全文获取类型
收费全文 | 117613篇 |
免费 | 3706篇 |
国内免费 | 1772篇 |
专业分类
电工技术 | 2585篇 |
技术理论 | 2篇 |
综合类 | 4488篇 |
化学工业 | 17530篇 |
金属工艺 | 6792篇 |
机械仪表 | 4977篇 |
建筑科学 | 4744篇 |
矿业工程 | 1609篇 |
能源动力 | 1967篇 |
轻工业 | 5500篇 |
水利工程 | 1791篇 |
石油天然气 | 2940篇 |
武器工业 | 242篇 |
无线电 | 13203篇 |
一般工业技术 | 20324篇 |
冶金工业 | 4179篇 |
原子能技术 | 687篇 |
自动化技术 | 29531篇 |
出版年
2024年 | 164篇 |
2023年 | 587篇 |
2022年 | 1002篇 |
2021年 | 1430篇 |
2020年 | 1091篇 |
2019年 | 907篇 |
2018年 | 15329篇 |
2017年 | 14431篇 |
2016年 | 10844篇 |
2015年 | 1885篇 |
2014年 | 1881篇 |
2013年 | 2236篇 |
2012年 | 5255篇 |
2011年 | 11697篇 |
2010年 | 10220篇 |
2009年 | 7336篇 |
2008年 | 8495篇 |
2007年 | 9388篇 |
2006年 | 1932篇 |
2005年 | 2835篇 |
2004年 | 2226篇 |
2003年 | 2109篇 |
2002年 | 1414篇 |
2001年 | 851篇 |
2000年 | 1044篇 |
1999年 | 1079篇 |
1998年 | 839篇 |
1997年 | 733篇 |
1996年 | 730篇 |
1995年 | 569篇 |
1994年 | 468篇 |
1993年 | 355篇 |
1992年 | 275篇 |
1991年 | 215篇 |
1990年 | 148篇 |
1989年 | 127篇 |
1988年 | 120篇 |
1987年 | 69篇 |
1986年 | 50篇 |
1982年 | 31篇 |
1968年 | 43篇 |
1967年 | 33篇 |
1966年 | 42篇 |
1965年 | 44篇 |
1959年 | 35篇 |
1958年 | 37篇 |
1957年 | 36篇 |
1956年 | 34篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
Nuonan Bai Weirong Chen Lijin Luo Wei Tong Cuilian Wen Xuan Zhan Baisheng Sa 《Journal of the American Ceramic Society》2021,104(7):3058-3072
In this paper, the boron-containing mesoporous bioactive glass (MBG) nanospheres have been successfully synthesized by modified sol-gel method assisted by surfactant, and the effect of boron substitution on structure and bioactivity was evaluated by combining experiments and ab initio molecular dynamics (AIMD) simulations. All of the samples exhibit regularly uniform mesoporous spherical microstructure with an average size of about 60 nm, and the boron-containing MBGs show higher specific surface area with the value up to 416.20 m2/g. The simulated body fluid (SBF) immersion test confirms that the deposited hydroxyapatite (HA) evidently increases with the increasing of boron content, indicating that the biological behavior has been significantly improved resulting from incorporation of boron. Additionally, our results also reveal that B2O3 substitution has positive impact on cell proliferation of human periodontal ligament cells (hPDLCs) at lower extracted concentration. Furthermore, AIMD simulation is employed to understand the relationship between structural changes and in vitro bioactivity in terms of structural information, especially the boron coordination number. The results illustrate that the boron-containing MBG nanospheres with excellent bioactivity are great potential for biomedical applications. 相似文献
942.
Jun Chen Wan-Qing Xue Chang-Ming Xu Pai-Feng Luo Ji-Gui Cheng Ying-Wei Lu 《Journal of the American Ceramic Society》2021,104(8):3855-3861
Monodisperse ZrO2 ceramic beads with size larger than 1 mm have been prepared by an improved micro-droplet spray forming process, through which a compressor and a dispenser were employed to produce droplets continuously. Furthermore, the slurry recipe and drying temperature have been optimized to enhance the sphericity and smoothness of the beads. The sintered ZrO2 ceramic beads present promising mechanical performance, including a relative density of 84.6%, a crush strength of 256.2 ± 36.6 N as well as a Vickers hardness of 1344.4 ± 58.3 HV. Such procedure reveals great potential in mass production of ceramic beads. 相似文献
943.
Hu Chuang Zang Guo-Long Luo Jun-Tao Liu Qi Zhao Quan 《Journal of Applied Electrochemistry》2021,51(6):847-859
Journal of Applied Electrochemistry - The electrocatalytic reduction of CO2 is a promising research direction in resource utilization and sustainable energy development. However, there is still a... 相似文献
944.
In this paper, aramid fiber (AF)/ethylene-propylene-diene monomer (EPDM) microcellular foams added with different content of AF are prepared by the supercritical foaming method. The effect of the AF content on the rheological behavior, mechanical properties, thermal properties and cellular structure of the AF/EPDM microcellular foams has been systematically studied. The research illustrates that compared with pure EPDM, the AF/EPDM matrix has greater viscosity and modulus, which is conducive to reduce the cell size and increase its density. And the thermal stability of EPDM foams is improved with the addition of aramid fiber. Meanwhile, when the content of AF is added to 1 wt%, the AF/EPDM microcellular foam exhibits a relatively low thermal diffusion coefficient and apparent density with the thermal conductivity to 0.06 W/mK. When the AF is added to 5 wt%, the tensile strength of the AF/EPDM microcellular foam increases to 1.95 MPa, which is improved by 47% compared with that of the pure EPDM foam. Furthermore, when the compressive strain reaches to 50%, the compressive strength of the AF/EPDM microcellular foam is 0.48 MPa, improved by 296% compared with that of the pure EPDM foam. 相似文献
945.
Polymer or polymer gels have been widely used to control excessive water during oil production by homogenizing injection profile and reducing water cut in the produced fluids. However, the gels used are generally unable to selectively minimize water production, and face the challenge of syneresis of gels under high temperature and high salinity environment. In this work, melamine-formaldehyde sponge was modified with AlCl3 solution, rendering a transition from hydrophilic to hydrophobic state with a water contact angle of 130° on the surface of the modified product. Filtration results show that mineral oil and water can be selectively separated with the hydrophobically modified sponge powders. Simulated water shutoff experiments demonstrated the blockage efficiency against water was 30% higher than that against oil, and the oil production was increased 7.4% after blocking. The parallel profile control tests confirmed that the fraction flow of high permeable channel decreased about 75%, accompanied with 60% rise of oil recovery factor. These results indicated that such hydrophobic materials can significantly reduce excessive water production, and this work provided a new idea to offer a low-cost hydrophobic material for conformance control and water shutoff during oil production. 相似文献
946.
947.
A. Luo D. L. Jacobson R. Ponnappan 《Journal of Materials Engineering and Performance》1992,1(6):755-761
Thermal energy storage capsules made of Inconel 617 alloy were filled with high- purity LiF- MgF2- KF salts and thermally
cycled at 983 ± 100 K in vacuum for up to 5 years. The containment life performance characteristics with fluoride salts and
in vacuum were examined. Metallographic study indicated that the inside surfaces of the post- test containers had a corrosion
damage of 100 um in depth after 5 years of thermal cycling. The outer surface showed a vaporization damage of 120 μm after
the same period. After 5 years of thermal cycling, the aluminum concentration at the capsule interior surface was reduced
to 0.424 wt% from a nominal concentration of 1.34 wt% and chromium was reduced to 18.7 wt% from a nominal concentration of
21.8 wt%. A more significant depletion of aluminum and chromium was observed at the outer surfaces. Atomic absorption spectroscopy
(AAS) and differential thermal analysis (DTA) were used to reveal the alloying element dissolution and the changes in melting
temperature and heat of fusion of fluoride salts during thermal cycling. A modified diffusion equation for a one-dimensional
semi-infinite bar was applied to the depletion of aluminum on the interior surfaces of the containers. Good agreement was
obtained between the analysis and the measured concentration profiles.
Inconel 617 is a registered trademark of the Inco Alloys International, Inc. 相似文献
948.
Ling Yang M. T. Simnad G. Derge 《JOM Journal of the Minerals, Metals and Materials Society》1956,8(11):1577-1580
Self-diffusion coefficients of iron in molten Fe-C alloys have been measured by using the capillary method. In addition, the samples have been autoradiographed and sectioned to insure that no significant convection has occurred during the diffusion. The results can be represented by the equation D = 4.3×10?3 exp (—12.200/RT) for carbon = 4.6 pct and T = 1513° to 1633°K; and D = 1.0×10?2 exp (—15,700/RT) for carbon = 2.5 pct and T = 1613° to 1673°K. The D values are higher and the heat of activation for diffusion lower in alloys containing more carbon. Calculation based on the Einstein-Stokes equation indicates that the diffusing species is iron ion. 相似文献
949.
Jeong-Sun Oh Joon-Hyung An Sun-Ok Lee Yeon-Hum Yun Bo-An Kang Sang-Bok Kim Kyu-Seog Hwang 《Metals and Materials International》2002,8(5):459-462
We prepared zirconia thin films on (100) Si wafer by using a chemical solution deposition with a zirconium naphthenate as
a starting material. The films were pyrolyzed at 500°C for 10 min and finally annealed for 30 min in air at 500°C. Amorphous
films after annealing had no distinct structure and were uniform along the cross section line.In vitro formation of the calcium phosphate was evaluated by the field emission-scanning electron microscope, energy dispersive X-ray
spectrometer and Fourier transform infrared spectroscopy. 相似文献
950.
Keiichiro Oh-ishi John Boydon Terry R. McNelley 《Journal of Materials Engineering and Performance》2004,13(6):710-719
The importance of grain size refinement in enabling superplasticity is reviewed, and the current understanding of grain boundary
characteristics is summarized. The application of orientation-imaging microscopy (OIM) methods to the processing response
and the deformation and failure modes in superplastic aluminum alloys are illustrated through microtexture analysis and determination
of grain boundary characteristics in selected commercial materials. Continuous and discontinuous recrystallization reactions
exhibit distinct microtextures and grain boundary characteristics. The application of OIM and microtexture analysis to the
evaluation of both deformation and failure mechanisms during superplastic forming is illustrated.
This paper was presented at the International Symposium on Superplasticity and Superplastic Forming, sponsored by the Manufacturing
Critical Sector at the ASM International AeroMat 2004 Conference and Exposition, June 8–9, 2004, in Seattle, WA. The symposium
was organized by Daniel G. Sanders, The Boeing Company. 相似文献