全文获取类型
收费全文 | 941篇 |
免费 | 46篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 7篇 |
综合类 | 1篇 |
化学工业 | 240篇 |
金属工艺 | 18篇 |
机械仪表 | 28篇 |
建筑科学 | 59篇 |
矿业工程 | 1篇 |
能源动力 | 18篇 |
轻工业 | 200篇 |
水利工程 | 11篇 |
石油天然气 | 1篇 |
无线电 | 32篇 |
一般工业技术 | 135篇 |
冶金工业 | 132篇 |
原子能技术 | 12篇 |
自动化技术 | 94篇 |
出版年
2023年 | 10篇 |
2022年 | 38篇 |
2021年 | 39篇 |
2020年 | 21篇 |
2019年 | 24篇 |
2018年 | 21篇 |
2017年 | 14篇 |
2016年 | 34篇 |
2015年 | 29篇 |
2014年 | 32篇 |
2013年 | 45篇 |
2012年 | 50篇 |
2011年 | 63篇 |
2010年 | 51篇 |
2009年 | 44篇 |
2008年 | 58篇 |
2007年 | 45篇 |
2006年 | 40篇 |
2005年 | 28篇 |
2004年 | 20篇 |
2003年 | 22篇 |
2002年 | 21篇 |
2001年 | 18篇 |
2000年 | 12篇 |
1999年 | 15篇 |
1998年 | 28篇 |
1997年 | 12篇 |
1996年 | 12篇 |
1995年 | 11篇 |
1994年 | 4篇 |
1993年 | 7篇 |
1992年 | 6篇 |
1991年 | 4篇 |
1990年 | 6篇 |
1989年 | 7篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1973年 | 4篇 |
1971年 | 3篇 |
1905年 | 14篇 |
1904年 | 16篇 |
1903年 | 13篇 |
1902年 | 11篇 |
1898年 | 2篇 |
排序方式: 共有989条查询结果,搜索用时 9 毫秒
41.
The purpose of these studies was to develop a conductimetric method for the rapid detection of Campylobacter jejuni. Numerous basal medium components were analyzed to develop a growth-enhancing broth medium for detection of freeze-injured Campylobacter cells using a conductimetric system. The final medium was composed of a modified Campy-Line agar from which the agar and triphenyltetrazolium chloride were removed and the amino acid, L-arginine was added. Pure isolates of C. jejuni. (frozen and thawed to produce stressed cells) were utilized to test the detection methodology. Monitoring of significant changes in the capacitance signal was found suitable for detection of Campylobacter proliferation. Using stressed pure cultures, Campylobacter growth was repeatedly detected at very low inoculum levels (about one cell per well). There was a direct linear relationship between detection times (DTs) and the initial inoculum level. For example, using a single strain, the mean DT (n = 20) at the 10 CFU/ml inoculum level was 28.6 h, with 100% of the inoculated wells detecting. The mean DTs at the 100, 1,000, and 10,000 CFU/ml inoculum levels were 24.9, 21.4, and 17.0 h, respectively. This study demonstrates that conductimetric methods can be utilized for the rapid detection of C. jejuni. 相似文献
42.
43.
Daniel Kirsten 《Theory of Computing Systems》2006,39(1):15-50
We introduce a new model of weighted automata: the desert automata. We show
that their limitedness problem is PSPACE-complete by solving the underlying
Burnside problem. As an application of this result, we give a positive
solution to the so-called finite substitution problem which was open for more
than 10 years: given recognizable languages K and L, decide whether there
exists a finite substitution σ such that σ(K) = L. 相似文献
44.
This article explores the use of a multimedia search interface for digital libraries based on strand maps developed by the American Association for the Advancement of Science. As semantic-spatial displays, strand maps provide a visual organization of relevant conceptual information that may promote the use of science content during digital library use. A study was conducted to compare users' cognitive processes during information seeking tasks when using a multimedia strand maps interface, versus the textual search interface currently implemented in the Digital Library for Earth System Education. Quantitative and qualitative data from think-aloud protocols revealed that students were more likely to engage with science content (e.g., analyzing the relevance of science concepts with regard to task needs) during search when using the strand maps interface compared to those using textual searching. In contrast, students using a textual search interface engaged more frequently with surface-level information (e.g., the type of a resource regardless of its science content) during search and retrieval. As a multimedia search interface for digital libraries, strand maps appear to be promising tools to promote conceptual discovery and learning through content-based processes that promote learner engagement with relevant science knowledge. 相似文献
45.
The properties of a 16-kbit bubble memory chip having a conventional major-minor loop organization are described. The chip can be operated up to a shift rate of 300 kHz which corresponds to a mean access time of 0.5 ms to blocks of 128 bits. Overall bias field margins of 13 percent were obtained, especially as the result of an appropriately selected layout of the transfer gates which is described in detail. Additional data are given concerning the influence of ambient temperature and of the number of propagation steps. The possibility of fabricating X-bar transfer gates using a single photomask step is demonstrated. 相似文献
46.
Soren Damgaard-Larsen Kirsten Ottar Jensen Ebba Lund Birte Nissen 《Water research》1977,11(6):503-508
Coxsackievirus and tritiated water were added to municipal sludges which were placed on lysimeters containing sandy soil or clay soil. It took 23 weeks during a normal Danish winter to inactivate virus from an initial 106tcid50/g sludge to a not demonstrable level. Irrespective of sludge and soil type no virus was demonstrated in the leachate water. The rainfall during December–May was 300 mm. 相似文献
47.
William Banks John L. Clapperton Morag E. Kelly Agnes G. Wilson Robert J. M. Crawford 《Journal of the science of food and agriculture》1980,31(4):368-374
The presence in the bovine mammary gland of a desaturase specific for the conversion of stearic to oleic acid allows the manipulation of the physical properties of milk fat by varying the dietary intake of C16 and C18 fatty acids. In particular, feeding the dairy cow an oil with a high C18: C16 ratio should allow the proportion of milk fat that is liquid at 5°C to be increased, with a consequent improvement in the low-temperature spreadability of butter. In this paper, the effect of feeding concentrate rations containing (a) soya oil as the free oil and as cracked soya beans; (b) various levels of soya oil, the ration being offered twice or 24-times daily, on the thermal properties of the milk fat and on the yield of milk constituents is examined in detail. Feeding ratios containing free soya oil greatly increased the proportion of milk fat liquid at 5°C, whereas cracked soya oil gave only slight increases. Proportion and yield of milk fat were decreased by feeding soya oil twice daily but were increased by continuous feeding. 相似文献
48.
The Cytosensor microphysiometer uses silicon chip technology to correlate changes in extracellular acidification rates with quantitative changes in cellular metabolism in response to ligand binding to surface receptors. This functional measure of physiology makes the Cytosensor a valuable tool in drug discovery research by allowing application of the instrument to screening of prospective pharmacologically active agents, characterizations of dose responses and structure-activity relationships, and investigation of mechanisms of action. 相似文献
49.
Rohrlack T Christoffersen K Hansen PE Zhang W Czarnecki O Henning M Fastner J Erhard M Neilan BA Kaebernick M 《Journal of chemical ecology》2003,29(8):1757-1770
This paper describes the purification and characterization of microviridin J, a newly discovered metabolite of Microcystis that causes a lethal molting disruption in Daphnia spp., upon ingestion of living cyanobacterial cells. Microviridin J consists of an acetylated chain of 13 amino acids arranged in three rings and two side chains. Unlike other known isoforms of microviridin, microviridin J contains arginine that imparts a unique solution conformation characterized by proximal hydrophobic interactions between Arg and other regions of the molecule. This eventually results in the formation and stabilization of an additional ring system. Microviridin J potently inhibits porcine trypsin, bovine chymotrypsin, and daphnid trypsin-like proteases. The activity against trypsin is most likely due to Arg and its distinctive conformational interactions. Overall, the data presented for microviridin J emphasize once again the ability of cyanobacteria to produce numerous and potent environmental toxins. 相似文献
50.
The present study examined quantitative electroencephalographic (QEEG) profile for children with autistic spectrum disorder (ASD). Five-minute QEEG data were obtained from 90 normal controls (NCs) and 66 children with ASD. Spectrum analyses revealed that ASD children showed significantly less relative alpha and more relative delta than NC. Specifically, 26% of ASD children and 2% of NCs showed 1.5 SDs of relative alpha below the normative mean. Children with this QEEG profile had 17 times the risk of having ASD than those without such a profile. Sensitivity and specificity of relative alpha were 91% and 73%, respectively. Split-half cross-validation yielded a sensitivity of 76%. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献