全文获取类型
收费全文 | 1413篇 |
免费 | 66篇 |
国内免费 | 7篇 |
专业分类
化学 | 898篇 |
晶体学 | 6篇 |
力学 | 60篇 |
数学 | 317篇 |
物理学 | 205篇 |
出版年
2023年 | 12篇 |
2022年 | 41篇 |
2021年 | 44篇 |
2020年 | 52篇 |
2019年 | 21篇 |
2018年 | 30篇 |
2017年 | 22篇 |
2016年 | 68篇 |
2015年 | 60篇 |
2014年 | 78篇 |
2013年 | 83篇 |
2012年 | 95篇 |
2011年 | 118篇 |
2010年 | 81篇 |
2009年 | 63篇 |
2008年 | 94篇 |
2007年 | 87篇 |
2006年 | 61篇 |
2005年 | 58篇 |
2004年 | 52篇 |
2003年 | 39篇 |
2002年 | 33篇 |
2001年 | 19篇 |
2000年 | 11篇 |
1999年 | 12篇 |
1998年 | 9篇 |
1997年 | 14篇 |
1996年 | 15篇 |
1995年 | 7篇 |
1994年 | 7篇 |
1993年 | 8篇 |
1992年 | 5篇 |
1991年 | 9篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 10篇 |
1987年 | 6篇 |
1986年 | 7篇 |
1985年 | 11篇 |
1984年 | 7篇 |
1983年 | 8篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1972年 | 1篇 |
1964年 | 1篇 |
1916年 | 1篇 |
1914年 | 1篇 |
1899年 | 1篇 |
排序方式: 共有1486条查询结果,搜索用时 15 毫秒
51.
52.
53.
Organic‐acid mediated bulk polymerization of ε‐caprolactam and its copolymerization with ε‐caprolactone 下载免费PDF全文
Ana Sanchez‐Sanchez Andere Basterretxea Daniele Mantione Agustin Etxeberria Cristina Elizetxea Amaia de la Calle Sonia García‐Arrieta Haritz Sardon David Mecerreyes 《Journal of polymer science. Part A, Polymer chemistry》2016,54(15):2394-2402
Polyamides (PA) constitute one of the most important classes of polymeric materials and have gained strong position in different areas, such as textiles, fibers, and construction materials. Whereas most PA are synthesized by step‐growth polycondensation, PA 6 is synthesized by ring opening polymerization (ROP) of ε‐caprolactam (ε‐CLa). The most popular ROP methods involve the use of alkaline metal catalyst difficult to handle at large scale. In this article, we propose the use of organic acids for the ROP of ε‐CLa in bulk at 180 °C (below the polymer's melting point). Among evaluated organic acids, sulfonic acids were found to be the most effective for the polymerization of ε‐CLa , being the Brønsted acid ionic liquid: 1‐(4‐sulfobutyl)?3‐methylimidazolium hydrogen sulfate the most suitable due to its higher thermal stability. End‐group analysis by 1H nuclear magnetic resonance and model reactions provided mechanistic insights and suggested that the catalytic activity of sulfonic acids was a function of not only the acid strength, but of the nucleophilic character of conjugate base as well. Finally, the ability of sulfonic acid to promote the copolymerization of ε‐CLa and ε‐caprolactone is demonstrated. As a result, poly(ε‐caprolactam‐co‐ε‐caprolactone) copolymers with considerably randomness are obtained. This benign route allows the synthesis of poly(ester amide)s with different thermal and mechanical properties. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2394–2402 相似文献
54.
55.
56.
57.
Roger Fosdick Pilade Foti Aguinaldo Fraddosio Mario Daniele Piccioni 《Continuum Mechanics and Thermodynamics》2010,22(2):77-97
We determine lower bound estimates for the critical load for hyperelastic solids under monotonic dead load processes. By considering
the Hadamard criterion of infinitesimal stability, we first determine a lower bound for the Hadamard stability functional;
then, we develop a procedure for optimal lower bound estimates for the critical load. As examples, we apply our procedure
to generalized Blatz-Ko solids under simple extension, simple compression and rectilinear shear, and compare our results with
other proposals contained in the literature. 相似文献
58.
A methodology for the determination of bismuth, based on under-potential deposition-stripping voltammetry (UPD-SV), was investigated. It makes use of mesoporous platinum microelectrodes (Pt-MEs) prepared by a liquid crystal templating technique. The mesoporous microelectrodes, which are characterised by a very high surface area, allowed the accumulation of relatively large amounts of bismuth at under-potential without saturation of the electrode surface. Calibration plots for quantification of bismuth at micromolar levels were constructed by using the charge involved in either the anodic or cathodic peak recoded by cyclic voltammetry that ensued the accumulation of bismuth at the electrode surface. During the anodic scan, the oxidation of metallic bismuth occurred; the cathodic scan involved irreversibly adsorbed bismuth species, which are retained on to the electrode surface. The reproducibility of the proposed UPD-SV procedure (which was within 5 %) was assured by the application to the Pt-MEs of a suitable potential waveform, properly designed to avoid memory effect due to the irreversibly deposited bismuth. The latter phenomenon along with UPD allowed to overcome interference due to copper, which is normally observed when quantification of bismuth is performed by anodic stripping voltammetry at solid electrodes involving bulk metal deposits. The usefulness of the proposed method for the determination of bismuth in real samples was demonstrated by the analysis of a tablet of a pharmaceutical preparation, which is used for curing ulcers. 相似文献
59.
Abstract We have studied the heat capacity of the thermotropic liquid crystal, octylcyanobiphenyl (8CB), confined to the nearly cylindrical, 0·2 μm diameter pores of Anopore membranes. Orientation of the nematic director within the pores can be controlled with surface treatment. It is known from NMR measurements that the nematic director is aligned parallel to the pore axis in the untreated membrane. A perpendicular alignment is obtained when the pore surface is treated with lecithin. The second order smectic A to nematic (SA–N) and the weakly first order nematic to isotropic (N–I) phase transitions of 8CB were studied in these pores, for both director orientations, using an AC calorimetry technique. Effects on heat capacity amplitudes, transition temperature shifts, rounding and broadening of these phase transitions will be presented and contrasted with bulk measurements. 相似文献
60.
Sergio Mauricio Bonesi Daniele Dondi Stefano Protti Maurizio Fagnoni Angelo Albini 《Tetrahedron letters》2014
Irradiation of triphenylamine (Ph3N) in nitrogen-flushed solution leads to 9-phenylcarbazole and two tetrahydroderivatives (1,2,3,4- and 1,2,7,8-) via disproportionation of the corresponding 4a,4b-dihydrocarbazole. In oxygen-equilibrated solution oxidative cyclization occurs through the intermediacy of a triplet peroxy diradical, which either abstracts a hydrogen atom intramolecularly or (mainly) cleaves back to the reagents. The role of the key intermediates is supported by DFT calculations and by trapping by triarylphosphines (that are thus efficiently oxidized, while preventing the cyclization of Ph3N). The hydroperoxide, on the other hand, causes inefficient co-oxidation of sulfides. 相似文献