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   874541篇
  免费   6672篇
  国内免费   2119篇
电工技术   16115篇
综合类   822篇
化学工业   135244篇
金属工艺   33951篇
机械仪表   26890篇
建筑科学   21476篇
矿业工程   4985篇
能源动力   22549篇
轻工业   75392篇
水利工程   9446篇
石油天然气   16443篇
武器工业   52篇
无线电   99660篇
一般工业技术   171134篇
冶金工业   154970篇
原子能技术   18497篇
自动化技术   75706篇
  2021年   7628篇
  2020年   6082篇
  2019年   7755篇
  2018年   11887篇
  2017年   12149篇
  2016年   13071篇
  2015年   8540篇
  2014年   14194篇
  2013年   40340篇
  2012年   22698篇
  2011年   31245篇
  2010年   24887篇
  2009年   27807篇
  2008年   28784篇
  2007年   28680篇
  2006年   25192篇
  2005年   22938篇
  2004年   22175篇
  2003年   21630篇
  2002年   20912篇
  2001年   20570篇
  2000年   19423篇
  1999年   19709篇
  1998年   45593篇
  1997年   33209篇
  1996年   25985篇
  1995年   20156篇
  1994年   18120篇
  1993年   17630篇
  1992年   13518篇
  1991年   12957篇
  1990年   12724篇
  1989年   12300篇
  1988年   11806篇
  1987年   10412篇
  1986年   10170篇
  1985年   11941篇
  1984年   11027篇
  1983年   10089篇
  1982年   9260篇
  1981年   9299篇
  1980年   8894篇
  1979年   8930篇
  1978年   8627篇
  1977年   9825篇
  1976年   12703篇
  1975年   7579篇
  1974年   7248篇
  1973年   7208篇
  1972年   6116篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
Translated from Kibernetika i Sistemnyi Analiz, No. 2, pp. 95–112, March–April, 1994.  相似文献   
103.
The study presents a hypothesis on how randomness could be simulated by human subjects. Three sources of deviation from randomness are predicted: (1) the preferred application of overlearned production schemata for producing sequences of digits, (2) a wrong concept of randomness, and (3) the impossibility to monitor for redundancies of higher- than those of first-order. Deviations of random generation of digits produced by healthy subjects, patients with chronic frontal lobe damage, and patients with Parkinson's disease from random sequences produced by a computer program can be explained by the differential influence of these factors. Whereas incorrect concepts of randomness and limits on monitoring capacity distinguished all sequences produced by humans from actual random sequences, persistence on a single production strategy distinguished brain-damaged patients from controls. Random generation of digits appears to be a theoretically transparent and clinically useful test of executive function.  相似文献   
104.
105.
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   
106.
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   
107.
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   
108.
109.
110.
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