全文获取类型
收费全文 | 50549篇 |
免费 | 5038篇 |
国内免费 | 2363篇 |
专业分类
化学 | 10204篇 |
晶体学 | 162篇 |
力学 | 3256篇 |
综合类 | 694篇 |
数学 | 13642篇 |
物理学 | 10978篇 |
无线电 | 19014篇 |
出版年
2024年 | 73篇 |
2023年 | 514篇 |
2022年 | 857篇 |
2021年 | 1157篇 |
2020年 | 1138篇 |
2019年 | 934篇 |
2018年 | 913篇 |
2017年 | 1404篇 |
2016年 | 1754篇 |
2015年 | 1754篇 |
2014年 | 2896篇 |
2013年 | 3268篇 |
2012年 | 2936篇 |
2011年 | 3034篇 |
2010年 | 2540篇 |
2009年 | 3068篇 |
2008年 | 3289篇 |
2007年 | 3269篇 |
2006年 | 2978篇 |
2005年 | 2363篇 |
2004年 | 2085篇 |
2003年 | 2187篇 |
2002年 | 1758篇 |
2001年 | 1457篇 |
2000年 | 1288篇 |
1999年 | 1139篇 |
1998年 | 996篇 |
1997年 | 761篇 |
1996年 | 678篇 |
1995年 | 576篇 |
1994年 | 482篇 |
1993年 | 442篇 |
1992年 | 480篇 |
1991年 | 323篇 |
1990年 | 252篇 |
1989年 | 218篇 |
1988年 | 201篇 |
1987年 | 190篇 |
1986年 | 135篇 |
1985年 | 180篇 |
1984年 | 150篇 |
1983年 | 97篇 |
1982年 | 172篇 |
1981年 | 225篇 |
1980年 | 253篇 |
1979年 | 268篇 |
1978年 | 219篇 |
1977年 | 161篇 |
1976年 | 161篇 |
1973年 | 92篇 |
排序方式: 共有10000条查询结果,搜索用时 982 毫秒
1.
大气波导干扰是特定气象条件下发生的时分双工(time-division duplex,TDD)系统内干扰,是TDD移动通信系统大规模组网面临的顽疾。在总结分析大气波导干扰成因和分类等的基础上,对大气波导干扰进行建模和表征,验证了海量干扰源在时域和频域的功率集总特征,并结合大量4G/5G现网实测数据给出了典型条件下内陆波导和海面波导的量化干扰信号传播模型,对于干扰的预测和预防具有重要意义。基于干扰特征,给出了TDD系统预防大气波导干扰的帧结构与组网的4项设计原则,5G现网数据表明干扰控制方案有效,上行干扰下降10 dB以上,相关原则对于6G系统的设计也具有指导意义。 相似文献
2.
深挖高职院校公选课“生活中的化学”的育人元素,精心设计教学内容,运用课堂主题辩论、趣味生活实验的设计与展示、探秘生活中的化学等理论知识传授与课内外实践相结合的教学方式,实现全过程育人,充分展现了公选课在立德树人方面的价值。 相似文献
3.
4.
《Annales de l'Institut Henri Poincaré (C) Analyse Non Linéaire》2021,38(5):1337-1371
In this paper we consider minimizers of the functional where is a bounded open set and where are the first k eigenvalues on Ω of an operator in divergence form with Dirichlet boundary condition and with Hölder continuous coefficients. We prove that the optimal sets have finite perimeter and that their free boundary is composed of a regular part, which is locally the graph of a -regular function, and a singular part, which is empty if , discrete if and of Hausdorff dimension at most if , for some . 相似文献
5.
6.
《Mechatronics》2022
This paper considers the shared path following control of an unmanned ground vehicle by a single person. A passive measure of human intent is used to blend the human and machine inputs in a mixed initiative approach. The blending law is combined with saturated super-twisting sliding mode speed and heading controllers, so that exogenous disturbances can be counteracted via equivalent control. It is proven that when the proposed blending law is used, the combined control signals from both the human and automatic controller respect the actuator magnitude constraints of the machine. To demonstrate the approach, shared control experiments are performed using an unmanned ground vehicle, which follows a lawn mower pattern shaped path. 相似文献
7.
Stefano Mariani Antonino Amedeo La Mattina Alessandro Paghi Lucanos Strambini Giuseppe Barillaro 《Advanced functional materials》2021,31(26):2100774
Here, a fluoride-assisted route for the controlled in-situ synthesis of metal nanoparticles (NPs) (i.e., AgNPs, AuNPs) on polydimethylsiloxane (PDMS) is reported. The size and coverage of the NPs on the PDMS surface are modulated with time and over space during the synthetic process, leveraging the improved yield (10×) and faster kinetics (100×) of NP formation in the presence of F− ions, compared to fluoride-free approaches. This enables the maskless preparation of both linear and step gradients and patterns of NPs in 1D and 2D on the PDMS surface. As an application in flexible plasmonics/photonics, continuous and step-wise spatial modulations of the plasmonic features of PDMS slabs with 1D and 2D AgNP gradients on the surface are demonstrated. An excellent spatially resolved tuning of key optical parameters, namely, optical density from zero to 5 and extinction ratio up to 100 dB, is achieved with AgNP gradients prepared in AgF solution for 12 minutes; the performance are comparable to those of commercial dielectric/interference filters. When used as a rejection filter in optical fluorescence microscopy, the AgNP-PDMS slabs are able to reject the excitation laser at 405 nm and retain the green fluorescence of microbeads (100 µm) used as test cases. 相似文献
8.
Dr. Chenge Li Dr. Alison G. Tebo Marion Thauvin Marie-Aude Plamont Prof. Dr. Michel Volovitch Dr. Xavier Morin Prof. Dr. Sophie Vriz Prof. Dr. Arnaud Gautier 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(41):18073-18079
Far-red emitting fluorescent labels are highly desirable for spectral multiplexing and deep tissue imaging. Here, we describe the generation of frFAST (far-red Fluorescence Activating and absorption Shifting Tag), a 14-kDa monomeric protein that forms a bright far-red fluorescent assembly with (4-hydroxy-3-methoxy-phenyl)allylidene rhodanine (HPAR-3OM). As HPAR-3OM is essentially non-fluorescent in solution and in cells, frFAST can be imaged with high contrast in presence of free HPAR-3OM, which allowed the rapid and efficient imaging of frFAST fusions in live cells, zebrafish embryo/larvae, and chicken embryos. Beyond enabling the genetic encoding of far-red fluorescence, frFAST allowed the design of a far-red chemogenetic reporter of protein–protein interactions, demonstrating its great potential for the design of innovative far-red emitting biosensors. 相似文献
9.
10.
《Wave Motion》2018
Large cable net structures have been widely applied in aerospace engineering due to the feature of light-weight, high packaging efficiency, and high thermal stability. Structural vibrations induced by a variety of disturbances are inevitable in the space environment, resulting in the requirement of effective vibration control strategies for large cable net structures. Since the large cable net structures have many closely spaced vibrational modes in the range of low frequencies, traditional modal based control may cause modal truncation and spillover problems. In this paper, a wave-based boundary control strategy is adopted and its effectiveness to control the vibration of cable net structures is investigated, by transfer function analysis and numerical methods. It is found that the structural vibration can be absolutely resisted by applying the wave-based boundary controllers onto all the exterior nodes, when disturbances come from the external boundaries of the cable net. Our results in this paper can provide a theoretical basis for the vibration control of large cable net structures. 相似文献