全文获取类型
收费全文 | 616篇 |
免费 | 14篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 8篇 |
综合类 | 5篇 |
化学工业 | 94篇 |
金属工艺 | 31篇 |
机械仪表 | 16篇 |
建筑科学 | 24篇 |
矿业工程 | 3篇 |
能源动力 | 15篇 |
轻工业 | 98篇 |
水利工程 | 6篇 |
石油天然气 | 3篇 |
无线电 | 47篇 |
一般工业技术 | 106篇 |
冶金工业 | 67篇 |
原子能技术 | 3篇 |
自动化技术 | 107篇 |
出版年
2023年 | 6篇 |
2022年 | 8篇 |
2021年 | 21篇 |
2020年 | 12篇 |
2019年 | 15篇 |
2018年 | 24篇 |
2017年 | 13篇 |
2016年 | 11篇 |
2015年 | 14篇 |
2014年 | 24篇 |
2013年 | 42篇 |
2012年 | 26篇 |
2011年 | 26篇 |
2010年 | 36篇 |
2009年 | 26篇 |
2008年 | 33篇 |
2007年 | 31篇 |
2006年 | 18篇 |
2005年 | 26篇 |
2004年 | 20篇 |
2003年 | 18篇 |
2002年 | 19篇 |
2001年 | 15篇 |
2000年 | 10篇 |
1999年 | 4篇 |
1998年 | 20篇 |
1997年 | 9篇 |
1996年 | 14篇 |
1995年 | 7篇 |
1994年 | 9篇 |
1993年 | 3篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1987年 | 3篇 |
1982年 | 2篇 |
1981年 | 6篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1972年 | 2篇 |
1960年 | 2篇 |
1944年 | 2篇 |
1943年 | 6篇 |
1934年 | 2篇 |
1932年 | 2篇 |
1930年 | 2篇 |
1929年 | 3篇 |
1928年 | 3篇 |
1927年 | 2篇 |
排序方式: 共有633条查询结果,搜索用时 15 毫秒
61.
62.
Since the 1950s, digital games in Finland have bridged gaps between professional users and the public as well as institutional and domestic environments. The early significance of Finland's 1970s and 1980s computer games hobbyist and hacker cultures is still evident: clear connections exist between the country's rich history of such subcultures and its modern international success in multimedia and mobile entertainment. 相似文献
63.
G. Petri P. Expert F. Turkheimer R. Carhart-Harris D. Nutt P. J. Hellyer F. Vaccarino 《Journal of the Royal Society Interface》2014,11(101)
Networks, as efficient representations of complex systems, have appealed to scientists for a long time and now permeate many areas of science, including neuroimaging (Bullmore and Sporns 2009 Nat. Rev. Neurosci.
10, 186–198. (doi:10.1038/nrn2618)). Traditionally, the structure of complex networks has been studied through their statistical properties and metrics concerned with node and link properties, e.g. degree-distribution, node centrality and modularity. Here, we study the characteristics of functional brain networks at the mesoscopic level from a novel perspective that highlights the role of inhomogeneities in the fabric of functional connections. This can be done by focusing on the features of a set of topological objects—homological cycles—associated with the weighted functional network. We leverage the detected topological information to define the homological scaffolds, a new set of objects designed to represent compactly the homological features of the correlation network and simultaneously make their homological properties amenable to networks theoretical methods. As a proof of principle, we apply these tools to compare resting-state functional brain activity in 15 healthy volunteers after intravenous infusion of placebo and psilocybin—the main psychoactive component of magic mushrooms. The results show that the homological structure of the brain''s functional patterns undergoes a dramatic change post-psilocybin, characterized by the appearance of many transient structures of low stability and of a small number of persistent ones that are not observed in the case of placebo. 相似文献
64.
Protocols and applications in wireless mesh networks often optimize their performance by measuring the quality of wireless links. However, measuring and characterizing link-quality is a challenging task due to the nature of wireless channel and device-specific properties of radios. The paper proposes two aspects of link-quality measurement and estimation in realistic networks that benefit higher-layer protocols. First, we analyze the statistical properties of link-quality metrics, such as received signal strength and packet error rates, in an indoor IEEE 802.11 mesh network. We show that the statistical distribution and memory properties vary across different links, but are predictable. The next contribution of the paper is a real-time measurement framework that enables higher-level protocols in wireless mesh networks. We discuss the architectural requirements and our implementation experiences of a measurement framework. In addition, we provide three concrete applications that use the measured link-quality and statistical inference to better adapt their behavior. 相似文献
65.
Professor Petri 《European Food Research and Technology》1943,85(5):496-496
66.
67.
Villaseñor M Coscioni AC Galvão KN Chebel RC Santos JE 《Journal of dairy science》2008,91(8):3015-3024
Our objectives were to determine the effects of dietary free gossypol (FG) intake on plasma and uterine gossypol concentrations and embryo development and viability before and after culture with gossypol. Fifty postpubertal Holstein heifers weighing (±SD) 406 ± 34.5 kg at 11.5 mo of age were blocked by age and body weight (BW) and randomly assigned to 1 of 3 isocaloric and isonitrogenous diets differing in their FG content: control (0 mg of FG/kg of BW), moderate (17.8 mg of FG/kg of BW), and high (36.8 mg of FG/kg of BW). Heifers were fed the diets for 70 d before superovulation and embryo collection. Superovulated heifers were flushed on d 5 after induction of ovulation, and early morulae were either stained, to determine the number and proportion of live and dead cells, or randomly assigned to an in vitro culture for 96 h in media containing either 0 or 10 μg/mL of gossypol acetic acid. Plasma and uterine gossypol concentrations increased with increasing gossypol intake. The number of low-quality embryos-ova was greater for the high than for the moderate and control diets. Embryos collected from the high diet had the least number of cells because of fewer live cells, and were smaller in diameter. Greater dietary gossypol reduced blastocyst development and extended the time to reach the blastocyst stage. Similarly, gossypol concentration at 10 μg/mL compromised in vitro development and increased the proportion of degenerated embryos at 96 h in culture. These findings provide in vivo and in vitro evidence that intake of 36.8 mg of FG/kg of BW per d and gossypol concentrations >7 μg/mL in plasma, in uterine flush, or in vitro compromise early embryo development, which might explain some of the negative effects of gossypol on the fertility of dairy cows. 相似文献
68.
RR Vines G Ramakrishnan JB Rogers LA Lockhart BJ Mann WA Petri 《Canadian Metallurgical Quarterly》1998,9(8):2069-2079
Killing of human cells by the parasite Entamoeba histolytica requires adherence via an amebic cell surface lectin. Lectin activity in the parasite is regulated by inside-out signaling. The lectin cytoplasmic domain has sequence identity with a region of the beta2 integrin cytoplasmic tail implicated in regulation of integrin-mediated adhesion. Intracellular expression of a fusion protein containing the cytoplasmic domain of the lectin has a dominant negative effect on extracellular lectin-mediated cell adherence. Mutation of the integrin-like sequence abrogates the dominant negative effect. Amebae expressing the dominant negative mutant are less virulent in an animal model of amebiasis. These results suggest that inside-out signaling via the lectin cytoplasmic domain may control the extracellular adhesive activity of the amebic lectin and provide in vivo demonstration of the lectin's role in virulence. 相似文献
69.
Cowdria ruminantium is the etiologic agent of heartwater, a tick-transmitted foreign animal disease with considerable potential for entrance into the USA. A competitive enzyme-linked immunosorbent assay (cELISA) was developed to detect serologic responses to C. ruminantium infection. The cELISA utilized a recombinant form of the C. ruminantium major antigenic protein (MAP-1) as the antigen and an anti-MAP-1 monoclonal antibody as the competing indicator reagent. Experimental antisera to C. ruminantium and a wide variety of related ehrlichial organisms were used to evaluate cELISA reactivity. Only sera against C. ruminantium, Ehrlichia canis, E. chaffeensis, and a recently discovered cervine ehrlichia-like organism reacted positively in the cELISA. Specificity of the cELISA was > or = 99.5% in a survey of 1,774 southeastern US and Puerto Rican slaughter cattle sera but was only 85% in a group of 79 hunter-killed white-tailed deer (Odocoileus virginianus) from the southeastern USA. Reference true-positive and cELISA false-positive sera were further analyzed by end point titrations using the cELISA and by indirect fluorescent antibody (IFA) tests for reactivity with C. ruminantium, E. canis, and E. chaffeensis antigens. True heartwater-positive sera were significantly more reactive using the cELISA and C. ruminantium IFA procedures (P < 0.05), whereas false-positive sera were significantly more reactive with the antigens used in the E. chaffeensis IFA procedure (P < 0.05). A group of sera from 210 field-origin ruminants residing on known or potentially heartwater-endemic Caribbean islands revealed a substantial (12.4%) prevalence of cELISA-positive specimens. The cELISA is a relatively specific serodiagnostic test for heartwater in cattle and could be used to monitor for possible introduction of the disease into the USA. The cELISA may also be an excellent tool for monitoring the success of an ongoing Caribbean Amblyomma tick eradication program designed to eliminate the biological vector responsible for the perpetuation and spread of this dangerous foreign animal disease. 相似文献
70.