全文获取类型
收费全文 | 5120篇 |
免费 | 138篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 77篇 |
综合类 | 5篇 |
化学工业 | 1008篇 |
金属工艺 | 120篇 |
机械仪表 | 74篇 |
建筑科学 | 203篇 |
矿业工程 | 27篇 |
能源动力 | 97篇 |
轻工业 | 399篇 |
水利工程 | 42篇 |
石油天然气 | 23篇 |
无线电 | 467篇 |
一般工业技术 | 853篇 |
冶金工业 | 1193篇 |
原子能技术 | 84篇 |
自动化技术 | 587篇 |
出版年
2022年 | 42篇 |
2021年 | 58篇 |
2020年 | 48篇 |
2019年 | 51篇 |
2018年 | 58篇 |
2017年 | 67篇 |
2016年 | 73篇 |
2015年 | 73篇 |
2014年 | 94篇 |
2013年 | 264篇 |
2012年 | 166篇 |
2011年 | 190篇 |
2010年 | 158篇 |
2009年 | 145篇 |
2008年 | 216篇 |
2007年 | 176篇 |
2006年 | 180篇 |
2005年 | 140篇 |
2004年 | 149篇 |
2003年 | 139篇 |
2002年 | 134篇 |
2001年 | 94篇 |
2000年 | 101篇 |
1999年 | 117篇 |
1998年 | 254篇 |
1997年 | 186篇 |
1996年 | 165篇 |
1995年 | 90篇 |
1994年 | 111篇 |
1993年 | 97篇 |
1992年 | 74篇 |
1991年 | 56篇 |
1990年 | 55篇 |
1989年 | 48篇 |
1988年 | 80篇 |
1987年 | 57篇 |
1986年 | 50篇 |
1985年 | 65篇 |
1984年 | 61篇 |
1983年 | 46篇 |
1982年 | 48篇 |
1981年 | 55篇 |
1980年 | 43篇 |
1979年 | 37篇 |
1978年 | 52篇 |
1977年 | 67篇 |
1976年 | 78篇 |
1975年 | 45篇 |
1974年 | 34篇 |
1972年 | 36篇 |
排序方式: 共有5259条查询结果,搜索用时 15 毫秒
101.
102.
Jian Li Carl Rau 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2005,230(1-4):518-523
Scanning ion microscopy with polarization analysis (SIMPA) is used to study the spin-resolved surface magnetic structure of nano-sized magnetic systems. SIMPA is utilized for in situ topographic and spin-resolved magnetic domain imaging as well as for focused ion beam (FIB) etching of desired structures in magnetic or non-magnetic systems. Ultra-thin Co films are deposited on surfaces of Si(1 0 0) substrates, and ultra-thin, tri-layered, bct Fe(1 0 0)/Mn/bct Fe(1 0 0) wedged magnetic structures are deposited on fcc Pd(1 0 0) substrates. SIMPA experiments clearly show that ion-induced electrons emitted from magnetic surfaces exhibit non-zero electron spin polarization (ESP), whereas electrons emitted from non-magnetic surfaces such as Si and Pd exhibit zero ESP, which can be used to calibrate sputtering rates in situ. We report on new, spin-resolved magnetic microstructures, such as magnetic “C” states and magnetic vortices, found at surfaces of FIB patterned magnetic elements. It is found that FIB milling has a negligible effect on surface magnetic domain and domain wall structures. It is demonstrated that SIMPA can evolve into an important and efficient tool to study magnetic domain, domain wall and other structures as well as to perform magnetic depth profiling of magnetic nano-systems to be used in ultra-high density magnetic recording and in magnetic sensors. 相似文献
103.
Both mechanical compaction and addition of pozzolanic silica fumes can provide low permeability interfacial transition zones around the fibers which reinforce a mortar matrix. This paper deals with the controversial effect of achieving a higher matrix compactness and its influence on the fracture behaviour of a mortar reinforced with amorphous cast iron fibers. Test were conducted in uniaxial tension on notched composite mortar prisms in order to plot load versus crack opening curves and evaluate the bridging energy provided by the fibers across a single opening crack. These measures were correlated to SEM observations of the microstructure of fiber/mortar interface, depending on the compaction energy and/or the mortar composition. It is relatively difficult to establish a compromise between ductility and high performance in terms of durability for the material system tested. Indeed, fibers were pulled out of low compactness mortars exhibiting large porous interfacial transition zones (ITZs) along the fiber surface. These zones mainly comprised fibrillous CSH, ettringite and large portlandite crystals. Conversely, when the ITZs around the fibers where filled with compact CSH, resulting from the pozzolanic reaction between silica fume and portlandite, no fiber slippage was observed, but the reinforced mortar broke in a quasi-brittle manner. 相似文献
104.
Sheikh M. Uddin Tanvir Mahmud Christoph Wolf Carsten Glanz Ivica Kolaric Christoph Volkmer Helmut Höller Ulrich Wienecke Siegmar Roth Hans-Jörg Fecht 《Composites Science and Technology》2010
Utilizing the extra-ordinary properties of carbon nanotube (CNT) in metal matrix composite (MMC) for macroscopic applications is still a big challenge for science and technology. Very few successful attempts have been made for commercial applications due to the difficulties incorporating CNTs in metals with up-scalable processes. CNT reinforced copper and copper alloy (bronze) composites have been fabricated by well-established hot-press sintering method of powder metallurgy. The parameters of CNT–metal powder mixing and hot-press sintering have been optimized and the matrix materials of the mixed powders and composites have been evaluated. However, the effect of shape and size of metal particles as well as selection of carbon nanotubes has significant influence on the mechanical and electrical properties of the composites. The hardness of copper matrix composite has improved up to 47% compared to that of pure copper, while the electrical conductivity of bronze composite has improved up to 20% compared to that of the pure alloy. Thus carbon nanotube can improve the mechanical properties of highly-conductive low-strength copper metals, whereas in low-conductivity high-strength copper alloys the electrical conductivity can be improved. 相似文献
105.
pH Sensing Properties of Flexible,Bias‐Free Graphene Microelectrodes in Complex Fluids: From Phosphate Buffer Solution to Human Serum 下载免费PDF全文
Jinglei Ping Jacquelyn E. Blum Ramya Vishnubhotla Amey Vrudhula Carl H. Naylor Zhaoli Gao Jeffery G. Saven Alan T. Charlie Johnson 《Small (Weinheim an der Bergstrasse, Germany)》2017,13(30)
Advances in techniques for monitoring pH in complex fluids can have a significant impact on analytical and biomedical applications. This study develops flexible graphene microelectrodes (GEs) for rapid (<5 s), very‐low‐power (femtowatt) detection of the pH of complex biofluids by measuring real‐time Faradaic charge transfer between the GE and a solution at zero electrical bias. For an idealized sample of phosphate buffer solution (PBS), the Faradaic current is varied monotonically and systematically with the pH, with a resolution of ≈0.2 pH unit. The current–pH dependence is well described by a hybrid analytical–computational model, where the electric double layer derives from an intrinsic, pH‐independent (positive) charge associated with the graphene–water interface and ionizable (negative) charged groups. For ferritin solution, the relative Faradaic current, defined as the difference between the measured current response and a baseline response due to PBS, shows a strong signal associated with ferritin disassembly and the release of ferric ions at pH ≈2.0. For samples of human serum, the Faradaic current shows a reproducible rapid (<20 s) response to pH. By combining the Faradaic current and real‐time current variation, the methodology is potentially suitable for use to detect tumor‐induced changes in extracellular pH. 相似文献
106.
107.
Carl J. McHargue Joseph P. Hammond 《JOM Journal of the Minerals, Metals and Materials Society》1953,5(1):57-61
The wire textures for cold rolled and recrystallized iodide titanium and the sheet textures for this material produced by cold and hot rolling, and recrystallization at a series of temperatures were determined. The effect of the α → β transformation on the sheet texture was noted. 相似文献
108.
Karl Sauer Diemair E. Dinslage Kanitz Schwaibold Willy Lindner Haevecker Lehnartz E. Becker W. Schreiber Werner Hofmann Eduard Hofmann Steinbeck H. Süllmann Griebel Rudolf Abderhalden Lars Erlandsen Heyns O. v. Soden C. Steinhoff J. Großfeld Frey-Wyssling W. Sutthoff Bäurle Willy Lindner Ed. Rentz Bandow Gerards K. N. v. Kaulla O. v. Soden Maria Cicconi Pawletta Baars R. Grau Lerche Beckel O. Windhausen Felicitas Rolleri Jesser Karl Boresch R. W. Seuffert K. Müller Schloemer K. Höll Johannes Wolf Brüning Patzsch W. Ludorff 《European Food Research and Technology》1941,81(3):223-288
109.
Kräß af Ekenstam R. Trendelenburg Zeller Frey-Wyssling M. Wolf G. Becker Liese Thienhaus Graf A. Troche A. v. Wacek O. Kratky M. Lüdtke Gustav G. Klem Schulz K. Storch Müller E. Becker Klauditz K. Nising A. Nowak L. Metz Egner Fessel Thiele Kraemer Lehnartz Kaiser Tiemann B. Thunell 《Holz als Roh- und Werkstoff》1940,3(11):383-393
Ohne Zusammenfassung 相似文献
110.
The change of operating parameters above threshold of (Ga, Al)As injection lasers with aging time was calculated assuming a uniform mode of degradation mechanism with temperature-dependent degradation rates. In the calculation, the degradation rate for the threshold current was assumed to be temperature dependent, but not explicitly dependent on aging time and pumping current. Optical output power was kept constant during aging. The calculated time variation of laser parameters predicts a runaway after an initial slow rise. The mathematical model thus provides the means to correlate time-to-failure data with initial degradation rates and permits the evaluation of the influence of various laser parameters on lifetime. A selected group of laser diodes were aged at 80 °C under the conditions specified by the model. Degradation rates for the threshold current varied between4 times 10^{-5} and5 times 10^{-4} h-1. These would extrapolate to lifetimes in excess of 10 000 h at the elevated temperature for half of the diodes in reasonable agreement with experimental values obtained by others. 相似文献