全文获取类型
收费全文 | 6419篇 |
免费 | 142篇 |
国内免费 | 36篇 |
专业分类
化学 | 4311篇 |
晶体学 | 65篇 |
力学 | 180篇 |
数学 | 753篇 |
物理学 | 1288篇 |
出版年
2021年 | 47篇 |
2020年 | 66篇 |
2019年 | 68篇 |
2018年 | 43篇 |
2017年 | 45篇 |
2016年 | 124篇 |
2015年 | 95篇 |
2014年 | 117篇 |
2013年 | 257篇 |
2012年 | 343篇 |
2011年 | 397篇 |
2010年 | 212篇 |
2009年 | 171篇 |
2008年 | 334篇 |
2007年 | 366篇 |
2006年 | 370篇 |
2005年 | 336篇 |
2004年 | 280篇 |
2003年 | 251篇 |
2002年 | 232篇 |
2001年 | 99篇 |
2000年 | 93篇 |
1999年 | 51篇 |
1998年 | 76篇 |
1997年 | 71篇 |
1996年 | 103篇 |
1995年 | 67篇 |
1994年 | 84篇 |
1993年 | 87篇 |
1992年 | 61篇 |
1991年 | 74篇 |
1990年 | 65篇 |
1989年 | 68篇 |
1988年 | 66篇 |
1987年 | 44篇 |
1986年 | 48篇 |
1985年 | 91篇 |
1984年 | 81篇 |
1983年 | 58篇 |
1982年 | 82篇 |
1981年 | 88篇 |
1980年 | 78篇 |
1979年 | 71篇 |
1978年 | 78篇 |
1977年 | 73篇 |
1976年 | 63篇 |
1975年 | 66篇 |
1974年 | 65篇 |
1973年 | 70篇 |
1972年 | 38篇 |
排序方式: 共有6597条查询结果,搜索用时 9 毫秒
31.
R. C. Heaton W. A. Taylor D. R. Phillips Sr. D. J. Jamriska J. B. Garcia 《Journal of Radioanalytical and Nuclear Chemistry》1995,195(2):271-277
Zinc oxide targets irradiated with high energy protons at the Los Alamos Meson Physics Facility (LAMPF) contain a number of radioactive spallation products in quantities large enough to warrant recovery. This paper describes methods for recovering7Be,46Sc, and48V from such targets and offers suggestions on possible ways to recover additional isotopes. The proposed methods are based on traditional precipitation and ion exchange techniques, are readily adaptable to hot cell use, and produce no hazardous waste components. The products are obtained in moderate to high yields and have excellent radionuclidic purity. 相似文献
32.
A detailed vibrational assignment is proposed for 1,3-dimethyl-1,3-diaza-2-boracyclopentanes: where X = Cl, Br or NMe2. The assignments are generally in accord with C2v symmetry, but there is some evidence for a slight breakdown, as some A2 modes appear in the IR. The BN2 stretches are near 1500 cm?1, (antisymmetric) and 1300 cm?1 (symmetric), consistent with a large degree of π-bonding. 相似文献
33.
Suman Dhami Garry Rumbles Alexander J. MacRobert David Phillips 《Photochemistry and photobiology》1997,65(1):85-90
Abstract— The photophysical properties of cis -disulfonated aluminum phthalocyanine (AlPcS2 ) in unilamellar vesicles (liposomes) of DL-a-dipalmitoyl-phosphatidylcholine have been measured. Both the fluorescence and triplet quantum yields decreased with increasing sensitizer concentration. The time-resolved fluorescence decays, analyzed by both the sum of exponentials and decay time distribution analyses, are compared with those reported for AlPcS2 in leukemic K562 cells. Information on the pho-todynamic transport and localization mechanism has been obtained by drawing correlations between the two systems, indicating active transport of the phthalocyanine into tumor cells involving lysosomal accumulation. 相似文献
34.
Microwave induced delayed phosphorescence (MIDP) measurements have been performed in the 00 bands of the phosphorescence spectrum of benzene dissolved in two phases of cyclohexane. From the relative radiative rates for decay of the three zero-field levels it is concluded that on the average the symmetry of the electronic structure is lower than D2h. In the monoclinic low temperature stable phase of cyclohexane (phase II) the structure is approximately antiquinoidal, and in the metastable phase III it is approximately quinoidal. 相似文献
35.
36.
37.
38.
Kozo Arai Atsushi Matsunaga Masaru Yoneyama Shoji Takigami Yoshio Nakamura Haydn E. Edwards Glyn O. Phillips 《Journal of polymer science. Part A, Polymer chemistry》1993,31(1):249-258
The reactions of heparin with 2,4,6-trinitrobenzenesulfonic acid (TNBS) were studied spectrometrically. Seven different commercial heparins were used in this study. The amino groups react with TNBS to form equimolar amounts of trinitrophenylated (TNP) amino groups and bisulfite ions. The TNP-amino groups further react with bisulfite ions to form the monosubstituted anionic sigma complex. The absorption spectrum with two maxima at approximately 350 nm and approximately 420 nm, characteristic of either the TNP-amino groups or the complex, was analyzed for the reaction of TNBS with heparin. It was shown that the reactivities of TNBS with amino groups from α-amino acid and hexosamine residues are greatly different. By combining the results of the reaction kinetics and the reaction of heparin with Sanger's reagent, the number of the α-amino groups and the free amino groups in hexosamine residues were determined. These data have been performed with a range of heparins from different commercial sources, of different activities and physical characteristics. No correlation was found between the free amino contents of these heparins and biological potency. © 1993 John Wiley & Sons, Inc. 相似文献
39.
[reaction: see text] Protein farnesyltransferase (PFTase) catalyzes alkylation of cysteine residues by farnesyl diphosphate (FPP). The dissociation constants for the PFTase-peptide analogue complexes for the series of analogues fl-RTRC(X)VIA (X = H, methyl, dodecyl, farnesyl) were measured by fluorescence anisotropy. The results indicate that an ionizable sulfhydryl moiety is important for substrate binding and the farnesyl group in the product facilitates binding. 相似文献
40.
Philip Wormald Kristina Wickholm Per Tomas Larsson Tommy Iversen 《Cellulose (London, England)》1996,3(1):141-152
An investigation into the effects of mechanical treatment and hydration on the order of cellulose substrates (microcrystalline cellulose and Cladophora cellulose) was performed by the use of ball milling followed by cyclic wetting and drying. The results, monitored by13C-CP/MAS NMR-spectroscopy, were evaluated by calculation of the crystallinity indices and principal component analysis of the NMR data acquired. The results showed that a large part of the disorder induced by the mechanical treatment of cellulose by ball milling is reversible and reordering upon hydration leads to the cellulose I form initially present. The C4 signals corresponding to the reversibly disordered cellulose chains are observed in the amorphous region between 79 and 86 ppm in the13C-CP/MAS NMR-spectra together with signals from cellulose chains on the surface of ordered regions. The peak cluster which contains the C2, C3 and C5 ring carbons can be divided into two specific spectral regions; one between 74 and 77 ppm largely originates from ring carbons within disordered cellulose structures, and one between 70 and 74 ppm contains larger contributions from ordered cellulose. The behaviour of the celluloses upon milling is in accordance with a concept of ordered cellulose fibrils containing amorphous cellulose mainly as surface layers and induced reversible lattice distortions. 相似文献