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   24859篇
  免费   2792篇
  国内免费   1740篇
电工技术   2931篇
技术理论   1篇
综合类   3038篇
化学工业   2603篇
金属工艺   1091篇
机械仪表   2362篇
建筑科学   1755篇
矿业工程   664篇
能源动力   766篇
轻工业   1050篇
水利工程   537篇
石油天然气   1586篇
武器工业   325篇
无线电   2558篇
一般工业技术   2488篇
冶金工业   718篇
原子能技术   322篇
自动化技术   4596篇
  2024年   124篇
  2023年   333篇
  2022年   655篇
  2021年   799篇
  2020年   830篇
  2019年   673篇
  2018年   643篇
  2017年   836篇
  2016年   901篇
  2015年   1023篇
  2014年   1589篇
  2013年   1610篇
  2012年   1869篇
  2011年   2001篇
  2010年   1460篇
  2009年   1521篇
  2008年   1387篇
  2007年   1595篇
  2006年   1419篇
  2005年   1185篇
  2004年   1042篇
  2003年   954篇
  2002年   837篇
  2001年   699篇
  2000年   608篇
  1999年   466篇
  1998年   382篇
  1997年   350篇
  1996年   286篇
  1995年   241篇
  1994年   221篇
  1993年   169篇
  1992年   167篇
  1991年   98篇
  1990年   93篇
  1989年   91篇
  1988年   54篇
  1987年   27篇
  1986年   31篇
  1985年   26篇
  1984年   23篇
  1983年   22篇
  1982年   14篇
  1981年   6篇
  1980年   4篇
  1979年   6篇
  1976年   3篇
  1959年   2篇
  1957年   2篇
  1956年   2篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
介绍了通过降低复合油相的凝固点来制备抗冻型岩石膨化硝铵炸药的方法,对多种抗冻剂的抗冻性能进行了测试和分析,并得出最佳的抗冻复合油相配方及其炸药。实验结果表明,该炸药在经过低温(-18℃)贮存后仍具有优良的物理性能和爆炸性能。  相似文献   
942.
以深度裂解石油渣油为原料,采用两段热缩聚法可制得软化点为268℃,可编性良好的中间相沥青。本文详细考察了温度,时间对中间相沥青软化点,可编性,中间相沥青形态及碳化收率的影响,并初步探讨了两段热缩聚反应的机理。研究结果表明反应温度,时间对中间相沥青的结构和性能影响较大,选择适宜石油渣油,采用加压-真空两段热缩聚法,调整反应条件,可制得可纺性良好的中间相沥青。  相似文献   
943.
PET高速纺丝方法及超高速纺丝纤维成形机理   总被引:1,自引:0,他引:1  
综述了 PET高速纺丝热辊法生产工艺 (MG)、冷辊拉伸蒸汽定型法生产工艺 (H 4S)、热管法生产工艺 (TCS)、热管拉伸法生产工艺 (HCS)以及超高速纺丝工艺 (SHSS) ;阐明了超高速纺在纺程上结构的发展与成形机理 ,以及超高速纺纺程上的细颈现象 ,超高速纺的成形机理与高速纺是不同的 ,明显区别在于细颈点的出现  相似文献   
944.
A hydrogen probe made of nickel tubing has been used to monitor the release of hydrogen from coal liquid solvents at elevated temperatures and pressures. A knowledge of this release rate is helpful in determining the overall hydrogen balance for coal liquefaction operations, in choosing among alternative solvents and in evaluating the validity of model compounds. The hydrogen release was found for coal liquids to reach a constant value when the reactor temperature was steady. In the case of some model compounds the amount of hydrogen released continued to increase and equilibrium was not attained during a 10 hours measurement period. For the coal liquids the total pressure of the system was found to increase sharply with time indicating the production of gases other than hydrogen, while for the model compounds the total pressure increases were almost parallel to the increases of the hydrogen partial pressure. A correlation was developed for the percentage of hydrogen released with the aromatic fraction distribution in the coal liquids. The hydrogen probe was a valuable instrument for continuously following the hydrogen changes in these dehydrogenation experiments.  相似文献   
945.
The surface-active properties and emulsification ability of sodium α-sulfonated fatty acid esters, CmH2m+1CH-(SO3Na)COOCnH2n+1, were studied as a function of the hydrophobic alkyl chainlength in the fatty acid (m=8−16) and the alcohol (n=8−18). As a result, it was discovered that sodium α-sulfonated fatty acid esters have a structural effect on the Krafft point different from that of amphiphiles with short alkyl chains. Moreover, some of the α-sulfonated fatty acid esters have quite low interfacial tensions, as well as non-foaming properties, which depend upon the total (m+n) number of carbon atoms in the alkyl chains.  相似文献   
946.
To increase the fertilizer-N efficiency in lowland rice (Oryza sativa L.) cultivation, new management practices are needed. Main cause of the present low efficiency is the low N recovery by plants, as a considerable part of the N applied is lost; deep placement techniques improve the recovery. A pneumatic injector, with which urea prills can be point-placed at a depth of 5–10 cm in paddy soils, was tested in 38 on-farm trials in 1989/90, mostly during the wet season. The experiments, located in Africa and Asia, focussed on differences in grain yield between conventional methods of broadcasting urea and injection by the pneumatic injector, at recommended N-rates. The study shows that the pneumatic injector is effective as a tool to improve the N fertilizer efficiency. The average yield increases per region, resulting from the use of the injector, ranged from about 250 to 1300 kg grain ha–1. The value of the yield increase would allow most farmers to recover the costs of the injector within one season, even if labour was hired to carry out the injections. The average labour requirement of the injector was 40 hours ha–1. In Indonesia, injection of prilled urea gave yields similar to those obtained with urea briquettes.  相似文献   
947.
Spherical bulb fibre optic probes, developed and applied for bubble characterization in a bubble column and a slurry bubble column at high temperature, were investigated. The principle of operation of these new optical fibre probes is based on the difference in refractive indices between the gas and the liquid phases. The interaction between the gas bubbles and the fibre optic probes in a bubble column was studied using photographic techniques. The first objective of these experiments was to study the response of the sensors upon contact with gas bubbles of various sizes. The second objective of this study was to establish, under controlled situations, the optical probe bubble detection performance and ability for local quantitative measurements of the bubble rise velocity and the gas hold-up.  相似文献   
948.
A one-dimensional steady-state mathematical model has been developed to simulate the process of calcination of petroleum coke in a rotary kiln. A simulation is made to reproduce the operating conditions prevailing during a normal working day, in order to validate the model, and to study the effects of the main process control variables. It has been found that of the energy provided by combustion, 59.5 % comes from hydrogen, 14.6 % from the carbon of the coke bed, 13.8 % from coke dust, 11.3 % from methane and 0.8 % from tar. A comparison with existing models is made to identify eventual similarities between the various kilns under study. It appears that maximum coke temperature occurs at 45 to 55 % of kiln length, while volatile matters evolution takes place between 5 and 60 % of kiln length, measured from feed end.  相似文献   
949.
Abstract. In this paper we consider techniques of spectral analysis for stationary point processes in order to study the behaviour of a complex physiological system. The estimates of the power spectrum are obtained by smoothing the periodogram which is computed very rapidly with the help of the fast Fourier transform algorithm. In the computation of the estimates we can use either the whole record of the data or a number of disjoint records.  相似文献   
950.
配煤线性规划模型的研究   总被引:9,自引:0,他引:9  
通过对配煤主要指标的理论分析和煤质实验结果的验证 ,得出了配煤的分析基灰分、水分、挥发分、硫分、固定碳、发热量、灰熔融温度都具有线性可加性的结论 ,并由此建立了配煤的线性规划模型  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