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   206326篇
  免费   2554篇
  国内免费   630篇
电工技术   3540篇
综合类   156篇
化学工业   30436篇
金属工艺   8150篇
机械仪表   6219篇
建筑科学   5137篇
矿业工程   1313篇
能源动力   5350篇
轻工业   17655篇
水利工程   2356篇
石油天然气   4065篇
武器工业   10篇
无线电   23672篇
一般工业技术   41107篇
冶金工业   38240篇
原子能技术   5119篇
自动化技术   16985篇
  2021年   1767篇
  2019年   1686篇
  2018年   2749篇
  2017年   2796篇
  2016年   2958篇
  2015年   1945篇
  2014年   3286篇
  2013年   9343篇
  2012年   5405篇
  2011年   7430篇
  2010年   5911篇
  2009年   6707篇
  2008年   6788篇
  2007年   6877篇
  2006年   5843篇
  2005年   5477篇
  2004年   5206篇
  2003年   5065篇
  2002年   4682篇
  2001年   4769篇
  2000年   4702篇
  1999年   4845篇
  1998年   11507篇
  1997年   8253篇
  1996年   6507篇
  1995年   4785篇
  1994年   4371篇
  1993年   4149篇
  1992年   3293篇
  1991年   3110篇
  1990年   2917篇
  1989年   3018篇
  1988年   2874篇
  1987年   2438篇
  1986年   2361篇
  1985年   2777篇
  1984年   2553篇
  1983年   2402篇
  1982年   2125篇
  1981年   2242篇
  1980年   2064篇
  1979年   2152篇
  1978年   2143篇
  1977年   2386篇
  1976年   3224篇
  1975年   1863篇
  1974年   1784篇
  1973年   1783篇
  1972年   1452篇
  1971年   1348篇
排序方式: 共有10000条查询结果,搜索用时 13 毫秒
91.
A wideband wattmeter for measuring active power over a frequency range of dc to 500 kHz is described. The wattmeter is based on the three-voltmeter method in which three rms voltage measurements are used to calculate power. The wattmeter active power uncertainty is estimated to be within 0.03% from dc to 20 kHz and within 1.5% to 500 kHz  相似文献   
92.
93.
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   
94.
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   
95.
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   
96.
97.
98.
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   
99.
Multicast (MC) routing algorithms capable of satisfying the quality of service (QoS) requirements of real-time applications will be essential for future high-speed networks. We compare the performance of all of the important MC routing algorithms when applied to networks with asymmetric link loads. Each algorithm is judged based on the quality of the MC trees it generates and its efficiency in managing the network resources. Simulation results over random networks show that unconstrained algorithms are not capable of fulfilling the QoS requirements of real-time applications in wide-area networks. Simulations also reveal that one of the unconstrained algorithms, reverse path multicasting (RPM), is quite inefficient when applied to asymmetric networks. We study how combining routing with resource reservation and admission control improves the RPM's efficiency in managing the network resources. The performance of one semiconstrained heuristic, MSC, three constrained Steiner tree (CST) heuristics, Kompella, Pasquale, and Polyzos (1992), constrained adaptive ordering (CAO), and bounded shortest multicast algorithm (BSMA), and one constrained shortest path tree (CSPT) heuristic, the constrained Dijkstra heuristic (CDKS) are also studied. Simulations show that the semiconstrained and constrained heuristics are capable of successfully constructing MC trees which satisfy the QoS requirements of real-time traffic. However, the cost performance of the heuristics varies. The BSMA's MC trees are lower in cost than all other constrained heuristics. Finally, we compare the execution times of all algorithms, unconstrained, semiconstrained, and constrained  相似文献   
100.
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   
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