全文获取类型
收费全文 | 165608篇 |
免费 | 3580篇 |
国内免费 | 2938篇 |
专业分类
化学 | 92556篇 |
晶体学 | 2341篇 |
力学 | 7260篇 |
综合类 | 240篇 |
数学 | 16658篇 |
物理学 | 53071篇 |
出版年
2021年 | 1459篇 |
2020年 | 1642篇 |
2019年 | 1717篇 |
2018年 | 1974篇 |
2017年 | 1985篇 |
2016年 | 3069篇 |
2015年 | 2271篇 |
2014年 | 3254篇 |
2013年 | 7381篇 |
2012年 | 6084篇 |
2011年 | 7492篇 |
2010年 | 5303篇 |
2009年 | 5240篇 |
2008年 | 6716篇 |
2007年 | 6711篇 |
2006年 | 6188篇 |
2005年 | 5675篇 |
2004年 | 4942篇 |
2003年 | 4301篇 |
2002年 | 4379篇 |
2001年 | 4770篇 |
2000年 | 3644篇 |
1999年 | 2798篇 |
1998年 | 2391篇 |
1997年 | 2292篇 |
1996年 | 2103篇 |
1995年 | 1985篇 |
1994年 | 1972篇 |
1993年 | 1775篇 |
1992年 | 2036篇 |
1991年 | 2163篇 |
1990年 | 1946篇 |
1989年 | 1940篇 |
1988年 | 1874篇 |
1987年 | 1780篇 |
1986年 | 1705篇 |
1985年 | 2210篇 |
1984年 | 2331篇 |
1983年 | 1906篇 |
1982年 | 2087篇 |
1981年 | 1967篇 |
1980年 | 1891篇 |
1979年 | 2035篇 |
1978年 | 2202篇 |
1977年 | 2069篇 |
1976年 | 2115篇 |
1975年 | 2022篇 |
1974年 | 2074篇 |
1973年 | 2062篇 |
1972年 | 1355篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
In this review paper, the NBS scale and its limitations are briefly discussed. The magnitude of liquid junction potentials and some calculated values are presented. The use of a molality scale for hydrogen electrode concentration cells at high temperatures is described, and results from measurements on ionization equilibria are summarized. Use of this scale is also recommended for certain circumstances with cells without liquid junction. As an alternative activity scale, use of the Pitzer ion-interaction treatment for ions is recommended for special cases. Finally, reference data are presented for ±HCl in HCl(aq) to 350°C and (HCl+NaCl)(aq) to 200°C that were derived by use of the Pitzer ion-interaction treatment.Presented at the Second International Symposium on Chemistry in High Temperature Water, Provo, UT, August 1991. 相似文献
992.
L. H. Tagle F. R. Diaz C. Margozzini 《Journal of Thermal Analysis and Calorimetry》1990,36(7-8):2521-2529
The thermal stability and kinetics parameters of polycarbonates and polythiocarbonates derived from diphenols with chlorinated aromatic side-rings were studied. The polycarbonates exhibited a higher thermal stability than the polythiocarbonates, except for polythiocarbonate Ib, which displayed similar behaviour to that of the analogous polycarbonate. The kinetic parameters of the thermal decomposition were determined by using the Arrhenius relationship and a computer program. In the considered temperature range, all the polymers degraded in a single stage with first-order kinetics.
The authors acknowledge financial support from the Dirección de Investigación of the Pontificia Universidad Católica de Chile. 相似文献
Zusammenfassung Es wurde die thermische Stabilität und die kinetischen Parameter von aus Diphenolen mit chlorierten aromatischen Nebenringen abgeleiteten Polycarbonate und Polythiocarbonate untersucht. Polycarbonate zeigen eine höhere thermische Stabilität als Polythiocarbonate. Eine Ausnahme bildet das Polythiocarbonat Ib, das in seinem Verhalten den Polycarbonaten gleicht. Mittels der Arrheniusschen Gleichung und einem Rechnerprogramm wurden die kinetischen Parameter der thermischen Zersetzung ermittelt. Im untersuchten Temperaturbereich zersetzen sich alle Polymere in einer einstufigen Reaktion erster Ordnung.
The authors acknowledge financial support from the Dirección de Investigación of the Pontificia Universidad Católica de Chile. 相似文献
993.
F. Catalina C. Peinado E. L. Madruga R. Sastre J. L. Mateo N. S. Allen 《Journal of polymer science. Part A, Polymer chemistry》1990,28(5):967-972
A novel monomer, 2-acryloyl thioxanthone (TXA), was prepared by reaction of 2-hydroxy thioxanthone with acryloyl chloride. Copolymerization of TXA with methyl methacrylate (MMA) in DMF at 80°C was studied in order to evaluate relative reactivities of these monomers. Values of 1.36 and 0.5 were found for the respective reactivity ratios of MMA and TXA, respectively. The resonance stabilization and polar properties were determined and discussed in terms of spectroscopic data. 相似文献
994.
995.
996.
F. Benedetti S. Bozzini M. Forchiassin G. Nardin G. Pitacco C. Russo E. Valentin 《Journal of heterocyclic chemistry》1989,26(2):301-305
The heterocyclization reaction of arylsulfonylhydrazones from alkyl substituted 1,2-cyclohexanediones is sensitive to the steric requirements of the alkyl groups. A mechanism for the cyclization in acidic medium is also reported. 相似文献
997.
998.
999.
Haisch C Niessner R Matveev OI Panne U Omenetto N 《Analytical and bioanalytical chemistry》1996,356(1):21-26
An experimental set-up for the detection of elemental chlorine in chlorinated hydrocarbons (CHCs) is described based on a miniaturized system, which could be used for on-line monitoring of chlorinated compounds. With an optimized time-resolved detection chlorine from CHCs like CCl4 can be determined by Laser-Induced-Breakdown-Spectroscopy (LIBS) with g/g-detection limits in the gas phase. The application of a miniaturized Nd : YAG laser resulted only in a minor loss in performance, hence it could be used for designing a rugged and small on-line sensor. In addition, preliminary results for the detection of chlorine via the formation of CuCl in the plasma formed by focussing the laser on a copper surface are reported. Utilizing the luminescence of the CuCl D-system at 440 nm, a tenfold improvement in the detection limits was obtained. It appears that the formation of ad hoc selected, small molecules in a laser plasma could be a promising alternative for the selective and sensitive analysis of gaseous chlorinated and other species. 相似文献
1000.