全文获取类型
收费全文 | 802篇 |
免费 | 29篇 |
专业分类
电工技术 | 4篇 |
综合类 | 1篇 |
化学工业 | 175篇 |
金属工艺 | 5篇 |
机械仪表 | 13篇 |
建筑科学 | 34篇 |
能源动力 | 28篇 |
轻工业 | 47篇 |
水利工程 | 7篇 |
石油天然气 | 1篇 |
无线电 | 94篇 |
一般工业技术 | 105篇 |
冶金工业 | 199篇 |
原子能技术 | 2篇 |
自动化技术 | 116篇 |
出版年
2023年 | 6篇 |
2022年 | 29篇 |
2021年 | 22篇 |
2020年 | 13篇 |
2019年 | 14篇 |
2018年 | 14篇 |
2017年 | 13篇 |
2016年 | 14篇 |
2015年 | 16篇 |
2014年 | 18篇 |
2013年 | 31篇 |
2012年 | 36篇 |
2011年 | 34篇 |
2010年 | 33篇 |
2009年 | 31篇 |
2008年 | 34篇 |
2007年 | 30篇 |
2006年 | 30篇 |
2005年 | 27篇 |
2004年 | 17篇 |
2003年 | 16篇 |
2002年 | 17篇 |
2001年 | 11篇 |
2000年 | 8篇 |
1999年 | 9篇 |
1998年 | 66篇 |
1997年 | 36篇 |
1996年 | 23篇 |
1995年 | 15篇 |
1994年 | 17篇 |
1993年 | 12篇 |
1992年 | 13篇 |
1991年 | 7篇 |
1990年 | 9篇 |
1989年 | 11篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 9篇 |
1985年 | 4篇 |
1984年 | 11篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 4篇 |
1977年 | 6篇 |
1976年 | 12篇 |
1975年 | 3篇 |
1968年 | 3篇 |
1929年 | 2篇 |
排序方式: 共有831条查询结果,搜索用时 18 毫秒
71.
Jeyasankar Alagarmalai David Nestel Daniela Dragushich Ester Nemny-Lavy Leonid Anshelevich Anat Zada Victoria Soroker 《Journal of chemical ecology》2009,35(5):542-551
The Ethiopian fruit fly, Dacus ciliatus, is an oligophagous pest of cucurbit crops, particularly melons, cucumbers, and marrows (summer squash). The present study
aimed to identify host attractants for D. ciliatus and was guided by a behavioral bioassay and an electrophysiological assay. We tested volatile compounds from the fruits of
a host plant, ripe and unripe Galia melon, Cucumis melo var. reticulates. Both sexes were attracted to melon volatiles. Those of ripe melon were preferred. Gas chromatography-electroantennographic
detection analysis of the behaviorally active ripe melon volatiles consistently showed that 14 compounds elicited similar
antennal responses from both sexes. Twelve compounds were identified by gas chromatography-mass spectrometry (GC-MS) using
GC-MS libraries, retention indices (RI), and authentic standards. The electrophysiological activities of the compounds that
were present at sufficient levels for identification, benzyl acetate, hexanyl acetate, (Z)-3-hexenyl acetate, (Z)-3-octenyl acetate, octanyl acetate, (Z)-3-decenyl acetate, and (E)-β-farnesene, were evaluated at six different dosage levels by using electroantennography (EAG). Benzyl and hexanyl acetates
elicited dose responses only in males, while other tested compounds elicited dose responses in both sexes. The strongest responses
were observed for doses between 100 ng and 10 μg. The dose response, in terms of attractiveness to synthetic compounds within
the active range (as determined by EAG), also was evaluated in the behavioral bioassay. Synthetic acetates were attractive
to both sexes when tested individually. Significant attraction was observed when individual compounds were applied in the
bioassay arena at doses of 0.5–1 μg/dispenser. Blends of compounds in equal proportions also were attractive to the insects.
The most attractive blend was a mixture of four or five identified acetates. The addition of an equal proportion of (E)-β-farnesene to this mixture had a deterrent effect. 相似文献
72.
Darin P. O'Brien Kristen A. Campbell Nathaniel W. Morken Robert J. Bair Ellen M. Heath 《Journal of The Association for Laboratory Automation》2001,6(2):67
Advancements in the fields of genomic screening, molecular pathology and clinical research have resulted in a major increase in the demand for high quality DNA and RNA. This escalating demand has resulted in a sample preparation bottleneck and an emphasis on the development of new technologies to automate the purification process. Gentra has developed the AUTOPURE LS™ nucleic acid purification instrument, a platform capable of high-throughput sample purification from large samples, such as 10 mL whole blood. This article presents data showing the equivalency of DNA purified using manual and automated processing. 相似文献
73.
Shorelines of Lake Algonquin, the largest of the glacial lakes of the Great Lakes area, are well known in southern Ontario, but are sporadic and difficult to trace northward onto the Precambrian shield. Improved knowledge of the extent and uplift pattern for Algonquin shorelines is needed to support geophysical models of isostatic response, interpretation of glacial and glacial lake history, and the search by archeologists for evidence of Paleoindian activity, shown to be localized along its shoreline. The Sudbury basin is one of the few areas of mapping of Quaternary geology on the Canadian shield that provides a record of Algonquin lake phases. Meltwaters from the northward-receding ice front formed a series of deltas southward into the Sudbury basin in central Ontario around the time the Cartier I moraine was deposited. Instrumental surveys of deltas, bars, and shorebluffs carried out in the northern Sudbury basin delineate several discrete water planes. Correlation with previously surveyed and correlated shorelines on Manitoulin Island, southwest of Sudbury, indicates the presence of an upper Algonquin shoreline and features correlated to the Cedar Point, Payette, Sheguiandah, and Korah levels. Features southwest of the Sudbury basin at Nairn correlate with Korah and post-Korah water levels. Land between Nairn and Sudbury is too elevated to have been reached by the later Nipissing transgression. Similar shoreline sequences have been surveyed near North Bay, with results supporting the findings of this study. 相似文献
74.
What is the value of limited feedback for MIMO channels? 总被引:7,自引:0,他引:7
Feedback in a communications system can enable the transmitter to exploit channel conditions and avoid interference. In the case of a multiple-input multiple-output channel, feedback can be used to specify a precoding matrix at the transmitter, which activates the strongest channel modes. In situations where the feedback is severely limited, important issues are how to quantize the information needed at the transmitter and how much improvement in associated performance can be obtained as a function of the amount of feedback available. We give an overview of some recent work in this area. Methods are presented for constructing a set of possible precoding matrices, from which a particular choice can be relayed to the transmitter. Performance results show that even a few bits of feedback can provide performance close to that with full channel knowledge at the transmitter. 相似文献
75.
76.
77.
78.
79.
80.