全文获取类型
收费全文 | 856篇 |
免费 | 39篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 2篇 |
综合类 | 2篇 |
化学工业 | 183篇 |
金属工艺 | 7篇 |
机械仪表 | 12篇 |
建筑科学 | 34篇 |
矿业工程 | 8篇 |
能源动力 | 14篇 |
轻工业 | 87篇 |
水利工程 | 6篇 |
石油天然气 | 4篇 |
无线电 | 54篇 |
一般工业技术 | 119篇 |
冶金工业 | 187篇 |
原子能技术 | 4篇 |
自动化技术 | 174篇 |
出版年
2024年 | 2篇 |
2023年 | 7篇 |
2022年 | 18篇 |
2021年 | 34篇 |
2020年 | 21篇 |
2019年 | 13篇 |
2018年 | 23篇 |
2017年 | 22篇 |
2016年 | 21篇 |
2015年 | 24篇 |
2014年 | 26篇 |
2013年 | 57篇 |
2012年 | 41篇 |
2011年 | 59篇 |
2010年 | 39篇 |
2009年 | 43篇 |
2008年 | 44篇 |
2007年 | 44篇 |
2006年 | 35篇 |
2005年 | 42篇 |
2004年 | 31篇 |
2003年 | 29篇 |
2002年 | 20篇 |
2001年 | 11篇 |
2000年 | 12篇 |
1999年 | 18篇 |
1998年 | 12篇 |
1997年 | 20篇 |
1996年 | 10篇 |
1995年 | 12篇 |
1994年 | 10篇 |
1993年 | 8篇 |
1992年 | 6篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 11篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 10篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1976年 | 4篇 |
1972年 | 4篇 |
1963年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有897条查询结果,搜索用时 15 毫秒
71.
A note on fracture criteria for interface fracture 总被引:1,自引:0,他引:1
Several criteria for interface fracture are examined and compared to test results obtained from glass/epoxy specimens. These include two energy release rate criteria, a critical hoop stress criterion and a critical shear stress criterion. In addition, approximate plastic zone size and shape within the epoxy are determined for these tests. 相似文献
72.
Reggia James A. Perricone Barry T. Nau Dana S. Peng Yun 《IEEE transactions on bio-medical engineering》1985,(4):268-272
This paper describes how a new method for answer justification in abductive diagnostic expert systems, presented in a preceding companion paper (Part I), can be supported in a domain-independent fashion. Both the issues of explaining why a disorder is included in a differential diagnosis and why it is ranked the way it is relative to its "competitors" are addressed. This approach to answer justification is then compared to previous work on answer justification in medical expert systems. 相似文献
73.
The issue of multiple memory systems is explored. Young and older adults (mean ages?=?20 and 71, respectively) named pictures and were tested immediately, 1, 7, or 21 days later. Episodic memory (recognition) for pictures was significantly lower in older relative to young adults and declined systematically across all retention intervals in both age groups. In contrast, procedural memory (repetition priming in picture naming) revealed no reliable age differences. In both age groups, priming declined within the first 24 hr, but unlike recognition, there was no further decrement from 1 to 21 days. There were also within-subject dissociations: The magnitude of priming was equivalent for remembered and forgotten items, and the relation between recognition and priming across intervals was nonmonotonic, revealing a reversed association. The findings were interpreted within a multiple-memory-systems framework. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
74.
75.
In most frame-based reasoning systems, the information being manipulated is represetned using frames, but the problem-solving knowledge that manipulates the frames is represented as production rules. One problem with this approach is that rules are not always a natrual way to represent knowledge; another is that systems containing lots of rules may suffer from problems with “exponetial blowup” in the amount of computation required. This paper describes a way to address these problems by organizing the problem-solving knowledge not as rules, but in a particular kind of frame hierarchy. the approach described in this paper has been implemented in a problem-solving system called SIPP (Semi-Intelligent Process Planner), which produces plans of action for the manufacture of metal parts. the paper gives an overview of SIPP, compares its knowledge representation and problem solving methods to approaches used in other knowledge-based systems, and describes goals for further research. 相似文献
76.
Xin Lu Anna Windmüller Dana Schmidt Sandro Schöner Roland Schierholz Chih-Long Tsai Hans Kungl Xunfan Liao Shicheng Yu Hermann Tempel Yiwang Chen Rüdiger-A. Eichel 《Small (Weinheim an der Bergstrasse, Germany)》2023,19(28):2300850
The structural and morphological changes of the Lithium superionic conductor Li10GeP2S12, prepared via a widely used ball milling-heating method over a comprehensive heat treatment range (50 – 700 °C), are investigated. Based on the phase composition, the formation process can be distinctly separated into four zones: Educt, Intermediary, Formation, and Decomposition zone. It is found that instead of Li4GeS4–Li3PS4 binary crystallization process, diversified intermediate phases, including GeS2 in different space groups, multiphasic lithium phosphosulfides (LixPySz), and cubic Li7Ge3PS12 phase, are involved additionally during the formation and decomposition of Li10GeP2S12. Furthermore, the phase composition at temperatures around the transition temperatures of different formation zones shows a significant deviation. At 600 °C, Li10GeP2S12 is fully crystalline, while the sample decomposed to complex phases at 650 °C with 30 wt.% impurities, including 20 wt.% amorphous phases. These findings over such a wide temperature range are first reported and may help provide previously lacking insights into the formation and crystallinity control of Li10GeP2S12. 相似文献
77.
Financial pressures on institutional health care in Canada in recent years have led to substantial pressures on institutional psychological services. These pressures have resulted in the elimination or substantial diminution of psychological services in some of these institutions, including the discontinuation of many longstanding psychology internship programs. It is therefore important for psychologists to demonstrate their cost-efficiency in delivering services. However, evidence for this efficiency in the current Canadian context is lacking. This investigation examines the costs and clinical activities of the interns and staff at a major Canadian teaching hospital in order to determine the degree to which the internship is a cost-efficient method of delivering services. The results indicate that there is a small increased cost to having the services delivered through an internship program. The results are viewed as part of a balanced scorecard approach to the evaluation of an internship program. From such a perspective, other factors can be seen as balancing out the slightly increased cost. Also, a number of strategies are outlined for increasing internship cost-efficiency. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
78.
Twinned Growth of Metal‐Free,Triazine‐Based Photocatalyst Films as Mixed‐Dimensional (2D/3D) van der Waals Heterostructures 下载免费PDF全文
Dana Schwarz Yu Noda Jan Klouda Karolina Schwarzová‐Pecková Ján Tarábek Jiří Rybáček Jiří Janoušek Frank Simon Maksym V. Opanasenko Jiří Čejka Amitava Acharjya Johannes Schmidt Sören Selve Valentin Reiter‐Scherer Nikolai Severin Jürgen P. Rabe Petra Ecorchard Junjie He Miroslav Polozij Petr Nachtigall Michael J. Bojdys 《Advanced materials (Deerfield Beach, Fla.)》2017,29(40)
Design and synthesis of ordered, metal‐free layered materials is intrinsically difficult due to the limitations of vapor deposition processes that are used in their making. Mixed‐dimensional (2D/3D) metal‐free van der Waals (vdW) heterostructures based on triazine (C3N3) linkers grow as large area, transparent yellow‐orange membranes on copper surfaces from solution. The membranes have an indirect band gap (E g,opt = 1.91 eV, E g,elec = 1.84 eV) and are moderately porous (124 m2 g?1). The material consists of a crystalline 2D phase that is fully sp2 hybridized and provides structural stability, and an amorphous, porous phase with mixed sp2–sp hybridization. Interestingly, this 2D/3D vdW heterostructure grows in a twinned mechanism from a one‐pot reaction mixture: unprecedented for metal‐free frameworks and a direct consequence of on‐catalyst synthesis. Thanks to the efficient type I heterojunction, electron transfer processes are fundamentally improved and hence, the material is capable of metal‐free, light‐induced hydrogen evolution from water without the need for a noble metal cocatalyst (34 µmol h?1 g?1 without Pt). The results highlight that twinned growth mechanisms are observed in the realm of “wet” chemistry, and that they can be used to fabricate otherwise challenging 2D/3D vdW heterostructures with composite properties. 相似文献
79.
Organic semiconductor-based photovoltaic devices offer the promise of a low-cost photovoltaic technology that could be manufactured via large-scale, roll-to-roll printing techniques. Existing organic photovoltaic devices have currently achieved solar power conversion efficiencies greater than 3%. Although encouraging, the reasons higher efficiencies have not been achieved are poor overlap between the absorption spectrum of the organic chromophores and the solar spectrum, non-ideal band alignment between the donor and acceptor species, and low charge carrier mobilities resulting from the disordered nature of organic semiconductors. To address the latter issues, we are investigating the development of nanostructured oxide/conjugated polymer composite photovoltaic (PV) devices. These composites can take advantage of the high electron mobilities attainable in oxide semiconductors and can be fabricated using low-temperature solution-based growth techniques. Additionally, the morphology of the composite can be controlled in a systematic way through control of the nanostructured oxide growth. ZnO nanostructures that are vertically aligned with respect to the substrate have been grown. Here we discuss the fabrication of such nanostructures and present results from ZnO nanofiber/poly(3-hexylthiophene) (P3HT) composite PV devices. The best performance with this cell structure produced an open circuit voltage (Voc) of 440 mV, a short circuit current density (Jsc) of 2.2 mA/cm2, a fill factor (FF) of 0.56, and a conversion efficiency (η) of 0.53%. Incorporation of a blend of P3HT and (6,6)-phenyl C61 butyric acid methyl ester (PCBM) into the ZnO nanofibers produced enhanced performance with a Voc of 475 mV, Jsc of 10.0 mA/cm2, FF of 0.43, and η of 2.03%. The power efficiency is limited in these devices by the large fiber spacing and the reduced Voc. 相似文献
80.