全文获取类型
收费全文 | 749185篇 |
免费 | 92569篇 |
国内免费 | 122254篇 |
专业分类
化学 | 503009篇 |
晶体学 | 7986篇 |
力学 | 39399篇 |
综合类 | 13498篇 |
数学 | 81784篇 |
物理学 | 318332篇 |
出版年
2024年 | 4168篇 |
2023年 | 12868篇 |
2022年 | 15766篇 |
2021年 | 14442篇 |
2020年 | 13119篇 |
2019年 | 16165篇 |
2018年 | 17770篇 |
2017年 | 14097篇 |
2016年 | 15738篇 |
2015年 | 16520篇 |
2014年 | 26991篇 |
2013年 | 23984篇 |
2012年 | 56294篇 |
2011年 | 70809篇 |
2010年 | 31821篇 |
2009年 | 27517篇 |
2008年 | 60747篇 |
2007年 | 60961篇 |
2006年 | 62420篇 |
2005年 | 58437篇 |
2004年 | 50325篇 |
2003年 | 40329篇 |
2002年 | 36070篇 |
2001年 | 27993篇 |
2000年 | 29896篇 |
1999年 | 15111篇 |
1998年 | 9002篇 |
1997年 | 7000篇 |
1996年 | 12296篇 |
1995年 | 10291篇 |
1994年 | 11450篇 |
1993年 | 12417篇 |
1992年 | 11783篇 |
1991年 | 7475篇 |
1990年 | 7342篇 |
1989年 | 6558篇 |
1988年 | 7131篇 |
1987年 | 6641篇 |
1986年 | 6425篇 |
1985年 | 5961篇 |
1984年 | 3731篇 |
1983年 | 3229篇 |
1982年 | 2572篇 |
1981年 | 2055篇 |
1980年 | 1410篇 |
1979年 | 921篇 |
1978年 | 570篇 |
1966年 | 372篇 |
1965年 | 449篇 |
1948年 | 903篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
We propose a system of time-division multiplexing(TDM) and spatial frequency-division multiplexing(SFDM). Extrinsic Fabry–Perot interferometric sensors are applied to detect weak acoustic signals. The broadband source is employed, the light from it is modulated by a pulse signal sequence and is efficiently amplified by semiconductor optical amplifiers. Experimental results show that the equivalent noise pressure spectrum level is-97.2 d B re 1 rad/√Hz below 1250 Hz, and the cross talk between two sensors in one TDM channel is-32.7 d B with a cavity length difference of 60 μm. The number of sensors in this multiplexing system can theoretically reach 160. 相似文献
72.
The CO_2 adsorption on CaO(001) surface at different coverages from 1/9 monolayer(ML) to 1 ML has been investigated using density functional theory calculations. With the analysis of the most stable adsorption structures at different coverages, the mechanism of CaO(001)surface carbonating into CaCO_3 has been explored. At low coverages(≤1/3 ML), CO_2 molecule prefers sitting in parallel pattern on the CaO(001) surface, while the structure of the CaO(001)surface remains unchanged. At medium coverage(4/9 ~ 2/3 ML), the repulsive interactions between oxygen atoms of CO_2 become stronger, and the calcium carbonation structure appears on the CaO(001) surface. At high coverage( ≥ 7/9 ML), the structure of the CaO(001) surface is deeply damaged, and a few CO_2 molecules have penetrated into the surface and bound to the O atom of the second layer(sub-surface), eventually forming the layered structure of CaCO_3.Additionally, herein has discussed the simulation of HREELS and thermodynamical stability of these structures at different coverages. 相似文献
74.
76.
In the excitation of the resonant state followed by the sequential cluster-decay,the in-plane angular correlation method is usually employed to determine the spin of the mother nucleus.However,the correlation pattern exhibited in a two-dimensional angular-correlation spectrum depends on the selected coordinate system.In particular,the parity-symmetric and axial-symmetric processes should be presented in a way to enhance the correlation pattern,whereas the non-symmetric process should be plotted separately to reduce the background.In this study,three coordinate systems previously adopted for correlation patterns in the literature are described and compared to each other.The consistency among these systems is evaluated based on the experimental data analysis for the 10.29-MeV state in ~(18) O.A spin-parity of 4~+ is obtained for all three coordinate systems. 相似文献
78.
We report on a data center network(DCN) architecture based on hybrid optical circuit switching(OCS) and optical burst switching(OBS) interconnect for dynamic DCN connectivity provisioning. With the combination of the centralized and distributed control of the software-defined optical networks, the proposed interconnect can achieve unprecedented flexibility in dealing with both mice and elephant flow in the DCN. Numerical simulation is employed to investigate the performance of the proposed architecture. The results show that the OBS module has preferable performance in dealing with a larger burst packet, and the throughput is constrained by the capacity of the server random access memory module. 相似文献