全文获取类型
收费全文 | 11418篇 |
免费 | 1407篇 |
国内免费 | 963篇 |
专业分类
化学 | 5679篇 |
晶体学 | 132篇 |
力学 | 477篇 |
综合类 | 72篇 |
数学 | 791篇 |
物理学 | 2949篇 |
综合类 | 3688篇 |
出版年
2024年 | 39篇 |
2023年 | 222篇 |
2022年 | 329篇 |
2021年 | 388篇 |
2020年 | 434篇 |
2019年 | 374篇 |
2018年 | 331篇 |
2017年 | 315篇 |
2016年 | 469篇 |
2015年 | 493篇 |
2014年 | 671篇 |
2013年 | 722篇 |
2012年 | 807篇 |
2011年 | 836篇 |
2010年 | 561篇 |
2009年 | 510篇 |
2008年 | 668篇 |
2007年 | 556篇 |
2006年 | 523篇 |
2005年 | 432篇 |
2004年 | 310篇 |
2003年 | 307篇 |
2002年 | 239篇 |
2001年 | 204篇 |
2000年 | 239篇 |
1999年 | 313篇 |
1998年 | 284篇 |
1997年 | 284篇 |
1996年 | 293篇 |
1995年 | 244篇 |
1994年 | 207篇 |
1993年 | 171篇 |
1992年 | 161篇 |
1991年 | 151篇 |
1990年 | 141篇 |
1989年 | 125篇 |
1988年 | 108篇 |
1987年 | 78篇 |
1986年 | 61篇 |
1985年 | 41篇 |
1984年 | 25篇 |
1983年 | 15篇 |
1982年 | 19篇 |
1981年 | 15篇 |
1980年 | 12篇 |
1979年 | 7篇 |
1975年 | 5篇 |
1974年 | 5篇 |
1970年 | 12篇 |
1937年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 359 毫秒
41.
42.
动态帧长ALOHA信令在集群移动通信中的应用 总被引:2,自引:0,他引:2
本文介绍了在集群动通信中,运用动态帧长ALOHA信令技术解决信道共用中停产碰撞问题的原理,并具体介绍了MPT-1327协议的接续原理,特点,信息格式及呼吊建立过程和举例,文中还对动态帧长的算法作了简介。 相似文献
43.
聊城地区历史悠久,旅游资源丰富,但旅游事业起步晚,开发利用不够.为此,本文在分析聊城地区旅游资源的功能和分布的基础上,①对旅游资源的特色进行了初步评价,进而提出开发聊城地区游资源的几点设想. 相似文献
44.
45.
本文采用激光衍射法和光学显微计算机图像系统及自行开发的软件,测量了三个典型煤在快速加热初期燃烧、等温加热燃烧和火焰燃烧方式的颗粒尺寸,运用分数维理论,建立了煤燃烧颗粒破碎理论,实验和理论研究揭示了煤燃烧中颗粒尺寸变化的本质,理论计算和实验结果符合良好。 相似文献
46.
47.
Preparation and microwave absorption properties of electroless Co-Ni-P coated strontium ferrite powder 总被引:1,自引:0,他引:1
A new type of Co-Ni-P coated strontium ferrite nanocomposite was prepared with electroless plating enhanced by ultrasonic wave at room temperature. The plating process was studied carefully. The morphology, crystal structure and microwave absorption properties of the Co-Ni-P coated powder were studied with field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), energy dispersive analysis of X-rays (EDX) and vector network analyzer. The results show that the strontium ferrite powder was successfully coated with Co-Ni-P alloy and possesses excellent microwave absorption properties. The maximum microwave loss of the composite powder reaches −44.12 dB. The bandwidth with the loss above −10 dB exceeds 13.8 GHz. 相似文献
48.
The dendrite growth process of transparent NaBi(WO4)2 with small prandtl and high melting point was studied by using the in-situ observation system. According to the dynamic images and detailed information, there are two kinds of restriction effect on
the dendrite growth, the competition between arms and branches and the convection in the melt. The dendrite growth rate was
time dependent, and the rate of arm growth reached the maximum 5.8 mm/s in the diffusive-advective region and rapidly decreased
in the diffusive-convective region. The growth rate of branch had the same change trends as the arm’s. Based on the EPMA-EDS
data of solidification structure of quenched NaBi(WO4)2 melt, it was found that there were component differences from stoichiometric concentration in the melt near the interface
during the growth process.
Supported by the National Natural Science Foundation of China (Grant No. 50331040) and the Innovation Funds from Shanghai
Institute of Ceramics, Chinese Academy of Sciences (Grant No. SCX0623) 相似文献
49.
For exponential weights, a necessary condition of weighted mean convergence for Lagrange interpolation is given. 相似文献
50.
Y. Zhang T. M. Benson P. Sewell A. Vukovic D. Zhang W. J. Pan A Loni D. Furniss A. B. Seddon 《Optical and Quantum Electronics》2006,38(1-3):97-110
This paper presents our recent simulation results and novel designs of single mode large cross-section glass-based waveguides for photonic integrated circuits (PICs). Simulations were performed using an in-house Finite Difference (FD) based mode solver and the FD Beam propagation Method (FD-BPM). Our simulation results show that this innovative technology could provide a simplified means to couple optical energy efficiently between optical components in a single chip. This would provide the base for the future large-scale integration of optical components in PICs. The novel idea of using single mode large cross-section glass-based waveguides as an optical integration platform is an evolutionary innovative solution for the monolithic integration of optical components, in which the glass-based structures act both as waveguides and as an optical bench for integration. This allows easy and efficient optical coupling between optical components and optical fibres, removing costly and tedious alignment problems and considerably reducing optical coupling losses in PICs. We expect that the glass-based waveguide PICs technology will enable the emergence of a new generation of compact, reliable, high speed, and multifunctional devices. 相似文献