全文获取类型
收费全文 | 46569篇 |
免费 | 4007篇 |
国内免费 | 2553篇 |
专业分类
电工技术 | 2978篇 |
技术理论 | 2篇 |
综合类 | 2600篇 |
化学工业 | 6933篇 |
金属工艺 | 2874篇 |
机械仪表 | 2307篇 |
建筑科学 | 3483篇 |
矿业工程 | 1052篇 |
能源动力 | 1386篇 |
轻工业 | 4153篇 |
水利工程 | 788篇 |
石油天然气 | 1732篇 |
武器工业 | 335篇 |
无线电 | 5752篇 |
一般工业技术 | 7563篇 |
冶金工业 | 2959篇 |
原子能技术 | 624篇 |
自动化技术 | 5608篇 |
出版年
2024年 | 234篇 |
2023年 | 794篇 |
2022年 | 1470篇 |
2021年 | 1879篇 |
2020年 | 1505篇 |
2019年 | 1217篇 |
2018年 | 1452篇 |
2017年 | 1522篇 |
2016年 | 1436篇 |
2015年 | 1784篇 |
2014年 | 2251篇 |
2013年 | 3150篇 |
2012年 | 3122篇 |
2011年 | 3432篇 |
2010年 | 2773篇 |
2009年 | 2798篇 |
2008年 | 2652篇 |
2007年 | 2488篇 |
2006年 | 2348篇 |
2005年 | 1856篇 |
2004年 | 1436篇 |
2003年 | 1168篇 |
2002年 | 1076篇 |
2001年 | 1042篇 |
2000年 | 1077篇 |
1999年 | 1000篇 |
1998年 | 1177篇 |
1997年 | 894篇 |
1996年 | 821篇 |
1995年 | 595篇 |
1994年 | 514篇 |
1993年 | 376篇 |
1992年 | 318篇 |
1991年 | 277篇 |
1990年 | 215篇 |
1989年 | 195篇 |
1988年 | 129篇 |
1987年 | 92篇 |
1986年 | 92篇 |
1985年 | 65篇 |
1984年 | 62篇 |
1983年 | 50篇 |
1982年 | 46篇 |
1981年 | 27篇 |
1980年 | 35篇 |
1979年 | 21篇 |
1978年 | 20篇 |
1977年 | 17篇 |
1974年 | 13篇 |
1970年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
通过花式捻线方法将中空涤纶、不锈钢长丝和竹炭纤维三种功能性纤维并捻获得复合纱线,利用纱线强度、毛羽和实际捻度测试,得到最佳的纱线纺制参数。并采用最佳工艺参数纺制的包绕纱线进行平纹织物织造,对其织物透湿性、远红外发射率以及保温性能进行测试表征,最终制备一种可用于防寒服的新型保温透湿织物。结果表明,缠绕捻度为上捻度200,下捻度0时,纺制的包芯纱具有最佳捻度。中空涤纶/不锈钢/竹炭织物透湿率为5 184g/(m2·24h),达到透湿织物透湿要求的2倍以上。一至四层织物的远红外发射率均在70%及以上,符合远红外发射率具有功能性结果的范围。织物克罗值达到7.355clo,高于极低温作业穿着克罗值51.6%,可满足极低温环境下的织物保温要求。织物保温率为62.43%,相比于棉、毛等传统纺织原料,织物保温率可以提升2倍以上。 相似文献
992.
制备钨合金面临着再结晶温度低、韧脆转变温度高、高温强度低及寿命短等问题。稀土氧化物氧化镧(La2O3)添加到钨合金内,再结晶温度提高、韧脆转变温度下降、高温强度提高,所以钨材料内添加La2O3是最近几年国内外的热门研究课题之一。主要介绍了高温强度强、再结晶温度低、寿命长的W-La2O3合金的最佳La2O3添加含量以及改善这些性质的一些方法,最后指出了该合金待解决的一些问题及其发展趋势。 相似文献
993.
本文基于Ciarlet-Lods-Miara定义的柔性壳模型提出一种Galerkin非协调有限元离散格式.首先,对积分区域进行Delaunay三角剖分,并在三角网格上对位移前两个分量用一次Lagrange多项式逼近,对第三个分量(即法向位移)用非协调Morley元逼近.其次,讨论了构造的Galerkin非协调有限元离散格式解的存在性、唯一性和先验误差估计.最后对特殊边界条件下的锥壳采用该方法进行数值实验,计算出不同网格下锥壳的位移,并通过分析数值实验结果证明有限元离散格式的收敛性和有效性. 相似文献
994.
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
995.
Duyao Zhang Shoujin Sun Dong Qiu Mark A. Gibson Matthew S. Dargusch Milan Brandt Ma Qian Mark Easton 《Advanced Engineering Materials》2018,20(5)
996.
Sub‐Micron Anisotropic InP‐based III–V Semiconductor Material Deep Etching for On‐Chip Laser Photonics Devices
下载免费PDF全文
![点击此处可从《Advanced Engineering Materials》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Doris Keh‐Ting Ng Chee Wei Lee Vivek Krishnamurthy Qian Wang 《Advanced Engineering Materials》2018,20(2)
997.
Afrin Mehjabeen Tingting Song Wei Xu Hui Ping Tang Ma Qian 《Advanced Engineering Materials》2018,20(9)
998.
The Influence of Carbon Nitride Nanosheets Doping on the Crystalline Formation of MIL‐88B(Fe) and the Photocatalytic Activities
下载免费PDF全文
![点击此处可从《Small (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Zhen‐Dong Lei Yuan‐Cheng Xue Wen‐Qian Chen Lin Li Wen‐Hui Qiu Yong Zhang Liang Tang 《Small (Weinheim an der Bergstrasse, Germany)》2018,14(35)
In this research, bulk graphitic carbon nitride (g‐C3N4) is exfoliated and transferred to the carbon nitride nanosheets (CNNSs), which are then coupled with MIL‐88B(Fe) to form the hybrid. From the results of the powder X‐ray diffraction, scanning electronic microscopy and thermogravimetric analysis, it is found that the doping of CNNSs on the surface of MIL‐88(Fe) could maintain the basic structure of MIL‐88B(Fe), and the smaller dimension of CNNSs might influence the crystallization process of metal‐organic frameworks (MOFs) compared to bulk g‐C3N4. Besides, the effects of the CNNSs incorporation on photocatalysis are also investigated. Through the photoluminescence spectra, electrochemical measurements, and photocatalytic experiments, the hybrid containing 6% CNNSs is certified to possess the highest catalytic activity to degrade methylene blue and reduce Cr(VI) under visible light. The improvement of the photocatalytic performance can be attributed to the matched energy level which favors the formation of the heterojunctions. Besides, it promotes the charge migration such that the contact between MOFs and CNNSs is more intimate, which can be inferred from the electronic microscopy images. Finally, a possible photocatalytic mechanism is put forward by the relative calculation and the employment of the scavengers to trap the active species. 相似文献
999.
Web‐Like Interconnected Carbon Networks from NaCl‐Assisted Pyrolysis of ZIF‐8 for Highly Efficient Oxygen Reduction Catalysis
下载免费PDF全文
![点击此处可从《Small (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Yuhong Qian Tao An Karl Erik Birgersson Zhaolin Liu Dan Zhao 《Small (Weinheim an der Bergstrasse, Germany)》2018,14(16)
The oxygen reduction reaction (ORR) is under intense research due to its significance in energy storage and conversion processes. Recent studies show that interconnected and hierarchically porous structures can further enhance ORR kinetics as well as catalyst durability, but their preparation can be quite time and/or chemical consuming. Here, a simple approach is reported to prepare such complex structures by pyrolyzing composites containing NaCl and ZIF‐8. The templating effect of molten NaCl connects ZIF‐8 particles into web‐like carbon networks. During ORR activity measurements, it achieves a 0.964 V onset potential and a 38 mV dec?1 Tafel slope, which are comparable to those of the benchmark Pt/C (0.979 V and 40 mV dec?1). Due to the metal‐free feature, this catalyst exhibits a 16 mV shift in half‐wave potential after a 10 000‐cycle durability test, which is only 60% of that of Pt/C. The catalyst is also tested in Zn–air batteries and the assemblies are able to work at above 1.2 V for 140 h, which triples the life held by those with Pt/C. This study demonstrates a facile strategy to prepare metal‐free ORR catalysts with interconnectivity and hierarchical porosity, and proves their great potentials in ORR catalysis and Zn–air batteries. 相似文献
1000.
本文研究了紫外光辐照对注射成型聚碳酸酯制品的光学性能和拉伸性能的影响。结果表明,紫外老化240h后,制品表面发生了光-弗里斯重排和光氧化反应,生成了有色基团,制品颜色变黄,紫外吸光率增加;拉伸强度和韧性降低。热氧老化对照实验表明,在60℃下,紫外光辐照对注射成型聚碳酸酯制品性能降低起主要作用。 相似文献