全文获取类型
收费全文 | 331470篇 |
免费 | 3102篇 |
国内免费 | 941篇 |
专业分类
化学 | 165922篇 |
晶体学 | 5382篇 |
力学 | 15552篇 |
综合类 | 7篇 |
数学 | 38645篇 |
物理学 | 110005篇 |
出版年
2021年 | 3178篇 |
2020年 | 3370篇 |
2019年 | 3790篇 |
2018年 | 5219篇 |
2017年 | 5456篇 |
2016年 | 7420篇 |
2015年 | 4179篇 |
2014年 | 7070篇 |
2013年 | 15972篇 |
2012年 | 12462篇 |
2011年 | 14934篇 |
2010年 | 11074篇 |
2009年 | 10960篇 |
2008年 | 13318篇 |
2007年 | 13269篇 |
2006年 | 12210篇 |
2005年 | 10619篇 |
2004年 | 9905篇 |
2003年 | 8737篇 |
2002年 | 8733篇 |
2001年 | 10423篇 |
2000年 | 7687篇 |
1999年 | 5982篇 |
1998年 | 4991篇 |
1997年 | 4829篇 |
1996年 | 4504篇 |
1995年 | 3884篇 |
1994年 | 3839篇 |
1993年 | 3724篇 |
1992年 | 4109篇 |
1991年 | 4311篇 |
1990年 | 4102篇 |
1989年 | 4016篇 |
1988年 | 3784篇 |
1987年 | 3923篇 |
1986年 | 3686篇 |
1985年 | 4635篇 |
1984年 | 4687篇 |
1983年 | 3887篇 |
1982年 | 3980篇 |
1981年 | 3713篇 |
1980年 | 3658篇 |
1979年 | 3923篇 |
1978年 | 3904篇 |
1977年 | 3911篇 |
1976年 | 3892篇 |
1975年 | 3684篇 |
1974年 | 3620篇 |
1973年 | 3653篇 |
1972年 | 2606篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
771.
Nanosize aluminum substituted nickel zinc ferrites were prepared through aerosol route and characterized using TEM, XRD, magnetic measurements and Mössbauer spectroscopy. The particle size of as obtained samples was found to be ∼10 nm which increases up to ∼85 nm upon annealing at 1200 °C. The unit cell parameter ‘a’ decreases linearly with concentration of aluminum due to the small ionic radius of aluminum. The saturation magnetization for all the samples after annealing at 1200 °C lies in the range 12.9–72.6 emu/g and decreases linearly with concentration of aluminum. Room temperature Mössbauer spectra of all as obtained samples of ferrite compositions exhibited a broad doublet suggesting super paramagnetic nature. This doublet is further resolved into two doublets and assigned to the surface region and internal region atoms of the particles. The samples annealed at 1200 °C show broad sextets, which were fitted with five sextets, indicating different local environment of both tetrahedrally and octahedrally coordinated Fe cation. 相似文献
772.
773.
774.
The Ni(II) ion catalyzed thermal decomposition of peroxomonosulfate (PMS) was studied in the pH range 3.42–5.89. The rate is first order in [PMS] and Ni(II) ion concentrations. At pH greater than or equal to 5.23, the reaction becomes zero order in [PMS] and this changeover in the order of the reaction occurs at a higher concentration of nickel ions. The first‐order kinetics in PMS can be explained as a rate‐limiting step and is the transformation of nickel peroxomonosulfate into nickel peroxide. This peroxide intermediate reacts rapidly with another PMS to give oxygen and Ni(II). The formation of nickel peroxide is associated with a small negative or nearly zero entropy of activation. The zero‐order kinetics in [PMS] can be explained by the fact that the hydrolysis of aquated nickel(II) ions into hydroxocompounds is the rate‐limiting step. The turnover number is 2 at pH 3.42 and increases with pH. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 320–237, 2007 相似文献
775.
The kinetics of oxidation of Fe2+ by [Co(C3H2O4)3]3? in acidic solutions at 605 nm showed a simple first-order dependence in each reactant concentration. The second-order rate constant dependence on [H+] is in accordance with eqn (i) k2 = k′2 + k3[H+] (i) where k′2 and k3 have values of 73.4 ± 14.0 M ?1 s?1 and 353 ± 41 M?2 s?1, respectively, at 1.0 M ionic strength (NaClO4) and 25°C. At 310 nm the formation and decomposition of an intermediate, believed to be [FeC3H2O4]+, was observed. The increase in the rate of oxidation with increasing [H+] was interpreted in terms of a “one-ended” dissociation mechanism which facilitates chelation of Fe2+ by the carbonyl oxygens of malonate in the transition state. 相似文献
776.
J. Sładkowski 《International Journal of Theoretical Physics》1991,30(4):517-520
A generalization of theG-theory defined by A. Heilet al. is presented. 相似文献
777.
S. E. Bogushevich V. N. Makatun A. K. Potapovich I. I. Ugolev 《Journal of Applied Spectroscopy》1991,55(4):1016-1020
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 55, No. 4, pp. 613–618, October, 1991. 相似文献
778.
J. Sładkowski 《International Journal of Theoretical Physics》1991,30(8):1075-1078
The possibility of inflation without any genuine scalar is discussed. It is suggested that drops of primordial plasma may drive inflation. The model, although naive, is consistent with observational data. 相似文献
779.
V. A. Nikitenko S. V. Mukhin S. P. Pivneva G. R. Vlas'yants I. A. Karetnikov S. G. Stoyukhin 《Journal of Applied Spectroscopy》1991,54(6):578-581
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 6, pp. 960–964, June, 1991. 相似文献
780.
S. I. Okrut 《Journal of Mathematical Sciences》1991,53(5):526-532
We consider strongly parabolic, Hilbert submanifolds in Riemannian Hilbert manifolds. We prove that their properties are analogous to the known properties in the finite-dimensional case. The main geometric result consists of Theorem 3: a complete, Riemannian, Hilbert submanifold of nonpositive extrinsic curvature and finite codimension in a Hilbert sphere is a great sphere.Translated from Ukrainskii Geometricheskii Sbornik, No. 33, pp. 91–100, 1990.The author expresses his thanks to Professor A. A. Borisenko for posing the problem and guiding the work. 相似文献