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   576篇
  免费   21篇
电工技术   3篇
化学工业   267篇
金属工艺   7篇
机械仪表   18篇
建筑科学   11篇
矿业工程   1篇
能源动力   14篇
轻工业   110篇
石油天然气   1篇
无线电   10篇
一般工业技术   81篇
冶金工业   18篇
原子能技术   1篇
自动化技术   55篇
  2023年   10篇
  2022年   58篇
  2021年   59篇
  2020年   18篇
  2019年   18篇
  2018年   13篇
  2017年   16篇
  2016年   18篇
  2015年   16篇
  2014年   18篇
  2013年   42篇
  2012年   33篇
  2011年   41篇
  2010年   36篇
  2009年   32篇
  2008年   42篇
  2007年   21篇
  2006年   17篇
  2005年   17篇
  2004年   12篇
  2003年   4篇
  2002年   6篇
  2001年   7篇
  2000年   8篇
  1999年   5篇
  1998年   4篇
  1997年   1篇
  1996年   3篇
  1995年   4篇
  1994年   4篇
  1992年   3篇
  1990年   5篇
  1989年   1篇
  1985年   3篇
  1984年   1篇
  1983年   1篇
排序方式: 共有597条查询结果,搜索用时 15 毫秒
91.
92.
Proanthocyanidins (PACs) are a group of bioactive molecules found in a variety of plants and foods. Their bioavailability depends on their molecular size, with monomers and dimers being more bioavailable than those that have a higher polymerization degree. This study aimed to develop a method to convert high-molecular-weight PACs to low-molecular-weight ones in a grape seed extract (GSE) from Vitis vinifera L. Therefore, GSE was subjected to alkaline treatment (ATGSE), and its difference in chemical composition, compared to GSE, was evaluated using a molecular networking (MN) approach based on results obtained from HPLC-ESI HRMS/MS characterization analysis. The network analysis mainly noted the PAC cluster with about 142 PAC compounds identified. In particular, the obtained results showed a higher content of monomeric and dimeric PACs in ATGSE compared to GSE, with 58% and 49% monomers and 31% and 24% dimers, respectively. Conversely, trimeric (9%), polymeric (4%), and galloylated PACs (14%) were more abundant in GSE than in ATGSE (6%, 1%, and 4%, respectively). Moreover, in vitro antioxidant and anti-inflammatory activities were investigated, showing the high beneficial potential of both extracts. In conclusion, ATGSE could represent an innovative natural matrix rich in bioavailable and bioaccessible PACs for nutraceutical applications with potential beneficial properties.  相似文献   
93.
Fenofibrate (FBR), an oral medication used to treat dyslipidemia, is a ligand of the peroxisome proliferator-activated receptor α (PPARα), a nuclear receptor that regulates the expression of metabolic genes able to control lipid metabolism and food intake. PPARα natural ligands include fatty acids (FA) and FA derivatives such as palmitoylethanolamide (PEA) and oleoylethanolamide (OEA), known to have anti-inflammatory and anorexigenic activities, respectively. We investigated changes in the FA profile and FA derivatives by HPLC and LC-MS in male C57BL/6J mice fed a standard diet with or without 0.2% fenofibrate (0.2% FBR) for 21 days. Induction of PPARα by 0.2% FBR reduced weight gain, food intake, feed efficiency, and liver lipids and induced a profound change in FA metabolism mediated by parallel enhanced mitochondrial and peroxisomal β-oxidation. The former effects led to a steep reduction of essential FA, particularly 18:3n3, with a consequent decrease of the n3-highly unsaturated fatty acids (HUFA) score; the latter effect led to an increase of 16:1n7 and 18:1n9, suggesting enhanced hepatic de novo lipogenesis with increased levels of hepatic PEA and OEA, which may activate a positive feedback and further sustain reductions of body weight, hepatic lipids and feed efficiency.  相似文献   
94.
Cancer is a set of diseases characterized by several hallmark properties, such as increased angiogenesis, proliferation, invasion, and metastasis. The increased angiogenic activity constantly supplies the tumors with nutrients and a plethora of cytokines to ensure cell survival. Along these cytokines is a newly discovered protein, called irisin, which is released into the circulation after physical exercise. Irisin is the product of fibronectin type III domain-containing protein 5 (FNDC5) proteolytic cleavage. Recently it has been the topic of investigation in several types of cancer. In this study, we conducted a systematic review and meta-analysis to investigate its implication in different types of cancer. Our results suggest that irisin expression is decreased in cancer patients, thus it can be used as a valid biomarker for the diagnosis of several types of cancer. In addition, our results indicate that irisin may have an important role in tumor progression and metastasis since it is involved in multiple signaling pathways that promote cell proliferation and migration.  相似文献   
95.
To identify behaviors related to acquisition of tool-use in tufted capuchins (Cebus apella), we presented two tool-using tasks to two groups, extending findings by Westergaard and Fragaszy (1987) and Visalberghi (in press). Five Ss learned to use the tools in each task. The primary predictor of success was level of interest in the task. Observation of others at the apparatus did not facilitate exploratory behaviors or contact with the tools in the observers. Most animals performed exploratory behaviors more often when they were at the apparatus alone than when with another, whether or not the other was using a tool. Observers were quick to learn the relationship between another's activities and the appearance of food. We conclude that capuchins do not readily learn about instrumental relations by observation of others or imitate other's acts. Imitation probably plays no role in the spread of novel instrumental behaviors among monkeys. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
96.
In this work a Sulzer structured packing, Mellapak 250Y, was studied for applications in the field of absorption. A new model was proposed which makes it possible to estimate the packing surface that actually takes part in the process. In the course of these studies, new experimental data were obtained relating to the absorption of 1,1,1-trichloroethane using Genosorb 300, a mixture of polyethylene glycol dimethyl ethers produced by Hoechst S.p.A., as absorption liquid. The results obtained with the proposed model are in agreement both with the experimental measurements made in the course of the work and with experimental absorption measurements reported by other authors on water systems.  相似文献   
97.
Two detoxification mechanisms working in the marine diatom Thalassiosira weissflogii to cope with mercury toxicity were investigated. Initially, the effect of mercury on the intracellular pool of non-protein thiols was studied in exponentially growing cultures exposed to sub-toxic HgCl2 concentrations. T. weissflogii cells responded by synthesizing metal-binding peptides, named phytochelatins (PCs), besides increasing the intracellular pool of glutathione and γ-glutamylcysteine (γ-EC). Intracellular Hg and PC concentrations increased with the Hg concentration in the culture medium, exhibiting a distinct dose-response relationship. However, considerations of the PCs-SH:Hg molar ratio suggest that glutathione could also be involved in the intracellular mercury sequestration. The time course of the non-protein thiol pool and Hg intracellular concentration shows that PCs, glutathione and γ-EC represent a rapid cellular response to mercury, although their role in Hg detoxification seems to lose importance at longer incubation times. The occurrence of a process of reduction of Hg(II) to Hg° and subsequent production of dissolved gaseous mercury (DGM) was also investigated at lower Hg concentrations, at which the PC synthesis doesn't seem to be involved. The significant (P < 0.01) correlation between the cellular density in solution and the production of DGM suggests that this diatom is capable of directly producing DGM, both in light and dark conditions. This finding has been confirmed by the absence of DGM production in the culture media containing formaldehyde-killed cells. Finally, the relationship between these two different pathways of Hg detoxification is discussed.  相似文献   
98.
99.
The use of biomass for the production of electrical energy is a promising technological solution for those countries where there are problems with the disposal of agricultural waste and/or the production of low-cost energy. The gasification and/or pyrolysis of the biomass produces a gas rich in hydrogen that can be used in a fuel cell system to produce electrical energy with reduced environmental impact and significant energy recovery.In this work, a study of the pyrolysis of Brazilian sugarcane bagasse was carried out. The experimental process consisted of the pyrolysis of the biomass material in a batch pyrolysis reactor. In some runs the biomass was dry, while in others it was pre-treated by the addition of water. It was noted that the water added to the biomass before the pyrolysis process resulted in a decrease in the quantity of steam added to the fuel cell feeding gas, necessary to avoid carbon deposition, and in an increase in cell power, but, at the same time, caused a decrease in the quantity of syngas produced.Then, the composition of the gas obtained from the experimental pyrolysis of the sugarcane was inserted in a simulation tool of a molten carbonate fuel cell system in order to estimate the feasibility of the entire process in terms of operating conditions and electrical performance.The present study indicates that the syngas obtained from the sugarcane biomass (about 40%) can be converted into electricity using a fuel cell system with a high efficiency.  相似文献   
100.
Co/CeO2 (Co 7.5 wt.%), Ni/CeO2 (Ni 7.5 wt.%) and Co–Ni/CeO2 (Co 3.75 wt.%, Ni 3.75 wt.%) catalysts were prepared by surfactant assisted co-precipitation method. Samples were characterized by X-Ray diffraction, BET surface areas measurements, temperature programmed reduction and tested for the dry reforming of methane CH4 + CO2 → 2CO + 2H2 in the temperature range 600–800 °C with a CH4:CO2:Ar 20:20:60 vol.% feed mixture and a total flow rate of 50 cm3 min−1 (GHSW = 30,000 mL g−1 h−1). The bimetallic Co–Ni/CeO2 catalyst showed higher CH4 conversion in comparison with monometallic systems in the whole temperature range, being 50% at 600 °C and 97% at 800 °C. H2/CO selectivity decreased in the following order: Co–Ni/CeO2 > Ni/CeO2 > Co/CeO2. Carbon deposition on spent catalysts was analyzed by thermal analysis (TG-DTA). After 20 h under stream at 750 °C, cobalt-containing catalysts, Co/CeO2 and Co–Ni/CeO2, showed a stable operation in presence of a deposited amorphous carbon of 6 wt.%, whereas Ni/CeO2 showed an 8% decrease of catalytic activity due to a massive presence of amorphous and graphitic carbon (25 wt.%).  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