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   203061篇
  免费   2496篇
  国内免费   614篇
电工技术   3483篇
综合类   150篇
化学工业   29644篇
金属工艺   8065篇
机械仪表   6097篇
建筑科学   4953篇
矿业工程   1307篇
能源动力   5176篇
轻工业   17513篇
水利工程   2340篇
石油天然气   4048篇
武器工业   8篇
无线电   23243篇
一般工业技术   40566篇
冶金工业   38330篇
原子能技术   5087篇
自动化技术   16161篇
  2021年   1694篇
  2019年   1622篇
  2018年   2656篇
  2017年   2731篇
  2016年   2859篇
  2015年   1881篇
  2014年   3183篇
  2013年   9133篇
  2012年   5222篇
  2011年   7323篇
  2010年   5813篇
  2009年   6553篇
  2008年   6689篇
  2007年   6736篇
  2006年   5768篇
  2005年   5386篇
  2004年   5131篇
  2003年   5004篇
  2002年   4635篇
  2001年   4730篇
  2000年   4643篇
  1999年   4787篇
  1998年   11407篇
  1997年   8177篇
  1996年   6448篇
  1995年   4712篇
  1994年   4297篇
  1993年   4101篇
  1992年   3242篇
  1991年   3083篇
  1990年   2889篇
  1989年   2971篇
  1988年   2837篇
  1987年   2411篇
  1986年   2318篇
  1985年   2727篇
  1984年   2515篇
  1983年   2352篇
  1982年   2091篇
  1981年   2208篇
  1980年   2032篇
  1979年   2126篇
  1978年   2122篇
  1977年   2368篇
  1976年   3189篇
  1975年   1837篇
  1974年   1761篇
  1973年   1772篇
  1972年   1444篇
  1971年   1339篇
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
91.
92.
Recent studies have identified molecules that interact with integrins and appear to participate in the signaling pathways that regulate integrin adhesiveness. Clues provided by studies of these molecules point to the integration by integrins of signal transduction pathways implicated in cell division and activation.  相似文献   
93.
The cytosolic chaperonin containing TCP-1 (CCT) is known to keep fold cytoskeletal proteins and is involved in the proper organization of the cytoskeleton. These studies are based on the assumption that growth responses linked to structural rearrangement of the plant cytoskeleton include the action of CCT and the need for newly synthesized tubulin. The presence of the alpha- and epsilon-subunits of CCT was investigated in soluble fractions of protein extracts from maize mesocotyls and coleoptiles at distinct growth stages. The CCT-subunits, tubulins and actin decreased in the coleoptile in response to far-red light. In addition, independent from light treatment, the amount of CCT epsilon abundance declined with age in coleoptiles and mesocotyls between 2 and 4.5 days after sowing. In contrast to CCT epsilon, no significant light regulation of CCT alpha was found in the mesocotyl. In two day old, light-grown rapidly elongating coleoptiles part of the CCT alpha subunit and the bulk of actin and tubulin was found shifted into fractions of high molecular weight complexes when compared to slowly elongating, dark grown coleoptiles. In 4.5 day old, etiolated and elongating coleoptiles, part of both CCT-subunits and cytoskeleton proteins were found in fractions of high molecular weight. A complete disappearance of these polypeptides was observed in old far-red irradiated growth-arrested coleoptiles. CCT epsilon was found to be colocalized to microtubular structures and to the nucleus. We conclude from our data that abundance of CCT-subunits in soluble extracts is dependent on age and light treatment, but independent from the growth stage of mesocotyl and coleoptile.  相似文献   
94.
MineSet aids knowledge discovery and supports decision making based on relational data. It uses visualization and data mining to arrive at interesting results. Providing diverse visualization tools lets users choose the most appropriate method for a given problem. The client-server architecture performs most of the computationally intensive tasks on a server, while the processed results return to the client for visualization. The paper discusses MineSet database visualization and data mining visualization  相似文献   
95.
96.
97.
A simplified flash EEPROM process was developed using high-temperature LPCVD oxide both as flash cells interpoly dielectrics and as peripheral transistors gate oxide (decoding logic). An O2 anneal at 850°C lowers charge trapping and interface trap density induced by Fowler-Nordheim injection. However, electron trapping remains slightly higher than with dry thermal oxide. Similar memory charge loss and write-erase endurance are obtained as for ONO-insulated cells. HTO thus proves to have the required quality and reliability to be used in flash EEPROMs  相似文献   
98.
A value-based test is presented for economic screening of electric utility demand-side management (DSM) programs. The widely used least cost test is valid if the programs do not alter the amount or value of energy services provided to customers. But, in general, DSM programs have such effects and, as a result, the value consumers receive is changed. A more general economic efficiency test, the most value test, provides a practical method for considering the effects of DSM on customer value. The version presented allows for multiple load periods and can account for rate impacts on several customer classes. Four typical DSM programs are evaluated as illustrations  相似文献   
99.
For multiuser packet communications with unpredictable user demands (e.g., in a local or metropolitan area network), coordination and control of access to the frequency-division multiplexing (FDM) channels are difficult. B. Glance (J. Lightwave Technol., vol.10, pp.1323-1328, Sep 1992) proposed using a simple protection-against-collision (PAC) circuit to solve this media access problem and achieve full optical connectivity. The PAC system has the potential to interconnect hundreds of ports, each transmitting at several gigabits per second. Performance aspects of the PAC optical packet network are discussed here. The delay-throughout performance of this network is analyzed for uniform traffic patterns. The results show that in geographically distributed applications the maximum achievable throughput (normalized to the transmission rate) is typically between 0.4 and 0.5 per channel. In a centralized switch the (normalized) maximum achievable throughput can approach 0.8 per channel  相似文献   
100.
Bowers  B. 《IEE Review》1995,41(6):239
Of all the products of electrical technology, none has made a more profound difference to our way of life than the humble light bulb. The author describes the history of the light bulb from the time it was introduced and started to replace gas lamps to the present day. In particular the author discusses the early developments in arc lighting and incandescent filament lamps. The author also discusses the introduction of mercury vapour lamps, fluorescent lamps, and evacuation of the lamps  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