全文获取类型
收费全文 | 272843篇 |
免费 | 76861篇 |
国内免费 | 50516篇 |
专业分类
电工技术 | 33634篇 |
技术理论 | 7篇 |
综合类 | 27892篇 |
化学工业 | 37597篇 |
金属工艺 | 30236篇 |
机械仪表 | 12763篇 |
建筑科学 | 19502篇 |
矿业工程 | 15845篇 |
能源动力 | 10635篇 |
轻工业 | 25922篇 |
水利工程 | 9142篇 |
石油天然气 | 17313篇 |
武器工业 | 4452篇 |
无线电 | 40090篇 |
一般工业技术 | 39473篇 |
冶金工业 | 10559篇 |
原子能技术 | 2427篇 |
自动化技术 | 62731篇 |
出版年
2024年 | 2727篇 |
2023年 | 5533篇 |
2022年 | 7246篇 |
2021年 | 8994篇 |
2020年 | 11156篇 |
2019年 | 19887篇 |
2018年 | 21579篇 |
2017年 | 23174篇 |
2016年 | 22778篇 |
2015年 | 22918篇 |
2014年 | 22476篇 |
2013年 | 22646篇 |
2012年 | 22622篇 |
2011年 | 19553篇 |
2010年 | 17890篇 |
2009年 | 14953篇 |
2008年 | 12729篇 |
2007年 | 11944篇 |
2006年 | 10557篇 |
2005年 | 9531篇 |
2004年 | 10802篇 |
2003年 | 9025篇 |
2002年 | 8657篇 |
2001年 | 7678篇 |
2000年 | 6788篇 |
1999年 | 6500篇 |
1998年 | 5468篇 |
1997年 | 4842篇 |
1996年 | 4556篇 |
1995年 | 4389篇 |
1994年 | 3659篇 |
1993年 | 3212篇 |
1992年 | 3000篇 |
1991年 | 2191篇 |
1990年 | 1735篇 |
1989年 | 1593篇 |
1988年 | 1218篇 |
1987年 | 418篇 |
1986年 | 372篇 |
1985年 | 243篇 |
1984年 | 186篇 |
1983年 | 128篇 |
1982年 | 180篇 |
1981年 | 170篇 |
1980年 | 120篇 |
1976年 | 243篇 |
1975年 | 210篇 |
1972年 | 240篇 |
1971年 | 130篇 |
1960年 | 205篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
61.
62.
Yong Xu Yun Li Songlin Li Francis Balestra Gerard Ghibaudo Wenwu Li Yen‐Fu Lin Huabin Sun Jing Wan Xinran Wang Yufeng Guo Yi Shi Yong‐Young Noh 《Advanced functional materials》2020,30(20)
Unreliable mobility values, and particularly greatly overestimated values and severely distorted temperature dependences, have recently hampered the development of the organic transistor field. Given that organic field‐effect transistors (OFETs) have been routinely used to evaluate mobility, precise parameter extraction using the electrical properties of OFETs is thus of primary importance. This review examines the origins of the various mobilities that must be determined for OFET applications, the relevant extraction methods, and the data selection limitations, which help in avoiding conceptual errors during mobility extraction. For increased precision, the review also discusses device fabrication considerations, calibration of both the specific gate‐dielectric capacitance and the threshold voltage, the contact effects, and the bias and temperature dependences, which must actually be handled with great care but have mostly been overlooked to date. This review serves as a systematic overview of the OFET mobility extraction process to ensure high precision and will also aid in improving future research. 相似文献
63.
中国的菊花主题花展(菊花展览)是最重要的赏菊形式,对我国3种主要类型的菊花展览,即综合性菊花展览(中国菊花展览会、国际博览会菊花专项展和各级城市菊花展)、菊花专类园和菊花花田花海的发展现状进行了研究,并分析了菊花展览在促进菊花产业发展、弘扬菊花文化、服务生态文明及美丽乡村建设、加强菊花非物质文化遗产保护中的重要作用,为推动我国菊花展览水平的提高提供借鉴。 相似文献
64.
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
65.
66.
67.
Qilin Liu Feng Ding 《International Journal of Adaptive Control and Signal Processing》2021,35(10):1970-1989
The identification of the Hammerstein–Wiener (H-W) systems based on the nonuniform input–output dataset remains a challenging problem. This article studies the identification problem of a periodically nonuniformly sampled-data H-W system. In addition, the product terms of the parameters in the H-W system are inevitable. In order to solve the problem, the key-term separation is applied and two algorithms are proposed. One is the key-term-based forgetting factor stochastic gradient (KT-FFSG) algorithm based on the gradient search. The other is the key-term-based hierarchical forgetting factor stochastic gradient (KT-HFFSG) algorithm. Compared with the KT-FFSG algorithm, the KT-HFFSG algorithm gives more accurate estimates. The simulation results indicate that the proposed algorithms are effective. 相似文献
68.
Baofeng Hou Hong He Ruixiu Jia Meilong Fu Yanbin Cao Shaoqun He Liwen Luo Youqing Huang 《应用聚合物科学杂志》2019,136(10):47161
The synthesis and performance of a novel temperature-tolerant foamed resin for enhanced oil recovery were investigated using various methods, including infrared, NMR, scanning electron microscopy (SEM), and displacement experiments. Polycondensation of furfuryl alcohol prepolymers was confirmed by the infrared and NMR results. The poor temperature tolerance of furfuryl alcohol prepolymers after gelation at high temperatures is mainly due to the fracture of furan rings. The addition of ester additives is an effective method of increasing the temperature tolerance of the prepared foamed resins and can effectively reduce the weight-loss rate of the polycondensation products. The SEM results show that the skeleton structure of the foamed resin remains intact after high-temperature treatment. Thus, the novel plugging agent system has excellent thermal stability and still has a high strength (>0.8 MPa) after high-temperature aging treatment for 40 days, giving the prepared foamed resin a good plugging performance (plugging rate > 91%) at 250 °C. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47161. 相似文献
69.
Dr. Jiayao Y. Wang Dr. Jiaqi Q. Li Prof. Dr. Yumei M. Xiao Prof. Dr. Bin Fu Prof. Dr. Zhaohai H. Qin 《ChemMedChem》2020,15(5):404-410
Mitochondrial oxidative damage and dysfunction contribute to a wide range of human diseases. Considering the limitation of conventional antioxidants and that mitochondria are the main source of reactive oxygen species (ROS) which induce oxidative damage, mitochondria-targeted antioxidants which can selectively block mitochondrial oxidative damage and prevent various types of cell death have been widely developed. As a lipophilic cation, triphenylphosphonium (TPP) has been commonly used in designing mitochondria-targeted antioxidants. Conjugated with the TPP moiety, antioxidants can achieve more than 1000-fold higher mitochondrial concentration depending on cell membrane potentials and mitochondrial membrane potentials. Herein we discuss the deficiencies of conventional antioxidants and the advantages of mitochondrial targeting, and review various types of TPP-based mitochondria-targeted antioxidants. These provide theoretical and background support for the design of new anti-oxidant. 相似文献
70.