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   4440篇
  免费   279篇
  国内免费   90篇
电工技术   175篇
综合类   250篇
化学工业   613篇
金属工艺   264篇
机械仪表   258篇
建筑科学   420篇
矿业工程   71篇
能源动力   126篇
轻工业   208篇
水利工程   65篇
石油天然气   328篇
武器工业   31篇
无线电   583篇
一般工业技术   632篇
冶金工业   250篇
原子能技术   55篇
自动化技术   480篇
  2025年   8篇
  2024年   65篇
  2023年   87篇
  2022年   99篇
  2021年   144篇
  2020年   123篇
  2019年   118篇
  2018年   128篇
  2017年   124篇
  2016年   109篇
  2015年   151篇
  2014年   168篇
  2013年   238篇
  2012年   232篇
  2011年   270篇
  2010年   198篇
  2009年   169篇
  2008年   207篇
  2007年   190篇
  2006年   226篇
  2005年   204篇
  2004年   152篇
  2003年   116篇
  2002年   99篇
  2001年   92篇
  2000年   116篇
  1999年   123篇
  1998年   134篇
  1997年   109篇
  1996年   107篇
  1995年   100篇
  1994年   81篇
  1993年   67篇
  1992年   58篇
  1991年   35篇
  1990年   43篇
  1989年   18篇
  1988年   14篇
  1987年   16篇
  1986年   15篇
  1985年   13篇
  1984年   11篇
  1983年   11篇
  1982年   6篇
  1981年   2篇
  1977年   3篇
  1976年   2篇
  1975年   2篇
  1967年   1篇
  1965年   1篇
排序方式: 共有4809条查询结果,搜索用时 15 毫秒
71.
    
The influences of heat treatment and test condition on the microstructure and stress rupture properties of a Ni-Mo-Cr-Fe base corrosion-resistant superalloy have been investigated in this paper. Optical microscope and scanning electron microscope were employed for the microstructure observation, and X-ray diffraction, electron probe micro-analyzer, and transmission electron microscope were used for phase determination. It was found that the grain size increased and the volume fractions of initial M6C carbides decreased along with the increase in solution treatment temperature. When tested at 650 °C/320 MPa, the stress rupture lives decreased with the increase in solution treatment temperature, but the stress rupture lives increased slightly at first and then decreased for the samples solution heat treated at 1220 °C when tested at 700 °C/240 MPa. The elongations showed the descendent trends under these two conditions. The stress rupture life and elongation for the aged samples all showed a noticeable improvement at 650 °C/320 MPa, but there was no noticeable improvement at 700 °C/240 MPa. The reasons can be attributed to the grain size, test conditions, and the initial and secondary carbides.  相似文献   
72.
库车坳陷中新生界天然气成藏动力学研究   总被引:3,自引:0,他引:3  
库车坳陷是塔里木盆地北部一近东西走向的狭长坳陷,以中新生代地层为主。地层压实排出水离心流区位于拜城凹陷和阳霞凹陷,克拉苏-依奇克里克构造带、东秋里塔克构造带和塔北前缘隆起带为越流泄水区。库车坳陷在早第三纪-库车早期主要为油藏、凝析油气藏形成时期;库车晚期-第四纪西域期是气藏的主要形成时期。天然气经短距离侧向汇聚,通过沟通源岩和圈闭的断裂垂向富集。在强烈的构造挤压和气体充注条件下,被具有很好封闭性的下第三系膏盐岩严密封闭,形成异常高压气藏。下伏三叠系-侏罗系源岩的沉积埋藏水、粘土矿物脱出水沿断裂带伴随天然气向浅部越流,在构造顶部形成相对低矿化度的地下水化学特征。  相似文献   
73.
Zhou  Zhixin  Shao  Chenning  Zheng  Haonan  Zhou  Huimin  Yang  Xin  Lou  Xiongwei  Li  Jian  Hui  Guohua  Zhao  Zhidong 《Wireless Networks》2020,26(4):2797-2808
Wireless Networks - Utility tunnel is one of the important infrastructures for the planning and building of smart city. It is of great significance to improve the efficiency of maintenance and...  相似文献   
74.
到目前为止,高效液相色谱仪及其与质谱仪的联用设备已经成为检测和研究工作的重要工具。高效液相色谱法对分析极性、难挥发和不稳定化合物是必不可少的,所以被广泛用于许多领域。不过,挥之不去的故障阴影在常规操作过程中总是影响测试结果的准确性和引起运行中断的运转效率。作为交流和参考用材料,本文提供了使用高效液相色谱仪例行分析过程中日常所遇到的故障问题(表现在泵、峰形、基线等方面)、原因分析及解决方法。  相似文献   
75.
Gold/1-butyl-3-methylimidazolium hexafluorophosphate (Au/[Bmim][PF6]) nanofluids containing different stabilizing agents were fabricated by a facile one-step chemical reduction method, of which the nanofluids stabilized by cetyltrimethylammonium bromide (CTABr) exhibited ultrahighly thermodynamic stability. The transmission electron microscopy, UV-visible absorption, Fourier transform infrared, and X-ray photoelectron characterizations were conducted to reveal the stable mechanism. Then, the tribological properties of these ionic liquid (IL)-based gold nanofluids were first investigated in more detail. In comparison with pure [Bmim][PF6] and the nanofluids possessing poor stability, the nanofluids with high stability exhibited much better friction-reduction and anti-wear properties. For instance, the friction coefficient and wear volume lubricated by the nanofluid with rather low volumetric concentration (1.02 × 10-3%) stabilized by CTABr under 800 N are 13.8 and 45.4% lower than that of pure [Bmim][PF6], confirming that soft Au nanoparticles (Au NPs) also can be excellent additives for high performance lubricants especially under high loads. Moreover, the thermal conductivity (TC) of the stable nanofluids with three volumetric fraction (2.55 × 10-4, 5.1 × 10-4, and 1.02 × 10-3%) was also measured by a transient hot wire method as a function of temperature (33 to 81°C). The results indicate that the TC of the nanofluid (1.02 × 10-3%) is 13.1% higher than that of [Bmim][PF6] at 81°C but no obvious variation at 33°C. The conspicuously temperature-dependent and greatly enhanced TC of Au/[Bmim][PF6] nanofluids stabilized by CTABr could be attributed to micro-convection caused by the Brownian motion of Au NPs. Our results should open new avenues to utilize Au NPs and ILs in tribology and the high-temperature heat transfer field.  相似文献   
76.
Zhang Z  Yu K  Liao N  Yin H  Lou L  Yu Q  Liao Y  Zhu Z 《Nanoscale》2011,3(12):5000-5006
A ZnO photonic amorphous diamond nanostructure was successfully synthesised using a feather barb of the Rosy-Faced Lovebird as supporting template via a facile sol-gel process. Different from ordered structures, an isotropic PBG around 500 nm was evidenced from reflectance spectra and an optical metallurgical microscopy image, which overlaps with the visible emission peak of ZnO. As a result, the inhibition of visible emission inside the PBG and the enhancement of UV emission at the PBG edges have both been observed, which is independent from the incident angle. Moreover, the rapid thermal annealing can also help improve the crystallinity of ZnO and raise the UV/visible emission ratio without affecting the structure. These results can be very useful for the study of the modification of the optical emission properties of ZnO and other semiconductor materials as well as research on ZnO random lasing.  相似文献   
77.
In the design of chemical/energy production systems, a major challenge is to identify the bottleneck issues and improve its sustainability effectively. Due to the multi-dimensional feature of sustainability, how to account for the impacts of various design factors and the cause-and-effect relationships can be very difficult. This paper will present a sustainability root cause analysis method based on the combination of Pareto Analysis and Fishbone diagram. The sustainability of the process is assessed incorporating economic, environmental, societal and efficiency concerns.This methodology is able to help the designers focus the attention on the most important fundamental causes, discover opportunities for sustainability improvement and provide critical guidance to design for sustainability. The efficacy of this methodology will be demonstrated through a case study on a biodiesel production technology.  相似文献   
78.
Cathodic reactions, specially the oxygen and hydrogen activities, have been extensively investigated on carbon steel in simulated fuel-grade ethanol (SFGE) environments using cathodic potentiodynamic polarization and electrochemical impedance spectroscopy. Under normal conditions, oxygen reduction is the major cathodic reaction for carbon steel in SFGE. Hydrogen evolution, confirmed by hydrogen permeation test, is activated by de-aeration and at much higher cathodic overpotential. The dissociation of acetic acid in SFGE enhances the proton related cathodic reactions. Water in ethanol can increase the proton dissociation rate, resulting in a higher cathodic current density. At potentials close to free corrosion potential, the reduction of surface oxidized products contributes to the cathodic activities in SFGE. Based on this study, the possible effects of cathodic reactions on corrosion of carbon steel in SFGE are also discussed.  相似文献   
79.
9-Amino epi-quinine was used as a ligand in the atom transfer radical polymerization (ATRP) for the first time, and high monomer conversion as well as small polydispersity could be obtained. The 9-amino epi-quinine-containing organosilane was synthesized and immobilized onto three different silica supports, i.e., fumed SiO2, SBA-15, and MCM-48, followed by complexing with CuBr. With the MCM-48 supported catalyst, polymerization of methyl methacrylate achieved high monomer conversion, small polydispersity, and low residual copper content in the product. This heterogeneous catalyst could also be recycled effectively.  相似文献   
80.
本文对封头旋压液压仿形活动模板的设计理论进行了研究和探索,首次得出了渐开线型活动模板有关参数的确定方法,并据之设计出了Φ2000×16封头的活动仿形模板。本文取得的结果还可为其它旋压件旋轮运动轨迹的确定提供参考。  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