全文获取类型
收费全文 | 15118篇 |
免费 | 544篇 |
国内免费 | 44篇 |
专业分类
化学 | 10253篇 |
晶体学 | 231篇 |
力学 | 465篇 |
综合类 | 1篇 |
数学 | 1248篇 |
物理学 | 3508篇 |
出版年
2024年 | 65篇 |
2023年 | 171篇 |
2022年 | 442篇 |
2021年 | 427篇 |
2020年 | 468篇 |
2019年 | 524篇 |
2018年 | 488篇 |
2017年 | 468篇 |
2016年 | 670篇 |
2015年 | 484篇 |
2014年 | 760篇 |
2013年 | 1279篇 |
2012年 | 1131篇 |
2011年 | 1198篇 |
2010年 | 782篇 |
2009年 | 604篇 |
2008年 | 753篇 |
2007年 | 749篇 |
2006年 | 577篇 |
2005年 | 517篇 |
2004年 | 394篇 |
2003年 | 322篇 |
2002年 | 262篇 |
2001年 | 161篇 |
2000年 | 135篇 |
1999年 | 104篇 |
1998年 | 82篇 |
1997年 | 106篇 |
1996年 | 105篇 |
1995年 | 83篇 |
1994年 | 75篇 |
1993年 | 99篇 |
1992年 | 100篇 |
1991年 | 84篇 |
1990年 | 78篇 |
1989年 | 74篇 |
1988年 | 51篇 |
1987年 | 45篇 |
1986年 | 43篇 |
1985年 | 68篇 |
1984年 | 66篇 |
1983年 | 53篇 |
1982年 | 47篇 |
1981年 | 37篇 |
1980年 | 45篇 |
1979年 | 62篇 |
1978年 | 48篇 |
1977年 | 53篇 |
1976年 | 43篇 |
1975年 | 34篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
Arvind Samariya S.N. Dolia Arun S. Prasad P.K. Sharma S.P. Pareek M.S. Dhawan Sudhish Kumar 《Current Applied Physics》2013,13(5):830-835
CaFe2O4 nanocrystalline powders were synthesized through sol–gel treatment in which the stoichiometric mixing of various nitrates involving calcium and iron in presence of citric acid was performed. Subsequently, the as prepared sample was annealed at various temperatures in order to obtain the fine distribution of size including the bulk counterpart. The samples were then characterized using powder X-ray diffraction followed by 57Fe Mössbauer spectroscopy, SQUID as well as vibrating sample magnetometry. The results of spectroanalyses revealed that the samples were formed in single phase cubic spinel structure and exhibits room temperature superparamagnetism, except the bulk one, which crystallizes in characteristic orthorhombic structure of CaFe2O4 and displays trivial coercivity and remanent magnetization at room temperature. 相似文献
112.
Liquid junction solar cell (LJSC) with vertically silicon nanowires (SiNWs) as the primary photosensitizer,co-sensitized with luminescent and narrow gap CdTe na... 相似文献
113.
Kittiya Somphol Mardi Santoso Mohan Bhadbhade Christopher Gardner Naresh Kumar David StC. Black 《Tetrahedron》2012,68(7):1862-1868
Cyclotriveratrylenes containing one benzene ring and two indole rings linked through N1 and C2 can be prepared by acid-catalysed reactions of formaldehyde and aryl aldehydes with 1,2-di-(1-indolylmethyl)benzene compounds. 相似文献
114.
115.
India is looking at the renewable alternative sources of energy to reduce its dependence on import of crude oil. As India imports 70?% of the crude oil, the country has been greatly affected by increasing cost and uncertainty. Biodiesel fuel derived by the two step acid transesterification of mixed non-edible oils from Jatropha curcas and Pongamia (karanja) can meet the requirements of diesel fuel in the coming years. In the present study, different proportions of Methanol, Sodium hydroxide, variation of Reaction time, Sulfuric acid and Reaction Temperature were adopted in order to optimize the experimental conditions for maximum biodiesel yield. The preliminary studies revealed that biodiesel yield varied widely in the range of 75–95?% using the laboratory scale reactor. The average yield of 95?% was obtained. The fuel and chemical properties of biodiesel, namely kinematic viscosity, specific gravity, density, flash point, fire point, calorific value, pH, acid value, iodine value, sulfur content, water content, glycerin content and sulfated ash values were found to be within the limits suggested by Bureau of Indian Standards (BIS 15607: 2005). The optimum combination of Methanol, Sodium hydroxide, Sulfuric acid, Reaction Time and Reaction Temperature are established. 相似文献
116.
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
117.
118.
119.
Kinetics of change in photoinduced currents (during illumination and after switching off light source) in the solid state
of some ferrocene derivatives, namely, ferrocenecarboxylic acid, acetylferrocene, ferrocenecarbaldehyde, hydroxymethyl ferrocene
have been studied in dry nitrogen gas atmosphere. Unusual/anomalous photocurrent versus time profiles were observed in some ferrocene derivatives at certain cell temperatures. The kinetics of current changes under
photoexcitation and after switching off the light source have been observed to be complicated in nature. Temperature-dependent
behavior of the studied kinetics indicates that charge carrier trapping/detrapping and recombination processes are significantly
temperature dependent. These processes have an important role in causing the temperature dependent unusual/anomalous photocurrent
versus time profiles in the ferrocene derivatives studied. 相似文献
120.