全文获取类型
收费全文 | 260103篇 |
免费 | 3192篇 |
国内免费 | 823篇 |
专业分类
电工技术 | 5130篇 |
综合类 | 330篇 |
化学工业 | 37225篇 |
金属工艺 | 10253篇 |
机械仪表 | 8485篇 |
建筑科学 | 6102篇 |
矿业工程 | 1076篇 |
能源动力 | 6389篇 |
轻工业 | 22880篇 |
水利工程 | 2562篇 |
石油天然气 | 3908篇 |
武器工业 | 68篇 |
无线电 | 34721篇 |
一般工业技术 | 50063篇 |
冶金工业 | 46534篇 |
原子能技术 | 5418篇 |
自动化技术 | 22974篇 |
出版年
2021年 | 2037篇 |
2019年 | 2032篇 |
2018年 | 3468篇 |
2017年 | 3535篇 |
2016年 | 3730篇 |
2015年 | 2319篇 |
2014年 | 4047篇 |
2013年 | 11283篇 |
2012年 | 6562篇 |
2011年 | 8874篇 |
2010年 | 6981篇 |
2009年 | 7848篇 |
2008年 | 8676篇 |
2007年 | 8615篇 |
2006年 | 7804篇 |
2005年 | 7140篇 |
2004年 | 6886篇 |
2003年 | 6732篇 |
2002年 | 6371篇 |
2001年 | 6469篇 |
2000年 | 6170篇 |
1999年 | 6253篇 |
1998年 | 14240篇 |
1997年 | 10292篇 |
1996年 | 8112篇 |
1995年 | 6411篇 |
1994年 | 5710篇 |
1993年 | 5582篇 |
1992年 | 4552篇 |
1991年 | 4211篇 |
1990年 | 4048篇 |
1989年 | 3779篇 |
1988年 | 3624篇 |
1987年 | 3170篇 |
1986年 | 3065篇 |
1985年 | 3610篇 |
1984年 | 3382篇 |
1983年 | 3031篇 |
1982年 | 2850篇 |
1981年 | 2952篇 |
1980年 | 2761篇 |
1979年 | 2648篇 |
1978年 | 2499篇 |
1977年 | 2945篇 |
1976年 | 3555篇 |
1975年 | 2316篇 |
1974年 | 2312篇 |
1973年 | 2318篇 |
1972年 | 1849篇 |
1971年 | 1747篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
901.
902.
KW Preidler G Ranner D Szolar C Walch W Anderhuber 《Canadian Metallurgical Quarterly》1996,38(4):378-380
Ganglioneuroma, a rare benign tumour, very occasionally presents in adult life. We report a case with the additional unusual feature of a retropharyngeal location. 相似文献
903.
The properties of glasses of the lithium-aluminoborosilicate system were investigated, namely, the density, spreadability, thermal expansion, and nature of crystallized phases at various temperatures. A crystal-optical analysis was conducted. The glasses were used to prepare abrasive compositions. Their strength properties were studied as a function of the composition of the glass binder and the regime of heat treatment.Translated from Steklo i Keramika, No. 3, pp. 27–30, March, 1996. 相似文献
904.
Low back pain (LBP), a common illness that may progress to chronic disability, costs many billions for care, lost work, and compensation. Conventional medicine does not effectively restore chronic LBP patients to work; multidisciplinary rehabilitation does, but limited or delayed access risks unnecessary costs, additional morbidity, and permanent disability. The authors examine costs of delayed treatment for 23 disabled LBP patients in a rehabilitation program. Compensation costs average $26,159 per patient, a sum covering treatment for 3 patients. Additional medical and societal costs are estimated. Factors causing delay, such as economic incentives and ignorance about pain, and policies to remediate these problems, are discussed. 相似文献
905.
Neudorf E.G. Kiguel D.L. Hamoud G.A. Porretta B. Stephenson W.M. Sparks R.W. Logan D.M. Bhavaraju M.P. Billinton R. Garrison D.L. 《Power Systems, IEEE Transactions on》1995,10(3):1667-1675
There is an emerging recognition that utility investments and other decisions that affect electric service reliability should be explicitly evaluated on the basis of their cost and benefit implications. A cost-benefit approach that quantifies the reliability benefits of alternatives in terms of the reduction in costs resulting from unserved energy enables the evaluation of generation and transmission capacity additions on a consistent, economic basis. This approach has been applied to two utility case studies. In a case study for Pacific Gas and Electric Company, it was used to evaluate three options for maintaining reliability in a major load center-two involving local generation, and the third, a new 230 kV transmission connection. In a case study for Duke Power Company, the approach was used to evaluate alternative designs for proposed additions to a transmission station. This paper describes the methodology and presents the two utility studies 相似文献
906.
Adrian Thomas Christopher D. Gilson Tanveer Ahmed 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1995,64(1):73-79
Equipment was developed to measure the time for complete gelling of sodium alginate fibres in calcium chloride solution, taken as the time to achieve maximum tensile strength. The effects of fibre diameter, alginate concentration, alginate composition and calcium chloride concentration on gelling time were investigated. A diffusional model, developed to predict the gelling time, agreed with experimental results except for the effect of calcium ion concentration which was modelled empirically. 相似文献
907.
The relationship between the distance properties of trellis codes and the computational effort and error performance of sequential decoding is studied and optimum distance profile (ODP) and optimum free distance (OFD) trellis codes are constructed for 8-PSK and 16 QAM modulation. A comparison of the performance of both the ODP and the OFD trellis codes reveals that neither class of codes results in the best trade-off between error performance and computational effort when sequential decoding is used. A new algorithm is then proposed to construct robustly good trellis codes for use with sequential decoding. New trellis codes with asymptotic coding gains up to 6.66 dB are obtained using this algorithm, and the new codes achieve nearly the same free distances as the OFD codes and nearly the same distance profiles as the ODP codes 相似文献
908.
Schubert E.F. Hunt N.E.J. Malik R.J. Micovic M. Miller D.L. 《Lightwave Technology, Journal of》1996,14(7):1721-1729
Resonant-cavity light-emitting diodes (RCLED) are novel, high-efficiency light-emitting diodes which employ optical microcavities. These diodes have higher intensities and higher spectral purity as compared to conventional LEDs. Analytical formulas are derived for the enhancement of the spontaneous emission along the optical axis of the cavity. The design rules for high-efficiency operation of RCLEDs are established. The temperature dependence of the emission intensity is analyzed in the range 20-80° and it is described by an exponential dependence with a characteristic temperature of 112 K. The modulation characteristics of RCLEDs exhibit 3 dB frequencies of 580 MHz. Eye diagrams at transmission rates of 622 Mb/s are wide open indicating the suitability of RCLEDs for high-speed data transmission 相似文献
909.
910.
The throughput performance of a broadcast DS/SSMA packet radio network using adaptive error control is investigated. Simulated results for the network throughput against offered load are presented and show that adaptive error control significantly increases the throughput performance at all offered loads 相似文献