全文获取类型
收费全文 | 1619篇 |
免费 | 83篇 |
国内免费 | 25篇 |
专业分类
化学 | 1176篇 |
晶体学 | 9篇 |
力学 | 84篇 |
数学 | 208篇 |
物理学 | 250篇 |
出版年
2023年 | 10篇 |
2022年 | 28篇 |
2021年 | 84篇 |
2020年 | 60篇 |
2019年 | 74篇 |
2018年 | 86篇 |
2017年 | 52篇 |
2016年 | 86篇 |
2015年 | 68篇 |
2014年 | 103篇 |
2013年 | 174篇 |
2012年 | 138篇 |
2011年 | 136篇 |
2010年 | 96篇 |
2009年 | 80篇 |
2008年 | 73篇 |
2007年 | 74篇 |
2006年 | 56篇 |
2005年 | 51篇 |
2004年 | 26篇 |
2003年 | 21篇 |
2002年 | 16篇 |
2001年 | 11篇 |
2000年 | 17篇 |
1999年 | 7篇 |
1998年 | 4篇 |
1997年 | 6篇 |
1996年 | 2篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 6篇 |
1986年 | 2篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 9篇 |
1982年 | 3篇 |
1981年 | 6篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1968年 | 2篇 |
1936年 | 1篇 |
1932年 | 1篇 |
排序方式: 共有1727条查询结果,搜索用时 31 毫秒
941.
Nabati Shoghl Sina Loloei Zakaria Keshavarz Moraveji Mostafa 《Journal of Thermal Analysis and Calorimetry》2019,136(4):1831-1846
Journal of Thermal Analysis and Calorimetry - Forced convection heat transfer of two different types of water-based nanofluids (Al2O3, TiO2) was investigated numerically. In this numerical... 相似文献
942.
Fatemeh Ghodsi Sayyed Mostafa Habibi-Khorassani Mehdi Shahraki Saeedreza Emamian Mar Ríos-Gutiérrez Luis R. Domingo 《Tetrahedron》2019,75(19):2807-2816
The domino reactions of alkyne-tethered N-mesylhydrazones yielding fused polycyclic pyrazoles have been studied within the Molecular Electron Density Theory (MEDT). Analysis of the Gibbs free energies indicates that the more favourable reactive path is the one in which the elimination of mesylate anion takes place before the intramolecular [3 + 2] cycloaddition (IM32CA) reaction, which corresponds with the rate-determining step of these domino processes. ELF topological analysis of the bond formation along the IM32CA reaction indicates that in spite of the high activation energy associated to this intramolecular reaction, it shows a pmr-type mechanism characterised by the presence of a pseudoradical carbon at the phenyldiazomethane framework. 相似文献
943.
944.
945.
I. Kashif Samy A. Rahman A.A. Soliman E.M. Ibrahim E.K. Abdel-Khalek A.G. Mostafa A.M. Sanad 《Physica B: Condensed Matter》2009,404(21):3842-3849
Sodium borate glasses containing iron and molybdenum ions with the total concentration of transition ions constant and gradual substitution of sodium oxide (network modifier) by borate oxide (network former) was prepared. Densities, molar volume, DC and AC conductivities are measured. The trends of these properties are attributed to changes in the glass network structure. Their DC and AC conductivity increased with increasing NaO concentration. The increase of AC conductivity of sodium borate glasses is attributed to the chemical composition and the hopping mechanism of conduction. Measurements of the dielectric constant (ε) and dielectric loss (tan δ) as a function of frequency (50 Hz–100 kHz) and temperature (RT—600 K) indicate that the increase in dielectric constant and loss (ε and tan δ) values with increasing sodium ion content could be attributed to the assumption that Fe and Mo ions tend to assume network-forming position in the glass compositions studied.The variation of the value of frequency exponent s for all glass samples as the function of temperature at a definite frequency indicates that the value of s decreases with increasing the temperature which agrees with the correlated barrier-hopping (CBH) model. 相似文献
946.
Malek Taher Maghsoodlou Sayyed Mostafa Habibi Khorassani Nourollah Hazeri Mohsen Rostamizadeh Seyed Sajad Sajadikhah Zahra Shahkarami Nariman Maleki 《Heteroatom Chemistry》2009,20(5):316-318
α‐Amino phosphonates were obtained in a one‐pot, simple, and efficient method from the reaction between aldehyde, aniline, trialkyl phosphite, and silica sulfuric acid as a catalyst in acetonitrile at room temperature. © 2009 Wiley Periodicals, Inc. Heteroatom Chem 20:316–318, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20543 相似文献
947.
Gibson JJ Sadek MA Stone DJ Hughes CE Hankin S Cendon DI Hollins SE 《Isotopes in environmental and health studies》2008,44(1):83-98
Deuterium and oxygen-18 enrichment in river water during its transit across dryland region is found to occur systematically along evaporation lines with slopes of close to 4 in (2)H-(18)O space, largely consistent with trends predicted by the Craig-Gordon model for an open-water dominated evaporating system. This, in combination with reach balance assessments and derived runoff ratios, strongly suggests that the enrichment signal and its variability in the Barwon-Darling river, Southeastern Australia is acquired during the process of evaporation from the river channel itself, as enhanced by the presence of abundant weirs, dams and other storages, rather than reflecting inherited enrichment signals from soil water evaporation in the watershed. Using a steady-state isotope mass balance analysis based on monthly (18)O and (2)H, we use the isotopic evolution of river water to re-construct a perspective of net exchange between the river and its contributing area along eight reaches of the river during a drought period from July 2002 to December 2003, including the duration of a minor flow event. The resulting scenario, which uses a combination of climatological averages and available real-time meteorological data, should be viewed as a preliminary test of the application rather than as a definitive inventory of reach water balance. As expected for a flood-driven dryland system, considerable temporal variability in exchange is predicted. While requiring additional real-time isotopic data for operational use, the method demonstrates potential as a non-invasive tool for detecting and quantifying water diversions, one that can be easily incorporated within existing water quality monitoring activities. 相似文献
948.
949.
Karmakar TK Chandra SK Ribas J Mostafa G Lu TH Ghosh BK 《Chemical communications (Cambridge, England)》2002,(20):2364-2365
A new tetranuclear double-open dicubane complex [Ni4(mu 2-N3)4(mu 3-N3)2(N3)2(enbzpy)2].2H2O (enbzpy = [N,N-bis(pyridin-2-yl)benzylidene]ethane-1,2-diamine) has been characterised structurally and magnetostructurally. 相似文献
950.
Ali Saadia A. Khalil Mostafa M. H. Ramadan Ramadan M. 《Transition Metal Chemistry》2000,25(2):121-125
Chloranilic acid (H2CA) reacts with Cr(CO)6 and CrCl3 to give the tris derivatives Cr(H2CA)3 and Cr(HCA)3. Spectroscopic measurements on the two complexes reveal that the ligand–metal bond is of the semiquinone type. Susceptibility determinations showed effective magnetic moments of 1.82 and 1.07B. Examination of Cr(H2CA)3 by cyclic voltammetry revealed two redox reactions due to tautomeric interconversion through electron transfer. Boiling Mo(CO)6 with H2CA in air gave MoO3(HCA) in which the molybdenum atom is in the +5 oxidation state. The i.r. spectrum of the MoO3(HCA) displayed bands due to terminal M=O bonds. The cluster compound Ru3(CO)12 reacted with H2CA to give Ru3(CO)10(-H)(HCA), the i.r. spectrum of which revealed that the ligand is bound to the metal as a catechol moiety. The spectroscopic and magnetic studies of the molybdenum and ruthenium complexes confirmed the proposed structures. 相似文献