全文获取类型
收费全文 | 245057篇 |
免费 | 3135篇 |
国内免费 | 1242篇 |
专业分类
电工技术 | 4839篇 |
综合类 | 268篇 |
化学工业 | 35733篇 |
金属工艺 | 10902篇 |
机械仪表 | 7096篇 |
建筑科学 | 6296篇 |
矿业工程 | 486篇 |
能源动力 | 6317篇 |
轻工业 | 24258篇 |
水利工程 | 1852篇 |
石油天然气 | 1343篇 |
武器工业 | 3篇 |
无线电 | 31206篇 |
一般工业技术 | 45091篇 |
冶金工业 | 50666篇 |
原子能技术 | 3867篇 |
自动化技术 | 19211篇 |
出版年
2021年 | 1581篇 |
2019年 | 1440篇 |
2018年 | 2346篇 |
2017年 | 2244篇 |
2016年 | 2472篇 |
2015年 | 1929篇 |
2014年 | 3195篇 |
2013年 | 10872篇 |
2012年 | 5488篇 |
2011年 | 7850篇 |
2010年 | 6317篇 |
2009年 | 7009篇 |
2008年 | 7606篇 |
2007年 | 7717篇 |
2006年 | 7060篇 |
2005年 | 6552篇 |
2004年 | 6269篇 |
2003年 | 6286篇 |
2002年 | 6267篇 |
2001年 | 6399篇 |
2000年 | 5822篇 |
1999年 | 6456篇 |
1998年 | 16740篇 |
1997年 | 11722篇 |
1996年 | 9024篇 |
1995年 | 6747篇 |
1994年 | 5946篇 |
1993年 | 5766篇 |
1992年 | 4072篇 |
1991年 | 4009篇 |
1990年 | 3603篇 |
1989年 | 3518篇 |
1988年 | 3467篇 |
1987年 | 2943篇 |
1986年 | 2860篇 |
1985年 | 3432篇 |
1984年 | 3072篇 |
1983年 | 2760篇 |
1982年 | 2572篇 |
1981年 | 2590篇 |
1980年 | 2449篇 |
1979年 | 2285篇 |
1978年 | 2248篇 |
1977年 | 2828篇 |
1976年 | 4206篇 |
1975年 | 1908篇 |
1974年 | 1803篇 |
1973年 | 1793篇 |
1972年 | 1468篇 |
1971年 | 1322篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
211.
T Takikawa H Hayashi N Nishimura M Yano T Isomura N Sakamoto 《Canadian Metallurgical Quarterly》1994,29(5):593-597
Chronic hepatitis C has been demonstrated to be associated with hepatic iron overload, and the hypothesis that the disease activity of hepatitis C is associated with iron cytotoxicity was tested in male volunteer blood donors. Sera with either antibody to hepatitis C virus or hepatitis B surface antigen were selected for determination of ferritin concentration and alanine aminotransferase activity. A correlation between serum ferritin concentration (Y; microgram/l) and alanine aminotransferase activity (X; IU/l) was found in donors with antibody to hepatitis C (log Y = 0.65 x log X + 0.98, r = 0.53, and P < 0.01). The correlation was lower in donors with hepatitis B surface antigen (r = 0.37; P < 0.01). Hepatitis C virus infection probably induces time-dependent iron accumulation associated with the progression of disease activity, while hepatitis B virus infection results in a variety of iron loads with different clinical features. The high disease activity related to hyperferritinemia suggests the presence of iron-induced liver damage in donors with hepatitis C. 相似文献
212.
Ipratropium bromide is a synthetic derivative of atropine with little absorption when used in inhalation, and therefore little secondary effects. The authors review its pharmacological properties and therapeutic efficacy in the treatment of asthma in children. Combined nebulized inhalation of ipratropium bromide and beta 2 sympathomimetic results in a more efficient and more sustained bronchodilatation than beta 2 sympathicomimetic alone in the treatment of acute asthma in children. Ipratropium bromide should be usefully introduced in the therapeutic scheme of acute asthma in children. Further studies will be necessary in order to determine its efficacy and tolerance in infants. 相似文献
213.
K. Nomoto H. Saitoh A. Chida H. Sannomiya M. Itoh Y. Yamamoto 《Solar Energy Materials & Solar Cells》1994,34(1-4)
a-Si alloy three-stacked solar cells have been studied to improve the stabilized efficiency of a-Si: H based solar cells. Based on the analysis by the individual characterization method of the component cells in stacked type cells, the a-Si :H middle cell was replaced with an a-SiGe :H cell. Furthermore, the optical confinement technology was improved to obtain a high-output current with thin i-layer thickness in the a-SiGe :H bottom cell. By this device design, the initial conversion efficiency was improved up to 12.4% and more than a 10% stabilized efficiency was obtained in a-SiC :H/a-SiGe :H/a-SiGe :H three-stacked cells. These cell characteristics were confirmed by measurements at the JQA Organization (the former JMI Institute). 相似文献
214.
Garner H.R. Balog R.P. Luebke K.J. 《IEEE engineering in medicine and biology magazine》2002,21(4):123-125
Given the enormous size of the genome and that there are potentially many other types of measurements we need to do to understand it, it has become necessary to pick and choose one's targets to measure because it is still impossible to evaluate the entire genome all at once. What has emerged is a need to have rapidly customizable microarrays. There are two dominant methods to accomplish custom microarray synthesis, Affymetrix-like microarrays manufactured using light projection rather than semiconductor-like masks used by Affymetrix to mass manufacture their GeneChip/sup TM/ arrays now, or the ink-jet printing method employed by Agilent. The manufacture of these custom Affymetrix-like microarrays can now be done on a digital optical chemistry (DOC) machine developed at the University of Texas Southwestern Medical Center, and this method offers much higher feature numbers and feature density than is possible with ink-jet printed arrays. On a microarray, each feature contains a single genetic measurement. The initial DOC prototype has been described in several publications, but that has now led to a second-generation machine. This machine reliably produces a number of arrays daily, has been deployed against a number of biomedical questions, is being used in new ways and has also led to a number of spin-off technologies. 相似文献
215.
216.
High-resolution positive and negative photoresists were used to fabricate ?/4-phase-shifted corrugations by holographic exposure. To avoid mixing these photoresists, cyclised polyisoprene was used as a midlayer. The shape and depth of the corrugations on the positive and negative photoresist regions were almost the same. Single-mode operation at the Bragg wavelength was confirmed in lasers with the corrugation. 相似文献
217.
Nagpal R. Zambonelli F. Sirer E.G. Chaouchi H. Smirnov M. 《Intelligent Systems, IEEE》2006,21(2):50-58
No generally accepted principles and guidelines currently exist to help engineers design local interaction mechanisms that result in a desired global behavior. However, several communities have developed ways of approaching this problem in the context of niched application areas. Because the ideas underlying these approaches are often obscured or underemphasized in technical papers, the authors review the role of self-organization in their work. They provide a better picture of the status of the emerging field of self-organizing systems or autonomic computing. 相似文献
218.
219.
Hayashi M. Tanaka H. Ohara K. Otani T. Suzuki M. 《Lightwave Technology, Journal of》2002,20(2):236-242
An all-optical multiplexing technique using wavelength division multiplexing (WDM)-time division multiplexing (TDM) conversion with an electroabsorption wavelength converter has been proposed and demonstrated. The effectiveness of this WDM-TDM conversion technique for various pulsewidth settings was experimentally investigated. The fluctuation of the signal performance, which was inevitably caused by the coherent crosstalk between adjacent pulses in the conventional optical time division multiplexing (OTDM) technique, were successfully suppressed, even in the case of wide pulse duration. High Q-factor performance has been maintained for a wide range of duty ration from 36% to 74%. By introducing this technique to the optical time division multiplexer, a highly stable and high-quality 40-Gb/s optical signal can be effectively produced without generating the short pulse or setting two tributaries at orthogonal polarization states, and without introducing high-speed electronics for signal multiplexing. The WDM-TDM conversion with an electroabsorption wavelength converter was extended to 60-Gb/s operation by using three 20-Gb/s tributaries. A clear eye opening was confirmed for a waveform after the WDM-TDM conversion of the 60-Gb/s signal 相似文献
220.
T. T. Wang T. H. Huang 《Tunnelling and Underground Space Technology incorporating Trenchless Technology Research》2002,17(4):425-436
Many tunnels will be constructed in southwestern Taiwan in the upcoming decade to meet the huge demands of transportation, energy and water infrastructure projects. Mudstone strata cover more than a 1000 km2 area, consisting mainly of massive mudstone or alternation of mudstone and sandy layer, exhibiting unfavorable geological and hydrological characteristics, making it extremely difficult for tunnelling. This paper presents the lessons learned from three tunnelling projects in the 1990s in a mudstone area. In addition to discussing the rock behavior in the vicinity of tunnel and its failure patterns, the monitoring data during tunnelling are presented as well. Finally, the effective method of design and construction are recommended for tunnelling in mudstone area. 相似文献