全文获取类型
收费全文 | 365篇 |
免费 | 5篇 |
专业分类
化学 | 243篇 |
晶体学 | 4篇 |
力学 | 4篇 |
数学 | 4篇 |
物理学 | 115篇 |
出版年
2023年 | 5篇 |
2022年 | 6篇 |
2021年 | 3篇 |
2020年 | 3篇 |
2019年 | 2篇 |
2017年 | 3篇 |
2016年 | 6篇 |
2015年 | 4篇 |
2013年 | 10篇 |
2012年 | 22篇 |
2011年 | 20篇 |
2010年 | 7篇 |
2009年 | 6篇 |
2008年 | 18篇 |
2007年 | 21篇 |
2006年 | 9篇 |
2005年 | 19篇 |
2004年 | 12篇 |
2003年 | 21篇 |
2002年 | 22篇 |
2001年 | 14篇 |
2000年 | 19篇 |
1999年 | 5篇 |
1998年 | 5篇 |
1997年 | 5篇 |
1996年 | 5篇 |
1995年 | 2篇 |
1994年 | 4篇 |
1993年 | 7篇 |
1992年 | 11篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 7篇 |
1988年 | 3篇 |
1987年 | 9篇 |
1986年 | 3篇 |
1985年 | 6篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1965年 | 1篇 |
1964年 | 1篇 |
1961年 | 1篇 |
排序方式: 共有370条查询结果,搜索用时 639 毫秒
91.
92.
An isothermal end-link reaction process in polydimethylsiloxanes is studied by Rayleigh-Brillouin scattering. From the onset of gelation, the Rayleigh line shows increases in intensity which are of the Brillouin lines intensity level, and which are ascribed to the occurrence of static density fluctuations, i. e., of inhomogeneities. Using a density correlation function of an exponential type, the extent and magnitude of the inhomogeneities are estimated from the Rayleigh line intensity corrected for thermal fluctuation factors, and inhomogeneities with correlation length of the order of 100 å are found to appear in network structures during the gelation process. It is suggested that the inhomogeneities results from nonuniform progress of crosslink reactions. These inhomogeneities do not affect the propagation of hypersonic sound. 相似文献
93.
Jürgen Baacke Yuji Igarashi Gerhard Kasperidus 《Zeitschrift fur Physik C Particles and Fields》1981,9(2):203-212
We calculate the self energy of a heavy quark in order α s of QCD confined to a spherical cavity. Only the radius-(and position-) dependent terms which cannot be renormalized away are taken into account. Besides the leadingO(M 0) contribution which acts as a confining potential we determine theO (1/M 2) corrections which contain orbital terms and contributions to theLS potential. This calculation completes the determination of the Breit-Fermi Hamiltonian for a confinedQ \(\bar Q\) system whose interaction parts have been discussed previously. We give some preliminary estimates of the resultant spin dependent level splittings in charmonium. 相似文献
94.
Sumino M Sekine T Ruangrungsi N Igarashi K Ikegami F 《Chemical & pharmaceutical bulletin》2002,50(11):1484-1487
Novel alkylphenols, ardisiphenols A-C (1-3) and a novel bergenin derivative, demethoxybergenin (10) were isolated from the fruits of Ardisia colorata (Myrsinaceae), together with known alkylresorcinols (4-6), embelin (7), myricetin (8), quercetin (9), bergenin (11), norbergenin (12), kaempferol (13), quercetin-3-O-beta-D-glucopyranoside (14) and gallic acid (15). Their structures were determined by NMR, MS(/MS) analyses and other spectroscopic methods. Ardisiphenols showed moderate scavenging activities toward 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals and showed cytotoxicity against the murine breast cancer cell line, FM3A. 相似文献
95.
Hitoshi Yamaguchi Sinji Itoh Shukuro Igarashi Kunishige Naitoh Ryosuke Hasegawa 《Fresenius' Journal of Analytical Chemistry》1998,362(4):395-398
Total reflection X-ray fluorescence (TXRF) analysis after the separation of matrix element was studied for the determination
of trace impurity elements (Ca, Sc, V, Cr, Mn, Fe, Co, Ni and Zn) in high purity copper. Matrix copper was removed by electrolysis
(0.2 A, 8 h) of a nitric acid solution. A 10 μL aliquot of the remaining solution of the electrolysis was dropped on a silicon-wafer
sample-carrier and dried in a vacuum. This was repeated five times and the precipitate of five 10 μL-aliquots was analyzed
by TXRF using a W-Lβ beam with an incident angle of 0.05 °. TXRF analytical values were obtained by using relative sensitivity
factors of the analytes to the internal standard element (Pd). Detection limits of the analytes ranges from 0.077 ng for Zn
to 0.785 ng for Ca.
Received: 25 December 1997 / Revised: 30 March 1998 / Accepted: 2 April 1998 相似文献
96.
Lee HI Benton PM Laryukhin M Igarashi RY Dean DR Seefeldt LC Hoffman BM 《Journal of the American Chemical Society》2003,125(19):5604-5605
A recent high-resolution X-ray crystallographic study (1.16 A) of the Azotobacter vinelandii nitrogenase MoFe protein revealed a previously undetected electron density associated with the active site FeMo-cofactor. The density is located inside the cluster at the center of the "trigonal prism" of six irons and is assigned to a species "X". The identity of species X was not resolved, although the electron density is consistent with a single N, O, or C atom. One proposal is that X is an N atom that derives from and exchanges with N from N2 during catalysis. In the present study, we have examined this possibility by employing 14N and 15N isotopes of N2 along with ENDOR and ESEEM spectroscopies. The WT MoFe protein and alpha-359Arg-->Lys and alpha-381Phe-->Leu variants were allowed to turn over in the presence of 14N2 or 15N2, and then were examined as resting enzymes by ENDOR and ESEEM at X- and Q-bands to look for all 14N and 15N signals coupled to the electron spin of the FeMo-cofactor and to determine if any exchanged during turnover. We have found five peaks in Q-band pulsed ENDOR spectra that appear to arise not only from previously reported N1/N2, which give rise to the ESEEM, but also from one or two additional coupled nitrogens. None of the ENDOR and ESEEM signals vanish or are altered by catalytic turnover with 15N2, and no new 15N signal is detected, leading to the conclusion that if species X is a nitrogen atom, it does not exchange during dinitrogen reduction. 相似文献
97.
Kakinoki K Yamane K Igarashi M Yamamoto M Teraoka R Matsuda Y 《Chemical & pharmaceutical bulletin》2005,53(7):811-815
To characterize the photocatalytic activity of TiO2 via solid-state reaction, the relationship between the physicochemical properties and photocatalytic activity of TiO2 was investigated and estimated from the results of photodegradation of nisoldipine. The photodegradation of nisoldipine was significantly enhanced by addition of TiO2. Two degradation products, nitroso-phenylpyridine derivative and nitro-phenylpyridine derivative, were formed. The degree of photocatalytic activity of TiO2 was quite different between the various types of TiO2 investigated, even when the crystalline phase was the same. As a result of the investigations into the relationship between the photocatalytic activity and physicochemical properties of TiO2, it was found that for the rutile form the photocatalytic activity has good correlation with specific surface area of TiO2, but poor correlation with water loss on drying of TiO2. However, for the anatase form, the photocatalytic activity has good correlation with water loss on drying of TiO2, but poor correlation with specific surface area. Moreover, it was found that the crystallinity of TiO2 has a moderate correlation with the photocatalytic activity of both crystal forms of TiO2. These results suggest that a degree of photocatalytic activity of TiO2 depends on the various physicochemical properties of each type of TiO2 investigated. 相似文献
98.
M Matsukura Y Daiku K Ueda S Tanaka T Igarashi N Minami 《Chemical & pharmaceutical bulletin》1992,40(7):1823-1827
A novel series of 2,2-dialkyl-1'-(N-substituted aminoalkyl)-spiro-[chroman-4,4' -imidazolidine]-2',5'-diones was synthesized and evaluated for antiarrhythmic activity in chloroform- or/and aconitine-induced ventricular arrhythmia in mice. Among these compounds, (-)-6-chloro-2,2-dimethyl-1'-[3-(4-hydroxypiperidino)propyl] -spiro-[chroman-4,4'-imidazolidine]-2',5' -dione was found to be more effective than reference agents and was selected for further development. 相似文献
99.
A novel class of inhibitors for human steroid 5 alpha-reductase: phenoxybenzoic acid derivatives. I.
S Igarashi T Kimura R Naito H Hara M Fujii H Koutoku H Oritani T Mase 《Chemical & pharmaceutical bulletin》1999,47(8):1073-1080
In a search for novel nonsteroidal inhibitors of human prostatic 5 alpha-reductase, we found a new series of phenoxybenzoic acid derivatives to be potent human prostatic 5 alpha-reductase inhibitors. Among them, 4-(biphenyl-4-yloxy)benzoic acid derivatives (2n, YM-31758), 2o and 2s showed more potent inhibitory activities than finasteride with IC50 values of 0.87, 0.67 and 0.56 nM, respectively. The optimized structures for the phenoxybenzoic acid derivatives 2d-2i were calculated by molecular modeling analysis, and the favorable distance between the carbon of the carboxyl group and the centroid of the phenyl group (benzene ring C) was found to be in the 9-11 A range. 相似文献
100.
Kenta Tanaka Emi Takayanagi Tetsutaro Igarashi Tadamitsu Sakurai 《Journal of polymer science. Part A, Polymer chemistry》2006,44(1):88-97
To establish the reaction condition under which the radical copolymerization of methyl methacrylate (MMA) with α‐(2‐hydroxy‐4‐methacryloyloxyphenyl)‐N‐(2,6‐dimethylphenyl)nitrone (HMDN) proceeds smoothly to give photoreactive copolymers, the effects of the nitrone chromophore on the extent to which the radical polymerization of MMA is inhibited were investigated. It was found that the reversible addition of initiating radical to the CH?N+(? O?) moiety in the nitrone chromophore readily occurs to give the nitroxyl radical. It was also found that the latter radical undergoes an efficient coupling reaction with propagating radical to inhibit the radical copolymerization of MMA with HMDN. However, on raising the reaction temperature and the radical concentration, the copolymerization was successfully carried out. This polymerization condition allowed us to prepare the HMDN/MMA, HMDN/styrene, and HMDN/cyclohexyl acrylate copolymers in good yields. The photoirradiation of the copolymer film prepared on a silicon wafer lowered its refractive index by 0.003–0.023, depending on the relative composition of the diarylnitrone chromophore in these copolymers. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 88–97, 2006 相似文献