全文获取类型
收费全文 | 112405篇 |
免费 | 12795篇 |
国内免费 | 6624篇 |
专业分类
电工技术 | 15505篇 |
技术理论 | 13篇 |
综合类 | 7920篇 |
化学工业 | 19674篇 |
金属工艺 | 6266篇 |
机械仪表 | 4829篇 |
建筑科学 | 13208篇 |
矿业工程 | 2615篇 |
能源动力 | 15899篇 |
轻工业 | 4069篇 |
水利工程 | 1883篇 |
石油天然气 | 3723篇 |
武器工业 | 1306篇 |
无线电 | 8538篇 |
一般工业技术 | 13680篇 |
冶金工业 | 5192篇 |
原子能技术 | 1927篇 |
自动化技术 | 5577篇 |
出版年
2024年 | 740篇 |
2023年 | 2468篇 |
2022年 | 3837篇 |
2021年 | 4476篇 |
2020年 | 4755篇 |
2019年 | 4206篇 |
2018年 | 3720篇 |
2017年 | 4445篇 |
2016年 | 4756篇 |
2015年 | 4718篇 |
2014年 | 7403篇 |
2013年 | 7509篇 |
2012年 | 8021篇 |
2011年 | 8708篇 |
2010年 | 6626篇 |
2009年 | 6798篇 |
2008年 | 6042篇 |
2007年 | 6970篇 |
2006年 | 5965篇 |
2005年 | 4612篇 |
2004年 | 3928篇 |
2003年 | 3263篇 |
2002年 | 2944篇 |
2001年 | 2536篇 |
2000年 | 2191篇 |
1999年 | 1744篇 |
1998年 | 1428篇 |
1997年 | 1204篇 |
1996年 | 1039篇 |
1995年 | 780篇 |
1994年 | 663篇 |
1993年 | 549篇 |
1992年 | 472篇 |
1991年 | 428篇 |
1990年 | 355篇 |
1989年 | 294篇 |
1988年 | 229篇 |
1987年 | 157篇 |
1986年 | 126篇 |
1985年 | 157篇 |
1984年 | 136篇 |
1983年 | 90篇 |
1982年 | 113篇 |
1981年 | 55篇 |
1980年 | 57篇 |
1979年 | 28篇 |
1978年 | 14篇 |
1977年 | 12篇 |
1959年 | 12篇 |
1951年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Meng Wai Woo 《Drying Technology》2008,26(1):15-26
Current methods in alleviating the wall deposition problem in spray drying emphasize mainly controlling the stickiness of the drying particles and less attention is placed on the properties of the dryer wall. In this experimental study, the effect of wall surface properties on the deposition mechanism has been investigated. Properties considered in classifying different wall materials were surface energy, roughness, and dielectric properties. The model solution contained sucrose, representing low-molecular-weight sugars commonly encountered in spray drying of fruit and vegetable juices. The effect of wall properties on deposition was explored at different drying rates producing particles of different surface rigidity. Larger surface roughness produced higher deposition fluxes for particles with high impact velocity and moisture. Surface energy and surface roughness were found to have no significant effect for dry rigid particles at the middle and bottom elevation of the drying chamber. However, material with lower surface energy (Teflon) exhibited less deposition for rubbery particles at such elevations. Analysis shows that dielectric wall material (Teflon) tends to enhance deposition of dry particles because of attrition at the surface. Higher wall temperature was found to produce slightly more deposition. The results of this work give a general indication of the effect of wall material on the deposition problem and provide the fundamental understanding for further studies along this line. Proper selection of dryer wall material will provide potential alternatives for reducing the deposition problem. 相似文献
42.
Mirna Suárez-Quiroz Béatrice De Louise Oscar Gonzalez-Rios Michel Barel Bernard Guyot Sabine Schorr-Galindo & Joseph-Pierre Guiraud 《International Journal of Food Science & Technology》2005,40(6):605-611
Roasting coffee led to a drop in the ochratoxin A (OTA) concentration, as measured by the reference method, especially for dark type roasts. The way the beverage was prepared also affected the OTA content, which could paradoxically be higher than that of the initial roasted coffee. Assays on the thermal stability of pure OTA showed that it ought to be found in larger quantities in roasted coffee. This suggested that OTA was masked by reactions with the substrate during roasting. The absence of OTA in green coffee is therefore the best guarantee of safety. 相似文献
43.
3-D MCM封装技术及其应用 总被引:1,自引:0,他引:1
介绍了超大规模集成电路(VLSI)用的3-D MCM封装技术的最新发展,重点介绍了3-D MCM封装垂直互连工艺,分析了3-D MCM封装技术的硅效率、复杂程度、热处理、互连密度、系统功率与速度等问题,并对3-D MCM封装的应用作了简要说明。 相似文献
44.
Non-pinched, minimum energy solutions are important class of distillation designs that offer the potential advantage of a better trade-off between capital investment and operating costs. In this paper, two important tasks associated with non-pinched distillation designs are studied. Thus the novel contributions of this work to the literature are
- (1) A comprehensive methodology for finding non-pinched minimum energy designs.
- (2) Understanding of the reasons for the existence of non-pinched distillation designs.
45.
《International Journal of Food Science & Technology》2003,38(3):297-304
Summary The heat resistance of a four‐strain mixture of Escherichia coli O157:H7 was tested. The temperature range was 55–62.5 °C and the substrate was beef at pH 4.5 or 5.5, adjusted with either acetic or lactic acid. Inoculated meat, packaged in bags, was completely immersed in a circulating water bath and cooked to an internal temperature of 55, 58, 60, or 62.5 °C in 1 h, and then held for pre‐determined lengths of time. The surviving cell population was enumerated by spiral plating meat samples on tryptic soy agar overlaid with Sorbitol MacConkey agar. Regardless of the acidulant used to modify the pH, the D ‐values at all temperatures were significantly lower (P < 0.05) in ground beef at pH 4.5 as compared with the beef at pH 5.5. At the same pH levels, acetic acid rendered E. coli O157:H7 more sensitive to the lethal effect of heat. The analysis of covariance showed evidence of a significant acidulant and pH interaction on the slopes of the survivor curves at 55 °C. Based on the thermal‐death–time values, contaminated ground beef (pH 5.5/lactic acid) should be heated to an internal temperature of 55 °C for at least 116.3 min and beef (pH 4.5/acetic acid) for 64.8 min to achieve a 4‐log reduction of the pathogen. The heating time at 62.5 °C, to achieve the same level of reduction, was 4.4 and 2.6 min, respectively. Thermal‐death–time values from this study will assist the retail food processors in designing acceptance limits on critical control points that ensure safety of beef originally contaminated with E. coli O157:H7. 相似文献
46.
ZnS, ZnSe, and CdTe polycrystals are experimentally investigated. Mechanisms are treated which restrict the thermal conductivity in samples prepared by recrystallization pressing and by deposition from the vapor phase and subjected to additional strain. Anomalies are observed on the temperature dependences of the thermal resistance of investigated samples, which are due to the special features of their phonon spectra and to the variation of the contribution made by longitudinal and transverse phonon branches to the heat transfer in the Debye temperature region and higher. 相似文献
47.
48.
49.
This paper provides a preliminary examination of present and projected land use in Africa to estimate the potential availability of land in 2025 for use in producing biomass energy. Fifty countries are included in the analysis. Future cropland requirements are projected on the basis of average African cereal crop yield improvements since 1972, and minimum nutritional requirements are assumed to be met in 2025 without increasing imports above present absolute levels. Cropland, natural forests and other wilderness areas are excluded from consideration for biomass energy use. Woody biomass energy yields are estimated on the basis of nationally averaged precipitation, using a yield-precipitation correlation for commercial eucalyptus plantations in Brazil. The total African bioenergy production potential in 2025 is estimated to be about 18 EJ per year for a set of baseline assumptions that includes planting only 10% of the available non-crop, non-forest, non-wilderness area with biomass energy crops. A preliminary cost assessment suggests that much of this biomass could be produced for $1–2 GJ−1. A number of uncertainties in the modelling assumptions are examined through a sensitivity analysis. Despite limitations in the model used here, one robust conclusion is that Africa as a whole has a significant biophysical potential for producing biomass energy. This result suggests that more detailed country and sub-country level assessments would be worthwhile to understand better the practical prospects for future biomass energy production in Africa. 相似文献
50.
Thermal water at Yufuin (Kyushu Island, Japan) is tapped through about 820 shallow wells and used mainly for hot-spring bathing purposes. Chemical and isotopic data for fluids from wells and fumaroles in Yufuin and Beppu indicate that the thermal activity at Yufuin represents a dilute, westward-flowing hydrothermal outflow plume from the Beppu hydrothermal system. Two other (eastward-flowing) outflow plumes have long been recognized at Beppu, but the Yufuin outflow plume is first recognized here. The Yufuin outflow plume is apparently a mixture of two end-member fluids: (1) deep high-temperature (250–300°C) fluid from the Beppu system having high chloride concentration (1400–1600 mg/L) and a δ18O value near −6.0%, and (2) meteoric water having low chloride concentration (≤7 mg/L) and a δ18O value near −9.2%.A permeable conduit for the vertical and lateral transport of deep fluid from the Beppu system is provided by the Yufuin Fault zone, which extends westward from the southern flank of Mt. Tsurumi volcano to the town of Yufuin. Stable isotope ratios and chloride concentrations for shallow groundwaters near the eastern end of the fault, at an elevation near 700 m, are consistent with those required for the low-chloride meteoric end-member of the Yufuin thermal waters. Recharge of this meteoric water, as well as mixing with the Beppu deep fluid, may occur along the Yufuin Fault. Enthalpy-chloride relations indicate additional conductive heating of the Yufuin waters, in the amount of 350–500 kJ/kg beyond that which can be accounted for by mixing between Beppu deep fluid and meteoric water. This could be a result of conductive heating with convection to a depth of 1–2 km. Estimates of the magnitude of the heat source for the Beppu hydrothermal system should take into account the heat being discharged at Yufuin. 相似文献