全文获取类型
收费全文 | 1225篇 |
免费 | 6篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 15篇 |
综合类 | 13篇 |
化学工业 | 111篇 |
金属工艺 | 9篇 |
机械仪表 | 65篇 |
建筑科学 | 74篇 |
矿业工程 | 8篇 |
能源动力 | 4篇 |
轻工业 | 240篇 |
水利工程 | 12篇 |
石油天然气 | 50篇 |
武器工业 | 5篇 |
无线电 | 61篇 |
一般工业技术 | 464篇 |
冶金工业 | 8篇 |
原子能技术 | 9篇 |
自动化技术 | 86篇 |
出版年
2023年 | 6篇 |
2022年 | 5篇 |
2021年 | 5篇 |
2019年 | 4篇 |
2017年 | 3篇 |
2015年 | 2篇 |
2014年 | 8篇 |
2013年 | 8篇 |
2012年 | 115篇 |
2011年 | 136篇 |
2010年 | 33篇 |
2009年 | 17篇 |
2008年 | 113篇 |
2007年 | 90篇 |
2006年 | 105篇 |
2005年 | 67篇 |
2004年 | 64篇 |
2003年 | 68篇 |
2002年 | 74篇 |
2001年 | 31篇 |
2000年 | 39篇 |
1999年 | 28篇 |
1998年 | 26篇 |
1997年 | 16篇 |
1996年 | 16篇 |
1995年 | 11篇 |
1994年 | 20篇 |
1993年 | 7篇 |
1992年 | 19篇 |
1991年 | 13篇 |
1990年 | 16篇 |
1989年 | 11篇 |
1987年 | 3篇 |
1986年 | 8篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1983年 | 7篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1972年 | 5篇 |
1968年 | 1篇 |
1967年 | 3篇 |
1965年 | 1篇 |
1957年 | 1篇 |
1948年 | 1篇 |
1947年 | 4篇 |
排序方式: 共有1234条查询结果,搜索用时 15 毫秒
51.
We conducted an experiment to evaluate the effectiveness of spatial audio displays on target acquisition performance. Participants performed a visual search task with and without the aid of a spatial audio display. Potential target locations ranged between plus and minus 180 degrees in azimuth and from -70 degrees to +90 degrees in elevation. Independent variables included the number of visual distractors present (1, 5, 10, 25, 50) and the spatial audio condition (no spatial audio, free-field spatial audio, virtual spatial audio). Results indicated that both free-field and virtual audio cues engendered a significant decrease in search times. Potential applications of this research include the design of spatial audio displays for aircraft cockpits and ground combat vehicles. 相似文献
52.
We report a fully automated mid-IR difference-frequency spectrometer with a spectral resolution under 70 MHz pumped by a pair of conventional room-temperature 800-900-nm diode lasers. 0.1 muW of tunable cw radiation is produced from incident-diode powers of 120 and 75 mW. The system has computer-controlled beam alignment with compact CCD cameras, motorized mirrors and positioners to obtain 0.01 degrees crystal-angle positioning, 4-mum beam overlap at the nonlinear crystal, and automated diode laser beam collimation. Computer-operated frequency control uses temperature tuning and current tuning of the free-running diode lasers. The system has been demonstrated by successfully scanning, without any human intervention, 64 randomly selected acetylene absorption lines between 12 and 15 mum. Spectral scans of ammonia are also presented. This mid-IR spectrometer is suitable for fully automated spectroscopy of an unlimited list of mid-IR frequencies and has the potential to detect any trace gas that has an acceptable absorption line within the large tuning range. 相似文献
53.
54.
Typical audible pedestrian signals indicate when the pedestrian walk interval is in effect but provide little, or even misleading information for directional alignment. In three experiments, blind and blindfolded sighted adults crossed a simulated crossing with recorded traffic noise to approximate street sounds. This was done to investigate how characteristics of signal presentation affected usefulness of the auditory signal for guiding crossing behaviour. Crossing was more accurate when signals came only from the far end of the crossing rather than the typical practice of presenting signals simultaneously from both ends. Alternating the signal between ends of the crossing was not helpful. Also, the customary practice of signalling two parallel crossings at the same time drew participants somewhat toward the opposite crossing. Providing a locator tone at the end of the crossing during the pedestrian clearance interval improved crossing accuracy. These findings provide a basis for designing audible pedestrian signals to enhance directional guidance. The principal findings were the same for blind and sighted participants and applied across a range of specific signals (e.g. chirps, clicks, voices). 相似文献
55.
This study is an attempt to show how a "standard" foot can be parameterized using foot length, foot width, foot height, and a measure of foot curvature so that foot shape can be predicted using these simple anthropometric measures. The prediction model was generated using 40 Hong Kong Chinese men, and the model was validated using a different group of 25 Hong Kong Chinese men. The results show that each individual foot shape may be predicted to a mean accuracy of 2.1 mm for the left foot and 2.4 mm for the right foot. Application of this research includes the potential design and development of custom footwear without the necessity of expensive 3-D scanning of feet. 相似文献
56.
Hypoxia occurs over large areas in aquatic systems worldwide, and there is growing concern that hypoxia may affect aquatic animals, leading to population decline and changes in community by elimination of sensitive species. For the first time, we report that sublethal levels of hypoxia can significantly increase (+77.4%) malformation in fish embryonic development. Disruption of apoptotic pattern was clearly evident at 24 h post-fertilization, which may be a major cause of malformation. Furthermore, embryonic development was delayed, and balance of sex hormones (testosterone and estradiol) was disturbed during embryonic stages, implicating that subsequent sexual development may also be affected. Overall, our results imply that hypoxia may have a teratogenic effect on fish and delay fish embryonic development, which may subsequently impair species fitness leading to natural population decline. 相似文献
57.
Sjödin A McGahee EE Focant JF Jones RS Lapeza CR Zhang Y Patterson DG 《Analytical chemistry》2004,76(15):4508-4514
A semiautomated extraction and cleanup method has been developed to measure eight polybrominated diphenyl ethers (PBDEs), 2,2',4,4',5,5'-hexabromobiphenyl (BB-153), and 2,2',4,4',5,5'-hexachlorobiphenyl (CB-153). The method employs solid-phase dispersion on diatomaceous earth in a solid-phase extraction cartridge followed by automated addition of internal standards ((13)C-labeled). Extraction is then performed using an automated modular solid-phase extraction system. The extraction procedure includes drying the sample on diatomaceous earth by pressurized nitrogen and eluting target analytes and lipids with dichloromethane. Lipid content is determined gravimetrically. Lipid determinations performed using this method are compared with other standard methods and with a certified reference material. A relative standard deviation of 7.9% was obtained for 130 determinations of the lipid content in a breast milk quality control sample. Final analytical determination of target analytes was performed by gas chromatography-isotope dilution high-resolution mass spectrometry. Relative standard deviations for the measurements of target analytes for which a labeled internal standard was available were below 10% for analytes at concentrations above 1 ng/g of lipid. Mean recoveries of the (13)C-labeled internal standards ranged from 60 to 89% for the eight PBDE congeners; 74 and 113% were recovered for BB-153 and CB-153, respectively. 相似文献
58.
The ability of nitric oxide to relax smooth muscle cells surrounding resistance vessels in vivo is well documented. Here, we describe a series of studies designed to quantify amounts of adenosine triphosphate (ATP), a known stimulus of NO production in endothelial cells, released from erythrocytes that are mechanically deformed as these cells traverse microbore channels in lithographically patterned microchips. Results indicate that micromolar amounts of ATP are released from erythrocytes flowing through channels having cross sectional dimensions of 60 x 38 micron (2.22 +/- 0.50 microM ATP). Microscopic images indicate that erythrocytes, when being pumped through the microchip channels, migrate toward the center of the channels, leaving a cell-free or skimming layer at the walls of the channel, a profile known to exist in circulatory vessels in vivo. A comparison of the amounts of ATP released from RBCs mechanically deformed in microbore tubing (2.54 +/- 0.15 microM) vs a microchip (2.59 +/- 0.32 microM) suggests that channels in microchips may serve as functional biomimics of the microvasculature. Control studies involving diamide, a membrane-stiffening agent, suggest that the RBC-derived ATP is not due to cell lysis but rather physical deformation. 相似文献
59.
It is important to assess the chronic effects of chemical, physical, and biological stressors on organisms in the environment. Appropriate methods must enable rapid, inexpensive, and multibiomarker analyses of organism health. Here we investigate withering syndrome in red abalone (Haliotis rufescens), an important wild and farmed shellfish species along the Pacific coast, using a metabolomic approach that combines the metabolic profiling capabilities of nuclear magnetic resonance spectroscopy (NMR) with pattern recognition methods. Foot muscle, digestive gland, and hemolymph samples were collected from healthy, stunted, and diseased abalone, and the extracts were analyzed by NMR. Following spectral preprocessing, principal components analyses of the metabolite profiles were conducted. Our results confirm that NMR-based metabolomics can successfully distinguish the biochemical profiles of the three groups of animals, in every type of tissue or biofluid studied. Furthermore, this discovery-based approach successfully identified novel metabolic biomarker profiles associated with withering syndrome. The application of these methods for investigating other environmental stressors is discussed, as are the advantages of NMR-based metabolomics for biomonitoring, particularly in conjunction with gene and protein expression profiling. 相似文献
60.
Coleman SJ Coronado PR Maxwell RS Reynolds JG 《Environmental science & technology》2003,37(10):2286-2290
Aqueous solutions of 100 parts per billion (ppb) uranium at pH 7 were treated with granulated activated carbon (GAC) that had been modified with various formulations of hydrophobic aerogels. The composite materials were found to be superior in removing uranium from a stock solution compared to GAC alone evaluated by a modified ASTM D 3860-98 method for batch testing. The testing results were evaluated using a Freundlich adsorption model. The best performing material has parameters of n = 287 and Kf = 1169 compared to n = 1.00, and Kf = 20 for GAC alone. The composite materials were formed by mixing (CH3O)4Si with the hydrophobic sol-gel precursor, (CH3O)3SiCH2CH2CF3 and with specified modifiers, such as H3PO4, Ca(NO3)2, and (C2H5O)3SiCH2CH2P(O)(OC2H5)2, elation catalysts, and GAC in a supercritical reactor system. After gelation, supercritical extraction, and sieving, the composites were tested. Characterization by FTIR and 31P NMR indicate the formation of phosphate in the case of the H3PO4 and Ca(NO3)2 composites and phosphonic acid related compounds in the phosphonate composite. These composite materials have potential application in the clean up of groundwater at DOE and other facilities. 相似文献