全文获取类型
收费全文 | 23358篇 |
免费 | 2736篇 |
国内免费 | 2869篇 |
专业分类
电工技术 | 1419篇 |
技术理论 | 1篇 |
综合类 | 2670篇 |
化学工业 | 4148篇 |
金属工艺 | 1806篇 |
机械仪表 | 1296篇 |
建筑科学 | 1494篇 |
矿业工程 | 343篇 |
能源动力 | 1454篇 |
轻工业 | 2124篇 |
水利工程 | 276篇 |
石油天然气 | 192篇 |
武器工业 | 39篇 |
无线电 | 2071篇 |
一般工业技术 | 3639篇 |
冶金工业 | 511篇 |
原子能技术 | 114篇 |
自动化技术 | 5366篇 |
出版年
2024年 | 129篇 |
2023年 | 836篇 |
2022年 | 1009篇 |
2021年 | 1194篇 |
2020年 | 1173篇 |
2019年 | 957篇 |
2018年 | 825篇 |
2017年 | 1074篇 |
2016年 | 1163篇 |
2015年 | 1011篇 |
2014年 | 1548篇 |
2013年 | 1726篇 |
2012年 | 2353篇 |
2011年 | 2400篇 |
2010年 | 1663篇 |
2009年 | 1751篇 |
2008年 | 1125篇 |
2007年 | 1840篇 |
2006年 | 1840篇 |
2005年 | 729篇 |
2004年 | 349篇 |
2003年 | 261篇 |
2002年 | 281篇 |
2001年 | 247篇 |
2000年 | 173篇 |
1999年 | 210篇 |
1998年 | 115篇 |
1997年 | 91篇 |
1996年 | 81篇 |
1995年 | 98篇 |
1994年 | 79篇 |
1993年 | 50篇 |
1992年 | 42篇 |
1991年 | 32篇 |
1990年 | 41篇 |
1989年 | 32篇 |
1988年 | 71篇 |
1987年 | 106篇 |
1986年 | 116篇 |
1985年 | 42篇 |
1984年 | 23篇 |
1983年 | 4篇 |
1982年 | 12篇 |
1981年 | 16篇 |
1980年 | 13篇 |
1979年 | 12篇 |
1978年 | 10篇 |
1977年 | 2篇 |
1976年 | 5篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
A double optimal projection method that involves projections for intra-cluster and inter-cluster dimensionality reduction are proposed for video fingerprinting. The video is initially set as a graph with frames as its vertices in a high-dimensional space. A similarity measure that can compute the weights of the edges is then proposed. Subsequently, the video frames are partitioned into different clusters based on the graph model. Double optimal projection is used to explore the optimal mapping points in a low-dimensional space to reduce the video dimensions. The statistics and geometrical fingerprints are generated to determine whether a query video is copied from one of the videos in the database. During matching, the video can be roughly matched by utilizing the statistics fingerprint. Further matching is thereafter performed in the corresponding group using geometrical fingerprints. Experimental results show the good performance of the proposed video fingerprinting method in robustness and discrimination. 相似文献
12.
《Food Control》2015
This study aimed to estimate the extent and level of Salmonella contamination of aquatic food products in China, and to determine serotype, virulotype, and the antimicrobial resistance profiles of recovered Salmonella isolates. Out of 554 samples collected from July 2011 to May 2014, 86 (15.5%) tested positive for Salmonella. The highest contamination rate occurred in oysters (23.1%, 6/26), followed by freshwater fish (18.6%, 43/231), shrimp (13.0%, 13/100), and saltwater fish (12.2%, 24/197). The contamination levels generally corresponded to a most probable number (MPN)/g of 0.3–10, although one sample exceeded 110 MPN/g. Among the 103 isolates, S. Typhimurium, S. Wandsworth, S. Thompson, and S. Derby were the most prevalent serovars. Sixty-eight isolates (66.0%) were resistant to at least one antimicrobial, and 35 (34.0%) were resistant to more than three. High rates of resistance were observed for tetracycline (35.9%), ampicillin (28.2%), nalidixic acid (26.2%), trimethoprim-sulfamethoxazole (25.2%), chloramphenicol (20.4%) and streptomycin (18.4%). Of note, S. Thompson isolates exhibited resistance to multiple extended-spectrum cephalosporins, ciprofloxacin, and other antimicrobials. PCR analysis of 15 virulence genes showed that ssaQ, mgtC, siiD, sopB, and bcfC were present in all 103 isolates, whereas the remaining loci were variably distributed. S. Typhimurium, S. Enteritidis, and S. Weltevreden isolates exhibited a wider range of pathogenicity determinants compared with the other strains. Our study provides a comprehensive surveillance on prevalence of Salmonella in aquatic food products from China and indicates its potential risk to public health. These data are valuable for epidemiological studies, risk management, and public health strategies. 相似文献
13.
14.
《Diamond and Related Materials》2005,14(10):1588-1591
X-ray microdiffraction is a non-destructive technique that allows for depth-resolved, strain measurements with submicron spatial resolution. These capabilities make this technique promising for understanding the mechanical properties of MicroElectroMechancial Systems (MEMS). This investigation examined the local strain induced by irradiating a polycrystalline diamond thin film with a dose of 2 × 1017 H+/cm2 protons. Preliminary results indicate that a measurable strain, on the order of 10− 3, was introduced into the film near the End of Range (EOR) region of the protons. 相似文献
15.
16.
17.
18.
《Journal of the European Ceramic Society》2005,25(6):857-862
Compressive creep tests in air were carried out on 1 cat.% Fe-doped alumina at a temperature T=1400 °C. Iron doping affected the plastic deformation by different ways in relation with Fe2+ cations population. Fe2+ cations sped up the deformation rates. FeAl2O4 spinel precipitates were identified and they were found (i) to interact with alumina grain boundaries (ii) to limit the grain growth within a range of strain. The Fe2+ cations underwent oxidation and this resulted in the dissolution of the some precipitates and in the decrease of deformation rates. It was suggested that deformation sped up this evolution through mass transport and that time was not a dominating parameter. 相似文献
19.
20.