全文获取类型
收费全文 | 111810篇 |
免费 | 10399篇 |
国内免费 | 5912篇 |
专业分类
电工技术 | 7373篇 |
技术理论 | 7篇 |
综合类 | 8337篇 |
化学工业 | 17621篇 |
金属工艺 | 6983篇 |
机械仪表 | 7623篇 |
建筑科学 | 9064篇 |
矿业工程 | 3642篇 |
能源动力 | 2991篇 |
轻工业 | 7009篇 |
水利工程 | 2279篇 |
石油天然气 | 6208篇 |
武器工业 | 1027篇 |
无线电 | 13100篇 |
一般工业技术 | 12662篇 |
冶金工业 | 4985篇 |
原子能技术 | 1370篇 |
自动化技术 | 15840篇 |
出版年
2024年 | 372篇 |
2023年 | 1559篇 |
2022年 | 3074篇 |
2021年 | 4392篇 |
2020年 | 3313篇 |
2019年 | 2701篇 |
2018年 | 3009篇 |
2017年 | 3392篇 |
2016年 | 3203篇 |
2015年 | 4651篇 |
2014年 | 5721篇 |
2013年 | 6901篇 |
2012年 | 7707篇 |
2011年 | 8340篇 |
2010年 | 7696篇 |
2009年 | 7600篇 |
2008年 | 7246篇 |
2007年 | 6948篇 |
2006年 | 6465篇 |
2005年 | 5615篇 |
2004年 | 3873篇 |
2003年 | 3402篇 |
2002年 | 3298篇 |
2001年 | 2984篇 |
2000年 | 2465篇 |
1999年 | 2471篇 |
1998年 | 1779篇 |
1997年 | 1531篇 |
1996年 | 1349篇 |
1995年 | 1105篇 |
1994年 | 926篇 |
1993年 | 669篇 |
1992年 | 522篇 |
1991年 | 401篇 |
1990年 | 323篇 |
1989年 | 275篇 |
1988年 | 205篇 |
1987年 | 128篇 |
1986年 | 122篇 |
1985年 | 54篇 |
1984年 | 58篇 |
1983年 | 39篇 |
1982年 | 42篇 |
1981年 | 33篇 |
1980年 | 29篇 |
1979年 | 20篇 |
1978年 | 13篇 |
1977年 | 9篇 |
1976年 | 20篇 |
1951年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
Baofeng Hou Hong He Ruixiu Jia Meilong Fu Yanbin Cao Shaoqun He Liwen Luo Youqing Huang 《应用聚合物科学杂志》2019,136(10):47161
The synthesis and performance of a novel temperature-tolerant foamed resin for enhanced oil recovery were investigated using various methods, including infrared, NMR, scanning electron microscopy (SEM), and displacement experiments. Polycondensation of furfuryl alcohol prepolymers was confirmed by the infrared and NMR results. The poor temperature tolerance of furfuryl alcohol prepolymers after gelation at high temperatures is mainly due to the fracture of furan rings. The addition of ester additives is an effective method of increasing the temperature tolerance of the prepared foamed resins and can effectively reduce the weight-loss rate of the polycondensation products. The SEM results show that the skeleton structure of the foamed resin remains intact after high-temperature treatment. Thus, the novel plugging agent system has excellent thermal stability and still has a high strength (>0.8 MPa) after high-temperature aging treatment for 40 days, giving the prepared foamed resin a good plugging performance (plugging rate > 91%) at 250 °C. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47161. 相似文献
52.
Dr. Jiayao Y. Wang Dr. Jiaqi Q. Li Prof. Dr. Yumei M. Xiao Prof. Dr. Bin Fu Prof. Dr. Zhaohai H. Qin 《ChemMedChem》2020,15(5):404-410
Mitochondrial oxidative damage and dysfunction contribute to a wide range of human diseases. Considering the limitation of conventional antioxidants and that mitochondria are the main source of reactive oxygen species (ROS) which induce oxidative damage, mitochondria-targeted antioxidants which can selectively block mitochondrial oxidative damage and prevent various types of cell death have been widely developed. As a lipophilic cation, triphenylphosphonium (TPP) has been commonly used in designing mitochondria-targeted antioxidants. Conjugated with the TPP moiety, antioxidants can achieve more than 1000-fold higher mitochondrial concentration depending on cell membrane potentials and mitochondrial membrane potentials. Herein we discuss the deficiencies of conventional antioxidants and the advantages of mitochondrial targeting, and review various types of TPP-based mitochondria-targeted antioxidants. These provide theoretical and background support for the design of new anti-oxidant. 相似文献
53.
54.
In this study, the crystal structure, thermal, oxygen transport, electrical conductivity and electrochemical properties of the perovskite NdBa0.5Sr0.5Co2O5+δ (NBSC55) are investigated. In the temperature range of 250 °C–350 °C, the weight loss upon heating was due to a partial loss of lattice oxygen and along with a reduction of Co4+ to Co3+. The tend of weight-loss slows down as temperature increased above 350 °C indicating a reduction of Co3+ to Co2+ during this stage. The oxygen migration is dominated by surface exchange process at high temperature range (650-800 °C); however, the bulk diffusion process prevails at low temperature range (500–600 °C). For long-term testing, the polarization resistance of NBSC55 increases gradually form 3.13 Ω cm2 for 2 h to 3.34 Ω cm2 for 96 h at 600 °C and an increasing-rate for polarization resistance is around 0.22% h?1. The power density of the single cell with NBSC55 cathode reached 341 mW cm?2 at 800 °C. 相似文献
55.
56.
57.
58.
Lei He Yan Xuan Feng Zhang Xue Wang Huaqing Pan Junfeng Ren Meina Chen 《International Journal of Hydrogen Energy》2021,46(1):1096-1105
Bulk and surface properties of proton stability and transportation in Y and Nd co-doped BaCeO3 (BCYN), especially the effect of Nd segregation, were investigated by first-principles calculations. Since the structure of doped BaCeO3 at the operating temperature of proton-conducting has been unclear for a long time, we have summarized the latest experimental results and calculated the structure of the asymmetric BCYN for the first time. The results show that compared with Y, Nd doping promotes oxygen vacancy formation, however reduces proton stability. Our calculation can also provide a possible explanation for the formation of space charge layer at the grain boundary of doped BaCeO3 in experiment. Unlike the stable Y in BCYN, Nd is calculated to be easily segregated, which can facilitate both proton hydration and proton transportation near the surface. Moreover, Nd segregation at the grain boundary is predicted to be beneficial for proton transportation between grains. 相似文献
59.
Yafei Liu Zhilong Fu Xingyu Chen Yaxin Wei Bo Zhang Aimin Chang 《Journal of the American Ceramic Society》2021,104(5):2134-2142
Rare-earth ions doped Ca0.9R0.1CeNbMoO8 (R = Y, Sm, Nd, La) ceramics have been successfully prepared by solid-state method, and their modifications to the microstructure and electrical properties are also investigated. The rare-earth ions doped ceramics exhibit the scheelite structure. With the increase in the radius of rare-earth ions, the lattice distortion and bond interaction will be enhanced, and the consistency of grain size will be reduced. The ceramics exhibit negative temperature coefficient (NTC) thermistor characteristics in the temperature range of 473 K-1273 K, and the activation energy decreases with the increase of the radius of rare-earth ions. Rare-earth ions doping can increase the content of Ce3+ ions and promote the conductivity of ceramics. Except for Sm3+-doped ceramics, the high-temperature aging rate of other ceramics is less than 2%. The existence of some metastable Sm2+ ions in Sm3+-doped ceramics not only increases the activation energy, but also reduces the high-temperature stability of the ceramics. 相似文献
60.
多井评价是建立在单井精细解释对比分析基础上的预测储层及含油气性平面分布规律的技术方法,而常规测井资料无法区分碳酸盐岩岩溶储层,因而利用多井评价结果确定岩溶发育程度在平面上的分布规律就显得十分重要。为此,在岩心标定成像测井的基础上,对四川盆地高石梯—磨溪地区15口井的成像测井岩溶发育特征进行分析,建立了中二叠统茅口组岩溶发育各分带的标准成像图版,利用交会图及直方图分析各分带的常规测井响应特征,在此基础上形成了电成像测井刻度常规测井识别岩溶发育带的新方法。研究结果表明:①高石梯—磨溪地区茅口组岩溶带自上而下可划分为风化壳残积带、垂直渗流岩溶带、水平潜流岩溶带以及受岩溶作用较弱的基岩;②风化壳残积带在成像测井图像显示为"暗—亮—暗"条带状模式,垂直渗流岩溶带为垂直线状与暗色斑状组合模式,水平潜流岩溶带为水平线状—层状与斑状组合模式,基岩整体显示为亮色块状模式偶见线状或斑状特征;③有效储层主要发育在垂直渗流带和水平潜流带的顶部;④该区茅口组岩溶发育主要受裂缝发育控制,而裂缝发育又与断层关系密切。结论认为,该新方法对碳酸盐岩岩溶储层的多井评价具有普遍适用性,为四川盆地中二叠统风险探井的部署提供了技术支撑。 相似文献