全文获取类型
收费全文 | 750862篇 |
免费 | 7171篇 |
国内免费 | 2846篇 |
专业分类
化学 | 384683篇 |
晶体学 | 10793篇 |
力学 | 37604篇 |
综合类 | 87篇 |
数学 | 101062篇 |
物理学 | 226650篇 |
出版年
2021年 | 6582篇 |
2020年 | 7186篇 |
2019年 | 8024篇 |
2018年 | 10708篇 |
2017年 | 10812篇 |
2016年 | 15260篇 |
2015年 | 8646篇 |
2014年 | 14135篇 |
2013年 | 33074篇 |
2012年 | 25919篇 |
2011年 | 31079篇 |
2010年 | 23037篇 |
2009年 | 22851篇 |
2008年 | 29307篇 |
2007年 | 29063篇 |
2006年 | 26675篇 |
2005年 | 23918篇 |
2004年 | 22090篇 |
2003年 | 19739篇 |
2002年 | 19560篇 |
2001年 | 20966篇 |
2000年 | 16177篇 |
1999年 | 12500篇 |
1998年 | 10693篇 |
1997年 | 10586篇 |
1996年 | 10033篇 |
1995年 | 8964篇 |
1994年 | 9101篇 |
1993年 | 8754篇 |
1992年 | 9456篇 |
1991年 | 9768篇 |
1990年 | 9360篇 |
1989年 | 9248篇 |
1988年 | 8986篇 |
1987年 | 8646篇 |
1986年 | 8430篇 |
1985年 | 10949篇 |
1984年 | 11375篇 |
1983年 | 9499篇 |
1982年 | 9880篇 |
1981年 | 9338篇 |
1980年 | 8839篇 |
1979年 | 9502篇 |
1978年 | 9885篇 |
1977年 | 9839篇 |
1976年 | 9845篇 |
1975年 | 9317篇 |
1974年 | 9221篇 |
1973年 | 9586篇 |
1972年 | 7059篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Motivated by recent experimental findings, we investigate the possible occurrence and characteristics of quasicrystalline order in two-dimensional mixtures of point dipoles with two sorts of dipole moments. Despite the fact that the dipolar interaction potential does not exhibit an intrinsic length scale and cannot be tuned a priori to support the formation of quasicrystalline order, we find that configurations with long-range quasicrystallinity yield minima in the potential energy surface of the many particle system. These configurations emanate from an ideal or perturbed ideal decoration of a binary tiling by steepest descent relaxation. Ground state energy calculations of alternative ordered states and parallel tempering Monte-Carlo simulations reveal that the quasicrystalline configurations do not correspond to a thermodynamically stable state. On the other hand, steepest descent relaxations and conventional Monte-Carlo simulations suggest that they are rather robust against fluctuations. Local quasicrystalline order in the disordered equilibrium states can be strong.Received: 15 September 2004, Published online: 26 November 2004PACS:
61.44.Br Quasicrystals - 75.50.Kj Amorphous and quasicrystalline magnetic materials - 82.70.Dd Colloids 相似文献
42.
We study the similarity of perturbed compact operators to operators of block-diagonal structure with respect to some family of orthogonal projection operators, which allows us to refine and essentially strengthen results due to R. Turner. We obtain information about the operator realizing the similarity transformation, present estimates for the eigenvalues and eigenvectors of the perturbed operator, and also study the inverse problem of spectral analysis. 相似文献
43.
44.
N. N. Pustovoitov 《Analysis Mathematica》2003,29(3):201-218
V stat'e izuchayutsya klassy periodicheskikh funktsii mnogikh peremennykh s zadannoi mazhorantoi smeshannykh modulei nepreryvnosti, prichem mazhoranta imeet spetsial'nyi vid. Rassmotreny nailuchshie priblizheniya ukazannykh klassov i vozmozhnost' kharakterizatsii 'etikh klassov cherez nailuchshie priblizheniya. 相似文献
45.
Fabrina R S Bentlin Fábio A Duarte Valderi L Dressler Dirce Pozebon 《Analytical sciences》2007,23(9):1097-1101
This work deals with As determination in marine sediment using ultrasound for sample preparation. It is shown that As can be quantitatively extracted from marine sediment using 20% (v/v) HCl and sonication. The slurry is centrifuged and the analyte is determined in the supernatant by hydride generation atomic absorption spectrometry (HG AAS). A flow injection (FI) system is employed for hydride generation, with 0.5% (m/v) NaBH(4) used as reducdant and a 20% (v/v) HCl used as sample carrier. The limit of quantification is 1.6 microg g(-1) of As, which is based on 800 microl of sample solution and 0.200 g of sample mass in a volume of 50 mL. Certified and non certified marine sediment samples were analyzed; the results were in accordance with the certified or reference values. Speciation analysis by HPLC-ICP-MS showed that As(V) is the only detectable As species present in the supernatant of the centrifuged sample. 相似文献
46.
47.
A. Khalafi-Nezhad A. Parhami A. Zare A. R. Moosavi Zare 《Journal of the Iranian Chemical Society》2008,5(3):413-419
A simple, clean and efficient solvent-free procedure for the preparation of aryl carboxylates is described from the direct reaction of carboxylic acids and phenols, in the presence of 1-methylimidazole as base and tosyl chloride (TsCl) as coupling agent. This method can be easily applied for different substituted phenols and carboxylic acids. It can also be applied for the selective acylation when other functional group such as hydroxyl is present on phenol ring. 相似文献
48.
Ricaurte Rodríguez Manuel Nogueras Justo Cobo John N. Low Christopher Glidewell 《Acta Crystallographica. Section C, Structural Chemistry》2008,64(7):o376-o378
Molecules of the title compound, C12H13ClN4, are linked by two independent N—H...N hydrogen bonds into a chain of edge‐fused R22(8) rings. The significance of this study lies in its attempt to rationalize the patterns of supramolecular aggregation in the title compound and in a range of analogous 4,6‐disubstituted 2‐aminopyrimidines. 相似文献
49.
50.
Gujie Qian S. Baccaro M. Falconieri Jiafang Bei A. Cecilia Guorong Chen 《Journal of Non》2008,354(40-41):4626-4629
Glasses in SiO2–ZnO–BaO system with the different ZnO/BaO ratio were studied. In some cases, BaF2 was introduced to substitute for BaO on the equal base. Photoluminescent spectra showed that ZnO in glass matrices behaved somewhat differently from ZnO crystals. Especially, the introduction of fluorine ions led to dramatic shift of UV emission band of glasses closer to that of ZnO crystals. Raman spectral analysis provided consistent results. In particular, Raman bands in the high frequency region are sensitive to effects of different ZnO/BaO or BaF2/BaO ratio on structure of glasses. 相似文献