全文获取类型
收费全文 | 97498篇 |
免费 | 6481篇 |
国内免费 | 2171篇 |
专业分类
电工技术 | 3321篇 |
技术理论 | 2篇 |
综合类 | 2588篇 |
化学工业 | 17591篇 |
金属工艺 | 4559篇 |
机械仪表 | 5846篇 |
建筑科学 | 4198篇 |
矿业工程 | 1325篇 |
能源动力 | 3332篇 |
轻工业 | 6650篇 |
水利工程 | 889篇 |
石油天然气 | 2658篇 |
武器工业 | 338篇 |
无线电 | 14855篇 |
一般工业技术 | 16557篇 |
冶金工业 | 8119篇 |
原子能技术 | 1095篇 |
自动化技术 | 12227篇 |
出版年
2024年 | 212篇 |
2023年 | 1279篇 |
2022年 | 1985篇 |
2021年 | 3430篇 |
2020年 | 2439篇 |
2019年 | 2366篇 |
2018年 | 2714篇 |
2017年 | 2728篇 |
2016年 | 2948篇 |
2015年 | 3080篇 |
2014年 | 4145篇 |
2013年 | 6024篇 |
2012年 | 5792篇 |
2011年 | 6866篇 |
2010年 | 5302篇 |
2009年 | 5468篇 |
2008年 | 5251篇 |
2007年 | 4554篇 |
2006年 | 4442篇 |
2005年 | 3703篇 |
2004年 | 3121篇 |
2003年 | 2827篇 |
2002年 | 2712篇 |
2001年 | 2226篇 |
2000年 | 2112篇 |
1999年 | 2129篇 |
1998年 | 2967篇 |
1997年 | 2116篇 |
1996年 | 1811篇 |
1995年 | 1467篇 |
1994年 | 1110篇 |
1993年 | 944篇 |
1992年 | 711篇 |
1991年 | 685篇 |
1990年 | 582篇 |
1989年 | 552篇 |
1988年 | 420篇 |
1987年 | 351篇 |
1986年 | 305篇 |
1985年 | 273篇 |
1984年 | 232篇 |
1983年 | 188篇 |
1982年 | 180篇 |
1981年 | 153篇 |
1980年 | 155篇 |
1979年 | 119篇 |
1978年 | 108篇 |
1977年 | 131篇 |
1976年 | 177篇 |
1975年 | 90篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Minds and Machines - To address the rising concern that algorithmic decision-making may reinforce discriminatory biases, researchers have proposed many notions of fairness and corresponding... 相似文献
102.
The molecular design of short peptides to achieve a tailor-made functional architecture has attracted attention during the past decade but remains challenging as a result of insufficient understanding of the relationship between peptide sequence and assembled supramolecular structures. We report a hybrid-resolution model to computationally explore the sequence–structure relationship of self-assembly for tripeptides containing only phenylalanine and isoleucine. We found that all these tripeptides have a tendency to assemble into nanofibers composed of laterally associated filaments. Molecular arrangements within the assemblies are diverse and vary depending on the sequences. This structural diversity originates from (1) distinct conformations of peptide building blocks that lead to different surface geometries of the filaments and (2) unique sidechain arrangements at the filament interfaces for each sequence. Many conformations are available for tripeptides in solution, but only an extended β-strand and another resembling a right-handed turn are observed in assemblies. It was found that the sequence dependence of these conformations and the packing of resulting filaments are determined by multiple competing noncovalent forces, with hydrophobic interactions involving Phe being particularly important. The sequence pattern for each type of assembly conformation and packing has been identified. These results highlight the importance of the interplay between conformation, molecular packing, and sequences for determining detailed nanostructures of peptides and provide a detailed insight to support a more precise design of peptide-based nanomaterials. 相似文献
103.
104.
105.
Wenyun Yang Qiwei Hu Guanyi Qiao Liang Zha Shunquan Liu Jingzhi Han Honglin Du Yan Zhang Yingchang Yang Changsheng Wang 《中国稀土学报(英文版)》2019,37(10):1102-1107
In this work, we report the tuning effect of the Si substitution on the magnetic and high frequency electromagnetic properties of R2Fe17 compounds and their paraffin composites. It is found that the introduction of Si can remarkably improve the magnetic and electromagnetic properties of the R2Fe17 compounds, making the R2Fe17–xSix-paraffin composites excellent microwave absorption materials (MAMs). By introducing the Si element, their saturation magnetizations decrease slightly, while much higher Curie temperatures are obtained. Furthermore, better impedance match is reached due to the decrease of the high-frequency permittivity ε′ by about 40%–50%, which finally enhances the performance of the microwave absorption. The peak frequency (fRL) of the reflection loss (RL) curve moves toward high frequency domain and the qualified bandwidth (QB, RL ≤ ?10 dB) increases remarkably. The maximum QB of 3.3 GHz (12.0–15.3 GHz) is obtained for the Sm1.5Y0.5Fe15Si2-paraffin composite (d = 1.0 mm) and the maximum RL of ?53.6 dB is achieved for Nd2Fe15Si2-paraffin composite (d = 2.2 mm), both surpassing most of the reported MAMs. Additionally, a distinguished dielectric microwave absorption peak is observed, which further increases the QB in these composites. 相似文献
106.
Mohammad Reza Gaeeni Morteza Sasani Ghamsari Abbas Majd Abadi Mohammad Hossein Majles Ara Wooje Han Hyung‐Ho Park 《Journal of the American Ceramic Society》2015,98(6):1818-1822
A facile sol–gel procedure has been developed for the synthesis of colloidal alumina nanocrystals. For the first time, optical characterization procedures were employed to study the quantum confinement effects in optical properties of the prepared Al2O3 sol. Accordingly, the hyperbolic band model was used to determine the optical band gap of colloidal alumina nanocrystals. X‐Ray diffraction pattern was used to study the crystallographic phase of the dried gel. Morphological characterization was performed using scanning electron microscopy (SEM). Inductively Coupled Plasma (ICP) emission spectroscopy was used to determination purity of the Al2O3 powder. High‐resolution TEM showed that the diameter of colloidal nanocrystals is about 10 nm. Photoluminescence spectroscopy demonstrated that quantum yields for colloidal nanocrystals are 68% with 300 nm excitation wavelength. The experimental observations confirm that highly stable alumina sol with strong UV emission was synthesized. The mentioned optical properties have not been reported before. 相似文献
107.
Inam Ridha Ali Basiri Sudhakar Godeshala Md Zubair Ebne Rafique Deepanjan Ghosh Jason Williams Nikhilesh Chawla Jung Keun Lee Jacquelyn Kilbourne Yu Yao Kaushal Rege 《Advanced functional materials》2021,31(6):2007811
Poor strength, infection, leakage, long procedure times, and inflammation limit the efficacy of common tissue sealing devices in surgeries and trauma. Light-activated sealing is attractive for tissue sealing and repair, and can be facilitated by the generation of local heat following absorption of nonionizing laser energy by chromophores. Here, the inherent ability of biomaterials is exploited to absorb nonionizing, mid-infrared (midIR) light in order to engender rapid photothermal sealing and repair of soft tissue wounds. In this approach, the biomaterial simultaneously acts as a photothermal convertor as well as a biosealant, which dispenses the need for exogeneous light-absorbing nanoparticles or dyes. Biomechanical recovery, mathematical modeling, histopathology analyses, tissue strain mapping using digital imaging correlation, and visualization of the biosealant-tissue interface using hyperspectral imaging indicate superior performance of midIR sealing in live mice compared to conventional sutures and glue. The midIR-biosealant approach demonstrates rapid sealing of soft tissues, improves cosmesis, lowers potential for scarring, obviates safety concerns because of the nonionizing light used, and allows adoption of a wide diversity of biomaterials. Taken together, the studies demonstrate a novel advance both in biomaterials for surgical sealing along with the use of nonionizing midIR light, with high potential for clinical translation. 相似文献
108.
109.
Youngseok Lee Cheolmin Park Nagarajan Balaji Youn-Jung Lee Vinh Ai Dao 《Israel journal of chemistry》2015,55(10):1050-1063
Over the past few decades, crystalline silicon solar cells have been extensively studied due to their high efficiency, high reliability, and low cost. In addition, these types of cells lead the industry and account for more than half of the market. For the foreseeable future, Si will still be a critical material for photovoltaic devices in the solar cell industry. In this paper, we discuss key issues, cell concepts, and the status of recent high-efficiency crystalline silicon solar cells. 相似文献
110.
Since researchers began studying the mechanism of flavonoids’ anticancer activity, little attention has been focused on the modulation of redox state in cells as a potential chemotherapeutic strategy. However, recent studies have begun identifying that the anticancer effect of flavonoids occurs both in their antioxidative activity which scavenges ROS and their prooxidative activity which generates ROS. Against this backdrop, this study attempts to achieve a comprehensive analysis of the individual and separate study findings regarding flavonoids’ modulation of redox state in cancer cells. It focuses on the mechanism behind the anticancer effect, and mostly on the modulation of redox potential by flavonoids such as quercetin, hesperetin, apigenin, genistein, epigallocatechin-3-gallate (EGCG), luteolin and kaempferol in both in vitro and animal models. In addition, the clinical applications of and bioavailability of flavonoids were reviewed to help build a treatment strategy based on flavonoids’ prooxidative potential. 相似文献