全文获取类型
收费全文 | 26498篇 |
免费 | 1405篇 |
国内免费 | 549篇 |
专业分类
电工技术 | 4076篇 |
综合类 | 2550篇 |
化学工业 | 4604篇 |
金属工艺 | 376篇 |
机械仪表 | 729篇 |
建筑科学 | 3291篇 |
矿业工程 | 867篇 |
能源动力 | 1404篇 |
轻工业 | 1549篇 |
水利工程 | 1184篇 |
石油天然气 | 784篇 |
武器工业 | 24篇 |
无线电 | 679篇 |
一般工业技术 | 1438篇 |
冶金工业 | 2006篇 |
原子能技术 | 959篇 |
自动化技术 | 1932篇 |
出版年
2024年 | 55篇 |
2023年 | 229篇 |
2022年 | 469篇 |
2021年 | 666篇 |
2020年 | 684篇 |
2019年 | 463篇 |
2018年 | 394篇 |
2017年 | 538篇 |
2016年 | 631篇 |
2015年 | 725篇 |
2014年 | 1983篇 |
2013年 | 1483篇 |
2012年 | 2119篇 |
2011年 | 2287篇 |
2010年 | 1960篇 |
2009年 | 1646篇 |
2008年 | 1318篇 |
2007年 | 1644篇 |
2006年 | 1615篇 |
2005年 | 1311篇 |
2004年 | 1099篇 |
2003年 | 1103篇 |
2002年 | 870篇 |
2001年 | 691篇 |
2000年 | 518篇 |
1999年 | 402篇 |
1998年 | 239篇 |
1997年 | 218篇 |
1996年 | 188篇 |
1995年 | 168篇 |
1994年 | 133篇 |
1993年 | 95篇 |
1992年 | 84篇 |
1991年 | 57篇 |
1990年 | 53篇 |
1989年 | 51篇 |
1988年 | 38篇 |
1987年 | 36篇 |
1986年 | 29篇 |
1985年 | 23篇 |
1984年 | 27篇 |
1983年 | 7篇 |
1982年 | 14篇 |
1981年 | 10篇 |
1980年 | 9篇 |
1979年 | 6篇 |
1963年 | 6篇 |
1961年 | 5篇 |
1959年 | 8篇 |
1954年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
A Quantitative Critical Thinking (QCT) software tool was developed in this study to facilitate students’ learning of quantitative critical thinking via repeated practice by chemical engineering students reading a core module called fluid-solid systems. The software tool generated detailed calculation steps to typical engineering design problems encountered in this module that contained weaknesses, flaws or even errors. Students utilized the software tool to practice identifying these weaknesses, flaws or errors in the design solutions and then present a better or correct design by applying the concepts and knowledge acquired in the module. Since the QCT software tool was built upon an existing design software tool that was able to generate the correct, detailed design calculation steps to design problems, students were able to check their own design calculations against those presented by the software tool during this second learning step, thereby engaging in and learning quantitative critical thinking via a repeated practice approach. The software tool was successful in enhancing the performance of second-year undergraduate students in solving a question that required quantitative critical thinking in the final examination of the module. The average percentage scores achieved by students for the question who reported higher frequencies of usage of the software were generally higher than those who reported lower frequencies of usage or did not utilize the software tool throughout the semester. 相似文献
22.
Mengzhan Li Mingfa Li Dingding Li Suo-Min Wang Hongju Yin 《International journal of molecular sciences》2021,22(4)
Drought and salinity can result in cell dehydration and water unbalance in plants, which seriously diminish plant growth and development. Cellular water homeostasis maintained by aquaporin is one of the important strategies for plants to cope with these two stresses. In this study, a stress-induced aquaporin, ZxPIP1;3, belonging to the PIP1 subgroup, was identified from the succulent xerophyte Zygophyllum xanthoxylum. The subcellular localization showed that ZxPIP1;3-GFP was located in the plasma membrane. The overexpression of ZxPIP1;3 in Arabidopsis prompted plant growth under favorable condition. In addition, it also conferred salt and drought tolerance with better water status as well as less ion toxicity and membrane injury, which led to more efficient photosynthesis and improved growth vigor via inducing stress-related responsive genes. This study reveals the molecular mechanisms of xerophytes’ stress tolerance and provides a valuable candidate that could be used in genetic engineering to improve crop growth and stress tolerance. 相似文献
23.
24.
《Contact lens & anterior eye》2021,44(2):368-397
Evidence-based contact lens practice involves finding, appraising and applying research findings as the basis for patient management decisions. These decisions should be informed by the strength of the research study designs that address the question, as well as by the experience of the practitioner and the preferences and environment of the patient. This reports reviews and summarises the published research evidence that is available to inform soft and rigid contact lens history and symptoms taking, anterior eye health examination (including the optimised use of ophthalmic dyes, grading scales, imaging techniques and lid eversion), considerations for contact lens selection (including the ocular surface measurements required to select the most appropriate lens parameter, lens modality and material selection), evaluation of lens fit, prescribing (teaching self-application and removal, adaptation, care regimen and cleaning instructions, as well as minimising risks of lens wear through encouraging compliance) and an aftercare routine. 相似文献
25.
Dairy goat kid rearing is the foundation of future milk production, yet little is known on this topic. References available to producers are limited, making it more difficult for dairy goat farms to reach their full production potential. This review paper aimed to identify the current recommendations on dairy goat kid rearing practices for intensive production systems and to assess whether the different recommendations were based on scientific literature. Recommendations on dairy goat kid rearing practices, from birth to weaning inclusively, were presented and compared between countries under similar intensive production systems, including Canada, the United States, and France. The different areas of rearing investigated included kidding management, colostrum management, liquid and solid feeding, health management, disbudding, housing, weaning, and growth monitoring. Gaps in the literature were identified in all areas except for disbudding. More research on the topic of goat kid raising practices would be beneficial to refine and validate current recommendations. 相似文献
26.
Mehmet Tontu Mehmet Bilgili Besir Sahin 《International Journal of Hydrogen Energy》2021,46(12):8391-8400
This study deals with the implementations of electrochemical technology for the on-site production of sodium hypochlorite (NaOCl) and hydrogen from seawater for utilization in the steam power plant. The effects of electrical current and seawater temperature on the performance of electrochlorination system are investigated. The obtained results show that current efficiency increases with increasing electrical current. The current efficiency of the system is calculated as 94% at a maximum electric current with a value of 4000 A and maximum temperature with a value of 30 °C. Electricity consumption increases for the unit generation of available chlorine in the case of both enhancements of electrical current and seawater. Hydrogen generation is directly proportional to the variation of the electrical current. Also, improvement in seawater temperature provides more efficient hydrogen generation. Moreover, energy and exergy efficiencies of the whole system are positively affected by an increase of current. However, energy and exergy efficiencies are determined to be 50.4% and 3.04%, respectively, under the best operational conditions. Besides, the cheapest product cost of the hydrogen gas is calculated as $4.04/kg under the greatest electrical current and seawater temperatures. 相似文献
27.
隔震技术能有效减小核电厂上部结构的加速度响应,但强地震作用下隔震层位移过大会导致管道断裂。本文基于曲面运动原理及预压弹簧伸缩特性提出了一种负刚度阻尼系统,通过球铰在拱球面曲线运动实现负刚度特性,并在弹簧压缩方向提供黏滞阻尼性能。提出了负刚度系统的理论恢复力模型并进行了力学特性分析,设计了负刚度装置并完成了静力试验,结果显示理论恢复力模型与试验结果的一致性较理想。将核电厂负刚度阻尼隔震结构与核电厂隔震结构进行了地震响应对比分析,比较了不同地震波输入下的地震响应。结果表明负刚度阻尼系统可有效同时减小核电厂上部加速度响应和隔震层位移响应。 相似文献
28.
29.
Jia Liang Balaji Devakumar Liangling Sun Qi Sun Shaoying Wang Bin Li Daqin Chen Xiaoyong Huang 《Ceramics International》2019,45(4):4564-4569
Novel Mn4+-activated KLaMgWO6 red phosphors with different Mn4+ concentrations were successfully synthesized via a high-temperature solid-state reaction method. The phase formation, microstructure, photoluminescence properties, decay lifetimes and internal quantum efficiency were discussed to analyze the properties of the as-prepared phosphors. The samples belonged to monoclinic crystal system with enough WO6 octahedrons that provided suitable sites for Mn4+ ions. Upon the excitation of 348?nm, KLaMgWO6:Mn4+ phosphors gave bright far-red emission around 696?nm due to the 2Eg→4A2g transition of Mn4+ ions. The critical concentration of Mn4+ was 0.6?mol% and the concentration quenching mechanism belonged to electric multipolar interaction. Besides, the CIE chromaticity coordinates of the KLaMgWO6:0.6%Mn4+ phosphor were (0.7205, 0.2794) which located in deep red range, and its color purity reached up to 96.6%. The KLaMgWO6:0.6%Mn4+ sample also exhibited high internal quantum efficiency of 43%. All of the admirable optical properties indicate that the KLaMgWO6:Mn4+ phosphors can be applied to indoor plant growth illumination. 相似文献
30.
Leentje Volker 《Construction Management & Economics》2019,37(1):13-23
In reaction to the recent call for critical debate in the field of construction management research, I argue that we should embrace the richness of adjacent fields of study in order to dynamically develop our own and face the plethora of contemporary societal challenges that exist in our industry. I introduce the concepts of other-than-rational thinking in decision-making and multiplicity in management responses as examples of inspirational sources from social sciences that would contribute to truly understanding the driving forces of construction management processes. I connect these concepts to contemporary studies in construction management and share my experiences with several positive collaborative approaches in conducting construction management research. 相似文献