首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   18913篇
  免费   739篇
  国内免费   44篇
电工技术   237篇
综合类   24篇
化学工业   3739篇
金属工艺   467篇
机械仪表   397篇
建筑科学   948篇
矿业工程   108篇
能源动力   600篇
轻工业   1634篇
水利工程   172篇
石油天然气   68篇
无线电   1457篇
一般工业技术   3364篇
冶金工业   3424篇
原子能技术   116篇
自动化技术   2941篇
  2023年   123篇
  2022年   210篇
  2021年   329篇
  2020年   234篇
  2019年   270篇
  2018年   368篇
  2017年   378篇
  2016年   413篇
  2015年   338篇
  2014年   513篇
  2013年   1218篇
  2012年   825篇
  2011年   1166篇
  2010年   799篇
  2009年   829篇
  2008年   930篇
  2007年   871篇
  2006年   759篇
  2005年   743篇
  2004年   594篇
  2003年   541篇
  2002年   526篇
  2001年   332篇
  2000年   303篇
  1999年   328篇
  1998年   355篇
  1997年   298篇
  1996年   326篇
  1995年   303篇
  1994年   289篇
  1993年   262篇
  1992年   259篇
  1991年   161篇
  1990年   230篇
  1989年   203篇
  1988年   167篇
  1987年   166篇
  1986年   156篇
  1985年   187篇
  1984年   197篇
  1983年   162篇
  1982年   170篇
  1981年   168篇
  1980年   143篇
  1979年   165篇
  1978年   123篇
  1977年   121篇
  1976年   162篇
  1975年   125篇
  1973年   108篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
This paper provides extensions of the work on subsampling by Bertail et al. in J. Econ. 120:295–326 (2004) for strongly mixing case to weakly dependent case by application of the results of Doukhan and Louhichi in Stoch. Proc. Appl. 84:313–342 (1999). We investigate properties of smooth and rough subsampling estimators for sampling distributions of converging and extreme statistics when the underlying time series is η- or λ-weakly dependent.  相似文献   
993.
994.
Die aktuelle E-Mail-Rechtssprechung macht es deutlich: Die Zeit der Beliebigkeit in der E-Mail-Kommunikation ist vorbei: E-Mails haben sich zu einer ernstzunehmenden und rechtswirksamen Kommunikationsform entwickelt.  相似文献   
995.
Millipede forming, a novel sheet metal forming method, has been proposed and developed recently to overcome fundamental limitations in conventional roll forming. For this new method, there are two main aspects: use of an optimal transitional surface and implementation of a method to feed the strip through the transition surface. Achieving the optimal transitional surface involves defining the change of surface shape between a flat strip and a final shaped product conceptualised to the strip's mid-surface, regardless of the strip's thickness.In this paper, one method of implementing a transition surface, Millipede forming, is introduced. A prototype has been built to demonstrate the working principle and can be used to produce some simple profiles, within a short forming length of 200 mm.  相似文献   
996.
The reactivity of three cytotoxic trans‐PtII complexes bearing aliphatic amine ligands, with transferrin and single‐stranded oligonucleotides as DNA models, was investigated by ESI‐MS and the results obtained are discussed in comparison with cisplatin. Tandem MS studies provided additional information on the preferential Pt binding sites. To determine whether trans‐PtII complexes can migrate from a peptide to an oligonucleotide, transfer experiments were also performed using ESI‐MS, and competitive binding of the trans‐PtII complexes toward a model peptide and different oligonucleotides was also investigated. Significant differences in the reactivity of the trans complexes with respect to cisplatin were observed. In general, adduct formation with the selected peptide is favored for the trans compounds, whereas cisplatin shows a preference for oligonucleotides, especially if adjacent G–G residues are present. The results are discussed in relation to the possible mechanism of action of the trans‐PtII complexes.  相似文献   
997.
The effects of projectile penetration into soft tissue are often studied using the tissue simulant ballistic soap. Consequently, a full understanding of the high strain-rate response of ballistic soap is desirable. Using the plate-impact technique, key shock parameters have been measured for impacts in the range 81–968 m/s, allowing derivation of the Hugoniot equation-of-state for soap in the USuP and σXuP planes. A polynomial Hugoniot relationship was found in the USuP plane, with the general form US = 1.96 + 2.41uP − 0.72uP2 (ρ0 = 1.107 g/cc). Further, embedded lateral manganin stress gauges were employed to interrogate the evolution of lateral stress within the soap. A gradient in lateral stress, whose magnitude increased incrementally with impact stress, was apparent behind the shock for σX >1 GPa. It is proposed that at higher values of σX, increased compression of hydrocarbon chains acts to increase the materials resistance to shear, a phenomenon consistent with steric hindrance.  相似文献   
998.
999.
1000.
We developed an unmanned air vehicle (UAV) suitable for small parabolic-flight experiments. The flight speed of 100 m s − 1 is sufficient for zero-gravity parabolas of 16 s duration. The flight path’s length of slightly more than 1 km and 400 m difference in altitude is suitable for ground controlled or supervised flights. Since this fits within the limits set for model aircraft, no additional clearance is required for operation. Our UAV provides a cost-effective platform readily available for low-g experiments, which can be performed locally without major preparation. A payload with a size of up to 0.9 ×0.3 ×0.3 m3 and a mass of ∼5 kg can be exposed to 0 g 0–5 g 0, with g 0 being the gravitational acceleration of the Earth. Flight-duration depends on the desired acceleration level, e.g. 17 s at 0.17 g 0 (lunar surface level) or 21 s at 0.38 g 0 (Martian surface level). The aircraft has a mass of 25 kg (including payload) and a wingspan of 2 m. It is powered by a jet engine with an exhaust speed of 450 m s − 1 providing a thrust of 180 N. The parabolic-flight curves are automated by exploiting the advantages of sophisticated micro-electronics to minimize acceleration errors.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号