全文获取类型
收费全文 | 49864篇 |
免费 | 8885篇 |
国内免费 | 9051篇 |
专业分类
化学 | 23207篇 |
晶体学 | 875篇 |
力学 | 2113篇 |
综合类 | 1012篇 |
数学 | 4536篇 |
物理学 | 14080篇 |
无线电 | 21977篇 |
出版年
2024年 | 190篇 |
2023年 | 880篇 |
2022年 | 1669篇 |
2021年 | 1814篇 |
2020年 | 1757篇 |
2019年 | 1665篇 |
2018年 | 1484篇 |
2017年 | 1934篇 |
2016年 | 1844篇 |
2015年 | 2353篇 |
2014年 | 2843篇 |
2013年 | 3585篇 |
2012年 | 3978篇 |
2011年 | 4183篇 |
2010年 | 3826篇 |
2009年 | 3902篇 |
2008年 | 4179篇 |
2007年 | 3832篇 |
2006年 | 3565篇 |
2005年 | 3075篇 |
2004年 | 2383篇 |
2003年 | 1784篇 |
2002年 | 1762篇 |
2001年 | 1716篇 |
2000年 | 1562篇 |
1999年 | 1064篇 |
1998年 | 633篇 |
1997年 | 501篇 |
1996年 | 529篇 |
1995年 | 412篇 |
1994年 | 384篇 |
1993年 | 378篇 |
1992年 | 328篇 |
1991年 | 254篇 |
1990年 | 236篇 |
1989年 | 198篇 |
1988年 | 185篇 |
1987年 | 171篇 |
1986年 | 122篇 |
1985年 | 111篇 |
1984年 | 110篇 |
1983年 | 90篇 |
1982年 | 74篇 |
1981年 | 56篇 |
1980年 | 35篇 |
1979年 | 42篇 |
1978年 | 23篇 |
1977年 | 15篇 |
1965年 | 14篇 |
1964年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 771 毫秒
941.
Fangchao Li Xuliang Zhang Junwei Shi Lujie Jin Jiawei Qiao Junjun Guo Hang Yin Youyong Li Jianyu Yuan Wanli Ma 《Advanced functional materials》2023,33(40):2302542
Organic–inorganic formamidinium lead triiodide (FAPbI3) hybrid perovskite quantum dot (QD) is of great interest to photovoltaic (PV) community due to its narrow band gap, higher ambient stability, and long carrier lifetime. However, the surface ligand management of FAPbI3 QD is still a key hurdle that impedes the design of high-efficiency solar cells. Herein, this study first develops a solution-mediated ligand exchange (SMLE) for preparing FAPbI3 QD film with enhanced electronic coupling. By dissolving optimal methylammonium iodide (MAI) into antisolvent to treat the FAPbI3 QD solution, the SMLE can not only effectively replace the long-chain ligands, but also passivate the A- and X-site vacancies. By combining experimental and theoretical results, this study demonstrates that the SMLE engineered FAPbI3 QD exhibits lower defect density, which is beneficial for fabricating high-quality QD arrays with desired morphology and carrier transport. Consequently, the SMLE FAPbI3 QD based solar cell outputs a champion efficiency of 15.10% together with improved long-term ambient storage stability, which is currently the highest reported value for hybrid perovskite QD solar cells. These results would provide new design principle of hybrid perovskite QDs toward high-performance optoelectronic application. 相似文献
942.
Chunliu Xu Weibo Hua Qinghua Zhang Yuan Liu Rongbin Dang Ruijuan Xiao Jin Wang Zhao Chen Feixiang Ding Xiaodong Guo Chao Yang Liangrong Yang Junmei Zhao Yong-Sheng Hu 《Advanced functional materials》2023,33(33):2302810
Na superionic conductor of Na3MnTi(PO4)3 only containing high earth-abundance elements is regarded as one of the most promising cathodes for the applicable Na-ion batteries due to its desirable cycling stability and high safety. However, the voltage hysteresis caused by Mn2+ ions resided in Na+ vacancies has led to significant capacity loss associated with Mn reaction centers between 2.5–4.2 V. Herein, the sodium excess strategy based on charge compensation is applied to suppress the undesirable voltage hysteresis, thereby achieving sufficient utilization of the Mn2+/Mn3+ and Mn3+/Mn4+ redox couples. These findings indicate that the sodium excess Na3.5MnTi0.5Ti0.5(PO4)3 cathode with Ti4+ reduction has a lowest Mn2+ occupation on the Na+ vacancies in its initial composition, which can improve the kinetics properties, finally contributing to a suppressed voltage hysteresis. Based on these findings, it is further applied the sodium excess route on a Mn-richer phosphate cathode, which enables the suppressed voltage hysteresis and more reversible capacity. Consequently, this developed Na3.6Mn1.15Ti0.85(PO4)3 cathode achieved a high energy density over 380 Wh kg−1 (based on active substance mass of cathode) in full-cell configurations, which is not only superior to most of the phosphate cathodes, but also delivers more application potential than the typical oxides cathodes for Na-ion batteries. 相似文献
943.
Yuan Deng Yihai Yang Yuanhang Xiao He-Lou Xie Ruochen Lan Lanying Zhang Huai Yang 《Advanced functional materials》2023,33(35):2301319
Switchable passive radiative cooling (PRC) smart windows can modulate sunlight transmission and spontaneously emit heat to outer space through atmospheric transparent window, presenting great potential in building energy conservation. However, realizing stable and on-demand control of the cooling efficiency for PRC materials is still challenging. Herein, an electro-controlled polymer-dispersed liquid crystal (PDLC) smart window showing PRC property is designed and prepared by adding mid-infrared emitting reactive monomers into the conventional PDLC matrix. It is found that not only the electro-optical properties but also the PRC efficiency of PRC PDLC film are tunable by regulating the content of the mid-infrared emitting components, film thickness, and micromorphology. This advanced PRC PDLC material achieves a near/sub-ambient temperature when the solar irradiance is below 400 W m−2 and can dynamically manage daytime cooling efficiency. Importantly, its PRC efficiency is capable of being tuned in an on-demand and ultrafast millisecond-scale way, whose controllable transparency enables multistage heat regulation. This study is hoped to provide new inspiration in the preparation of advanced optical devices and energy-efficient equipment. 相似文献
944.
Zhao-Yang Yin Yang Chen Yang-Yang Zhang Yu Yuan Qian Yang Ya-Nan Zhong Xu Gao Jing Xiao Zhao-Kui Wang Jian-Long Xu Sui-Dong Wang 《Advanced functional materials》2023,33(33):2302199
Minimizing reverse bias dark current density (Jdark) while retaining high external quantum efficiency is crucial for promising applications of perovskite photodiodes, and it remains challenging to elucidate the ultimate origin of Jdark. It is demonstrated in this study that the surface defects induced by iodine vacancies are the main cause of Jdark in perovskite photodiodes. In a targeted way, the surface defects are thoroughly passivated through a simple treatment with butylamine hydroiodide to form ultrathin 2D perovskite on its 3D bulk. In the passivated perovskite photodiodes, Jdark as low as 3.78 × 10-10 A cm-2 at -0.1 V is achieved, and the photoresponse is also enhanced, especially at low light intensities. A combination of the two improvements realizes high specific detectivity up to 1.46 × 1012 Jones in the devices. It is clarified that the trap states induced by the surface defects can not only raise the generation-recombination current density associated with the Shockley–Read–Hall mechanisms in the dark (increasing Jdark), but also provide additional carrier recombination paths under light illumination (decreasing photocurrent). The critical role of surface defects on Jdark of perovskite photodiodes suggests that making trap-free perovskite thin films, for example, by fine preparation and/or surface engineering, is a top priority for high-performance perovskite photodiodes. 相似文献
945.
Implicit polynomials (IPs) are considered as a powerful tool for object curve fitting tasks due to their simplicity and fewer parameters. The traditional linear methods, such as 3L, MinVar, and MinMax, often achieve good performances in fitting simple objects, but usually work poorly or even fail to obtain closed curves of complex object contours. To handle the complex fitting issues, taking the advantages of deep neural networks, we designed a neural network model continuity-sparsity constrained network (CSC-Net) with encoder and decoder structure to learn the coefficients of IPs. Further, the continuity constraint is added to ensure the obtained curves are closed, and the sparseness constraint is added to reduce the spurious zero sets of the fitted curves. The experimental results show that better performances have been obtained on both simple and complex object fitting tasks. 相似文献
946.
We systematically investigate the influence of growth interruption time on the properties of InAs/GaSb type-II superlattices (T2SLs) epitaxial materials grown by molecular beam epitaxy (MBE). X-ray diffraction (XRD) and atomic force microscope (AFM) are used to characterize the material quality and morphology. The full width at half maximum (FWHM) of the XRD 0th satellite peaks ranges from 32'' to 41'', and the root mean square (RMS) roughness on a 5 μm×5 μm scan area is 0.2 nm. Photoluminescence (PL) test is used to reveal the influence of the growth interruption time on the optical property. Grazing incidence X-ray reflectivity (GIXRR) measurements are performed to analyze the roughness of the interface. The interface roughness (0.24 nm) is optimal when the interruption time is 0.5 s. The crystal quality of T2SLs can be optimized with appropriate interruption time by MBE, which is a guide for the material epitaxy of high performance T2SL infrared detector. 相似文献
947.
Pengyu Dong Xin Xiang Yuan Liang Peng Wang Rui Wang 《International Journal of Communication Systems》2023,36(4):e5403
In this paper, the channel estimation and signal-to-noise ratio (SNR) estimation technique of single-carrier frequency domain equalization (SC-FDE) system under low SNR in aeronautical multipath channel are studied, a SNR estimation algorithm which is easy to implement in engineering and an improved LS channel estimation algorithm based on Kalman filter using minimum error entropy (MEE-KF) are proposed. This paper first introduces the SC-FDE system and introduces the principle of MEE-KF, and then, the channel estimation flow based on MEE-KF is obtained by combining it with the traditional LS channel estimation algorithm, which makes the estimation results perform better. Simulation results show that after getting more accurate noise variance, the channel estimation results can better follow the changes of the channel after MEE-KF processing, so as to resist the doppler frequency offset effect and make the channel estimation results more accurate, that is the channel response results of the data part can be closer to the real situation, so that the communication performance of SC-FDE system has also been greatly improved. 相似文献
948.
Tai Li Wei Luo Shangfeng Liu Jiajia Yang Renchun Tao Ye Yuan Zhaoying Chen Jinlin Wang Tao Wang Xin Rong Duo Li Zhen Huang Weiyun Wang Junjie Kang Xinqiang Wang 《Advanced functional materials》2023,33(3):2208171
AlGaN-based ultraviolet-B light-emitting diodes (UVB-LEDs) exhibit great potential in phototherapy, vitamin D3 synthesis promotion, plant growth regulation, and so on. However, subjected to the excess compressive strain induced by the large lattice mismatch between multiple quantum wells (MQWs) and AlN, UVB-LEDs that simultaneously satisfy the requirements of high light output power (LOP), low working voltage, and excellent stability are rarely reported. Here, a substrate-dominated strain-modulation strategy is proposed. By precisely manipulating the strain in AlN grown on nano-patterned sapphire substrate (NPSS) to a slightly tensile one, the compressive strain in the following Al0.55Ga0.45N underlayer and Al0.28Ga0.72N/Al0.45Ga0.55N MQWs is successfully suppressed. As a result, an outstanding UVB-LED with a peak wavelength at 303.6 nm is achieved. The 20 × 20 mil2 UVB-LED chip shows a wall-plug efficiency (WPE) of 3.27% under a forward current of 20 mA and a high LOP of 57.2 mW with an extremely low voltage of 5.87 V under a forward current of 800 mA. It is more exciting that the LOP degradation is as low as 17% after 1000 h operation under a forward current density of 75 A cm−2, showing excellent stability. The here-developed UVB-LED, with a high LOP and excellent reliability, will definitely promote the applications of AlGaN-based UVB-LEDs. 相似文献
949.
在智慧图书馆的建设中,广泛应用人工智能技术对图书馆传统的服务模式进行了突破。人工智能技术在信息化程度、读者服务、文献资源建设、信息咨询服务等方面都发挥了重要作用,要将人工智能与图书馆知识服务深度融合,全面提升智慧图书馆的智慧化知识服务水平。基于此,文中阐述了人工智能技术对智慧图书馆建设的意义,分析了人工智能技术在智慧图书馆建设中的具体应用,以期能为相关人员提供参考。 相似文献
950.
直放站在通信系统中十分重要,是一种中继产品,其质量好坏的衡量指标包括技术服务、整机是否可靠、低噪音系数、低IP3、智能化水平等。为了更好地发挥直放站的作用,需要创建监控系统,用于监控其电源质量。文中设计的监控系统,其控制核心为LPC1768,该处理器为嵌入式,能够对直放站中的多种供电电源进行监控。配合隔离ADC电路,可以实时监控直流供电与交流供电的电源质量。该监控系统能够同时完成和多接口通道的配合,并把供电数据传输到网管平台,使用平台对数据进行分析,从而达成直放站设备供电状况的实时监控、提前预警,以防电源质量问题给直放站造成不良影响,确保供电系统的安全与稳定。 相似文献