全文获取类型
收费全文 | 711篇 |
免费 | 42篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 3篇 |
综合类 | 3篇 |
化学工业 | 199篇 |
金属工艺 | 21篇 |
机械仪表 | 16篇 |
建筑科学 | 20篇 |
能源动力 | 51篇 |
轻工业 | 79篇 |
水利工程 | 5篇 |
石油天然气 | 7篇 |
无线电 | 76篇 |
一般工业技术 | 123篇 |
冶金工业 | 44篇 |
原子能技术 | 3篇 |
自动化技术 | 110篇 |
出版年
2024年 | 6篇 |
2023年 | 13篇 |
2022年 | 39篇 |
2021年 | 77篇 |
2020年 | 35篇 |
2019年 | 47篇 |
2018年 | 61篇 |
2017年 | 35篇 |
2016年 | 40篇 |
2015年 | 24篇 |
2014年 | 34篇 |
2013年 | 47篇 |
2012年 | 40篇 |
2011年 | 49篇 |
2010年 | 30篇 |
2009年 | 37篇 |
2008年 | 20篇 |
2007年 | 20篇 |
2006年 | 12篇 |
2005年 | 8篇 |
2004年 | 9篇 |
2003年 | 7篇 |
2002年 | 6篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 3篇 |
1998年 | 8篇 |
1997年 | 6篇 |
1996年 | 4篇 |
1995年 | 7篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 4篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1956年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有760条查询结果,搜索用时 15 毫秒
41.
Rahman Saeed‐ur Shujaul Mulk Khan Mushtaq Ahmad Muhammad Zafar Raees Khan Muhammad Khalid Hui Nan Farooq Jan Sadaf‐Ilyas Kayani Sajad Hussain 《Microscopy research and technique》2020,83(5):541-550
Taxonomy of the genus Berberis is quite complex, due to overlapping morphological characters, making it very difficult to differentiate the species within the genus. In order to resolve this taxonomic complexity, the foliar anatomy of 10 Berberis L. species was carried out, for the first time from Pakistan, using light microscopy (LM). Significant variation in terms of epidermal cells shape, size, cell wall pattern, and stomata type was observed. B. baluchistanica has the largest epidermal cells, Adaxial: length = 45–(53.9 ± 3.6)–62.5 μm; and width = 22.5–(26.3 ± 1.3)–30 μm; Abaxial: length = 37.5–(43.25 ± 2.5)–50 μm; and width = 20–(22.6 ± 0.8)–25. The highest number of stomata was observed in B. glaucocarpa as 62 on the abaxial surface while the lowest number of stomata was recorded in B. baluchistanica as 8 on the adaxial surface. Of 10 investigated species, 6 possess anomocytic type stomata, while 2 species that is, B. aitchisonii and B. parkeriana have both anomocytic and anisocytic stomata while B. baluchistanica and B. calliobotrys have only paracytic type stomata. The highest number of cells per unit area was present on the adaxial surface of B. calliobotrys ranging from 245–(252.4)–260 followed by B. parkeriana with 209–(227.8)–250 on the abaxial surface. Stomatal index (SI) also varied considerably and was the lowest (2.6) percentage in B. baluchistanica and highest (31.9) percentage in B. kunawurensis. A taxonomic key based on micro‐morphological characters is provided for species identification. 相似文献
42.
In this paper, we analyze the problem of throughput-efficient distributed coalition formation (CF) of selfish/altruistic nodes in ad hoc radio networks. We formulate the problem as a hedonic CF game with non-transferable utility and propose different preference relations (CF rules) based on individual/group rate improvement of distributed nodes. We develop a hedonic CF algorithm, through which distributed nodes may self-organize into stable throughput-efficient disjoint coalitions. We apply the concept of frequency reuse over different coalitions, such that the members of each coalition will transmit over orthogonal sub-bands with the available spectrum being optimally allocated among them. We study the computational complexity and convergence properties of the proposed hedonic CF algorithm under selfish and altruistic preferences, and present means to guarantee Nash-stability. In addition, we identify the scenarios in which a CF process might lead to instability (CF cycle), and we propose methods to avoid cycles and define different exit procedures if a CF cycle is inevitable. Performance analysis shows that the proposed algorithm with optimal bandwidth allocation provides a substantial gain, in terms of average payoff per link, over existing coalition formation algorithms for a wide SNR range. 相似文献
43.
Aamir Farooq Wei Ren King Y. Lam David F. Davidson Ronald K. Hanson Charles K. Westbrook 《Combustion and Flame》2012,159(11):3235-3241
Methyl butanoate pyrolysis and decomposition pathways were studied in detail by measuring concentration time-histories of CO, CO2, CH3, and C2H4 using shock tube/laser absorption methods. Experiments were conducted behind reflected shock waves at temperatures of 1200–1800 K and pressures near 1.5 atm using mixtures of 0.1%, 0.5%, and 1% methyl butanoate in Argon. A novel laser diagnostic was developed to measure CO in the ν1 fundamental vibrational band near 4.56 μm using a new generation of quantum-cascade lasers. Wavelength modulation spectroscopy with second-harmonic detection (WMS-2f) was used to measure CO2 near 2752 nm. Methyl radical was measured using UV laser absorption near 216 nm, and ethylene was monitored using IR gas laser absorption near 10.53 μm. An accurate methyl butanoate model is critical in the development of mechanisms for larger methyl esters, and the measured time-histories provide kinetic targets and strong constraints for the refinement of the methyl butanoate reaction mechanism. Measured CO mole fractions reach plateau values that are the same as the initial fuel mole fraction at temperatures higher than 1500 K over the maximum measurement time of 2 ms or less. Two recent kinetic mechanisms are compared with the measured data and the possible reasons for this 1:1 ratio between MB and CO are discussed. Based on these discussions, it is expected that similar CO/fuel and CO2/fuel ratios for biodiesel molecules, particularly saturated components of biodiesel, should occur. 相似文献
44.
Ahmad Umar 《Nanoscale research letters》2009,4(9):1004-1008
Dye-sensitized solar cells (DSSCs) were fabricated by using well-crystallized ZnO nanocombs directly grown onto the fluorine-doped
tin oxide (FTO) via noncatalytic thermal evaporation process. The thin films of as-grown ZnO nanocombs were used as photoanode
materials to fabricate the DSSCs, which exhibited an overall light to electricity conversion efficiency of 0.68% with a fill
factor of 34%, short-circuit current of 3.14 mA/cm2, and open-circuit voltage of 0.671 V. To the best of our knowledge, this is first report in which thin film of ZnO nanocombs
was used as photoanode materials to fabricate the DSSCs. 相似文献
45.
The pentacene thin film transistor was fabricated on a SiO2/Si substrate by thermal evaporated method at room temperature. Electrical characteristics of the pentacene transistor subjected to a UV light excitation at a wavelength of 365 nm were analyzed. A significant increase in the drain current of the pentacene thin film transistor under a UV excitation of 365 nm is observed with a maximum photosensitivity of 4.51 in the depletion regime. It is concluded that the pentacene thin film transistor can be used in UV photo-detecting devices. 相似文献
46.
Afshan Shafi Umar Farooq Kashif Akram Mahgul Jaskani Farzana Siddique Amna Tanveer 《Comprehensive Reviews in Food Science and Food Safety》2014,13(2):229-239
Various Lactobacillus species possess antidiarrheal properties due to their probiotic effects and could be utilized in the form of fermented foods for the treatment of diarrheal disease. Diarrhea is the condition of having 3 or more loose or watery bowel movements per day. This disease is a global problem causing several million deaths each year, and the major victims are children. So its prevention and control is crucial. For the treatment of diarrheal disease, antibiotics and oral rehydration solutions are used, but these therapies are not always effective to reduce the duration and frequency of diarrhea and of increase consistency. Recent studies have demonstrated the effectiveness of the natural mode (fermented food) of disease management because of its easy availability, low cost, and efficacy against diarrhea. 相似文献
47.
48.
49.
Umar K. Mirza Nasir Ahmad Khanji Harijan Tariq Majeed 《Renewable & Sustainable Energy Reviews》2009,13(4):927-931
To ensure a sustainable energy future for Pakistan, it is necessary that the energy sector be accorded a high priority. Pakistan remains predominantly reliant on fossil fuels as its primary source of energy. Efforts to reduce reliance on fossil fuels through increasing the share of renewable energy in the energy supply systems have met with little success so far. The barriers to development of renewable energy can be broadly classified as policy and regulatory barriers, institutional barriers, fiscal and financial barriers, market-related barriers, technological barriers and information and social barriers. In this article, an effort has been made to identify the barriers that limit the use of renewable energy technologies in general and with specific reference to Pakistan, and outline the measures to address these barriers. 相似文献
50.