全文获取类型
收费全文 | 289849篇 |
免费 | 26157篇 |
国内免费 | 17860篇 |
专业分类
化学 | 166001篇 |
晶体学 | 4245篇 |
力学 | 13337篇 |
综合类 | 23篇 |
数学 | 35984篇 |
物理学 | 114276篇 |
出版年
2022年 | 2215篇 |
2021年 | 2695篇 |
2020年 | 3075篇 |
2019年 | 3733篇 |
2018年 | 3993篇 |
2017年 | 4708篇 |
2016年 | 6642篇 |
2015年 | 5379篇 |
2014年 | 6706篇 |
2013年 | 14408篇 |
2012年 | 13057篇 |
2011年 | 16211篇 |
2010年 | 15368篇 |
2009年 | 15327篇 |
2008年 | 12937篇 |
2007年 | 12128篇 |
2006年 | 11557篇 |
2005年 | 10975篇 |
2004年 | 11087篇 |
2003年 | 9528篇 |
2002年 | 9084篇 |
2001年 | 8914篇 |
2000年 | 6766篇 |
1999年 | 5922篇 |
1998年 | 4964篇 |
1997年 | 4706篇 |
1996年 | 5075篇 |
1995年 | 5100篇 |
1994年 | 5135篇 |
1993年 | 5116篇 |
1992年 | 4912篇 |
1991年 | 4507篇 |
1990年 | 4074篇 |
1989年 | 4102篇 |
1988年 | 4063篇 |
1987年 | 3389篇 |
1986年 | 3302篇 |
1985年 | 3782篇 |
1984年 | 3901篇 |
1983年 | 2970篇 |
1982年 | 3627篇 |
1981年 | 3339篇 |
1980年 | 3283篇 |
1979年 | 3186篇 |
1978年 | 3212篇 |
1977年 | 3184篇 |
1976年 | 3573篇 |
1975年 | 2749篇 |
1974年 | 2738篇 |
1973年 | 3114篇 |
排序方式: 共有10000条查询结果,搜索用时 20 毫秒
91.
Ingrid Lukkari Jaromir Ruzicka Gary D. Christian 《Fresenius' Journal of Analytical Chemistry》1993,346(6-9):813-818
Summary Automated methods for the determination of ammonium and ammonia are reviewed, and techniques based on gas diffusion using a semi-permeable membrane were selected for the determination of both total ammonium-nitrogen and free ammonia in fermentation samples. A simple and robust instrument based on sequential injection analysis (SIA) consisting of a piston pump and two selector valves was used. Two different methods of ammonia detection, the Berthelot method and detection using pH-indicators, have been evaluated and compared. The indicator method showed higher reproducibility and the range of determination could easily be adjusted to match the concentrations of the samples. The range of determination could be adjusted from 0.05 mmol/l to 350 mmol/l, depending on choice of acceptor solution. This method has been evaluated with fermentation medium samples and tested on-line in a yeast fermentation process.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday 相似文献
92.
We study a generalization of the notion of the chromatic number of a graph in which the colors assigned to adjacent vertices are required to be, in a certain sense, far apart. © 1993 John Wiley & Sons, Inc. 相似文献
93.
94.
We show how methods for estimating the concentration function of the sum of independent random variables can be used to obtain estimates of the concentration function for the values of additive functions under suitable conditions. Previously obtained estimates of the concentration function are consequences of the estimate obtained in the present paper for functions from of the class under consideration. 相似文献
95.
The Mathematical Intelligencer encourages comments about the material in this issue. Letters to the editor should be sent
to either of the editors-in-chief, Chandler Davis or Marjorie Senechal. 相似文献
96.
Q. Gong R. N tzel P.J. van Veldhoven T.J. Eijkemans J.H. Wolter 《Journal of Crystal Growth》2005,280(3-4):413-418
We report on the shape transition from InAs quantum dashes to quantum dots (QDs) on lattice-matched GaInAsP on InP(3 1 1)A substrates. InAs quantum dashes develop during chemical-beam epitaxy of 3.2 monolayers InAs, which transform into round InAs QDs by introducing a growth interruption without arsenic flux after InAs deposition. The shape transition is solely attributed to surface properties, i.e., increase of the surface energy and symmetry under arsenic deficient conditions. The round QD shape is maintained during subsequent GaInAsP overgrowth because the reversed shape transition from dot to dash is kinetically hindered by the decreased ad-atom diffusion under arsenic flux. 相似文献
97.
The microstructure evolution of decagonal quasicrystals in Al72Ni12Co16 alloy was investigated by the electromagnetic melting and cyclic superheating method. Single-phase decagonal quasicrystals have been obtained when the undercoolings were larger than 60 K. The decagonal quasicrystals formed at various undercoolings show different microstructural morphologies. Furthermore, grain refinement was found near the undercooling of 120 K. Based on current thermodynamic and dendrite growth theories, a dimensionless superheating parameter was adopted to explain the effect of processing conditions on the microstructure of Al72Ni12Co16 alloy. The result indicate that the fine equiaxied microstructure of decagonal quasicrystal (D-phase) formed near on undercooling of 120 K originates from the break-up of dendrites. 相似文献
98.
99.
The effect of hydrostatic pressure on the structure of a plastic columnar discotic triphenylene has been investigated. The goal was to determine whether pressure can be used to modify electronic properties via changes in structural properties of columnar discotics to any significant extent. The findings are that (i) the intra- and inter-columnar distances are reduced in a nearly isotropic fashion, (ii) that the crystal sizes are reduced and (iii) that a transition takes place from a more highly ordered plastic columnar to a less ordered hexagonal columnar state with increasing pressure. The induced decrease of the molecular distances, amounting to 6% for pressures up to 17 kbar, are clearly too small to induce an appreciable modification of the electronic structure and thus opto-electronic properties. 相似文献
100.