全文获取类型
收费全文 | 519篇 |
免费 | 17篇 |
国内免费 | 22篇 |
专业分类
化学 | 296篇 |
晶体学 | 9篇 |
力学 | 19篇 |
综合类 | 5篇 |
数学 | 162篇 |
物理学 | 67篇 |
出版年
2023年 | 4篇 |
2022年 | 10篇 |
2021年 | 13篇 |
2020年 | 4篇 |
2019年 | 13篇 |
2018年 | 6篇 |
2017年 | 21篇 |
2016年 | 8篇 |
2015年 | 5篇 |
2014年 | 13篇 |
2013年 | 44篇 |
2012年 | 15篇 |
2011年 | 22篇 |
2010年 | 13篇 |
2009年 | 23篇 |
2008年 | 25篇 |
2007年 | 14篇 |
2006年 | 23篇 |
2005年 | 19篇 |
2004年 | 14篇 |
2003年 | 10篇 |
2002年 | 13篇 |
2001年 | 16篇 |
2000年 | 10篇 |
1999年 | 10篇 |
1998年 | 14篇 |
1997年 | 11篇 |
1996年 | 8篇 |
1995年 | 17篇 |
1994年 | 13篇 |
1993年 | 10篇 |
1992年 | 8篇 |
1991年 | 10篇 |
1990年 | 4篇 |
1989年 | 6篇 |
1988年 | 8篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 9篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1982年 | 7篇 |
1981年 | 13篇 |
1980年 | 7篇 |
1979年 | 16篇 |
1978年 | 4篇 |
1976年 | 2篇 |
1973年 | 1篇 |
排序方式: 共有558条查询结果,搜索用时 171 毫秒
11.
V. G. Berezkin V. R. Alishoyev E. N. Victorova V. S. Gavrichev V. M. Fateeva 《Chromatographia》1982,16(1):126-131
Summary The use of crystallohydrates, crystallohydrate solutions and melts as stationary phases in gas chromatography has been proposed. Crystallohydrates have been shown to display high selectivity in the separation of polar organic compounds when use is made of water vapours as the mobile phase. Some aspects of gas-liquid chromatography in water vapours and with the stationary phase comprising crystallohydrates have been studied, and the preliminary results obtained point to the desirability of further progress in this field.Presented at the 14th International Symposium on Chromatography London, September, 1982 相似文献
12.
13.
14.
《Operations Research Letters》2022,50(1):1-7
Fisher linear discriminant analysis is a well-known technique for dimensionality reduction and classification. The method was first formulated in 1936 by Fisher. In this paper we concentrate on three different formulations of the multi-dimensional problem. We provide a mathematical explanation why two of the formulations are equivalent and prove that this equivalency can be extended to a broader class of objective functions. The second contribution is a rate of convergence of a fixed point method for solving the third model. 相似文献
15.
The interaction of cyanamide with -ketocarboxylic esters in the presence of Ni(acac)2 affords N-unsubstituted aminals of acyl(alkoxycarbonyl)ketenes.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 419–421, February, 1993. 相似文献
16.
Ajay K. Bose Maghar S. Manhas Suhas Pednekar Subhendu N. Ganguly Hoang Dang William He Arun Mandadi 《Tetrahedron letters》2005,46(11):1901-1903
An important stage in process development is kilo scale preparation of the target compound. For this reason, a procedure involving water-based biphasic reaction media has been developed for conducting some exothermic reactions on a large scale. This protocol is illustrated by the energy-efficient and rapid preparation of dihydropyrimidinones by a solvent-free, green chemistry procedure applied to the Biginelli reaction using p-toluenesulfonic acid as catalyst. 相似文献
17.
A. Meddour J. Courtieu W. Abdelhadi S. Guermouche M. H. Guermouche 《Chromatographia》1996,43(7-8):387-392
Summary Comparative gas chromatographic properties of two thermotropic Poly(L-glutamates) with long alkyl side chains (10 and 16 carbons called Poly 10 and Poly 16 respectively) are studied.Their thermal properties were established with differential scanning calorimetry (DSC) and gas chromatography. They present a cholesteric liquid crystal in a large temperature range.The chromatographic separation abilities of the two polymers in the liquid crystal state were studied using capillary glass columns. Interesting analytical performances were obtained in different fields: isomeric separation of alkanes, aromatics, polyaromatics, volatile aroma compounds and cis and trans isomers. Some differences were noticed in their behaviours; 2 and 3-methyloctane and xylene isomers are separated only on Poly 10 while limonene and eucalyptol are separated only on Poly 16. 相似文献
18.
Alenka Turi?nik 《Journal of fluorine chemistry》2003,121(2):245-251
[Mg(HF)2](SbF6)2 and [Ca(HF)2](SbF6)2 monocrystals were grown from the corresponding hexafluoroantimonates(V) dissolved in anhydrous hydrogen fluoride. [Mg(HF)2](SbF6)2 crystallizes in the space group Pnma (no. 62) with a=1249.1(4) pm, b=1230.2(4) pm, c=699.1(2) pm, V=1.0742(6) nm3, Z=4. Magnesium is octahedrally coordinated by six fluorine atoms from which two belong to two HF molecules. The structure can be represented by alternating rows of magnesium and antimony atoms running parallel to the c-axis. Magnesium atoms are connected by cis bridging Sb(2)F6 units along the a-axis and by trans bridging Sb(1)F6 units along the b-axis. In this way a three-dimensional network is formed.[Ca(HF)2](SbF6)2 crystallizes in the space group P21/n (no. 14) with a=935.2(3) pm, b=1088.7(3) pm, c=1104.8(3) pm, β=106.697(5)°, V=1.0774(5) nm3, Z=4. The coordination sphere around the calcium atom consists of eight fluorine atoms which define the vertices of an Archimedean antiprism. The two HF molecules directly coordinate the calcium atom and their fluorine atoms are placed in the corners of different square faces of the Archimedean antiprism. The Ca-F(HF) distances are shorter than the Ca-F(Sb) distances. The Sb(1)F6 and Sb(2)F6 groups have four equatorial bridging fluorine atoms, while the Sb(3)F6 groups have only two bridging trans F ligands. The Ca atoms in the [−1,0,1] plane are connected by equatorial F ligands of Sb(1)F6 and Sb(2)F6 units, forming a [Ca(SbF6)+]n layer. These layers are connected by trans bridging Sb(3)F6 groups. HF molecules occupy the space between these layers and additionally contribute to the connection between the layers by hydrogen bonding. 相似文献
19.
O. Nilsson 《Journal of separation science》1979,2(12):720-722
Kaiser's “abt” concept rests on the experimental establishment of a linear relation between band width at half height, b0.5, and capacity ratio, k, according to His column specification quantity, hreal, is dependent on the square of the slope a, obtained from a linear regression analysis based on this relation. It is shown in the present paper that an improvement of the experimental conditions leading to a lower extra-column contribution to band broadening, b, introduces a tendency towards a negative curvature in the plot at low k values. The mean slope increases, and an uncritical linear regression would yield an hreal-value which is higher than before and which would be in the opposite direction to the requirements of a reliable column specification. Generally the linear regression analysis has to be moved to higher k regions in cases of curvature, especially as it is also shown that hreal is an estimation of the traditional HETP value, H∞, that would be obtained when k approaches infinity. This theoretically expected relation is a strong motivation for the use of hreal as a column specification, since the b0.5-value associated with H∞ is expected to be practically independent of b. 相似文献
20.
A starter culture ofTrichoderma reesei (Rut-C30) prepared in a liquid fluidized bed reactor (LFBR) gave better growth and greater cellulase production in submerged
fermentation than a conventional shake flask inoculum. The LFBR starter was prepared by first coatingT. reesei spores to 0.25 mm size corncob (1.0x108g-1) in a medium containing 1.0% corncob, 0.5 gL-1 xylose and 0.1 gL-1 lactose in a balanced salt solution, then fluidizing the particles in the LFBR for 36 h to allow germination of the spores,
and covering the particles with an approx 30 μm thick biofilm. This biofilm that developed in constant adherence to the lignocellulosic
carrier, apparently became well adapted to grow rapidly on insoluble cellulose substrates (Solca Floc), and had the enzymes
of the cellulase complex induced for increased cellulase production.
The LFBR starter used in a stirred tank reactor (STR) gave 15 gL-1 biomass production and 6.5 IU mL-1 overall cellulase activity with a volumetric productivity of 64 IU L-1h-1 in a 5 d fermentation, compared with a 7 d shake flask inoculum that gave 11 gL-1 biomass and 3.2 IU mL-1 cellulase activity, with a volumetric productivity of 31IU L-1h-1. The LFBR starter culture retained its viability in dry storage for 6–9 mo. 相似文献