全文获取类型
收费全文 | 51047篇 |
免费 | 5741篇 |
国内免费 | 3280篇 |
专业分类
电工技术 | 3410篇 |
技术理论 | 1篇 |
综合类 | 4080篇 |
化学工业 | 7983篇 |
金属工艺 | 2989篇 |
机械仪表 | 3307篇 |
建筑科学 | 3596篇 |
矿业工程 | 1370篇 |
能源动力 | 1228篇 |
轻工业 | 5678篇 |
水利工程 | 1181篇 |
石油天然气 | 2072篇 |
武器工业 | 488篇 |
无线电 | 5935篇 |
一般工业技术 | 5784篇 |
冶金工业 | 2039篇 |
原子能技术 | 595篇 |
自动化技术 | 8332篇 |
出版年
2024年 | 293篇 |
2023年 | 851篇 |
2022年 | 1648篇 |
2021年 | 2128篇 |
2020年 | 1615篇 |
2019年 | 1401篇 |
2018年 | 1601篇 |
2017年 | 1725篇 |
2016年 | 1652篇 |
2015年 | 2250篇 |
2014年 | 2816篇 |
2013年 | 3452篇 |
2012年 | 3905篇 |
2011年 | 4365篇 |
2010年 | 3949篇 |
2009年 | 3889篇 |
2008年 | 3736篇 |
2007年 | 3511篇 |
2006年 | 3166篇 |
2005年 | 2631篇 |
2004年 | 1891篇 |
2003年 | 1448篇 |
2002年 | 1366篇 |
2001年 | 1144篇 |
2000年 | 877篇 |
1999年 | 654篇 |
1998年 | 395篇 |
1997年 | 328篇 |
1996年 | 275篇 |
1995年 | 209篇 |
1994年 | 176篇 |
1993年 | 151篇 |
1992年 | 110篇 |
1991年 | 96篇 |
1990年 | 64篇 |
1989年 | 53篇 |
1988年 | 39篇 |
1987年 | 35篇 |
1986年 | 27篇 |
1985年 | 13篇 |
1984年 | 11篇 |
1983年 | 11篇 |
1982年 | 17篇 |
1980年 | 7篇 |
1979年 | 12篇 |
1978年 | 9篇 |
1977年 | 10篇 |
1976年 | 13篇 |
1975年 | 9篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Jing Qian Min Shen Shan Zhou Chi-Ta Lee Ming Zhao Zhiheng Lyu Zachary D. Hood Madeline Vara Kyle D. Gilroy Kun Wang Younan Xia 《Materials Today》2018,21(8):834-844
Engineering the shape and thus surface structure of Pt nanocrystals is an effective strategy for optimizing their catalytic activities toward various reactions. However, different protocols are typically used to produce Pt nanocrystals with distinctive shapes, making it difficult to directly compare their catalytic activities owing to the complication of surface contamination. Here we demonstrate that Pt nanocrystals with a variety of shapes, including those enclosed with low- or high-index facets, can be synthesized using the same protocol by simply adjusting the concentration of reducing agent and/or the reaction time. Specifically, when the reducing agent was used at a relatively low concentration, Pt truncated cubes, cuboctahedrons, truncated octahedrons, and octahedrons were produced sequentially upon the increase in reaction time. When 67% more reducing agent was used, Pt cubes and concave cubes were obtained consecutively as the reaction time was prolonged. Our quantitative analysis suggests that the diversity of shape and difference in size can be resulted from the difference in reduction kinetics. In evaluating their structure–activity relationship for oxygen reduction, it was established that the high-index facets on Pt concave cubes possessed a specific activity of 6.3 and 1.3 times greater than those of Pt cubes and octahedrons exposed by {1?0?0} and {1?1?1} facets, respectively. This work not only offers a general method for the synthesis of Pt nanocrystals having diverse shapes and thus different types of facets but also highlights the significance of reduction kinetics in controlling the structure evolution of other metal nanocrystals. 相似文献
992.
MWCNTs as Conductive Network for Monodispersed Fe3O4 Nanoparticles to Enhance the Wave Absorption Performances 下载免费PDF全文
Kaili Yu Min Zeng Yichao Yin Xiaojun Zeng Jue Liu Ya Li Wukui Tang Yu Wang Jing An Jun He Ronghai Yu 《Advanced Engineering Materials》2018,20(2)
993.
Lighting Up MicroRNA in Living Cells by the Disassembly of Lock‐Like DNA‐Programmed UCNPs‐AuNPs through the Target Cycling Amplification Strategy 下载免费PDF全文
Keying Zhang Shuting Song Shan Huang Lin Yang Qianhao Min Xingcai Wu Feng Lu Jun‐Jie Zhu 《Small (Weinheim an der Bergstrasse, Germany)》2018,14(40)
Intracellular microRNAs imaging based on upconversion nanoprobes has great potential in cancer diagnostics and treatments. However, the relatively low detection sensitivity limits their application. Herein, a lock‐like DNA (LLD) generated by a hairpin DNA (H1) hybridizing with a bolt DNA (bDNA) sequence is designed, which is used to program upconversion nanoparticles (UCNPs, NaYF4@NaYF4:Yb, Er@NaYF4) and gold nanoparticles (AuNPs). The upconversion emission is quenched through luminescence resonance energy transfer (LRET). The multiple LLD can be repeatedly opened by one copy of target microRNA under the aid of fuel hairpin DNA strands (H2) to trigger disassembly of AuNPs from the UCNP, resulting in the lighting up of UCNPs with a high detection signal gain. This strategy is verified using microRNA‐21 as model. The expression level of microRNA‐21 in various cells lines can be sensitively measured in vitro, meanwhile cancer cells and normal cells can be easily and accurately distinguished by intracellular microRNA‐21 imaging via the nanoprobes. The detection limit is about 1000 times lower than that of the previously reported upconversion nanoprobes without signal amplification. This is the first time a nonenzymatic signal amplification method has been combined with UCNPs for imaging intracellular microRNAs, which has great potential for cancer diagnosis. 相似文献
994.
Jian Qiao Jiangtao Di Susheng Zhou Kaiyun Jin Sha Zeng Na Li Shaoli Fang Yanhui Song Min Li Ray H. Baughman Qingwen Li 《Small (Weinheim an der Bergstrasse, Germany)》2018,14(38)
Artificial muscles are reported in which reduced graphene oxide (rGO) is trapped in the helical corridors of a carbon nanotube (CNT) yarn. When electrochemically driven in aqueous electrolytes, these coiled CNT/rGO yarn muscles can contract by 8.1%, which is over six times that of the previous results for CNT yarn muscles driven in an inorganic electrolyte (1.3%). They can contract to provide a final stress of over 14 MPa, which is about 40 times that of natural muscles. The hybrid yarn muscle shows a unique catch state, in which 95% of the contraction is retained for 1000 s following charging and subsequent disconnection from the power supply. Hence, they are unlike thermal muscles and natural muscles, which need to consume energy to maintain contraction. Additionally, these muscles can be reversibly cycled while lifting heavy loads. 相似文献
995.
Sheng Huang Chao Meng Min Xiao Shan Ren Shuanjin Wang Dongmei Han Yuning Li Yuezhong Meng 《Small (Weinheim an der Bergstrasse, Germany)》2018,14(21)
Sodium ion batteries (SIB) are considered promising alternative candidates for lithium ion batteries (LIB) because of the wide availability and low cost of sodium, therefore the development of alternative sodium storage materials with comparable performance to LIB is urgently desired. The sodium ions with larger sizes resist intercalation or alloying because of slow reaction kinetics. Most pseudocapacitive sodium storage materials are based on subtle nanomaterial engineering, which is difficult for large‐scale production. Here, ferroelectric Sn2P2S6 with layered nanostructure is developed as sodium ion storage material. The ferroelectricity‐enhanced pseudocapacitance of sodium ion in the interlayer spacing makes the electrochemical reaction easier and faster, endowing the Sn2P2S6 electrode with excellent rate capability and cycle stability. Furthermore, the facile solid state reaction synthesis and common electrode fabrication make the Sn2P2S6 that becomes a promising anode material of SIB. 相似文献
996.
997.
998.
一种基于聚苯胺(PANI)开发可再生的指标,可应用于智能包装表明罗非鱼新鲜程度。从绿到蓝孔雀的聚苯胺膜显示的颜色变化,表现为挥发性盐基氮量即将达到临界值(20毫克/100克),该聚苯胺膜可以回收至少3次。这种指示器是环保的和可再生,有助于生产厂家降低成本。 相似文献
999.
采用电石渣对石英岩尾砂进行煅烧改性,利用X射线衍射仪、背散射扫描电镜和能谱分析等方法对改性石英岩尾砂矿物组成和微观结构进行表征,并研究了改性石英岩尾砂的水化性能。通过背散射扫描电镜和压汞仪分析了掺改性石英岩尾砂水泥浆体的微界面结构与孔结构。结果表明:改性石英岩尾砂具有复合结构,内部是惰性的石英岩尾砂,表层为矿物β-C2S层。改性石英岩尾砂可水化生成C-S-H凝胶,改善了石英岩尾砂与水泥浆体的微界面,降低了水泥浆体的孔隙率。 相似文献
1000.
本文将抗硫酸盐水泥和中热水泥掺粉煤灰制备的水泥浆体浸泡在5%Na2SO4溶液至1110d,研究长龄期硫酸盐侵蚀下各试件的力学性能和微观结构。结果表明:限制空间中形成的细小钙矾石是引起基体开裂的主要原因,石膏的形成会引起水泥基材料剥落,抗硫酸盐水泥不能有效防止石膏型硫酸盐侵蚀;大掺量粉煤灰的二次水化反应能够消耗大量氢氧化钙,从而降低侵蚀过程中石膏相的形成且能有效改善浆体微结构;水电工程中采用中热水泥+50%粉煤灰制备的水泥基材料能够有效抑制钙矾石和石膏的形成,其抗硫酸盐侵蚀性能和经济性明显优于抗硫酸盐水泥制备的水泥基材料。 相似文献