全文获取类型
收费全文 | 1516篇 |
免费 | 37篇 |
专业分类
电工技术 | 5篇 |
综合类 | 1篇 |
化学工业 | 228篇 |
金属工艺 | 33篇 |
机械仪表 | 20篇 |
建筑科学 | 67篇 |
矿业工程 | 4篇 |
能源动力 | 26篇 |
轻工业 | 168篇 |
水利工程 | 7篇 |
石油天然气 | 8篇 |
无线电 | 73篇 |
一般工业技术 | 205篇 |
冶金工业 | 499篇 |
原子能技术 | 7篇 |
自动化技术 | 202篇 |
出版年
2022年 | 13篇 |
2021年 | 21篇 |
2020年 | 15篇 |
2019年 | 11篇 |
2018年 | 15篇 |
2017年 | 15篇 |
2016年 | 20篇 |
2015年 | 17篇 |
2014年 | 25篇 |
2013年 | 64篇 |
2012年 | 40篇 |
2011年 | 77篇 |
2010年 | 47篇 |
2009年 | 57篇 |
2008年 | 53篇 |
2007年 | 64篇 |
2006年 | 53篇 |
2005年 | 40篇 |
2004年 | 44篇 |
2003年 | 61篇 |
2002年 | 49篇 |
2001年 | 27篇 |
2000年 | 19篇 |
1999年 | 25篇 |
1998年 | 46篇 |
1997年 | 41篇 |
1996年 | 32篇 |
1995年 | 32篇 |
1994年 | 24篇 |
1993年 | 36篇 |
1992年 | 21篇 |
1991年 | 11篇 |
1990年 | 25篇 |
1989年 | 25篇 |
1988年 | 25篇 |
1987年 | 13篇 |
1986年 | 19篇 |
1985年 | 19篇 |
1984年 | 32篇 |
1983年 | 23篇 |
1982年 | 22篇 |
1981年 | 29篇 |
1980年 | 25篇 |
1979年 | 20篇 |
1978年 | 18篇 |
1977年 | 13篇 |
1976年 | 17篇 |
1973年 | 13篇 |
1971年 | 9篇 |
1970年 | 10篇 |
排序方式: 共有1553条查询结果,搜索用时 31 毫秒
41.
In this paper are presented and discussed tabulations of the cumulative distribution functions of quasimidranges and mixtures of quasimidranges of samples from a normal distribution. The tabulations extend up to samples of size 21. For quasimidranges not involving the extreme values of the sample, the departure from normality is very small. The physical problem giving rise to the mixtures is discussed. 相似文献
42.
Michael Ferrara Michael Stephens Leslie Marchut Chris Yang Ventony Fryar Preston Scott 《Microelectronics Reliability》2012,52(1):9-15
With the increasing complexity of the power amplifier (PA) module architecture, the probability of a thermally induced stress related failure mechanism increases. To help evaluate the increase in module complexity, a more sophisticated in situ monitored thermal cycle reliability test is available. The module is monitored in real time using a resistance daisy chain methodology designed to provide coverage using resistance feedback throughout the entire hierarchy of the module and carrier board interface. Monitored temperature cycling allows for real time failure feedback and enhanced failure signature information. Further, the testing technique has proven to be a valuable method for capturing the early stages of a module mechanical failure at the temperature extremes. Moreover, statistical evaluation of the failure data (Weibull analysis) is improved and better accuracy of the failures in time (FIT) rate can be determined. 相似文献
43.
The objective of this study was to evaluate the utility of a digital Brix refractometer for the assessment of success of passive transfer of maternal immunoglobulin compared with the measurement of serum total protein (STP) by refractometry. Blood samples (n = 400) were collected from calves at 3 to 6d of age. Serum IgG concentration was determined by radial immunodiffusion (RID), and STP and percentage Brix (%Brix) were determined using a digital refractometer. The mean IgG concentration was 24.1 g/L [standard deviation (SD) ± 10.0] with a range from 2.1 to 59.1 g/L. The mean STP concentration was 6.0 g/dL (SD ± 0.8) with a range from 4.4 to 8.8 g/dL. The mean %Brix concentration was 9.2% (SD ± 0.9) with a range of 7.3 to 12.4%. Brix percentage was highly correlated with IgG (r = 0.93). Test characteristics were calculated to assess failure of passive transfer (FPT; serum IgG <10 g/L). The sensitivity and specificity of STP at 5.5 g/dL were 76.3 and 94.4%, respectively. A receiver operating characteristic curve was created to plot the true positive rate against the false positive rate for consecutive %Brix values. The optimal combination of sensitivity (88.9%) and specificity (88.9%) was at 8.4% Brix. Serum total protein was also positively correlated with %Brix (r = 1.00) and IgG (r = 0.93). Dairy producers can successfully monitor their colostrum management and the overall success of passive transfer using a digital Brix refractometer to estimate IgG concentration of colostrum and calf serum. 相似文献
44.
45.
46.
47.
Xu Chen Andre Sutrisno Lingyang Zhu Leslie J. Struble 《Journal of the American Ceramic Society》2017,100(5):2285-2295
The nanostructural evolution during formation of geopolymers and its correlation with setting have not been well understood. In this study, penetration resistance and ultrasonic wave reflection tests were conducted to measure setting, and solid‐state 27Al NMR and liquid‐state 29Si NMR were used to examine nanostructural changes in a metakaolin geopolymer as a function of time. Aluminum was released rapidly during the first 10 hour after mixing and immediately condensed with silicate species in solution to form larger sized aluminosilicate oligomers, which then condensed to form large structural units. Our evidence suggests these units form near metakaolin particle surface. Smaller sized silicate ions in the sol phase then attach to these units to form a gel with a more interconnected network structure. The initial stage of this attaching process was seen to be associated with set, which in this mixture occurred at 15 hour. 相似文献
48.
The aim of this study was to characterise the microbiological quality of selected common fresh vegetables and fruits commercially sold in Singapore in order to provide insight into any potential health hazards associated with consumption of these commodities. A total of 125 samples, collected from major supermarkets and local markets, were tested for aerobic mesophilic and psychrotrophic bacterial counts. One hundred samples were analysed for enumeration of yeasts and moulds, enumeration of coliforms and detection of Escherichia coli O157:H7 and Salmonella spp. Aerobic mesophilic counts ranged from 1.6 to 9.1 log cfu/g, with the lowest and the highest counts recorded for orange and bean sprouts, respectively. The highest level of coliforms was found in bean sprouts and fresh-cut salad, with 50% of samples containing more than 5 log cfu/g. Like coliform counts, the highest counts of yeasts and moulds were obtained in bean sprouts and fresh-cut salads. Fresh-cut salads also had the highest mean psychrotrophic plate count of 4.9 log cfu/g. Although no E. coli O157:H7 or Salmonella spp. was detected in the fruits and vegetables analysed in this study, high bacterial counts, especially in bean sprouts and fresh-cut salad, imply that effective control measures should be implemented to improve the microbiological quality of fresh produce sold in Singapore. 相似文献
49.
McCullough Michael E.; Friedman Howard S.; Enders Craig K.; Martin Leslie R. 《Canadian Metallurgical Quarterly》2009,97(5):866
Religious people tend to live slightly longer lives (M. E. McCullough, W. T. Hoyt, D. B. Larson, H. G. Koenig, & C. E. Thoresen, 2000). On the basis of the principle of social investment (J. Lodi-Smith & B. W. Roberts, 2007), the authors sought to clarify this phenomenon with a study of religion and longevity that (a) incorporated measures of psychological religious commitment; (b) considered religious change over the life course; and (c) examined 19 measures of personality traits, social ties, health behaviors, and mental and physical health that might help to explain the religion–longevity association. Discrete-time survival growth mixture models revealed that women (but not men) with the lowest degrees of religiousness through adulthood had shorter lives than did women who were more religious. Survival differences were largely attributable to cross-sectional and prospective between-class differences in personality traits, social ties, health behaviors, and mental and physical health. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
50.
Carmen Carney Clifford Leslie Eric Jones 《International Journal of Applied Ceramic Technology》2016,13(2):295-301
Ceramic matrix composites with SylramicTM and CG NicalonTM SiC fibers and SiC‐HfB2 matrices derived from a combination of polymer‐derived SiC ceramic and HfB2 particulate slurries were prepared. The composites were tested for oxidation resistance by laser heating at 2 MW/m2 to achieve temperatures near 1600°C. The oxidation resistance was compared between uncoated CG NicalonTM and BN‐coated SylramicTM fiber‐based composites. Oxidation resulted in precipitated nano‐sized HfO2 independent of the fibers and fiber coatings. 相似文献