全文获取类型
收费全文 | 4658篇 |
免费 | 620篇 |
国内免费 | 618篇 |
专业分类
化学 | 3695篇 |
晶体学 | 53篇 |
力学 | 220篇 |
综合类 | 76篇 |
数学 | 450篇 |
物理学 | 1402篇 |
出版年
2024年 | 6篇 |
2023年 | 63篇 |
2022年 | 99篇 |
2021年 | 141篇 |
2020年 | 162篇 |
2019年 | 193篇 |
2018年 | 144篇 |
2017年 | 155篇 |
2016年 | 214篇 |
2015年 | 211篇 |
2014年 | 256篇 |
2013年 | 301篇 |
2012年 | 364篇 |
2011年 | 409篇 |
2010年 | 302篇 |
2009年 | 272篇 |
2008年 | 332篇 |
2007年 | 298篇 |
2006年 | 264篇 |
2005年 | 231篇 |
2004年 | 243篇 |
2003年 | 164篇 |
2002年 | 180篇 |
2001年 | 146篇 |
2000年 | 115篇 |
1999年 | 86篇 |
1998年 | 49篇 |
1997年 | 45篇 |
1996年 | 57篇 |
1995年 | 55篇 |
1994年 | 42篇 |
1993年 | 31篇 |
1992年 | 34篇 |
1991年 | 38篇 |
1990年 | 22篇 |
1989年 | 26篇 |
1988年 | 16篇 |
1987年 | 20篇 |
1986年 | 13篇 |
1985年 | 15篇 |
1984年 | 10篇 |
1983年 | 16篇 |
1982年 | 10篇 |
1980年 | 4篇 |
1979年 | 6篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1975年 | 6篇 |
1974年 | 4篇 |
1973年 | 3篇 |
排序方式: 共有5896条查询结果,搜索用时 531 毫秒
31.
32.
强混合样本下回归加权估计的一致渐近正态性 总被引:5,自引:0,他引:5
在强混合样本下,讨论固定设计回归模型的加权函数估计的一致渐近正态性,给出一致渐近正态性的收敛速度,这个速度接近n-1/6. 相似文献
33.
一类多线性积分算子的端点有界性 总被引:3,自引:0,他引:3
本文对一类相关于非卷积型算子的多线性算子,证明了其在端点情形上的有界性,该算子包括Littlewood-Paley算子和Marcinkiewicz算子. 相似文献
34.
35.
The sorption, diffusion, and pervaporation (PV) properties of benzene/cyclohexane (Bz/Cx) mixtures on cation-exchange membranes containing copper ions (Cu(II)) were investigated. The equilibrium sorption isotherms of pure vapors in the membranes and the partial solubility of binary solutions in the membranes were described using the UNIQUAC model. The τiM and τMi values were 0.978 and 0.591 for Bz, and 0.922 and 0.475 for Cx. The transient regimes of vapor sorption were employed to calculate the concentration-dependent diffusion coefficients. Long’s model sufficiently explained the diffusivity of Bz and Cx in the membranes. The pre-exponential factors were 3×10−13 m2/s and the plasticization factors were 3.0 and 3.6 for Bz and Cx, respectively. Excellent agreement was found with the experimental results applying the solubility and diffusivity data to simulate the pervaporation performance (flux and selectivity) using the modified Maxwell–Stefan equation. The membrane containing Cu(II) demonstrates better facilitating capability for Bz transport than that with Na(I), mainly due to its preferential sorption property toward Bz. Replacing Na(I) with Cu(II) into a Neosepta membrane resulted in better separation efficiency and higher Bz flux throughout the entire Bz concentration range. 相似文献
36.
Triterpenoid Constituents of Huperzia miyoshiana 总被引:1,自引:0,他引:1
Thirteen triterpenoids, including three new ones, miyoshianois A (1), B (2) and C (3), were isolated from Huperzia miyoshiana. The structures of these new compounds were established as 3-O-dihydroferuloyltohogenol (1), 16-oxo-3β,21β-dihydrox-y-serrat-14-en-24-ferulate (2) and 16-oxo-3a, 21β-dihydroxy-serrat-14-en-24-ferulate (3), respectively, on the basis of their spectroscopic analysis. 相似文献
37.
QiaoHongYAO FuYouLI LuSHAN ChunHuiHUANG DongDongYIN 《中国化学快报》2003,14(11):1185-1188
A new photoresponsive D-π-A dye, mPS, has been designed and synthesized.Compared to the parent dye PS, IPCE values in the region from 400 nm to 560 nm was greatly improved upon changing the attaching group from the p- position to the o- position of the π-conjugation bridge. A solar cell based on mPS generated a remarkably high overall yield η of 5.4% under irradiation of 80.0 mW cm^-2 white light from a Xe lamp, Compared with PS, the overall yield η increased by 64%. 相似文献
38.
Conductive composite films of poly(styrene‐co‐n‐butylacrylate) copolymers filled with low‐density, Ni‐plated core‐shell polymeric particles were prepared and their behaviors of positive temperature coefficient of resistance (PTCR) were investigated. When the conductive fillers in the composite film were loaded beyond the critical volume, 10 up to 25 vol %, composite films exhibited a unique electrical resistant transition behavior, which the electrical resistance rapidly increased by several orders of magnitude at the critical temperature. The PTCR transition temperature, in general, occurred before the glass transition temperature of polymer matrix. Further increased the conductive filler loading to 30 vol %, the overpacked conduction paths were formed in the entire composite and the PTCR effects became blurred. While the composite film treated with thermal cycle several times from room temperature up to 120 °C, the electrical resistivity increased accompanied with the shift of the PTCR transition to lower temperature. The reason might have been caused by the formed interfacial cracks within the composite film. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 322–329, 2007 相似文献
39.
Zhao‐Peng Deng Shan Gao Li‐Hua Huo Hui Zhao 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(5):m225-m227
In the title complex, [Mn(SO4)(C3H7NO)(H2O)2]n, each MnII ion has a distorted octahedral geometry formed by three O atoms of three different sulfate groups, one O atom of a dimethylformamide ligand and two water molecules. The sulfate groups act as tridentate bridging ligands connecting the MnII ions into a two‐dimensional layer structure which can be regraded as a 4.82 network. 相似文献
40.
采用均相沉积法制备了不同Er3+离子浓度掺杂的Y2O3纳米晶, 应用XRD,SEM和PL光谱对该体系材料进行了表征.在Y2O3:Er3+纳米材料体系中, 观察和研究了Stokes及anti-Stokes PL谱强度与Er3+离子摩尔浓度变化的关系, 当Er3+离子浓度为2.0mol%时, anti-Stokes PL强度最强.粉末X
关键词:
氧化钇纳米晶
anti-Stokes PL
双光子吸收 相似文献