全文获取类型
收费全文 | 1088篇 |
免费 | 38篇 |
国内免费 | 7篇 |
专业分类
化学 | 795篇 |
晶体学 | 10篇 |
力学 | 13篇 |
数学 | 203篇 |
物理学 | 112篇 |
出版年
2023年 | 6篇 |
2021年 | 9篇 |
2020年 | 14篇 |
2019年 | 11篇 |
2018年 | 12篇 |
2017年 | 15篇 |
2016年 | 24篇 |
2015年 | 34篇 |
2014年 | 23篇 |
2013年 | 44篇 |
2012年 | 68篇 |
2011年 | 75篇 |
2010年 | 42篇 |
2009年 | 39篇 |
2008年 | 57篇 |
2007年 | 69篇 |
2006年 | 62篇 |
2005年 | 68篇 |
2004年 | 72篇 |
2003年 | 53篇 |
2002年 | 44篇 |
2001年 | 24篇 |
2000年 | 16篇 |
1999年 | 12篇 |
1998年 | 16篇 |
1997年 | 12篇 |
1996年 | 15篇 |
1995年 | 8篇 |
1994年 | 10篇 |
1993年 | 10篇 |
1992年 | 3篇 |
1991年 | 6篇 |
1990年 | 10篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 10篇 |
1985年 | 16篇 |
1984年 | 22篇 |
1983年 | 8篇 |
1982年 | 15篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1978年 | 4篇 |
1976年 | 9篇 |
1973年 | 3篇 |
1971年 | 2篇 |
1970年 | 3篇 |
1969年 | 6篇 |
1938年 | 2篇 |
排序方式: 共有1133条查询结果,搜索用时 15 毫秒
1.
2.
3.
Joan Porti 《Proceedings of the American Mathematical Society》2004,132(11):3423-3431
We prove the Mayberry-Murasugi formula for links in homology 3-spheres, which was proved before only for links in the 3-sphere. Our proof uses Franz-Reidemeister torsions.
4.
Robert Andreu Gerard Lligadas Joan Carles Ronda Marina Galià Virginia Cádiz 《Journal of polymer science. Part A, Polymer chemistry》2007,45(21):4965-4973
A new oxazolidine derivative was obtained from phenol, 2‐amino‐2‐methylpropane‐1,3‐diol and paraformaldehyde. The reaction of this novel oxazolidine diol with phenylisocyanate lead to a urethane model compound which can be polymerized thermally by oxazolidine ring opening to give a Mannich bridge structure. Linear segmented polyurethanes were prepared by reaction of different ratios of oxazolidine diol and commercial polyethylenglycol (Mw ~ 400) with 4,4′‐methylenbis (cyclohexylisocyanate) (HMDI, 90% isomers mixture). The polyurethanes were thermally characterized and crosslinked by oxazolidine ring opening to obtain materials which showed improved thermal stability. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4965–4973, 2007 相似文献
5.
Previous work carried out in our laboratories has focused on the formation and investigation of a dextran and concanavalin A (con A) based gel, which has the ability to alter its conformational structure in the presence and absence of free and terminal glucoses such that a gel–sol phase transition occurs. Here we report the diffusion and rheological investigations in to the effects of the addition of insulin and varyingconcentrations of magnesium chloride hexahydrate (Mg2Cl26H2O) at 20 and 37 °C. Rheological examination of glucose-sensitive (dextran-con A) gels were conducted using a cone and plate viscometer used in continual rotation and oscillatory modes. The results are interpreted in terms of the structure of the gel network and suggest rheological assessment provides an effective method of assessing the properties of gel systems. The subsequent testing of such formulations in in-vitro diffusion experiments revealed a reduction in the rate of diffusivity in the insulin marker, poly R-478 dye. The performance of this self-regulating drug delivery system has been examined and the addition of insulin and magnesium chloride may alter the way in which the gel operates as a drug delivery device and in the delivery of insulin. This may have implications for other ligands. 相似文献
6.
A critical review of known results about the permanence conditions for the null character of the solutions to the (vacuum) Maxwell equations, is presented. Concomitants of the electromagnetic field and the metric tensor are constructed, which give the principal directions of the field in covariant form. The known permanence conditions are generalized in order to includeall the (local) null fields; the above concomitants allow these conditions to be explicitly formulated in terms of the electromagnetic field.Supported in part by Conselleria de Cultura, Educació i Ciència de la Generalitat Valenciana. 相似文献
7.
Suńol J. J. Saurina J. Carrillo F. Colom X. 《Journal of Thermal Analysis and Calorimetry》2003,72(2):753-758
Comparison of Lyocell, modal and viscose fibers was performed by means of differential scanning calorimetry, thermogravimetry
and scanning electron microscopy. Thermal analysis was performed in air atmosphere. Samples were mercerized (21.3 g 100 mL-1)
or submitted to solar radiation (seven months). Solar degraded samples presents a higher thermal stability and are initially
less degraded. Furthermore, Lyocell fiber is the most stable under thermal degradation conditions. Heating produces a reduction
of the fiber diameter (about 50%).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
Various types of glycosaminoglycans (GAGs) including heparins, chondroitin sulfates, dermatan sulfate and hyaluronic acid were studied from their proton nuclear magnetic resonance (1H NMR) spectra using chemometric techniques. Despite the complexity of the 1H NMR signals, data analysis using principal component analysis enabled the different GAG classes to be distinguished and permitted their classification according to their chemical structure. The analysis of the composition of the major disaccharide unit and other relevant chemical structures in the heparin samples was performed using partial least squares regression. 相似文献
9.
Joan Albaigés Josep M. Bayona Pilar Fernandez Joan Grimalt Antoni Rosell Rafel Simó 《Mikrochimica acta》1991,104(1-6):13-27
An analytical procedure is described for a comprehensive determination of the composition of hydrocarbons in the atmosphere, based on: (a) aerosol filtration and subsequent adsorption of the vapor phase onto active charcoal and polyurethane foam; (b) GPC and HPLC fractionation of the extracts, and (c) analysis of the fractions by GC-MS under EI and NICI modes. Special emphasis is placed onn-alkanes, PAHs and their oxygenated derivatives.The characterization of samples collected in a coastal urban area (Barcelona city), and far away over the Western Mediterranean, at sea level and at 1100 m of altitude, revealed significant changes in the aerosol composition, mainly attributed to initial vapor-particle partitioning processes, influenced by ambient temperature variations, and to others taking place during long-range atmospheric transport, related with the different compound photoreactivities and with an unexplained source-decoupling phenomenon. 相似文献
10.
Paital AR Mitra T Ray D Wong WT Ribas-Ariño J Novoa JJ Ribas J Aromí G 《Chemical communications (Cambridge, England)》2005,(41):5172-5174
Based on a combined theoretical-experimental study, we propose that substituted m-phenylene ligands (m-N-Phi-N) can act as tuneable strong ferromagnetic couplers connecting Cu(II) ions; a new complex presenting that bridge with J close to +15 cm(-1) has been suggested and synthesized. 相似文献