全文获取类型
收费全文 | 807篇 |
免费 | 23篇 |
国内免费 | 1篇 |
专业分类
化学 | 462篇 |
晶体学 | 5篇 |
力学 | 69篇 |
数学 | 63篇 |
物理学 | 232篇 |
出版年
2022年 | 5篇 |
2021年 | 10篇 |
2020年 | 9篇 |
2019年 | 7篇 |
2018年 | 8篇 |
2017年 | 7篇 |
2016年 | 13篇 |
2015年 | 20篇 |
2014年 | 25篇 |
2013年 | 38篇 |
2012年 | 35篇 |
2011年 | 30篇 |
2010年 | 32篇 |
2009年 | 20篇 |
2008年 | 46篇 |
2007年 | 35篇 |
2006年 | 29篇 |
2005年 | 25篇 |
2004年 | 30篇 |
2003年 | 19篇 |
2002年 | 17篇 |
2001年 | 18篇 |
2000年 | 27篇 |
1999年 | 13篇 |
1998年 | 7篇 |
1997年 | 10篇 |
1996年 | 20篇 |
1995年 | 15篇 |
1994年 | 20篇 |
1993年 | 23篇 |
1992年 | 16篇 |
1991年 | 9篇 |
1990年 | 16篇 |
1989年 | 18篇 |
1988年 | 14篇 |
1987年 | 24篇 |
1986年 | 7篇 |
1985年 | 14篇 |
1984年 | 6篇 |
1982年 | 11篇 |
1981年 | 7篇 |
1980年 | 9篇 |
1979年 | 6篇 |
1978年 | 8篇 |
1977年 | 7篇 |
1976年 | 9篇 |
1975年 | 7篇 |
1974年 | 10篇 |
1973年 | 8篇 |
1972年 | 4篇 |
排序方式: 共有831条查询结果,搜索用时 46 毫秒
111.
Künsch (1989, Ann. Statist.17 1217-1241) and Liu ane Singh (1992, in Exploring Limits of Bootstrap (R. Le Page and L. Billard, Eds.), pp. 225-248, Wiley, New York) have recently introduced a block resampling method that is successful in deriving consistent bootstrap estimates of distribution and variance for the sample mean of a strong mixing sequence. Raïs and Moore (1990, in Interface ′90) and Raïs (1992, Ph.D. Thesis, University of Montreal) extended the results of Künsch and Liu and Singh in the case of the sample mean of a homogeneous strong mixing random field in two dimensions (n = 2). In this paper, the general case (n Z+) is considered, and a resampling technique for strong mixing random fields is formulated, which is an extension of the "blocks of blocks" resampling scheme for sequences in Politis and Romano (1992, Ann. Statist.20 (4) 1985-2007). The "blocks of blocks" method can be used to construct asymptotically correct confidence intervals for parameters of the whole (infinite-dimensional) joint distribution of the random field, for example, the spectral density at a point. A variation of the "blocks of blocks" resampling scheme that involves "wrapping" the data around on a torus will also be studied, in view of its property to yield an unbiased bootstrap distribution. 相似文献
112.
F. Strieder L. Gialanella U. Greife C. Rolfs S. Schmidt W. H. Schulte H. P. Trautvetter D. Zahnow F. Terrasi L. Campajola A. D’Onofrio V. Roca M. Romano M. Romoli 《Zeitschrift für Physik A Hadrons and Nuclei》1996,355(1):209-218
The absolute cross sectionσ of thed(7Li,p)8Li reaction near theE cm=0.61 MeV resonance has been measured using a7Li ion beam and a windowless gas target system filled with D2 gas. The proton yield of the reaction and theβ-delayedα-activity of the residual nuclides8Li were observed both concurrently with the elastic scattering yield, relatingσ to the Rutherford scattering cross sectionσ R. The resulting values,σ (fromp)=143.6±8.9 mb andσ (from8Li)=151±20 mb, lead to a weighted mean value ofσ=153±6 mb (x 2=2.26) including all available values andσ=146±5 mb (x 2=0.05) removing some values from the data set. The consequences for the expected flux of high-energy solar neutrinos are discussed. 相似文献
113.
Summary The use of 4-(6-methylnaphthalen-2-yl)-4-oxobuten-2-oic acid as a fluorogenic reagent in pre-column derivatization for the high-performance liquid chromatography (HPLC) of biologically important thiols (L-cysteine, glutathione, N-acetylcysteine, homocysteine and mercaptopropionylglycine) was investigated. The aroylacrylic acid reacts selectively and rapidly (15 min. at room temperature) with the thiol compounds to give stable fluorescent adducts which can be separated by reversedphase HPLC and detected fluorometrically (ex 300nm); em 445nm). The experimental conditions for the thiol derivatization and chromatographic separation are discussed. Applications to the determination of N-acetylcysteine, mercaptopropionylglycine and cysteine are described.Presented in part at Bononiachem, XVI Congresso Nazionale di Chimica, Bologna, October 9–14, 1988. 相似文献
114.
Giorgio Barbieri Rois Benassi Romano Grandi Ugo Maria Pagnoni Ferdinando Taddei 《Magnetic resonance in chemistry : MRC》1979,12(3):159-162
The relative reactivity toward protonation and methylation of the two nitrogen atoms in N,N-dimethylaminopyridines has been examined by 1H NMR. The ring position of the dimethylamino group has no influence on protonation, which occurs in all the derivatives at the heterocyclic nitrogen. The N-methylation reaction does not follow a homogeneous behaviour, occurring at the exocyclic nitrogen in the 2-substituted dimethylamino derivative. The electronic characteristics of the molecules, determined by MO calculations at a semi-empirical level, indicate that both protonation and methylation should occur at the heterocyclic nitrogen; the calculated relative stabilites, however, of the N-protonated and N-methylated forms are in full agreement with the experimental results, and it appears that the anomalous behaviour of 2-dimethylaminopyridine in the N-methylation reaction is caused by steric factors. 相似文献
115.
G Musumarra G Scarlata G Cirma G Romano S Palazzo S Clementi G Giulietti 《Journal of chromatography. A》1985,350(1):151-168
Principal component analysis of standardized RF values in four eluent systems [ethyl acetate-methanol-30% ammonia (85:10:15), cyclohexane-toluene-diethylamine (65:25:10), ethyl acetate-chloroform (50:50) and acetone, with the plate dipped in potassium hydroxide solution] provided a two-component model which accounts for 73% of the total variance. The "scores" plot allowed the restriction of the range of inquiry to a few candidates. This result is of great practical significance in analytical toxicology, especially when account is taken of the cost, the time, the analytical instrumentation and the simplicity of the calculations required by the method. 相似文献
116.
Maurizio Zandomeneghi Marino Cavazza Luigi Moi Francesco Pietra 《Tetrahedron letters》1980,21(2):213-214
Kr-ion laser irradiation of carvone () at 350.7 and 356.4 nm gave carvonecamphor () in a much higher yield (88%) than in conventional photochemistry, while () was a primary photo-by-product. 相似文献
117.
118.
Stress-induced crystallization of a crosslinked polybutadiene with a high 1,4-cis content is investigated, at room temperature. The change in the fraction of crystallinity with deformation is evaluated by two different methods. The first is based on simultaneous measurement of birefringence and stress. The second is based on calorimetric analysis. The data on crystallinity obtained by these two methods are in good agreement in the range of low deformations, while, in the range of higher deformation (λ > 5), the degree of crystallinity obtained by calorimetry is higher than that obtained by the optical method. Qualitative information on the crystallization was also obtained by optical analysis of the hysteresis behavior. The hysteresis data show the presence of ordering phenomena at deformations at which there seems to be no crystallinity according to both quantitative methods. 相似文献
119.
120.
Tobón YA Nieto LI Romano RM Della Védova CO Downs AJ 《The journal of physical chemistry. A》2006,110(8):2674-2681
The photolytically induced reactions of a dihalogen XY (= Cl2, ICl, or IBr) with OCS isolated together in an Ar matrix at about 15 K lead to different photoproducts depending on the natures of X and Y. In addition to the known species ClCO*, OCCl2, syn-ClC(O)SCl, syn-ClC(O)SSCl, IC(O)Cl, IC(O)Br, and syn-BrC(O)SBr, syn-iodocarbonylsulfenyl bromide, syn-IC(O)SBr, has thus been identified for the first time as a photoproduct of the reactions involving IBr. The first product to be formed in the reactions with Cl2 or ICl is the ClCO* radical which reacts subsequently with halogen or sulfur atoms or other matrix guests to give the corresponding carbonyl dihalide (OCCl2 and IC(O)Cl), syn-ClC(O)SCl or syn-ClC(O)SSCl. The analogous reaction with IBr affords syn-BrC(O)SBr, IC(O)Br, and syn-IC(O)SBr. The changes have been followed, the products characterized experimentally by IR measurements, and the spectra analyzed in the light of the results of appropriate theoretical calculations. 相似文献