首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   455篇
  免费   9篇
电工技术   5篇
化学工业   43篇
金属工艺   1篇
机械仪表   3篇
建筑科学   16篇
矿业工程   2篇
能源动力   7篇
轻工业   54篇
水利工程   2篇
石油天然气   2篇
无线电   29篇
一般工业技术   54篇
冶金工业   177篇
原子能技术   3篇
自动化技术   66篇
  2023年   2篇
  2021年   5篇
  2020年   4篇
  2018年   6篇
  2017年   3篇
  2016年   8篇
  2015年   6篇
  2014年   9篇
  2013年   17篇
  2012年   15篇
  2011年   30篇
  2010年   21篇
  2009年   19篇
  2008年   21篇
  2007年   31篇
  2006年   11篇
  2005年   15篇
  2004年   14篇
  2003年   15篇
  2002年   14篇
  2001年   9篇
  2000年   7篇
  1999年   12篇
  1998年   37篇
  1997年   23篇
  1996年   10篇
  1995年   12篇
  1994年   13篇
  1993年   4篇
  1992年   3篇
  1991年   2篇
  1990年   3篇
  1989年   2篇
  1988年   3篇
  1987年   5篇
  1986年   4篇
  1985年   2篇
  1984年   4篇
  1983年   4篇
  1981年   5篇
  1980年   3篇
  1979年   3篇
  1978年   2篇
  1977年   4篇
  1976年   10篇
  1975年   5篇
  1973年   1篇
  1972年   1篇
  1970年   1篇
  1969年   2篇
排序方式: 共有464条查询结果,搜索用时 15 毫秒
1.
The objective of this study was to determine the effect of temperature on whole milk density measured at four different temperatures: 5, 10, 15, and 20 °C. A total of ninety-three individual milk samples were collected from morning milking of thirty-two Holstein Friesian dairy cows, of national average genetic merit, once every two weeks over a period of 4 weeks and were assessed by Fourier transform infrared spectroscopy for milk composition analysis. Density of the milk was evaluated using two different analytical methods: a portable density meter DMA35 and a standard desktop model DMA4500M (Anton Paar GmbH, UK). Milk density was analysed with a linear mixed model with the fixed effects of sampling period, temperature and analysis method; triple interaction of sampling period x analysis method x temperature; and the random effect of cow to account for repeated measures. The effect of temperature on milk density (ρ) was also evaluated including temperature (t) as covariate with linear and quadratic effects within each analytic method. The regression equation describing the curvature and density–temperature relationship for the DMA35 instrument was ρ = 1.0338−0.00017T−0.0000122T2 (R2 = 0.64), while it was ρ = 1.0334 + 0.000057T−0.00001T2 (R2 = 0.61) for DMA4500 instrument. The mean density determined with DMA4500 at 5 °C was 1.0334 g cm−3, with corresponding figures of 1.0330, 1.0320 and 1.0305 g cm−3 at 10, 15 and 20 °C, respectively. The milk density values obtained in this study at specific temperatures will help to address any bias in weight–volume calculations and thus may also improve the financial and operational control for the dairy processors in Ireland and internationally.  相似文献   
2.
Healthcare institutions typically post their privacy practices online as privacy policy documents. We conducted a longitudinal study that examines the effects of HIPAA's enactment on a collection of privacy policy documents for a fixed set of organizations over a four-year period. We present our analysis of 24 healthcare privacy policy documents from nine healthcare Web sites, analyzed using goal mining, a content-analysis method that supports extraction of useful information about institutions' privacy practices from documents. We compare our results to our pre-HIPAA study of these same institutions' online privacy practices and evaluate their evolution in the presence of privacy laws  相似文献   
3.
Contends, on the basis of posited social-role theory of gender and helping, that the male gender role fosters helping that is heroic and chivalrous, whereas the female gender role fosters helping that is nurturant and caring. In social psychological studies, helping behavior has mainly been examined in the context of short-term encounters with strangers. This focus has tended to exclude from the research literature those helping behaviors prescribed by the female gender role, because they are displayed primarily in long-term, close relationships. In contrast, the helping behaviors prescribed by the male gender role have been generously represented in research findings because they are displayed in relationships with strangers as well as in close relationships. Results from a meta-analytic review of sex differences in 172 studies (appended) in helping behavior indicate that in general men helped more than women and women received more help than men. Nevertheless, sex differences in helping were inconsistent across studies and were successfully predicted by various attributes of the studies and the helping behaviors. (96 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
4.
We report a 16-year-old boy, born to consanguineous parents, with mental retardation, gait disturbances and dysarthria; brain magnetic resonance showed features consistent with rhombencephalosynapsis. This condition is characterised by a hypoplastic single-lobed cerebellum. The interest of this case is the presence of common ancestors, pointing to an autosomal recessive inheritance of the malformation.  相似文献   
5.
The experiments reported are part of our effort to dissociate the tumor-enhancing effects of dietary fat and high caloric intake. Rats either were fed ad libitum diets containing 4% corn oil or their calories were restricted by 40% and their diets contained 13.1% corn oil. Incidence of 7,12-dimethylbenz(a)anthracene (DMBA)-induced mammary tumors was 80% in rats fed ad libitum and 20% in those fed the calorie-restricted diets. Incidence of 1,2-dimethylhydrazine (DMH)-induced colon tumors was 100% in rats fed ad libitum and 53% in those whose caloric intake was restricted by 40%. The tumor yield (tumors per tumor-bearing rat) was significantly lower in rats on caloric restriction. In another series, rats were fed diets containing 5, 15 or 20% corn oil ad libitum or were fed calorie-restricted (by 25%) diets which provided 20 or 26.6% corn oil (therefore, the same absolute amount of fat was consumed in each of the pair-fed groups). Tumor incidence and tumor yield in the two calorie-restricted groups were similar to those seen in the rats fed 5% fat ad lititum; tumor burden (total g of tumor) was 45–65% lower in the calorie-restricted rats. The data suggest that caloric intake is a more stringent determinant of tumor growth than fat intake.  相似文献   
6.
This paper addresses the problem of learning situation models for providing context-aware services. Context for modeling human behavior in a smart environment is represented by a situation model describing environment, users, and their activities. A framework for acquiring and evolving different layers of a situation model in a smart environment is proposed. Different learning methods are presented as part of this framework: role detection per entity, unsupervised extraction of situations from multimodal data, supervised learning of situation representations, and evolution of a predefined situation model with feedback. The situation model serves as frame and support for the different methods, permitting to stay in an intuitive declarative framework. The proposed methods have been integrated into a whole system for smart home environment. The implementation is detailed, and two evaluations are conducted in the smart home environment. The obtained results validate the proposed approach.  相似文献   
7.
Enantioselective catalytic epoxidation of olefins is an important problem from both practical and mechanistic points of view. The origins of chiral induction by asymmetric porphyrin and salen complexes were investigated by FT-NMR T1 relaxation techniques. A new chiral vaulted porphyrin (1) that carries (S)-binaphthyl-L-alanine straps across both faces of the porphyrin macrocycle was synthesized and characterized. (R)-styrene oxide was obtained in > 90% ee in the initial stages of styrene epoxidation with F5PhIO catalyzed by 1-Fe(III)Cl. The transition state for olefin epoxidation with high-valent metal-oxo species was modeled by coordinating epoxides to paramagnetic copper complexes of the corresponding ligands. The epoxide enantiomer that better fit the chiral cavity of the catalyst, as revealed by T1 relaxation measurements, was also the major product of catalytic olefin epoxidation. These results are consistent with the "lock-and-key" mechanism of asymmetric catalysis by metalloporphyrins. The copper complex of a chiral salen ligand showed no differentiation in terms of T1 relaxation rates between the enantiomers of cis-beta-methylstyrene oxide in contrast to the high enantioselectivity observed for catalytic epoxidation.  相似文献   
8.
OBJECTIVE: The study was done to determine whether thermal comfort (TC), thermal sensation (TS), and subjective factors gauging environmental stress were negatively affected with different cooling methods in men exercising in chemical protective clothing. BACKGROUND: Previous studies have reported that intermittent regional cooling improved the efficacy of cooling as compared with constant cooling (CC), but no studies have addressed whether there is any improvement in thermal comfort. METHODS: Eight male volunteers exercised at moderate work intensity (425 W) in three microclimate cooling tests. The circulating fluid in the cooling garment was provided during exercise to the head (6% body surface area [BSA]), torso (22% BSA), and thighs (44% BSA) and manipulated under three methods: (a) CC, (b) pulsed cooling (PC), and (c) PC activated by mean skin temperature (T(sk)) control (PC(skin)). TC and TS ratings were recorded every 20 min during the 80-min test. RESULTS: TC and TS ratings were not different for PC(skin) and CC; thus the participants perceived PC(skin) as being similar to CC. TS was significantly warmer with PC than with PC(skin) and CC (p < .001). In PC(skin), T(sk) was significantly higher than in PC and CC (p < .001), and PC(skin) was rated as being not as warm as PC according to TS. CONCLUSION: This indicates that the PC(skin) method was perceived as being as cool as CC and cooler than PC. APPLICATION: These findings indicate that the PC(skin) cooling method is an acceptable alternative to CC and PC based on human perceptions.  相似文献   
9.
This paper defines the difference of low-pass (DOLP) transform and describes a fast algorithm for its computation. The DOLP is a reversible transform which converts an image into a set of bandpass images. A DOLP transform is shown to require O(N2) multiplies and produce O(N log(N)) samples from an N sample image. When Gaussian low-pass filters are used, the result is a set of images which have been convolved with difference of Gaussian (DOG) filters from an exponential set of sizes. A fast computation technique based on ``resampling' is described and shown to reduce the DOLP transform complexity to O(N log(N)) multiplies and O(N) storage locations. A second technique, ``cascaded convolution with expansion,' is then defined and also shown to reduce the computational cost to O(N log(N)) multiplies. Combining these two techniques yields an algorithm for a DOLP transform that requires O(N) storage cells and requires O(N) multiplies.  相似文献   
10.
Short-term selective breeding created mouse lines divergent for ethanol drinking (high drinking short-term selected line [STDRHI], low drinking [STDRLO]) or ethanol-induced conditioned taste aversion (CTA; high [HTA], low [LTA]). Compared with STDRLO, STDRHI mice consumed more saccharin and less quinine, exhibited greater ethanol-induced conditioned place preference (CPP), and showed reduced ethanol stimulation and sensitization under some conditions; a line difference in ethanol-induced CTA was not consistently found. Compared with LTA, HTA mice consumed less ethanol but were similar in saccharin consumption, sensitivity to ethanol-induced CPP, and ethanol-induced locomotor stimulation and sensitization. These data suggest that ethanol drinking is genetically associated with several reward-and aversion-related traits. The interpretation of ethanol-induced CTA as more genetically distinct must be tempered by the inability to test the CTA lines beyond Selection Generation 2. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号