全文获取类型
收费全文 | 37855篇 |
免费 | 5131篇 |
国内免费 | 3444篇 |
专业分类
化学 | 18438篇 |
晶体学 | 286篇 |
力学 | 1433篇 |
综合类 | 161篇 |
数学 | 2904篇 |
物理学 | 10302篇 |
综合类 | 12906篇 |
出版年
2024年 | 165篇 |
2023年 | 717篇 |
2022年 | 1209篇 |
2021年 | 1276篇 |
2020年 | 1217篇 |
2019年 | 1154篇 |
2018年 | 1145篇 |
2017年 | 992篇 |
2016年 | 1496篇 |
2015年 | 1629篇 |
2014年 | 2002篇 |
2013年 | 2364篇 |
2012年 | 2862篇 |
2011年 | 2965篇 |
2010年 | 2156篇 |
2009年 | 1994篇 |
2008年 | 2264篇 |
2007年 | 2004篇 |
2006年 | 1779篇 |
2005年 | 1579篇 |
2004年 | 1217篇 |
2003年 | 1053篇 |
2002年 | 1263篇 |
2001年 | 1037篇 |
2000年 | 841篇 |
1999年 | 1120篇 |
1998年 | 876篇 |
1997年 | 875篇 |
1996年 | 787篇 |
1995年 | 661篇 |
1994年 | 633篇 |
1993年 | 555篇 |
1992年 | 415篇 |
1991年 | 440篇 |
1990年 | 365篇 |
1989年 | 299篇 |
1988年 | 262篇 |
1987年 | 183篇 |
1986年 | 110篇 |
1985年 | 81篇 |
1984年 | 68篇 |
1983年 | 37篇 |
1982年 | 34篇 |
1981年 | 26篇 |
1980年 | 27篇 |
1978年 | 13篇 |
1976年 | 16篇 |
1975年 | 15篇 |
1973年 | 15篇 |
1968年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 68 毫秒
91.
本文提出了可行状态点,可行边和可行策略等概念,建立了一种新的解决多目标多阶段决策问题的方法,介绍了这一方法的应用实例: 相似文献
92.
新的基团法估算沸点下蒸发焓 总被引:5,自引:0,他引:5
提出了估算沸点下蒸发焓的含基团重量分率的基团法和估算式,拟合团贡献值,对385种有机物的计算平均偏差约为1.5%。所提出的新方法明显优于3种对应状态和用蒸发熵的基团法。 相似文献
93.
A novel type of corner reflector for the reflection of surface plasmon polariton (SPP) is proposed. The reflector consists
of two layers of compensatory media whose permittivity and permeability take opposite signs to that of the corresponding layer
of the SP waveguide. By rigorously solving Maxwell's equations, the reflected SPP is proved to exist. The transverse wave
vector of the reflected SPP is always antiparallel to that of the incident SPP and no phase retardation is introduced. 相似文献
94.
Hong-Chao Ma 《Applied Surface Science》2006,252(24):8593-8597
In this paper, we found that boron deposited on the surface of support when sodium borohydride used as reducing agent during the preparation of Pt/C catalyst. The deposition of boron markedly reduces particle size of Pt, raises electrochemical active surface (EAS) area of catalyst and electrochemical activity for hydrogen evolution or oxygen reduction reaction (ORR) compared with which prepared using other reducing agents (hydrogen and formaldehyde). 相似文献
95.
Yi Jiang Chuan-Lei Jia Xue-Lin Wang Ke-Ming Wang Hong-Ji Ma 《Applied Surface Science》2006,253(5):2674-2677
A planar optical waveguide has been formed in a LiB3O5 crystal using 6.0 MeV Cu+-ions with a dose of 1 × 1015 ions/cm2 at room temperature. Possible propagating modes were measured at a wavelength of 633 nm using the prism-coupling method. The refractive index profiles of the waveguide were reconstructed by an effective refractive index method and the beam propagation method was used to investigate the properties of the propagation modes in the formed waveguide. The results suggest that the fundamental TE0 and TM0 modes may be well-confined and propagate a longer distance inside the waveguide. The implantation process was also simulated using the transport of ions in matter code (TRIM), which indicates that the nuclear energy deposition may be the main factor for the refractive index change. 相似文献
96.
A fluoroionophore sensor, N-[4-(1-pyrene)butyroyl]-L-tryptophan (PLT), has been reported. It can distinguish lead ion from other 12 metal ions via forming a pyrene dimer and it exhibits a very high sensitivity (0.15 microM) in aqueous solution (Chem. Commun., 2006, 2702). When the indole moiety in PLT was changed to benzene, in forming a new fluoroionophore of N-[4-(1-pyrene)butyroyl]-L-phenylalanine (PLP), it could not form a pyrene dimer in response to Pb(2+) in water. The present study describes the spectroscopic clarification of the intrinsic differences of the binding model between PLP and PLT in binding with Pb(2+). The model shows identical chelating bidentate coordination between COO(-) and Pb(2+) both in PLP-Pb and PLT-Pb; however, there is no indication of the interaction between the phenyl ring and the metal ion or the hydrogen bonding between amide groups in PLP-Pb. These differences in the binding model between PLP-Pb and PLT-Pb illustrate that the indole ring in PLT appears to play a crucial role in the high selectivity and sensitivity of PLT to lead(II) ion. 相似文献
97.
The new phenylpropanoid diglycoside ligusinenoside A ( 1 ), and the two new 8,4′‐oxyneolignan(‘8‐O‐4′‐neolignan’) diglycosides ligusinenosides B ( 2 ) and C ( 3 ), together with nine known compounds, were isolated from the rhizomes of Ligusticum sinensis Oliv. The structures of 1 – 3 were elucidated on the basis of spectroscopic analyses. 相似文献
98.
99.
文章详细描述了航空兵机场塔台辅助指挥系统之通信分系统设计的特点与功能、硬件结构、软件设计原则以及接口通信协议等问题。该分系统设计已在航空兵塔台辅助指挥系统研究中得到应用 ,并达到了良好的控制效果。 相似文献
100.