全文获取类型
收费全文 | 417742篇 |
免费 | 71798篇 |
国内免费 | 46710篇 |
专业分类
电工技术 | 31932篇 |
综合类 | 20472篇 |
化学工业 | 56656篇 |
金属工艺 | 33425篇 |
机械仪表 | 12817篇 |
建筑科学 | 16783篇 |
矿业工程 | 13451篇 |
能源动力 | 15086篇 |
轻工业 | 40297篇 |
水利工程 | 9196篇 |
石油天然气 | 14791篇 |
武器工业 | 3505篇 |
无线电 | 62312篇 |
一般工业技术 | 76739篇 |
冶金工业 | 54462篇 |
原子能技术 | 6031篇 |
自动化技术 | 68295篇 |
出版年
2024年 | 2512篇 |
2023年 | 4695篇 |
2022年 | 5820篇 |
2021年 | 7004篇 |
2020年 | 9715篇 |
2019年 | 19663篇 |
2018年 | 22451篇 |
2017年 | 23743篇 |
2016年 | 23632篇 |
2015年 | 21094篇 |
2014年 | 21317篇 |
2013年 | 27870篇 |
2012年 | 21626篇 |
2011年 | 20147篇 |
2010年 | 17454篇 |
2009年 | 15448篇 |
2008年 | 14078篇 |
2007年 | 13490篇 |
2006年 | 11586篇 |
2005年 | 10497篇 |
2004年 | 13367篇 |
2003年 | 12313篇 |
2002年 | 11495篇 |
2001年 | 11209篇 |
2000年 | 10219篇 |
1999年 | 10494篇 |
1998年 | 20273篇 |
1997年 | 14794篇 |
1996年 | 12048篇 |
1995年 | 9881篇 |
1994年 | 8615篇 |
1993年 | 8364篇 |
1992年 | 6574篇 |
1991年 | 5769篇 |
1990年 | 5217篇 |
1989年 | 4930篇 |
1988年 | 4529篇 |
1987年 | 3316篇 |
1986年 | 3202篇 |
1985年 | 3419篇 |
1984年 | 3064篇 |
1983年 | 2936篇 |
1982年 | 2790篇 |
1981年 | 2701篇 |
1980年 | 2572篇 |
1979年 | 2382篇 |
1978年 | 2201篇 |
1977年 | 2642篇 |
1976年 | 3779篇 |
1975年 | 1948篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
积分中值屈服准则解析厚板轧制椭圆速度场 总被引:1,自引:0,他引:1
为解决非线性Mises比塑性功率积分困难以及由此导致的轧制功率解析式难以获得的问题,本文通过建立并利用线性比塑性功率表达式对提出的椭圆速度场进行能量分析,得到了轧制力能参数的解析解.文中通过对变角度屈服函数求积分中值,构建了一个新的屈服准则,它是主应力分量的线性组合,在π平面上的轨迹是逼近Mises圆的等边非等角的十二边形,其基于Lode参数表达式的理论结果也与实验数据吻合较好.同时,根据厚板轧制时金属流动速度从入口到出口逐渐增大的特点,提出了水平速度分量满足椭圆方程的速度场,该速度场满足运动许可条件.通过相应的轧制能量分析,获得了基于线性屈服准则的内部变形功率以及基于应变矢量内积法上的摩擦功率与剪切功率.在此之上,通过泛函的极值变分导出了轧制力矩、轧制力以及应力状态系数的解析解,并与现场实测数据进行了对比,结果表明利用本文提出的屈服准则与速度场所建立的轧制力矩与轧制力模型与实测值吻合较好,其中轧制力误差小于5.3%,轧制力矩误差在6%左右. 相似文献
72.
Manoj Karakoti Ritu Jangra Sandeep Pandey Pawan Singh Dhapola Sunil Dhali Suman Mahendia Pramod K Singh Nanda Gopal Sahoo 《International Journal of Applied Ceramic Technology》2020,17(4):1899-1908
This study deals with the utility of mini spray dryer process to improve the dispersibility, of graphene oxide(GO) and its application for high-performance supercapacitor. Initially, the neutral solution of GO was obtained using the modified Hummer's method. After this, the prepared GO solution was processed by mini spray dryer to obtain a more purified, lighter, and dispersed form of GO which is named as spray dryer processed GO (SPGO). The SPGO thus obtained showed excellent dispersibility behavior with various solvents, which is not found in case of conventional oven drying. Furthermore, utility of SPGO and its reduced form (r-SPGO) for supercapacitor applications have been investigated. Results obtained from the cyclic voltammetry(CV) analysis, impedance, and charge-discharge behavior of supercapacitor fabricated using r-SPGO shows enhanced features. Therefore, the simple spray dried GO and its reduced form, that is, r-SPGO can be utilized as a potential candidate for the supercapacitor application. Herein, as synthesized SPGO exhibited the specific capacitance of 12.07 and 37.6 F/g with PVA-H3PO4 and 1 mol/L H3PO4, respectively, at a scan rate of 5 mV/s. On the other hand, reduced form of SPGO, that is, r-SPGO showed the specific capacitance of 27.16 and 230 F/g with PVA-H3PO4 and 1 mol/L H3PO4, respectively. 相似文献
73.
Konstantinos Spyrou Matteo Calvaresi Evmorfia K. Diamanti Theodoros Tsoufis Dimitrios Gournis Petra Rudolf Francesco Zerbetto 《Advanced functional materials》2015,25(2):263-269
Experimental and theoretical studies are performed in order to illuminate, for first time, the intercalation mechanism of polycyclic aromatic molecules into graphite oxide. Two representative molecules of this family, aniline and naphthalene amine are investigated. After intercalation, aniline molecules prefer to covalently connect to the graphene oxide matrix via chemical grafting, while napthalene amine molecules bind with the graphene oxide surface through π–π interactions. The presence of intercalated aromatic molecules between the graphene oxide layers is demonstrated by X‐ray diffraction, while the type of interaction between graphene oxide and polycyclic organic molecules is elucidated by X‐ray photoelectron spectroscopy. Combined quantum mechanical and molecular mechanical calculations describe the intercalation mechanism and the aniline grafting, rationalizing the experimental data. The present work opens new perspectives for the interaction of various aromatic molecules with graphite oxide and the so‐called “intercalation chemistry”. 相似文献
74.
75.
Emma Layton Anna-Marie Fairhurst Sam Griffiths-Jones Richard K. Grencis Ian S. Roberts 《International journal of molecular sciences》2020,21(23)
In eukaryotes, microRNAs (miRNAs) have roles in development, homeostasis, disease and the immune response. Recent work has shown that plant and mammalian miRNAs also mediate cross-kingdom and cross-domain communications. However, these studies remain controversial and are lacking critical mechanistic explanations. Bacteria do not produce miRNAs themselves, and therefore it is unclear how these eukaryotic RNA molecules could function in the bacterial recipient. In this review, we compare and contrast the biogenesis and functions of regulatory RNAs in eukaryotes and bacteria. As a result, we discovered several conserved features and homologous components in these distinct pathways. These findings enabled us to propose novel mechanisms to explain how eukaryotic miRNAs could function in bacteria. Further understanding in this area is necessary to validate the findings of existing studies and could facilitate the use of miRNAs as novel tools for the directed remodelling of the human microbiota. 相似文献
76.
77.
78.
79.
80.