全文获取类型
收费全文 | 39371篇 |
免费 | 3345篇 |
国内免费 | 1672篇 |
专业分类
电工技术 | 2310篇 |
技术理论 | 1篇 |
综合类 | 2469篇 |
化学工业 | 6564篇 |
金属工艺 | 1995篇 |
机械仪表 | 2580篇 |
建筑科学 | 3135篇 |
矿业工程 | 1227篇 |
能源动力 | 1073篇 |
轻工业 | 2513篇 |
水利工程 | 760篇 |
石油天然气 | 2321篇 |
武器工业 | 309篇 |
无线电 | 4724篇 |
一般工业技术 | 4923篇 |
冶金工业 | 1907篇 |
原子能技术 | 483篇 |
自动化技术 | 5094篇 |
出版年
2024年 | 76篇 |
2023年 | 700篇 |
2022年 | 943篇 |
2021年 | 1555篇 |
2020年 | 1220篇 |
2019年 | 1092篇 |
2018年 | 1167篇 |
2017年 | 1259篇 |
2016年 | 1155篇 |
2015年 | 1520篇 |
2014年 | 2008篇 |
2013年 | 2422篇 |
2012年 | 2560篇 |
2011年 | 2635篇 |
2010年 | 2290篇 |
2009年 | 2236篇 |
2008年 | 2072篇 |
2007年 | 2063篇 |
2006年 | 2138篇 |
2005年 | 1900篇 |
2004年 | 1227篇 |
2003年 | 1120篇 |
2002年 | 1126篇 |
2001年 | 971篇 |
2000年 | 981篇 |
1999年 | 1041篇 |
1998年 | 879篇 |
1997年 | 740篇 |
1996年 | 720篇 |
1995年 | 570篇 |
1994年 | 470篇 |
1993年 | 352篇 |
1992年 | 274篇 |
1991年 | 224篇 |
1990年 | 165篇 |
1989年 | 132篇 |
1988年 | 99篇 |
1987年 | 54篇 |
1986年 | 47篇 |
1985年 | 33篇 |
1984年 | 29篇 |
1983年 | 21篇 |
1982年 | 33篇 |
1981年 | 21篇 |
1980年 | 9篇 |
1979年 | 11篇 |
1976年 | 5篇 |
1973年 | 3篇 |
1970年 | 3篇 |
1969年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Shujuan Liu Qidong Xie Lixue Zhang Yingying Zhao Xuan Wang Pu Mao Jiping Wang Xiaojie Lou 《Journal of the European Ceramic Society》2018,38(14):4664-4669
The electrocaloric effect and energy storage property are tuned in the Ba1-xCexTi0.99Mn0.01O3 ceramics prepared by the solid state reaction method. The ceramics with lower Ce content (x?=?0.005, 0.015) show a better ΔT and ΔT/ΔE response. The ceramics with higher Ce content (x?=?0.030, 0.040, 0.045) represent the broader ΔT peaks (50?K–60?K), and the higher energy storage density and efficiency. The largest electrocaloric response (ΔTmax?=?1.22?K, ΔT/ΔE?=?0.41?K mm/kV) is found in the Ba0.995Ce0.005Ti0.99Mn0.01O3 ceramics, which is comparable or even higher than that of the most isovalent substituting BaTiO3-based ceramics reported before. The maximum energy storage density 0.11?J/cm3 (E?=?30?kV/cm) is obtained for the Ba0.970Ce0.030Ti0.99Mn0.01O3 ceramics, with high efficiency of 65–88% over a wide temperature range of 72?K. This work may open more opportunities to design high electrocalaric and energy storage performance lead-free systems from the viewpoint of the heterovalent and size mismatch substitution. 相似文献
102.
为了探明辽河油田地下水环境中CO2对Q235钢和X70管线钢的腐蚀规律,采用动电位极化技术及交流阻抗技术研究了不同CO2浓度对该环境下两种钢腐蚀行为的影响,并利用光学显微镜对试样腐蚀界面进行表征。结果表明:随着CO2浓度的增加,Q235和X70钢的交流阻抗图谱的半径均减小,腐蚀电流密度增大,腐蚀坑数量、深度和面积都增加,腐蚀敏感性增大。在低浓度CO2环境下(CO2含量为10%时),Q235钢的腐蚀敏感性比X70钢更高;而在高浓度CO2环境下(CO2含量为20%、40%、60%时),Q235钢的腐蚀速率反而较小,耐腐蚀性更好。 相似文献
103.
Junyuan Bai Xueyong Pang Xiangying Meng Hongbo Xie Hucheng Pan Yuping Ren Min Jiang Gaowu Qin 《材料科学技术学报》2020,(1):167-175
The crystal structure of the single-unit-cell thickness γ " phase,as a key strengthening phase in Mg-REZn(Ag) series alloys,has been extensively studied,and several structural models have been proposed in the past two decades.However,these reported models,and even the lattice constants at the same proposed structure,are scattered severely,which has led to considerable confusion and not available for further mechanical property simulation and prediction of Mg alloys containing this phase.In this study,by using first-principles calculations,the crystal structure of y" phase is clarified,resolving the discrepancies among different experiments,and its intrinsic mechanical properties have also been studied for the first time.It is verified that the γ " phase contains quasi-five atomic layers,instead of the previously reported tri-layer,and surprisingly,its crystal structure has many variants,which would change with the alloy composition.Besides,with the help of the simulated selected area electron diffraction(SAED) patterns,it is found that the atoms in the central layer remain partially ordered distribution,and this ordered extent primarily depends on the atomic ratio of RE:Zn(Ag) and the solute content in an alloy.That is,the ordered extent increases with decreasing the atomic ratio of RE:Zn(Ag) and/or increasing solute content of alloy,and vice versa.Ag and Zn dissolved in the γ" phase would produce almost opposed mechanical anisotropy for the γ " phase under the identical crystal structure,and the addition of Ag shows more efficient on increasing the shear modulus of γ" phase. 相似文献
104.
Zhen Luo Zhuoqing Li Zhe Xie Inna M. Sokolova Lan Song Willie J. G. M. Peijnenburg Menghong Hu Youji Wang 《Small (Weinheim an der Bergstrasse, Germany)》2020,16(36)
Titanium dioxide nanoparticles (nano‐TiO2) are widely used in consumer products, raising environmental and health concerns. An overview of the toxic effects of nano‐TiO2 on human and environmental health is provided. A meta‐analysis is conducted to analyze the toxicity of nano‐TiO2 to the liver, circulatory system, and DNA in humans. To assess the environmental impacts of nano‐TiO2, aquatic environments that receive high nano‐TiO2 inputs are focused on, and the toxicity of nano‐TiO2 to aquatic organisms is discussed with regard to the present and predicted environmental concentrations. Genotoxicity, damage to membranes, inflammation and oxidative stress emerge as the main mechanisms of nano‐TiO2 toxicity. Furthermore, nano‐TiO2 can bind with free radicals and signal molecules, and interfere with the biochemical reactions on plasmalemma. At the higher organizational level, nano‐TiO2 toxicity is manifested as the negative effects on fitness‐related organismal traits including feeding, reproduction and immunity in aquatic organisms. Bibliometric analysis reveals two major research hot spots including the molecular mechanisms of toxicity of nano‐TiO2 and the combined effects of nano‐TiO2 and other environmental factors such as light and pH. The possible measures to reduce the harmful effects of nano‐TiO2 on humans and non‐target organisms has emerged as an underexplored topic requiring further investigation. 相似文献
105.
106.
中国观念艺术三十多年的发展,是一场"没有坐标的运动。"中国观念艺术曾在一定时期和范围内偏离了人本主义思想的轨迹,没有沿着健康的道路发展。本文将从"后殖民化"与"本土化""智力"与"智慧""大众"与"精英"三悖论,对中国观念艺术发展的症候进行分析。 相似文献
107.
108.
曲江矿井主井井塔+54m平台上,需安装1台Gm=32/5T型电动双梁吊钩桥式起重机。由于吊装高度较高,空间狭小,井塔封屋顶面期间,在屋顶面预留400mm×400mm小孔,作为+46m平台的提升吊装孔;在屋顶面中间预留600mm×600mm小孔,作为+54m平台吊装孔。吊装时,先吊装左梁,再吊装右梁,小车正好落在组装好的左、右梁轨道上;然后将起重机推到机房中间位置,进行调试,完成安装。 相似文献
109.
110.
从连铸机喷嘴的分类入手,对各种喷嘴的特性进行了简要说明并结合研究实践,对某板坯连铸机选用的D25型系列喷嘴的测试做了探讨,包括测试内容、测试结果以及高差对水喷嘴喷水量的影响情况等。 相似文献