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   33837篇
  免费   805篇
  国内免费   47篇
电工技术   444篇
综合类   17篇
化学工业   6854篇
金属工艺   609篇
机械仪表   605篇
建筑科学   1399篇
矿业工程   348篇
能源动力   765篇
轻工业   2194篇
水利工程   281篇
石油天然气   252篇
武器工业   1篇
无线电   2395篇
一般工业技术   4976篇
冶金工业   8851篇
原子能技术   331篇
自动化技术   4367篇
  2022年   281篇
  2021年   453篇
  2020年   294篇
  2019年   385篇
  2018年   495篇
  2017年   422篇
  2016年   550篇
  2015年   462篇
  2014年   701篇
  2013年   1894篇
  2012年   1087篇
  2011年   1385篇
  2010年   1059篇
  2009年   1120篇
  2008年   1341篇
  2007年   1257篇
  2006年   1163篇
  2005年   1061篇
  2004年   906篇
  2003年   855篇
  2002年   843篇
  2001年   625篇
  2000年   532篇
  1999年   607篇
  1998年   1192篇
  1997年   837篇
  1996年   796篇
  1995年   648篇
  1994年   661篇
  1993年   626篇
  1992年   556篇
  1991年   381篇
  1990年   506篇
  1989年   493篇
  1988年   440篇
  1987年   503篇
  1986年   453篇
  1985年   562篇
  1984年   563篇
  1983年   470篇
  1982年   460篇
  1981年   380篇
  1980年   372篇
  1979年   426篇
  1978年   365篇
  1977年   335篇
  1976年   369篇
  1975年   280篇
  1974年   258篇
  1973年   274篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
BACKGROUND: In a series of 229 patients infected with mycobacterial organisms, we noted a specific female phenotype that involves isolated infections of the middle lobe and lingula. METHODS: Thirteen patients were found to have infections of the middle lobe, lingula, or both. All of them were infected with Mycobacterium other then Mycobacterium tuberculosis, all were women, 12 of the 13 were slender, and most had variable combinations of skeletal abnormalities. All underwent resection of the middle lobe, lingula, or both. RESULTS: There were no operative deaths. Only 2 patients have had reactivation requiring additional antibiotic therapy. All patients have had a decreased number of pulmonary infections in the postoperative period. Anatomic findings at operation included a complete major fissure and at least a partially complete minor fissure with middle lobe resections or an elongated lingula. CONCLUSIONS: Mycobacterial infection of the middle lobe and lingula is primarily a disease of asthenic women and is often associated with skeletal abnormalities and complete fissures or an elongated lingula. We recommend that surgical intervention be performed early once the condition is identified.  相似文献   
42.
A technique is presented which allows efficient calculation of substrate-coupling macromodels in integrated circuits. the technique can be used to calculate node-to-node resistances or impedances in substrate models. Examples of the technique applied to several test structures are presented.  相似文献   
43.
Text search is a type of strategic reading that involves locating specific goal-relevant information. Previous research has indicated that college and high school students often exhibit inefficient or unsuccessful text-search performance. Consequently, the effects of 2 manipulations on text-search performance were investigated: (1) the presence of indexed terms in a text-search task and (2) the use of a planning prompt before beginning a task. 34 college students engaged in 6 text-search tasks. Half of these tasks contained terms that could be used in an index; half required that a search term be generated. Half of the subjects were randomly assigned to a prompt condition in which they were prompted to plan their search before beginning each task. The results indicated that a planning prompt raised the success level of search performance, as did the presence of terms that were searchable in the textbook's index. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
44.
Direct monitoring of the free Ca2+ concentration in the sarcoplasmic reticulum (SR) was carried out in rat skeletal myotubes transfected with a specifically targeted aequorin chimera (srAEQ). Myotubes were also transfected with a chimeric aequorin (erAEQ) that we have demonstrated previously is retained in the endoplasmic reticulum (ER). Immunolocalization analysis showed that although both recombinant proteins are distributed in an endomembrane network identifiable with immature SR, the erAEQ protein was retained also in the perinuclear membrane. The difficulty of measuring [Ca2+] in 100-1000 microM range was overcome with the use of the synthetic coelenterazine analogue, coelenterazine n. We demonstrate that the steady state levels of [Ca2+] measured with srAEQ is around 300 microM, whereas that measured with erAEQ is significantly lower, i.e. around 200 microM. The effects of caffeine, high KCl, and nicotinic receptor stimulation, in the presence or absence of external calcium or after blockade of the Ca-ATPase, were investigated with both chimeras. The kinetics of [Ca2+] changes revealed by the erAEQ were similar, but not identical, neither quantitatively nor qualitatively, to those monitored with the srAEQ, indicating that at this stage of muscle development, differences exist between SR and ER in their mechanisms of Ca2+ handling. The functional implications of these findings are discussed.  相似文献   
45.
A distinction is made between atheromatous plaque formation and arteriosclerosis, only this second process is strictly age-dependent. Interactions between lipids and constituents of the vascular wall are however involved in both processes, although by different mechanisms. The progressive increase with age of elastase activity is a second important factor in the age-dependent progression of arteriosclerosis. The fragmentation of elastic fibers produces elastin peptides, present in the circulating blood in microgram/ml conc-s, increasing in several arteriopathies. The constant presence of elastin peptides in the circulation maintains activated the elastin receptor (16) on endothelial cells producing NO* with vasorelaxing activity (18). The simultaneous production of superoxyde leads to the formation of peroxynitrate, neutralized by reduced glutathion. This process, maintained over decades may well impair the antiradical defense mechanisms of the cells and deprive the endothelium from the vasorelaxing activity of NO*. We propose therefore that the maintained activation of the elastin receptor with free radical and lytic enzyme production might well represent the initiating process underlying atherogenesis.  相似文献   
46.
47.
Robert D. Cook 《Thin》1985,3(4):365-372
A cylindrical tank is mounted with its axis horizontal. Supports on either side run lengthwise. If the tank wall is thin, deformations significantly affect the stresses, so that standard stress formulae (which ignore deformations) may over-estimate stresses by a factor of ten or more. In this paper, deformations are accounted for by a nonlinear analysis. Stresses and deformed shapes are reported for various positions of the supports, radius to thickness ratios, and depths of fill.  相似文献   
48.
49.
Nicht-funktionale Anforderungen an ein Softwaresystem beschreiben Aspekte, die nicht direkt die Funktionalit?t, wie sie der Benutzer sieht, betreffen.  相似文献   
50.
Assuming significant technical success in the ITER project by the year 2015, it is likely that governments will want to develop a more comprehensive plan for DT tokamak fusion power commercialization. To provide a glimpse into many of the related issues, we construct conversations between the director of the U.S. fusion program and three specialists key to commercial fusion success: an environment and safety regulator, an environmentalist, and an electric generation investor. The insights from these imagined conversations will hopefully be of value as tokamak fusion power proponents plan beyond ITER.  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