全文获取类型
收费全文 | 39761篇 |
免费 | 3419篇 |
国内免费 | 1582篇 |
专业分类
电工技术 | 3719篇 |
技术理论 | 2篇 |
综合类 | 3860篇 |
化学工业 | 3123篇 |
金属工艺 | 2064篇 |
机械仪表 | 2733篇 |
建筑科学 | 7119篇 |
矿业工程 | 1037篇 |
能源动力 | 3492篇 |
轻工业 | 2244篇 |
水利工程 | 990篇 |
石油天然气 | 1401篇 |
武器工业 | 400篇 |
无线电 | 1707篇 |
一般工业技术 | 4110篇 |
冶金工业 | 2725篇 |
原子能技术 | 489篇 |
自动化技术 | 3547篇 |
出版年
2024年 | 142篇 |
2023年 | 486篇 |
2022年 | 994篇 |
2021年 | 1165篇 |
2020年 | 1224篇 |
2019年 | 970篇 |
2018年 | 957篇 |
2017年 | 1127篇 |
2016年 | 1345篇 |
2015年 | 1378篇 |
2014年 | 2867篇 |
2013年 | 2560篇 |
2012年 | 2554篇 |
2011年 | 2980篇 |
2010年 | 2231篇 |
2009年 | 2550篇 |
2008年 | 2254篇 |
2007年 | 2798篇 |
2006年 | 2330篇 |
2005年 | 1952篇 |
2004年 | 1674篇 |
2003年 | 1576篇 |
2002年 | 1312篇 |
2001年 | 1046篇 |
2000年 | 818篇 |
1999年 | 721篇 |
1998年 | 504篇 |
1997年 | 434篇 |
1996年 | 402篇 |
1995年 | 295篇 |
1994年 | 239篇 |
1993年 | 168篇 |
1992年 | 127篇 |
1991年 | 97篇 |
1990年 | 97篇 |
1989年 | 76篇 |
1988年 | 53篇 |
1987年 | 43篇 |
1986年 | 28篇 |
1985年 | 27篇 |
1984年 | 31篇 |
1983年 | 25篇 |
1982年 | 19篇 |
1981年 | 10篇 |
1980年 | 15篇 |
1979年 | 11篇 |
1965年 | 5篇 |
1964年 | 5篇 |
1963年 | 5篇 |
1959年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
121.
The primary purpose of this work is to review the literature about what is and is not known about using ethylene vinyl acetate (EVA0 copolymer as the encapsulant (or pottant) material in photovoltaic (PV) modules. Secondary purposes include elucidating the complexity of the encapsulation problem, providing an overview about encapsulation of PV cells and modules, providing a historical overview of the relevant research and development on EVA, summarizing performance losses reported for PV systems deployed since ca. 1981, and summarizing the general problems of polymer stability in a solar environment. We also provide a critical review of aspects of reported work for cases that we believe are important.Failure modes resolved in the early work to establish reliability of deployed modules and the purposes and properties of pottants, are summarized. Typical performance losses in large field-deployed, large-scale systems ranging from 1% to 10% per year are given quantitatively, and qualitative reports of EVA discoloration are summarized with respect to ultraviolet (UV), world-wide location and site dependence.The general stability of polymers and their desirable bulk properties for solar utilization are given. The stabilization formulation for EVA, its effectiveness, and changes in it during degradation are discussed. The degradation mechanisms for the base resin, e.g., unstabilized Elvax 150TM, and stabilized EVA are indicated for literature dating to the early 1950s, and the role played by unsaturated chromophores is indicated. The limited number of studies relating discoloration and PV cell efficiency are summarized.Observed degradation of EVA or the unstabilized base resin in the laboratory and examples used to measure the degradation are summarized in sections entitled: (1) thermally-induced degradation; (2) photodegradation and photothermal degradation of EVA in different temperature regimes; (3) photobleaching and photodegradation of the UV absorber and cross-linking agent; (4) acetic acid and metal and metal-oxide catalyzed oxidative degradation; and (5) discolaration and PV cell efficiency losses.Processing effects/influences on EVA stability are discussed in sections entitled: (1) EVA raw materials and extruded, uncured films; (2) thermal encapsulation processes; (3) effects of lamination, curing, and curing peroxide on gel content and chromophores formed; and (4) incomplete shielding of curing-generated chromophores. A summary is given for the limited number of accelerated lifetime testing efforts and examples of erroneous service lifetime predictions for EVA are discussed. The known factors that effect the discoloration rate of several EVA formulations are discussed in which the reduction in rate by using UV-absorbing superstrates is a prime example. A summary is given of what is and is not known about EVA degradation mechanisms, degradation from exposures in field-deployed modeules and/or laboratory testing, and factors that contribute to EVA stability or degradation. Finally, conclusions about using Elvax 150 in EVA formulations are summarized, and future prospects for developing the next-generation pottant for encapsulating PV modules are discussed. 相似文献
122.
Ir.H.E.M. Stassen 《Renewable Energy》1994,5(5-8)
Within the European Community, the interest in energy generation from biomass and waste is increasing. A brief overview is given of several thermal conversion technologies, of biomass production and waste availability in the Netherlands. Based on this, the possibilities for energy generation from biomass and waste in the Netherlands are evaluated. 相似文献
123.
The engineering and management of human safety is an important societal objective that includes extensive efforts by governments, both legislative and administrative, to enhance the health and safety of the public. Although the achievement of safety goals depend primarily on individuals and organizations responsible for safety, much support is drawn from expertise in diverse scientific and engineering disciplines. The activities range from structural safety (dams, tunnels, bridges to tall buildings) to safe operation of hazardous industrial installations (energy generation facilities, LNG terminals, petrochemical plants) to transportation systems (airline, rail, car safety) to technologies designed to minimize adverse impacts on the environment. All these activities are crucially concerned with risk: with the likelihood and the probable effects of various measures on life and health. We have developed a unified rationale and a clear basis for effective strategic management of risk across diverse sectors. Safety is an important objective in society but it is not the only one. The allocation of society's resources devoted to safety must be continually appraised in light of competing needs, because there is a limit on the resources that can be expended to extend life. The paper presents the Life Quality Index (LQI) as a tool for the assessment of risk reduction initiatives that would support the public interest and enhance safety and quality of life. The paper provides an intuitive reformulation of the LQI as equivalent to a valid utility function that is consistent with the principles of rational decision analysis. The LQI is further refined to consider the issues of discounting of life years, competing background risks, and population age and mortality distribution. The LQI is applied to quantify the societal willingness-to-pay, which is an acceptable level of public expenditure in exchange for a reduction in the risk of death that results in improved life-quality. 相似文献
124.
PZT铁电薄膜的制备及电学性能研究 总被引:6,自引:1,他引:5
使用硝酸锆作锆源的溶胶-凝胶方法制备PZT铁电薄膜。他们的电学性能被测试包括电滞回线,电流I(t)特性,漏电流,矫顽场疲劳和老化。测到的PZT薄膜剩余极化8.2μC/cm~2,矫顽场68kV/cm.簿膜的寿命可超过10~(11)周期。 相似文献
125.
C/O测井中采用同步测量技术来分析非弹性γ与俘获γ,但在一些MSI C/O测井中发现非弹性γ的一小部分或一大部分超前于非弹性门而进入俘获门,我们把这一问题叫做“错位”。“错位”使得C/O的CI值不正常,测井曲线不合格。这样的仪器不能用来测井。吉林油田测井公司碳氧比维修班成功地解决了C/O仪器“错位”等技术难题,在该油田所使用的CZF90-94-09发生器已测井88口,累计打靶时间230h,并且至今 相似文献
126.
本文主要论述了开关磁阻电机传动技术的工作原理,系统结构和技术性能。介绍了该技术的发展背景、目前的应用情况和国内外发展水平。并对其前景表明了一些看法。 相似文献
127.
The influence of irreversibility of finite-rate heat transfer on the performance of an absorption refrigerator is investigated using an endoreversible cycle model with continuous flow. The cooling rate is adopted as an objective function for refrigerator optimization. The maximum cooling rate and the corresponding coefficient of performance are derived. The optimal performance with respect to heat transfer areas of the refrigerator is analysed. In addition, certain significant conclusions are reached. 相似文献
128.
油田开发经济运行质量研究与应用 总被引:1,自引:1,他引:0
提出了油田开发经济运行质量的研究方法和技术思路。对胜利油区几种典型的油藏类型进行了经济运行质量评价。以老河口油田桩106块为例,提出了提高油田经济运行质量的三条基本途径,取得了较好的实际应用效果。 相似文献
129.
130.
稀疏效应下一类捕食者与食饵系统极限环 总被引:1,自引:0,他引:1
蔡淑云 《吉林化工学院学报》2002,19(4):95-97
研讨了稀疏效应下一类捕食者与食饵系统 :x· =x(x(r-x) -y) ,y· =b0 y(x -m) .讨论了该系统平衡点的性态 ,并证明了该系统极限环的存在性和唯一性 . 相似文献