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   278173篇
  免费   3097篇
  国内免费   1285篇
电工技术   4811篇
综合类   527篇
化学工业   40263篇
金属工艺   11124篇
机械仪表   8415篇
建筑科学   6400篇
矿业工程   1576篇
能源动力   6967篇
轻工业   22461篇
水利工程   3038篇
石油天然气   5783篇
武器工业   43篇
无线电   33499篇
一般工业技术   56465篇
冶金工业   50863篇
原子能技术   7497篇
自动化技术   22823篇
  2021年   2154篇
  2019年   2060篇
  2018年   3576篇
  2017年   3669篇
  2016年   3899篇
  2015年   2485篇
  2014年   4344篇
  2013年   11957篇
  2012年   7061篇
  2011年   9699篇
  2010年   7528篇
  2009年   8745篇
  2008年   9090篇
  2007年   9129篇
  2006年   7800篇
  2005年   7247篇
  2004年   7196篇
  2003年   6972篇
  2002年   6713篇
  2001年   6844篇
  2000年   6477篇
  1999年   6761篇
  1998年   16295篇
  1997年   11578篇
  1996年   8915篇
  1995年   6843篇
  1994年   6015篇
  1993年   6051篇
  1992年   4395篇
  1991年   4180篇
  1990年   4073篇
  1989年   4055篇
  1988年   3750篇
  1987年   3387篇
  1986年   3392篇
  1985年   3739篇
  1984年   3460篇
  1983年   3217篇
  1982年   3024篇
  1981年   3038篇
  1980年   3037篇
  1979年   2829篇
  1978年   2869篇
  1977年   3141篇
  1976年   4096篇
  1975年   2416篇
  1974年   2379篇
  1973年   2396篇
  1972年   2018篇
  1971年   1781篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
Manikandan  P.  Natrayan  L.  Duraimurugan  S.  Vasugi  V. 《SILICON》2022,14(13):7799-7808
Silicon - The formation of alkali-activated binders from industrial end products and landfill materials attracts considerable interest in construction technology since it diminishes the waste...  相似文献   
112.
Metal Science and Heat Treatment - Results of a study of transportation of chromium and iron by iodine at various temperatures of diffusion chromizing of armco iron are presented. The phase...  相似文献   
113.
Metal Science and Heat Treatment - Composites obtained by powder metallurgy from a mixture of copper powders and graphene nanosheets are studied. The response surface methodology is used to design...  相似文献   
114.
115.
Protection of Metals and Physical Chemistry of Surfaces - In this work, preparation of thermal barrier coatings based on zirconium oxide is shown. The phased treatment of the copper substrate is...  相似文献   
116.
We investigated metal-organic vapor phase epitaxy grown (InGa)(AsSb)/GaAs/GaP Stranski–Krastanov quantum dots (QDs) with potential applications in QD-Flash memo...  相似文献   
117.
Elevated circulating platelet-derived extracellular vesicles (pEVs) have been associated with arterial hypertension. The role of hypertension-mediated organ damage (HMOD) to induce EV release is still unknown. We studied the micro- and macro-vascular changes (retinal vascular density and pulse wave velocity), endothelial function (flow-mediated vasodilation of brachial artery and finger plethysmography), and assessed the psychosocial status (anxiety and depression) in hypertensive patients to determine their relationship with EV release. Pulse wave velocity showed a significant positive correlation with pEVs (r = 0.33; p = 0.01). Systolic blood pressure (SBP) negatively correlated with retinal vascularity. The superficial retinal vascular plexus density in the whole image showed a significant negative correlation with 24 h SBP (r = −0.38, p < 0.01), day-SBP (r = −0.35, p = 0.01), and night-SBP (r = −0.27, p = 0.04). pEVs did not show significant associations with microvascular damage (retinal vascular density), endothelial function (flow-mediated vasodilation of brachial artery and finger plethysmography), or psychosocial status (anxiety and depression). Our results indicate that the pEV levels were associated with macrovascular damage measured by PWV, whereas no significant association between pEVs and microvascular damage, endothelial function, or emotional status could be detected. The potential utility of pEV in clinical practice in the context of HMOD may be limited to macrovascular changes.  相似文献   
118.
Lipase B from Candida antarctica was immobilized on heterofunctional support octyl agarose activated with vinyl sulfone to prevent enzyme release under drastic conditions. Covalent attachment was established, but the blocking step using hexylamine, ethylenediamine or the amino acids glycine (Gly) and aspartic acid (Asp) altered the results. The activities were lower than those observed using the octyl biocatalyst, except when using ethylenediamine as blocking reagent and p-nitrophenol butyrate (pNPB) as substrate. The enzyme stability increased using these new biocatalysts at pH 7 and 9 using all blocking agents (much more significantly at pH 9), while it decreased at pH 5 except when using Gly as blocking agent. The stress inactivation of the biocatalysts decreased the enzyme activity versus three different substrates (pNPB, S-methyl mandelate and triacetin) in a relatively similar fashion. The tryptophane (Trp) fluorescence spectra were different for the biocatalysts, suggesting different enzyme conformations. However, the fluorescence spectra changes during the inactivation were not too different except for the biocatalyst blocked with Asp, suggesting that, except for this biocatalyst, the inactivation pathways may not be so different.  相似文献   
119.
The development of multi-target-directed ligands (MTDLs) would provide effective therapy of neurodegenerative diseases (ND) with complex and nonclear pathogenesis. A promising method to create such potential drugs is combining neuroactive pharmacophoric groups acting on different biotargets involved in the pathogenesis of ND. We developed a synthetic algorithm for the conjugation of indole derivatives and methylene blue (MB), which are pharmacophoric ligands that act on the key stages of pathogenesis. We synthesized hybrid structures and performed a comprehensive screening for a specific set of biotargets participating in the pathogenesis of ND (i.e., cholinesterases, NMDA receptor, mitochondria, and microtubules assembly). The results of the screening study enabled us to find two lead compounds (4h and 4i) which effectively inhibited cholinesterases and bound to the AChE PAS, possessed antioxidant activity, and stimulated the assembly of microtubules. One of them (4i) exhibited activity as a ligand for the ifenprodil-specific site of the NMDA receptor. In addition, this lead compound was able to bypass the inhibition of complex I and prevent calcium-induced mitochondrial depolarization, suggesting a neuroprotective property that was confirmed using a cellular calcium overload model of neurodegeneration. Thus, these new MB-cycloalkaneindole conjugates constitute a promising class of compounds for the development of multitarget neuroprotective drugs which simultaneously act on several targets, thereby providing cognitive stimulating, neuroprotective, and disease-modifying effects.  相似文献   
120.
Cannabis sativa (Cannabis) has recently been legalized in multiple countries globally for either its recreational or medicinal use. This, in turn, has led to a marked increase in the number of Cannabis varieties available for use in either market. However, little information currently exists on the genetic distinction between adopted varieties. Such fundamental knowledge is of considerable value and underpins the accelerated development of both a nascent pharmaceutical industry and the commercial recreational market. Therefore, in this study, we sought to assess genetic diversity across 10 Cannabis varieties by undertaking a reduced representation shotgun sequencing approach on 83 individual plants to identify variations which could be used to resolve the genetic structure of the assessed population. Such an approach also allowed for the identification of the genetic features putatively associated with the production of secondary metabolites in Cannabis. Initial analysis identified 3608 variants across the assessed population with phylogenetic analysis of this data subsequently enabling the confident grouping of each variety into distinct subpopulations. Within our dataset, the most diagnostically informative single nucleotide polymorphisms (SNPs) were determined to be associated with the long-terminal repeat (LTRs) class of retroelements, with 172 such SNPs used to fully resolve the genetic structure of the assessed population. These 172 SNPs could be used to design a targeted resequencing panel, which we propose could be used to rapidly screen different Cannabis plants to determine genetic relationships, as well as to provide a more robust, scientific classification of Cannabis varieties as the field moves into the pharmaceutical sphere.  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