全文获取类型
收费全文 | 1804篇 |
免费 | 54篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 14篇 |
综合类 | 1篇 |
化学工业 | 444篇 |
金属工艺 | 45篇 |
机械仪表 | 24篇 |
建筑科学 | 38篇 |
能源动力 | 94篇 |
轻工业 | 136篇 |
水利工程 | 8篇 |
石油天然气 | 14篇 |
无线电 | 182篇 |
一般工业技术 | 241篇 |
冶金工业 | 350篇 |
原子能技术 | 12篇 |
自动化技术 | 260篇 |
出版年
2022年 | 25篇 |
2021年 | 39篇 |
2020年 | 34篇 |
2019年 | 23篇 |
2018年 | 44篇 |
2017年 | 35篇 |
2016年 | 35篇 |
2015年 | 26篇 |
2014年 | 32篇 |
2013年 | 97篇 |
2012年 | 65篇 |
2011年 | 99篇 |
2010年 | 74篇 |
2009年 | 67篇 |
2008年 | 83篇 |
2007年 | 73篇 |
2006年 | 50篇 |
2005年 | 34篇 |
2004年 | 42篇 |
2003年 | 30篇 |
2002年 | 48篇 |
2001年 | 38篇 |
2000年 | 37篇 |
1999年 | 27篇 |
1998年 | 77篇 |
1997年 | 45篇 |
1996年 | 45篇 |
1995年 | 37篇 |
1994年 | 37篇 |
1993年 | 36篇 |
1992年 | 30篇 |
1991年 | 18篇 |
1990年 | 24篇 |
1989年 | 23篇 |
1988年 | 32篇 |
1987年 | 21篇 |
1986年 | 17篇 |
1985年 | 27篇 |
1984年 | 21篇 |
1983年 | 20篇 |
1982年 | 19篇 |
1981年 | 14篇 |
1980年 | 13篇 |
1979年 | 11篇 |
1978年 | 17篇 |
1977年 | 13篇 |
1976年 | 23篇 |
1975年 | 11篇 |
1974年 | 12篇 |
1973年 | 13篇 |
排序方式: 共有1863条查询结果,搜索用时 15 毫秒
121.
Infrared fiber optic radiometry was used for noncontact thermometry of gray bodies whose temperature was close to room temperature (40-70 degrees C). We selected three gray bodies, one with high emissivity (epsilon = 0.97), one with medium emissivity (epsilon = 0.71), and one with low emissivity (epsilon = 0.025). We carried out optimization calculations and measurements for a multiband fiber optic radiometer that consisted of a silver halide (AgClBr) infrared-transmitting fiber, a dual-band cooled infrared detector, and a set of 18 narrowband infrared filters that covered the 2-14-microm spectral range. We determined the optimal spectral range, the optimal number of filters to be used, and the optimal chopping scheme. Using these optimal conditions, we performed measurements of the three gray bodies and obtained an accuracy of better than 1 degrees C for body temperature and for room temperature. An accuracy of 0.03 was obtained for body emissivity. 相似文献
122.
123.
A method has been outlined for the calculation of the pressure gradient that can exist within the reacted shell when a spherical
pellet reacts with a gas and undergoes a transport controlled topochemical reaction. It is known that pressure gradients can
arise because of Knudsen flow existing in the reacted shell with small pores and the reactant gas having a different diffusivity
than that of the product gas. The phenomena can be represented by a boundary value problem involving a set of partial differential
equations with a moving boundary, incorporating time and positional dependence of diffusivities of the reactant and product
gases. In the present work, the resulting equations have been solved numerically. A study has been made of the influence of
the relevant parameters like total and Knudsen diffusivity ratios of the reactant and product gases, the porosity to tortuosity
ratio of the reacted shell, the Biot modulus, the equilibrium constant of the reaction and the viscous flow parameter on the
pressure build up inside the reacted shell. 相似文献
124.
A detailed analysis of the effect of chamber volume, orifice radius, orifice submergence and contact angle on quasi-static formation of bubbles is presented. It is shown, that many aspects of slow bubble formation, involving phenomena leading to various modes of the bubble release, as well as the maximum orifice diameter which sustains a bubble at equilibrium, can be explained on the basis of information on equilibrium shapes and conditions. Scaling rules enabling adoption of results for water to other liquids are also presented. 相似文献
125.
A sub-sea deployable fiber-optic sensor system for the continuous determination of a range of environmentally relevant volatile organic compounds in seawater has been developed. The prototype of a robust, miniaturized Fourier transform infrared (FT-IR) spectrometer for in situ underwater pollution monitoring was designed, developed, and built in our research group. The assembled instrument is enclosed in a sealed aluminium pressure vessel and is capable of maintenance-free operation in an oceanic environment down to depths of at least 300 m. The whole system can be incorporated either in a tow frame or a remotely operated vehicle (ROV). A suitable fiber-optic sensor head was developed, optimized in terms of sensitivity and hydrodynamics, and connected to the underwater FT-IR spectrometer. Due to a modular system design, various other sensor head configurations could be realized and tested, ensuring facile adaptation of the instrument to future tasks. The sensor system was characterized in a series of laboratory and simulated field tests. The sensor proved to be capable of quantitatively detecting a range of chlorinated hydrocarbons and monocyclic aromatic hydrocarbons in seawater down to the low ppb (microg/L) concentration range, including mixtures of up to 6 components. It has been demonstrated that varying amounts of salinity, turbidity, or humic acids, as well as interfering seawater pollutants, such as aliphatic hydrocarbons or phenols, do not significantly influence the sensor characteristics. In addition, the sensor exhibits sufficient long-time stability and a low susceptibility to sensor fouling. 相似文献
126.
Fermentation of deproteinised whey with kefir grains CIDCA AGK1 was studied focusing on polysaccharide production from lactose. Kefir grains were able to acidify whey at different rates depending on the grain/whey ratio. During fermentation, kefir grains increased their weight and a water-soluble polysaccharide was released to the media. Exopolysaccharide concentration increased with fermentation time, reaching values of 57.2 and 103.4 mg/l after 5 days of fermentation in cultures with 10 and 100 g kefir grains/l, respectively. The polysaccharide fraction quantified after fermentation corresponded to the soluble fraction, because part of the polysaccharide became a component of the grain. Weight of kefir grains varied depending on the time of fermentation. Polysaccharide production was affected by temperature. Although the highest concentration of polysaccharide in the media was observed at 43 degrees C at both grain/whey ratios, the weight of the grains decreased in these conditions. In conclusion, kefir grains were able to acidify deproteinised whey, reducing lactose concentration, increasing their weight and producing a soluble polysaccharide. 相似文献
127.
128.
Abraham Kandel 《Information Sciences》2007,177(2):329-331
129.
In this paper, we describe a granular algorithm for translating information between two granular worlds, represented as fuzzy rulebases. These granular worlds are defined on the same universe of discourse, but employ different granulations of this universe. In order to translate information from one granular world to the other, we must regranulate the information so that it matches the information granularity of the target world. This is accomplished through the use of a first-order interpolation algorithm, implemented using linguistic arithmetic, a set of elementary granular computing operations. We first demonstrate this algorithm by studying the common “fuzzy-PD” rulebase at several different granularities, and conclude that the “3 × 3” granulation may be too coarse for this objective. We then examine the question of what the “natural” granularity of a system might be; this is studied through a 10-fold cross-validation experiment involving three different granulations of the same underlying mapping. For the problem under consideration, we find that a 7 × 7 granulation appears to be the minimum necessary precision. 相似文献
130.
J.S. Wright L. Stafford B.P. Gila D.P. Norton S.J. Pearton Hung-Ta Wang F. Ren 《Journal of Electronic Materials》2007,36(4):488-493
The effect of cryogenic temperatures during metal deposition on the contact properties of Pd, Pt, Ti, and Ni on bulk single-crystal
n-type ZnO has been investigated. Deposition at both room and low temperature produced contacts with Ohmic characteristics
for Ti and Ni metallizations. By sharp contrast, both Pd and Pt contacts showed rectifying characteristics after deposition
with barrier heights between 0.37 eV and 0.69 eV. Changes in contact behavior were measured on Pd to anneal temperatures of
∼300 °C, showing an increase in barrier height along with a decrease in ideality factor with increasing annealing temperature.
This difference with annealing temperature is in sharp contrast to previous results for Au contacts to ZnO. There were no
differences in near-surface stoichiometry for the different deposition temperatures; however, low temperature contacts demonstrated
some peeling/cracking for Pt and Pd. 相似文献