全文获取类型
收费全文 | 322175篇 |
免费 | 29409篇 |
国内免费 | 17340篇 |
专业分类
电工技术 | 18020篇 |
技术理论 | 37篇 |
综合类 | 31678篇 |
化学工业 | 44310篇 |
金属工艺 | 11435篇 |
机械仪表 | 13871篇 |
建筑科学 | 48998篇 |
矿业工程 | 21532篇 |
能源动力 | 13484篇 |
轻工业 | 22068篇 |
水利工程 | 27792篇 |
石油天然气 | 22868篇 |
武器工业 | 3494篇 |
无线电 | 16214篇 |
一般工业技术 | 22696篇 |
冶金工业 | 15813篇 |
原子能技术 | 2959篇 |
自动化技术 | 31655篇 |
出版年
2024年 | 1388篇 |
2023年 | 4301篇 |
2022年 | 8293篇 |
2021年 | 10538篇 |
2020年 | 10537篇 |
2019年 | 8189篇 |
2018年 | 7826篇 |
2017年 | 9709篇 |
2016年 | 11390篇 |
2015年 | 11892篇 |
2014年 | 21299篇 |
2013年 | 19731篇 |
2012年 | 23419篇 |
2011年 | 25201篇 |
2010年 | 18655篇 |
2009年 | 19093篇 |
2008年 | 17339篇 |
2007年 | 21412篇 |
2006年 | 19592篇 |
2005年 | 17424篇 |
2004年 | 14283篇 |
2003年 | 12564篇 |
2002年 | 10418篇 |
2001年 | 8576篇 |
2000年 | 7253篇 |
1999年 | 5805篇 |
1998年 | 4175篇 |
1997年 | 3633篇 |
1996年 | 2907篇 |
1995年 | 2539篇 |
1994年 | 2060篇 |
1993年 | 1507篇 |
1992年 | 1196篇 |
1991年 | 879篇 |
1990年 | 741篇 |
1989年 | 691篇 |
1988年 | 434篇 |
1987年 | 350篇 |
1986年 | 289篇 |
1985年 | 306篇 |
1984年 | 235篇 |
1983年 | 180篇 |
1982年 | 102篇 |
1981年 | 90篇 |
1980年 | 108篇 |
1979年 | 68篇 |
1978年 | 27篇 |
1977年 | 30篇 |
1964年 | 21篇 |
1959年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
13.
Combination of heat treatment and chitosan coating to improve postharvest quality of wolfberry (Lycium barbarum) 下载免费PDF全文
Zhaojun Ban Wenwen Wei Xiangzheng Yang Jianhua Feng Junfeng Guan Li Li 《International Journal of Food Science & Technology》2015,50(4):1019-1025
The synergistic application of hot water dip at 42 °C for 30 min and 1% chitosan coating on differentiation in postharvest quality traits, microstructure as well as microbiological evolution of wolfberry fruits was investigated. Fresh wolfberry fruits were stored at 2 ± 0.5 °C and 90% relative humidity (RH) for 28 days. Results indicated the combination of prestorage heat treatment and chitosan coating maintained higher levels of ascorbic acid, total phenolic contents and antioxidant capacity as well as lower decay, compared with untreated wolfberry fruits. The possible mechanism was that the heat treatment almost sealed open stomata to limit the sites of pathogen penetration into fruits independently, followed by the biofilm formed by chitosan which controlled secondary infections as well as slowed changes in fruit respiration and metabolic activity in wolfberries. The synergistically treated fruit also exhibited a higher acceptability obtained by sensory analysis after cold storage. In this sense, the integrated application of heat treatment and chitosan coating could be regarded as an effective strategy to extend storage life and maintain the postharvest quality of wolfberry fruits. 相似文献
14.
ABSTRACTIn this paper, we review some algebraic control system. Precisely, linear and bilinear systems on Euclidean spaces and invariant and linear systems on Lie groups. The fourth classes of systems have a common issue: to any class, there exists an associated subgroup. From this object, we survey the controllability property. Especially, from those coming from our contribution to the theory. 相似文献
15.
The Vehicle Routing Problem with Simultaneous Pickup and Delivery (VRPSPD) is an extension to the classical Vehicle Routing Problem (VRP), where customers may both receive and send goods simultaneously. The Vehicle Routing Problem with Mixed Pickup and Delivery (VRPMPD) differs from the VRPSPD in that the customers may have either pickup or delivery demand. However, the solution approaches proposed for the VRPSPD can be directly applied to the VRPMPD. In this study, an adaptive local search solution approach is developed for both the VRPSPD and the VRPMPD, which hybridizes a Simulated Annealing inspired algorithm with Variable Neighborhood Descent. The algorithm uses an adaptive threshold function that makes the algorithm self-tuning. The proposed approach is tested on well-known VRPSPD and VRPMPD benchmark instances derived from the literature. The computational results indicate that the proposed algorithm is effective in solving the problems in reasonable computation time. 相似文献
16.
概述了氢的主要工业生产方法和实际应用,详细介绍了氯碱氢三级脱水工艺过程,并运用在线分析手段,准确显示了干燥过程中的氯碱氢水分含量变化规律。 相似文献
17.
Abrasive water jet technology can be used for micro-milling using recently developed miniaturized nozzles. Abrasive water jet (AWJ) machining is often used with both the nozzle tip and workpiece submerged in water to reduce noise and contain debris. This paper compares the performance of submerged and unsubmerged abrasive water jet micro-milling of channels in 316L stainless steel and 6061-T6 aluminum at various nozzle angles and standoff distances. The effect of submergence on the diameter and effective footprint of AWJ erosion footprints was measured and compared. It was found that the centerline erosion rate decreased with channel depth due to the spreading of the jet as the effective standoff distance increased, and because of the growing effect of stagnation as the channel became deeper. The erosive jet spread over a larger effective footprint in air than in water, since particles on the jet periphery were slowed much more quickly in water due to increased drag. As a result, the width of a channel machined in air was wider than that in water. Moreover, it was observed that the instantaneous erosion rate decreased with channel depth, and that this decrease was a function only of the channel cross-sectional geometry, being independent of the type of metal, the jet angle, the standoff distance, and regardless of whether the jet was submerged or in air, in either the forward or backward directions. It is shown that submerged AWJM results in narrower features than those produced while machining in air, without a decrease in centerline etch rate. 相似文献
18.
ABSTRACT The concept of digital game-based learning (DGBL) evolves rapidly together with technological enhancements of virtual reality (VR) and smart phones. However, the mental workload (MWL) that VR-training applications demand and motivational qualities originating from user experience (UX) should be identified in order to create effective and enjoyable training/learning challenges that fit with individual users’ capabilities. This study examined the effects of reality-based interaction (RBI) and VR on measures of student motivation and MWL, in a mental arithmetic game for secondary school pupils. In a randomised controlled trial with sixty school children, a mental arithmetic game was tested with three different interaction and two different presentation methods – VR RBI, VR head-mounted-display tapping and tablet flick-gesture. Results found a significant effect of RBI on MWL but no differences in enjoyment of training were found between VR-experience and tablet training-experience. In fact, adding the gaming-context to the mental arithmetic task created an enjoyable, motivating experience regardless of presentation or interaction-style. 相似文献
19.
《Intermetallics》2015
An equiatomic CoCrFeNiMn high-entropy alloy was synthesized by mechanical alloying (MA) and spark plasma sintering (SPS). During MA, a solid solution with refined microstructure of 10 nm which consists of a FCC phase and a BCC phase was formed. After SPS consolidation, only one FCC phase can be detected in the HEA bulks. The as-sintered bulks exhibit high compressive strength of 1987 MPa. An interesting magnetic transition associated with the structure coarsening and phase transformation was observed during SPS process. 相似文献
20.