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   981篇
  免费   60篇
  国内免费   2篇
电工技术   3篇
综合类   2篇
化学工业   343篇
金属工艺   12篇
机械仪表   11篇
建筑科学   51篇
能源动力   12篇
轻工业   202篇
水利工程   6篇
石油天然气   2篇
无线电   50篇
一般工业技术   155篇
冶金工业   61篇
原子能技术   4篇
自动化技术   129篇
  2024年   3篇
  2023年   8篇
  2022年   43篇
  2021年   42篇
  2020年   38篇
  2019年   18篇
  2018年   29篇
  2017年   26篇
  2016年   31篇
  2015年   31篇
  2014年   42篇
  2013年   72篇
  2012年   64篇
  2011年   69篇
  2010年   63篇
  2009年   60篇
  2008年   56篇
  2007年   55篇
  2006年   47篇
  2005年   49篇
  2004年   33篇
  2003年   21篇
  2002年   23篇
  2001年   11篇
  2000年   22篇
  1999年   12篇
  1998年   9篇
  1997年   11篇
  1996年   10篇
  1995年   6篇
  1994年   11篇
  1993年   8篇
  1992年   2篇
  1991年   2篇
  1990年   7篇
  1989年   3篇
  1987年   1篇
  1982年   1篇
  1981年   1篇
  1934年   3篇
排序方式: 共有1043条查询结果,搜索用时 15 毫秒
991.
992.
Agrochemicals are amongst the contaminants most widely encountered in surface and subterranean hydrological systems. They comprise a variety of molecules, with properties that confer differing degrees of persistence and mobility in the environment, as well as different toxic, carcinogenic, mutagenic and teratogenic potentials, which can affect non-target organisms including man. In this work, alginate/chitosan nanoparticles were prepared as a carrier system for the herbicide paraquat. The preparation and physico-chemical characterization of the nanoparticles was followed by evaluation of zeta potential, pH, size and polydispersion. The techniques employed included transmission electron microscopy, differential scanning calorimetry and Fourier transform infrared spectroscopy. The formulation presented a size distribution of 635 ± 12 nm, polydispersion of 0.518, zeta potential of -22.8 ± 2.3 mV and association efficiency of 74.2%. There were significant differences between the release profiles of free paraquat and the herbicide associated with the alginate/chitosan nanoparticles. Tests showed that soil sorption of paraquat, either free or associated with the nanoparticles, was dependent on the quantity of organic matter present. The results presented in this work show that association of paraquat with alginate/chitosan nanoparticles alters the release profile of the herbicide, as well as its interaction with the soil, indicating that this system could be an effective means of reducing negative impacts caused by paraquat.  相似文献   
993.
994.
Zusammenfassung Frische Moosbeeren, die im Laufe der Monate November 1931–Februar 1932 untersucht wurden, zeigten durchschnittlich eine antiskorbutische Aktivität, die zwischen 100 und 200 Einheiten in 1 Liter Saft oder 80–160 Einheiten in 1 kg Produkt liegt. Es wurde kein Unterschied in der antiskorbutischen Wirkung des Saftes und der Moosbeeren—in Mengen, die dem Safte entsprechen—gefunden.bedeutet mit Abbildungen.  相似文献   
995.
Inflammatory processes are involved in the etiology of diseases. We analyzed the effect of resveratrol, piceatannol, synthetic tri-acetoxystilbene (TAS), and genistein (Bonistein(TM)) on the production of inflammatory mediators including prostaglandin E2 (PGE2), tumor necrosis factor-alpha (TNF-alpha), interleukins, and chemokines, which participate in the progression of inflammation. In order to induce inflammatory responses, human peripheral blood mononuclear and/or polymorphonuclear leukocytes were stimulated with lipopolysaccharide (LPS) and interferon-gamma (IFN(gamma)) and the production of PGE2, interleukin-8 (IL-8), and TNF-alpha was determined. In response to the stimuli, genes were substantially activated within < 2 h (e. g., TNF-alpha, IL-1alpha), or at a later stage, (e. g., COX-2, IL-6, IL-8). Unlike genistein, resveratrol and related compounds dose-dependently reduced PGE2 production. Genistein, piceatannol, and TAS diminished secretion of TNF-alpha, and IL-8. TAS reduced mRNA levels of COX-2, TNF-alpha, IL-8, IL-6, and IL-1alpha, while resveratrol impaired early expression of IL-8 and TNF-alpha. Piceatannol out-performed resveratrol, yet without matching TAS. Genistein downregulated TNF-alpha and IL-8 expression. These substances altered the LPS/IFNgamma-induced gene expression in mononuclear cells rather than in polymorphonuclear leukocytes. Immunoblot analyses corroborated the distinct activity pattern of resveratrol and genistein. In conclusion, resveratrol and their derivatives attenuated the inflammatory response of PBLs at several levels, whereas genistein acts on cytokines and pro-inflammatory interleukins.  相似文献   
996.
Even though it generates healthy adults, nuclear transfer in mammals remains an inefficient process. Mainly attributed to abnormal reprograming of the donor chromatin, this inefficiency may also be caused at least partly by a specific effect of the cloning technique which has not yet been well investigated. There are two main procedures for transferring nuclei into enucleated oocytes: fusion and piezoelectric microinjection, the latter being used mostly in mice. We have, therefore, decided to compare the quality and the developmental ability, both in vivo and in vitro, of embryos reconstructed with electrofusion or piezoelectric injection. In addition, the effect of piezo setups of differing electric strengths was investigated. Along with the record of the rate of development, we compared the nuclear integrity in the blastomeres during the first cleavages as well as the morphological and cellular quality of the blastocysts. Our results show that the piezo-assisted micromanipulation can induce DNA damage in the reconstructed embryos, apoptosis, and reduced cell numbers in blastocysts as well as a lower rate of development to term. Even if piezo-driven injection facilitates a faster and more efficient rate of reconstruction, it should be used with precaution and with as low parameters as possible.  相似文献   
997.
Using an enriched library method, seven polymorphic microsatellite loci were isolated from the barley stem gall midge, Mayetiola hordei. Polymorphism at loci was surveyed on 57 individual midges collected on barley in Tunisia. Across loci, polymorphism ranged from two to six alleles per locus. The observed heterozygosity varied between 0.070 and 0.877. Based on the number of alleles detected and the associated levels of heterozygosity, we believe that these loci will prove useful for population genetic studies on M. hordei.  相似文献   
998.
Interesterification is an important modification technique for fats and oils resulting in the redistribution of the fatty acids among the glycerol backbone and thus changing the physico-chemical properties of the modified fat. In this study palm oil, palm olein and soft palm mid fraction (PMF) were subjected to both enzymatic (batchwise) and chemical interesterification. The reaction products were characterized before, during and after interesterification by HPLC, pulsed NMR (p-NMR) and differential scanning calorimetry (DSC). Interesterification led to more uniform triacylglycerol (TAG) compositions with smaller differences in final physico-chemical properties between the studied substrates. The degree of interesterification was evaluated on the basis of TAG composition and solid fat content (SFC). Significant differences between both methods were observed. The degree of interesterification based on SFC is therefore a better tool to evaluate the rate constant of the reaction as the TAG composition method does not take into consideration the formation of positional isomers at the end of the enzymatic process.  相似文献   
999.
This work deals with zinc beneficiation of industrial solid waste by an electrochemical technique combining electroleaching and electrodeposition in a single-cell process. This technique is based on leaching of the solid waste by the protons generated at the anode and migration of the resulting ions toward the cathode where deposition takes place. A laboratory cell was built for testing the method. It consisted of three compartments, two electrode compartments and a solid waste chamber placed between these. Catholyte and anolyte were sulphuric/sulphate solutions at optimised concentrations. Experiments were first carried out using a zinc solution and an inert matrix in the central compartment, then using a synthetic waste prepared by dispersing zinc oxide in silicon dioxide. Best performance was obtained with treatment duration of 6h, at 4.5Adm(-2) and with catholyte circulation. In this case, a 97% of zinc oxide lixiviation and 75% of zinc-plated were achieved.  相似文献   
1000.
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