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   1519915篇
  免费   26027篇
  国内免费   7059篇
电工技术   34273篇
综合类   6392篇
化学工业   271346篇
金属工艺   64293篇
机械仪表   42615篇
建筑科学   46826篇
矿业工程   11478篇
能源动力   50264篇
轻工业   115502篇
水利工程   15431篇
石油天然气   37410篇
武器工业   130篇
无线电   196309篇
一般工业技术   285715篇
冶金工业   171379篇
原子能技术   33931篇
自动化技术   169707篇
  2021年   15558篇
  2020年   11858篇
  2019年   14657篇
  2018年   15227篇
  2017年   14474篇
  2016年   21201篇
  2015年   17304篇
  2014年   28707篇
  2013年   87843篇
  2012年   35907篇
  2011年   48290篇
  2010年   42338篇
  2009年   50714篇
  2008年   45094篇
  2007年   42390篇
  2006年   45250篇
  2005年   39864篇
  2004年   41978篇
  2003年   41808篇
  2002年   40794篇
  2001年   37851篇
  2000年   36168篇
  1999年   35378篇
  1998年   48341篇
  1997年   41047篇
  1996年   36457篇
  1995年   31403篇
  1994年   29292篇
  1993年   29136篇
  1992年   26234篇
  1991年   23414篇
  1990年   23709篇
  1989年   22726篇
  1988年   21327篇
  1987年   19551篇
  1986年   18898篇
  1985年   22284篇
  1984年   22422篇
  1983年   20417篇
  1982年   19315篇
  1981年   19446篇
  1980年   18075篇
  1979年   18612篇
  1978年   17812篇
  1977年   17704篇
  1976年   18664篇
  1975年   16067篇
  1974年   15581篇
  1973年   15696篇
  1972年   13129篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
An InAs/AlGaAs quantum-dot infrared photodetector based on bound-to-bound intraband transitions in undoped InAs quantum dots is reported. AlGaAs blocking layers were employed to achieve low dark current. The photoresponse peaked at 6.2 /spl mu/m. At 77 K and -0.7 V bias, the responsivity was 14 mA/W and the detectivity, D*, was 10/sup 10/ cm/spl middot/Hz/sup 1/2//W.  相似文献   
993.
994.
European remote sensing (ERS) satellites synthetic aperture radar (SAR) wind retrievals using CMOD-IFR2 are, for the first time, retrieved in the marginal ice zone (MIZ) and in Arctic coastal areas and compared with in situ observations from reseach vessels (RVs) and output from a high-resolution atmospheric model. The root mean squares (rms) of the comparisons were 1.6 m s/sup -1/ and 2 m s/sup -1/, respectively. The spatial variation of the SAR wind fields established a decrease in wind speed close to the ice edge for the late summer situations where the wind was along the ice edge with the ice to the left. This decrease is believed to be due to changes in atmospheric stability, possibly through development of an internal boundary layer caused by the cold ice cover and melt water. Lower wind speed near the ice edge is confirmed by the atmospheric model and the in situ observations. Furthermore, good results are obtained from SAR wind retrieval in leads when compared with model output during a cold-air outbreak. Routine measurements in the MIZ are useful for estimating the wind stress, and therefore SAR may play an important role in this region. Finally, the identification of a jet out from Hinlopen Strait in the Svalbard region and low wind wakes along the coast in the SAR-retrieved wind field is confirmed by in situ observations as the RV moves through the region. The jet is also confirmed by the atmospheric model, which is able to reproduce the situation.  相似文献   
995.
A study of the noise performance of gate overlapped polycrystalline silicon thin-film transistors (TFTs) is presented. Low-frequency noise measurements were carried out on n- and p-type samples fabricated by excimer laser crystallization. It is shown that the carrier number fluctuation model applies not only to n-type but also to p-type devices. The density of oxide traps was extracted from the noise measurements and was of the order of 1018-1019 eV-1 cm-3  相似文献   
996.
We prove that the entropy is a supermodular and subadditive function on the lattice of all n-dimensional probability distributions, ordered according to the partial order relation defined by majorization among vectors  相似文献   
997.
998.
Identification of Lophius budegassa(black‐bellied angler) and L. piscatorius(angler) (Lophiiformes) was carried out on the amplification of a 486 bp tRNAGlu/cytochrome b segment using the polymerase chain reaction (PCR). Direct DNA sequencing of 6 PCR products was carried out. Six restriction endonucleases (AluI, CfoI, HaeIII, HinfI, Mae, and ScrFI) with different species‐specific restriction fragment length polymorphism (RFLP) were selected. Digestions of PCR products from 30 individuals showed no intraspecific polymorphism. Double digestions (CfoI and HinfI, and HaeIII and ScrFI) were simpler and more rapid than single digestions. This technique is suitable for distinguishing tails of both Lophius species.  相似文献   
999.
Accuracy of approximations in MOSFET charge models   总被引:2,自引:0,他引:2  
This paper analyzes the results of common approximations made in MOSFET charge modeling. The basis for the comparison is a charge-sheet model that is valid in all regions of operation. We show that proper modeling of surface potential as a function of position along the channel is more important for capacitance coefficient modeling accuracy than partitioning of inversion charge between source and drain. In addition, we show that there is a numerical error in previous charge-sheet formulations, and provide a solution for this problem  相似文献   
1000.
In this paper, a physics-based mismatch model is presented. It is demonstrated on a 0.18-/spl mu/m technology that a simple mismatch model can still be used to characterize deep-submicron technologies. The accuracy of the model is examined and found to be within 20% in the strong inversion region. Bulk bias dependence is modeled in a physical way. To extract the mismatch parameters, a weighted fit is introduced. It is shown that the width and length dependence of the mismatch parameters is given by the Pelgrom model.  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