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   748304篇
  免费   8406篇
  国内免费   2202篇
电工技术   13594篇
综合类   956篇
化学工业   115662篇
金属工艺   30138篇
机械仪表   23450篇
建筑科学   17138篇
矿业工程   5085篇
能源动力   19390篇
轻工业   60449篇
水利工程   8848篇
石油天然气   17929篇
武器工业   76篇
无线电   81830篇
一般工业技术   151532篇
冶金工业   131792篇
原子能技术   18519篇
自动化技术   62524篇
  2021年   6782篇
  2019年   6441篇
  2018年   11135篇
  2017年   11366篇
  2016年   11905篇
  2015年   7571篇
  2014年   12801篇
  2013年   34119篇
  2012年   19965篇
  2011年   27154篇
  2010年   21676篇
  2009年   24381篇
  2008年   24752篇
  2007年   24473篇
  2006年   21172篇
  2005年   19376篇
  2004年   18799篇
  2003年   18329篇
  2002年   17714篇
  2001年   17297篇
  2000年   16474篇
  1999年   16636篇
  1998年   39155篇
  1997年   28305篇
  1996年   21918篇
  1995年   16888篇
  1994年   15117篇
  1993年   14934篇
  1992年   11345篇
  1991年   11003篇
  1990年   10736篇
  1989年   10486篇
  1988年   9981篇
  1987年   9038篇
  1986年   8861篇
  1985年   9934篇
  1984年   9061篇
  1983年   8582篇
  1982年   7798篇
  1981年   7913篇
  1980年   7644篇
  1979年   7575篇
  1978年   7526篇
  1977年   8292篇
  1976年   10542篇
  1975年   6661篇
  1974年   6400篇
  1973年   6474篇
  1972年   5519篇
  1971年   5071篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
Translated from Kibernetika i Sistemnyi Analiz, No. 2, pp. 95–112, March–April, 1994.  相似文献   
83.
84.
85.
The process of combustion of homogeneous and heterogeneous nongasifying and slightly gasifying systems over the range of a number of parameters characterizing the reactive composition and the conditions for the arrangement of the combustion process is studied by using thermocouple and optical methods. The regions of the implementation of different combustion regimes, namely, steady, pulsating, multiple-point, and spin, are determined experimentally.Institute of Structural Macrokinetics, Russian Academy of Sciences, Chernogolovka. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 65, No. 4, pp. 407–411, October, 1993.  相似文献   
86.
An extended logistic model with a varying asymptotic upper bound for long-range peak demand forecasting is described. The model has been applied to a typical fast growing system, the Saudi Consolidated Electric Company. The forecasts are compared with actual demands and with those obtained from classical forecasting methods. The model gave relatively accurate peak demand forecasts compared with other classical methods. The model with a single load observation is capable of producing several peak demand forecasts corresponding to different levels of maximum temperature and various levels of social activity. The forecasts produced by the model were also stable irrespective of the length of the ex-post simulation period  相似文献   
87.
An experimental and theoretical analysis of the nonlinear coupling mechanism between the two solitary pulses circulating in a two-color femtosecond laser is presented. Two operation regimes; synchronized; and nonsynchronized; and a hysteresis of the transition between the two regimes are clearly observed; while independent modelocking and tunability of the output pulse trains is found in both regimes. Pulses in the range from 15 to 100 fs are synchronized with a timing jitter below 2 fs. The combined effects of cross-phase modulation and negative group velocity dispersion are shown to be responsible for the strong pulse correlation in the synchronized regime. Our experimental observations are in agreement with numerical simulations, thus confirming the theoretical model  相似文献   
88.
89.
90.
The deletion of nine residues from the C-terminus of the bacterialchloramphenicol acetyltransferase (CAT) results in depositionof the mutant protein in cytoplasmic inclusion bodies and lossof chloramphenicol resistance in Escherichia coli. This foldingdefect is relieved by C-terminal fusion of the polypeptide withas few as two residues. Based on these observations, efficientpositive selection for the cloning of DNA fragments has beendemonstrated. The cloning vector encodes a C-terminally truncatedCAT protein. Restriction sites in front of the stop codon allowthe insertion of target DNA, resulting in the production ofproperly folded CAT fusion proteins and regained chloramphenicolresistance. The positive selection of recombinants is accomplishedby growth of transformants on chloramphenicol-containing agarplates. The method appears particularly convenient for the cloningof DNA fragments amplified by the PCR because minimal informationto restore CAT folding can be included in the primers. The cloningof random sequences shows that the folding defect can be relievedby fusion to a wide variety of peptides, providing great flexibilityto the positive selection system. This vector may also contributeto the determination of the role of the C-terminus in CAT folding.  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