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   707439篇
  免费   28167篇
  国内免费   13743篇
电工技术   25217篇
技术理论   56篇
综合类   20034篇
化学工业   112716篇
金属工艺   32163篇
机械仪表   32611篇
建筑科学   35410篇
矿业工程   12186篇
能源动力   20045篇
轻工业   53993篇
水利工程   8376篇
石油天然气   26686篇
武器工业   2618篇
无线电   85905篇
一般工业技术   111832篇
冶金工业   87078篇
原子能技术   10109篇
自动化技术   72314篇
  2023年   5939篇
  2022年   10614篇
  2021年   15257篇
  2020年   11747篇
  2019年   10514篇
  2018年   13221篇
  2017年   14490篇
  2016年   13597篇
  2015年   15207篇
  2014年   21090篇
  2013年   35926篇
  2012年   28652篇
  2011年   34354篇
  2010年   28741篇
  2009年   29246篇
  2008年   29758篇
  2007年   29241篇
  2006年   28860篇
  2005年   25713篇
  2004年   19683篇
  2003年   18637篇
  2002年   17233篇
  2001年   16994篇
  2000年   16823篇
  1999年   18860篇
  1998年   29831篇
  1997年   22341篇
  1996年   18641篇
  1995年   14887篇
  1994年   13012篇
  1993年   11496篇
  1992年   8868篇
  1991年   8185篇
  1990年   7537篇
  1989年   7019篇
  1988年   6588篇
  1987年   5549篇
  1986年   5296篇
  1985年   5749篇
  1984年   5194篇
  1983年   4927篇
  1982年   4608篇
  1981年   4425篇
  1980年   4217篇
  1979年   4035篇
  1978年   3723篇
  1977年   4496篇
  1976年   5905篇
  1975年   3196篇
  1974年   3032篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
971.
Business process redesign (BPR) has been widely touted as a means for leveraging the power of information technology to change business processes radically, resulting in substantial improvements in organizational effectiveness and efficiency. This study represents an early attempt at examining the strategic nature of the phenomenon. Because BPR is radical change and has the ability to alter both the competitive and operational nature of the corporation, it is critical that BPR be coordinated with corporate strategy. Through a survey of information system executives, the relationships between corporate competitive strategy and three types of BPR – intrafunctional, interfunctional and interorganizational – were examined. It was found that organizations following a cost strategy tended to do more BPR projects on interfunctional processes. Furthermore, the positive effect of a cost strategy on interfunctional BPR was found to be strengthened by the degree of integration of IS and business planning. It was also found that while interorganizational BPR was not related to a specific strategy, it was strongly related directly with IS–business planning integration.  相似文献   
972.
973.
The philosophy of group technology (GT) is an important concept in the design of flexible manufacturing systems and manufacturing cells. Group technology is a manufacturing philosophy that identifies similar parts and groups them into families. Beside assigning unique codes to these parts, group technology developers intend to take advantage of part similarities during design and manufacturing processes. GT is not the answer to all manufacturing problems, but it is a good management technique with which to standardize efforts and eliminate duplication. Group technology classifies parts by assigning them to different families based on their similarities in: (1) design attributes (physical shape and size), and/or (2) manufacturing attributes (processing sequence). The manufacturing industry today is process focused; departments and sub units are no longer independent but are interdependent. If the product development process is to be optimized, engineering and manufacturing cannot remain independent any more: they must be coordinated. Each sub-system is a critical component within an integrated manufacturing framework. The coding and classification system is the basis of CAPP and the functioning and reliability of CAPP depends on the robustness of the coding system. The proposed coding system is considered superior to the previously proposed coding systems, in that it has the capability to migrate into multiple manufacturing environments. This article presents the design of a coding and classification system and the supporting database for manufacturing processes based on both design and manufacturing attributes of parts. An interface with the spreadsheet will calculate the machine operation costs for various processes. This menu-driven interactive package is implemented using dBASE-IV. Part Family formation is achieved using a KAMCELL package developed in TURBO Pascal.  相似文献   
974.
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   
975.
The effect of cycloheximide on increased splanchnic prostacyclin release following acute hemorrhage was studied in the rat. Male Sprague-Dawley rats were anesthetized and subjected to acute hemorrhage to 30 mm Hg for 30 min (shock) or sham shock. The superior mesenteric artery was cannulated and removed with its end organ intestine (SV + SI preparation) and perfused in vitro with oxygenated Krebs-Henseleit buffer. Cycloheximide was infused in half of the sham and acute hemorrhage SV + SI preparations at 50 micrograms/ml. Venous effluent from all groups were analyzed for prostanoid release by radioimmunoassay. The SV + SI released 10-fold more 6-keto-prostaglandin (PG) F1 alpha than PGE2 and thromboxane. Acute hemorrhage increased SV + SI release of 6-keto-PGF1 alpha 3-fold compared to sham. Cycloheximide abolished the increased 6-keto-PGF1 alpha following acute hemorrhage but not the basal release in the sham group. Indomethacin decreased PG synthesis in all groups by 90%. Sham PG release was dependent on a stable pool of cyclooxygenase with a long half-life and was not affected by cycloheximide treatment. Acute hemorrhage stimulated a rapid induction of enzymes (cyclooxygenase, prostacyclin synthase) responsible for prostacyclin synthesis and release which were dependent on de novo protein synthesis.  相似文献   
976.
977.
978.
979.
Over 2000 electrocution deaths were identified among U.S. construction workers from 1980 to 1991, with the highest mean annual crude mortality rate (2.5 per 100,000 people), and second highest mean age-adjusted rate (2.7 per 100,000 people) of all industries. Although the crude fatality rates showed a downward trend, construction workers are still about four times more likely to be electrocuted at work than are workers in all industries combined. Nearly 40% of the 5083 fatal electrocutions in all industries combined occurred in construction, and 80% were associated with industrial wiring, appliances, and transmission lines. Electrocutions ranked as the second leading cause of death among construction workers, accounting for an average of 15% of traumatic deaths in the industry from 1980 to 1991. The study indicates that the workers most at risk of electrical injury are male, young, nonwhite, and electricians, structural metal workers, and laborers. The most likely time of injury is 11 a.m. to 3 p.m. from June to August. Focusing prevention on these populations and characteristics through better methods of worker and supervisor electrical safety training, use of adequate protective clothing, and compliance with established procedures could minimize the average annual loss of 168 U.S. construction workers.  相似文献   
980.
The phrase “not much mathematics required” can imply a variety of skill levels. When this phrase is applied to computer scientists, software engineers, and clients in the area of formal specification, the word “much” can be widely misinterpreted with disastrous consequences. A small experiment in reading specifications revealed that students already trained in discrete mathematics and the specification notation performed very poorly; much worse than could reasonably be expected if formal methods proponents are to be believed  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