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   291464篇
  免费   6136篇
  国内免费   2076篇
电工技术   6842篇
技术理论   1篇
综合类   2255篇
化学工业   42761篇
金属工艺   11816篇
机械仪表   10580篇
建筑科学   8646篇
矿业工程   2085篇
能源动力   7214篇
轻工业   24831篇
水利工程   3105篇
石油天然气   5972篇
武器工业   280篇
无线电   38422篇
一般工业技术   53884篇
冶金工业   48089篇
原子能技术   5793篇
自动化技术   27100篇
  2022年   2115篇
  2021年   3269篇
  2020年   2453篇
  2019年   2863篇
  2018年   4376篇
  2017年   4515篇
  2016年   4584篇
  2015年   3465篇
  2014年   5576篇
  2013年   13071篇
  2012年   8489篇
  2011年   10886篇
  2010年   8763篇
  2009年   9590篇
  2008年   10277篇
  2007年   10236篇
  2006年   9554篇
  2005年   8710篇
  2004年   7892篇
  2003年   7646篇
  2002年   7255篇
  2001年   7237篇
  2000年   7049篇
  1999年   7196篇
  1998年   15011篇
  1997年   10953篇
  1996年   8767篇
  1995年   6935篇
  1994年   6142篇
  1993年   5900篇
  1992年   4806篇
  1991年   4408篇
  1990年   4194篇
  1989年   3893篇
  1988年   3718篇
  1987年   3219篇
  1986年   3099篇
  1985年   3632篇
  1984年   3399篇
  1983年   3042篇
  1982年   2871篇
  1981年   2964篇
  1980年   2763篇
  1979年   2650篇
  1978年   2499篇
  1977年   2945篇
  1976年   3554篇
  1975年   2316篇
  1974年   2312篇
  1973年   2318篇
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
1.
Virtual Reality - It is generally accepted that natural environments reduce stress and improve mood. Since access to natural environments is sometimes limited, virtual natural environments,...  相似文献   
2.
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   
3.
The effects of high-pressure-modified soy 11S globulin (0.1, 200, and 400 MPa) on the gel properties, water-holding capacity, and water mobility of pork batter were investigated. The high-pressure-modified soy 11S globulin significantly increased (P < 0.05) the emulsion stability, cooking yield, hardness, springiness, chewiness, resilience, cohesiveness, the a* and b* values, and the G′ and G′′ values of pork batter at 80 °C, compared with those of 0.1 MPa-modified globulin. In contrast, the centrifugal loss and initial relaxation time of T2b, T21, and T22 significantly decreased (P < 0.05). Meanwhile, the microstructure was denser, and the voids were smaller and more uniform compared with those of 0.1 MPa-modified globulin. In addition, the sample with 11S globulin modified at 400 MPa had the best water-holding capacity, gel structure, and gel properties among the samples. Overall, the use of high-pressure-modified soy 11S globulin improved the gel properties and water-holding capacity of pork batter, especially under 400 MPa.  相似文献   
4.
Engineering new glass compositions have experienced a sturdy tendency to move forward from (educated) trial-and-error to data- and simulation-driven strategies. In this work, we developed a computer program that combines data-driven predictive models (in this case, neural networks) with a genetic algorithm to design glass compositions with desired combinations of properties. First, we induced predictive models for the glass transition temperature (Tg) using a dataset of 45,302 compositions with 39 different chemical elements, and for the refractive index (nd) using a dataset of 41,225 compositions with 38 different chemical elements. Then, we searched for relevant glass compositions using a genetic algorithm informed by a design trend of glasses having high nd (1.7 or more) and low Tg (500 °C or less). Two candidate compositions suggested by the combined algorithms were selected and produced in the laboratory. These compositions are significantly different from those in the datasets used to induce the predictive models, showing that the used method is indeed capable of exploration. Both glasses met the constraints of the work, which supports the proposed framework. Therefore, this new tool can be immediately used for accelerating the design of new glasses. These results are a stepping stone in the pathway of machine learning-guided design of novel glasses.  相似文献   
5.
With the continuous development of bionics, such as, geckos and virginia creeper with both superhydrophobic and super-adhesive, the surface wetting and super-adhesive properties of various porous materials have attracted extensive attention of the scientific and medical communities. Here, the honeycomb polyurethane (PU) porous films with strong adhesion were successfully prepared by microphase separation method and the effects of growth parameters on their microstructure and adhesive strength to ice were investigated. It was found that a high relative humidity (e.g., 100%) and a low solution concentration (e.g., 2%) facilitated the formation of ordered honeycomb PU porous films, and as-prepared PU pores with average pore diameter as small as 5 μm are better ordered and more uniform than these in related documents. Although the contact angle of water droplets on the surface of PU porous films increased from the premodification value of 85–130° to more than 160° after surface modification with polydopamine (PDA), the corresponding rolling angle remained approximately constant (180°), indicating that the surface of PU porous films has strong adhesion similar to geckos and virginia creeper. Furthermore, at lower temperature, the PU porous films exhibited the high adhesive strength of 142.13 kPa on ice, which was strongly dependent on the porous microstructures and surface compositions. The improved adhesive behavior to ice of honeycomb PU porous films modified with PDA provides new strategies for surface modification of materials and potential applications in medical domain.  相似文献   
6.
To investigate the evolution of the structural and enhanced magnetic properties of GdMnO3 systems induced by the substitution of Mn with Cr, polycrystalline GdMn1-xCrxO3 samples were synthesized via solid-state reactions. XRD characterization shows that all GdMn1-xCrxO3 compounds with single-phase structures crystallize well and that Cr3+ ions entering the lattice sites of GdMnO3 induce structural distortion. SEM results indicate that the grain size of the synthesized samples (a few microns) decreases as the Cr substitution concentration increases. Positron annihilation lifetime spectroscopy reveals that vacancy-type defects occur in GdMn1-xCrxO3 ceramics and that the vacancy size and concentration clearly change with the Cr content. The temperature and field dependence of the magnetization curves show that Cr substitution significantly influences the magnetic ordering of the gadolinium sublattice, improving the weak ferromagnetic transition temperature and magnetization of GdMn1-xCrxO3. The enhanced magnetization of GdMn1-xCrxO3 is closely related to the vacancy defect concentration.  相似文献   
7.
Semiconductors - Abstract—In our work, we carry out a structural-spectroscopic study of AlGaN/GaN epitaxial layers grown by molecular-beam epitaxy with nitrogen-plasma activation on a hybrid...  相似文献   
8.
Journal of Communications Technology and Electronics - In recent years, there has been a rapid improvement in photonics products due to the use of multilayer heterostructures grown on the basis of...  相似文献   
9.
In this investigation, low-cement castables were prepared using 70% alumina grog aggregates obtained from crushed alumina brick waste. The aggregates were thermally treated at 1550 °C for 3 h. Four types of low-cement castables were prepared with various types of aggregates (alumina grog with or without thermal treatment) and fillers (with or without zircon addition), and they were evaluated in terms of their physical, thermal, and chemical properties. Microstructural analysis via scanning electron microscopy (SEM) was performed on the castables before and after slag attack. Compared to the other fabricated castables, the thermally treated alumina grog castables with zircon showed better physical properties, such as a higher bulk density, cold crushing strength, and modulus of rupture and a lower apparent porosity and water absorption. In addition, they had a higher positive linear thermal expansion, refractoriness under load, permanent linear change, and hot modulus of rupture. The results of the SEM with energy dispersive X-ray analysis of the prepared castables confirmed that the mullite and anorthite phases were predominant when zircon was not added and the zircon–mullite phase additionally appeared upon the incorporation of zircon. A quantitative elemental analysis via X-ray fluorescence spectroscopy was employed to determine the composition of the castables. X-ray diffraction analysis showed that the alumina grog castables had a high mullite and low anorthite content, and the thermally treated alumina grog had a high anorthite, low mullite, and high zircon content. The improvement in the mechanical and thermo-mechanical properties of the castables with thermally treated alumina grog and added zircon can be attributed to the formation of the zircon–mullite phase with a low mullite phase content.  相似文献   
10.
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