全文获取类型
收费全文 | 238065篇 |
免费 | 17084篇 |
国内免费 | 630篇 |
专业分类
电工技术 | 4220篇 |
综合类 | 163篇 |
化学工业 | 46525篇 |
金属工艺 | 8495篇 |
机械仪表 | 6802篇 |
建筑科学 | 6497篇 |
矿业工程 | 1325篇 |
能源动力 | 6071篇 |
轻工业 | 24500篇 |
水利工程 | 2566篇 |
石油天然气 | 4093篇 |
武器工业 | 8篇 |
无线电 | 29716篇 |
一般工业技术 | 51346篇 |
冶金工业 | 37799篇 |
原子能技术 | 5096篇 |
自动化技术 | 20557篇 |
出版年
2021年 | 2131篇 |
2020年 | 2690篇 |
2019年 | 4805篇 |
2018年 | 5776篇 |
2017年 | 6132篇 |
2016年 | 6760篇 |
2015年 | 5743篇 |
2014年 | 7038篇 |
2013年 | 14122篇 |
2012年 | 7828篇 |
2011年 | 9377篇 |
2010年 | 8214篇 |
2009年 | 8897篇 |
2008年 | 8479篇 |
2007年 | 8353篇 |
2006年 | 7184篇 |
2005年 | 6516篇 |
2004年 | 6297篇 |
2003年 | 6156篇 |
2002年 | 5759篇 |
2001年 | 5737篇 |
2000年 | 5616篇 |
1999年 | 5169篇 |
1998年 | 11417篇 |
1997年 | 8157篇 |
1996年 | 6421篇 |
1995年 | 4687篇 |
1994年 | 4293篇 |
1993年 | 4095篇 |
1992年 | 3238篇 |
1991年 | 3091篇 |
1990年 | 2892篇 |
1989年 | 2958篇 |
1988年 | 2833篇 |
1987年 | 2407篇 |
1986年 | 2323篇 |
1985年 | 2733篇 |
1984年 | 2532篇 |
1983年 | 2374篇 |
1982年 | 2107篇 |
1981年 | 2223篇 |
1980年 | 2046篇 |
1979年 | 2139篇 |
1978年 | 2124篇 |
1977年 | 2374篇 |
1976年 | 3195篇 |
1975年 | 1841篇 |
1974年 | 1765篇 |
1973年 | 1778篇 |
1972年 | 1445篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
Joon‐Young Jun Sosuke Nakajima Koji Yamazaki Yuji Kawai Hajime Yasui Yasuyuki Konishi 《International Journal of Food Science & Technology》2015,50(4):871-877
Cystoseira hakodatensis is an unutilised brown algae belonging to family Sargassaceae. A crude methanol extract from the algae showed inhibitory effects on the growths of Bacillus cereus and Bacillus licheniformis. To isolate the major antimicrobial agent, a sequential active‐guided isolation procedure was applied: liquid–liquid extraction, column chromatography and bio‐autography. A marked antimicrobial agent (active α) was isolated in hydrophobic fraction and was determined to phenolics without carbohydrates and proteins by phytochemical test. Regarding the antimicrobial potential, the isolated active α showed better inhibitory effects against B. cereus and B. licheniformis at 2 and 4 times of lower concentrations (62.5 and 31.3 μg mL?1) in comparison with epigallocatechin gallate. These results showed that C. hakodatensis is a potential source of antimicrobial agent capable of preventing the growth of the two bacteria. 相似文献
73.
A conceptualization of intended learning outcomes supporting self‐regulated learners in indicating learning paths 下载免费PDF全文
P. Tangworakitthaworn L. Gilbert G.B. Wills 《Journal of Computer Assisted Learning》2015,31(5):393-404
Intended learning outcomes (ILOs) indicate what learners will be able to achieve after they are taught. Traditionally, ILOs are expressed as plain text or unstructured documents. What if all ILOs of a specific course of study can be conceptualized through a structured diagrammatic technique? It was hypothesized that learners can benefit from this conceptualization in learning, especially in self‐regulated learning. The aim of this study was to investigate whether the ILOs represented in unstructured or structured formats can facilitate learners to identify learning paths. The results revealed that the mean ratings of all learning paths were statistically significantly higher with structured ILOs. 相似文献
74.
75.
76.
77.
78.
Machine Learning - We propose a data-driven approach to quantify the uncertainty of models constructed by kernel methods. Our approach minimizes the needed distributional assumptions, hence,... 相似文献
79.
Manjin Kim Qinfen Gu Tanveer Hussain Yahia Ali Trevor B. Abbott Kazuhiro Nogita 《International Journal of Hydrogen Energy》2021,46(53):27096-27106
With superior properties of Mg such as high hydrogen storage capacity (7.6 wt% H/MgH2), low price, and low density, Mg has been widely studied as a promising candidate for solid-state hydrogen storage systems. However, a harsh activation procedure, slow hydrogenation/dehydrogenation process, and a high temperature for dehydrogenation prevent the use of Mg-based metal hydrides for practical applications. For these reasons, Mg-based alloys for hydrogen storage systems are generally alloyed with other elements to improve hydrogen sorption properties. In this article, we have added Na to cast Mg–La alloys and achieved a significant improvement in hydrogen absorption kinetics during the first activation cycle. The role of Na in Mg–La has been discussed based on the findings from microstructural observations, crystallography, and first principles calculations based on density functional theory. From our results in this study, we have found that the Na doped surface of Mg–La alloy systems have a lower adsorption energy for H2 compared to Na-free surfaces which facilitates adsorption and dissociation of hydrogen molecules leading to improvement of absorption kinetic. The effect of Na on the microstructure of these alloys, such as eutectic refinement and a density of twins is not highly correlated with absorption kinetics. 相似文献
80.
Matthew O'Sullivan Daire
hUallachin Patrícia Oliveira Antunes Eleanor Jennings Mary Kelly‐Quinn 《河流研究与利用》2019,35(2):146-158
Cattle access to streams has been linked globally with degradation of stream water quality, driven largely by bank erosion and resultant instream, fine sediment deposition. The majority of evidence on such effects is however based in arid and semiarid regions of the United States and Australia, with few studies relating to cool temperate climates such as Northwest Europe. In this study, “Quorer” resuspendable sediment samples were taken from riffle geomorphic units upstream (control) and at two points downstream (pressure and recovery) of cattle access points in headwater streams in agricultural catchments in Ireland to assess levels of deposited stream sediment. Samples were taken in April/May (2016) prior to the grazing season and in October (2016) at the end of the grazing season. Sites in good‐high ecological status catchments and less than good ecological status catchments were included in the study. Higher levels of sediment were found downstream of cattle access points in both good‐high status and less than good status catchments; however, the impacts of access points were spatially confined to, in most cases, the area immediately downstream of the point of access. There was a strong correlation between deposited sediment mass and organic matter (OM) mass, with levels of OM increasing linearly with deposited sediment mass. Levels of measured sediment were negatively correlated with riparian habitat health (measured using a qualitative habitat assessment). The results of this study highlight the need for measures to prevent cattle access to headwater streams where access points can be many in order to manage local habitat quality and downstream water quality issues. 相似文献