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   4239篇
  免费   248篇
  国内免费   3篇
电工技术   74篇
综合类   13篇
化学工业   979篇
金属工艺   112篇
机械仪表   103篇
建筑科学   181篇
矿业工程   7篇
能源动力   81篇
轻工业   340篇
水利工程   19篇
石油天然气   3篇
无线电   332篇
一般工业技术   888篇
冶金工业   682篇
原子能技术   15篇
自动化技术   661篇
  2023年   36篇
  2022年   34篇
  2021年   86篇
  2020年   77篇
  2019年   78篇
  2018年   114篇
  2017年   115篇
  2016年   130篇
  2015年   119篇
  2014年   155篇
  2013年   234篇
  2012年   207篇
  2011年   274篇
  2010年   171篇
  2009年   186篇
  2008年   202篇
  2007年   188篇
  2006年   156篇
  2005年   113篇
  2004年   102篇
  2003年   96篇
  2002年   62篇
  2001年   83篇
  2000年   61篇
  1999年   86篇
  1998年   204篇
  1997年   141篇
  1996年   111篇
  1995年   73篇
  1994年   53篇
  1993年   65篇
  1992年   32篇
  1991年   41篇
  1990年   30篇
  1989年   41篇
  1988年   32篇
  1987年   29篇
  1986年   32篇
  1985年   40篇
  1984年   28篇
  1983年   23篇
  1982年   23篇
  1981年   28篇
  1980年   22篇
  1979年   24篇
  1978年   27篇
  1977年   28篇
  1976年   50篇
  1974年   16篇
  1973年   15篇
排序方式: 共有4490条查询结果,搜索用时 46 毫秒
81.
This study focused on the exploration of the potentials of extracting antioxidants from peels and stems of yellow-fleshed and white cassava varieties. The effect of particle size (0.2 and 0.5 mm) and variety on the phenolic content and antioxidant activity was assessed. The peels of the yellow-fleshed cassava variety with a particle size of 0.2 mm showed the highest phenolic content with 681.5 GAE mg 100 g−1 and antioxidant activity of 19% and 425 μM TE g−1 dry matter using DPPH and FRAP assays respectively. The stems of the white cassava with a particle size of 0.2 mm exhibited high phenolic content (442.4 GAE mg 100 g−1) and antioxidant activity of 12.8% and 234 μM TE g−1, better than the stem of the yellow-fleshed cassava. These results indicate that phenolic and antioxidant extractions were influenced by variety, the plant parts and particle size for the antioxidant assays.  相似文献   
82.
83.
The apparent particle density of particulate matter with aerodynamic diameter < 2.5 microm (rho2.5) was determined at an urban site in Augsburg, Germany and its correlation with chemical composition and meteorological conditions was investigated. rho2.5 showed strong day-to-day variation from 1.05 to 2.36 g cm(-3) (5 to 95% percentile), and nearly 64% of the daily variability could be explained by a multiple variable regression model. A minimum in the morning and afternoon (about 1.5 g cm(-3)), and a maximum (near 1.8 g cm(-3)) during midday was observed. The minima represent fresh primary aerosol emissions, which were related to traffic soot particles with low density due to their agglomerate structure, especially observed in the early morning hours of weekdays. The maximum is likely due to increased secondary particle production and the presence of more aged particles with the built-up of the convectively mixed boundary layer. rho2.5 has the potential to serve as a crude tracer for chemical composition and atmospheric processing and might play an important role when considering the associations between health effects and ambient particles.  相似文献   
84.
PURPOSE: Polyvinyl alcohol (PVA) is a successful tear film stabiliser and is widely used in comfort drops and some soft contact lens materials. A PVA-containing lens, nelfilcon A has been modified to include additional (non-functional) PVA in order to provide improved comfort. This study aims to examine the clinical performance of this nelfilcon A lens with AquaRelease (AquaRelease). METHODS: Two contralateral, investigator masked, open label, subjective and objective evaluations were conducted. The first examined the effect of adding increased molecular weight PVA to nelfilcon A (n=5), and the second compared this AquaRelease lens to ocufilcon B (n=34). The principal measures were non-invasive break-up time (NIBUT) and subjective comfort, which were assessed at the beginning and end of a week of daily wear, and three times throughout 1 day at 8, 12 and 16 h. RESULTS: All subjects successfully completed the daily wearing schedule of 16h. On initial insertion, subjective comfort and NIBUT improved for AquaRelease than original nelfilcon A lenses (p<0.05). Initial comfort was better for AquaRelease compared to ocufilcon B lenses (p=0.01); however, NIBUT was not statistically different (11.7+/-15.6s versus 8.4+/-6.8s; p=0.26). Subjective comfort decreased with time (p<0.001), but there was no significant difference between AquaRelease and ocufilcon B lenses (p=0.16). NIBUT was not significantly affected by time (p=0.56) or between lenses (p=0.33). At the end of a weeks' wear, subjective initial, end-of-day, overall comfort and vision were rated significantly better with AquaRelease than ocufilcon B (p<0.01). CONCLUSIONS: Release of additional non-functionalised PVA from the nelfilcon A lenses appears to enhance comfortable contact lens wear.  相似文献   
85.
In this study, drying of red-fleshed dragon fruit at different temperatures (40, 50, 60, 70 and 80 °C) and air velocities (1.0 and 1.5 m s−1) was conducted under the specific humidity of 25 g H2O kg−1 dry air. The results showed that drying at higher temperatures resulted in shorter drying times. However, temperature and air velocity did not significantly affect the total betacyanin contents and antioxidant capacities in dried products. Seven betacyanins identified by LC-MS were betanin, isobetanin, phyllocactin, isophyllocactin, betanidin 5 –O-(6′O-3-hydroxybutyryl)-β-glucoside, isobetanidin 5 –O-(6′O-3-hydroxybutyryl)-β-glucoside and decarboxylated phyllocactin. In addition, the temperature increased the isomerisation of betacyanins. The most preferable condition for preserving the colour and betacyanin contents of red-fleshed dragon fruit was the drying at a temperature of 80 °C and air velocity of 1.5 m s−1 since it could shorten the drying time and give a bright red colour to the dried product as well as it had no significant impact on the betacyanins.  相似文献   
86.
87.
The protein encoded by the pancreatic colipase (CLPS) gene is an essential cofactor needed by pancreatic triglyceride lipase (PNLIP) for efficient dietary lipid hydrolysis. Since the inhibition of lipase activity was shown to reduce the incidence of type 2 diabetes mellitus, we tested the hypothesis that genetic variations in the CLPS and PNLIP genes are associated with type 2 diabetes; 47 unrelated subjects were screened for polymorphisms of the CLPS and PNLIP genes. A nested-case control study of 192 incident type 2 diabetes subjects and 384 sex- and age-matched controls taken from the European Prospective Investigation into Cancer and Nutrition Potsdam Cohort (EPIC) was employed for association studies. The Metabolic Intervention Cohort Kiel (MICK) consisting of 716 males was used for verification. A novel putative functional polymorphism (Arg109Cys) was identified in the CLPS gene. The frequencies of the Arg/Cys genotype were 2.6% in EPIC and 2.2% in MICK study subjects. No homozygotes for the Cys/Cys genotype were found in either study population. Logistic regression analysis showed a statistically significant association of the Arg/Cys genotype with an increased risk of type 2 diabetes. The odds ratios estimated by the model were 3.75 (95%CI = 1.13-12.49, p = 0.03) in EPIC and 4.86 (95%CI = 1.13-20.95, p = 0.03) in MICK. No comparable associations were found with other traits of the insulin-resistance syndrome (e. g.; body mass index, waist to hip ratio). In conclusion, we obtained evidence in two German Caucasian study populations that the variant of the rare CLPS Arg109Cys polymorphism might contribute to increased susceptibility of type 2 diabetes.  相似文献   
88.
89.
An investigation of the shape of the lactation curve and the mastitis incidence was conducted to identify whether management interventions of the lactation curve constitute a potential for reducing incidence of mastitis at herd level. Lactation curves were estimated to describe the variation of daily milk yield during the 305-d lactation period in Norwegian Red cows. Associations between mastitis incidence at herd level and lactation curve characteristics such as production level at onset of lactation, magnitude and time of peak milk yield, and increase and decrease of milk yield rates were studied. Data from 250,303 lactations occurring during 2005 and 2006 from 14,766 herds were obtained from the Norwegian Dairy Herd Recording System. Besides veterinary treatments, the records included information on monthly test-day milk yields. The shapes of the lactation curves at herd level were parameterized using a modified Wilmink model in two separate mixed model analyses. In the first analysis a subset of lactations with no records of veterinary treatments was used. Lactation curves from herds with high (>0·31 cases/305-d lactation) and low (<0·07 cases/305-d lactation) herd mastitis incidence rate were parameterized and compared for three separate strata of parity. The result showed that high herd mastitis incidence rate was associated with a low intercept (P<0·05), a steep slope before peak milk yield (P<0·01) and a rapid decline after peak milk yield (P<0·01). In the second analysis a subset of high-yielding lactations with veterinary treatments of mastitis only and lactations with no records of veterinary treatment were compared. This was done to investigate whether the findings at herd level were also reflected at cow level. These results showed that lactation curves from lactations with mastitis cases were associated with a steep slope before peak milk yield (P<0·05) in second and later parities and a rapid decline after peak milk yield (P<0·01) in all three parity groups.  相似文献   
90.
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