全文获取类型
收费全文 | 1854篇 |
免费 | 206篇 |
国内免费 | 61篇 |
专业分类
电工技术 | 24篇 |
综合类 | 21篇 |
化学工业 | 342篇 |
金属工艺 | 11篇 |
机械仪表 | 34篇 |
建筑科学 | 30篇 |
矿业工程 | 5篇 |
能源动力 | 58篇 |
轻工业 | 1098篇 |
水利工程 | 24篇 |
石油天然气 | 117篇 |
无线电 | 59篇 |
一般工业技术 | 110篇 |
冶金工业 | 11篇 |
原子能技术 | 18篇 |
自动化技术 | 159篇 |
出版年
2024年 | 12篇 |
2023年 | 93篇 |
2022年 | 183篇 |
2021年 | 171篇 |
2020年 | 107篇 |
2019年 | 91篇 |
2018年 | 95篇 |
2017年 | 101篇 |
2016年 | 103篇 |
2015年 | 84篇 |
2014年 | 142篇 |
2013年 | 154篇 |
2012年 | 192篇 |
2011年 | 180篇 |
2010年 | 129篇 |
2009年 | 77篇 |
2008年 | 12篇 |
2007年 | 18篇 |
2006年 | 20篇 |
2005年 | 16篇 |
2004年 | 8篇 |
2003年 | 8篇 |
2002年 | 15篇 |
2001年 | 17篇 |
2000年 | 9篇 |
1999年 | 11篇 |
1998年 | 8篇 |
1997年 | 7篇 |
1996年 | 4篇 |
1995年 | 1篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1990年 | 1篇 |
1989年 | 5篇 |
1988年 | 2篇 |
1987年 | 15篇 |
1986年 | 13篇 |
1985年 | 3篇 |
1980年 | 1篇 |
排序方式: 共有2121条查询结果,搜索用时 234 毫秒
1.
《International Journal of Hydrogen Energy》2022,47(20):11007-11027
Cathode channel of a PEM fuel cell is the critical domain for the transport of water and heat. In this study, a mathematical model of water and heat transport in the cathode channel is established by considering two-phase flow of water and air as well as the phase change between water and vapor. The transport process of the species of air is governed by the convection-diffusion equation. The VOSET (coupled volume-of-fluid and level set method) method is used to track the interface between air and water, and the phase equilibrium method of water and vapor is employed to calculate the mass transfer rate on the two-phase interface. The present model is validated against the results in the literature, then applied to investigate the characteristics of two-phase flow and heat transfer in the cathode channel. The results indicate that in the inlet section, water droplets experience three evolution stages: the growing stage, the coalescence stage and the generation stage of dispersed water drops. However, in the middle and outlet sections of the channel, there are only two stages: the growth of water droplets, and the formation of a water film. The mass transfer rate of phase change in the inlet section of the channel varies over time, exhibiting an initial increase, a decrease followed, and a stabilization finally, with the maximum and stable values of 1.78 × 10?4 kg/s and 1.52 × 10?4 kg/s for Part 1, respectively. In the middle and outlet sections, the mass transfer rate increase firstly and then keeps stable gradually. Furthermore, regarding the distribution of the temperature and vapor mass fraction in the channel, near the upper surface of the channel, the temperature and vapor mass fraction first change slightly (x < 0.03 m) and then rapidly decrease with fluctuations (x > 0.03 m). In the middle of the channel, the temperature and vapor mass fraction slowly decrease with fluctuation. 相似文献
2.
3.
4.
《Materials Letters》2007,61(8-9):1881-1884
Organic ultraviolet (UV) ray absorbents, cinnamic acid (CA) and p-methoxycinnamic acid (PMOCA) were intercalated into Zn2Al layered double hydroxides (Zn2Al-LDHs) by co-precipitation reaction. The organic–inorganic nanocomposites, Zn2Al-LDH/CA and Zn2Al-LDH/PMOCA were obtained. The samples showed excellent UV ray absorption ability and their catalytic activity for the air oxidation of castor oil greatly decreased when the organic UV ray absorbents were intercalated in the layers of the Zn2Al-LDHs. The studies suggested that Zn2Al-LDH/organic UV absorbent nanocomposites might be used as safe sunscreen materials. 相似文献
5.
In this paper, we propose a new face recognition algorithm based on a single frontal-view image for each face subject, which considers the effect of the face manifold structure. To compare two near-frontal face images, each face is considered a combination of a sequence of local image blocks. Each of the image blocks of one image can be reconstructed according to the corresponding local image block of the other face image. Then an elastic local reconstruction (ELR) method is proposed to measure the similarities between the image block pairs in order to measure the difference between the two face images. Our algorithm not only benefits from the face manifold structure, in terms of being robust to various image variations, but also is computationally simple because there is no need to build the face manifold. We evaluate the performance of our proposed face recognition algorithm with the use of different databases, which are produced under various conditions, e.g. lightings, expressions, perspectives, with/without glasses and occlusions. Consistent and promising experimental results were obtained, which show that our algorithm can greatly improve the recognition rates under all the different conditions. 相似文献
6.
《Materials Letters》2007,61(11-12):2434-2438
Temperature dependence of viscosities of liquid Sn, Cu, Pb38.1Sn61.9, Pb44.8Bi55.2, and Cu0.7Sn99.3 has been studied by a torsional oscillation viscometer. During the measurement process, a deviation from the Arrhenius behavior is found when the temperature is lowered to about 60 K higher than the melting point. The abnormal increasing of the viscosity and the activation energy indicates the changes of the elementary melt structure during cooling towards the melting point. The deviation region from Arrhenius viscosity is defined as the transition state. The differential scanning calorimeter experiments also show the existence of the critical transition state in liquid metals near the melting point. The drastic increase of the viscosity in the transition state can be regarded as continuum transition and be presented well by the amended Arrhenius equation which is based on the critical phenomenon. 相似文献
7.
《Food Control》2006,17(1):5-13
The applicability of an electronic nose for the quality control of modified atmosphere (MA) packaged broiler chicken cuts was evaluated in different temperature regimes. The electronic nose results were compared with those obtained by microbiological, sensory and headspace GC analyses. The electronic nose could clearly distinguish broiler chicken packages with deteriorated quality from fresh packages either earlier than or at the same time as the sensory quality deteriorated. Concerning the microbiological quality, the counts of Enterobacteriaceae and hydrogen sulphide-producing bacteria were most consistent with the electronic nose results. The results indicated that the electronic nose was capable of detecting even early signals of spoilage in MA packed poultry meat. 相似文献
8.
《Food Control》2006,17(1):30-36
A semi-quantitative PCR-based system has been developed for detection of DNA sequences for the soybean allergen Gly m Bd 30K. The selected primers were highly specific for soybean and did not show amplification from a panel of legume relatives. Repeatability was assessed in a spiking experiment of soybean in wheat flour (0.0001–100% soybean), using known standards for comparison of the amount of output DNA from different PCR reactions. The frequency of PCR reactions with successful amplification of the soybean allergen sequence was highly dependent on initial target DNA concentration, and showed a rapid sigmoidal decrease, when target concentration approached the detection limit (0.01%). For samples with successful amplification there was a good correlation between the initial amount of soybean in the mixture and the output from PCR, when suitable block designs were used to control experimental errors. The simple approach used for quantification in this study proved efficient for assessment of homogeneity of self-prepared soybean bars used for provocation tests of food allergic patients in clinical practice. In addition the method was efficient in detecting soybean allergen sequences in a number of processed foods. 相似文献
9.
10.
Due to the decreasing threshold voltages, shrinking feature size, as well as the exponential growth of on-chip transistors, modern processors are increasingly vulnerable to soft errors. However, traditional mechanisms of soft error mitigation take actions to deal with soft errors only after they have been detected. Instead of the passive responses, this paper proposes a novel mechanism which proactively prevents from the occurrence of soft errors via architecture elasticity. In the light of a predictive model, we adapt the processor architectures h01istically and dynamically. The predictive model provides the ability to quickly and accurately predict the simulation target across different program execution phases on any architecture configurations by leveraging an artificial neural network model. Experimental results on SPEC CPU 2000 benchmarks show that our method inherently reduces the soft error rate by 33.2% and improves the energy efficiency by 18.3% as compared with the static configuration processor. 相似文献