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   18398篇
  免费   1966篇
  国内免费   1027篇
电工技术   1243篇
技术理论   3篇
综合类   1383篇
化学工业   2846篇
金属工艺   1065篇
机械仪表   1219篇
建筑科学   1662篇
矿业工程   501篇
能源动力   492篇
轻工业   1276篇
水利工程   318篇
石油天然气   925篇
武器工业   172篇
无线电   2192篇
一般工业技术   2141篇
冶金工业   968篇
原子能技术   196篇
自动化技术   2789篇
  2024年   150篇
  2023年   363篇
  2022年   688篇
  2021年   946篇
  2020年   697篇
  2019年   534篇
  2018年   548篇
  2017年   583篇
  2016年   567篇
  2015年   806篇
  2014年   943篇
  2013年   1025篇
  2012年   1113篇
  2011年   1139篇
  2010年   1060篇
  2009年   962篇
  2008年   1036篇
  2007年   958篇
  2006年   933篇
  2005年   864篇
  2004年   704篇
  2003年   528篇
  2002年   536篇
  2001年   467篇
  2000年   455篇
  1999年   449篇
  1998年   367篇
  1997年   350篇
  1996年   304篇
  1995年   250篇
  1994年   211篇
  1993年   193篇
  1992年   130篇
  1991年   92篇
  1990年   87篇
  1989年   80篇
  1988年   51篇
  1987年   36篇
  1986年   35篇
  1985年   16篇
  1984年   17篇
  1983年   17篇
  1982年   18篇
  1981年   9篇
  1980年   24篇
  1979年   6篇
  1978年   5篇
  1977年   13篇
  1973年   4篇
  1971年   4篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
A novel conjugated cationic polyfluorene containing aminated tetraphenylethene (ATPE) unit is developed as a sensitive and selective fluorescence probe for heparin detection based on the combination of aggregation-induced emissive property of the ATPE units and the FRET process from the blue-emissive polyfluorene segments to the yellow-emissive ATPE units. The addition of anionic heparin will lead to the formation of heparin/polymer complexes, and turn on the aggregation-induced yellow emission of the ATPE units. A good linear relationship is found between the yellow emission intensity of the ATPE units and the heparin concentrations with a limit of detection of 30 nM in aqueous buffer.  相似文献   
992.
Metal-based anticancer agents with non-DNA targets are anticipated for overcoming cisplatin resistance problems. Gold complexes are generally known to undergo ligand exchange or redox reactions with thiols, and hence, are potentially useful agents that could target thiol-containing enzymes, but not DNA. Recent studies have shown that deubiquitinases (DUBs), key enzymes regulating proteasome-related protein homeostasis, are potential anticancer targets of both gold(I) and gold(III) complexes. In this review, the current status of gold complexes as DUB inhibitors is discussed. In particular, auranofin and cyclometalated gold(III) complexes containing dithiocarbamate ligands (e.g., [(AuIII(C N)(DEDT)]+, HC N=2-phenylpyridine, DEDT=diethyldithiocarbamate) are highlighted as examples of DUB inhibitors. The mechanisms of their anticancer action, together with in vitro and/or in vivo antitumor potencies, are also explored.  相似文献   
993.
Tensile properties of the high-deformability dual-phase ferrite-bainite X70 pipeline steel have been investigated at room temperature under the strain rates of 2.5 × 10?5, 1.25 × 10?4, 2.5 × 10?3, and 1.25 × 10?2 s?1. The microstructures at different amount of plastic deformation were examined by using scanning and transmission electron microscopy. Generally, the ductility of typical body-centered cubic steels is reduced when its stain rate increases. However, we observed a different ductility dependence on strain rates in the dual-phase X70 pipeline steel. The uniform elongation (UEL%) and elongation to fracture (EL%) at the strain rate of 2.5 × 10?3 s?1 increase about 54 and 74%, respectively, compared to those at 2.5 × 10?5 s?1. The UEL% and EL% reach to their maximum at the strain rate of 2.5 × 10?3 s?1. This phenomenon was explained by the observed grain structures and dislocation configurations. Whether or not the ductility can be enhanced with increasing strain rates depends on the competition between the homogenization of plastic deformation among the microconstituents (ultra-fine ferrite grains, relatively coarse ferrite grains as well as bainite) and the progress of cracks formed as a consequence of localized inconsistent plastic deformation.  相似文献   
994.
An analytical method for synthesizing and selecting desired four-bar straight-line mechanisms based on solution regions is presented. Given two fixed pivots, the point position and direction of the target straight-line, an infinite number of mechanism solutions can be produced by employing this method, both in the general case and all three special cases. Unifying the straight-line direction and the displacement from the given point to the instant center into the same form with different angles as parameters, infinite mechanism solutions can be expressed with different solution region charts. The mechanism property graphs have been computed to enable the designers to find out the involved mechanism information more intuitively and avoid aimlessness in selecting optimal mechanisms.  相似文献   
995.
This study aimed to evaluate the effects of microbial transglutaminase (MTG)‐mediated modification on the structure, digestibility and immunoreactivities of glycinin. Glycinin was separated from soya bean and cross‐linked with MTG, and the sulphate‐polyacrylamide gel electrophoresis (SDS‐PAGE) showed that the molecular weight of cross‐linked glycinin was higher than that of native glycinin. Individual MTG cross‐linking could maintain stable secondary structures and spatial structure. Sequential heat denaturation and MTG cross‐linking could promote the unfolding of protein structures and reduce their hydrophobicity. The digestibility of glycinin was decreased, and its immunoreactivities were increased because of MTG‐induced structural alteration, including primary and spatial structures.  相似文献   
996.
Nonalcoholic beverages are usually consumed accompanying alcoholic drinks, and their effects on alcohol metabolism are unclear in vivo. In this study, the effects of 20 nonalcoholic beverages on alcohol metabolism and liver injury caused by alcohol were evaluated in mice. Kunming mice were orally fed with alcohol (52%, v/v) and beverages. The concentrations of ethanol and acetaldehyde in blood as well as the activities of alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) in liver were assessed to indicate alcohol metabolism. The levels of aspartate aminotransferase (AST) and alanine transaminase (ALT) in serum as well as the levels of malonaldehyde (MDA) and superoxide dismutase (SOD) in liver were measured to reflect the alcohol-induced liver injury. The results showed that the treatment of soda water, green tea and honey chrysanthemum tea could accelerate ethanol metabolism and prevent liver injuries caused by alcohol when companied with excessive alcohol drinking. They might be potential dietary supplements for the alleviation of harmful effects from excessive alcohol consumption. On the contrary, some beverages such as fresh orange juice and red bull are not advised to drink when companied with alcohol consumption due to their adverse effects on ethanol induced liver injury.  相似文献   
997.
研究一类含参数的非线性四阶多点边值问题,当参数属于一定范围时,利用常数变易法求得与边值问题等价的函数,并对它进行上下界估计,同时利用锥不动点定理,证明该四阶边值问题正解的存在性.  相似文献   
998.
A broadband circularly polarized patch antenna with suspended structure is proposed. The suspended patch has a bow‐tie structure and a gap‐coupled feed. By connecting a resistor load to another gap‐coupled feed port at the opposite position, a wide impedance and axial ratio (AR) bandwidths are obtained. The proposed design has a very simple antenna structure with an impedance bandwidth of 44.5% and a 3‐dB AR bandwidth of 33.8%, respectively. The results show that the bandwidth of the patch antenna is successfully broadened using the suspended configuration, gap‐coupled feed, and resistor loading. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:587–593, 2014.  相似文献   
999.
童欣瑜 《建筑施工》2014,(8):895-897
在沿海地区软土地基工程建设中,大面积地坪的不均匀沉降一直是一个令人头痛的问题.以上海浦东国际机场西货运区3#货运站工程为例,介绍了真空预压法首次在单体面积超过9万m2的仓库项目工程中的使用,对真空预压的各个技术要点进行了阐述,在工程实践中取得了良好的成效,为相关工程积累了宝贵经验.  相似文献   
1000.

Relationships among average spectral reflectance measured in the visible and near infrared (VNIR) region (0.4-2.5 w m), dielectric constant measured in the microwave region (0.5-18 GHz) and chemical content of 34 sedimentary rock samples were measured. The natural logarithm of the average spectral reflectance and that of the imaginary part of the dielectric constant were negatively correlated ( 𝜌 =-0.60). The average spectral reflectance correlated negatively with Fe2O3 ( 𝜌 =-0.61), Al2O3 ( 𝜌 =-0.63), K2O ( 𝜌 =-0.60), TiO2 ( 𝜌 =-0.64), and P2O5 ( 𝜌 =-0.60). The average imaginary part of the dielectric constant correlated positively with Fe2O3 ( 𝜌 =0.76), K2O ( 𝜌 =0.62), and TiO2 ( 𝜌 =0.70). The average real part of the dielectric constant is highly correlated with the weight loss of the rocks due to burning (burnt loss) ( 𝜌 =0.92), SiO2 ( 𝜌 =-0.96), and CaO ( 𝜌 =0.91).  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