全文获取类型
收费全文 | 213篇 |
免费 | 12篇 |
专业分类
电工技术 | 2篇 |
化学工业 | 26篇 |
金属工艺 | 1篇 |
机械仪表 | 2篇 |
建筑科学 | 15篇 |
能源动力 | 5篇 |
轻工业 | 16篇 |
石油天然气 | 1篇 |
无线电 | 43篇 |
一般工业技术 | 44篇 |
冶金工业 | 46篇 |
自动化技术 | 24篇 |
出版年
2023年 | 4篇 |
2022年 | 1篇 |
2021年 | 7篇 |
2020年 | 3篇 |
2019年 | 4篇 |
2018年 | 2篇 |
2017年 | 2篇 |
2016年 | 7篇 |
2015年 | 9篇 |
2014年 | 14篇 |
2013年 | 13篇 |
2012年 | 10篇 |
2011年 | 12篇 |
2010年 | 8篇 |
2009年 | 5篇 |
2008年 | 12篇 |
2007年 | 9篇 |
2006年 | 2篇 |
2005年 | 8篇 |
2004年 | 6篇 |
2003年 | 3篇 |
2002年 | 4篇 |
2000年 | 7篇 |
1999年 | 5篇 |
1998年 | 21篇 |
1997年 | 12篇 |
1996年 | 8篇 |
1995年 | 4篇 |
1994年 | 5篇 |
1993年 | 7篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1976年 | 2篇 |
1969年 | 1篇 |
排序方式: 共有225条查询结果,搜索用时 31 毫秒
1.
SA Syed KS Zahir JR Zink O Saglaam RJ Restifo JG Thomson 《Canadian Metallurgical Quarterly》1997,38(4):396-403
Reinstatement and spontaneous recovery of previously extinguished nicotine-taking behavior were examined in rats. Male subjects were trained to self-administer nicotine (30 microg/kg per infusion, IV; one 60-min session per day for 3 weeks). Extinction sessions were then given for 5-10 days during which saline was substituted for nicotine. Subsequently, in the first set of tests for nicotine seeking, the reinstatement of lever presses that previously delivered nicotine was examined after priming injections of saline and nicotine (75, 150 and 300 microg/kg, SC; and 30 and 60 microg/kg, IV). In the second set of tests for nicotine-seeking, rats were tested after an additional 21-day drug-free period during which they were not exposed to the self-administration chambers (a test for the spontaneous recovery of drug seeking), and after priming injections of nicotine (150 and 300 microg/kg, SC). Reinstatement of extinguished food-reinforced behavior after exposure to nicotine was also determined. Priming injections of nicotine reinstated nicotine seeking regardless of the route of administration. In addition, previously extinguished nicotine seeking recovered spontaneously after a 21-day period during which rats were not exposed to the drug-taking environment. Nicotine also reinstated extinguished food-reinforced behavior in rats with a history of nicotine self-administration, but not in drug-naive rats. The present results extend previous work with opioid and stimulant drugs on reinstatement of drug seeking by the self-administered drug. It also appears that, as with other positive reinforcers, the mere passage of time is a sufficient condition for the spontaneous recovery of extinguished nicotine seeking. 相似文献
2.
3.
The barrier function of cultured, macrovascular endothelial cells derived from bovine aorta was analyzed using confluent monolayers of cells and measuring the exchange of fluorescein dextrans of different molecular masses. The effects of beta-adrenoceptor agonists with different selectivity for beta 1- and beta 2-adrenoceptors (AR) were investigated. Formoterol, a novel high-affinity agonist for beta 2-AR recently introduced in the treatment of bronchial asthma, showed a significant reduction of cell permeability with subnanomolar concentrations, whereas the catecholamines (-)-isoproterenol and (-)-norepinephrine only showed significant effects with micromolar concentrations. In order to elucidate if this difference in potential to regulate cell permeability is related to appropriate changes in the selectivity and affinity of the agonists for beta 2 AR, we investigated the beta AR-coupled adenylate cyclase (AC) in membranes from endothelial cells and compared AC stimulation with the binding of agonists to the receptors using [125I](-)-iodopindolol as radioligand. beta-Adrenoceptors revealed to be closely coupled to AC as assessed by a similar magnitude of effects by receptor agonists in comparison to GTP analogues and direct stimulants of AC activity. AC activity was increased by formoterol in parallel to its receptor occupancy of beta 2AR with nanomolar concentrations which were 50-fold higher than those used for the regulation of cell permeability indicating the existence of spare receptors. In contrast to formoterol, the catecholamines (-)-isoproterenol and (-)-norepinephrine stimulated AC activity through both beta 1AR and beta 2AR. From the overproportional high contribution of beta 1AR to AC stimulation (42%) in comparison to its low fraction (13%) in receptor binding we calculated that beta 1AR is 3-4-fold more effectively coupled to AC than beta 2 AR. 相似文献
4.
5.
Tachikawa M. Evenson K.M. Zink L.R. Maki A.G. 《Quantum Electronics, IEEE Journal of》1996,32(10):1732-1736
We have measured frequencies of N2O transitions by heterodyning sub-Doppler fluorescence-stabilized N2O laser radiation with that from a reference CO2 laser. A high-resolution cavity incorporates a ribbed tube and a highly reflective grating, permitting the CW oscillation of both the 100 0-0200 9-μm and the 1000-0001 10-μm regular bands. This is the first sub-Doppler frequency measurement of the 9-μm band. The accuracy in the determination of the rotational constants for both bands has been improved by an order of magnitude, and calculated transition frequencies are presented 相似文献
6.
A Bedekar RM Zink DH Sherman TV Line JF Van Pilsum 《Canadian Metallurgical Quarterly》1998,119(4):677-690
The amino acid sequences of the amidinotransferases and the nucleotide sequences of their genes or cDNA from four Streptomyces species (seven genes) and from the kidneys of rat, pig, human and human pancreas were compared. The overall amino acid and nucleotide sequences of the prokaryotes and eukaryotes were very similar and further, three regions were identified that were highly identical. Evidence is presented that there is virtually zero chance that the overall and high identity regions of the amino acid sequence similarities and the overall nucleotide sequence similarities between Streptomyces and mammals represent random match. Both rat and lamprey amidinotransferases were able to use inosamine phosphate, the amidine group acceptor of Streptomyces. We have concluded that the structure and function of the amidinotransferases and their genes has been highly conserved through evolution from prokaryotes to eukaryotes. The evolution has occurred with: (1) a high degree of retention of nucleotide and amino acid sequences; (2) a high degree of retention of the primitive Streptomyces guanine + cytosine (G + C) third codon position composition in certain high identity regions of the eukaryote cDNA; (3) a decrease in the specificities for the amidine group acceptors; and (4) most of the mutations silent in the regions suggested to code for active sites in the enzymes. 相似文献
7.
Che-Chung Chou Evenson K.M. Zink K.R. Maki A.G. Jow-Tsong Shy 《Quantum Electronics, IEEE Journal of》1995,31(2):343-345
Nineteen new laser lines in the 11-μm wavelength region have been observed in CW oscillation from a CO2 laser with a high-Q, high-resolution cavity at a higher than usual current density. The frequency of each line has been measured using heterodyne frequency measurement techniques. Analysis of the frequencies shows that 15 lines are rotation-vibration transitions of the 0112-[1111,0311]I band (the first sequence hot band) of the CO2 molecule and four lines belong to the rotation-vibration transitions of the 0221-[12 20, 0420]I band of CO2 相似文献
8.
This paper presents an innovative approach for initiating processes of a transactive memory system in newly formed groups of experts collaborating computer-supported in a complex problem-solving task. Our empirical study compared 15 experimental and 15 control groups, each consisting of triads. In the experimental condition, the triads were provided with a tool for fostering knowledge and information awareness, that is, being informed about the knowledge and the underlying information of the collaboration partners in form of digital concept maps. In the control condition, the groups had no access to this tool. Results confirmed the potential of the tool to initiate processes of a transactive memory system: shared agreement of the knowledge of the other group members’ knowledge proved to influence group performance positively. In addition, previous findings of the tool’s potential to establish knowledge and information awareness and to augment group performance could be replicated. However, the postulated mediating effect of processes of a transactive memory system concerning the impact of knowledge and information awareness on group performance did not reach statistical significance. Aspects for future studies and implications of these findings regarding their practical implementation, for example, in teams of organizations, are discussed. 相似文献
9.
Contour line and geographic feature extraction from USGS color topographical paper maps 总被引:4,自引:0,他引:4
Khotanzad A. Zink E. 《IEEE transactions on pattern analysis and machine intelligence》2003,25(1):18-31
This paper presents a method for the extraction of contour lines and other geographic information from scanned color images of topographical maps. Although topographic maps are available from many suppliers, this work focuses on United States Geological Survey (USGS) maps. The extraction of contour lines, which are shown with brown color on USGS maps, is a difficult process due to aliasing and false colors induced by the scanning process and due to closely spaced and intersecting/overlapping features inherent to the map. These difficulties render simple approaches such as clustering ineffective. The proposed method overcomes these difficulties using a multistep process. First, a color key set, designed to comprehend color aliasing and false colors, is generated using an eigenvector line-fitting technique in RGB space. Next, area features, representing vegetation and bodies of water, are extracted using RGB color histogram analysis in order to simplify the next stage. Then, linear features corresponding to roads and rivers including contours, are extracted using a valley seeking algorithm operating on a transformed version of the original map. Finally, an A* search algorithm is used to link valleys together to form linear features and to close the gaps caused by intersecting features. The performance of the algorithm is tested on a number of USGS topographic map samples. 相似文献