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   138757篇
  免费   11162篇
  国内免费   5080篇
电工技术   6325篇
技术理论   6篇
综合类   11208篇
化学工业   34003篇
金属工艺   11074篇
机械仪表   5742篇
建筑科学   14747篇
矿业工程   4205篇
能源动力   10275篇
轻工业   10897篇
水利工程   2960篇
石油天然气   8468篇
武器工业   778篇
无线电   4750篇
一般工业技术   11534篇
冶金工业   10316篇
原子能技术   1783篇
自动化技术   5928篇
  2024年   482篇
  2023年   1480篇
  2022年   3361篇
  2021年   3850篇
  2020年   3765篇
  2019年   2884篇
  2018年   2829篇
  2017年   3551篇
  2016年   3901篇
  2015年   4055篇
  2014年   8070篇
  2013年   7730篇
  2012年   9892篇
  2011年   9621篇
  2010年   7709篇
  2009年   8270篇
  2008年   6820篇
  2007年   9771篇
  2006年   9546篇
  2005年   7907篇
  2004年   6199篇
  2003年   5960篇
  2002年   4967篇
  2001年   4048篇
  2000年   3432篇
  1999年   2826篇
  1998年   2205篇
  1997年   1846篇
  1996年   1467篇
  1995年   1294篇
  1994年   1009篇
  1993年   779篇
  1992年   680篇
  1991年   504篇
  1990年   385篇
  1989年   361篇
  1988年   246篇
  1987年   220篇
  1986年   164篇
  1985年   162篇
  1984年   175篇
  1983年   119篇
  1982年   110篇
  1981年   37篇
  1980年   54篇
  1979年   33篇
  1978年   22篇
  1977年   17篇
  1959年   39篇
  1951年   31篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
151.
The airborne sex pheromone components (Z,E)-9,12-tetradeca-dien-1-yl acetate and (Z)-9-tetradecen-1-y1 acetate from single calling females ofEphestia cautella (Walker) were trapped within glass capillary tubes and were measured by gas chromatography-mass spectrometry. Broad and similar distributions of relative quantities were found for a laboratory strain and three Australian field strains, and means differed strongly from those reported previously for this species. The overall mean proportion of the two components found for Australian females was 8812. The composition in individuals ranged from 6327 to 973. The proportions for individuals appeared to vary slightly in a random fashion from day to day, and proportions for first-generation progeny were influenced by the maternal blend.Author order in this paper is alphabetical  相似文献   
152.
For the first time, graphite fibers have been electrochemically intercalated with Br that have the same structure and properties as those intercalated from vapor phase Br2. This was accomplished by intercalating pitch-based Thornel® K-1100 graphite fibers at low temperature (near 0 °C) and high currents (2 A) for long times (6 h). The mechanism appears to be that Br is oxidized to aqueous Br2 which, when sufficient local concentration builds up, intercalates the fiber. This was confirmed by intercalating K-1100 fiber in a saturated aqueous Br2 solution without passing an electrical current. The applied voltage does apparently lower the activation energy of the reaction as evidenced by the observation that P-120 and P-100 fibers will not intercalate in aqueous Br2 unless a voltage is applied.  相似文献   
153.
电解法处理利福霉素SV钠废渣分离液的研究   总被引:2,自引:0,他引:2  
刘瑛  王娉 《工业水处理》2002,22(2):30-31
根据电化学原理,采用电解法,利用铁屑与炭粒作电极,处理利福霉素SV钠药渣分离液,讨论各种因素对分离液污染物作效果的影响,COD去除率可达91.8%左右,脱色率可达95%左右。  相似文献   
154.
十二烷基苯磺酸钠水溶液聚集性质的研究   总被引:8,自引:0,他引:8  
用滴体积法测出十二烷基苯磺酸钠(SDBS)稀水溶液的表面张力;然后求出其临界胶束浓度(CMC)。同时通过溶液的电导率、吸收光谱以及荧光光谱测定求出其CMC。这样测出的CMC值为1.2~1.6×10-3mol/L,与文献值相符。也研究了部分水解的聚丙烯酰胺(PHPAM)对SDBS聚集性质的影响;发现SDBS的CMC值随PHPAM的加人而减少并且PHPAM水溶液的粘度随SDBS的存在而急剧降低(类似盐效应)。这些方法与性质对强化采油(EOR)是重要的。  相似文献   
155.
156.
The effect of recycle on heat (and mass) transfer in concentric circular tubes has been investigated by finite difference methods. Theoretical results show that recycle can enhance the heat transfer rate for large Graetz numbers compared with that in an open tube (without an inner tube inserted and without recycle). Competition between a preheating effect and a residence-time effect can be used to explain the heat transfer behavior. The heat transfer rate can be further augmented, with nearly no increase in total pressure drop, by employing flow pattern B instead of flow pattern A.  相似文献   
157.
Heat transfer characteristics for a falling turbulent liquid film flow over a fin are analyzed using the conjugate convection-conduction theory. Numerical results are obtained from a simultaneous solution of the energy equations of the fluid and the fin. Results are presented for the fin temperature distribution, dimensionless heat transfer coefficients, local heat fluxes, and fin efficiencies.  相似文献   
158.
A single sex pherormone component was isolated from abdominal tip extracts of female Bruce spanworm.Operophtera bruceata (Hulst). This was identified as (Z,Z,Z)-1,3,6,9-nonadecatetraene by capillary gas chromatography (GC), electroantennography, and mass spectrometry. In addition, hexane extracts of female abdominal tips from Bruce spanworm and the winter moth.O. brumata L., were analyzed by GC coupled to an electroantennographic detector (GC-EAD). The extracts ofO. bruceata andO. brumata females elicited only a single response, at the same retention time, from antennae of their conspecific and reciprocal males. In field tests conducted in Saskatchewan, traps baited with the synthetic tetraene captured Bruce spanworm males. In tests carried out on Vancouver Island, British Columbia, where the two species coexist, both Bruce spanworm and winter moth males were captured. The attractancy of lures containing the synthetic pheromone alone and in combination with several structurally related analogs was field tested at both locations. One of these, an isomer of the natural pheromone, (E,Z,Z)-1,3,6,9-nonadecatetraene, inhibited the capture of Bruce spanworm males but had no effect upon the number of winter moth males which were taken. Thus, populations of these two very similar species can be distinguished by employing traps baited with pheromone ± the inhibitor. Coneorifice Hara traps were found useful for field trapping males of both species.Issued as NRCC No. 26107  相似文献   
159.
介绍板壳式换热器的主要特点和应用。当壳体与板束温差较大时,笔者通过对产品开发的生产实践,提出解决板壳式换热器要否设置膨胀节的类似判定方法。  相似文献   
160.
塑料啤酒瓶开发现状   总被引:1,自引:0,他引:1  
介绍了塑料啤酒瓶的优点,详细介绍了各种以PET为基础的改性啤酒瓶材料,并列举了大量的开发实例。  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