 | 787篇 |
国内免费 | 332篇 |
专业分类
电工技术 | 394篇 |
综合类 | 404篇 |
化学工业 | 1676篇 |
金属工艺 | 579篇 |
机械仪表 | 677篇 |
建筑科学 | 554篇 |
矿业工程 | 188篇 |
能源动力 | 330篇 |
轻工业 | 488篇 |
水利工程 | 170篇 |
石油天然气 | 348篇 |
武器工业 | 39篇 |
无线电 | 1477篇 |
一般工业技术 | 1670篇 |
冶金工业 | 921篇 |
原子能技术 | 97篇 |
自动化技术 | 1343篇 |
出版年
2024年 | 45篇 |
2023年 | 151篇 |
2022年 | 271篇 |
2021年 | 366篇 |
2020年 | 283篇 |
2019年 | 301篇 |
2018年 | 293篇 |
2017年 | 293篇 |
2016年 | 277篇 |
2015年 | 382篇 |
2014年 | 439篇 |
2013年 | 622篇 |
2012年 | 614篇 |
2011年 | 644篇 |
2010年 | 539篇 |
2009年 | 556篇 |
2008年 | 493篇 |
2007年 | 494篇 |
2006年 | 438篇 |
2005年 | 424篇 |
2004年 | 283篇 |
2003年 | 282篇 |
2002年 | 267篇 |
2001年 | 253篇 |
2000年 | 218篇 |
1999年 | 266篇 |
1998年 | 270篇 |
1997年 | 220篇 |
1996年 | 189篇 |
1995年 | 166篇 |
1994年 | 139篇 |
1993年 | 108篇 |
1992年 | 94篇 |
1991年 | 82篇 |
1990年 | 64篇 |
1989年 | 71篇 |
1988年 | 59篇 |
1987年 | 48篇 |
1986年 | 38篇 |
1985年 | 43篇 |
1984年 | 33篇 |
1983年 | 22篇 |
1982年 | 35篇 |
1981年 | 26篇 |
1980年 | 18篇 |
1979年 | 14篇 |
1977年 | 20篇 |
1976年 | 19篇 |
1974年 | 19篇 |
1973年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
41.
Fabrication and characteristics of high-speed implant-confined index-guided lateral-current 850-nm vertical cavity surface-emitting lasers 总被引:2,自引:0,他引:2
Dang G.T. Mehandru R. Luo B. Ren F. Hobson W.S. Lopata J. Tayahi M. Chu S.N.G. Pearton S.J. Chang W. Shen H. 《Lightwave Technology, Journal of》2003,21(4):1020-1031
Process technology of high-speed implant-apertured index-guide lateral-current-injection top dielectric-mirror quantum-well 850-nm vertical cavity surface-emitting lasers (VCSELs) has been developed. Oxygen and helium implantation for aperture definition and extrinsic capacitance reduction, dielectric mirror formation, p- and n-ohmic contact formation, VCSEL resistance, and thermal analysis were investigated. Employing this technology, GaAs/AlGaAs-based 850-nm VCSELs with small signal modulation bandwidths up to 11.5 Gb/s and an eye diagram generated at 12 Gb/s by a pseudorandom bit sequence of 2/sup 31/-1 were achieved. The bit-error rates were below 10/sup -13/. The threshold current is as low as 0.8 mA for 7-/spl mu/m-diameter current apertures and typical slope efficiencies of 0.45-0.5 mA/mW were obtained. 相似文献
42.
Access path deployment is a critical issue in physical database design. Access paths typically include a clustered index as the primary access path and a set of secondary indexes as auxiliary access paths. To deploy the right access paths requires an effective algorithm and accurate estimation of the parameters used by the algorithm. One parameter central to any index-selection algorithm is the block selectivity of a query. Existing methods for estimating block selectivities are limited by restrictive assumptions. Furthermore, most existing methods produce estimates useful for aiding the selection of secondary indexes only. Little research has been done in the area of estimating block selectivities for supporting the selection of the clustered index. The paper presents a set of methods that do not depend on any specific assumption, produce accurate estimates, and can be used to aid in selecting the clustered index as well as secondary indexes 相似文献
43.
Very high-order microring resonator filters for WDM applications 总被引:6,自引:0,他引:6
B.E. Little S.T. Chu P.P. Absil J.V. Hryniewicz F.G. Johnson F. Seiferth D. Gill V. Van O. King M. Trakalo 《Photonics Technology Letters, IEEE》2004,16(10):2263-2265
High-order microring resonators having from 1 to 11 coupled cavities are demonstrated. These filters exhibit low loss, flat tops, and out-of-band rejection ratios that can exceed 80 dB. They achieve performance that is suitable for commercial applications. 相似文献
44.
45.
We studied the long-term clinical course of five patients with chronic manganese intoxication. The mean scores of the King's College Hospital Rating Scale for Parkinson's disease increased from 15.0 +/- 4.2 in 1987 to 28.3 +/- 6.70 in 1991 and then to 38.1 +/- 12.9 in 1995. The deterioration was most prominent in gait, rigidity, speed of foot tapping, and writing. Tissue concentrations of manganese in blood, urine, scalp hair, and pubic hair returned to normal. Follow-up MRIs did not show paramagnetic high-signal intensity on T1-weighted images. The data indicate that clinical progression in patients with manganese parkinsonism continues even 10 years after cessation of exposure. 相似文献
46.
47.
大型离心复合球墨铸铁轧辊的生产 总被引:1,自引:0,他引:1
简述了我公司为舞阳铜厂试制4200mm厚板轧机离心复合球墨铸铁轧辊的性能要求、内外层双重金属铸造工艺参数的选择及整个铸造生产工艺过程。 相似文献
48.
Ismail K. Meyerson B.S. Rishton S. Chu J. Nelson S. Nocera J. 《Electron Device Letters, IEEE》1992,13(5):229-231
The authors report on the fabrication and the resultant device characteristics of the first 0.25-μm gate-length field-effect transistor based on n-type modulation-doped Si/SiGe. Prepared using ultrahigh vacuum/chemical vapor deposition (UHV/CVD), the mobility and electron sheet charge density in the strained Si channel are 1500 (9500) cm2/V-s and 2.5×1012 (1.5×1012 ) cm-2 at 300 K (77 K). At 77 K, the devices have a current and transconductance of 325 mA/mm and 600 mS/mm, respectively. These values far exceed those found in Si MESFETs and are comparable to the best results achieved in GaAs/AlGaAs modulation-doped transistors 相似文献
49.
用傅里叶变换红外扫描光致发光方法研究了Hg1-xCdxTe体单晶样品,该方法可直接得到HgCdTe晶片组分的二维平面分布,并可得到辐射复合在复合机制中所占比重的平面分布,以及晶体中非平衡载流子寿命的分布 相似文献
50.
Microring resonator channel dropping filters 总被引:17,自引:0,他引:17
Little B.E. Chu S.T. Haus H.A. Foresi J. Laine J.-P. 《Lightwave Technology, Journal of》1997,15(6):998-1005
Microring resonators side coupled to signal waveguides provide compact, narrow band, and large free spectral range optical channel dropping filters. Higher order filters with improved passband characteristics and larger out-of-band signal rejection are realized through the coupling of multiple rings. The analysis of these devices is approached by the novel method of coupling of modes in time. The response of filters comprised of an arbitrarily large dumber of resonators may be written down by inspection, as a continued fraction. This approach simplifies both the analysis and filter synthesis aspects of these devices 相似文献