全文获取类型
收费全文 | 454147篇 |
免费 | 63410篇 |
国内免费 | 43301篇 |
专业分类
电工技术 | 44467篇 |
技术理论 | 26篇 |
综合类 | 43816篇 |
化学工业 | 60105篇 |
金属工艺 | 18069篇 |
机械仪表 | 32278篇 |
建筑科学 | 27092篇 |
矿业工程 | 9242篇 |
能源动力 | 11349篇 |
轻工业 | 28753篇 |
水利工程 | 6963篇 |
石油天然气 | 10691篇 |
武器工业 | 4989篇 |
无线电 | 60258篇 |
一般工业技术 | 41547篇 |
冶金工业 | 14097篇 |
原子能技术 | 4906篇 |
自动化技术 | 142210篇 |
出版年
2024年 | 1119篇 |
2023年 | 7345篇 |
2022年 | 13364篇 |
2021年 | 17427篇 |
2020年 | 16112篇 |
2019年 | 14201篇 |
2018年 | 13447篇 |
2017年 | 17308篇 |
2016年 | 19942篇 |
2015年 | 22594篇 |
2014年 | 27876篇 |
2013年 | 29867篇 |
2012年 | 34245篇 |
2011年 | 36300篇 |
2010年 | 27762篇 |
2009年 | 28116篇 |
2008年 | 29067篇 |
2007年 | 33872篇 |
2006年 | 31330篇 |
2005年 | 26747篇 |
2004年 | 21680篇 |
2003年 | 17990篇 |
2002年 | 14137篇 |
2001年 | 10944篇 |
2000年 | 8804篇 |
1999年 | 7167篇 |
1998年 | 5526篇 |
1997年 | 4500篇 |
1996年 | 3858篇 |
1995年 | 3273篇 |
1994年 | 2854篇 |
1993年 | 2158篇 |
1992年 | 1759篇 |
1991年 | 1293篇 |
1990年 | 1212篇 |
1989年 | 975篇 |
1988年 | 713篇 |
1987年 | 434篇 |
1986年 | 425篇 |
1985年 | 442篇 |
1984年 | 404篇 |
1983年 | 333篇 |
1982年 | 363篇 |
1981年 | 221篇 |
1980年 | 236篇 |
1979年 | 127篇 |
1978年 | 83篇 |
1977年 | 88篇 |
1962年 | 85篇 |
1959年 | 66篇 |
排序方式: 共有10000条查询结果,搜索用时 245 毫秒
51.
Cyril Poriel Cassandre Quinton Fabien Lucas Joëlle Rault-Berthelot Zuo-Quan Jiang Olivier Jeannin 《Advanced functional materials》2021,31(43):2104980
Spirobifluorene (SBF) is one of the most important scaffolds used in the design of organic semi-conductors (OSCs) for electronics. In recent years, among all the structures developed for these applications, SBF dimers have been highlighted due to their great potential in thermally activated delayed fluorescence and in phosphorescent organic light-emitting diodes. Attaching two SBF units generate 10 dimers, each possessing its own structural specificity, which in turn drives its electronic properties. These ten SBF dimers are gathered herein. Understanding how the molecular assembly determines the electronic properties has been one of the pillars of organic electronics. This is the goal of this article. As positional isomerism is a key tool to design OSCs, defining the design guidelines for the SBF scaffold appears of interest for the future of this building block. Herein, the importance of the two main parameters involved in the electrochemical and photophysical properties, namely the nature of the phenyl linkages and the steric congestion between the two SBF units is discussed. The combination of these two parameters drives the electronic properties but their respective weight is different as a function of the regioisomer involved or of the property considered (frontier orbitals energy level, absorption, fluorescence, phosphorescence). 相似文献
52.
53.
54.
55.
56.
研究辊速差对连铸连轧7075铝板显微组织、织构及力学性能的影响。采用3种不同上辊/下辊转速比(ω/ω0,ω为上辊转速,ω0为下辊转速)1:1、1:1.2及1:1.4进行多次试验。结果显示,在最大辊速差条件下(ω/ω0=1:1.4),7075铝板在轧制方向的屈服强度和极限抗拉强度分别提高41.5%和21.9%。此外,当辊速比ω/ω0为1:1.4时,成品轧制板的平均晶粒尺寸减小36%,横剖面平均硬度增加约9.2%。织构研究结果显示,辊速差越大,成品各向同性及硬度越大。然而,采用不同辊速度的连铸连轧会导致变形板伸长率降低约6%。 相似文献
57.
Zhiwei Qiao Lifeng Li Shuhua Li Hong Liang Jian Zhou Randall Q. Snurr 《American Institute of Chemical Engineers》2021,67(10):e17352
Computational screening was employed to calculate the enantioseparation capabilities of 45 functionalized homochiral metal–organic frameworks (FHMOFs), and machine learning (ML) and molecular fingerprint (MF) techniques were used to find new FHMOFs with high performance. With increasing temperature, the enantioselectivities for (R,S)-1,3-dimethyl-1,2-propadiene are improved. The “glove effect” in the chiral pockets was proposed to explain the correlations between the steric effect of functional groups and performance of FHMOFs. Moreover, the neighborhood component analysis and RDKit/MACCS MFs show the highest predictive effect on enantioselectivities among the four ML classification algorithms with nine MFs that were tested. Based on the importance of MF, 85 new FHMOFs were designed, and a newly designed FHMOF, NO2-NHOH-FHMOF, with high similarity to the optimal MFs achieved improved chiral separation performance, with enantioselectivities of 85%. The design principles and new chiral pockets obtained by ML and MFs could facilitate the development of new materials for chiral separation. 相似文献
58.
59.
目的:研究抗坏血酸(ascorbic acid,AsA)-还原型谷胱甘肽(reduced glutathione,GSH)循环代谢在水杨酸处理采后甜瓜诱导的过量H2O2清除过程中的作用。方法:用4 mmol/L水杨酸浸泡‘玉金香’厚皮甜瓜10 min,测定处理后果实常温贮藏过程中丙二醛(malondialdehyde,MDA)含量,分析活性氧的积累水平、超氧化物歧化酶(superoxide dismutase,SOD)和过氧化氢酶(catalase,CAT)活力,以及AsA-GSH循环过程相关酶活力及产物和底物含量。结果:水杨酸处理降低了果实MDA含量,第10天处理组MDA含量较对照组降低14.6%;显著提高了果实O2-·的产生速率和H2O2含量(P<0.05),其中处理后第2天O2-·的产生速率高出同期对照组的1.9 倍,第6天H2O2含量高出对照组果实29.7%;提高了果实SOD活力,但抑制了CAT活力,说明H2O2的清除可能是依赖于除酶促系统外的其他系统。此外,水杨酸处理提高了果实抗坏血酸过氧化物酶、单脱氢抗坏血酸过氧化物酶、脱氢抗坏血酸还原酶和谷胱甘肽还原酶的活力,增加了AsA和氧化型谷胱甘肽的含量,降低了脱氢抗坏血酸和GSH的含量。结论:水杨酸处理诱导了厚皮甜瓜果实的氧爆,抑制了MDA产生,由水杨酸诱导产生的过量H2O2主要依靠AsA-GSH循环系统清除。 相似文献
60.
Mit Rita Goswami Prayas Singh Pankaj Chamoli Sumit Bhardwaj Kuldeep Kumar Raina Ravi Kumar Shukla 《应用聚合物科学杂志》2021,138(43):51260
ZnO rice like nonarchitects are grafted on the graphene carbon core via a rapid microwave synthesis route. The prepared grafted systems are characterized via XRD, SEM, RAMAN, and XPS to examined the structural and morphological parameters. Zinc oxide grafted graphene sheets (ZnO-G) are further doped in β-phase of polyvinylidene fluoride (PVDF) to prepare the polymer nanocomposites (PNCs) via mixed solvent approach (THF/DMF). β-phase confirmation of PVDF PNCs is done by FTIR studies. It is observed that ZnO-G filler enhances the β-phase content in the PNCs. Non-doped PVDF and PNCs are further studied for rheological behavior under the shear rate of 1–100 s−1. Doping of ZnO-G dopant to the PVDF matrix changes its discontinuous shear thickening (DST) behavior to continues shear thickening behavior (CST). Hydrocluster formation and their interaction with the dopant could be the reason for this striking DST to CST behavioral change. Strain amplitude sweep (10−3% -10%) oscillatory test reveals that the PNCs shows extended linear viscoelastic region with high elastic modulus and lower viscous modulus. Effective shear thickening behavior and strong elastic strength of these PNCs present their candidature for various fields including mechanical and soft body armor applications. 相似文献