全文获取类型
收费全文 | 23217篇 |
免费 | 1568篇 |
国内免费 | 62篇 |
专业分类
电工技术 | 290篇 |
综合类 | 23篇 |
化学工业 | 5095篇 |
金属工艺 | 855篇 |
机械仪表 | 1427篇 |
建筑科学 | 494篇 |
矿业工程 | 16篇 |
能源动力 | 808篇 |
轻工业 | 2151篇 |
水利工程 | 120篇 |
石油天然气 | 38篇 |
无线电 | 3761篇 |
一般工业技术 | 4877篇 |
冶金工业 | 2134篇 |
原子能技术 | 293篇 |
自动化技术 | 2465篇 |
出版年
2023年 | 226篇 |
2022年 | 369篇 |
2021年 | 665篇 |
2020年 | 461篇 |
2019年 | 550篇 |
2018年 | 626篇 |
2017年 | 704篇 |
2016年 | 800篇 |
2015年 | 694篇 |
2014年 | 1008篇 |
2013年 | 1539篇 |
2012年 | 1443篇 |
2011年 | 1748篇 |
2010年 | 1283篇 |
2009年 | 1292篇 |
2008年 | 1248篇 |
2007年 | 964篇 |
2006年 | 812篇 |
2005年 | 756篇 |
2004年 | 710篇 |
2003年 | 636篇 |
2002年 | 635篇 |
2001年 | 491篇 |
2000年 | 439篇 |
1999年 | 444篇 |
1998年 | 827篇 |
1997年 | 584篇 |
1996年 | 386篇 |
1995年 | 288篇 |
1994年 | 279篇 |
1993年 | 260篇 |
1992年 | 174篇 |
1991年 | 148篇 |
1990年 | 143篇 |
1989年 | 147篇 |
1988年 | 92篇 |
1987年 | 92篇 |
1986年 | 77篇 |
1985年 | 106篇 |
1984年 | 84篇 |
1983年 | 51篇 |
1982年 | 50篇 |
1981年 | 51篇 |
1980年 | 44篇 |
1979年 | 40篇 |
1978年 | 36篇 |
1977年 | 55篇 |
1976年 | 85篇 |
1975年 | 41篇 |
1973年 | 36篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
Concerns regarding the high level of research and development (R&D) expenditure on military technology have prompted many nations to pursue a dual-use regime in military R&D. However, the value of dual-use military technology has not yet been quantitatively investigated. We explore whether military technology with a higher level of duality has been more valuable than that with a lower level of duality. We assume that the patent of valuable military technology was renewed until its termination. We retrieve military patents from the United States Patent and Trademark Office during 1976–2014 based on their International Patent Classification (IPC) as F41 or F42. Then, we propose three indicators to assess the duality level of them. The first indicator is based on the determination of whether the patented technology is utilizable in both the military and the civilian sectors using its IPC. For the second indicator, we estimate the potential of convergence of a patented technology with various technological fields using the degree of centrality of the IPC’s co-occurrence network. The third indicator is based on ratio of forward citation by the civilian sector over the total number of forward citations as a measurement of technology diffusion toward the civilian sector. Using logistic regression, we found that the first two indicators are positively associated with patent renewal decision, while the last indicator is nonsignificant. The effects of the two significant indicators suggests that military technologies are more valuable when the technology itself can be used in various sectors, including the civilian sector, and can be converged with technologies in different fields. However, the nonsignificant influence of the third variable suggests that the relation between patent value and diffusion effects toward following inventions is not confined to the civilian sector. Our findings provide evidence of the impact of dual-use policies in military R&D. 相似文献
952.
Young‐Ran Song Nam‐Sik Shin Sang‐Ho Baik 《International Journal of Food Science & Technology》2014,49(11):2491-2498
The aim of this study was to utilise by‐product pepper leaves for vinegar production due to its nutritional value. Changes in physicochemical and functional properties in four main process from raw material (leaves) to lactic acid (juice), alcohol (wine) and acetic acid (vinegar) fermentations were evaluated and compared. Their nutritional compositions were significantly different and particularly the wine and vinegar had higher total phenol content and their expanded diversity than the juice and then leaves (P < 0.05). Difference in values for phenolic compound was highly correlated with their α‐glucosidase inhibitory (AGI) and antioxidant capacities in DPPH and superoxide radical scavenging and reducing power assays (r = 0.919–0.981); vinegar ≥ wine > juice > leaves. Especially, AGI activity was greatly enhanced depending on fermentation steps beyond expectation. Thus, these data confirm that pepper leaves is a good functional source and the vinegar fermentation improved the functionality in stages. 相似文献
953.
Han In Seok Kim Young Eun Jung Sunghwan 《Journal of Mechanical Science and Technology》2012,26(6):1857-1864
Journal of Mechanical Science and Technology - The cervical intervertebral disc has a unique feature in that a fissure or cleft runs along the uncinate process toward the nucleus pulposus called... 相似文献
954.
Kwan-Ho Park Sin-Wook You Soon-Chul Ur Il-Ho Kim Soon-Mok Choi Won-Seon Seo 《Journal of Electronic Materials》2012,41(6):1051-1056
The thermal stability of skutterudite-based thermoelectric modules is of great importance since they are used at elevated temperatures. This study examined the high-temperature stability of In-filled and Fe-doped skutterudites (In0.25Co3FeSb12) as a function of the following aging variables: atmosphere (vacuum and air), temperature, and time. Sb-based oxides are produced preferentially on exposure to high temperatures in air. The oxide layer produced during aging at 823?K in air was much thinner than that produced during aging at 723?K in air. The formation of InSb is believed to retard the oxidation of Sb and act as an obstacle to the growth of the oxide layer. The CoSb3-based skutterudites were stable at 823?K if they were not exposed to air, and InSb phases were not produced in the In0.25Co3FeSb12 skutterudites. 相似文献
955.
Joo Hee Kim Seok Hyun Nam Catherine W. Rico Mi Young Kang 《International Journal of Food Science & Technology》2012,47(6):1176-1182
The antioxidative and anti‐allergic activities of fresh and aged black garlic extracts were investigated. The garlic samples were extracted with 70% ethanol (v/v) and the total phenolic content was measured. The antioxidant capacity of extracts was assessed by determining the scavenging activities on 1,1‐diphenyl‐2‐picrylhydrazyl and hydroxyl radicals, ferricyanide reducing power, ferrous ion‐chelating ability and inhibitory effect on linoleic acid peroxidation. The anti‐allergic activity of extracts was analysed by measuring their inhibitory effects against β‐hexosaminidase release. The aged black garlic exhibited significantly higher phenolic content and greater antioxidative activity than fresh garlic. Both garlic extracts showed strong antioxidant capacity in a dose‐dependent manner. On the other hand, a considerably higher suppression of β‐hexosaminidase release was found in fresh garlic extract at lower concentration compared with that of the black garlic. Results of this study illustrate that ageing of garlic could enhance its antioxidant capacity, but could decrease its anti‐allergic activity. 相似文献
956.
A three-dimensional analysis procedure for the detailed phenomenon in a fin-tube heat exchanger has been developed and applied to predict the heat/mass transfer characteristics of the wave-fin heat exchangers. The continuity, Navier–Stokes and energy equations together with the species equation for the air–vapor mixture are solved in a coupled manner, so that the inter-dependence between the temperature and the humidity can be properly taken into account, by using the SIMPLE-type finite volume method. Having validated the procedure, calculations have been carried out for various frontal-velocity and inlet-humidity conditions. It has been shown that the flow characteristics, such as the temperature and humidity fields, along with the local heat flux and the condensation rate, can be successfully captured. The numerical results reveal that the existing correlations considerably underestimate the fin efficiency especially for multi-row heat exchangers. For dehumidifying cases, the sensible heat-transfer rate seems insensitive to the inlet-humidity change. The rate changes mostly in the narrow band of partially wet regime between 25% and 40% of inlet relative humidity. The range of the frontal velocity that gives the best performance for various numbers of rows is also estimated. The analogy between the heat and mass transfer on the fin surface is also examined. 相似文献
957.
The creep behavior of a squeeze-cast, short fiber reinforced Al metal matrix composite (MMC), consisting of an Al-11 wt.% Zn-0.2 wt.% Mg alloy reinforced with 15 vol.% Al2O3 Saffil® short fibers is investigated using miniature creep specimens. The small dimensions of the miniature creep specimens permit them to be machined from regions of an MMC block with different microstructures, thus allowing the effect of grain size and fiber texture on creep to be investigated on a more local level than is possible using conventional specimen geometries. The miniature creep specimens are subjected to uniaxial tensile stresses ranging from 3 to 40 MPa at temperatures between 573 and 623 K. It is shown that tests performed using the miniature creep specimen geometry are in good agreement with results previously obtained with standard creep specimens. Through interrupted creep experiments, it is observed that the creep back flow that occurs after unloading increases with increasing accumulated plastic strain. In the as-cast MMC, synchrotron microtomography reveals a fine distribution of pores whose spatial density increases with the spatial density of the fibers. The presence of fractured fibers in the crept MMC is also revealed. Some of the regions between fractured fiber fragments appear to be filled with matrix material, while others are voided. 相似文献
958.
Hwa Jung Kim Jeongah Ko Charlotte Storni Hong Ji Song Young Gyu Cho 《Journal of Functional Foods》2012,4(1):287-293
Overweight and obesity have become a global epidemic and they may impair health. Traditional use and growing evidence indicate that mate (Ilex paraguariensis A. St.-Hil.) may be helpful in losing excessive weight and fat. The present randomized, double-blind, placebo-controlled study evaluated efficacy and safety of an extract from green mate in 60 overweight subjects aged 20–39 years during 6-weeks. Body composition was measured by Dual-Energy X-ray Absorptiometry (DEXA) at baseline and after 6 weeks. Body weight, body mass index (BMI), waist circumference (WC) and various safety parameters were monitored. After 6 weeks, subjects taking mate experienced a significantly greater reduction of percent of body fat (?0.3% vs. +0.6%, p = 0.04) and fat mass (?0.5 kg vs. +0.2 kg, p = 0.04) than placebo. No significant differences were observed in other measurements. No adverse events occurred and all safety parameters were within normal ranges during the study in both groups. Thus, taking green mate extract reduced body fat after 6 weeks, while the treatment was safe and well tolerated. 相似文献
959.
Seung Jin Oh Yoon Joon Lee Kuan Chen Young Min Kim Sang Hoon Lim Wongee Chun 《国际能源研究杂志》2012,36(2):249-258
An embedded two‐axis solar tracking system using Laboratory Virtual Instrumentation Engineering Workbench to write the operation and control algorithms was developed for enhancing solar energy utilization. The system consists of a real‐time processor, two motion‐control modules, two step drives, two step motors, feedback devices, and other accessories needed for functional stability. The real‐time processor allows the solar tracker to be used as a stand‐alone, real‐time system that can operate automatically without any external control. The system combines two different solar tracking methods: the optical method and the astronomical method. Cadmium Sulfide (CdS) sensors are employed to continuously generate feedback signals to the controller, ensuring high‐precision solar tracking even under adverse conditions. The CdS sensor is a resistor whose electric resistance decreases with increasing incident light intensity. A database of solar altitude, azimuth, and sunrise and sunset times is provided by this solar tracking system. Other solar trackers operating in an astronomical method may access and use this database over the Internet. Solar position and sunrise and sunset times in the database were compared with those of the Astronomical Applications Department of the U.S. Naval Observatory. The differences were found to be negligible. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
960.
This paper introduces a new motion‐synthesis technique for animating multiple characters. At a high level, we introduce a hub‐sub‐control‐point scheme that automatically generates many different spline curves from a user scribble. Then, each spline curve becomes a trajectory along which a 3D character moves. Based on the given curves, our algorithm synthesizes motions using a cyclic motion. In this process, space‐time warp curves, which are time‐warp curves, are embedded in the 3D environment to control the speed of the motions. Since the space‐time warp curve represents a trajectory over the time domain, it enables us to verify whether the trajectory causes any collisions between characters by simply checking whether two space‐time warp curves intersect. In addition, it is possible to edit space‐time warp curves at run time to change the speed of the characters. We use several experiments to demonstrate that the proposed algorithm can efficiently synthesize a group of character motions. Our method creates collision‐avoiding trajectories ten times faster than those created manually. 相似文献