全文获取类型
收费全文 | 1580篇 |
免费 | 37篇 |
国内免费 | 7篇 |
专业分类
化学 | 977篇 |
晶体学 | 6篇 |
力学 | 44篇 |
数学 | 226篇 |
物理学 | 371篇 |
出版年
2022年 | 10篇 |
2021年 | 12篇 |
2020年 | 13篇 |
2019年 | 16篇 |
2018年 | 13篇 |
2017年 | 11篇 |
2016年 | 36篇 |
2015年 | 30篇 |
2014年 | 27篇 |
2013年 | 64篇 |
2012年 | 83篇 |
2011年 | 84篇 |
2010年 | 59篇 |
2009年 | 52篇 |
2008年 | 60篇 |
2007年 | 67篇 |
2006年 | 59篇 |
2005年 | 64篇 |
2004年 | 67篇 |
2003年 | 61篇 |
2002年 | 62篇 |
2001年 | 38篇 |
2000年 | 38篇 |
1999年 | 23篇 |
1998年 | 30篇 |
1997年 | 29篇 |
1996年 | 20篇 |
1995年 | 13篇 |
1994年 | 24篇 |
1993年 | 28篇 |
1992年 | 19篇 |
1991年 | 24篇 |
1990年 | 19篇 |
1989年 | 14篇 |
1988年 | 19篇 |
1987年 | 15篇 |
1985年 | 23篇 |
1984年 | 26篇 |
1983年 | 15篇 |
1982年 | 23篇 |
1981年 | 19篇 |
1980年 | 20篇 |
1979年 | 16篇 |
1978年 | 20篇 |
1977年 | 9篇 |
1976年 | 10篇 |
1975年 | 19篇 |
1974年 | 12篇 |
1973年 | 12篇 |
1969年 | 9篇 |
排序方式: 共有1624条查询结果,搜索用时 15 毫秒
31.
Pierre-Anton Aichinger Martin Michel Colin Servais Marie-Lise Dillmann Martine Rouvet Nicola D''Amico Ralf Zink Henning Klostermeyer David S. Horne 《Colloids and surfaces. B, Biointerfaces》2003,31(1-4):243-255
Fermentation of a reconstituted skim milk concentrate (8% protein) was investigated to elucidate the effects of various fermentation parameters on the structural, rheological and visual (wheying-off) properties of the resulting gels (pH 4.60). Fermentation trials were performed with non-exocellular polysaccharide-producing strains of Streptococcus thermophilus at various fermentation temperatures and at various chymosin levels. Oscillatory vane rheometry carried out on the intact gels (at 4 °C) showed that the level of chymosin had a significant impact on the gel strength (storage modulus G′). This can be explained by the arrangement of casein micelles into more compact aggregates and the enhanced fusion of aggregated casein micelles as revealed by transmission electron microscopy for the gels fermented with chymosin. Wheying-off of the stirred gels as measured by a centrifugation test (at 4 °C) and pore size of the intact gel structures investigated by scanning electron microscopy both increased with increasing level of chymosin and increasing fermentation temperature (resulting in an increase in acidification rate). A higher level of syneresis (wheying-off) is explained by the larger pore size, since larger pores present a lower resistance to the outflow of whey from the gel. 相似文献
32.
Sadowsky JD Schmitt MA Lee HS Umezawa N Wang S Tomita Y Gellman SH 《Journal of the American Chemical Society》2005,127(34):11966-11968
Molecules that bind to specific surface sites on proteins are of great interest from both fundamental and practical perspectives. We are exploring a ligand development strategy that is based on oligomers with discrete folding propensities ("foldamers"); we target a specific cleft on the cancer-associated protein Bcl-xL because this system is well characterized structurally. In vivo, this cleft binds to alpha-helical segments (BH3 domains) of other proteins. We evaluated several types of helical foldamer, built entirely from beta-amino acid residues or from mixtures of alpha- and beta-amino acid residues, and ultimately identified foldamers in the latter class that bind very tightly to Bcl-xL. Our results suggest that combining different types of foldamer backbones will be an effective and general strategy for creating high-affinity and specific ligands for protein surface sites. 相似文献
33.
34.
The elements are separated from iron by solvent-extraction. Cr, V and Mn are separated by ion-exchange chromatography with a strong acidic cation-exchanger. The elements are determined by 14 MeV-neutron activation analysis using γ-spectroscopy. The method is suitable for a concentration range of 0.05 to 5%. 相似文献
35.
Didier Jamois Martine Tessier Ernest Marchal 《Journal of polymer science. Part A, Polymer chemistry》1993,31(8):1923-1939
The cationic polymerization of isobutylene initiated by 4-(2-hydroxy-2-propyl)phenol/BCl3 system results mainly in α-phenol-ω-chlorooligoisobutylene; however p-(2-chloro-2,4-dimethyl-4-pentyl)phenol is present in all cases. α-Methyl-ω-chlorooligoisobutylene is formed only when the temperature is below?50°C; it results from initiation by the phenol/BCl3 system. Thermal dehydrochlorination of α-phenol-ω-chlorooligoisobutylene is quantitative and leads to a mixture of isomeric ω-unsaturated oligoisobutylenes. α-Methyl-ω-phenololigoisobutylene is prepared by the Friedel—Crafts reaction between industrial unsaturated oligoisobutylene and phenol in the presence of SnCl4 at ?30°C; the reaction is quantitative between ?50 and ?30°C degradation takes place. © 1993 John Wiley & Sons, Inc. 相似文献
36.
We have studied the adsorption of a copolymer of acrylonitrile and methacrylate of nonaethyleneglycol on a kidney dialysis membrane, which contains mostly nitrile groups. The kinetics study reveals at first a rapid increase of the adsorbance, followed by slow variations suggesting rearrangements at the interface. The isotherms do not present a true plateau at high concentration. The high adsorbance observed at low pH or high salt concentration could be related to the ability of polyethyleneoxide to form a complex with cations. 相似文献
37.
Nernst R Antreasyan D Aschman D Besset D Bienlein JK Bloom ED Brock I Cabenda R Cartacci A Cavalli-Sforza M Clare R Conforto G Cooper S Cowan R Coyne D de Judicibus D Edwards C Engler A Folger G Fridman A Gaiser J Gelphman D Godfrey G Heimlich FH Hofstadter R Irion J Jakubowski Z Keh S Kilian H Kirkbride I Kloiber T Koch W König AC Königsmann K Kraemer RW Lee R Leffler S Lekebusch R Lezoch P Litke AM Lockman W Lowe S Lurz B Marlow D Maschmann W Matsui T Messing F Metzger WJ Monteleoni B 《Physical review letters》1985,54(20):2195-2198
38.
As supported PtxNi1–x catalysts are used for hydrogenation reactions, it seemed necessary to assess the surface composition of the reduced samples. To approach the usual reduction conditions we applied in situ reduction in a reaction chamber (1 mbar H2 up to 500 °C) placed in ultra high vacuum recipient (UHV: 10–9 to 2.10–10mbar). All ion scattering spectroscopy measurements were performed in UHV. Charging of the samples was avoided by electron bombardment (5 eV). The variation of the surface composition was determined after subsequent sputtering, thermal treatment at 500 °C and during oxygen adsorption. A comparison with previous results of surface compositions of binary alloys (polycrystalline foils [1, 2] and single crystals PtxNi1–x [3]) is given.Dedicated to Professor Dr. rer. nat. Dr. h. c. Hubertus Nickel on the occasion of his 65th birthday 相似文献
39.
Martin TC Moecks J Belooussov A Cawthraw S Dolenko B Eiden M Von Frese J Kohler W Schmitt J Somorjai R Udelhoven T Verzakov S Petrich W 《The Analyst》2004,129(10):897-901
Signatures of Bovine Spongiform Encephalopathy (BSE) have been identified in serum by means of "Diagnostic Pattern Recognition (DPR)". For DPR-analysis, mid-infrared spectroscopy of dried films of 641 serum samples was performed using disposable silicon sample carriers and a semi-automated DPR research system operating at room temperature. The combination of four mathematical classification approaches (principal component analysis plus linear discriminant analysis, robust linear discriminant analysis, artificial neural network, support vector machine) allowed for a reliable assignment of spectra to the class "BSE-positive" or "BSE-negative". An independent, blinded validation study was carried out on a second DPR research system at the Veterinary Laboratory Agency, Weybridge, UK. Out of 84 serum samples originating from terminally-ill, BSE-positive cattle, 78 were classified correctly. Similarly, 73 out of 76 BSE-negative samples were correctly identified by DPR such that, numerically, an accuracy of 94.4 % can be calculated. At a confidence level of 0.95 (alpha = 0.05) these results correspond to a sensitivity > 85% and a specificity > 90%. Identical class assignment by all four classifiers occurred in 75% of the cases while ambiguous results were obtained in only 8 of the 160 cases. With an area under the ROC (receiver operating charateristics) curve of 0.991, DPR may potentially supply a valuable surrogate marker for BSE even in cases in which a deliberate bias towards improved sensitivity or specificity is desired. To the best of our knowledge, DPR is the first and--up to now--only method which has demonstrated its capability of detecting BSE-related signatures in serum. 相似文献
40.
The present work discusses the grafting by electron beam irradiation of poly(ethylene oxide) (PEO) star-shaped polymers onto porous expanded polytetrafluoroethylene (EXPTFE) surfaces. The resulting materials are intended to combine the good biocompatible properties of PEO with the outstanding mechanical properties of PTFE. The star-shaped PEOs were synthesized via anionic polymerization. 3 Mev electron beam irradiation was applied to graft these PEO stars onto porous EXPTFE surfaces. The hydrophobic EXPTFE surface had to be pre-modified with N-vinylpyrrolidone. ESCA was used to quantify the amount of grafted star-shaped PEO. Unmodified EXPTFE surfaces are well known, when implanted in a body, to be rapidly covered by a layer of cells and fibrin. The EXPTFE coated with PEO were implanted in the peritoneal cavity of rats (or under the back skin). This implantation did not induce any inflammation reactions and SEM analysis had attested the absence of adsorbed cells and fibrin. The glucose diffusion properties of these membranes were studied by a lag time analysis method and compared to those of pure PEO hydrogels. As expected, glucose diffuses through the hydrogel coated membrane and diffusion is not affected by the presence of the EXPTFE membrane. 相似文献