全文获取类型
收费全文 | 20303篇 |
免费 | 598篇 |
国内免费 | 341篇 |
专业分类
电工技术 | 324篇 |
技术理论 | 6篇 |
综合类 | 655篇 |
化学工业 | 3091篇 |
金属工艺 | 541篇 |
机械仪表 | 769篇 |
建筑科学 | 2223篇 |
矿业工程 | 563篇 |
能源动力 | 2347篇 |
轻工业 | 894篇 |
水利工程 | 3385篇 |
石油天然气 | 1167篇 |
武器工业 | 39篇 |
无线电 | 537篇 |
一般工业技术 | 1248篇 |
冶金工业 | 1289篇 |
原子能技术 | 301篇 |
自动化技术 | 1863篇 |
出版年
2024年 | 31篇 |
2023年 | 288篇 |
2022年 | 529篇 |
2021年 | 535篇 |
2020年 | 502篇 |
2019年 | 486篇 |
2018年 | 455篇 |
2017年 | 516篇 |
2016年 | 497篇 |
2015年 | 547篇 |
2014年 | 919篇 |
2013年 | 1236篇 |
2012年 | 978篇 |
2011年 | 1481篇 |
2010年 | 1141篇 |
2009年 | 1341篇 |
2008年 | 1124篇 |
2007年 | 1202篇 |
2006年 | 1070篇 |
2005年 | 951篇 |
2004年 | 790篇 |
2003年 | 728篇 |
2002年 | 576篇 |
2001年 | 464篇 |
2000年 | 436篇 |
1999年 | 448篇 |
1998年 | 342篇 |
1997年 | 290篇 |
1996年 | 260篇 |
1995年 | 244篇 |
1994年 | 211篇 |
1993年 | 117篇 |
1992年 | 122篇 |
1991年 | 82篇 |
1990年 | 58篇 |
1989年 | 58篇 |
1988年 | 39篇 |
1987年 | 43篇 |
1986年 | 31篇 |
1985年 | 26篇 |
1984年 | 11篇 |
1983年 | 9篇 |
1982年 | 13篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
On irrigation schemes with rotational irrigation systems in semiarid tropics, the existing rules for water allocation are based on applying a fixed depth of water with every irrigation irrespective of the crops, their growth stages, and soils on which these crops are grown. However, when water resources are scarce, it is necessary to allocate water optimally to different crops grown in the irrigation scheme taking account of different soils in the command area. Allocating water optimally may lead to applying less water to crops than is needed to obtain the maximum yield. In this paper, a three stage approach is proposed for allocating water from a reservoir optimally based on a deficit irrigation approach, using a simulation-optimization model. The allocation results with a deficit irrigation approach are compared for a single crop (wheat) in an irrigation scheme in India, first with full irrigation (irrigation to fill the root zone to field capacity) and second with the existing rule. The full irrigation with a small irrigation interval was equivalent to adequate irrigation (no stress to the crop). It is found that practicing deficit irrigation enables the irrigated area and the total crop production in the irrigation scheme used for the case study to be increased by about 30–45% and 20–40%, respectively, over the existing rule and by 50 and 45%, respectively, over the adequate irrigation. Allocation of resources also varied with soil types. 相似文献
82.
引用某热电厂100MW机组给水系统的变频改造实际运行和测试结果,证明在电厂给水系统中应用给水变频控制系统进行改造是切实可行的。不仅可以有效改善系统自动化水平和控制品质,而且可以取得良好的经济效益。 相似文献
83.
The catalytic activity of fresh Pd and Pt catalysts supported on γ-alumina in the complete oxidation of CH4 traces under lean-burn conditions was studied in the presence or the absence of water or H2S. Steam-aged catalysts were also studied in order to simulate long-term ageing in real lean-burn natural gas fuelled vehicles (NGVs) exhaust conditions. Without water or H2S added to the feed, Pd catalysts exhibit a superior catalytic activity in methane oxidation compared to Pt ones, whatever the catalysts were fresh or aged. The addition of 10 vol.% water vapour to the feed strongly affects the activity of the fresh Pd catalyst, thus being only slightly more efficient than the fresh Pt one. H2S has a strong poisoning effect on the catalytic activity of Pd catalysts, while Pt catalysts are more resistant. The fresh H2S-poisoned Pd/Al2O3 catalyst was studied by TPD in O2/He. Poisoning species decompose above 873 K as SO2 and O2 in relative concentrations consistent with the decomposition of surface sulphate species. However, a treatment in O2/He at temperatures as high as 923 K does not allow the complete regeneration of the catalytic activity of H2S-poisoned Pd/Al2O3. A mechanism involving the poisoning of PdO by sulphate species is proposed. Different diffusion processes by which these sulphate species can migrate back and forth between PdO and the support, depending on the experimental conditions, are suggested. 相似文献
84.
Stakeholder involvement is essential to the development of a total maximum daily load (TMDL) and its implementation plan. A tool, beyond a simulation model, is needed to support the decision making process that requires negotiation and compromise among stakeholders. The decision support system (DSS) described herein has a TMDL module to calculate various combinations of point and nonpoint loads that can meet the water quality criteria. Its Consensus module allows stakeholders to formulate, evaluate, modify, and vote for alternatives. The DSS displays bar charts for pollution loads from various subwatersheds and attributes the nonpoint loads to land uses. The water quality consequence of the pollution loads is output in maps, which shows sections meeting criteria in green and those not in red. The DSS requires a front end effort of site specific adaptation and model calibration. An Internet-based stakeholder process was developed to allow more concerned citizens to participate in management decisions. 相似文献
85.
86.
注水开发油田砂砾岩储层含油饱和度解释模型 总被引:2,自引:1,他引:1
本文利用常规测井资料,结合储层岩性、物性、含油性之间的地质规律,解决了储层岩石粒度变化及水淹层混合水电阻率变化对储层电阻率的影响;研究出了一种对电阻率测井资料标准化的校正方法;建立了储层原始、剩余、残余油饱和度解释模型。计算的储层原始、剩余、残余油地质储量,经生产验证相对下误差小于10%;计算产水率,试油验证平均绝对误差小于10%;划分水淹油层等级,试油验证符合率在80%以上。 相似文献
87.
文章介绍了宝钢自备电厂在改善锅炉燃烧工况,控制锅炉水冷壁结焦所采取的技术措施,分析了锅炉水冷壁结焦量与锅炉二次再热器烟气出口平均温度的关系,为解决锅炉水冷壁结焦所引发的二次再热器超温爆漏问题提供了依据。 相似文献
88.
五强溪水电站主体工程混凝土浇筑垂直运输在大坝两岸分高、低层布置4台平移式20t缆索起重机。其中2台高缆从德国引进,属世界上首次采用全遥控的缆机,同时也是国内塔架最高的缆机;2台低缆属我国目前自行设计制造安装的规格最大、速度最高的缆机。 相似文献
89.
利用理想的地质体积模型和电阻率测井的供电电流流过模型的导电机理,推导出一种不需要含水饱和度参数即能定量计算含水饱和度的方法,即岩性类比解释法。经过初步实践,该方法应用于砂泥岩地层的测井分析,效果良好。 相似文献
90.
岩心PI值试验研究及应用 总被引:5,自引:0,他引:5
主要论述了在多功能采油化学用剂评价仪上进行的岩心PI值试验的步骤,现象及结论。重点考察了岩心PI值与渗透率、流量及注入截面面积的关系;平行管岩心复合PI值和其中单管岩心PI值的关系。 相似文献