全文获取类型
收费全文 | 3188篇 |
免费 | 131篇 |
国内免费 | 3篇 |
学科分类
工业技术 | 3322篇 |
出版年
2023年 | 43篇 |
2022年 | 57篇 |
2021年 | 120篇 |
2020年 | 66篇 |
2019年 | 77篇 |
2018年 | 72篇 |
2017年 | 70篇 |
2016年 | 104篇 |
2015年 | 85篇 |
2014年 | 141篇 |
2013年 | 176篇 |
2012年 | 194篇 |
2011年 | 225篇 |
2010年 | 150篇 |
2009年 | 150篇 |
2008年 | 163篇 |
2007年 | 152篇 |
2006年 | 136篇 |
2005年 | 130篇 |
2004年 | 108篇 |
2003年 | 69篇 |
2002年 | 69篇 |
2001年 | 41篇 |
2000年 | 61篇 |
1999年 | 50篇 |
1998年 | 65篇 |
1997年 | 60篇 |
1996年 | 58篇 |
1995年 | 49篇 |
1994年 | 42篇 |
1993年 | 28篇 |
1992年 | 20篇 |
1991年 | 26篇 |
1990年 | 18篇 |
1989年 | 19篇 |
1988年 | 20篇 |
1987年 | 17篇 |
1986年 | 9篇 |
1985年 | 17篇 |
1984年 | 10篇 |
1983年 | 21篇 |
1982年 | 15篇 |
1981年 | 17篇 |
1980年 | 10篇 |
1979年 | 11篇 |
1978年 | 12篇 |
1976年 | 14篇 |
1975年 | 7篇 |
1972年 | 7篇 |
1969年 | 6篇 |
排序方式: 共有3322条查询结果,搜索用时 15 毫秒
91.
Experiments on transition and flow boiling heat transfer with refrigerant R114 inside a horizontal tube were performed at bubble flow, critical heat flux and in the transition region between bubble flow and film boiling at mass fluxes between 1200 and 4000 kg/m2 s and in the pressure range between 5 and 15 bar. In comparison with pool boiling bubble flow heat transfer depends essentially on the mass flow rates and on the vapor quality. The critical heat flux depends less on the temperature difference than in pool boiling heat transfer and exhibits a maximal and a minimal value as a function of the pressure. The critical heat flux increases with mass flow rate as already shown by Collier. In the region of transition boiling the heat flux over the difference between wall and saturation temperature approaches a horizontal curve. Therefore in this region an evaporator may always be operated under stable conditions and burn out does not occur. 相似文献
92.
The layered Li[Li0.07Ni0.1Co0.6Mn0.23]O2 materials were synthesized by sol-gel method with glycine or citric acid as chelating agent. The prepared materials were characterized by means of XRD, SEM and Raman spectroscopy. Li/Li[Li0.07Ni0.1Co0.6Mn0.23]O2 cells were assembled and subjected to charge-discharge studies at different C rates, viz 0.2, 1, 2 and 4 C. Although the samples showed less discharge capacity at 4 C rate the fade in capacity per cycle is lesser than that of capacity fade at 0.2 C rate. The citric acid assisted sample is found to be superior in terms of discharge capacity, capacity retention rate and also in thermal stability to that of sample prepared with glycine as chelating agent. 相似文献
93.
Duochun Sun Stephan Senz Dietrich Hesse 《Journal of the American Ceramic Society》2003,86(6):1049-1051
Thin-film solid-state reactions in the system MgO–Nb2 O5 are experimentally investigated. MgO (001) substrates are subjected to Nb-O vapor at different temperatures in high vacuum. Thin films containing the phases Mg4 Nb2 O9 and MgNb2 O6 are formed by a vapor–solid reaction between the Nb-O vapor and the substrate. The crystallographic orientations of these phases are studied by X-ray diffractometry including pole figure analysis. Mg4 Nb2 O9 grows (11.4)-, (11.6)-, and (11.9)-oriented, whereas MgNb2 O6 grows with a preferential (241) orientation. The crystallographic relationships and their origins are discussed. 相似文献
94.
Influence of growth conditions on biofilm development and mass transfer at the bulk/biofilm interface 总被引:8,自引:0,他引:8
In a long-term study on heterotrophic biofilms in tube reactors, this investigation focused on mass transfer at the bulk/biofilm interface, biofilm density and substrate conversion rates. Several biofilms were cultivated under different substrate and hydrodynamic conditions. Oxygen concentration profiles were measured with microelectrodes in the biofilm and in the boundary layer directly in the biofilm tube reactors. The thickness of the concentration boundary layer was found to depend on the surface structure of the biofilm. The hydrodynamic conditions and the substrate load during the growth phase of the biofilm in biofilm systems are two key parameters that influence the biofilm growth, particularly the structure, density and thickness. The measured substrate conversion rates, biofilm densities and the boundary layer thickness were used to formulate an equation for the mass transfer in biofilm tube reactors. 相似文献
95.
Stephan Bose-O'Reilly Gustav Drasch Saulo Rodrigues-Filho Beate Lettmeier Alexandra Maydl Uwe Siebert 《The Science of the total environment》2010,408(4):713-1000
Small scale miners use mercury to extract gold from ore in many countries. An environmental and health assessment was performed in Indonesia in two regions, Galangan in Central Kalimantan and Talawaan in Northern Sulawesi. The environmental assessment showed severe mercury contamination of the sediments, and increased mercury levels in local fish. For the health investigation 281 volunteers were recruited and examined by a standardized questionnaire, a neurological examination and neuro-psychological tests. A medical score was used consisting of significant factors of mercury intoxication. Mercury exposed workers showed typical symptoms of mercury intoxication, such as movement disorders (ataxia, tremor, dysdiadochokinesia, etc.). Blood, urine and hair samples were taken from any participant and analyzed for mercury. The mercury concentration in the biomonitors was high, partly extreme high in the working population, increased in the population living in the same habitat and low in the control group. By a standard protocol which includes a combination of threshold values of mercury in the biomonitors and a medical sum score the diagnosis of chronic mercury intoxication was made for highly burdened workers (amalgam smelters) in 55% in Sulawesi and in 62% in Kalimantan. Less exposed mineral processors and the general population in the mining areas were also intoxicated to a high percentage. 相似文献
96.
In this paper, a novel cooling strategy for high performance cutting is presented. A metalworking fluid, composed of water and polyhydric alcohols is applied at temperatures below 0 °C, but above the temperatures used for cryogenic cutting. This cooling strategy is applied when rough turning Ti-6Al-4V. An analysis of temperatures, forces, tool wear and chip formation is carried out. The results are compared with those obtained using emulsion, CO2, LN2, and dry turning. It can be shown that when tempering the sub-zero metalworking fluid down to ?30° C, tool temperatures as well as tool wear are reduced, and favourable chips are produced. 相似文献
97.
Dietmar Gerteisen Nada ZamelChristian Sadeler Florian GeigerVictor Ludwig Christopher Hebling 《International Journal of Hydrogen Energy》2012
Understanding losses in polymer electrolyte membrane fuel cells, in the form of ohmic and mass transport, is of great importance to their commercialization. In this study, we use a spatially resolved cell consisting of 49 segments to measure the local current density distribution and high frequency resistance (HFR). A parametric study is used to investigate the effects of cell voltage, inlet relative humidity and flow rate and configuration using a three-channel serpentine flow field. We found that as the cell voltage decreased, the current density increased, while the HFR decreased. However, at a low cell voltage of 200 mV, we found the HFR to be higher than that at 500 mV. This increase is attributed to the increased electro-osmotic drag. This trend is independent of the flow configuration. Further, we found that the effect of the inlet relative humidity on the HFR highly depends on the flow configurations. Finally, a sharp decrease in the current density at some specific bend segments was observed, which correlates with lower OCV values and higher HFR values at this position. 相似文献
98.
Gerardo Valadez Huerta Johanan Álvarez Jordán Michael Dragon Keno Leites Stephan Kabelac 《International Journal of Hydrogen Energy》2018,43(34):16684-16693
Solid oxide fuel cell (SOFC) systems with anode off-gas recirculation (AGR) and diesel pre-reforming are advantageous because they can operate with the current fuel infrastructure. In the SchIBZ-project, the prototype of such a SOFC system for maritime applications has already been commissioned. In this first paper, we model the system devices to conduct an exergy analysis of this real SOFC plant and validate them with experimental values from experiments in laboratory scale. The results of our simulation agree well with the experimental values. The calculations with the validated results may be closer to the real thermodynamic behavior of such system components than previous literature. 相似文献
99.
Schnedl Wolfgang J. Schenk Michael Lackner Sonja Enko Dietmar Mangge Harald Forster Florian 《Food science and biotechnology》2019,28(6):1779-1784
Food Science and Biotechnology - Histamine intolerance (HIT) is thought to be caused by a disproportionate amount of histamine in the body. The enzyme diamine oxidase (DAO) is considered for the... 相似文献
100.
In this study, the influence of pressure during processing on the refractive index (RI) of polycarbonate (PC) was investigated by transmission measurements on glass-filled samples with a spectrometer. In order to isolate the pressure dependence of the RI from other influencing parameters such as cooling rate, orientation and stress states, the samples were prepared in a pressure-specific volume-Temperature (pvT) instrument under constant cooling rate and temperature history and without shear effects. Subsequently, the RI was determined at the intersection of the dispersion curves of the glass and the polymer by evaluating the wavelength of the maximal transmission of the samples. The mean RI over the entire cross section of the sample is determined by the transmission measurements without complex sample preparation. The investigations show that the RI of PC increases by 3.26 E-6 per bar with increasing pressure. POLYM. ENG. SCI., 60:512–516, 2020. © 2019 The Authors. Polymer Engineering & Science published by Wiley Periodicals, Inc. on behalf of Society of Plastics Engineers. 相似文献