全文获取类型
收费全文 | 1472篇 |
免费 | 68篇 |
国内免费 | 8篇 |
专业分类
电工技术 | 17篇 |
化学工业 | 384篇 |
金属工艺 | 35篇 |
机械仪表 | 28篇 |
建筑科学 | 45篇 |
矿业工程 | 2篇 |
能源动力 | 48篇 |
轻工业 | 186篇 |
水利工程 | 8篇 |
石油天然气 | 14篇 |
无线电 | 151篇 |
一般工业技术 | 250篇 |
冶金工业 | 242篇 |
原子能技术 | 10篇 |
自动化技术 | 128篇 |
出版年
2023年 | 17篇 |
2022年 | 52篇 |
2021年 | 68篇 |
2020年 | 35篇 |
2019年 | 25篇 |
2018年 | 64篇 |
2017年 | 33篇 |
2016年 | 30篇 |
2015年 | 29篇 |
2014年 | 46篇 |
2013年 | 106篇 |
2012年 | 71篇 |
2011年 | 73篇 |
2010年 | 66篇 |
2009年 | 64篇 |
2008年 | 69篇 |
2007年 | 50篇 |
2006年 | 39篇 |
2005年 | 39篇 |
2004年 | 34篇 |
2003年 | 34篇 |
2002年 | 27篇 |
2001年 | 23篇 |
2000年 | 15篇 |
1999年 | 24篇 |
1998年 | 66篇 |
1997年 | 31篇 |
1996年 | 24篇 |
1995年 | 16篇 |
1994年 | 24篇 |
1993年 | 18篇 |
1992年 | 15篇 |
1991年 | 24篇 |
1990年 | 15篇 |
1989年 | 21篇 |
1988年 | 15篇 |
1987年 | 14篇 |
1984年 | 8篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1979年 | 10篇 |
1978年 | 10篇 |
1977年 | 9篇 |
1976年 | 18篇 |
1975年 | 8篇 |
1974年 | 8篇 |
1973年 | 8篇 |
1972年 | 5篇 |
1970年 | 4篇 |
1969年 | 4篇 |
排序方式: 共有1548条查询结果,搜索用时 18 毫秒
141.
Oil expression tests were conducted to evaluate the performance of a novel oil expeller designed and fabricated to operate on a 200 W solar photovoltaic (PV) power system as a sole power source. The oil press was designed to press oilseeds meal with intermediate moisture content of 12±1% (w.b.) and 0.5–2 mm particle sizes. Freshly grated coconuts and ground peanuts were used to determine the oil expression efficiency of the press. The oilseed samples were pressed for 12 min with a maximum pressure of 3.0 MPa being reached at 6 min of pressing for peanuts and 8 min of pressing for coconuts. The pressure was then held for the rest of the pressing time. The press attained an average oil expression efficiency of 73% for coconuts and 70% for peanuts. The force-vs.-deformation studies indicated that peanut press meal was compacted at a higher rate as compared to coconuts. The observation on the energy consumption indicated that there was a significant increase (P<0.05) in the specific energy requirement for both coconuts and peanuts after 6 min of pressing, which resulted from the solidification of the press cake. An average specific energy of 36.55 and 20.35 Wh/kg was recorded for peanuts and coconuts, respectively, after 12 min of pressing. 相似文献
142.
Turunen MJ Saarakkala S Rieppo L Helminen HJ Jurvelin JS Isaksson H 《Applied spectroscopy》2011,65(6):595-603
The molecular composition of the organic and inorganic matrices of bone undergoes alterations during maturation. The aim of this study was to compare Fourier transform infrared (FT-IR) and near-infrared (NIR) Raman microspectroscopy techniques for characterization of the composition of growing and developing bone from young to skeletally mature rabbits. Moreover, the specificity and differences of the techniques for determining bone composition were clarified. The humeri of female New Zealand White rabbits, with age range from young to skeletally mature animals (four age groups, n = 7 per group), were studied. Spectral peak areas, intensities, and ratios related to organic and inorganic matrices of bone were analyzed and compared between the age groups and between FT-IR and Raman microspectroscopic techniques. Specifically, the degree of mineralization, type-B carbonate substitution, crystallinity of hydroxyapatite (HA), mineral content, and collagen maturity were examined. Significant changes during maturation were observed in various compositional parameters with one or both techniques. Overall, the compositional parameters calculated from the Raman spectra correlated with analogous parameters calculated from the IR spectra. Collagen cross-linking (XLR), as determined through peak fitting and directly from the IR spectra, were highly correlated. The mineral/matrix ratio in the Raman spectra was evaluated with multiple different peaks representing the organic matrix. The results showed high correlation with each other. After comparison with the bone mineral density (BMD) values from micro-computed tomography (micro-CT) imaging measurements and crystal size from XRD measurements, it is suggested that Raman microspectroscopy is more sensitive than FT-IR microspectroscopy for the inorganic matrix of the bone. In the literature, similar spectroscopic parameters obtained with FT-IR and NIR Raman microspectroscopic techniques are often compared. According to the present results, however, caution is required when performing this kind of comparison. 相似文献
143.
Series of superconducting samples of type Cu0.5Tl0,5 Ba2Ca2?y R y Cu3O10??? , where R=Pr and La with 0??y??0.20, were prepared in a sealed quartz tube via a single-step solid-state reaction technique. The prepared samples were characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM), and electron dispersive X-ray (EDX). XRD studies indicated that the tetragonal structure of (Cu0.5Tl0.5)-1223 phase does not change by Pr or La-substitutions whereas the lattice parameters a and c do. The elemental compositions analysis, determined from EDX, indicated that both Pr and La were successfully introduced into the microstructure of (Cu0.5Tl0.5)-1223 phase. The electrical resistivity ??(T) was measured as a function of temperature using conventional dc four-probe technique. The fluctuation conductivity ????, above the superconducting transition temperature T c, was analyzed as a function of temperature using Aslamazov and Larkin model. It exhibits four different fluctuation regions namely critical (cr), three-dimensional (3D), two-dimensional (2D), and short-wave (sw). The zero-temperature coherence length, effective layer thickness of the two-dimensional system and inter-layer coupling strength were estimated as a function of the substitution-content y. Furthermore, the thermodynamics critical field, lower critical magnetic field, upper critical magnetic field, critical current density and Fermi energy were calculated from the Ginzburg number. The data indicated that both Pr and La-substitutions have quite similar behaviors. 相似文献
144.
145.
146.
FW Hanna 《Canadian Metallurgical Quarterly》1996,7(4):U125-U130
147.
148.
Mutations were made in the activation loop tyrosine of the kinase domain of the oncoprotein v-Fps to assess the role of autophosphorylation in catalysis. Three mutant proteins, Y1073E, Y1073Q, and Y1073F, were expressed and purified as fusion proteins of glutathione-S-transferase from Escherichia coli and their catalytic properties were evaluated. Y1073E, Y1073Q, and Y1073F have k(cat) values that are reduced by 5-, 35-, and 40-fold relative to the wild-type enzyme, respectively. For all mutant enzymes, the Km values for ATP and a peptide substrate, EAEIYEAIE, are changed by 0.4-2-fold compared to the wild-type enzyme. The slopes for the plots of relative turnover versus solvent viscosity [(k(cat))eta] are 0.71 +/- 0.08, 0.10 +/- 0.06, and approximately 0 for wild type, Y1073Q, and Y1073E, respectively. These results imply that the phosphoryl transfer rate constant is reduced by 19- and 130-fold for Y1073E and Y1073Q compared to the wild-type enzyme. The dissociation constant of the substrate peptide is 1.5-2.5-fold lower for the mutants compared to wild type. The inhibition constant for EAEIFEAIE, a competitive inhibitor, is unaffected for Y1073E and raised 3-fold for Y1073Q compared to wild type. Y1073E and Y1073Q are strongly activated by free magnesium to the same extent and the apparent affinity constant for the metal is similar to that for the wild-type enzyme. The data indicate that the major role of autophosphorylation in the tyrosine kinase domain of v-Fps is to increase the rate of phosphoryl transfer without greatly affecting active-site accessibility or the local environment of the activating metal. Finally, the similar rate enhancements for phosphoryl transfer in v-Fps compared to protein kinase A [Adams et al. (1995) Biochemistry 34, 2447-2454] upon autophosphorylation suggest a conserved mechanism for communication between the activation loop and the catalytic residues of these two enzymes. 相似文献
149.
K Hariharan G Braslawsky RS Barnett LG Berquist T Huynh N Hanna A Black 《Canadian Metallurgical Quarterly》1998,12(6):1229-1235
Induction of CD8+ cytotoxic T lymphocytes (CTLs) specific for human papillomavirus (HPV) antigens provides an attractive strategy for immunotherapy of HPV-related cancers in humans. In this study, we investigated the potential of utilizing soluble E7 protein of HPV 16 in an adjuvant formulation, PROVAX as a vaccine against a progressively growing E7 transfected K1735-X21 (H-2k) metastatic melanoma cells (HOPE2) in a mouse model. Vaccination of HOPE2 tumor bearing mice (C3H) with E7 protein in PROVAX resulted in significant inhibition of tumor growth, compared to mice vaccinated with E7 in Alum or saline. In vivo depletion of CD8+ or CD4+ cells indicated that CD8+ cells are the major effector cells in mediating the anti-tumor activity in this model. Furthermore, E7-specific CTL activity in vitro was detected in tumor bearing mice vaccinated with E7-PROVAX. Our studies suggest that recombinant HPV antigens in combination with PROVAX could serve as an effective subunit vaccine to stimulate tumor specific CD8+ T cell mediated immunity against HPV-related cancers. 相似文献
150.
Parpal J.-L. Awad R. Choquette M. Becker J. Hiivala L. Chatterjee S. Kojima T. Rosevear R.D. Morelli O. 《Power Delivery, IEEE Transactions on》1997,12(2):547-550
Extruded polymeric cables and accessories are an alternative to self-contained fluid filled (SCFF) cables for extra-high-voltage (EHV) systems. Crosslinked polyethylene (XLPE) insulated cables have many advantages over the traditional fluid-filled pressurized cable system with the elimination of the hydraulic system and the associated equipment and complications during the installation and operation/maintenance of such systems. Other advantages of the extruded cable system arise from the new accessory technologies and the use of splices and terminations that are prefabricated and pretested in the factory and require less time to install on site. Concerns over the long term reliability of high voltage cable systems, in particular the accessories and the lack of service experience above 300 kV led to the decision of Hydro-Quebec to carry out a prequalification (long-term) test program to assess the reliability of the cable materials and to verify the cable and accessory installation methods to be employed. The cables were installed in duct banks and manholes simulating actual installation conditions used in Hydro-Quebec underground cable network. This paper describes the program and results of the prequalification tests of 345-kV XLPE cables and accessories performed at Hydro-Quebec's Research Institute (IREQ) in partnership with three international cable manufacturers, Alcatel, Fujikura and Pirelli 相似文献