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   4019篇
  免费   19篇
  国内免费   1篇
电工技术   20篇
综合类   17篇
化学工业   282篇
金属工艺   55篇
机械仪表   29篇
建筑科学   34篇
矿业工程   11篇
能源动力   11篇
轻工业   119篇
水利工程   17篇
石油天然气   3篇
武器工业   2篇
无线电   68篇
一般工业技术   251篇
冶金工业   2981篇
原子能技术   26篇
自动化技术   113篇
  2023年   8篇
  2021年   10篇
  2018年   7篇
  2016年   8篇
  2014年   26篇
  2013年   44篇
  2012年   45篇
  2011年   62篇
  2010年   48篇
  2009年   48篇
  2008年   57篇
  2007年   77篇
  2006年   46篇
  2005年   41篇
  2004年   40篇
  2003年   45篇
  2002年   36篇
  2001年   21篇
  2000年   26篇
  1999年   101篇
  1998年   869篇
  1997年   510篇
  1996年   294篇
  1995年   190篇
  1994年   186篇
  1993年   200篇
  1992年   29篇
  1991年   69篇
  1990年   57篇
  1989年   51篇
  1988年   48篇
  1987年   46篇
  1986年   55篇
  1985年   49篇
  1984年   14篇
  1983年   18篇
  1982年   25篇
  1981年   41篇
  1980年   29篇
  1979年   14篇
  1978年   23篇
  1977年   113篇
  1976年   189篇
  1975年   12篇
  1974年   15篇
  1973年   14篇
  1972年   8篇
  1971年   7篇
  1970年   7篇
  1966年   8篇
排序方式: 共有4039条查询结果,搜索用时 9 毫秒
91.
水资源优化配置调度系统信息传输通道建设   总被引:2,自引:0,他引:2  
监测站分中心省中心图1信息传递流程示意图2传输通道建设本系统设分中心站2个(鞍山水文分局、辽阳水文分局),端站16个。超短波电台采用进口专用数传电台,工作频率段为国家无委专为水利系统批准的230MHz数传频点。辽宁中部地区的水系主要包括辽河干流、浑河、太子河、大辽河、绕  相似文献   
92.
Aqueous film-forming foams (AFFF) are complex mixtures containing fluorocarbon- and hydrocarbon-based surfactants that are used to fight hydrocarbon-fueled fires. The military is the largest consumer of AFFF in the United States, and fire-training activities conducted at military bases have led to groundwater contamination by unspent fuels and AFFF chemicals. A direct-injection, liquid-chromatography tandem mass spectrometry (LC MS/MS) method was developed to quantify a suite of fluorotelomer sulfonate surfactants in groundwater collected from military bases where fire-training activities were conducted. The 4:2, 6:2, and 8:2 fluorotelomer sulfonates were detected and quantified in groundwater from two of the three military bases. The total fluorotelomer sulfonate concentrations observed at Wurtsmith AFB, MI, and Tyndall AFB, FL, ranged respectively from below quantitation (< or = 0.60) to 182 microg/L and from 1100 to 14,600 microg/L. Analyses of a fluorotelomer-based AFFF concentrate by negative ion fast atom bombardment/mass spectrometry and LC MS/MS analyses indicate that the AFFF concentrate contains only a small amount of fluorotelomer sulfonates and that fluoroalkylthioamido sulfonates are the main anionic fluorosurfactant in the mixtures. More research is needed to determine the fate of fluoroalkylthioamido sulfonates in the environment.  相似文献   
93.
While deep hydrodesulfurization of gas oil is more and more important, elimination of sulfur compounds such as 4,6-dialkyldibenzothio-phenes still attracts considerable attention. A new process based on the association of a separation process by charge-transfer complex (CTC) formation and classical catalytic hydrotreating (HDT) was evaluated. The results indicated that a CTC pretreatment allows the rate of hydrodesulfurization (HDS) to increase and the final sulfur level to decrease. This process is even more efficient for feeds difficult to desulfurize.  相似文献   
94.
稀土与L-酪氨酸甘氨酸三元固态配合物的合成与表征   总被引:1,自引:0,他引:1  
刘颖  宝迪  嘎日迪 《化学世界》2000,41(7):358-359,365
在乙醇溶液中合成了四种稀土与 L-酪氨酸、甘氨酸的三元固态配合物 RE( Tyr) 1.5 ( Gly) 4 ( Cl O4) 3( RE=La3+、Ce3+、Gd3+、Y3+) ,并通过摩尔电导、热分析、红外光谱等进行了表征。  相似文献   
95.
In this fish‐feeding study, we tested similarity patterns between fatty acids (FA) in diets and common carp (Cyprinus carpio) of fish ponds used for semi‐intensive aquaculture, containing naturally occurring pond zooplankton and different feeds (marine or terrestrial feeds) until carp reached market size. We evaluated if and how total lipid contents in dorsal fillets can reflect dietary FA compositions in farm‐raised common carp and hypothesized that increasing total lipid contents in dorsal fillets significantly increase the similarity between dietary and dorsal fillets’ FA compositions. Results of this study showed that carps had higher total lipids when supplied with marine feeds and dietary FA compositions were indeed more strongly reflected in fatty (i.e. high total lipid contents) than in leaner dorsal fillets (low total lipid contents). Increasing total lipid contents in dorsal fillets significantly increased the similarity between the dietary and dorsal fillets’ FA compositions. In contrast, leaner dorsal fillets had FA patterns that were more distinct from dietary FA. Total lipid contents higher than ~60 mg/g dry weight in dorsal fillets had only limited effects on increasing the similarity between FA compositions of diets and dorsal fillets, and were independent of feed sources. It is thus suggested that higher total lipid contents in dorsal fillets can be used as a proxy to predict dietary FA profiles in common carps, or perhaps even in farm‐raised fish in general.  相似文献   
96.
以2,4,6-三甲基苯甲醛为原料,通过相转移催化反应在水-氯仿体系中先合成α-羟基-2,4,6-三甲基苯乙酸(收率52%);再通过次磷酸还原α-羟基-2,4,6-三甲基苯乙酸得到最终产物2,4,6-三甲基苯乙酸(收率91%)。此法绿色便捷,成本相对较低。  相似文献   
97.
主蒸汽压力是电厂热工过程控制中的重要参数,由于锅炉燃烧工况变化较大,主汽压对象模型具有不确定性,常规控制方法很难得到预期的控制效果。为提高系统控制品质,提出了主汽压系统的H∞混合灵敏度设计方法,给出了选择加权函数的具体方法,采用MATLAB软件进行仿真计算,得到H∞最优控制器。仿真结果表明,在对象模型参数发生较大变化时,与常规PID调节方法相比,H∞最优控制器能使主汽压控制系统具有良好的鲁棒稳定性和动态性能。  相似文献   
98.
地方煤矿安全现状的模糊综合评价研究   总被引:2,自引:0,他引:2  
对山西省临汾地区4个县的地方煤矿安全现状进行研究,收集了200多份地方煤矿安全现状综合评价资料。利用层次分析法,建立了地方煤矿安全现状综合评价指标体系;采用模糊综合评价方法,对临汾地区4个县的地方煤矿以县级为单位分别进行了模糊综合评价及分析比较研究,论述了模糊综合评价方法的有效性及其在地方煤矿系统安全评价中的应用前景,为模糊综合评价方法在矿业系统工程的推广应用拓展了思路。  相似文献   
99.
This paper develops and applies a model that locates hydrogen stations to refuel the maximum volume of vehicle flows. Inputs to the model include a road network with average speeds; the origin–destination flow volumes between each origin and destination; a maximum driving range between refueling stops; and the number of stations to build. The Flow-Refueling Location Model maximizes the flow volumes that can be refueled, measured either in number of trips or vehicle-miles traveled. Geographic Information Systems and heuristic algorithms are integrated in a spatial decision support system that researchers can use to develop data, enter assumptions, analyze scenarios, evaluate tradeoffs, and map results. For the Florida Hydrogen Initiative, we used this model to investigate strategies for rolling out an initial refueling infrastructure in Florida at two different scales of analysis: metropolitan Orlando and statewide. By analyzing a variety of scenarios at both scales of analysis, we identify a robust set of stations that perform well under a variety of assumptions, and develop a strategy for phasing in clustered and connecting stations in several stages or tiers.  相似文献   
100.
Recycling water is not new. Yet, there are many examples from around the world of recycled water projects that have failed because of public opposition. This article reviews the literature investigating factors associated with public acceptance of recycled water, as well as publicly accessible reports and case studies, which have developed or tested approaches to increase public acceptance. The article concludes by summarizing the state of knowledge in this area, and advancing key research questions relating to public acceptance of recycled water that urgently need to be investigated.  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