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   86970篇
  免费   7222篇
  国内免费   3696篇
电工技术   3763篇
技术理论   8篇
综合类   7879篇
化学工业   15609篇
金属工艺   1574篇
机械仪表   1980篇
建筑科学   13392篇
矿业工程   5022篇
能源动力   5210篇
轻工业   5120篇
水利工程   18766篇
石油天然气   7685篇
武器工业   199篇
无线电   1247篇
一般工业技术   3956篇
冶金工业   3216篇
原子能技术   1122篇
自动化技术   2140篇
  2024年   201篇
  2023年   930篇
  2022年   1845篇
  2021年   2304篇
  2020年   2483篇
  2019年   2108篇
  2018年   2029篇
  2017年   2477篇
  2016年   2821篇
  2015年   2798篇
  2014年   5336篇
  2013年   5346篇
  2012年   6611篇
  2011年   6596篇
  2010年   4880篇
  2009年   5075篇
  2008年   4474篇
  2007年   5936篇
  2006年   5519篇
  2005年   5076篇
  2004年   3955篇
  2003年   3617篇
  2002年   3148篇
  2001年   2542篇
  2000年   2122篇
  1999年   1620篇
  1998年   1183篇
  1997年   973篇
  1996年   748篇
  1995年   680篇
  1994年   497篇
  1993年   381篇
  1992年   304篇
  1991年   236篇
  1990年   175篇
  1989年   187篇
  1988年   114篇
  1987年   126篇
  1986年   96篇
  1985年   95篇
  1984年   89篇
  1983年   53篇
  1982年   27篇
  1981年   10篇
  1980年   16篇
  1979年   17篇
  1978年   3篇
  1977年   8篇
  1976年   5篇
  1951年   8篇
排序方式: 共有10000条查询结果,搜索用时 468 毫秒
991.
刘立凡  郭晶  阮彩群 《精细化工》2007,24(11):1115-1118
HHE-P7为从活性污泥中筛选出的一株高效絮凝剂产生菌。通过实验确定了HHE-P7最优营养成分和培养条件:葡萄糖为碳源,酵母膏作氮源,培养基初始pH=5.0,250mL三角瓶中装液量为140mL,种子接入量为培养液容积的2%,摇床温度30℃、转速150r/min。在此操作条件下培养2d后,所产微生物絮凝剂对高岭土悬液的凝絮率为97%,絮凝剂粗品产量达4.0g/L。  相似文献   
992.
纳米二氧化钛的杀菌性能测试   总被引:9,自引:0,他引:9  
采用新工艺制备出具有光催化性的纳米二氧化钛。为了验证其杀菌性,以工业循环冷却水中的异养菌为实验对象进行杀菌实验,结果表明:自制纳米二氧化钛具有良好的杀菌性,杀菌率可达99.2%,而且可以回收,循环使用,产品有广阔的应用前景。  相似文献   
993.
Fanor Mondragon  Koji Ouchi 《Fuel》1984,63(7):973-977
Model compound studies were carried out to elucidate the reaction mechanisms taking place during the liquefaction of coal with the hydrogen produced from the reaction of zinc and water. In compounds of the type Ph-(CH2)n-Ph the splitting of the aliphatic bridge was easier with higher n values. Ether type compounds such as diphenylether were unreactive although the C-O bond in dibenzylether was easily cleaved. Condensed ring aromatic compounds gave low conversion with hydrogenation being facilitated by an increase in ring number. Phenolic compounds such as phenol did not react well, but the reactivity increased with increase in aromatic ring size. The cleavage of the aliphatic bridge was accelerated by the OH group, for example, in the case of 4-hydroxydiphenylmethane bond scission was about 15 times higher than that of diphenylmethane. Heterocyclic compounds were unreactive.  相似文献   
994.
The Rus-Umm Er Radhuma aquifer in Bahrain is a non-renewable source of brackish water (8-15 g/L), which forms a lens underlain everywhere with brines of over 100 g/L. Aquifer utilization has started in 1984 to feed a reverse osmosis (RO) desalination plant, with an economic life of 25 years (2010). Future plant upgrade strategy is formulated around boosting the plant production, which will require increasing the we llfield abstraction, in addition to a possible future rehabilitation program to extend the plant life by another 15 years (2025). The limiting factor in expanding the RO plant and its rehabilitation is the future feed water salinity, which have to be assessed before any investments are made to expand the RO plant and commission additional abstraction wells and implement the rehabilitation program. The aquifer management is based on mining a one-time brackish water reserve stored in the aquifer, the main management objective is stated as to sustain the aquifer future availability in feeding the desalination plant with a specified salinity limit of 20 g/L over the economic life of the plant of 25 years (1985-2010), and also over the plant extension period by rehabilitation (2010-2025). The stochastic analysis methodology utilizing conditional simulation is applied to conduct a risk assessment of violating these two pre-specified sustainability constraints under the proposed abstraction increase; and provided a tool to aid the decision-making process in the development and management of the aquifer under large uncertainties. Simulation results indicated that the risk of having the salinity of the wellfi eld produced water to increase due to the proposed increase in the wellfield abstraction to reach 20 g/L over the economic life of the plant (2010) is very small and minimal. However, it is questionable that the feed water salinity will be maintained under the proposed rehabilitation program to extend the plant economic life by another 15 years (2011-2025). For this option, it is recommended that model post-auditing be performed, and new updated predictions should be made as more data of potentiometry. salinity. and hydraulic parameters become available.  相似文献   
995.
本文阐述了在循环经济理论指导下,依靠科技进步自主创新改革氧化工艺,开创了治理DSD酸氧化废水的新路:源头上减少资源的投入,实现″减量化″;末端采用资源化处理技术,回收废水中有用的资源,实现″再利用″、″再循环″。成功的解决了曾经困扰DSD酸行业发展的老大难问题,促进了我国DSD酸工业的发展,从DSD酸生产和出口大国正发展成为强国。  相似文献   
996.
Fatigue crack propagation (FCP) tests were conducted at various frequencies on nylon-6,6 specimens equilibrated over a range of moisture levels to determine the crack growth rates and the crack-tip temperatures as a function of water content. Frequency-sensitivity was correlated with the amount of crack-tip heating taking place, with crack-tip temperature being found to depend strongly on the estimated loss compliance, D″, of the material. The frequency-sensitivity of FCP in nylon was seen also to be affected by mean stress, suggesting that creep processes are often significant in FCP of nylon.  相似文献   
997.
本文扼要介绍了中央空调循环冷却水和冷冻水系统中常见的问题及其原因,并对冷却水和冷冻水的处理程序作了初步的阐述.  相似文献   
998.
Different structured activated carbons were prepared from Terminalia arjuna nuts, an agricultural waste, by chemical activation with zinc chloride for the adsorption of Cr(VI) from dilute aqueous solutions. The most important parameter in chemical activation was found to be the chemical ratio (activating agent/precursor, g/g). Carbonization temperature and time are the other two important variables, which had significant effect on the pore structure of carbon. A high surface area of was obtained at a chemical ratio of 300%, carbonization time and temperature of 1 h and 500 °C, respectively. The activated carbon developed shows substantial capability to adsorb Cr(VI) from dilute aqueous solutions. The parameters studied include pH, adsorbent dosage, contact time, and initial concentrations. The kinetic data were best fitted to the Lagergren pseudo-first-order model. The isotherm equilibrium data were well fitted by the Langmuir and Freundlich models. The maximum removal of chromium was obtained at pH 1.0 (about 99% for adsorbent dose of 2 g/l and 10 mg/l initial concentration).  相似文献   
999.
分别采用二氧化氯溶液和臭氧水溶液对制药厂纯化水系统的贮罐和管道进行灭菌处理,比较灭菌效果和操作过程,最终认定臭氧水溶液灭菌方法在灭菌效率和水资源节约等方面优于二氧化氯溶液,适用于制药厂水系统管路、贮罐的灭菌处理.  相似文献   
1000.
本文通过分析传统水浴提取紫甘蓝红色素的传质机理,建立了提取过程中紫甘蓝红色素得率与各工艺条件的动力学模型。经验证,所建立的动力学理论模型与实测数据相吻合,可良好地模拟色素提取过程,用于指导工业生产。  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