全文获取类型
收费全文 | 1263篇 |
免费 | 20篇 |
国内免费 | 8篇 |
专业分类
化学 | 800篇 |
晶体学 | 6篇 |
力学 | 11篇 |
数学 | 235篇 |
物理学 | 194篇 |
无线电 | 45篇 |
出版年
2021年 | 13篇 |
2020年 | 10篇 |
2019年 | 16篇 |
2018年 | 12篇 |
2017年 | 11篇 |
2016年 | 25篇 |
2015年 | 25篇 |
2014年 | 26篇 |
2013年 | 46篇 |
2012年 | 53篇 |
2011年 | 54篇 |
2010年 | 41篇 |
2009年 | 34篇 |
2008年 | 62篇 |
2007年 | 67篇 |
2006年 | 63篇 |
2005年 | 47篇 |
2004年 | 39篇 |
2003年 | 36篇 |
2002年 | 47篇 |
2001年 | 10篇 |
2000年 | 8篇 |
1999年 | 9篇 |
1998年 | 10篇 |
1996年 | 12篇 |
1992年 | 8篇 |
1991年 | 20篇 |
1989年 | 10篇 |
1986年 | 8篇 |
1985年 | 12篇 |
1982年 | 8篇 |
1981年 | 12篇 |
1979年 | 10篇 |
1978年 | 11篇 |
1977年 | 8篇 |
1975年 | 7篇 |
1974年 | 8篇 |
1957年 | 7篇 |
1935年 | 7篇 |
1927年 | 9篇 |
1926年 | 7篇 |
1913年 | 7篇 |
1912年 | 11篇 |
1911年 | 7篇 |
1910年 | 9篇 |
1909年 | 19篇 |
1903年 | 8篇 |
1898年 | 7篇 |
1890年 | 8篇 |
1885年 | 11篇 |
排序方式: 共有1291条查询结果,搜索用时 453 毫秒
991.
We consider smooth bounded pseudoconvex domains Ω in Cn whose boundary points of infinite type are contained in a smooth submanifoldM (with or without boundary) of the boundary having its (real) tangent space at each point contained in the null space of the Levi form ofbΩ at the point. (In particular, complex submanifolds satisfy this condition.) We consider a certain one-form α onbΩ and show that it represents a De Rham cohomology class on submanifolds of the kind described. We prove that if α represents the trivial cohomology class onM, then the Bergman projection and the \(\bar \partial - Neumann\) operator on Ω are continuous in Sobolev norms. This happens, in particular, ifM has trivial first De Rham cohomology, for instance, ifM is simply connected. 相似文献
992.
V. Evrard R. De Giacomi G. A. Korshenowski J. N. Rekeda B. O. Ljubin N. D. Buchmann W. D. Ugrjumov I. M. Korenman N. I. Tarassewitsch Je. S. Prshewalski Rufina W. Teiss J. M. Josefinowa-Goldfein L. Klinc E. Stotz S. C. Ganguly G. Semerano I. S. Rao A. P. Terentjew E. M. Terentjewa K. K. Magaram A. I. Neljubina Gertrud Woker Ilse Antener W. Traube Emil Fischer H. Schrades Ch. Valencien J. Deshusses E. T. Illing G. Illari A. Banchetti E. Storfer A. Lespagnol J. Bruneel A. G. Kuhlmann 《Analytical and bioanalytical chemistry》1942,124(9-10):351-361
993.
B. Schöndorff H. Jessen-Hansen Ivar Bang Matthew Steel William J. Gies F. G. Benedikt V. C. Myers W. Wiechowski Frank P. Underhill Israel S. Kleiner Eduard Strauss H. Schulz Emil Osterber Charles G. R. Wolff Arthur Konschegg Emil Abderhalden C. Funk G. Modrakowski Leo Hess R. Engeland C. A. Herter 《Analytical and bioanalytical chemistry》1909,48(11):721-726
994.
Adolf Emil Siegrist 《Helvetica chimica acta》1981,64(3):662-680
Preparation of Styryl and Stilbenyl Derivatives of 1H-Benzotriazoles 1-(p-Tolyl)-substituted 1H-benzotriazoles react with anils of aromatic aldehydes in the presence of dimethylformamide and potassium hydroxide to yield the corresponding 1-(styr-4′-yl)-1H-benzotriazoles and 1-(stilben-4′-yl)-1H-benzotriazoles, respectively (‘anil synthesis’). Further, under the same reaction conditions, the Schiff's bases derived from p-chloroaniline and 4-(1′H-benzotriazol-1′-yl)benzaldehydes give, with p-tolyl-substituted heterocycles, the corresponding heterocyclic substituted stilbenyl derivatives. 相似文献
995.
[reaction: see text] An expeditious procedure for the direct formation of stereochemically well-defined macrodiolides is described. Cyclodimerizations of enantioenriched C7 and C8 hydroxy esters 6 in the presence of catalytic amounts of distannoxane transesterification catalysts afford 14- to 22-membered macrodiolides 7-9 bearing up to six stereocenters. Additional structural diversity is introduced by further stereoselective reactions on selected macrodiolides 7a, 7g, 10a, and 11. 相似文献
996.
Erich Widmer Reinhard Zell Emil Albin Broger Yvo Crameri Hans Peter Wagner Josef Dinkel Markus Schlageter T+odor Luk
《Helvetica chimica acta》1981,64(7):2436-2446
Technical Procedures for the Synthesis of Carotenoids and Related Compounds from 6-Oxo-isophorone. II. A Novel Concept for the Synthesis of (3RS, 3′RS)-Astaxanthin Starting from 6-oxo-isophorone ( 2 ) a new concept for a seven-step synthesis of (3RS, 3′RS)-astaxanthin ( 1 ) has been developed. As a key feature of the new approach, the oxidation state of astaxanthin ( 1 ) is adjusted already at an early stage of the synthesis. Thus, manipulation on more complex intermediates later in the synthesis is reduced to a minimum. Acetonide 10 or dimer 13 represent the key intermediates of this concept (Scheme 2). The whole sequence has been run on a kg scale with an overall yield of 52% (s. Scheme 5). 相似文献
997.
A pressure-actuated on-chip injection system has been developed that is compatible with shallow microchannels with a very large aspect ratio, i.e. 1 microm deep and up to 1000 microm wide. Such channels offer potential advantages in the miniaturisation of liquid chromatography and other separation methods as they allow high loadability and low sample dispersion at the same time. Computational fluid dynamics simulations were performed to predict the flow profiles and the transport of a sample in the system and to justify the injection principle. Based on these simulations, a prototype integrated into a chip for hydrodynamic chromatography has been realised and tested experimentally. The performance of the device is satisfactory and the results are in qualitative agreement with the numerical models. 相似文献
998.
Chibowski EJ 《Advances in colloid and interface science》2005,113(2-3):121-131
Using the literature data of the advancing and receding contact angles for water, diiodomethane and hexadecane measured on various hydrophobic silyl layers (mostly monolayers) produced on silicon wafers the apparent surface free energies gamma(s)(tot) were calculated by applying new model of the contact angle hysteresis interpretation. It was found that, for the same silyl layer, the calculated gamma(s)(tot) values to some degree depended on the probe liquid used. Therefore, thus calculated the surface free energies should be considered as apparent ones. Moreover, also the values of the dispersion component gamma(s)(d) of these layers depend on the probe liquid used, but to a less degree. This must be due to the strength of the force field originating from the probe liquid and the spacing between the interacting molecules. The relationships between gamma(s)(tot) and gamma(s)(d) are discussed on the basis of the equations derived. It may be postulated that applying proposed model of the contact angle hysteresis and calculating the apparent total surface free energies and the dispersion contributions better insight into wetting properties of the silyled silicon surface can be achieved. 相似文献
999.
Emil Paleček Viktor Brabec František Jelen Zdeněk Pechan 《Journal of Electroanalytical Chemistry》1977,75(2):471-485
Nucleic acids and proteins were studied by means of derivative and normal pulse polarography, and d.c. and a.c. polarography in connection with the dropping mercury electrode. It was shown that natural ribonucleic acids, as transfer, ribosomal and viral RNAs yield derivative pulse-polarographic peaks; from their heights and potentials conclusions can be made about their content of ordered structure in solution, similarly as in the case of deoxyribonucleic acids studied earlier. Synthetic single-stranded polyribo-cytidylic acid yields a well developed peak, whereas in the double-helical complex with polyriboguanylie acid it is inactive when using either derivative pulse polarography or d.c. polarography. Well developed peaks were obtained also with albumin (a protein containing reducible?S?S? groups), while only an inflex was observed on the d.c. polarogram. Proteins were also studied in media containing cobalt (Brdi?ka's solution) or nickel and it was shown that derivative pulse polarography due to its high sensitivity and accuracy enables us to carry out the measurements even in less common media than Brdi?ka's solution. This fact could be exploited in clinical chemistry as well as in the investigation of the nature of catalytic currents of proteins. The currents of double-helical polynucleotides obtained by means of normal pulse polarography exhibit a marked dependence on the initial potential and cannot represent a reliable indicator of structural changes of biopolymers in solution. They can however, be used in studies of the influence of the polynucleotide adsorption at different potentials on the subsequent reduction. 相似文献
1000.
Byrne CM Allen SD Lobkovsky EB Coates GW 《Journal of the American Chemical Society》2004,126(37):11404-11405
The alternating copolymerization of (R)- or (S)-limonene oxide and CO2 using beta-diiminate zinc acetate catalysts is reported. At 100 psi CO2 and 25 degrees C, the catalyst exhibits a high selectivity for the trans isomer and produces regioregular polycarbonate. The copolymer contains >99% carbonate linkages, a narrow molecular weight distribution, and an Mn value consistent with the [epoxide]/[Zn] ratio. 相似文献