全文获取类型
收费全文 | 11681篇 |
免费 | 1291篇 |
国内免费 | 627篇 |
专业分类
电工技术 | 417篇 |
技术理论 | 4篇 |
综合类 | 1010篇 |
化学工业 | 1684篇 |
金属工艺 | 1197篇 |
机械仪表 | 940篇 |
建筑科学 | 1230篇 |
矿业工程 | 592篇 |
能源动力 | 391篇 |
轻工业 | 311篇 |
水利工程 | 693篇 |
石油天然气 | 383篇 |
武器工业 | 527篇 |
无线电 | 349篇 |
一般工业技术 | 2333篇 |
冶金工业 | 688篇 |
原子能技术 | 163篇 |
自动化技术 | 687篇 |
出版年
2024年 | 60篇 |
2023年 | 197篇 |
2022年 | 328篇 |
2021年 | 425篇 |
2020年 | 463篇 |
2019年 | 348篇 |
2018年 | 389篇 |
2017年 | 453篇 |
2016年 | 521篇 |
2015年 | 537篇 |
2014年 | 779篇 |
2013年 | 947篇 |
2012年 | 844篇 |
2011年 | 935篇 |
2010年 | 699篇 |
2009年 | 613篇 |
2008年 | 605篇 |
2007年 | 663篇 |
2006年 | 612篇 |
2005年 | 508篇 |
2004年 | 415篇 |
2003年 | 338篇 |
2002年 | 293篇 |
2001年 | 290篇 |
2000年 | 244篇 |
1999年 | 200篇 |
1998年 | 160篇 |
1997年 | 118篇 |
1996年 | 127篇 |
1995年 | 100篇 |
1994年 | 103篇 |
1993年 | 56篇 |
1992年 | 46篇 |
1991年 | 37篇 |
1990年 | 43篇 |
1989年 | 22篇 |
1988年 | 19篇 |
1987年 | 9篇 |
1986年 | 5篇 |
1985年 | 7篇 |
1984年 | 7篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1959年 | 2篇 |
1957年 | 2篇 |
1955年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Barry D. Solomon 《Energy Policy》1985,13(1):97-101
The prospects for rapid near-term development of a synfuel industry in the USA have decreased, due to depressed world oil prices, synfuel project cost overruns, and the lukewarm support of the Reagan administration. Nonetheless, socioeconomic and environmental impact analysis studies can provide valuable information for determining the regional welfare effects of proposed projects. The author discusses the results of a regional econometric analysis of the synfuel projects planned for Western Kentucky, which focuses on environmental impacts, and reveals the inevitable trade-offs that would accompany synfuel development. Some policy issues are briefly reviewed, especially that of efficient energy pricing. 相似文献
42.
该文研究了T300碳纤维单向增强的环氧复合材料,在应变率从10~(-3)/s到10~3/s范围内的冲击拉伸行为.通过对实验数据进行拟合,得出该范围内材料对应变率具有弱的敏感性,表现在破坏强度及破坏应变随应变率增加不显著变化,平均模量几乎不受应变率的影响.分析了试件的几何尺寸效应,讨论了应力波作用对破坏形态的影响以及实验中观察到的拔出现象.从应变率在10~2~10~3/s附近材料行为某些非确定性,指出在更宽范围内了解其性能的必要性. 相似文献
43.
44.
水电站的技术供水系统要根据水电站的基本技术参数及设备要求的技术供水参数进行详细设计和论证,并结合电站所在区域的实际情况,使系统满足机组在各种工况下的正常安全稳定运行。主要阐述米角河一级水电站立轴冲击式水轮发电机组技术供水系统的优化设计,采用一次冷却供水和冷却水二次循环供水相结合的设计方案,避免供水水质变化时停机造成的经济损失,提高了供水系统的运行可靠性,减少了检修维护量,为电站"无人值班,少人值守"创造了必要条件。 相似文献
45.
Seepage well is an emerging Low Impact Development (LID) technology that can effectively control the storm runoff. However, its rainwater infiltration rate and storage capacity still require further enhancement. By setting a horizontal infiltration structure at the bottom of conventional rainwater seepage well (CSW), an enhanced seepage well (ESW) was proposed in this study, and its infiltration performances compared with the permeable pavement (PP) and the CSW were systemically investigated using static infiltration experiment and HYDRUS-2D simulation. The results showed that the infiltration efficiency of ESW was significantly higher than that of PP and CSW, and the process of water infiltrated through soil mainly controlled the macroscopic infiltration rate. The Nash-Sutcliff Efficient (NSE) index was used to evaluate the accuracy and reliability of the HYDRUS-2D model, and the results of NSE values greater than 0.75 (varied between 0.75 and 0.91) confirmed the applicability of HYDRUS-2D to describe correctly the hydraulic behavior of the ESW system. Simulation infiltration tests showed that the ESW performed a higher average infiltration rate and fewer total runoff volume than the CSW, indicating the effectively enhancement of the infiltration and water retention capacity of ESW, especially under heavy rainfall intensities. Additionally, the ESW system exhibited an excellent runoff-control and rainwater retention capacity in an actual rainfall scenario. 相似文献
46.
47.
Discusses retouching of the Kallikak family photographs in H. H. Goddard's (1912) study of mental retardation and heredity, with reference to analyses by R. E. Fancher (see record 1987-31600-001) and S. J. Gould (1981), and concurs with Fancher that the retouching was probably not done for deceitful purposes. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
48.
It appears that those federal agencies responsible for enforcement persist in the belief that a given test score can mean one thing in one subgroup and something else in another and/or that inferences from a set of test scores can be valid for one subgroup but not for another. First surfacing in early agency regulations in connection with the now discontinued "differential validity" requirement, the belief still manifests itself in the concepts of "unfairness" and "adverse impact." Furthermore, the determination of the presence or absence of adverse impact on the basis of the impact ratio involves numerous statistical and measurement issues. Use of the impact ratio to establish the prosecutorial posture of an enforcement agency is clearly flawed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
49.
N. Z. Mehdizadeh M. Lamontagne C. Moreau S. Chandra J. Mostaghimi 《Journal of Thermal Spray Technology》2005,14(3):354-361
Plasma-sprayed molten molybdenum particles (∼40 μm in diameter) were photographed impinging at high velocity (∼140 m/s) on
a glass substrate at room temperature. An optical sensor detected thermal radiation emitted by a droplet as it approached
the substrate and activated a time delay unit. After a selected time interval, an Nd:YAG laser was triggered, emitting a 5
ns pulse that provided illumination for a charge-coupled device (CCD) camera to photograph the impacting droplet through a
long-range microscope. By varying the delay before pulsing the laser, different stages of droplet deformation were recorded.
Impacting droplets spread into a thin circular film that ruptured and broke into small fragments. An optical detector recording
thermal radiation from the impacting droplet gave a signal that increased as the droplet spread out, reached a maximum when
the liquid film began to rupture, and decreased as portions of the droplet recoiled because of surface tension and then flew
out of view of the photodetector. 相似文献
50.
利用citespace关键词共现分析方法,梳理了1980年以来人工智能对劳动就业影响的国内相关文献,发现目前的研究议题主要包括人工智能影响就业的机制、人工智能对就业规模的影响、人工智能对收入分配的影响、人工智能对就业形态的影响、人工智能对劳动过程与劳动关系的影响. 总体来看,目前的研究主要集中在与劳动力市场相关的议题; 理论性的论述占大多数,而具有说服力的实证研究较少; 宏观性的研究较多,深入企业与生产现场考察的微观研究较少. 未来应进一步拓展研究主题,进行多种视角与跨学科研究,重视实证研究与微观研究. 相似文献