全文获取类型
收费全文 | 288471篇 |
免费 | 24556篇 |
国内免费 | 13004篇 |
专业分类
电工技术 | 17380篇 |
技术理论 | 25篇 |
综合类 | 19757篇 |
化学工业 | 47219篇 |
金属工艺 | 16614篇 |
机械仪表 | 18620篇 |
建筑科学 | 22469篇 |
矿业工程 | 9409篇 |
能源动力 | 7942篇 |
轻工业 | 19764篇 |
水利工程 | 5235篇 |
石油天然气 | 18787篇 |
武器工业 | 2400篇 |
无线电 | 31797篇 |
一般工业技术 | 32895篇 |
冶金工业 | 15216篇 |
原子能技术 | 3144篇 |
自动化技术 | 37358篇 |
出版年
2024年 | 1369篇 |
2023年 | 4875篇 |
2022年 | 8801篇 |
2021年 | 12044篇 |
2020年 | 9323篇 |
2019年 | 7638篇 |
2018年 | 8593篇 |
2017年 | 9683篇 |
2016年 | 8587篇 |
2015年 | 11607篇 |
2014年 | 14913篇 |
2013年 | 17511篇 |
2012年 | 19130篇 |
2011年 | 20515篇 |
2010年 | 18255篇 |
2009年 | 17073篇 |
2008年 | 16609篇 |
2007年 | 15991篇 |
2006年 | 15861篇 |
2005年 | 13597篇 |
2004年 | 9299篇 |
2003年 | 7657篇 |
2002年 | 6798篇 |
2001年 | 5964篇 |
2000年 | 6399篇 |
1999年 | 7132篇 |
1998年 | 5781篇 |
1997年 | 4776篇 |
1996年 | 4485篇 |
1995年 | 3733篇 |
1994年 | 2977篇 |
1993年 | 2102篇 |
1992年 | 1630篇 |
1991年 | 1295篇 |
1990年 | 980篇 |
1989年 | 795篇 |
1988年 | 583篇 |
1987年 | 354篇 |
1986年 | 295篇 |
1985年 | 202篇 |
1984年 | 156篇 |
1983年 | 119篇 |
1982年 | 129篇 |
1981年 | 110篇 |
1980年 | 89篇 |
1979年 | 44篇 |
1978年 | 26篇 |
1977年 | 22篇 |
1976年 | 36篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
Lu Xu Baijun Liu Mingyao Zhang Yang Bai Jinming Zhang Jiayin Song 《Polymer Engineering and Science》2020,60(6):1194-1201
A series of methacrylate-acrylonitrile-butadiene-styrene (MABS) resins was prepared using bulk polymerization. The polarity of the continuous phase and the compatibility of two phases were changed by adjusting the methyl methacrylate (MMA) content, choosing values that were close to styrene-butadiene rubber solubility value. The possibility of controlling the microstructure of the MABS resin by changing the polarity of the components and the compatibility of two phases was assessed. The dynamic mechanical analysis shows that the compatibility of two phases varies with the MMA content. The morphological analysis shows that increasing MMA contents results in a gradual decrease in the sub-inclusion structure with a network skeleton of rubber particles, and that all the particles become solid rubber when the MMA content reaches 75%. The sub-inclusion structure reappears but does not have a network skeleton when the MMA content is 90%. The impact strength and morphological analysis indicate that the solid rubber particles and the sub-inclusion structure with a network skeleton provide excellent toughness, while the sub-inclusion structure without a network skeleton does not. In contrast, the transmittance of the ABS resin first increased and then decreased with increasing MMA content. 相似文献
92.
为了避免回收单一钕铁硼废料中有价元素带来的操作复杂和资源浪费等问题,本研究采用共沉淀法共沉淀出钕铁硼废料中的有价元素Me(Nd,Pr,Co,Fe),制备可用于生产再生钕铁硼的原料;根据质量守恒和同时平衡原理,采用MATLAB软件建立Me(Nd,Pr,Co,Fe)-OH--NH3热力学模型,绘制lg[Me]-p H曲线模拟共沉淀工艺,并根据模拟结果确立了共沉淀工艺;模拟和实验的结果表明:根据lg[Me]-p H模拟结果可以确立一步共沉淀法的p H:6~10,Fe3+比Fe2+更易于沉淀完全;在上述条件下获得的共沉淀粉末主相均为Nd,Pr,Co,Fe的化合物,且有价元素的百分比含量均大于99.4%;其中,当p H值在8左右时回收率最高,在该条件下金属元素Me(Nd,Pr,Co,Fe)的沉淀效率分别为:98.7%,99.9%,93.6%,99.9%。该结果也表明共沉淀法工艺不仅高效,而且所制备的共沉淀粉末可以满足制备二次钕铁硼的需要。 相似文献
93.
94.
95.
96.
陕南山地烟田不同植烟年限土壤养分的变化 总被引:1,自引:0,他引:1
为给陕南山地烟草生产布局及有针对性的施肥措施提供依据,分析了陕南山地烟田不同植烟年限(0~15年)与土壤养分含量的关系。结果表明:随着植烟年限延长,有机质线性下降,全氮和速效钾显著上升,有效磷先上升后下降;氯、有效铁、有效锰、有效硼和有效铜无显著变化或变化很小,有效锌则在第1年急剧下降,之后保持稳定,10年后再次显著下降。认为陕南山地烟区烟叶生产中应适当增加有机肥的施用而合理控制氮肥、磷肥和钾肥的施用,并要注意锌肥的补充。 相似文献
97.
Weikang Dong Ruishi Qi Tiansheng Liu Yi Li Ning Li Ze Hua Zirui Gao Shuyuan Zhang Kaihui Liu Jiandong Guo Peng Gao 《Advanced materials (Deerfield Beach, Fla.)》2020,32(46):2002014
Hyperbolic phonon polaritons (HPhPs) in orthorhombic-phase molybdenum trioxide (α-MoO3) show in-plane hyperbolicity, great wavelength compression, and ultralong lifetime, therefore holding great potential in nanophotonic applications. However, its polaritonic response in the far-infrared (FIR) range remains unexplored due to challenges in experimental characterization. Here, monochromated electron energy loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM) is used to probe HPhPs in α-MoO3 in both mid-infrared (MIR) and FIR frequencies and correlate their behaviors with microstructures and orientations. It is found that low structural symmetry leads to various phonon modes and multiple Reststrahlen bands (RBs) over a broad spectral range (over 70 meV) and in different directions (55–63 meV and 119–125 meV along the b-axis, 68–106 meV along the c-axis, and 101–121 meV along the a-axis). These HPhPs can be selectively excited by controlling the direction of swift electrons. These findings provide new opportunities in nanophotonic and optoelectronic applications, such as directed light propagation, hyperlenses, and heat transfer. 相似文献
98.
Kai He Zhe Li Longfei Liu Mengxi Zheng Prof. Chengde Mao 《Chembiochem : a European journal of chemical biology》2020,21(15):2132-2136
As a giant leap in DNA self-assembly, DNA origami has exhibited an unprecedented ability to construct nanostructures with arbitrary shapes and sizes. In typical DNA origami, hundreds of short DNA staple strands fold a long, single-stranded (ss) DNA scaffold cooperatively into designed nanostructures. However, large numbers of DNA strands are expensive and would hinder applications such as pharmaceutical investigations because of the complicated components. Therefore, one challenge is how to reduce the number of staple strands needed to construct DNA origami. For a DNA origami structure, the scale-free folding pattern of the scaffold strand is determined by staple strands at the branching vertexes. Simple duplex regions help to define the size-related features of the origami geometry. In this study, we hypothesized that a scaffold strand can be correctly folded into a designed topology by using only staple strands involved in branching vertexes. After assembly, any remaining, flexible, single-stranded regions of the scaffold could be converted into rigid duplexes by DNA polymerase to achieve the designed geometric structures. To demonstrate the concept, we used only 18 staple strands (covering 15 % of the scaffold strand) to assemble a porous DNA nanostructure, which was visualized by atomic force microscopy (AFM). This study helps understanding of the role of cooperativity in origami folding, and provides a cost-effective approach for small-scale prototyping DNA origami. 相似文献
99.
Yu-Jiao Liu Xiao-Yang Fan Dr. Dong-Dong Zhang Yin-Zheng Xia Dr. Yan-Jun Hu Feng-Lei Jiang Prof. Fu-Ling Zhou Prof. Yi Liu 《ChemMedChem》2020,15(6):552-558
Based on the potential therapeutic value in targeting mitochondria and the fluorophore tracing ability, a fluorescent mitochondria-targeted organic arsenical PDT-PAO-F16 was fabricated, which not only visualized the cellular distribution, but also exerted anti-cancer activity in vitro and in vivo via targeting pyruvate dehydrogenase complex (PDHC) and respiratory chain complexes in mitochondria. In details, PDT-PAO-F16 mainly accumulated into mitochondria within hours and suppressed the activity of PDHC resulting in the inhibition of ATP synthesis and thermogenesis disorder. Moreover, the suppression of respiratory chain complex I and IV accelerated the mitochondrial dysfunction leading to caspase family-dependent apoptosis. In vivo, the acute promyelocytic leukemia was greatly alleviated in the PDT-PAO-F16 treated group in APL mice model. Our results demonstrated the organic arsenical precursor with fluorescence imaging and target-anticancer efficacy is a promising anticancer drug. 相似文献
100.