全文获取类型
收费全文 | 21123篇 |
免费 | 2442篇 |
国内免费 | 1177篇 |
专业分类
电工技术 | 3723篇 |
综合类 | 1680篇 |
化学工业 | 2696篇 |
金属工艺 | 874篇 |
机械仪表 | 844篇 |
建筑科学 | 1620篇 |
矿业工程 | 663篇 |
能源动力 | 1125篇 |
轻工业 | 2481篇 |
水利工程 | 1016篇 |
石油天然气 | 939篇 |
武器工业 | 97篇 |
无线电 | 2148篇 |
一般工业技术 | 1753篇 |
冶金工业 | 842篇 |
原子能技术 | 474篇 |
自动化技术 | 1767篇 |
出版年
2024年 | 115篇 |
2023年 | 365篇 |
2022年 | 721篇 |
2021年 | 851篇 |
2020年 | 786篇 |
2019年 | 647篇 |
2018年 | 649篇 |
2017年 | 807篇 |
2016年 | 897篇 |
2015年 | 852篇 |
2014年 | 1323篇 |
2013年 | 1630篇 |
2012年 | 1460篇 |
2011年 | 1597篇 |
2010年 | 1177篇 |
2009年 | 1210篇 |
2008年 | 1033篇 |
2007年 | 1315篇 |
2006年 | 1159篇 |
2005年 | 997篇 |
2004年 | 847篇 |
2003年 | 681篇 |
2002年 | 643篇 |
2001年 | 513篇 |
2000年 | 451篇 |
1999年 | 364篇 |
1998年 | 244篇 |
1997年 | 248篇 |
1996年 | 205篇 |
1995年 | 179篇 |
1994年 | 161篇 |
1993年 | 127篇 |
1992年 | 90篇 |
1991年 | 73篇 |
1990年 | 49篇 |
1989年 | 58篇 |
1988年 | 47篇 |
1987年 | 31篇 |
1986年 | 42篇 |
1985年 | 27篇 |
1984年 | 15篇 |
1983年 | 10篇 |
1982年 | 15篇 |
1981年 | 3篇 |
1980年 | 7篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1964年 | 2篇 |
1959年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
The objectives of this article is to propose a new drying model for the second falling rate period known as the variable diffusion controlled period that follows after the first falling rate period and to propose a new method to determine the second critical moisture content that separates these two periods. Experimental work on paddy drying at minimum fluidization velocity was carried out in a rapid bin dryer. The effects of operating temperatures (60-120°C) and bed depths (2-6 cm) on the paddy drying characteristics were investigated. It was found that the normalized drying rate of paddy was proportional to the normalized moisture content in the first falling rate period but in the second falling rate period, the normalized drying rate of the material varies exponentially with the normalized moisture content. The different relationship between the normalized drying rate and the normalized moisture content in the first and second falling rate periods indicate that two different mechanism of moisture transport are at work. The new exponential model of the second falling rate period and the linear model of the first falling rate period were found to fit the experimental data very well. Derivation from variable diffusion equation shows that the linear model is the result of constant diffusion coefficient whereas the new exponential model is the result of linear diffusion coefficient. This also implies that the first falling rate period is a constant diffusion controlled period and the second falling rate period is a variable diffusion controlled period. In addition, drying kinetics data of a drying process that fits the exponential model over a very slow drying period will show that the drying process is under the effect of a linear diffusion coefficient. It was also found that the proposed new method to determine the second critical moisture content that distinguishes between the first and second falling rate periods by using a sudden change in the value of the drying rate gradient to a much lower value at that point is more rigorous and yet simpler than the method of determining the specific location of the receding drying boundary since it is based on the behavior of the actual drying kinetic data. 相似文献
92.
In keeping with the advance of more compact and more power-saving electronic equipment, the demand is increasing for smaller and more efficient switching power supply. Therefore, it is necessary to provide the adequate magnetic power ferrite materials to satisfy the demand. Such ferrite materials have to meet the following main requirement: 1) high initial permeability (μ i ); 2) high saturation magnetic induction (Bs); 3) high Curie temperature (Tc); 4) high electrical resistivity (ρ ); 5)… 相似文献
93.
The distribution of ergosterol in different parts of shiitake mushrooms was studied in order to optimize the conversion of ergosterol to vitamin D2 during drying. The effect of moisture on the conversion of ergosterol to vitamin D2 was also investigated by adjusting the moisture content of fresh mushrooms to different levels in a large vacuum desiccator and subjecting them to UV irradiation at 290-320 nm wavelength, for 2 h. The moisture, ergosterol and vitamin D2 contents were determined using standard procedures. It was found that the ergosterol content on a dry matter basis of fresh shiitake mushroom was highest in the gills (10.6 ± 0.99 mg/g DM), followed by the cap or pileus (5.34 ± 0.64 mg/g DM) and was least in the stalk or stipe (2.97 ± 0.56). The moisture content had a marked influence on the conversion of ergosterol to vitamin D2, the best conversion taking place at a moisture content of about 70% on a wet basis. 相似文献
94.
E. P. Chang 《The Journal of Adhesion》1991,34(1):189-200
A viscoelastic window (VW) concept has been proposed to identify different types of pressure-sensitive adhesives (PSA's). Such viscoelastic windows are constructed from the values of dynamic storage modulus: G' and dynamic loss modulus G' at frequencies of 10-2 and 102 rad/sec. These frequencies are chosen because the range covers most of the time scales corresponding to the uses of PSA's at different application rates in performance tests. A four quadrant concept has also been recommended to categorize different types of PSA's based on the location of their VW's on the log-log cross plot of G' and G'. It was found that for most PSA's, the range of G' and G' at room temperature within these selected frequencies falls between 103 and 106 Pascals. The proposed four-quadrants (top-left hand quadrant of high G' and low G', top-right hand quadrant of high G' and high G', lower left hand quadrant of low G' and low G', and lower right-hand quadrant of low G' and high G') correspond respectively to (1) non-PSA or release coatings (2) high shear PSA's, (3) removable PSA's and medical PSA's and (4) quick and cold stick PSA's. It was also observed that the VW's of general purpose permanent PSA's occupy the central region which straddles part of the four quadrants. 相似文献
95.
用屏蔽暂堵技术封堵水平井裂缝性漏层 总被引:1,自引:1,他引:0
克拉玛依油田HW702水平井的大斜度段和水平段,将穿越纵向裂缝发育的二叠系佳木河组储层。为安全钻进和保护油层,用超细碳酸钙和磺化沥青复配后加入复合离子钻井液中成屏蔽暂堵的堵漏钻井液。室内用岩心试验,屏蔽暂堵后渗透率可降为0,暂堵深度小于3cm,可用酸化和射孔解堵。现场使用效果也很好,使HW702水平井顺利完钻,并获得工业油气流。 相似文献
96.
The effect of solute impregnation on water loss and oil uptake during potato strip frying was studied. Blanched potato strips were impregnated at 25°C by soaking in a solution of sucrose-NaCl-water, 20-5-75% by weight. After rinsing and air drying, strips were deep fried in sunflower oil at 160, 170 and 180°C. A control treatment, consisting of potato strips blanched but not soaked and later air dried was also conducted. Solute impregnation provided a decrease of the oil uptake. Two models, based on Fick's law were used to describe water loss during frying. The first one is the classic model with an effective moisture diffusion coefficient assumed a constant value. The second model considers that diffusion coefficient varies during the frying process. For a given frying temperature, constant diffusion coefficient for control potatoes resulted in lower values than the impregnated ones. The variable diffusivity model showed a two-stage behavior: during the first stage of frying, diffusion coefficient increased with frying temperatures, but from a given time on an inverse behavior began. This last fact was found to be related to an increase of the measured peak force needed to penetrate the potato crust. 相似文献
97.
98.
天馈线电压驻波比是微波电路运行的重要指标,通过典型事例来阐述天馈线电压驻波比的劣化对微波电路的影响,并根据多年实践经验提出天馈线维护需注意的事项。 相似文献
99.
100.