全文获取类型
收费全文 | 41024篇 |
免费 | 4081篇 |
国内免费 | 2408篇 |
专业分类
电工技术 | 2914篇 |
综合类 | 3466篇 |
化学工业 | 5963篇 |
金属工艺 | 2846篇 |
机械仪表 | 3326篇 |
建筑科学 | 2482篇 |
矿业工程 | 1425篇 |
能源动力 | 1436篇 |
轻工业 | 1380篇 |
水利工程 | 1077篇 |
石油天然气 | 1059篇 |
武器工业 | 762篇 |
无线电 | 5982篇 |
一般工业技术 | 7539篇 |
冶金工业 | 1372篇 |
原子能技术 | 1468篇 |
自动化技术 | 3016篇 |
出版年
2024年 | 138篇 |
2023年 | 612篇 |
2022年 | 1036篇 |
2021年 | 1352篇 |
2020年 | 1286篇 |
2019年 | 1065篇 |
2018年 | 1029篇 |
2017年 | 1384篇 |
2016年 | 1483篇 |
2015年 | 1454篇 |
2014年 | 2428篇 |
2013年 | 2604篇 |
2012年 | 2797篇 |
2011年 | 3466篇 |
2010年 | 2517篇 |
2009年 | 2816篇 |
2008年 | 2365篇 |
2007年 | 2583篇 |
2006年 | 2173篇 |
2005年 | 1905篇 |
2004年 | 1618篇 |
2003年 | 1495篇 |
2002年 | 1254篇 |
2001年 | 990篇 |
2000年 | 820篇 |
1999年 | 689篇 |
1998年 | 568篇 |
1997年 | 528篇 |
1996年 | 463篇 |
1995年 | 431篇 |
1994年 | 362篇 |
1993年 | 300篇 |
1992年 | 259篇 |
1991年 | 246篇 |
1990年 | 196篇 |
1989年 | 156篇 |
1988年 | 111篇 |
1987年 | 73篇 |
1986年 | 68篇 |
1985年 | 86篇 |
1984年 | 87篇 |
1983年 | 52篇 |
1982年 | 72篇 |
1981年 | 18篇 |
1980年 | 16篇 |
1979年 | 10篇 |
1978年 | 4篇 |
1976年 | 6篇 |
1959年 | 14篇 |
1956年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
81.
The thick film of Zn-Sb-O was prepared by coating the paste of nanoparticles mixture (Sb2O3:ZnO=1:3) on the alumina substrate, followed by sintering at 500-900 °C for 2 h in air. The electrical resistance and gas-sensing properties to benzene, alcohol and acetone of Zn-Sb-O films were found to be dependent on the change of phase structure caused by sintering temperature. 相似文献
82.
83.
A SAXS method for the quantitative assessment of the morphology of polymer layered silicate nanocomposites is proposed. Fitting the SAXS patterns, the number of clay layers, the periodicity of the layers in the tactoids, the thickness of the regions interposed between the clay platelets and their distributions can be measured. A good agreement with TEM data was obtained, avoiding the inconsistencies with microscopical observations often reported in the literature. 相似文献
84.
Dianjun Yao 《Polymer》2005,46(12):4390-4396
The crystalline conformations of perylene polyimides (PPIs), with alkyl spacers varying in length from C3 to C12 are discussed. Although modeling of single chains would suggest the possibility that those with odd number of CH2 groups adopt a flat helical shape, X-ray diffraction suggests that the chains with odd and even spacers have the same conformation, due to the necessity to pack the perylene units. Upon annealing, the UV-vis absorption maximum red-shifts by about 10 nm, indicating enhanced π-stacking between the perylenes. Several changes in the spectra are seen with an increase in annealing time, at a given temperature. With an increase in annealing time, X-ray diffraction patterns show changes in the number of reflections, indicative of a crystal to mesogenic transition. The time required for this transition increases with a decrease in the spacer length, and annealing temperature, suggesting that the dynamics of this transition is very slow. 相似文献
85.
Hydroprocessing catalysts based on Ni, Co, Mo and W are used in various refinery processing applications where several deactivation mechanisms become of importance (coke formation, active phase sintering, metals deposition, poisoning) in the catalyst's life cycle. The life cycle of commercial hydroprocessing catalysts is very complex and includes the catalyst production, sulfidation, use, oxidative regeneration followed by re-sulfidation and reuse or, if reuse is not possible, recycling or disposal. To understand the changes in catalyst properties taking place during a life cycle, the catalyst quality in the different stages can be best monitored by using advanced analytical techniques. The catalyst's life cycle is further complicated by numerous technical, environmental and organizational issues involved. In principle, different companies can be involved in each of the life cycle steps. Leading catalyst manufacturers, together with specialized firms, offer refineries a total catalyst management concept, starting with the purchase of the fresh catalyst and ending with its final recycling or disposal. Total catalyst management includes a broad range of services, ensuring optimal timing during the change-out process, reliable, smooth and safe operations, minimal downtime and maximum catalyst and unit performance. 相似文献
86.
This work demonstrated a novel and potentially important application of two-dimensional small-angle X-ray scattering (2D-SAXS) to investigate powder compaction. SAXS from powder compacts of three materials commonly used for pharmaceutical tabletting exhibited azimuthal variations, with stronger intensity in the direction of the applied compaction force, relative to the transverse direction. This implied that compaction of a (macroscopic) powder could also produce changes on the molecular (nanometre) scale, which can be probed by 2D-SAXS. Two possible explanations for this effect were suggested. A combination of anisometric (i.e. elongated or flattened) granules with anisotropic morphologies could result in azimuthal variation in X-ray scattering due to granule orientation. It is expected that this mechanism would require relatively low packing density, so may operate during die filling. Granule re-orientation appeared less likely at higher packing densities and compaction pressures, however. Under these conditions, the changes in the 2D-SAXS patterns would be consistent with the powder granules becoming relatively flattened in the compression direction, with corresponding changes in their nano-scale morphology. The magnitude of this effect was found to vary between the materials used and increased with compaction pressure. This suggested that 2D-SAXS studies could provide useful information on force-transmission within a compressed powder. Further analysis of the data also suggested differences in the compaction mechanisms (i.e. granule re-orientation, deformation or fragmentation) between the materials studied. 相似文献
87.
D. M. Suckling R. W. Peck L. M. Manning L. D. Stringer J. Cappadonna A. M. El-Sayed 《Journal of chemical ecology》2008,34(12):1602-1609
Disruption of Argentine ant trail following and reduced ability to forage (measured by bait location success) was achieved
after presentation of an oversupply of trail pheromone, (Z)-9-hexadecenal. Experiments tested single pheromone point sources and dispersion of a formulation in small field plots. Ant
walking behavior was recorded and digitized by using video tracking, before and after presentation of trail pheromone. Ants
showed changes in three parameters within seconds of treatment: (1) Ants on trails normally showed a unimodal frequency distribution
of walking track angles, but this pattern disappeared after presentation of the trail pheromone; (2) ants showed initial high
trail integrity on a range of untreated substrates from painted walls to wooden or concrete floors, but this was significantly
reduced following presentation of a point source of pheromone; (3) the number of ants in the pheromone-treated area increased
over time, as recruitment apparently exceeded departures. To test trail disruption in small outdoor plots, the trail pheromone
was formulated with carnuba wax-coated quartz laboratory sand (1 g quartz sand/0.2 g wax/1 mg pheromone). The pheromone formulation,
with a half-life of 30 h, was applied by rotary spreader at four rates (0, 2.5, 7.5, and 25 mg pheromone/m2) to 1- and 4-m2 plots in Volcanoes National Park, Hawaii. Ant counts at bait cards in treated plots were significantly reduced compared to
controls on the day of treatment, and there was a significant reduction in ant foraging for 2 days. These results show that
trail pheromone disruption of Argentine ants is possible, but a much more durable formulation is needed before nest-level
impacts can be expected.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
88.
Chun Yang Yin Sharifah Aishah Syed Abdul KadirYing Pei Lim Sharifah Nawirah Syed-AriffinZurinawati Zamzuri 《Fuel Processing Technology》2008
Ash derived from combustion of Malaysian oil palm biomass (empty fruit bunches consisting of fibers) was physically and chemically characterized in order to provide a comprehensive understanding of its specific properties in terms of toxicity, compositions and reusability. Principal analyses conducted include particle size distribution, scanning electron microscopy, elemental dispersive X-ray, elemental analysis, toxicity characteristic leaching procedure (TCLP) as well as thermogravimetric, X-ray diffractometry and Fourier-transform infrared analyses. TCLP result indicated that the oil palm ash (OPA) should not be classified as toxic wastes in terms of heavy metal leachability since leachable copper, cadmium, lead and nickel concentrations were detected below the stipulated leachability limits. It was determined that the OPA contained high amount of potassium as well as presence of silica which implied its suitability to be reused as crude fertilizer or cement replacement material. 相似文献
89.
本文介绍了磁电机点火系统的点火提前角测量原理。对点火系统的点火信号和触发信号进行采集、调理,再用单片机进行处理,最后用LabVIEW进行点火提前角数据存储和显示。 相似文献
90.
CAO Wei-feng WANG Wen-boBeijing University of Posts Telecommunications Beijing P.R. China 《中国邮电高校学报(英文版)》2005,12(4)
1IntroductionCurrently,smart antenna technology can greatly en-hance system performance and i mprove the system ca-pacity so that it has been considered as a keytechnologyinthe third generation wireless communicationsystems .The researches on channel model , beamforming algo-rithms and receive algorithms have been widely carriedout and a great many of proposition have beensubmittedtothe 3th Generation Project Partner (3GPP) . Fromthe viewpoint of link-level and system-level research,many asp… 相似文献