全文获取类型
收费全文 | 438篇 |
免费 | 16篇 |
专业分类
电工技术 | 5篇 |
综合类 | 31篇 |
化学工业 | 106篇 |
金属工艺 | 18篇 |
机械仪表 | 7篇 |
建筑科学 | 21篇 |
能源动力 | 12篇 |
轻工业 | 57篇 |
水利工程 | 4篇 |
无线电 | 16篇 |
一般工业技术 | 51篇 |
冶金工业 | 66篇 |
原子能技术 | 1篇 |
自动化技术 | 59篇 |
出版年
2023年 | 2篇 |
2022年 | 7篇 |
2021年 | 10篇 |
2020年 | 7篇 |
2019年 | 12篇 |
2018年 | 8篇 |
2017年 | 11篇 |
2016年 | 12篇 |
2015年 | 5篇 |
2014年 | 13篇 |
2013年 | 15篇 |
2012年 | 17篇 |
2011年 | 28篇 |
2010年 | 19篇 |
2009年 | 10篇 |
2008年 | 27篇 |
2007年 | 16篇 |
2006年 | 19篇 |
2005年 | 12篇 |
2004年 | 11篇 |
2003年 | 9篇 |
2002年 | 12篇 |
2001年 | 10篇 |
2000年 | 5篇 |
1999年 | 5篇 |
1998年 | 25篇 |
1997年 | 11篇 |
1996年 | 8篇 |
1995年 | 4篇 |
1994年 | 8篇 |
1993年 | 4篇 |
1992年 | 4篇 |
1991年 | 4篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1987年 | 11篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1984年 | 5篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 7篇 |
1976年 | 4篇 |
1975年 | 7篇 |
1974年 | 6篇 |
1970年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有454条查询结果,搜索用时 15 毫秒
81.
Pascal Leterme Maria‐Fernanda García Angela‐Maria Londoo Miriam‐Gisela Rojas Andr Buldgen Wolfgang‐Bernhard Souffrant 《Journal of the science of food and agriculture》2005,85(9):1505-1512
The peach palm (Bactris gasipaes Kunth) is the starchy fruit of a palm tree widely cultivated in Central and South America. The present study aimed at determining its chemical composition and its nutritive value in rats. The average chemical composition of 17 samples was as follows: 410 g kg?1 water and, in g kg?1 of dry matter (DM), 54 g crude protein, 114 g oil, 39 g neutral detergent fibre, 716 g starch, 21 g sugars and 18 g ash. The main variability was observed for the oil (60–180 g kg?1 DM) and starch (590–780 g DM) contents. The proteins contained, on average, in g kg?1 of proteins, 49 g lysine, 13 g methionine, 19 g cysteine, 39 g threonine and 7 g tryptophan. The mineral fraction contained, per kg DM: 1.0 g Ca, 0.8 g P, 0.6 g Mg, 0.3 g Na, 44 mg Fe, 4 mg Cu and 10 mg Zn. The digestibility of four peach palm genotypes was determined in rats fed a diet composed of 350 g kg?1 of peach palm and 650 g of a control diet based on maize and soybean meal. The digestibility of DM, energy, starch and protein of peach palm alone reached, on average 91, 87, 96 and 95%, respectively. No difference was observed between varieties, except for starch (p < 0.05). On average, peach palm contained 51 g of truly digestible protein kg?1 DM and 3.691 kcal digestible energy kg?1 DM. A growth trial was also carried out for 1 month on rats (initial weight: 78 g) fed a diet containing 0, 200, 400, 600 or 800 g peach palm kg?1, at the expense of a diet composed of maize starch and casein. The growth rate of the rats decreased (p < 0.05) as the peach palm concentration increased. The growth decrease was due to a decrease (p < 0.05) in DM intake and to the lower quality of the peach palm protein. It is concluded that peach palm is mainly an energy source for humans and animals. It is poor in protein and minerals but can be consumed in large amounts. Copyright © 2005 Society of Chemical Industry 相似文献
82.
This article presents results from a numerical study of pulsating jet impingement heat transfer. The motivation is to seek conditions offering a significant enhancement compared to steady flow impingement drying. The CFD software package FLUENT was used for simulating slot-type pulsating jet impingement flows with confinement. The parameter study included velocity amplitude ratio, mean jet velocity, and pulsation frequency. The distance from nozzle exit to surface was three times the hydraulic diameter of the nozzle. The Reynolds number based on the nozzle hydraulic diameter and jet temperature was 2,460 with a mean jet velocity of 30 m/s, which is the base case of the numerical experiments. Results showed that time-averaged surface heat transfer increased with increasing velocity amplitude for the same mean jet velocity. Large velocity amplitudes helped enhance heat transfer by two mechanisms: high jet velocity during the positive cycle and strong recirculating flows during the negative cycle. For the cases with different mean jet velocities but the same maximum velocity, time-averaged surface heat flux decreased with decreasing mean jet velocity. As for the effects of pulsation frequency, with high-velocity amplitude ratio, time-averaged surface heat fluxes were at the same level regardless of frequency. However, at low-velocity amplitude ratio, high frequency caused stronger recirculating flows resulting in greater heat transfer compared to the cases with a lower frequency. 相似文献
83.
High intensity drying occurs when one web surface is heated to the thermodynamic saturation temperature corresponding to the local hydraulic pressure. Rapid vapor generation causes the process to be driven by a total pressure gradient, so vapor leaves the web by a bulk flow mechanism rather than a slower diffusion mechanism. Vapor pressure build-up promotes rapid web heating and offers the opportunity for liquid removal by displacement. Lower energy usage can result if only a part of the moisture is evaporated. 相似文献
84.
John D. O'Keefe Sarah T. Stewart Michael E. Lainhart Thomas J. Ahrens 《International Journal of Impact Engineering》2001,26(1-10):543-553
We explored simple geologic strength and material response models to determine which have the capability to simulate impact-induced faulting, complicated ejecta patterns and complex crater shapes. This led us to develop models for material damage, dilatancy, and inhomogeneous materials (mixtures). We found that a strength degradation (damage) model was necessary to produce faulting in homogeneous materials. Both normal and thrust ring faults may occur and extend relatively deeply into the planet during the transient cavity radial expansion. The maximum depth of fault development is about the depth of maximum penetration by the projectile. Dilatancy in geologic materials may reduce the final bulk density compared to the pristine state because of irreversible fracturing. When we include the effects of dilatancy, the radial position of faulting is displaced because of greater upward motions. In addition, the late time crater profile is shallower and the expression of features such as central peaks and rings may be more pronounced. Both damage and rock-ice mixtures effect the distribution of ejecta. The excavation flow field within the heavily damaged region is similar to flow fields in Mohr-Coulomb materials with no zero-pressure strength. In the outer, less damaged zone within the excavation cavity, the material trajectories collapse back into the crater. This effect creates a zone of reduced ejecta emplacement near the edge of the final crater. In the case of rock-ice mixtures, energy is preferentially deposited in the more compressible volatile component and the ejecta pattern is dependent upon the location of shock-induced phase changes in the volatile material. 相似文献
85.
Anne Lanfer Karin Bammann Kolja Knof Kirsten Buchecker Paola Russo Toomas Veidebaum Yiannis Kourides Stefaan de Henauw Dénes Molnar Silvia Bel-Serrat Lauren Lissner Wolfgang Ahrens 《Food quality and preference》2013,27(2):128-136
The present study investigated taste preferences in a sample of 1705 children aged 6 to 9 years from survey centres in Italy, Estonia, Cyprus, Belgium, Sweden, Germany, Hungary, and Spain and aimed to identify factors correlated with taste preference. Children’s preferences for varying levels of sucrose (sweet) in apple juice and fat, sodium chloride (salt) and monosodium glutamate (umami) in crackers were assessed using paired-comparison tests. Socio-demographics (age, sex, parental education), early feeding practises (breastfeeding, introduction of fruits), parenting behaviour (TV viewing, using food as a reward) and taste threshold sensitivity for sucrose (sweet), sodium chloride (salt), caffeine (bitter) and monosodium glutamate (umami) were investigated as possible correlates of taste preferences. Parents reported on socio-demographics, early feeding and parenting behaviour. Taste thresholds were determined via a paired-comparison staircase method. Country of residence was the strongest factor related to preferences for all four tastes. Taste preferences also differed by age. Preference for sugar and salt increased between 6 and 9 years of age while preference for monosodium glutamate decreased. The age differences remained significant even after adjustment for sex, country of residence, parental education and early feeding habits. Sex, parental education, early feeding habits, TV viewing, using food as a reward and taste thresholds were not consistently related to taste preferences among the survey centres. In summary, the results highlight the importance of culture and age in taste preferences in children younger than 10 years of age. 相似文献
86.
LA Ahrens SH Aronson PL Connolly BG Gibbard MJ Murtagh SJ Murtagh S Terada DH White JL Callas D Cutts JS Hoftun M Diwan RE Lanou T Shinkawa Y Kurihara K Amako S Kabe Y Nagashima Y Suzuki S Tatsumi Y Yamaguchi K Abe EW Beier DC Doughty LS Durkin SM Heagy M Hurley AK Mann FM Newcomer HH Williams T York D Hedin MD Marx E Stern 《Canadian Metallurgical Quarterly》1987,35(3):785-809
87.
M Paulussen S Ahrens AW Craft J Dunst B Fr?hlich S Jabar C Rübe W Winkelmann S Wissing A Zoubek H Jürgens 《Canadian Metallurgical Quarterly》1998,16(9):3044-3052
PURPOSE: To analyze event-free survival (EFS) and prognostic factors in patients who present with Ewing's tumors (ET) of bone and synchronous pulmonary and/or pleural metastases (ppm). PATIENTS AND METHODS: Of 1,270 patients (pts) registered at the continental office of the German/European Intergroup Cooperative Ewing's Sarcoma Studies (CESS81, CESS86, EICESS92), 114 were diagnosed ET with ppm. Patients underwent neoadjuvant therapy and local treatment of the primary tumor. Whole-lung irradiation 15 to 18 Gy was applied to 75 ppm-pts. EFS and 95% confidence intervals (CIs) were estimated according to the Kaplan-Meier method, and prognostic factors were analyzed by log-rank tests and Cox and logistic regression procedures. RESULTS: On November 1, 1997, at a median time under study of 5.9 years, the 5-year EFS was 0.36 (95% CI, 0.26 to 0.46) and the 10-year EFS was 0.30 (95% CI, 0.19 to 0.41). Thirty-seven of 59 (63%) first relapses involved lung and/or pleura, and the lungs were the only site of relapse in 26 of 59 (44%) ppm-pts. Risk factors identified in univariate and multivariate tests were poor response of the primary tumor toward chemotherapy, metastatic lesions in both lungs, and treatment without additional lung irradiation. CONCLUSION: Chemotherapy response of the primary tumor is a prognostic factor in patients with ET with ppm. Strategies of treatment intensification warrant further evaluation. 相似文献
88.
A graphical method is given for the analysis of repairable systems failing according to a Weilbull process. The integrated hazard rate is plotted in a logarithmic co-ordinate system. If the process is of Weibull type the observed data will be located around a straight line. The plot provides estimates of the parameters. The graphical procedure is completed by confidence bands and variation bands built either around the observed failure numbers at fixed time or vice versa. 相似文献
89.
In a case-control study of 1,004 lung cancer cases and 1,004 population controls, all nonsmokers (71 cases, 236 controls) were interviewed for their exposure to environmental tobacco smoke. On the basis of indices of duration, we separated intermediate and high exposures from low or no exposure. The odds ratio for high exposure was 2.09 (95% confidence interval = 1.02-4.28). Exposure from the spouse was only weakly associated with lung cancer risk. We found little association for exposure during childhood. High exposure at the work place showed an odds ratio of 1.91. There was little indication of confounding by dietary habits. 相似文献
90.
C Frahm M B?hre KH Ahrens S Eckerle K Sommer C Frahm E Richter 《Canadian Metallurgical Quarterly》1998,37(2):57-61
To assess the role of insulin in the development of obesity induced by antipsychotic drugs, a glucose tolerance test was conducted in 40 female rats during the peak of sulpiride-induced weight gain and in 40 vehicle-treated animals. The glucose area under the curve did not differ between the groups (P = 0.24), however, the area under the insulin curve was significantly decreased by sulpiride (55.2 +/- 2.8 versus 115.6 +/- 18.9, P = 0.007). The results suggest that insulin resistance and hyperinsulinaemia are not involved in the excessive weight gain observed in this animal model of drug-induced obesity. Alternatively, the insulin-dampened response observed in the sulpiride-treated rats may be related to increased insulin sensitivity, which may promote weight gain as proposed by Ravussin (1995). 相似文献