全文获取类型
收费全文 | 171088篇 |
免费 | 1799篇 |
国内免费 | 507篇 |
专业分类
化学 | 88271篇 |
晶体学 | 3039篇 |
力学 | 7154篇 |
综合类 | 3篇 |
数学 | 19514篇 |
物理学 | 55413篇 |
出版年
2020年 | 1398篇 |
2019年 | 1552篇 |
2018年 | 1980篇 |
2017年 | 2065篇 |
2016年 | 3184篇 |
2015年 | 1889篇 |
2014年 | 3112篇 |
2013年 | 7660篇 |
2012年 | 5747篇 |
2011年 | 6877篇 |
2010年 | 5021篇 |
2009年 | 5003篇 |
2008年 | 6534篇 |
2007年 | 6429篇 |
2006年 | 6076篇 |
2005年 | 5502篇 |
2004年 | 5091篇 |
2003年 | 4593篇 |
2002年 | 4451篇 |
2001年 | 5218篇 |
2000年 | 3862篇 |
1999年 | 2969篇 |
1998年 | 2481篇 |
1997年 | 2385篇 |
1996年 | 2239篇 |
1995年 | 2113篇 |
1994年 | 2092篇 |
1993年 | 2001篇 |
1992年 | 2305篇 |
1991年 | 2244篇 |
1990年 | 2193篇 |
1989年 | 2123篇 |
1988年 | 2121篇 |
1987年 | 2124篇 |
1986年 | 2020篇 |
1985年 | 2629篇 |
1984年 | 2684篇 |
1983年 | 2381篇 |
1982年 | 2492篇 |
1981年 | 2307篇 |
1980年 | 2284篇 |
1979年 | 2426篇 |
1978年 | 2462篇 |
1977年 | 2388篇 |
1976年 | 2436篇 |
1975年 | 2360篇 |
1974年 | 2327篇 |
1973年 | 2504篇 |
1972年 | 1623篇 |
1971年 | 1337篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
An extension of the transverse-momentum analysis of Danielewicz and Odyniec is proposed. This extension involves a consideration of baryonic pT-distribution widths in and out of the reaction plane. Calculations within one- and two-fluid mean-field models show that such an analysis allows us to extract more information on the nuclear equation of state and stopping power than the conventional one does. Different criteria for selecting collision events (i.e. sorting them out according to impact parameters) are also examined. Selections according to the baryonic multiplicity in the midrapidity region and the transversal-to-longitudinal energy ratio are found to be suitable for this purpose. 相似文献
942.
M M Zuk B D Rihter M E Kenney M A Rodgers M Kreimer-Birnbaum 《Journal of chromatography. A》1991,568(2):437-444
Bis(di-isobutyl octadecylsiloxy)silicon 2,3-naphthalocyanine (isoBOSINC) is a synthetic potential photosensitizer for tumor therapy. A new method, which combines solvent extraction and several purification steps, has been developed to determine its presence in tissues. Separation and quantitation of isoBOSINC is done by high-performance liquid chromatography on a silica column with toluene as a mobile phase and using fluorescence detection (lambda ex = 365 nm, lambda em = 750 nm). For recovery studies, isoBOSINC was added to muscles at levels of 0.067 and 0.67 micrograms/g; the mean recoveries were 100%, with coefficients of variation of 6.1 and 6.4%, respectively. For liver samples, the amounts added were 0.67 and 6.7 micrograms/g and for serum 0.67 and 6.70 micrograms/ml. The mean recoveries for liver were 86 and 93%, with coefficients of variation of 7.7 and 4.4%, respectively. For serum, the mean recoveries were 99 and 96%, with coefficients of variation of 2.6 and 6.9%, respectively. Due to its low detection limit and selectivity, the method is appropriate for pharmacokinetic as well as tumor uptake studies following in vivo exposure to isoBOSINC. Preliminary data on tissue distribution of the photosensitizer in normal rats are also presented. 相似文献
943.
The study of Wiener-Levinson digital filters leads to certain classes of polynomials orthogonal on the unit circle (Szeg
polynomials). Here we present theorems that show that the unknown frequencies in a periodic discrete time signal can be determined from the limiting behavior (as N → ∞) of the zeros of fixed degree Szeg
polynomials that are orthogonal with respect to a distribution defined from N successive samples of the signal. This proves an essential part of a conjecture due to Jones, Njåstad, and Saff concerning the frequency analysis problem. 相似文献
944.
A. M. Gilinsky K. S. Zhuravlev D. I. Lubyshev V. P. Migal V. V. Preobrazhenskii B. R. Semiagin 《Superlattices and Microstructures》1991,10(4)
Photoluminescence spectra of δ-p-doped GaAs structures of different doping levels are studied experimentally. It is found that set of PL bands observed in δ-p-doped samples recently is regularly broadened with doping concentration increase due to appearance of additional low-energy bands and their subsequent red shift at higher doping levels. A red shift of the bands and a change of their relative intensities were caused also by excitation laser intensity decrease and/or temperature increase. These results confirm our previous assumption that the bands are due to radiative recombination of spatially separated photoelectrons with holes occupying size-quantization levels of δ-layer potential well. 相似文献
945.
Liquid crystal televisions have been employed as spatial light modulators in a variety of optical image processing applications. We have used such devices to develop techniques in speckle metrology for the electronic addition of speckle patterns and the display of speckle correlation, and also for the real-time display of object motion. Factors which affect the performance in terms of the useful working range and the accuracy of displacement measurement are discussed. Some modifications to the LCTV which should increase the potential of these devices as spatial light modulators, when used in both amplitude and phase modulation, are considered briefly. 相似文献
946.
In this paper we present photoionization cross sections of the Cu and Al dimers and tetramers. The local spin density method is applied to calculate the electronic structure and the ground state potential. The cross sections are calculated using the continuum multiple scattering method, and a basic analysis of the photoionization process is given within the independent particle picture. 相似文献
947.
Three-dimensional astigmatic resonators, typical examples of which are the resonators bounded by cylindrical-spherical mirrors and cylindrical-cylindrical mirrors oriented at an arbitrary crossed angle, are investigated in detail by using a complex curvature tensor concept and generalized tensor ABCD law. Computerized numerical calculations illustrate some interesting characteristics of these astigmatic resonators. 相似文献
948.
T Christensen E B Jensen F Junker H Dalb?ge F Abildgaard J J Led 《Acta chemica Scandinavica (Copenhagen, Denmark : 1989)》1992,46(1):97-99
Biosynthetic human growth hormone specifically 13C-labelled in the carbonyl positions of all 26 leucine residues has been obtained by recombinant DNA techniques using 13C-labelled leucine and an E. coli strain that requires leucine. It is shown that, on the whole, the labelling is specific with no significant mislabelling as would have been the case had the 13C-labelled leucine been metabolized. 相似文献
949.
G. I. Koldobskii Yu. E. Myznikov A. B. Zhivich V. A. Ostrovskii V. S. Poplavskii 《Chemistry of Heterocyclic Compounds》1992,28(6):626-631
In this review we discuss results obtained in the development of methods for the synthesis of tetrazoles and tetrazolium salts together with studies of alkylation, acylation, and imidoylation of tetrazole and 5-substituted tetrazoles under conditions of phase-transfer catalysis.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 754–761, June, 1992. 相似文献
950.
The reduction of chromate by glutathione, its mono- and diethyl esters,
-cysteine, 2-mercapto-propionic acid and mercapto-succinic acid has been studied. The empirical rate law kobs = ab[Thiol]2/(1 + b[Thiol]) is obeyed by all of these thiols, at neutral pH. No evidence could be obtained for a first-order pathway in glutathione under these conditions. These observations are used to comment on the stability of intermediates potentially important in explaining chromate toxicity. 相似文献