全文获取类型
收费全文 | 262362篇 |
免费 | 11589篇 |
国内免费 | 1997篇 |
专业分类
化学 | 158291篇 |
晶体学 | 3825篇 |
力学 | 10175篇 |
综合类 | 5篇 |
数学 | 28032篇 |
物理学 | 75620篇 |
出版年
2021年 | 2121篇 |
2020年 | 3413篇 |
2019年 | 4921篇 |
2018年 | 4227篇 |
2017年 | 3739篇 |
2016年 | 7839篇 |
2015年 | 6304篇 |
2014年 | 7534篇 |
2013年 | 14529篇 |
2012年 | 11767篇 |
2011年 | 12729篇 |
2010年 | 9766篇 |
2009年 | 9395篇 |
2008年 | 11787篇 |
2007年 | 11368篇 |
2006年 | 10525篇 |
2005年 | 9727篇 |
2004年 | 8810篇 |
2003年 | 7641篇 |
2002年 | 8116篇 |
2001年 | 8230篇 |
2000年 | 6587篇 |
1999年 | 4475篇 |
1998年 | 3319篇 |
1997年 | 3261篇 |
1996年 | 3102篇 |
1995年 | 2812篇 |
1994年 | 2656篇 |
1993年 | 2580篇 |
1992年 | 2911篇 |
1991年 | 2825篇 |
1990年 | 2729篇 |
1989年 | 2510篇 |
1988年 | 2551篇 |
1987年 | 2560篇 |
1986年 | 2384篇 |
1985年 | 3119篇 |
1984年 | 3345篇 |
1983年 | 2738篇 |
1982年 | 2894篇 |
1981年 | 2857篇 |
1980年 | 2703篇 |
1979年 | 2805篇 |
1978年 | 2893篇 |
1977年 | 2887篇 |
1976年 | 2955篇 |
1975年 | 2735篇 |
1974年 | 2695篇 |
1973年 | 2853篇 |
1972年 | 1801篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
981.
Juan F García-Reyes Pilar Ortega-Barrales Antonio Molina-Díaz 《Analytical sciences》2007,23(4):423-428
A combined approach based on solid-phase optosensing and multicommutation principles has been applied to develop a method for the simultaneous analysis of two pharmaceuticals (naproxen and salicylic acid) in biological fluids. The multicommuted flow-through optosensor was based on direct native fluorescence measurements of both analgesics using a non-polar sorbent (C18 silica gel) as a solid sensing zone. The flow system was controlled by Java-written home-made software and designed using three-way solenoid valves for an independent automated manipulation of sample and carrier solutions. Using an optimized sampling time, the method was calibrated in the range of 1 - 25 and 5 - 200 ng mL(-1). The obtained detection limits were 0.3 and 1.3 ng mL(-1) for naproxen and salicylic acid, respectively, with RSD (%) values of better than 2% for both analytes. The proposed methodology was successfully applied to urine, serum and pharmaceutical preparations. Recovery percentages ranging from 96.1 to 104% were obtained for both analytes. 相似文献
982.
O. D. Greenwood S. Tasker J. P. S. Badyal 《Journal of polymer science. Part A, Polymer chemistry》1994,32(13):2479-2486
Dielectric barrier air discharge treatment of polyethylene, polypropylene, polyisobutylene, polystyrene, and polyisoprene substrates has been characterized by x-ray photoelectron spectroscopy (XPS). The relative reactivities of these polymers towards silent discharge oxidation are rationalized in terms of ozone molecules interacting with an excited surface. © 1994 John Wiley & Sons, Inc. 相似文献
983.
984.
Rajnikant D. Watkin G. Tranter 《Acta Crystallographica. Section C, Structural Chemistry》1995,51(10):2071-2073
985.
986.
M. D. Roberts 《Czechoslovak Journal of Physics》1992,42(2):151-158
It is shown that: i) the Weyl tensor can be expressed in terms of the sum of a tensor and its double dual, where the tensor is constructed from the covariant derivatives of the Lanczos tensor, ii) a similar expression does not exist for the Riemann tensor in electromagnetic theory, iii) the electromagnetic field cannot be identified with the differential gauge freedom of the Lanczos tensor, iv) the symmetries of Einstein Maxwell theory and the Lanczos tensor do not prohibit the identification of the electromagnetic field with the algebraic gauge freedom of the Lanczos tensor, these symmetries require a differential equation relating the electromagnetic field tensor to the algebraic gauge vector and this is given. 相似文献
987.
988.
A. S. Peregudov L. N. Usatova E. I. Smyslova E. I. Fedin D. N. Kravtsov 《Russian Chemical Bulletin》1995,44(8):1513-1519
It has been shown by the19F NMR method that the relative polarities of nitrogenelement bonds in 2-(4-fluorophenyl)benzimidazole and its PhHg and PPh3Au derivatives increase in the order N-H19F NMR. It has been found that these reactions occur by a bimolecular associative mechanism and that the N-H bond is substantially less reactive than the N-Hg and N-Au bonds, which have identical reactivities within the limits of sensitivity of the method used.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1574–1580, August, 1995.This work was carried out with financial support from the Russian Foundation for Basic Research (Project No. 93-03-5528). 相似文献
989.
990.
The analysis in this paper looks at two important elements in modelling the market for timber in the United States. First, the issue of directional causality between price and quantity and its implications in a modelling effort is investigated. Second, the extent of the geographic market for timber is discussed and a method of detecting it is suggested. The method for detecting the extent of the geographical market is tractable and can be applied in a straightforward way. Both considerations are applied to the softwood lumber market in the United States. 相似文献