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   360篇
  免费   20篇
电工技术   36篇
综合类   2篇
化学工业   118篇
金属工艺   4篇
机械仪表   8篇
建筑科学   6篇
能源动力   16篇
轻工业   62篇
石油天然气   2篇
无线电   27篇
一般工业技术   58篇
冶金工业   5篇
原子能技术   3篇
自动化技术   33篇
  2022年   1篇
  2021年   9篇
  2020年   2篇
  2019年   5篇
  2018年   4篇
  2017年   8篇
  2016年   7篇
  2015年   7篇
  2014年   8篇
  2013年   31篇
  2012年   17篇
  2011年   21篇
  2010年   12篇
  2009年   8篇
  2008年   8篇
  2007年   15篇
  2006年   10篇
  2005年   14篇
  2004年   17篇
  2003年   16篇
  2002年   7篇
  2001年   6篇
  2000年   5篇
  1999年   10篇
  1998年   6篇
  1997年   8篇
  1996年   9篇
  1995年   9篇
  1994年   7篇
  1993年   2篇
  1992年   5篇
  1991年   7篇
  1990年   3篇
  1989年   3篇
  1988年   4篇
  1987年   4篇
  1986年   5篇
  1985年   5篇
  1984年   13篇
  1983年   4篇
  1982年   6篇
  1981年   7篇
  1980年   3篇
  1979年   7篇
  1978年   5篇
  1977年   6篇
  1976年   1篇
  1973年   1篇
  1970年   1篇
  1960年   1篇
排序方式: 共有380条查询结果,搜索用时 46 毫秒
371.
Scope: Peroxisome proliferator‐activated receptor‐α (PPARα) is a key regulator of circulating lipid level. Thus, various food‐derived compounds that activate PPARα as agonists have been screened and characterized. Methods and results: We investigated the effects of auraptene, a citrus‐derived compound serving as a PPARα agonist in vitro, on abnormalities in lipid and glucose metabolisms. In high‐fat‐diet (HFD)‐fed KK‐Ay diabetic obese mice, auraptene treatment suppressed hyperlipidemia and triglyceride accumulation in the liver and skeletal muscle, and increased the mRNA expression levels of the PPARα target genes involved in fatty acid oxidation in the liver and skeletal muscle. Moreover, the adipocyte size in the auraptene‐treated mice was significantly smaller than that in the control HFD‐fed mice resulting in the improvement of HFD‐induced hyperglycemia and abnormalities in glucose tolerance. Conclusions: These findings indicate that auraptene activates PPARα also in vivo and its treatment may improve abnormalities in lipid and glucose metabolisms, suggesting that auraptene is a valuable food‐derived compound for managing metabolic disorders.  相似文献   
372.
A randomized, double-blind human trial was conducted to assess the effect of 4- or 12-week astaxanthin supplementation (1 or 3 mg/day) on the carotenoid compositions of erythrocytes in Japanese middle-aged and senior subjects. Erythrocyte astaxanthin concentrations after 4- or 12-weeks of supplementation (3 mg/day) was significantly higher than after placebo or 1 mg astaxanthin supplementations. No differences were observed in either the carotenoid compositions or the phospholipid hydroperoxide concentrations in erythrocytes after astaxanthin intake in both the 1 and 3 mg/day groups.  相似文献   
373.
Hydroxy lipids (L-OH) and 4-hydroxy-2-hexenal (HHE) levels as well as other parameters such as lipid level, lipid class, fatty acid composition, and other aldehydes levels in the liver of diseased fish were investigated. Although significant differences in lipid level, lipid class, fatty acid composition, and other aldehyde levels were not always observed between normal and diseased fish, L-OH and HHE levels were significantly higher in the liver of the diseased fish than in that of the normal fish cultured with the same feeds under the same conditions. In the liver of puffer fish (Fugu rubripes) infected with Trichodina, L-OH and HHE levels significantly increased from 25.29 ± 5.04 to 47.70 ± 5.27 nmol/mg lipid and from 299.79 ± 25.25 to 1,184.40 ± 60.27 nmol/g tissue, respectively. When the levels of HHE and other aldehydes in the liver of the normal and diseased puffer fish were plotted, a linear relationship with a high correlation coefficient was observed between HHE and propanal (r 2 = 0.9447). Increased L-OH and HHE levels in the liver of the diseased fish and a high correlation between HHE and propanal in the liver of the normal and diseased fish were also observed in flat fish (Paralichthys olivaceus) infected with streptococcus, yellowtail (Seriola quinqueradiata) infected with jaundice, and amberjack (S. purpurascens) infected with Photobacterium damselae subsp. piscicida.  相似文献   
374.
碳纳米管具有高弹模和电导率的力学性能。形状记忆聚合物作为智能材料具有非凡的再修复和形状记忆效应,但是,其强度和弹性模量等力学性能较低。研究了带有纳米超长碳纤维的典型碳纳米管-形状记忆纳米聚合物,通过形状记忆聚合物基体获得纳米超长碳纤维均质分布。研究了不同纳米超长碳纤维质量分数,如形状记忆聚合物质量百分比为1.7%,3.3%和5.0%样本的动力学性质及变形恢复性能。研究发现:随着纳米超长碳纤维质量分数的增加,储能弹性模量明显提高,碳纳米管-形状记忆纳米聚合物显示了良好的形状记忆效应。质量分数3·3%的碳纳米管-形状记忆聚合物的恢复应力约为形状记忆聚合物的两倍。  相似文献   
375.
We have previously reported on a maskless photolithography device for surface micropatterning and microfabrication by modifying a commercially available liquid crystal display projector. For the prototype, 10-microm resolution was achieved by downsizing the image on a 0.7-in. liquid crystal display panel to an area of 8 x 6 mm and projecting it on a fixed stage. Here, we report on a second-generation maskless photolithography device having two novel features. First, the sliding lens system with variable focal distances and exchangeable objective lenses achieves a variable resolution of 2-8 mum. Second, the synchronous control of displayed images generated by a personal computer and the movement of a XY-positioning stage allows for the fabrication of micropatterns over a larger area (over 50 x 50 mm). Here, we show examples fabricated with the two novel features.  相似文献   
376.
Thiabendazole (TBZ), a pesticide with antifungal activity, was detected in toasted and seasoned laver which had been reported as tasting unpleasant by consumers in March 2008. From a survey of the manufacturing process, it was concluded that the TBZ contamination had originated from a sponge-roller which was used to paste seasoned liquid onto the toasted laver. At that time it was found that TBZ is widely used to prevent fungal contamination of sponge-rollers. For further survey of TBZ contamination in the laver, we developed a more sensitive detection method using LC-MS/MS. With our new method, six commercial products harvested in March 2008 and July 2009, respectively, were tested. Five out of six samples harvested in 2008 were positive for TBZ, with values in the range from 0.014 to 1.736 μg/g. Only one sample harvested in 2009 contained a detectable level of TBZ. The data obtained here contributed to the improvement of the manufacturing process.  相似文献   
377.
Selection of informative wavelengths is a crucial step for online spectral imaging applications. In this paper, four cultivars of apples were utilized to select effective wavelengths for bruise detection within 380-1000 nm. Each of the wavelength variables was considered as an independent classifier for bruised/normal classification, and all classifiers were evaluated and compared by receiver operating characteristic (ROC) analysis. According to the area under the ROC curve (AUC), the reflectance difference between two wavelengths (R(λ1) − R(λ2)), was determined as the best wavelength pair for the Fuji, Jonagold, Orin and Sinano Gold cultivars as follows: R(808 nm) − R(760 nm), R(832 nm) − R(772 nm), R(834 nm) − R(762 nm) and R(788 nm) − R(742 nm), respectively. The performance of the wavelengths selected in this paper was measured by comparing the predicted sensitivity, predicted specificity and predicted classification accuracy with those of the model proposed by partial least squares discriminant analysis (PLSDA), which used all of the wavelength variables. The results showed that the predictive ability of both methods was generally on the same level.  相似文献   
378.
Di-d-fructofuranosyl 2,6′:2′,6 anhydride (DFA IV) was produced directly from sucrose using a single culture of recombinant Bacillus subtilis 168 carrying the levan fructotransferase (lft) gene. In this study, three plasmids carrying the degQ36 gene, which is a degQ allele of B. subtilis (degQ36) with a degQ36 mutation on its promoter, were constructed to overproduce intact DegQ in B. subtilis 168. The transformant B. subtilis/pHT-D36 (with the degQ36 gene) consumed sucrose and produced levan at a higher rate than B. subtilis/pHT43 (without the degQ36 gene). The transformant B. subtilis/pLFT-GD36, carrying the lft and degQ36 genes, also consumed sucrose at a higher rate and produced more DFA IV than B. subtilis/pLFT-G, carrying the lft but without the degQ36 gene. B. subtilis/pLFT-GD36 produced 43.5 g/l of DFA IV and consumed 240 g/l of sucrose (96% of added sucrose) by 72 h of cultivation, whereas B. subtilis/pLFT-G produced 23.4 g/l of DFA IV with 76.9 g/l of sucrose still remaining in the system. Sucrose-inducible expression vectors were also constructed, which made it possible to produce DFA IV without IPTG induction. Using these vectors, sucrose consumption rates were enhanced and DFA IV production was increased upon introduction of the degQ36 gene. From these results, it can be concluded that the additionally introduced regulatory gene, degQ, was able to stimulate sucrose conversion to levan, and therefore increased DFA IV production in this system.  相似文献   
379.
Random Walk Routing in WSNs with Regular Topologies   总被引:3,自引:0,他引:3       下载免费PDF全文
Topology is one of the most important characteristics for any type of networks because it represents the network's inherent properties and has great impact on the performance of the network. For wireless sensor networks (WSN), a well-deployed regular topology can help save more energy than what a random topology can do. WSNs with regular topologies can prolong network lifetime as studied in many previous work. However, little work has been done in developing effective routing algorithms for WSNs with regular topologies, except routing along a shortest path with the knowledge of global location information of sensor nodes. In this paper, a new routing protocol based on random walk is proposed. It does not require global location information. It also achieves load balancing property inherently for WSNs which is difficult to achieve by other routing protocols. In the scenarios where the message required to be sent to the base station is in comparatively small size with the inquiry message among neighboring nodes, it is proved that the random walk routing protocol can guarantee high probability of successful transmission from the source to the base station with the same amount of energy consumption as the shortest path routing. Since in many applications of WSNs, sensor nodes often send only beep-like small messages to the base station to report their status, our proposed random walk routing is thus a viable scheme and can work very efficiently especially in these application scenarios. The random walk routing provides load balancing in the WSN as mentioned, however, the nodes near to the base station are inevitably under heavier burden than those far away from the base station. Therefore, a density-aware deployment scheme is further proposed to guarantee that the heavy-load nodes do not affect the network lifetime even if their energy is exhausted. The main idea is deploying sensors with different densities according to their distance to the base station. It will be shown in this paper that incorporating the random walk routing protocol with the density-aware deployment scheme can effectively prolong the network lifetime.  相似文献   
380.
Resistant starch content of high‐amylose corn starch (HAS) was doubled by heat‐moisture treatment. Resistant starch content of HAS and heat‐moisture treated high‐amylose corn starch (HMT‐HAS) were 31.8 and 67.3%, respectively, as determined by enzymatic‐gravimetric method. Effects of the two types of high‐amylose corn starches, HAS and HMT‐HAS, on starch fermentation, microflora, pH, short chain fatty acid (SCFA) content and β‐glucuronidase activity in the cecal content have been investigated. Rats were given ordinary corn starch (OCS; control), HAS or HMT‐HAS at 10% level for 10 13 days. The cecal and colorectal content s weights were larger in HAS and HMT‐HAS groups than in the OCS group. The cecal content s weight did not differ between HAS and HMT‐HAS groups, while the colorectal content s weight was higher in the HMT‐HAS group than in the HAS group. The upper and lower small intestinal and cecal starch contents were significantly higher in the HAS and HMT‐HAS groups than in the OCS group, whereas there were no differences between colorectal starch content in group OCS and HAS. Starch excretion in feces was significantly higher in groups HAS and HMT‐HAS than in group OCS, the increase in the HMT‐HAS group was especially remarkable. The composition of the cecal microflora was not effected by the diet. β‐Glucuronidase activities in rats fed HAS or HMT‐HAS decreased. SCFA concentration was higher in groups HAS and HMT‐HAS than in group OCS, and the cecal pH was lower in groups HAS and HMT‐HAS than in group OCS.  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