全文获取类型
收费全文 | 2976篇 |
免费 | 100篇 |
国内免费 | 10篇 |
专业分类
化学 | 2333篇 |
晶体学 | 20篇 |
力学 | 46篇 |
数学 | 267篇 |
物理学 | 420篇 |
出版年
2023年 | 16篇 |
2022年 | 82篇 |
2021年 | 95篇 |
2020年 | 53篇 |
2019年 | 64篇 |
2018年 | 44篇 |
2017年 | 46篇 |
2016年 | 92篇 |
2015年 | 79篇 |
2014年 | 95篇 |
2013年 | 134篇 |
2012年 | 191篇 |
2011年 | 176篇 |
2010年 | 134篇 |
2009年 | 103篇 |
2008年 | 184篇 |
2007年 | 172篇 |
2006年 | 154篇 |
2005年 | 196篇 |
2004年 | 141篇 |
2003年 | 132篇 |
2002年 | 109篇 |
2001年 | 52篇 |
2000年 | 35篇 |
1999年 | 41篇 |
1998年 | 21篇 |
1997年 | 38篇 |
1996年 | 33篇 |
1995年 | 23篇 |
1994年 | 25篇 |
1993年 | 21篇 |
1992年 | 17篇 |
1991年 | 18篇 |
1990年 | 19篇 |
1989年 | 15篇 |
1988年 | 15篇 |
1987年 | 20篇 |
1986年 | 12篇 |
1985年 | 23篇 |
1984年 | 17篇 |
1983年 | 17篇 |
1982年 | 14篇 |
1981年 | 14篇 |
1980年 | 16篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1976年 | 11篇 |
1975年 | 12篇 |
1974年 | 8篇 |
1972年 | 6篇 |
排序方式: 共有3086条查询结果,搜索用时 15 毫秒
11.
Fabiana Quaglia Giuseppe Fusco Giuseppe De Rosa Francesca Ungaro Agnese Miro Maria Immacolata La Rotonda 《Journal of inclusion phenomena and macrocyclic chemistry》2007,57(1-4):669-674
The aim of this work was to produce lycopene-containing powders from tomato products by a solvent-free method making use of
β-cyclodextrin (βCD). Powders were prepared by spray-drying a tomato concentrate (TC), one of the most bioavailable form of
lycopene, after mechanical treatment with βCD in different weight ratios. The obtained product was centrifuged to eliminate
partly food matrix and characterized for the amount of lycopene hydrodispersed/hydrosolubilized in the aqueous fraction. The
chemical antioxidant activity of sera was evaluated too. Powders obtained by spray-drying sera exhibited good flow properties,
a lycopene content between 0.4 and 1.09 mg/g and excellent water dispersability. The process developed, which makes use of
βCD for the treatment of tomato products, turns to be of great interest to obtain a bulk material for nutraceuticals displaying
superior biovailability of lycopene. 相似文献
12.
Nguyen Hoa Hong Joe Sakai Ngo Thu Huong Virginie Brizé 《Journal of magnetism and magnetic materials》2006
Laser-ablated Co-doped In2O3 thin films were fabricated under various growth conditions on R-cut Al2O3 and MgO substrates. All Co:In2O3 films are well-crystallized, single phase, and room temperature ferromagnetic. Co atoms were well substituted for In atoms, and their distribution is greatly uniform over the whole thickness of the films. Films grown at 550 °C showed the largest magnetic moment of about 0.5 μB/Co, while films grown at higher temperatures have magnetic moments of one order smaller. The observed ferromagnetism above room temperature in Co:In2O3 thin films has confirmed that doping few percent of magnetic elements such as Co into In2O3 could result in a promising magnetic material. 相似文献
13.
A simple field sampling-preconcentration method for zinc determination in seawater is described. Seawater was collected in situ by pumping it through a minicolumn packed with a chelating resin (Chelite P) connected to a field flow preconcentration system (FFPS). These packed minicolumns retain the dissolved zinc, and once are loaded with the analyte, they are returned to the laboratory where they are sequentially inserted into a flow injection system for on-line zinc elution with diluted hydrochloric acid and flame atomic absorption spectrometric detection. A factorial design has been used to optimize the FFPS and the flow injection elution process. The proposed method has a linear calibration range from 0.07 to at least 9.4 microg L(-1) of zinc, with a detection limit of 0.02 microg L(-1) and a throughput of 26 samples h(-1). Validation was carried out against certified reference water samples. This procedure has been successfully applied to the determination of Zn in seawater samples from Galicia (Spain). 相似文献
14.
15.
G. Balducci L. Bencivenni G. De Rosa R. Gigli B. Martine S.Nunziante Cesaro 《Journal of Molecular Structure》1980
The infrared and Raman spectra of some cyclopentadienyl compounds of the transition metals, namely Ti(C5H5)Cl3 and M(C5H5)2Cl2 (M = Ti, Zr and Hf), are reported and discussed. The infrared spectra of the gaseous species isolated in argon matrices at 10 K provide structural information about the single molecules. Particular attention has been paid to the low-frequency region in order to achieve more reliable assignments for the internal-rotation modes. The structural data and the fundamental frequencies derived from the spectra are employed in a calculation of the thermodynamic functions for these compounds in the ideal gas state. 相似文献
16.
17.
Om Prakash Ajay Kumar Richa Prakash Rosa M. Claramunt Ibon Alkorta José Elguero 《Tetrahedron》2005,61(27):6642-6651
Treatment of α,β-unsaturated carbonyl compounds, obtained by the reaction of DHA and aromatic (or heteroaromatic) aldehydes, with o-aminothiophenol results in the formation of 1,5-benzothiazepines and/or 1,4-benzothiazines depending upon the reaction conditions and structure of the aldehydes. The products were characterized by the combined use of multinuclear 1D and 2D NMR and GIAO/DFT calculations of 1H, 13C and 15N chemical shifts. The tautomerism of these compounds in solution was determined, they have an exocyclic CC double bond. 相似文献
18.
19.
The method of differences is used to establish that every 2-regular multigraph onv– 10,2 (mod 3) points occurs as the neighbourhood graph of an element in a twofold triple system of orderv, with two exceptions: C2C3and C3C3.Dedicated to Professor Hanfried Lenz on the occasion of his seventieth birthday 相似文献
20.
Pyrazoles as molecular probes to study the properties of co-crystals by solid state NMR spectroscopy
Concepción López Rosa M. Claramunt M. Ángeles García José Elguero 《Central European Journal of Chemistry》2004,2(4):660-671
Equimolar mixtures of 3,5-dimethylpyrazole (1) with four NH-imidazoles (2–5) have been studied by13C and 15N CPMAS NMR and by DSC. In three cases, the solid mixture behaves as the sum of the individual components [imidazole (2), 2-methylimidazole (3) and 2,4(5)-dimethylimidazole (5)]. In one case [4,5-dimethylimidazole (4)], the mixture corresponds to a new species in which the dynamic behavior of1 no longer exists. 相似文献