全文获取类型
收费全文 | 60196篇 |
免费 | 6868篇 |
国内免费 | 4708篇 |
专业分类
电工技术 | 5319篇 |
综合类 | 6670篇 |
化学工业 | 8004篇 |
金属工艺 | 3993篇 |
机械仪表 | 4271篇 |
建筑科学 | 4311篇 |
矿业工程 | 2743篇 |
能源动力 | 1738篇 |
轻工业 | 6255篇 |
水利工程 | 1840篇 |
石油天然气 | 2616篇 |
武器工业 | 1048篇 |
无线电 | 5926篇 |
一般工业技术 | 5056篇 |
冶金工业 | 2297篇 |
原子能技术 | 1102篇 |
自动化技术 | 8583篇 |
出版年
2024年 | 310篇 |
2023年 | 1006篇 |
2022年 | 2396篇 |
2021年 | 3016篇 |
2020年 | 2168篇 |
2019年 | 1498篇 |
2018年 | 1689篇 |
2017年 | 1830篇 |
2016年 | 1533篇 |
2015年 | 2595篇 |
2014年 | 3406篇 |
2013年 | 4025篇 |
2012年 | 5055篇 |
2011年 | 5087篇 |
2010年 | 4956篇 |
2009年 | 4669篇 |
2008年 | 4893篇 |
2007年 | 4688篇 |
2006年 | 3986篇 |
2005年 | 3316篇 |
2004年 | 2482篇 |
2003年 | 1655篇 |
2002年 | 1459篇 |
2001年 | 1364篇 |
2000年 | 1066篇 |
1999年 | 505篇 |
1998年 | 189篇 |
1997年 | 157篇 |
1996年 | 134篇 |
1995年 | 138篇 |
1994年 | 92篇 |
1993年 | 64篇 |
1992年 | 46篇 |
1991年 | 44篇 |
1990年 | 38篇 |
1989年 | 48篇 |
1988年 | 33篇 |
1987年 | 22篇 |
1986年 | 23篇 |
1985年 | 9篇 |
1984年 | 4篇 |
1983年 | 9篇 |
1982年 | 5篇 |
1981年 | 14篇 |
1980年 | 14篇 |
1979年 | 5篇 |
1966年 | 2篇 |
1965年 | 2篇 |
1959年 | 10篇 |
1951年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
4.
Xiaozhen Li Chao Yin Si Si Liew Chun-Sing Lee Kanyi Pu 《Advanced functional materials》2021,31(46):2106154
Optical imaging has played a pivotal role in deciphering in vivo bioinformatics but is limited by shallow penetration depth and poor imaging performance owing to interfering tissue autofluorescence induced by concurrent photoexcitation. The emergence of near-infrared (NIR) self-luminescence imaging independent of real-time irradiation has timely addressed these problems. There are two main kinds of self-luminescent agents, namely inorganic and organic luminophores. Inorganic luminophores usually suffer from long-term biotoxicity concerns resulting from potential heavy-metal ions leakage and nonbiodegradability, which hinders their further translational application. In contrast, organic luminophores, especially organic semiconducting luminophores (OSLs) with good biodegradable potential, tunable design, and outstanding optical properties, are preferred in biological applications. This review summarizes the recent progress of OSLs used in NIR afterglow, chemiluminescence, and bioluminescence imaging. Molecular manipulation and nanoengineering approaches of OSLs are discussed, with emphasis on strategies that can extend the emission wavelength from visible to NIR range and amplify luminescence signals. This review concludes with a discussion of current challenges and possible solutions of OSLs in the self-luminescence field. 相似文献
5.
针对伊拉克米桑油田盐膏层巨厚、钻井液密度窗口窄、存在高压盐水层,储层段漏塌同层导致复杂时效高等问题,通过对比分析国内外盐膏层和窄压力窗口地层钻井技术,总结了米桑油田钻井面临的主要技术难点,从井身结构优化、钻井提速和复杂预防等方面入手,研究形成了适合米桑油田的钻井关键技术,并进行了现场试验应用,取得了显著的效果.伊拉克米桑油田钻井关键技术对该地区钻井技术方案设计和钻井提速提效具有较强的借鉴和指导作用. 相似文献
6.
Pu Mao Jiping Wang Peng Xiao Lixue Zhang Fang Kang Hao Gong 《Ceramics International》2021,47(1):111-120
In this work, we developed a novel system of isovalent Zr4+ and donor Nb5+ co-doped CaCu3Ti4O12 (CCTO) ceramics to enhance dielectric response. The influences of Zr4+ and Nb5+ co-substituting on the colossal dielectric response and relaxation behavior of the CCTO ceramics fabricated by a conventional solid-phase synthesis method were investigated methodically. Co-doping of Zr4+ and Nb5+ ions leads to a significant reduction in grain size for the CCTO ceramics sintered at 1060 °C for 10 h. XRD and Raman results of the CaCu3Ti3.8-xZrxNb0.2O12 (CCTZNO) ceramics show a cubic perovskite structure with space group Im-3. The first principle calculation result exhibits a better thermodynamic stability of the CCTO structure co-doped with Zr4+ and Nb5+ ions than that of single-doped with Zr4+ or Nb5+ ion. Interestingly, the CCTZNO ceramics exhibit greatly improved dielectric constant (~105) at a frequency range of 102–105 Hz and at a temperature range of 20–210 °C, indicating a giant dielectric response within broader frequency and temperature ranges. The dielectric properties of CCTZNO ceramics were analyzed from the viewpoints of defect-dipole effect and internal barrier layer capacitance (IBLC) model. Accordingly, the immensely enhanced dielectric response is primarily ascribed to the complex defect dipoles associated with oxygen vacancies by co-doping Zr4+ and Nb5+ ions into CCTO structure. In addition, the obvious dielectric relaxation behavior has been found in CCTZNO ceramics, and the relaxation process in middle frequency regions is attributed to the grain boundary response confirmed by complex impedance spectroscopy and electric modulus. 相似文献
7.
8.
采用水溶液聚合法制备了低分子量聚丙烯酸钾(PAAK),并作为新型消焰剂加入单基发射药中。通过火焰原子吸收光谱法测试了PAAK中钾的含量;用乌氏黏度计测定了特性黏度;采用DSC法研究不同pH值的PAAK与硝化棉(NC)的相容性;利用充氮氧弹法对添加PAAK、硝酸钾KNO3、硫酸钾K2SO4的单基发射药的燃烧残渣进行了对比研究。结果表明,合成的PAAK中,钾的质量分数为15.21%,相对分子量在3 000左右,有利于和NC均匀混合,且在中性或微碱性(pH=7.0~7.5)的情况与NC相容性良好。与传统的KNO3、K2SO4消焰剂相比,PAAK能够和NC均匀混合,制备均质透明的单基发射药;PAAK发射药的燃烧残渣最少,占发射药质量的0.18%。 相似文献
9.
为了提高煤炭资源回收率,对岳城煤矿3号煤三盘区最后两个小工作面回采区域的回收布置进行了研究,利用巷道外错布置工艺,对该区域进行整体布置,优化工作面设计,既回采了两个小工作面,又回收了与1308工作面之间的煤柱和原南河滩煤矿的部分大巷煤柱,增加了资源回收,简化了生产系统,实现了科学高效回采。 相似文献
10.
To overcome the drawbacks of solid microporous materials for CO2 capture, this proof‐of‐concept study demonstrates a low‐cost and rapid method for producing composites consisting of hypercrosslinked polymers (HCP) with a polyethyleneimine (PEI) binder. The resulting materials capture CO2 through physical and chemical absorption simultaneously. Compared with HCP, the composites exhibit higher CO2 uptake, higher volumetric density, and improved tolerance to water which is attributed to the PEI binder. 相似文献