全文获取类型
收费全文 | 1579篇 |
免费 | 47篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 25篇 |
综合类 | 1篇 |
化学工业 | 190篇 |
金属工艺 | 31篇 |
机械仪表 | 42篇 |
建筑科学 | 59篇 |
矿业工程 | 8篇 |
能源动力 | 50篇 |
轻工业 | 170篇 |
水利工程 | 13篇 |
石油天然气 | 1篇 |
无线电 | 117篇 |
一般工业技术 | 183篇 |
冶金工业 | 557篇 |
原子能技术 | 12篇 |
自动化技术 | 169篇 |
出版年
2023年 | 12篇 |
2022年 | 17篇 |
2021年 | 34篇 |
2020年 | 22篇 |
2019年 | 20篇 |
2018年 | 22篇 |
2017年 | 19篇 |
2016年 | 36篇 |
2015年 | 19篇 |
2014年 | 39篇 |
2013年 | 79篇 |
2012年 | 56篇 |
2011年 | 63篇 |
2010年 | 33篇 |
2009年 | 53篇 |
2008年 | 72篇 |
2007年 | 64篇 |
2006年 | 54篇 |
2005年 | 41篇 |
2004年 | 31篇 |
2003年 | 34篇 |
2002年 | 39篇 |
2001年 | 36篇 |
2000年 | 32篇 |
1999年 | 29篇 |
1998年 | 114篇 |
1997年 | 76篇 |
1996年 | 57篇 |
1995年 | 39篇 |
1994年 | 28篇 |
1993年 | 36篇 |
1992年 | 15篇 |
1991年 | 14篇 |
1990年 | 19篇 |
1989年 | 21篇 |
1988年 | 23篇 |
1987年 | 19篇 |
1986年 | 13篇 |
1985年 | 19篇 |
1984年 | 20篇 |
1983年 | 16篇 |
1982年 | 11篇 |
1981年 | 7篇 |
1980年 | 11篇 |
1979年 | 9篇 |
1978年 | 13篇 |
1977年 | 18篇 |
1976年 | 19篇 |
1974年 | 12篇 |
1972年 | 6篇 |
排序方式: 共有1628条查询结果,搜索用时 15 毫秒
71.
72.
The rabbit platelet metabolizes platelet-activating factor (PAF) intracellulary. PAF is deacetylated to produce lysoPAF which,
in turn, can be acylated to produce 1-O-alkyl-2-acyl-sn-glycero-3-phosphocholine (alkylacyl GPC). Some PAF receptor antagonists have been shown to inhibit this metabolic conversion.
In the present study we examined whether the PAF receptor antagonists SRI 63-441 and WEB 2086 would inhibit the metabolism
of PAF by intact rabbit platelets. In addition, we examined whether iloprost, a stable analogue of prostaglandin I2 (PGI2), and a potent inhibitor of platelet activation induced by a range of agonists, would also inhibit PAF metabolism. We found
that SRI 63-441 and WEB 2086 caused an almost complete inhibition of the conversion of PAF to alkylacyl GPC. Iloprost caused
up to a 50% inhibition of PAF metabolism compared to antagonist-free controls. Iloprost (and PGI2) is thought to inhibit platelet response by elevation of cAMP, while receptor antagonists act by blocking PAF binding to
its receptor. Since iloprost caused partial inhibition of PAF metabolism, the results of this study suggest that inhibition
of PAF metabolism does not occur solely due to competitive inhibition of PAF binding to its receptor.
Based on a paper presented at the Third International Conference on Platelet Activating Factor and Structurally Related Alkyl
Ether Lipids, Tokyo, Japan, May 1989. 相似文献
73.
Darrell Sparks Rafael Hernandez Mark Zappi Dean Blackwell Trey Fleming 《Journal of the American Oil Chemists' Society》2006,83(10):885-891
Extraction of rice bran lipids was performed using supercritical carbon dioxide (SC−CO2) and liquid propane. To provide a basis for extraction efficiency, accelerated solvent extraction with hexane was performed
at 100°C and 10.34 MPa. Extraction pressure was varied for propane and SC−CO2 extractions. Also, the role of temperature in SC−CO2 extraction efficiency was investigated at 45,65, and 85°C. For the SC−CO2 experiments, extraction efficiencies were proportional to pressure and inversely proportional to temperature, and the maximal
yield of oil achieved using SC−CO2 was 0.222±0.013 kg of oil extracted per kg of rice bran for conditions of 45°C and 35 MPa. The maximal yield achieved with
propane was 0.224±0.016 kg of oil per kg of rice bran at 0.76 MPa and ambient temperature. The maximum extraction efficiencies
of both SC−CO2 and propane were found to be significantly different from the hexane extraction baseline yield, which was 0.261±0.005 kg
oil extracted per kg of rice bran. A simulated economic analysis was performed on the possibility of using SC−CO2 and propane extraction technologies to remove oil from rice bran generated in Mississippi. Although the economic analysis
was based on the maximal extraction efficiency for each technology, neither process resulted in a positive rate of return
on investment. 相似文献
74.
Éstimates of grain hardness from measurements of milling energy were made on four hundred and eighty barley cultivars. The same cultivars were also subjected to an infra-red analysis used to predict soluble β-glucan and nitrogen contents. The results demonstrated variation for these endosperm characters, with eighteen cultivars having a lower milling energy, and more than a hundred cultivars with a lower soluble β-glucan content than Gerkra, a barley with good malting quality. Of these, nine cultivars were lower for both characteristics. Information about this variation is, therefore, potentially useful when breeding for malting quality. 相似文献
75.
Ruppel Susan E.; Fleming Carmen N.; Hubbard Timothy L. 《Canadian Metallurgical Quarterly》2009,63(1):49
The influence of feedback on representational momentum for the final location of a moving target was examined in 3 experiments. The presence of binary feedback (correct, error) during practise trials or during larger blocks of experimental trials did not reduce representational momentum, nor did the presence of more informative feedback specifying the direction of error (error—in front of, error—behind) during larger blocks of experimental trials reduce representational momentum. Effects on representational momentum of whether feedback was consistently provided were inconsistent. Even though feedback did not reduce representational momentum per se, feedback did influence the probability of a same response for different probe positions. Implications of the data for R. A. Finke and J. J. Freyd's (1985; J. J. Freyd, 1987) claim that representational momentum is impervious to error feedback, and possible roles of perceptual learning in representational momentum, are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
76.
The objective of this study was to standardize the infrared spectra obtained over time and across 2 milk laboratories of Canada to create a uniform historical database and allow (1) the retroactive application of calibration models for prediction of fine milk composition; and (2) the direct use of spectral information for the development of indicators of animal health and efficiency. Spectral variation across laboratories and over time was inspected by principal components analysis (PCA). Shifts in the PCA scores were detected over time, leading to the definition of different subsets of spectra having homogeneous infrared signal. To evaluate the possibility of using common equations on spectra collected by the 2 instruments and over time, we developed a standardization (STD) method. For each subset of data having homogeneous infrared signal, a total of 99 spectra corresponding to the percentiles of the distribution of the absorbance at each wavenumber were created and used to build the STD matrices. Equations predicting contents of saturated fatty acids, short-chain fatty acids, and C18:0 were created and applied on different subsets of spectra, before and after STD. After STD, bias and root mean squared error of prediction decreased by 66% and 32%, respectively. When calibration equations were applied to the historical nonstandardized database of spectra, shifts in the predictions could be observed over time for all investigated traits. Shifts in the distribution of the predictions over time corresponded to the shifts identified by the inspection of the PCA scores. After STD, shifts in the predicted fatty acid contents were greatly reduced. Standardization reduced spectral variability between instruments and over time, allowing the merging of milk spectra data from different instruments into a common database, the retroactive use of calibrations equations, or the direct use of the spectral data without restrictions. 相似文献
77.
Jie Song Shou-Mei Xiong Mei Li John Allison 《Materials Science and Engineering: A》2009,520(1-2):197-201
In situ observation of HPDC AM50 alloy in the SEM chamber was performed to study the changes of the micro-voids and the β phase during tensile deformation. The results suggested that micro-voids had little change in the elastic region, opened linearly with increasing load in the plastic region and led to final fracture. The detachment of β phase from the interface was also observed in the plastic region and there was no evidence to suggest that the detachment led to the final fracture. 相似文献
78.
Jon R Saunders Heather Allison Chloe E James Alan J McCarthy Richard Sharp 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2001,76(7):662-666
Bacteriophages as accessory genetic elements play a crucial role in the dissemination of genes and the promotion of genetic diversity within bacterial populations. Such horizontal transfer of DNA is critical in the emergence of new pathogenic organisms, through the dissemination of genes encoding virulence factors such as toxins, adhesins and agressins. Phages can transfer genes that are not necessary for bacteriophage persistence and are generally recognised by their ability to convert their host bacteria to new phenotypes. This phenomenon is known as phage conversion. If such converting genes encode for virulence factors, the consequences of phage infection may include increased virulence of the host bacteria, and the conversion of a non‐pathogenic strain to a potentially dangerous pathogen. A number of virulence factors in bacteria causing diseases in plants, animals and humans are encoded by converting phages, the vast majority of which are temperate as opposed to lytic in nature. © 2001 Society of Chemical Industry 相似文献
79.
Stephen Fleming 《Architectural Theory Review》2013,18(1):88-103
This paper is part of a larger series, attempting to align Louis Kahn's ‘form and design’ theory with Platonism.1 One obstacle to this alignment is the commonly held view that Kalm drew on historic precedents when conceiving his fundamental planning strategies, or die ‘form’ of his buildings, since Plato would have architects copy the Forms, or Ideas, directly. The opinions of the ‘source-hunters’ are reviewed, but found to contradict much of what Kahn said, as well as die opinions ofodier scholars and associates of Kahn's. The weight of the latter views casts doubt on those of die ‘source-hunters’, leaving open the possibility that Kahn drew on Forms directly, as Plato would have ‘craftsmen’ do. 相似文献
80.
King Kevin M.; Fleming Charles B.; Monahan Kathryn C.; Catalano Richard F. 《Canadian Metallurgical Quarterly》2011,25(1):69
Although deficits in impulse control have been linked to adolescent use of alcohol and illicit drugs, less attention has been given to variability in change in impulse control across adolescence and whether this variability may be a signal of risk for early substance use. The goals of the current study were to examine growth in two aspects of impulse control, self-control problems and attention problems, across middle adolescence, and to test the prospective effects of level and change in these variables on levels and change over time in substance use. Data are from a community sample of 955 adolescents interviewed (along with their parents and teachers) annually from 6th to 11th grade. Results indicated that greater self-control problems and attentional problems in the 6th grade and increases in these problems over time were associated with higher levels of substance use at 11th grade. Our results suggest that modeling change over time enhances the understanding of how impulse control influences the development of substance use. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献