全文获取类型
收费全文 | 759347篇 |
免费 | 6880篇 |
国内免费 | 2134篇 |
专业分类
化学 | 374791篇 |
晶体学 | 10748篇 |
力学 | 40225篇 |
综合类 | 26篇 |
数学 | 119886篇 |
物理学 | 222685篇 |
出版年
2021年 | 5848篇 |
2020年 | 6522篇 |
2019年 | 7317篇 |
2018年 | 19311篇 |
2017年 | 19207篇 |
2016年 | 19427篇 |
2015年 | 8483篇 |
2014年 | 13007篇 |
2013年 | 30421篇 |
2012年 | 26429篇 |
2011年 | 36797篇 |
2010年 | 25363篇 |
2009年 | 25517篇 |
2008年 | 31828篇 |
2007年 | 33696篇 |
2006年 | 24058篇 |
2005年 | 22395篇 |
2004年 | 21055篇 |
2003年 | 19607篇 |
2002年 | 18609篇 |
2001年 | 18985篇 |
2000年 | 14900篇 |
1999年 | 11534篇 |
1998年 | 10037篇 |
1997年 | 9942篇 |
1996年 | 9392篇 |
1995年 | 8442篇 |
1994年 | 8543篇 |
1993年 | 8134篇 |
1992年 | 8689篇 |
1991年 | 9124篇 |
1990年 | 8772篇 |
1989年 | 8534篇 |
1988年 | 8469篇 |
1987年 | 8312篇 |
1986年 | 7904篇 |
1985年 | 10222篇 |
1984年 | 10764篇 |
1983年 | 9067篇 |
1982年 | 9420篇 |
1981年 | 8947篇 |
1980年 | 8643篇 |
1979年 | 9032篇 |
1978年 | 9509篇 |
1977年 | 9354篇 |
1976年 | 9357篇 |
1975年 | 8852篇 |
1974年 | 8744篇 |
1973年 | 9068篇 |
1972年 | 6586篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
Journal d'Analyse Mathématique - 相似文献
942.
In this paper, we obtain a nonlinear Poisson structure and two first integrals in the problem of the plane motion of a circular cylinder and n point vortices in an ideal fluid. This problem is a priori not Hamiltonian; specifically, in the case n= 1 (i.e., in the problem of the interaction of a cylinder with a vortex) it is integrable. 相似文献
943.
944.
The first diastereoselective cycloaddition of a nitrile oxide with a homoallylic alcohol is discussed. The reaction of benzonitrile oxide with the magnesium alkoxides of chiral homoallylic alcohols has been shown to proceed with good diastereoselectivity, favoring the syn isomer of the resulting 2-isoxazoline. 相似文献
945.
E. L. Kristallovich A. G. Eshimbetov N. D. Chuvylkin L. I. Belen'kii Kh. M. Shakhidoyatov 《Chemistry of Natural Compounds》2003,39(5):495-500
The principal types of electronic transitions in absorption spectra of deoxyvasicinone and its 6-amino- and 6-nitro-derivatives were determined by analyzing the electron-density distributions in excited states calculated using ZINDO/S. 相似文献
946.
Marcelino Maneiro Manuel R. Bermejo M. Isabel Fernndez Ana M. Gonzlez‐Noya Alexei M. Tyryshkin Robin G. Pritchard 《无机化学与普通化学杂志》2003,629(2):285-290
A new MnIII‐Schiff base complex, [MnL(OH2)](ClO4) ( 1 ) (H2L = N, N′‐bis‐(3‐Br‐5‐Cl‐salicylidene)‐1, 2‐diimino‐2‐methylethane), an inorganic model of the catalytic center (OEC, Oxygen Evolving Complex) in photosystem II (PSII), has been synthesized and characterized by elemental analysis, IR and EPR spectroscopy, mass spectrometry, magnetic susceptibility measurement and the study of its redox properties by cyclic and normal pulse voltammetry. This complex mimics reactivity (showing a relevant photolytic activity), and also some structural characteristics (parallel‐mode MnIII EPR signal from partially assembled OEC cluster) of the natural OEC. The complex 1 was found to rearrange in solution into a crystallographically solved square‐pyramidal complex, [MnLL′] ( 2 ) (HL′ = 6‐bromo‐4‐chloro‐2‐cyanophenol), through a process, which probably liberates radical species (detected by EPR), and provokes a C—N bond cleavage in the ligand. A photo‐radical mechanism is discussed to explain this rearrangement. 相似文献
947.
Non-isothermal short-range-order kinetics of binary alloys as influenced by solute-vacancy complexes
A model describing the roles of bound and unbound vacancies is proposed in order to predict defect decay and short-range-order
kinetics of quenched binary alloys during linear heating experiments. This is an alternative treatment of a previous approach.
The model has been applied to the differential scanning calorimetry (DSC) curves of Cu-5 at.% Zn quenched from different temperatures.
An expression to calculate the activation energy for migration of solute-vacancy complexes was also developed which make use
of DSC trace data. A value of 89.12±0.32 kJ mol-1 was obtained for the above alloy. The relative contribution of bound and unbound vacancies to partition of effective activation
energy corresponding to the ordering process as influenced by quenching temperature was also assessed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
948.
Chris Hope 《The Journal of the Operational Research Society》2003,54(11):1167-1176
What strategy should a football (soccer, in American parlance) club adopt when deciding whether to sack its manager? This paper introduces a simple model assuming that a club's objective is to maximize the number of league points that it scores per season. The club's strategy consists of three choices: the length of the honeymoon period during which it will not consider sacking a new manager, the level of the performance trapdoor below which the manager get the sack, and the weight that it will give to more recent games compared to earlier ones. Some data from the last six seasons of the English Premiership are used to calibrate the model. At this early stage of the research, the best strategy appears to have only a short honeymoon period of eight games (much less than the actual shortest period of 12 games), to set the trapdoor at 0.74 points per game, and to put 47% of the weight on the last five games. A club adopting this strategy would obtain on average 56.8 points per season, compared to a Premiership average of 51.8 points. 相似文献
949.
Various antimonate compounds are well known as important inorganic ion exchangers, since they resist radiation and chemical degradation and also exhibit selectivities towards different cations. Ceric, silicon, titanium and ferric antimonates were prepared as inorganic ion exchangers. Characterization of these materials has been described using different techniques, including thermal analysis, surface area measurements, X-ray diffraction and IR-spectroscopy. In batch distribution experiments the influence of HNO3 molarity and Mo concentration for Mo sorption on different matrices is described in terms of their retention capacities and distribution coefficients.The selectivities of these exchangers towards molybdenum are in the order: CeSb > SiSb > FeSb > TiSb. 相似文献
950.
Results of two urgent and practically important directions of research on the indirect oxidation of organic compounds by highly reactive intermediates generated electrochemically from oxygen (HO2
–, HO2
·, HO·) are considered and orderly arranged. The studies in question are the indirect synthesis and mineralization of organic toxicants in waste water. 相似文献