全文获取类型
收费全文 | 1849篇 |
免费 | 53篇 |
国内免费 | 4篇 |
专业分类
化学 | 1118篇 |
晶体学 | 4篇 |
力学 | 110篇 |
数学 | 340篇 |
物理学 | 334篇 |
出版年
2023年 | 16篇 |
2022年 | 20篇 |
2021年 | 63篇 |
2020年 | 38篇 |
2019年 | 39篇 |
2018年 | 34篇 |
2017年 | 32篇 |
2016年 | 67篇 |
2015年 | 61篇 |
2014年 | 54篇 |
2013年 | 93篇 |
2012年 | 103篇 |
2011年 | 149篇 |
2010年 | 61篇 |
2009年 | 61篇 |
2008年 | 117篇 |
2007年 | 110篇 |
2006年 | 107篇 |
2005年 | 81篇 |
2004年 | 74篇 |
2003年 | 60篇 |
2002年 | 73篇 |
2001年 | 22篇 |
2000年 | 15篇 |
1999年 | 22篇 |
1998年 | 15篇 |
1997年 | 21篇 |
1996年 | 30篇 |
1995年 | 18篇 |
1994年 | 11篇 |
1993年 | 17篇 |
1992年 | 9篇 |
1991年 | 6篇 |
1990年 | 12篇 |
1989年 | 13篇 |
1988年 | 9篇 |
1987年 | 17篇 |
1986年 | 7篇 |
1985年 | 9篇 |
1984年 | 9篇 |
1983年 | 7篇 |
1982年 | 9篇 |
1981年 | 5篇 |
1980年 | 8篇 |
1979年 | 10篇 |
1978年 | 14篇 |
1977年 | 12篇 |
1976年 | 11篇 |
1975年 | 5篇 |
1972年 | 4篇 |
排序方式: 共有1906条查询结果,搜索用时 15 毫秒
51.
Ceramic Foams from a Preceramic Polymer and Polyurethanes: Preparation and Morphological Investigations 总被引:1,自引:0,他引:1
Colombo Paolo Griffoni Martina Modesti Michele 《Journal of Sol-Gel Science and Technology》1998,13(1-3):195-199
Open-cell ceramic foams were obtained from a preceramic polymer (silicone resin) and blown polyurethanes. The preceramic polymer, which is crosslinked by condensation of silanol groups, was dissolved in CH2Cl2 and added to a liquid polyol containing the surfactant and the amine catalyst. Isocyanate was then added to the mixture and the foam was obtained through a twofold blowing mechanism (physical and chemical blowing). The morphology of the expanded polyurethane, which can be flexible or semirigid, characterized the final structure of the ceramic foam. The materials obtained were pyrolyzed in a nitrogen flux at temperatures of 1000–1200°C, thus allowing for the polymer-to-ceramic transformation to occur in the preceramic polymer. The ceramic foams produced in this way consisted of an amorphous silicon oxycarbide ceramic (SiOC). They presented a density ranging from 0.1 to 0.3 g/cm3. The average pore diameter ranged from 200 to 400 m and they possessed 80 to 90% open porosity. 相似文献
52.
Nicol Vivona Michele Ruccia Vincenzo Frenna Domenico Spinelli 《Journal of heterocyclic chemistry》1980,17(2):401-402
3-Benzoyl-5-phenyl-1,2,4-oxadiazole (I) with phenylhydrazine in acetic acid gives the two geometrical isomers, phenylhydrazones II-Z and II-E, which have been characterized by uv-visible, ir, and nmr spectra. The possible II-E ? II-Z isomerization as well as the rearrangement of II-Z and of II-E into 2,5-diphenyl-4-benzoylamino-1,2,3-triazole (III) has been pointed out. 相似文献
53.
Stone MM Franz AH Lebrilla CB 《Journal of the American Society for Mass Spectrometry》2002,13(8):964-974
Non-covalent inclusion complexes formed between amino acids and derivatized calix[6]arenes are observed in MALDI mass spectrometry. The methyl, ethyl, and propyl ester derivatives of calix[6]arene yielded amino acid complexes, while the smaller calix[4]arene analogs did not. Similarly the underivatized calix[6]arene and calix[4]arene did not produce complexes. Amino acid complexes were observed for nearly all 20 amino acids in time-of-flight (TOF) analysis. In Fourier transform mass spectrometry (FTMS) analysis, however, only the most basic amino acids arginine, histidine, and lysine formed stable adducts. The complexes were abundant under matrix-assisted laser desorption ionization (MALDI) conditions, which suggested favorable interactions between host and guest. 相似文献
54.
Following an approach to density functional theory calculations based on the matrix representation of operators, we implemented
a scheme as an alternative to traditional grid-based methods. These techniques allow integrals over exchange-correlation operators
to be evaluated through matrix manipulations. Both local and gradient-corrected functionals can be treated in a similar way.
After deriving all the required expressions, selected examples with various functionals are given.
Received: 7 March 1998 / Accepted: 21 May 1998 / Published on line: 6 August 1998 相似文献
55.
Aresta M Tommasi I Quaranta E Fragale C Mascetti J Tranquille M Galan F Fouassier M 《Inorganic chemistry》1996,35(14):4254-4260
Extended labeling experiments have shown that formation of rhodium peroxocarbonate from CO(2) and [RhCl(eta(2)-O(2))(P)(3)] (P is PEt(2)Ph or PEtPh(2)) proceeds through O-O bond cleavage and CO(2) insertion. O-transfer to ancillary phosphine ligand to give R(3)P=O selectively (>85%) involves the Rh-linked O atom of the peroxo group of RhCl(CO(4))(P)(3). 相似文献
56.
57.
58.
59.
Fernanda Cortez Lopes Deise Michele Tichota Jamile Queiroz Pereira Jéferson Segalin Alessandro de Oliveira Rios Adriano Brandelli 《Applied biochemistry and biotechnology》2013,171(3):616-625
The search for new sources of natural pigments has increased, mainly because of the toxic effects caused by synthetic dyes used in food, pharmaceutical, textile, and cosmetic industries. Fungi provide a readily available alternative source of natural pigments. In this context, the fungi Penicillium chrysogenum IFL1 and IFL2, Fusarium graminearum IFL3, Monascus purpureus NRRL 1992, and Penicillium vasconiae IFL4 were selected as pigments producers. The fungal identification was performed using ITS and part of the β-tubulin gene sequencing. Almost all fungi were able to grow and produce water-soluble pigments on agro-industrial residues, with the exception of P. vasconiae that produced pigments only on potato dextrose broth. The production of yellow pigments was predominant and the two strains of P. chrysogenum were the largest producers. In addition, the production of pigments and mycotoxins were evaluated in potato dextrose agar using TOF-MS and TOF-MS/MS. Metabolites as roquefortine C, chrysogine were found in both extracts of P. chrysogenum, as well fusarenone X, diacetoxyscirpenol, and neosolaniol in F. graminearum extract. In the M. purpureus extract, the pigments monascorubrin, rubropunctatin, and the mycotoxin citrinin were found. The crude filtrates have potential to be used in the textile industry; nevertheless, additional pigment purification is required for food and pharmaceutical applications. 相似文献
60.
Xiaoyu Zhang Michele E. Lake Adam S. Butterbaugh Kirk A. VanDer Kamp 《液相色谱法及相关技术杂志》2017,40(20):1015-1019
This study demonstrates the first use of a reversed-phase (RP) high-performance liquid chromatography method with a high-pH buffer for the analysis of sodium stearyl fumarate (SSF) from a tablet formulation. After examining the retention time and peak shape using various buffer concentrations, buffer pH, and RP stationary phases, an optimized method was established using the XBridge® BEH C18 at high pH. This column was further evaluated for method specificity, accuracy, precision, linearity, stability, and sensitivity. Finally, the method was successfully used as a convenient and robust analytical procedure to accurately quantitate SSF in stratified tablets from a continuous manufacturing process to confirm the excipient uniformity throughout the process. 相似文献