全文获取类型
收费全文 | 1889篇 |
免费 | 4篇 |
专业分类
电工技术 | 22篇 |
综合类 | 1篇 |
化学工业 | 66篇 |
金属工艺 | 4篇 |
机械仪表 | 5篇 |
建筑科学 | 17篇 |
矿业工程 | 3篇 |
能源动力 | 43篇 |
轻工业 | 21篇 |
水利工程 | 2篇 |
石油天然气 | 2篇 |
无线电 | 20篇 |
一般工业技术 | 29篇 |
冶金工业 | 1625篇 |
原子能技术 | 1篇 |
自动化技术 | 32篇 |
出版年
2022年 | 2篇 |
2021年 | 4篇 |
2020年 | 2篇 |
2018年 | 6篇 |
2017年 | 2篇 |
2015年 | 5篇 |
2014年 | 2篇 |
2013年 | 22篇 |
2012年 | 8篇 |
2011年 | 8篇 |
2010年 | 14篇 |
2009年 | 9篇 |
2008年 | 11篇 |
2007年 | 15篇 |
2006年 | 10篇 |
2005年 | 4篇 |
2004年 | 8篇 |
2002年 | 6篇 |
2001年 | 6篇 |
2000年 | 7篇 |
1999年 | 60篇 |
1998年 | 482篇 |
1997年 | 267篇 |
1996年 | 191篇 |
1995年 | 102篇 |
1994年 | 90篇 |
1993年 | 112篇 |
1992年 | 19篇 |
1991年 | 24篇 |
1990年 | 21篇 |
1989年 | 37篇 |
1988年 | 27篇 |
1987年 | 27篇 |
1986年 | 16篇 |
1985年 | 18篇 |
1984年 | 7篇 |
1983年 | 11篇 |
1982年 | 14篇 |
1981年 | 12篇 |
1980年 | 15篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1977年 | 41篇 |
1976年 | 117篇 |
1975年 | 3篇 |
1973年 | 7篇 |
1972年 | 3篇 |
1971年 | 3篇 |
1961年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有1893条查询结果,搜索用时 15 毫秒
61.
Douglas A Stow Allen Hope David Verbyla Fred Huemmrich Charles Racine Kenneth Tape Kenji Yoshikawa Brian Noyle David Douglas Gensuo Jia Donald Walker Aaron Petersen Ranga Myneni 《Remote sensing of environment》2004,89(3):281-308
The objective of this paper is to review research conducted over the past decade on the application of multi-temporal remote sensing for monitoring changes of Arctic tundra lands. Emphasis is placed on results from the National Science Foundation Land-Air-Ice Interactions (LAII) program and on optical remote sensing techniques. Case studies demonstrate that ground-level sensors on stationary or moving track platforms and wide-swath imaging sensors on polar orbiting satellites are particularly useful for capturing optical remote sensing data at sufficient frequency to study tundra vegetation dynamics and changes for the cloud prone Arctic. Less frequent imaging with high spatial resolution instruments on aircraft and lower orbiting satellites enable more detailed analyses of land cover change and calibration/validation of coarser resolution observations.The strongest signals of ecosystem change detected thus far appear to correspond to expansion of tundra shrubs and changes in the amount and extent of thaw lakes and ponds. Changes in shrub cover and extent have been documented by modern repeat imaging that matches archived historical aerial photography. NOAA Advanced Very High Resolution Radiometer (AVHRR) time series provide a 20-year record for determining changes in greenness that relates to photosynthetic activity, net primary production, and growing season length. The strong contrast between land materials and surface waters enables changes in lake and pond extent to be readily measured and monitored. 相似文献
62.
A. S. Hope Corresponding author K. R. Pence D. A. Stow 《International journal of remote sensing》2013,34(20):4237-4250
The relationship between normalized difference vegetation index (NDVI) patterns obtained from high spatial resolution aircraft and low spatial resolution satellite data (Advanced Very High Resolution Radiometer (AVHRR)) was investigated with the intent of using multilevel data to scale carbon flux models in Arctic tundra ecosystems. Despite variable illumination conditions during the aircraft missions and maximum value compositing of the AVHRR data, the difference between 3?km average aircraft and AVHRR NDVI values was generally constant along each flight transect. However, the magnitude of the offset differed between flight dates and small lakes had a greater effect on area averaged aircraft NDVI values than on the satellite values. A cloud index was calculated using incident solar radiation measured by the aircraft and this index was used to identify periods when the aircraft NDVI values may have been biased by cloud cover. Removal of NDVI values based on a cloud index threshold did not appear to be justified given the marginal improvement in the relationship between the two NDVI datasets. If the systematic difference between AVHRR and aircraft NDVI values can be determined, then the scaling of carbon flux models based on the NDVI should be a viable approach in Arctic ecosystems. 相似文献
63.
Hope Hui Rising 《Journal of Urban Design》2019,24(3):424-442
Kevin Lynch’s theory of imageability was used to examine the contributions of imageability elements (landmarks, paths, nodes, edges and districts) and components (structure, identity and meaning) to the image of the water city. Through conducting cognitive mapping, photovoice and non-visual protocols in eight cities, waterscape mappability, identifiability and attachment were measured as water-based structure, identity and meaning. To generate measures for the image of the water city, independent raters evaluated the identifiability of sketch maps. Regression analyses suggest that only canal mappability (the structure of water-based paths) significantly contributed to all measures for the image of the water city. 相似文献
64.
Julie I. Jay Shetha Shukair Kristofer Langheinrich Melissa C. Hanson Gianguido C. Cianci Todd J. Johnson Meredith R. Clark Thomas J. Hope Patrick F. Kiser 《Advanced functional materials》2009,19(18):2969-2977
Materials that respond to physiological stimuli are important in developing advanced biomaterials for modern therapies. The reversibility of covalent crosslinks formed by phenylboronate (PBA) and salicylhydroxamate (SHA) has been exploited to provide a pH‐responsive gel for application to the vaginal tract. Dynamic rheology reveals that the gel frequency‐dependent viscoelastic properties are modulated by pH. At pH 4.8 the viscous component dominates throughout most of the frequency range. As the pH increases, the characteristic relaxation time continues to increase while the G′Plateau levels off above pH 6. At pH 7.5, the elastic component dominates throughout the frequency sweep and is predominately independent of frequency. Particle tracking assesses the transport of both fluorescently labeled HIV‐1 and 100‐nm latex particles in the PBA–SHA crosslinked gel as a function of pH. At pH 4.8 the ensemble‐averaged mean squared displacement at lag times greater than three seconds reveals that transport of the HIV‐1 and 100‐nm particles becomes significantly impeded by the matrix, exhibiting diffusion coefficients less than 0.0002 µm2 s?1. This pH‐responsive gel thus displays properties that have the potential to significantly reduce the transport of HIV‐1 to susceptible tissues and thus prevent the first stage of male‐to‐female transmission of HIV‐1. 相似文献
65.
O.P. Malik G.S. Hope M.A.H. Sheirah 《International Journal of Electrical Power & Energy Systems》1983,5(3):159-165
The processing capability of computers makes it feasible to implement sophisticated techniques for process control. However, to minimize the software development costs, it is desirable to develop algorithms that can have a wider application. In keeping with this, an AVR and speed governor for a generating unit have been designed using the same algorithm, called the selftuning regulator. The selftuning AVR and speed governor have been implemented using a microprocessor and a minicomputer online. The feasibility of developing unified algorithms is demonstrated by means of realtime tests, in which the two controllers are used simultaneously for a generating unit physical model. 相似文献
66.
O.P. Malik G.S. Hope Ju M. Gorski V.A. Ushakov 《International Journal of Electrical Power & Energy Systems》1983,5(1):61-71
Results of experimental tests carried out with microprocessor-based voltage and speed regulators using a digital-analogue-physical model complex of a large power system at the Siberian Power Institute of the USSR Academy of Sciences are described. The physical test facility, and the test objectives and procedures are also outlined. Tests were carried out on a Soviet-built microprocessor AVR and a Canadian-built microprocessor AVR and speed governor. The work described shows that the development of speed and voltage regulators using microprocessors is a feasible and promising proposition. 相似文献
67.
Although research has found an association between social anxiety and alcohol use in noncollege samples, results have been mixed for college samples. College students face many novel social situations in which they may drink to reduce social anxiety. In the current study, the authors tested a model of college problem drinking, incorporating social anxiety and related psychosocial variables among 228 undergraduate volunteers. According to structural equation modeling (SEM) results, social anxiety was unrelated to alcohol use and was negatively related to drinking consequences. Perceived drinking norms mediated the social anxiety-alcohol use relation and was the variable most strongly associated with problem drinking. College students appear to be unique with respect to drinking and social anxiety. Although the notion of social anxiety alone as a risk factor for problem drinking was unsupported, additional research is necessary to determine whether there is a subset of socially anxious students who have high drinking norms and are in need of intervention. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
68.
The effect of converting from pravastatin to simvastatin on the pharmacodynamics of warfarin 总被引:1,自引:0,他引:1
Glycosylated amino acids and glycosylated human serum albumin reduce nitrite to nitric oxide under anaerobic conditions. The amount of nitric oxide produced was recorded by generation of nitrosoHb from deoxyHb. Without preincubation after the addition of sodium nitrite, glucose or a mixture of glucose with amino acid or serum albumin did not cause spectrophotometrically detectible transformation of deoxyHb into nitrosoHb. The generation of NO increased with an increase in content of colored "final" products of amino acid and serum albumin glycosylation in the incubation mixture. The incubation of blood plasma of patients with diabetes mellitus with nitrite also resulted in the increased production of NO as compared to blood plasma of healthy subjects. During the incubation of healthy subjects' blood plasma with nitrite a small amount of NO was produced. The removal of low-molecular-weight compounds was accompanied by a significantly decreased generation of NO by blood plasma. 相似文献
69.
DA Toke WL Bennett DA Dillon WI Wu X Chen DB Ostrander J Oshiro A Cremesti DR Voelker AS Fischl GM Carman 《Canadian Metallurgical Quarterly》1998,273(6):3278-3284
Diacylglycerol pyrophosphate (DGPP) is involved in a putative novel lipid signaling pathway. DGPP phosphatase (DGPP phosphohydrolase) is a membrane-associated 34-kDa enzyme from Saccharomyces cerevisiae which catalyzes the dephosphorylation of DGPP to yield phosphatidate (PA) and then catalyzes the dephosphorylation of PA to yield diacylglycerol. Amino acid sequence information derived from DGPP phosphatase was used to identify and isolate the DPP1 (diacylglycerol pyrophosphate phosphatase) gene encoding the enzyme. Multicopy plasmids containing the DPP1 gene directed a 10-fold overexpression of DGPP phosphatase activity in S. cerevisiae. The heterologous expression of the S. cerevisiae DPP1 gene in Sf-9 insect cells resulted in a 500-fold overexpression of DGPP phosphatase activity over that expressed in wild-type S. cerevisiae. DGPP phosphatase possesses a Mg2+-independent PA phosphatase activity, and its expression correlated with the overexpression of DGPP phosphatase activity in S. cerevisiae and in insect cells. DGPP phosphatase was predicted to be an integral membrane protein with six transmembrane-spanning domains. The enzyme contains a novel phosphatase sequence motif found in a superfamily of phosphatases. A dpp1Delta mutant was constructed by deletion of the chromosomal copy of the DPP1 gene. The dpp1Delta mutant was viable and did not exhibit any obvious growth defects. The mutant was devoid of DGPP phosphatase activity and accumulated (4-fold) DGPP. Analysis of the mutant showed that the DPP1 gene was not responsible for all of the Mg2+-independent PA phosphatase activity in S. cerevisiae. 相似文献
70.
FI Meredith RT Riley CW Bacon DE Williams DB Carlson 《Canadian Metallurgical Quarterly》1998,61(8):1034-1038
The purpose of this study was (i) to determine whether pure fumonisin B1 could be incorporated into, recovered, and detected by high-pressure liquid chromatographic analysis from the semipurified Oregon test diet (OTD) used in rainbow trout feeding studies, and (ii) to determine if the incorporated fumonisin B1 was biologically available using the change in free sphingoid bases in liver, kidney, and serum as a mechanism-based biomarker. The results indicate that fumonisin is not easily quantified in the OTD. Recoveries ranged from 12 to 81% of the calculated concentrations based on the fumonisin B1 added to the OTD. However, the fumonisin B1 in the OTD was readily absorbed and biologically active as evidenced by marked increases in free sphinganine in liver, kidney, and serum. The magnitude of the increase in free sphinganine at 100 ppm in the OTD was comparable to that known to be associated with liver toxicity in rats, pigs, and ponies. 相似文献