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   258871篇
  免费   22049篇
  国内免费   12206篇
电工技术   16148篇
技术理论   12篇
综合类   16712篇
化学工业   39560篇
金属工艺   16157篇
机械仪表   16854篇
建筑科学   17598篇
矿业工程   7019篇
能源动力   6595篇
轻工业   15631篇
水利工程   5621篇
石油天然气   13934篇
武器工业   2300篇
无线电   28774篇
一般工业技术   36054篇
冶金工业   14411篇
原子能技术   6267篇
自动化技术   33479篇
  2023年   3291篇
  2022年   6298篇
  2021年   9478篇
  2020年   7216篇
  2019年   6114篇
  2018年   7422篇
  2017年   8252篇
  2016年   7688篇
  2015年   9585篇
  2014年   12402篇
  2013年   14823篇
  2012年   16751篇
  2011年   18177篇
  2010年   16203篇
  2009年   15731篇
  2008年   15678篇
  2007年   14940篇
  2006年   13905篇
  2005年   11492篇
  2004年   8652篇
  2003年   7811篇
  2002年   7731篇
  2001年   6843篇
  2000年   5685篇
  1999年   4666篇
  1998年   3393篇
  1997年   2873篇
  1996年   2508篇
  1995年   2196篇
  1994年   1813篇
  1993年   1518篇
  1992年   1390篇
  1991年   1224篇
  1990年   1198篇
  1989年   1102篇
  1988年   950篇
  1987年   884篇
  1986年   804篇
  1985年   729篇
  1984年   714篇
  1982年   681篇
  1981年   686篇
  1979年   744篇
  1978年   780篇
  1977年   747篇
  1976年   758篇
  1975年   714篇
  1974年   720篇
  1973年   723篇
  1972年   705篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
Synthetic active matters are perfect model systems for non-equilibrium thermodynamics and of great potential for novel biomedical and environmental applications. However, most applications are limited by the complicated and low-yield preparation, while a scalable synthesis for highly functional microswimmers is highly desired. In this paper, an all-solution synthesis method is developed where the gold-loaded titania-silica nanotree can be produced as a multi-functional self-propulsion microswimmer. By applying light, heat, and electric field, the Janus nanotree demonstrated multi-mode self-propulsion, including photochemical self-electrophoresis by UV and visible light radiation, thermophoresis by near-infrared light radiation, and induced-charge electrophoresis under AC electric field. Due to the scalable synthesis, the Janus nanotree is further demonstrated as a high-efficiency, low-cost, active adsorbent for water decontamination, where the toxic mercury ions can be reclaimed with enhanced efficiency.  相似文献   
62.
In order to prepare waterborne polyurethane with excellent water resistance and thermodynamic properties, a series of side chain fluorinated waterborne polyurethane-urea (FWPU-UA) was synthesized with polytetramethylene ether glycol, N-(2-methyl-1,3-propanediol-2′-)-perfluoro-1-butanesulfonyl amine (NPBA), isophorone diisocyanate, and isophoronediamine. With the increase of NPBA content, the weight loss temperature, glass transition temperature, and tensile strength of FWPU-UA were all improved. Gaussian fitting analysis of infrared data and density functional theory simulation proved that the introduction of fluorine side chains increased the interaction of hydrogen bonding in the FWPU-UA. X-ray photoelectron spectroscopy analysis indicated that the aggregation of fluorine atoms on the surface of film were caused by the migration and enrichment of fluorine side chains. Furthermore, the water resistance of polyurethane-urea film could be significantly improved by adding a small amount of NPBA, and the seven-day water absorption rate of polyurethane-urea film was reduced from 30.13% to 12.55%.  相似文献   
63.
Cytochrome P450s are heme-thiolate enzymes that participate in carbon source assimilation, natural compound biosynthesis and xenobiotic metabolism in all kingdoms of life. P450s can catalyze various reactions by using a wide range of organic compounds, thus exhibiting great potential in biotechnological applications. The catalytic reactions of P450s are driven by electron equivalents that are sourced from pyridine nucleotides and delivered by cognate or matching redox partners (RPs). The electron transfer (ET) route from RPs to P450s involves one or more redox center-containing domains. As the rate of ET is one of the main determinants of P450 efficacy, an in-depth understanding of the P450 ET pathway should increase our knowledge of these important enzymes and benefit their further applications. Here, the various P450 RP systems along with current understanding of their ET routes will be reviewed. Notably, state-of-the-art structural studies of the two main types of self-sufficient P450 will also be summarized.  相似文献   
64.
The sea urchin Diadema setosum is edible and desirable as food by locals in central Vietnam and a promising target for potential fishing. The lipid profiles of the gonads of the sea urchin inhabiting the coastal area in Nha Trang Bay are studied for the first time. The determination of the content of the total lipids (TL), total phospholipids (PL), monoacylglycerols (MAG), diacylglycerols (DAG), triacylglycerols (TAG), cholesterol (Chol), sterol esters, and free fatty acids (FFA) is analyzed by high-performance thin layer chromatography (HPTLC); the phosphatidylserine (PS), phosphatidylethanolamine (PE), phosphatidylinositol (PI), phosphatidylcholine (PC), lysophosphatidylcholine (LPC), and sphingomyelin (SM) are determined by high-pressure liquid chromatography (HPLC); and the fatty acid levels of TLs are identified using gas chromatography (GC). Non-polar TAG, FFA, Chol, and DAG dominated. The content of total PL is significant. PC is abundant among PL fractions, followed by PE, PI, and PS. The TLs contain a high proportion of PUFA, mainly due to arachidonic fatty acid and eicosapentanoic fatty acid. The (n−6)/(n−3) ratio is 1.68, and the atherogenic and thrombogenic indexes of D. setosum are 1.13 and 0.73. The results can be used in the development of marine bioprospecting and methodological approaches for the creation of functional substances.  相似文献   
65.
Refractories and Industrial Ceramics - The paper introduces a promising technology for utilizing a traditional scheme for implementing a flow-through micro-arc oxidation method to restore localized...  相似文献   
66.
高俊 《陶瓷》2021,(3):76-77
文化、精神以及思想等抽象内涵是紫砂壶艺术魅力的重要组成部分,这是由紫砂壶高雅超逸的艺术特征所决定的,是促进紫砂壶发展的内在动力。“汲浪壶”小巧雅致的身躯中包含着乘风破浪的勇敢无畏,是中华民族精神的一部分,由外在的艺术美过渡至内在的精神表达,体现出民族艺术品格。  相似文献   
67.
多堆厂址一级概率安全评价(PSA)研究中,机组数目的增加使得建模工作量剧增,给整个核电厂的风险评估带来困难。结合已有基础,本文研究了多堆厂址始发事件分析的筛选方法,提出利用堆芯损伤频率(CDF)上下限值评估方法,分析厂址内不同机组数对厂址CDF的影响。结果表明,双机组厂址适合优先进行具体分析。针对双机组核电站,对多堆厂址内各始发事件进行筛选。结果表明,丧失厂外电、丧失热阱等事件适合建模分析,并对其他筛选结果给出后续分析建议,为多堆厂址一级PSA后续事故序列建模工作提供了重要基础。  相似文献   
68.
69.
Protection of Metals and Physical Chemistry of Surfaces - Abstract—The ability of improving the protective properties of layers formed on zinc in the presence of sodium dodecylphosphonate...  相似文献   
70.
以4'-去甲基表鬼臼毒素和N-苄氧羰基甘氨酰-L-脯氨酸为原料,通过酯化反应首次得到两种不同构型的拼接产物(3a、3b),其结构经1HNMR、13C NMR和ESI-MS确认.利用MTT法考察化合物3a、3b对HepG2、THP-1、Hela、MCF-7细胞的抑制活性.结果表明,化合物3a、3b对四种细胞都具有抑制作用,以化合物3b对THP-1细胞的作用最突出,其抑制强度是依托泊苷的16.5倍.  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