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   337篇
  免费   17篇
电工技术   3篇
化学工业   65篇
金属工艺   3篇
机械仪表   3篇
建筑科学   33篇
能源动力   4篇
轻工业   23篇
水利工程   1篇
石油天然气   5篇
无线电   47篇
一般工业技术   50篇
冶金工业   34篇
原子能技术   3篇
自动化技术   80篇
  2024年   2篇
  2023年   7篇
  2022年   14篇
  2021年   21篇
  2020年   16篇
  2019年   15篇
  2018年   23篇
  2017年   15篇
  2016年   23篇
  2015年   7篇
  2014年   12篇
  2013年   19篇
  2012年   22篇
  2011年   16篇
  2010年   22篇
  2009年   23篇
  2008年   22篇
  2007年   9篇
  2006年   11篇
  2005年   8篇
  2004年   5篇
  2003年   7篇
  2002年   5篇
  2001年   3篇
  2000年   1篇
  1999年   4篇
  1998年   4篇
  1997年   2篇
  1996年   5篇
  1995年   4篇
  1994年   1篇
  1993年   2篇
  1991年   1篇
  1990年   1篇
  1980年   1篇
  1977年   1篇
排序方式: 共有354条查询结果,搜索用时 140 毫秒
51.
This report explores the available curative molecules directed against hepatocellular carcinoma (HCC). Limited efficiency as well as other drawbacks of existing molecules led to the search for promising potential alternatives. Understanding of the cell signaling mechanisms propelling carcinogenesis and driven by cell proliferation, invasion, and angiogenesis can offer valuable information for the investigation of efficient treatment strategies. The complexity of the mechanisms behind carcinogenesis inspires researchers to explore the ability of various biomolecules to target specific pathways. Natural components occurring mainly in food and medicinal plants, are considered an essential resource for discovering new and promising therapeutic molecules. Novel biomolecules normally have an advantage in terms of biosafety. They are also widely diverse and often possess potent antioxidant, anti-inflammatory, and anti-cancer properties. Based on quantitative structure–activity relationship studies, biomolecules can be used as templates for chemical modifications that improve efficiency, safety, and bioavailability. In this review, we focus on anti-HCC biomolecules that have their molecular targets partially or completely characterized as well as having anti-cancer molecular mechanisms that are fairly described.  相似文献   
52.
The first aim of this study was to create, test, and apply a quick, easy, cheap, effective, rugged, and safe (QuEChERS) method, based on acetonitrile extraction, for simultaneous determination of pesticide residues in green chili pepper (fresh and dried forms). There is a group of 86 repeatedly detected pesticides in the agricultural food commodity in Al-Qassim region, Saudi Arabia. The suggested method is utilizing GC-MS/MS for simultaneous determination of those 86 pesticides. The limit of quantitation (LOQ) for each pesticide was set as the lowest fortification level that achieved acceptable recoveries in the range 70–120% with precision (RSD ≤ 20%). The results indicated that two organophosphorus pesticides, ethion and profenofos, in the analyzed chili pepper samples have significantly exceeded the European maximum residual limit (MRL) for pesticides. The second purpose of the study was to evaluate the effect of some different household-type treatment and processing procedures on the detected pesticide residues and on capsaicinoids (particularly, capsaicin and dihydrocapsaicin) which are responsible for the pungency of chili pepper, using GC-MS/MS and HPLC. Some recommendations were concluded for the best practices.  相似文献   
53.
The protein A encoding gene spa of four Staphylococcus aureus strains isolated from bovine clinical mastitis was amplified by PCR and sequenced. The four strains were selected after an initial screening of spa gene of 41 strains isolated from mastitic cows and were subjected to detailed investigations. According to the sequencing results the spa gene of three strains (M1, M2, M3) appeared with gene segments encoding five (E, D, A, B and C) and four (E, A, B and C) IgG binding domains for two (M1, M3) and one (M2) strain, respectively and with gene segments encoding four, two and two repeats of the octapeptide Xr-repeats for the strains M1, M2 and M3, respectively. For the remaining Staph. aureus strain (M4) gene segments encoding IgG binding domains E, D and A and a new domain BC with a size of 219 bp could be observed. The BC domain appears, with a deletion of a 123 bp segment from the border region between both domains, as fused domain of both previously characterized domains. The Xr-region of this strain had 11 octapeptide repeats.  相似文献   
54.
Steering quantum dynamics such that the target states solve classically hard problems is paramount to quantum simulation and computation. And beyond, quantum control is also essential to pave the way to quantum technologies. Here, important control techniques are reviewed and presented in a unified frame covering quantum computational gate synthesis and spectroscopic state transfer alike. We emphasize that it does not matter whether the quantum states of interest are pure or not. While pure states underly the design of quantum circuits, ensemble mixtures of quantum states can be exploited in a more recent class of algorithms: it is illustrated by characterizing the Jones polynomial in order to distinguish between different (classes of) knots. Further applications include Josephson elements, cavity grids, ion traps and nitrogen vacancy centres in scenarios of closed as well as open quantum systems.  相似文献   
55.
Amr Ibrahim  Saiful Bari 《Fuel》2008,87(10-11):1824-1834
Natural gas has been recently used as an alternative to conventional fuels in order to satisfy some environmental and economical concerns. In this study, a natural gas spark-ignition engine employing cooled exhaust gas recirculation (EGR) strategy in a high pressure inlet condition was optimized. Both engine compression ratio and start of combustion timing were optimized in order to obtain the lowest fuel consumption accompanied with high power and low emissions. That was achieved numerically by developing a computer simulation of the four-stroke spark-ignition natural gas engine. A two-zone combustion model was developed to simulate the in-cylinder conditions during combustion. A kinetic model based on the extended Zeldovich mechanism was also developed in order to predict NO emission. In addition, a knocking model was incorporated with the two-zone combustion model in order to predict any auto-ignition that might occur. It was found that the value of the compression ratio at which the minimum fuel consumption occurs varies with the engine speed. A minimum fuel consumption of about 200 g/kW h was achieved at an engine speed of 1500 rpm, inlet conditions of 200 kPa and 333 K, and a compression ratio of about 12. Also, it was found that cooled EGR can significantly reduce NO emission at high compression ratio conditions. NO emission decreased by about 28% when EGR was increased from 20% at compression ratio of 10 to 27% at compression of 12 at the same engine speed of 3000 rpm.  相似文献   
56.
This paper reports on the constants of elasticity of xPbO-RNa2B4O7-(100 ? R ? x) CAS with 0 ?? x ?? 50, and 50 ?? R ?? 75 mol % glass system (CAS is calcium alumino silicate glasses). The constants of elasticity were calculated in terms of the bond compression model and Makishima-Mackenzie model. The average cross-link density, the number of network bonds per unit volume, the average stretching-force constant, and the ratio of the estimated bulk modulus (K bc ) to the experimentally determined (K e ), have been calculated and discussed in terms of the bond compression model to analyze the role of PbO. Young??s modulus, the packing density and dissociation energy have been calculated and analyzed according to the Makishima-Mackenzie model. The dimensionality of the glassy network has been calculated in terms of the d ratio (4C 44/C 12) and discussed in terms of the cross-link density of these glasses. C 12 = C 11?2C 44, C 11 and C 44 are the longitudinal and shear elastic constant. The results show good agreement between the experimental and theoretical data for the representation of the constants of elasticity of borosilicate glasses.  相似文献   
57.
This paper investigates the implications of ground motion spatial variability on the seismic response of an extended highway bridge. An existing 59-span, 2,164-meter bridge with several bearing types and irregularity features was selected as a reference structure. The bridge is located in the New Madrid Seismic Zone and supported on thick layers of soil deposits. Site-specific bedrock input ground motions were selected based on a refined probabilistic seismic hazard analysis of the bridge site. Wave passage and ground motion incoherency effects were accounted for after propagating the bedrock records to the ground surface. The results obtained from inelastic response-history analyses confirm the significant impact of wave passage and ground motion incoherency on the seismic behavior of the bridge. The amplification in seismic demands exceeds 150%, whereas the maximum suppression of these demands is less than 50%. The irregular and unpredictable changes in structural response owing to asynchronous earthquake records necessitate in-depth seismic assessment of major highway bridges with advanced modeling techniques to realistically capture their complex seismic response.  相似文献   
58.
The volatile aroma components of Egyptian green garlic leaves essential oil was investigated for the first time. After the utilization of garlic bulbs to prepare garlic oil or after drying the bulbs to produce garlic powder, garlic leaves are considered to be waste material, which is disposed of without any benefit. In this investigation, green garlic leaves were distilled and the essential oil was subjected to GC and GC-MS identification. The yield of the oil was 0.06% (based on wet weight of the leaves). The most prominent compounds of the essential oil were diallyl trisulfide (32.32%), followed by diallyl disulfide (31.35%) and methyl allyl trisulfide (11.40%); these compounds are the same as those found in garlic bulb oil. This means that garlic leaf oil is a rich, renewable and priceless source of garlic aroma compounds which could be utilized in fortification and enriching of garlic bulb essential oil to increase its quantity without changing the quality. Utilization of green garlic leaves for production of essential oil will also save, to some extent, the costs of disposing of large amounts of leaves in garlic possessing factories, transforming them into profits.  相似文献   
59.
Sheep's anhydrous butter fat as prepared by including separately heat grits, turmeric, rosemary, sage, rue and fennel at a level of 75 g dry matter kg?1 butter. The product as stored at room temperature in clear glass jars for a period of one year. The storage stabilities of the anhydrous butter fat samples ere compared ith a control and ith a sample treated ith a 1:1 mixture of BHA and BHT at a level of 0.25 g kg?1. Both storage time and type of treatment had highly significant effects (P?0.01) on the peroxide value and free fatty acid content of the product. None of the treatments succeeded in keeping the peroxide value belo 5 mEq O2 kg?1 beyond the fourth month of storage. The BHA-BHT mixture and rosemary helped extend the peroxide induction period to 10 and 6 months respectively. Turmeric and heat grits ere as effective as BHA-BHT in controlling the oxidative rancidity during the first four months of storage. The rest of the herbs exhibited a pro-oxidant effect throughout the study hen they ere used separately. In a second experiment, some cases of positive synergistic interactions ere observed beteen turmeric and heat grits on one hand and the herbs used in the study on the other. This pattern as not regular as negative interactions ere also observed in some other cases. Free fatty acid content of all the samples remained belo 10 g kg?1 as oleic acid; hoever, fennel had a significant (P?0.05) effect on controlling the evolution of free fatty acids.  相似文献   
60.
Wireless mesh networks (WMNs) have emerged as a promising technology that provides low‐cost broadband access to the Internet for fixed and mobile wireless end users. An orthogonal evolution in computer networking has been the rise of peer‐to‐peer (P2P) applications such as P2P data sharing. It is of interest to enable effective P2P data sharing in this type of networks. Conventional P2P data sharing systems are not cognizant of the underlying network topology and therefore suffer from inefficiency. We argue for dual‐layer mesh network architecture with support from wireless mesh routers for P2P applications. The main contribution of this paper is P2PMesh: a topology‐aware system that provides combined architecture and efficient schemes for enabling efficient P2P data sharing in WMNs. The P2PMesh architecture utilizes three schemes: (i) an efficient content lookup that mitigates traffic load imbalance at mesh routers; (ii) an efficient establishment of download paths; and (iii) a data transfer protocol for multi‐hop wireless networks with limited capacity. We note here that the path establishment and data transfer schemes are specific to P2P traffic and that other traffic would use routes determined by the default routing protocol in the WMN. Simulation results suggest that P2PMesh has the potential to improve the performance of P2P applications in a wireless multi‐hop setting; specifically, we focused on data sharing, but other P2P applications can also be supported by this approach. Copyright © 2011 John Wiley & Sons, Ltd.  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