全文获取类型
收费全文 | 7958篇 |
免费 | 211篇 |
国内免费 | 44篇 |
专业分类
化学 | 5844篇 |
晶体学 | 39篇 |
力学 | 143篇 |
综合类 | 1篇 |
数学 | 1253篇 |
物理学 | 933篇 |
出版年
2021年 | 44篇 |
2020年 | 82篇 |
2019年 | 80篇 |
2018年 | 42篇 |
2017年 | 54篇 |
2016年 | 143篇 |
2015年 | 155篇 |
2014年 | 157篇 |
2013年 | 365篇 |
2012年 | 326篇 |
2011年 | 476篇 |
2010年 | 218篇 |
2009年 | 224篇 |
2008年 | 378篇 |
2007年 | 384篇 |
2006年 | 405篇 |
2005年 | 386篇 |
2004年 | 388篇 |
2003年 | 279篇 |
2002年 | 283篇 |
2001年 | 110篇 |
2000年 | 115篇 |
1999年 | 108篇 |
1998年 | 90篇 |
1997年 | 100篇 |
1996年 | 107篇 |
1995年 | 88篇 |
1994年 | 103篇 |
1993年 | 94篇 |
1992年 | 98篇 |
1991年 | 84篇 |
1990年 | 67篇 |
1989年 | 69篇 |
1988年 | 77篇 |
1987年 | 57篇 |
1986年 | 79篇 |
1985年 | 110篇 |
1984年 | 122篇 |
1983年 | 89篇 |
1982年 | 116篇 |
1981年 | 125篇 |
1980年 | 124篇 |
1979年 | 98篇 |
1978年 | 127篇 |
1977年 | 91篇 |
1976年 | 95篇 |
1975年 | 85篇 |
1974年 | 72篇 |
1973年 | 69篇 |
1972年 | 51篇 |
排序方式: 共有8213条查询结果,搜索用时 484 毫秒
71.
Ian K. Boddy J. Boniface Richard C. Cambie Peter A. Craw David S. Larsen Hamish McDonald Peter S. Rutledge Paul D. Woodgate 《Tetrahedron letters》1982,23(42):4407-4408
Gentle heating of allyloxyanthraquinones with sodium dithionite in dimethylformanide - water effects a rapid and controlled rearrangement to give high yields of 2-allyanthraquinones. 相似文献
72.
Dr. Gerhard Banik Herbert Stachelberger Alfred Vendl Robert Kellner Manfred Grasserbauer 《Mikrochimica acta》1981,76(1-2):93-109
Summary The fundamental importance of scientific research for the preservation and restoration of works of art is uncontestable. The methods described in this paper, such as light microscopy, microchemical tests, emission spectroscopy, chromatography, scanning electron analysis, electron microprobe analysis and infrared spectroscopy, are of special significance in this filed. Nevertheless a better understanding of the problems that arise out of new special questions of art history can be obtained only by the right interpretation of the data obtained by scientific methods.
Mikrochemische Charakterisierung von Gemälden
Zusammenfassung Die grundlegende Bedeutung wissenschaftlicher Forschung für die Erhaltung und Restaurierung von Kunstwerken ist unbestritten. Die hier beschriebenen Methoden (Lichtmikroskopie, mikrochemische Reaktionen, Emissionsspektroskopie, Chromatographie, Rasterelektronen-Analyse und Infrarotspektroskopie) sind hierfür von zunehmender Bedeutung. Sie ermöglichen ein besseres Verständnis neuerer kunsthistorischer Probleme nur durch die richtige Interpretation der Ergebnisse wissenschaftlicher Methoden.相似文献
73.
74.
Daniel E. Lynch Gillian E. Spicer Ian Mcclenaghan 《Journal of heterocyclic chemistry》2005,42(7):1363-1368
Three α‐phenylmalonamides have been prepared by the selective nucleophilic cleavage of 5,7‐dimethyl‐2‐phenyl‐1‐oxo‐1H‐pyrazolo[1,2‐a]pyrazol‐4‐ylium‐3‐olate in solventless microwave syntheses. The three weak nucleophiles employed were aniline, p‐chloroaniline and m‐toluidine. The α‐phenylmalonamides of these three aniline derivatives could not be prepared using the previously reported solvent syntheses via 3‐oxopyrazolo[1,2‐a]pyrazol‐8‐ylium‐1‐olates. All products were characterised using, infrared spectroscopy, 1H nmr and electrospray mass spectrometry. The single crystal X‐ray structures of the starting pyrazolo‐[1,2‐a]pyrazole and α‐phenylmalon‐m‐toluidide are also reported. 相似文献
75.
Rongbiao?WangEmail author Herbert?Schmiedel Bernd-Reiner?Paulke 《Colloid and polymer science》2004,283(1):91-97
Isothermal titration calorimetry (ITC) measurements of the mixture of the cationic surfactant cetyl trimethyl ammonium bromide (CTAB) with negatively charged, hairy copolymer latices (poly-(2,3-epoxypropylmethacrylate-co-methacrylic acid) in different ratio) at high water excess indicate a monomer adsorption mechanism of CTAB by the polymer particles. The number of adsorbed CTAB molecules at saturation corresponds approximately to the number of negative elementary charges bound at the surface of the latices. The mixing enthalpy is the sum of demicellization and sorption enthalpies. At 25 °C for CTAB the demicellization enthalpy amounts to 10 kJ/mol, whereas the adsorption enthalpy varies from –7 kJ/mol (surface charge density of the latices
=–0.37 C/m2) to +3 kJ/mol (=–0.085 C/m2). The hydrodynamic radius
RH of the latex particles upon titration of cationic detergent and salt (NaBr) decreases by about 2 nm until the onset of aggregation near the isoelectric point. Titration of nonionic or anionic detergents has much less influence on the hydrodynamic radius and produces no measurable adsorption heat. The results are consistent within a model of latex particles with extended negatively charged polymer chains interacting predominantly via Coulombic forces with detergents. 相似文献
76.
Harry J. Whitlow Margaretha Andersson Mikael Hult Leif Persson Mohamed El Bouanani Mikael Östling Carina Zaring Nils Lundberg David D. Cohen Nick Dytlewski Peter N. Johnston Ian F. Bubb Scott R. Walker Erik Johanson Sture Hogmark P. Anders Ingemarsson 《Mikrochimica acta》1995,120(1-4):171-181
Recoil Spectrometry covers a group of techniques that are very similar to the well known Rutherford backscattering Spectrometry technique, but with the important difference that one measures the recoiling target atom rather than the projectile ion. This makes it possible to determine both the identity of the recoil and its depth of origin from its energy and velocity, using a suitable detector system. The incident ion is typically high-energy (30–100MeV)35C1,81Br or127I. Low concentrations of light elements such as C, O and N can be profiled in a heavy matrix such as Fe or GaAs. Here we present an overview of mass and energy dispersive recoil Spectrometry and illustrate its successful use in some typical applications. 相似文献
77.
78.
79.
Summary Under suitable conditions, we prove the convergence of the Bateman method for integral equations defined over bounded domains inR
d
,d1. The proof makes use of Hilbert space methods, and requires the integral operator to be non-negative definite. For one-dimensional integral equations over finite intervals, estimated rates of convergence are obtained which depend on the smoothness of the kernel, but are independent of the inhomogeneous term. In particular, for aC
kernel andn reasonably spaced Bateman points, the convergence is shown to be faster than any power of 1/n. Numerical calculations support this result. 相似文献
80.
N-Alkoxycarbonyl- and N-carboxamido-oxaziridines are shown to react with aromatic alkenes to give epoxide, aziridine or hydro-oxidation products, in ratios depending on the oxaziridine structure. Chiral oxaziridines can effect epoxidation and hydro-oxidation with promising levels of asymmetric induction. 相似文献