全文获取类型
收费全文 | 42896篇 |
免费 | 5058篇 |
国内免费 | 2397篇 |
专业分类
电工技术 | 5889篇 |
技术理论 | 4篇 |
综合类 | 3144篇 |
化学工业 | 3232篇 |
金属工艺 | 1302篇 |
机械仪表 | 3009篇 |
建筑科学 | 1893篇 |
矿业工程 | 779篇 |
能源动力 | 5561篇 |
轻工业 | 5207篇 |
水利工程 | 1123篇 |
石油天然气 | 1239篇 |
武器工业 | 493篇 |
无线电 | 3628篇 |
一般工业技术 | 3644篇 |
冶金工业 | 689篇 |
原子能技术 | 242篇 |
自动化技术 | 9273篇 |
出版年
2024年 | 377篇 |
2023年 | 1199篇 |
2022年 | 1826篇 |
2021年 | 2045篇 |
2020年 | 2047篇 |
2019年 | 1797篇 |
2018年 | 1485篇 |
2017年 | 1639篇 |
2016年 | 1624篇 |
2015年 | 1816篇 |
2014年 | 2836篇 |
2013年 | 2489篇 |
2012年 | 3075篇 |
2011年 | 3365篇 |
2010年 | 2407篇 |
2009年 | 2393篇 |
2008年 | 2272篇 |
2007年 | 2671篇 |
2006年 | 2376篇 |
2005年 | 2045篇 |
2004年 | 1789篇 |
2003年 | 1413篇 |
2002年 | 1163篇 |
2001年 | 954篇 |
2000年 | 732篇 |
1999年 | 517篇 |
1998年 | 376篇 |
1997年 | 274篇 |
1996年 | 244篇 |
1995年 | 196篇 |
1994年 | 173篇 |
1993年 | 125篇 |
1992年 | 117篇 |
1991年 | 76篇 |
1990年 | 53篇 |
1989年 | 49篇 |
1988年 | 46篇 |
1987年 | 42篇 |
1986年 | 33篇 |
1985年 | 47篇 |
1984年 | 28篇 |
1983年 | 23篇 |
1982年 | 19篇 |
1981年 | 15篇 |
1980年 | 10篇 |
1979年 | 7篇 |
1977年 | 7篇 |
1976年 | 8篇 |
1975年 | 7篇 |
1974年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
本文以云杉八齿小蠹Ips typographus Linnaeus为例,经标本选取,观察虫体整体形态,绘制整体结构草图,电子显微镜观察局部、得到局部数字图像,分别建立虫体每一部分的高精度细节。把模型每部分拼装在一起组成整体模型,构建出了云杉八齿小蠹三维虚拟昆虫数字化模型。 相似文献
2.
Zenan Yu Julian Moore Jean Calderon Lei Zhai Jayan Thomas 《Small (Weinheim an der Bergstrasse, Germany)》2015,11(39):5289-5295
Cable‐shaped supercapacitors (SCs) have recently aroused significant attention due to their attractive properties such as small size, lightweight, and bendability. Current cable‐shaped SCs have symmetric device configuration. However, if an asymmetric design is used in cable‐shaped supercapacitors, they would become more attractive due to broader cell operation voltages, which results in higher energy densities. Here, a novel coil‐type asymmetric supercapacitor electrical cable (CASEC) is reported with enhanced cell operation voltage and extraordinary mechanical‐electrochemical stability. The CASECs show excellent charge–discharge profiles, extraordinary rate capability (95.4%), high energy density (0.85 mWh cm−3), remarkable flexibility and bendability, and superior bending cycle stability (≈93.0% after 4000 cycles at different bending states). In addition, the CASECs not only exhibit the capability to store energy but also to transmit electricity simultaneously and independently. The integrated electrical conduction and storage capability of CASECS offer many potential applications in solar energy storage and electronic gadgets. 相似文献
3.
AbstractIndustry 4.0 aims at providing a digital representation of a production landscape, but the challenges in building, maintaining, optimizing, and evolving digital models in inter-organizational production chains have not been identified yet in a systematic manner. In this paper, various Industry 4.0 research and technical challenges are addressed, and their present scenario is discussed. Moreover, in this article, the novel concept of developing experience-based virtual models of engineering entities, process, and the factory is presented. These models of production units, processes, and procedures are accomplished by virtual engineering object (VEO), virtual engineering process (VEP), and virtual engineering factory (VEF), using the knowledge representation technique of Decisional DNA. This blend of the virtual and physical domains permits monitoring of systems and analysis of data to foresee problems before they occur, develop new opportunities, prevent downtime, and even plan for the future by using simulations. Furthermore, the proposed virtual model concept not only has the capability of Query Processing and Data Integration for Industrial Data but also real-time visualization of data stream processing. 相似文献
4.
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
5.
Goat milk has specific chemical composition and physical properties. The purpose of this study was to investigate the change of milk quality and emulsion stability during 60 d frozen storage. Milk sample was taken from three Ettawah Crossedbred goats that were divided into three groups. Samples were frozen and stored for 0, 30 and 60 days. At the end of each storage periode, milk sample was thawed in the refrigerator and analyzed for total number of bacteria, chemical (acidity, pH, free fatty acids), physical (alcohol test, clot on boiling test) quality, and emulsion stability. The microbiological and chemical data were analyzed statistically using one way ANOVA, whereas physical quality and emulsion stabilty were expressed qualitatively. There were no change in the total bacteria, acidity, pH and free fatty acid (FFA) of milk during storage, whereas the assessment by 70% alcohol showed positive since 0 d. Emulsions stability changed after 30 d of storage. While, the clot on boiling (COB) test of milk was positive at 60 d of storage. Recommendation is frozen storage of goat milk should not longer than 30 d. 相似文献
6.
This study aimed to know the effect of adding pulp in rambutan fruit juice on the characteristics of rambutan juice during storage. Research using the CRD, the treatment were kind of pulp (mandarin and rambutan) and pulp concentration (5%, 7.5%, and 10%). The results showed that the addition of pulp significantly affect the characteristics of rambutan juice (pH, vitamin C, total acid) during storage. Pulpy juice with the most prefered was addition of rambutan pulp as much as 7.5% (w/v) and the addition of citrus pulp as much as 7.5% (w/v) with the score of 3-4 (moderate like - like). 相似文献
7.
To improve the electrochemical properties of rare-earth–Mg–Ni-based hydrogen storage alloys, the effects of stoichiometry and Cu-substitution on the phase structure and thermodynamic properties of the ... 相似文献
8.
Katarzyna Samborska Elwira Langa Sławomir Bakier 《International Journal of Food Science & Technology》2015,50(6):1359-1365
Honey powders produced by spray drying with the addition of Arabic gum and sodium caseinate were characterised in terms of the influence of storage time on the following physical properties: particle size, moisture content, water activity, bulk density, flowability and hygroscopicity. The storage affected those properties; after 12 weeks of storage, particle size decreased (except Arabic gum powder treated as a control sample), moisture content and water activity increased, hygroscopicity decreased. Changes in bulk density, particle size and moisture content caused the rise of Hausner ratio value; however, the powders were still characterised by a very good flow properties and low cohesiveness. The colour of reconstituted powders was also affected by storage; in most of samples, the darkening, reduction in redness and yellowness were observed. Colour parameters were the most stable in powders obtained with the addition of 2% w/w of sodium caseinate. 相似文献
9.
A novel synthetic route has been proposed to prepare hausmannite nanoparticles. The synthetic route comprises an iron mediated constant current cathodic electrodeposition of manganite and heat treatment of the latter to obtain hausmannite. The obtained nanostructures have been characterized using X-ray Diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX) and Fourier transform Infrared Spectrometry (FTIR). The role of iron in the formation of manganite precursor has been studied by cyclic voltammetry (CV) and differential thermal analysis (DTA). A formation mechanism based on iron mediated formation of Mn3+ and subsequent cathodic reduction of the disproportionated products has been proposed accordingly. The prepared nanoparticles exhibited specific capacitance of 143 F g−1 in 0.5 M Na2SO4 solution. The retained specific capacity was 87% after 2000 cycles. 相似文献
10.
Effect of Stoichiometry on Properties of Rare-Earth-Based Hydrogen Storage Alloy for Nickel-Metal Hydride Secondary Battery 总被引:2,自引:0,他引:2
Effect of stoichiometry on microstructures, electrochemical properties and PCT characteristics of the alloys MI(Ni0.71Co0.15-Al0.06Mn0.08)x (MI=Lanthanum-rich Michmetal, x=4.6~5.2) have been investigated. The lattice constants a, c, and cellvolumes of non-stoichiometric alloys are bigger than those of the stoichiometric alloy. With the increasing stoichiometry x,the value of a decreases, and the value of c and cell volume increases except for those of the stoichiometric alloy; the plateaupressure of PCT curve, discharge capacity and cycling stability all increase. The alloy with x=5.2 shows the highest dischargecapacity and the best cycling stability among the studied alloys. 相似文献