全文获取类型
收费全文 | 1216篇 |
免费 | 59篇 |
国内免费 | 1篇 |
专业分类
化学 | 879篇 |
晶体学 | 14篇 |
力学 | 35篇 |
数学 | 99篇 |
物理学 | 249篇 |
出版年
2023年 | 6篇 |
2022年 | 17篇 |
2021年 | 23篇 |
2020年 | 34篇 |
2019年 | 27篇 |
2018年 | 36篇 |
2017年 | 38篇 |
2016年 | 61篇 |
2015年 | 41篇 |
2014年 | 52篇 |
2013年 | 96篇 |
2012年 | 102篇 |
2011年 | 75篇 |
2010年 | 42篇 |
2009年 | 44篇 |
2008年 | 89篇 |
2007年 | 51篇 |
2006年 | 52篇 |
2005年 | 47篇 |
2004年 | 41篇 |
2003年 | 27篇 |
2002年 | 34篇 |
2001年 | 10篇 |
2000年 | 7篇 |
1999年 | 4篇 |
1998年 | 5篇 |
1997年 | 9篇 |
1996年 | 13篇 |
1995年 | 4篇 |
1992年 | 6篇 |
1991年 | 11篇 |
1990年 | 5篇 |
1986年 | 7篇 |
1985年 | 11篇 |
1984年 | 11篇 |
1983年 | 5篇 |
1981年 | 10篇 |
1980年 | 4篇 |
1979年 | 6篇 |
1978年 | 13篇 |
1977年 | 5篇 |
1969年 | 6篇 |
1968年 | 7篇 |
1964年 | 4篇 |
1963年 | 6篇 |
1962年 | 6篇 |
1961年 | 12篇 |
1958年 | 7篇 |
1957年 | 3篇 |
1955年 | 5篇 |
排序方式: 共有1276条查询结果,搜索用时 135 毫秒
71.
N1-Hydroxy-2,4,5-trisubstituted imidazoles were synthesized starting from 1,2-diketones. The crystal structure of 4,5-dimethyl-2-(3-nitrophenyl)-1H-imidazol-1-ol has been determined. An unusual intermolecular hydrogen bonding through the association of water molecule has been reported. These imidazole derivatives can be thought of as the organic precursor for the synthesis of zinc oxide nano particles. 相似文献
72.
73.
Dr. Staffan Bergwall Dr. Arun S. Nigavekar 《Zeitschrift für Physik B Condensed Matter》1969,10(2):107-115
The results of a systematic investigation of the intensity distribution near the short wavelength limit of the continuous X-ray spectrum for the most common rare earth oxides are reported. Anomalies in the band structure of some oxides have been observed and are discussed in terms of localized energy levels in the forbidden band due to the existence of colour centres. This implies that the physical properties of pure compounds strongly depend on the precise experimental conditions of preparation. 相似文献
74.
We report the integration of inorganic nanotubes into metal-oxide-solution field effect transistors (FETs) which exhibit rapid field effect modulation of ionic conductance. Surface functionalization, analogous to doping in semiconductors, can switch the nanofluidic transistors from p-type to ambipolar and n-type field effect transistors. Transient study reveals the kinetics of field effect modulation is controlled by ion-exchange step. Nanofluidic FETs have potential implications in subfemtoliter analytical technology and large-scale nanofluidic integration. 相似文献
75.
Couturier M Ménard F Ragan JA Riou M Dauphin E Andresen BM Ghosh A Dupont-Gaudet K Girardin M 《Organic letters》2004,6(11):1857-1860
Lewis-base-catalyzed cycloisomerization of bis(enones) to decalins has been demonstrated as an alternative to the traditional Lewis acid catalyzed Diels-Alder cycloaddition. In this process, a trialkylphosphine mediates both bond formation steps in two distinct catalytic cycles. The single-pot operation generates two carbon-carbon bonds and up to five contiguous stereocenters in one step, starting from achiral, aliphatic substrates; eight examples are provided. [reaction: see text] 相似文献
76.
Arun Kumar Gupta 《Tetrahedron letters》2004,45(21):4113-4116
1-(2-Iodophenyl)-1H-tetrazole 2 was synthesized by the reaction of 2-iodoaniline, sodium azide and triethyl orthoformate in acetic acid. The newly synthesized ligand 2 was successfully used in Heck reaction to give the cross-coupled products in excellent yields. 相似文献
77.
We demonstrate resonant tunneling of ultracold atoms through potentials produced by the interaction of atoms with the vacuum field of a system of cavities. We show the close connection of the transmission characteristics to the resonant states in vacuum induced potentials. Transmission of cold atoms, though sharing some features with tunneling in finite semiconductor superlattices, is strongly dependent on the coherent addition of amplitudes from various wells and barriers. 相似文献
78.
M. Sreenivasulu K. Arun KumarK. Sateesh Reddy K. Siva KumarP. Rajender Kumar K.B. ChandrasekharManojit Pal 《Tetrahedron letters》2011,52(6):727-732
A rapid, economic, and high yielding methodology has been developed for hydroacylation/reduction of activated ketones by using 1,3-bis(2,4,6-trimethylphenyl)imidazolium chloride as a catalyst in combination with triethylamine. The reaction proceeded at an ambient temperature via generating N-heterocyclic carbene in situ that interacted with the (hetero)aryl aldehyde employed. While the reduction of ketones takes place in MeOH, the hydroacylation process was found to be effective in THF for both electron rich and deficient aldehydes. 相似文献
79.
Magnetic nanocomposite material composed of poly vinyl alcohol encapsulated Ni0.2Ca0.8Gd0.08Fe1.92O4 was synthesized by a two step chemical method including sol-gel combustion and solvent casting technique. The obtained samples were characterized by powder X-ray diffraction; transmission electron microscopy and Fourier transform infrared spectroscopy. The results of spectroanalysis pointed towards the existence of a considerably feasible interaction between the polymer chain and the ferrite particles. The dc magnetization measurements divulged that both pristine and the nanocomposite samples under applied magnetic field exhibit no hysteretic behavior at room temperature, symptomatic of the superparamagnetic behavior. The departure of field cooled and zero field cooled curves in the moment-versus-temperature plot further confirmed the room temperature superparamagnetic behavior. The extrapolation of the slope of the curves to M=0 imparted the average value of Curie temperature at ∼323 K (50 °C) for both the samples, suggestive of the efficacy of the material for finding application in self controlled hyperthermia. 相似文献
80.