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   654033篇
  免费   7701篇
  国内免费   1911篇
电工技术   11084篇
综合类   2696篇
化学工业   97565篇
金属工艺   31579篇
机械仪表   22760篇
建筑科学   13665篇
矿业工程   5476篇
能源动力   15344篇
轻工业   38972篇
水利工程   8407篇
石油天然气   17231篇
武器工业   36篇
无线电   71098篇
一般工业技术   140831篇
冶金工业   100268篇
原子能技术   16630篇
自动化技术   70003篇
  2021年   5526篇
  2020年   4274篇
  2019年   5428篇
  2018年   23312篇
  2017年   22438篇
  2016年   19992篇
  2015年   6812篇
  2014年   10765篇
  2013年   27028篇
  2012年   19058篇
  2011年   29977篇
  2010年   24750篇
  2009年   24373篇
  2008年   25952篇
  2007年   26479篇
  2006年   16812篇
  2005年   15962篇
  2004年   15292篇
  2003年   15137篇
  2002年   13881篇
  2001年   13299篇
  2000年   12756篇
  1999年   12628篇
  1998年   29792篇
  1997年   21116篇
  1996年   16145篇
  1995年   12232篇
  1994年   10914篇
  1993年   11038篇
  1992年   8375篇
  1991年   8064篇
  1990年   8128篇
  1989年   7685篇
  1988年   7374篇
  1987年   6729篇
  1986年   6520篇
  1985年   7222篇
  1984年   6781篇
  1983年   6241篇
  1982年   5788篇
  1981年   5905篇
  1980年   5645篇
  1979年   5769篇
  1978年   5878篇
  1977年   6354篇
  1976年   7791篇
  1975年   5205篇
  1974年   5116篇
  1973年   5216篇
  1972年   4546篇
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
991.
Investigation of continuously cast low-carbon aluminum-killed steel has great practical importance. Its structure and properties depend on the reeling temperature after hot rolling. After reeling at a low temperature the steel exhibits a capacity for deep drawing, whereas after reeling at a high temperature it is suitable for enameling.Translated from Metallovedenie i Tetmicheskaya Obrabotka Metallov, No. 8, pp. 23 – 24, August, 1996.  相似文献   
992.
The technological process of cold forging applied for the first time in the production of the casing of the internal joint with races is described. The process operations of cold forging and the annealing and carburizing regimes for this part me described.  相似文献   
993.
994.
Summary Polyimides (PI) having different molecular weights were prepared by condensation of oxydiphthalic anhydride with 9,9-bis-(4-aminophenyl)fluorene in nitrobenzene solution at 180°C. These polyimides carried two amino chain ends which allowed us to fix polycaprolactam chains (PA6) to obtain PA6-PI-PA6 type copolymers. The elemental analysis and infrared spectroscopic determination gave the proportion of PA6 (or PI) in the copolymers. The studies of thermal properties-DSC and TGA-allowed us to characterize the copolymers.  相似文献   
995.
The intracellular distribution of the anthracyclinic antibiotic adriamycin in living cultured cells has been investigated by confocal microscopy. In human melanoma cells (M14), adriamycin was localized inside the nuclei. When adriamycin-treated M14 cells were allowed to recover in drug-free medium, a complete efflux of the drug from the nucleus was revealed. In recovered cells, a weakly fluorescent signal was observed in the perinuclear region. When M14 cells were recovered in a medium containing colcemid, a microtubule depolymerizing agent, the drug transport from the nucleus to the cell periphery appeared to be inhibited, suggesting that the microtubule network is strongly involved in drug transport mechanisms. In multidrug-resistant (MDR) cells the intracellular location of adriamycin was shown to be noticeably different from that of the parental wild-type cells. In particular, in resistant human breast carcinoma cells (MCF-7), adriamycin appeared to be exclusively located within the cytoplasm whereas the nuclei were shown to be completely negative. When adriamycin treatment was performed in association with MDR revertants, such as Lonidamine (inhibitor of the energy metabolism) or verapamil (inhibitor of the P-glycoprotein efflux pump), a marked enhancement of the cytoplasmic signal was observed in resistant cells. Under these conditions, adriamycin appeared concentrated in the perinuclear region, but the nuclei were still negative. Confocal microscopy proved to be a very useful method for the study of the intracellular transport of fluorescent substances, such as anthracyclinic antibiotics, and for the investigation of the multidrug resistance phenomenon in tumour cells.  相似文献   
996.
The authors describe 5 cases, 3 boys and 2 girls, with idiopathic growth hormone deficiency in prepubertal age, treated with human growth hormone. In four of five cases the response to treatment with GH was relevant. Only in one case (F1) the response was negative. The results of this study confirm that rhGH is a safe and effective therapy in children with GHD.  相似文献   
997.
A fiber optic ring network, such as fiber distributed data interface (FDDI), can be operated over multiple wavelengths on its existing fiber plant consisting of point-to-point fiber links. Using wavelength division multiplexing (WDM) technology, FDDI nodes can be partitioned to operate over multiple subnetworks, with each subnetwork operating independently on a different wavelength, and inter-subnetwork traffic forwarding performed by a bridge. For this multiwavelength version of FDDI, which we refer to as wavelength distributed data interface (WDDI), we examine the necessary upgrades to the architecture of a FDDI node, including its possibility to serve as a bridge. The main motivation behind this study is that, as network traffic scales beyond (the single-wavelength) FDDI's information-carrying capacity, its multiwavelength version, WDDI, can gracefully accommodate such traffic growth. A number of design choices exist in constructing a good WDDI network. Specifically, we investigate algorithms using which, based on prevailing traffic conditions, partitioning of nodes into subnetworks can be performed in an optimized fashion. Our algorithms partition the nodes into subrings, such that the total traffic flow in the network and/or the network-wide average packet delay is minimized  相似文献   
998.
The proportion of the population over age 65 years is steadily increasing in Canada and the elderly who are unable to live independently are frequently institutionalized in chronic care facilities. We report our observations on movement disorders (MD) in an institutionalized elderly population of Saskatchewan. A representative sample of 67 subjects aged > or = 65 years had a detailed neurological evaluation on three separate occasions. MD were detected in 13 (19%) cases. The majority, 11 (16%), were females. Seven (10%) had essential tremor, 4 (6%) Parkinson's disease and 2 (3%) had drug-induced parkinsonism.  相似文献   
999.
Kale  I. Cain  G.D. Morling  R.C.S. 《Electronics letters》1995,31(20):1728-1729
A new practical design approach for minimum-phase FIR or IIR filters, setting out from a high dimensionality FIR linear-phase prototype is described. The novelty of this technique lies in overcoming the inherent problem of finding the roots of a high order polynomial with repeated and/or very closely clustered roots  相似文献   
1000.
The magnetization of a melt-texture growth (MTG) HTSC ring has been studied. It is shown that the magnetic field inside the ring is larger than the external field under a certain range of external magnetic fields. We have also investigated the magnetic field dependence of the response of a detective coil near a rotating superconducting ring. The responses of the MTG sample are different for different cooling methods.  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