全文获取类型
收费全文 | 3116篇 |
免费 | 93篇 |
国内免费 | 6篇 |
专业分类
化学 | 2178篇 |
晶体学 | 24篇 |
力学 | 79篇 |
数学 | 457篇 |
物理学 | 477篇 |
出版年
2023年 | 33篇 |
2022年 | 68篇 |
2021年 | 87篇 |
2020年 | 83篇 |
2019年 | 73篇 |
2018年 | 47篇 |
2017年 | 35篇 |
2016年 | 106篇 |
2015年 | 91篇 |
2014年 | 95篇 |
2013年 | 199篇 |
2012年 | 213篇 |
2011年 | 252篇 |
2010年 | 125篇 |
2009年 | 116篇 |
2008年 | 152篇 |
2007年 | 156篇 |
2006年 | 162篇 |
2005年 | 128篇 |
2004年 | 83篇 |
2003年 | 98篇 |
2002年 | 85篇 |
2001年 | 29篇 |
2000年 | 25篇 |
1998年 | 21篇 |
1997年 | 28篇 |
1996年 | 28篇 |
1995年 | 24篇 |
1994年 | 27篇 |
1993年 | 15篇 |
1992年 | 20篇 |
1991年 | 22篇 |
1990年 | 24篇 |
1989年 | 19篇 |
1988年 | 16篇 |
1985年 | 14篇 |
1984年 | 19篇 |
1983年 | 20篇 |
1982年 | 30篇 |
1981年 | 30篇 |
1980年 | 26篇 |
1979年 | 23篇 |
1978年 | 18篇 |
1977年 | 19篇 |
1976年 | 17篇 |
1975年 | 17篇 |
1974年 | 14篇 |
1973年 | 19篇 |
1972年 | 17篇 |
1971年 | 13篇 |
排序方式: 共有3215条查询结果,搜索用时 12 毫秒
41.
Marcelo Samuel Berman 《International Journal of Theoretical Physics》1990,29(12):1415-1417
A very general flat solution for Brans-Dicke cosmology with a perfect-fluid, Robertson-Walker metric and a perfect gas law of state is examined regarding density perturbations. The model has growing instabilities, but not of exponential character. 相似文献
42.
Marcelo Samuel Berman 《General Relativity and Gravitation》1990,22(4):389-392
A well-known solution, for a flat model in general relativity obeying the Robertson-Walker metric, a perfect fluid energy-tensor and a perfect gas law of state, with constant deceleration parameter, is now shown to yield growing scalar density perturbations, provided thatq > 0. This study generalizes Weinberg's results for the radiation phase, and shows that any realistic model of this kind contains gravitational instabilities 相似文献
43.
Zhixun Ma Kin Man Yu Wladek Walukiewicz Peter Y. Yu Samuel S. Mao 《Applied Physics A: Materials Science & Processing》2009,96(2):379-384
We have deposited CdTe films by laser-assisted epitaxy approach and investigated the influence of substrate and film thickness
on the film properties. Grown on Si(001), GaAs(001), and quartz substrates; the CdTe films exhibit preferential orientation
along the cubic CdTe(111) direction. When the films are thin (<500 nm), a blueshift of the band gap and splitting of valence
bands were observed. These results are attributed to the existence of residual strains induced by mismatch of the film lattice
constant with that of the substrate, and by their difference in thermal expansion coefficients. The bulk band-gap energy of
1.5 eV was achieved on the surface of thick CdTe films grown on Si(001) substrate, indicating that strain was almost completely
relaxed in this case. Our results demonstrate that by a proper selection of substrate and film thickness it is possible to
grow film semiconductors with band gap approaching those of bulk crystals. 相似文献
44.
Sundararajan Parani Giridharan Bupesh Elayaperumal Manikandan Kannaiyan Pandian Oluwatobi Samuel Oluwafemi 《Journal of nanoparticle research》2016,18(11):347
Water-soluble, mercaptosuccinic acid (MSA)-capped CdTe/CdS/ZnS core/double shell quantum dots (QDs) were prepared by successive growth of CdS and ZnS shells on the as-synthesized CdTe/CdSthin core/shell quantum dots. The formation of core/double shell structured QDs was investigated by ultraviolet-visible (UV–Vis) absorption and photoluminescence (PL) spectroscopy, PL decay studies, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The core/double shell QDs exhibited good photoluminescence quantum yield (PLQY) which is 70% higher than that of the parent core/shell QDs, and they are stable for months. The average particle size of the core/double shell QDs was ~3 nm as calculated from the transmission electron microscope (TEM) images. The cytotoxicity of the QDs was evaluated on a variety of cancer cells such as HeLa, MCF-7, A549, and normal Vero cells by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) cell viability assay. The results showed that core/double shell QDs were less toxic to the cells when compared to the parent core/shell QDs. MCF-7 cells showed proliferation on incubation with QDs, and this is attributed to the metalloestrogenic activity of cadmium ions released from QDs. The core/double shell CdTe/CdS/ZnS (CSS) QDs were conjugated with transferrin and successfully employed for the biolabeling and fluorescent imaging of HeLa cells. These core/double shell QDs are highly promising fluorescent probe for cancer cell labeling and imaging applications. 相似文献
45.
46.
Abstract Energy Dispersive X-ray Diffraction (EDXD) was performed at room temperature to gather structural data on CaS between approximately 1.7 GPa to nearly 150GPa. In these experiments, CaS retained the B1 structure up to approximately 40 GPa above which it began to transform to the B2 structure. The B2 structure remained stable to the highest pressure reached, 149 GPa, where the relative volume V/V0 was 0.490. Previous studies on CaS extended only up to 52 GPa, which is barely 10 GPa after the B1 phase changes to the B2 structure. Thus it was not possible to accurately extrapolate the equation of state (EOS) for the B2 phase region to significantly higher pressures. In the present study EOS data for CaS was collected to 150 GPa and no other structural change was observed. EOS parameters for the B1 and B2 phase regions agree well with values reported in the literature. 相似文献
47.
Samuel Jorice Raccurt Olivier Poncelet Olivier Auger Aurélien Ling Wai-Li Cherns Peter Grunwald Didier Tillement Olivier 《Journal of nanoparticle research》2010,12(6):2255-2265
Journal of Nanoparticle Research - Fluorescent silica nanoparticles are widely used for various applications from mechanical reinforcement to biology. In many cases, their surface has to be... 相似文献
48.
Using a CO2 laser, Stark shifted resonances have been measured for the CF stretching fundamental (ν3) of FCN near 9.3 μm, and for two nearby “hot” bands. The band centers measured are 1076.492007 ± 0.000013 cm?1 for 0001-0000, 1085.741046 ± 0.000050 cm?1 for 0111-0110, and 1091.16222 ± 0.00015 cm?1 for 0201-0200. The ground state dipole moment of FCN is found to be 2.1203 ± 0.0010 D and dipole moments are also given for the other states observed. Values are given for the rotational constant and l-doubling constant for the 0111 state. 相似文献
49.
Dr. Renata Kaczmarek Samuel Ward Dipra Debnath Taisiya Jacobs Alexander D. Stark Dariusz Korczyński Prof. Dr. Anil Kumar Prof. Dr. Michael D. Sevilla Dr. Sergey A. Denisov Dr. Viacheslav Shcherbakov Dr. Pascal Pernot Prof. Dr. Mehran Mostafavi Prof. Dr. Roman Dembinski Prof. Dr. Amitava Adhikary 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(43):9495-9505
The directionality of the hole-transfer processes between DNA backbone and base was investigated by using phosphorodithioate [P(S−)=S] components. ESR spectroscopy in homogeneous frozen aqueous solutions and pulse radiolysis in aqueous solution at ambient temperature confirmed initial formation of G.+-P(S−)=S. The ionization potential of G-P(S−)=S was calculated to be slightly lower than that of guanine in 5′-dGMP. Subsequent thermally activated hole transfer from G.+ to P(S−)=S led to dithiyl radical (P-2S.) formation on the μs timescale. In parallel, ESR spectroscopy, pulse radiolysis, and density functional theory (DFT) calculations confirmed P-2S. formation in an abasic phosphorodithioate model compound. ESR investigations at low temperatures and higher G-P(S−)=S concentrations showed a bimolecular conversion of P-2S. to the σ2-σ*1-bonded dimer anion radical [-P-2S 2S-P-]− [ΔG (150 K, DFT)=−7.2 kcal mol−1]. However, [-P-2S 2S-P-]− formation was not observed by pulse radiolysis [ΔG° (298 K, DFT)=−1.4 kcal mol−1]. Neither P-2S. nor [-P-2S 2S-P-]− oxidized guanine base; only base-to-backbone hole transfer occurs in phosphorodithioate. 相似文献
50.
Samuel O. Grim Anthony W. Yankowsky 《Phosphorus, sulfur, and silicon and the related elements》2013,188(2):191-195
Abstract The 31P chemical shifts of eleven (4-ZC6H4)3P compounds show a slight correlation with the Hammet [sgrave]para constant of Z. The unusually large upfield chemical shifts of (2-ZC6H4)3P compounds are attributed to an extreme “gamma” effect caused by the restricted conformations due to the steric influence of the ortho substituents. Chemical shifts are given for about thirty triarylphosphines, and group contributions to phosphine chemical shifts are listed for twenty-one aryl groups. 相似文献