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   286439篇
  免费   3482篇
  国内免费   301篇
电工技术   4302篇
综合类   118篇
化学工业   47113篇
金属工艺   15793篇
机械仪表   10787篇
建筑科学   5345篇
矿业工程   3832篇
能源动力   4617篇
轻工业   14630篇
水利工程   4425篇
石油天然气   13129篇
武器工业   32篇
无线电   22310篇
一般工业技术   69259篇
冶金工业   41657篇
原子能技术   11272篇
自动化技术   21601篇
  2021年   3573篇
  2020年   2848篇
  2019年   3362篇
  2018年   6805篇
  2017年   7109篇
  2016年   7501篇
  2015年   4064篇
  2014年   6599篇
  2013年   12604篇
  2012年   9497篇
  2011年   10955篇
  2010年   8889篇
  2009年   9535篇
  2008年   9851篇
  2007年   9317篇
  2006年   7449篇
  2005年   6462篇
  2004年   6319篇
  2003年   6052篇
  2002年   5798篇
  2001年   5367篇
  2000年   5364篇
  1999年   4790篇
  1998年   10198篇
  1997年   7628篇
  1996年   5607篇
  1995年   4341篇
  1994年   4017篇
  1993年   4202篇
  1992年   3397篇
  1991年   3561篇
  1990年   3677篇
  1989年   3560篇
  1988年   3437篇
  1987年   3417篇
  1986年   3326篇
  1985年   3502篇
  1984年   3418篇
  1983年   3269篇
  1982年   3138篇
  1981年   3201篇
  1980年   3214篇
  1979年   3372篇
  1978年   3589篇
  1977年   3640篇
  1976年   4303篇
  1975年   3291篇
  1974年   3354篇
  1973年   3411篇
  1972年   3018篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
994.
Two pairs of expanded granular sludge bed (EGSB) bioreactors, R1/R2 and R3/R4, were designed. R1/R2 were used for mesophilic (37 degrees C) treatment of synthetic wastewater over a 100-day trial. A successful start-up was achieved by R1 and R2, with COD removal over 90%. Both reactors were operated under identical parameters; however, increased organic loading induced a reduction in COD removal by R1, while R2 maintained satisfactory performance throughout the experiment. R3/R4 were operated at 15 degrees C throughout a 422-day trial and were used for the stabilisation of volatile fatty acid-based wastewater. Phenol was introduced to R4 at an applied loading rate of 1 kg phenol m(-3)d(-1), which was increased to 2 kg phenol m(-3)d(-1). No phenol was supplied to R3. Efficient COD conversion was recorded in both R3 and R4, thus demonstrating the feasibility of high-rate phenol degradation under psychrophilic conditions. Terminal restriction fragment length polymorphism analysis was applied to the characterisation of microbial community dynamics within each of the reactors. The results indicated a microbiological basis for the deviation, in terms of operational performance, of R1 and R2. TRFLP analyses indicated stable microbial communities in R3 and R4, but detected changes in the abundance of specific ribotypes in response to phenol mineralisation.  相似文献   
995.
A study has been made on the effects of loading scheme and conditions restricting macroscopic strain on the work-hardening kinetics and strain accumulation in the solid state in sintering materials with bimodal pore size distributions. Active loading intensifies the reduction in the small pores. The greatest effect comes from combining sintering with hydrostatic compression. At the same time, kinematic constraints (partial or complete adhesion in surfaces) substantially retards the shrinkage of large pores, which means that the porous structure can be controlled. __________ Translated from Poroshkovaya Metallurgiya, Nos. 5–6(449), pp. 10–15, May–June, 2006.  相似文献   
996.
The status of invasive dreissenid mussels (Dreissena polymorpha and D. bugensis) and native amphipods (Diporeia spp.) in Lake Ontario was assessed in 2003 and compared with historical data. D. polymorpha (zebra mussels) were rarely observed in 2003, having been displaced by D. bugensis (quagga mussels). D. bugensis expanded its depth range from 38 m depth in 1995 to 174 m in 2003 and this dreissenid reached densities averaging 8,000/m2 at all sites < 90 m. During the same time period, Diporeia populations almost completely disappeared from 0–90 m depth, continuing a declining trend from 1994–1997 reported in previous studies. The average density of Diporeia in the 30–90 m depth interval decreased from 1,380/m2 to 63/m2 between 1997 and 2003. Prior to 2003, areas deeper than 90 m represented a refuge for Diporeia, but even these deep populations decreased, with densities declining from 2,181/m2 in 1999 to 545/m2 in 2003. Two common hypotheses for the decline of Diporeia in the Great Lakes are food limitation and a toxin/pathogen associated with dreissenid pseudofeces. The Diporeia decline in deep waters preceded the expansion of D. bugensis to these depths, and suggests that shallow dreissenid populations remotely influence profundal habitats. This pattern of decline is consistent with mechanisms that act from some distance including nearshore dreissenid grazing and downslope transport of pseudofeces.  相似文献   
997.
Studies have shown that when smaller NiS inclusions are present the “heat-soak” method of rejecting toughened glasses does not completely guarantee that these glasses cannot fail spontaneously while in use. It is posited that the reason why glasses fail spontaneously is not so much the polymorphism of NiS as high stresses around NiS inclusions and, in consequence, a limitation on the “life” time of glass in accordance with the kinetic theory of long-term strength. __________ Translated from Steklo i Keramika, No. 5, pp. 3–6, May, 2007.  相似文献   
998.
999.
Translated from Khimicheskoe i Neftyanoe Mashinostroenie, No. 3, pp. 8–9, March, 1992.  相似文献   
1000.
Measurement of cerebrospinal concentrations of oxytocin (OT) in intact and peridural-anesthetized ewes showed that central release of OT during parturition is inhibited by this anesthesia. Also, observations of maternal behavior and attraction to amniotic fluid (AF) in inexperienced peridural-anesthetized parturient ewes after intracerebroventricular injections of either OT (2?×?10 μg) or saline showed that OT infusions increased the proportion of maternal females (2/17 vs 10/20; p?=?.01) and attraction to AF. This study confirms that in sheep vaginocervical stimulation activates the oxytocinergic system, which induces the onset of maternal behavior, and that this action is not limited to maternally experienced females. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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