全文获取类型
收费全文 | 15477篇 |
免费 | 1320篇 |
国内免费 | 639篇 |
专业分类
化学 | 15420篇 |
晶体学 | 322篇 |
力学 | 18篇 |
综合类 | 9篇 |
数学 | 4篇 |
物理学 | 1663篇 |
出版年
2024年 | 15篇 |
2023年 | 157篇 |
2022年 | 542篇 |
2021年 | 471篇 |
2020年 | 473篇 |
2019年 | 354篇 |
2018年 | 295篇 |
2017年 | 273篇 |
2016年 | 548篇 |
2015年 | 548篇 |
2014年 | 585篇 |
2013年 | 1138篇 |
2012年 | 714篇 |
2011年 | 660篇 |
2010年 | 746篇 |
2009年 | 745篇 |
2008年 | 768篇 |
2007年 | 785篇 |
2006年 | 760篇 |
2005年 | 705篇 |
2004年 | 758篇 |
2003年 | 668篇 |
2002年 | 1397篇 |
2001年 | 367篇 |
2000年 | 310篇 |
1999年 | 311篇 |
1998年 | 288篇 |
1997年 | 211篇 |
1996年 | 418篇 |
1995年 | 396篇 |
1994年 | 142篇 |
1993年 | 111篇 |
1992年 | 128篇 |
1991年 | 79篇 |
1990年 | 51篇 |
1989年 | 67篇 |
1988年 | 66篇 |
1987年 | 36篇 |
1986年 | 40篇 |
1985年 | 55篇 |
1984年 | 39篇 |
1983年 | 24篇 |
1982年 | 22篇 |
1981年 | 19篇 |
1980年 | 14篇 |
1979年 | 10篇 |
1978年 | 13篇 |
1975年 | 7篇 |
1971年 | 48篇 |
1970年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
102.
The structure of the complex, [Fe2(II)Fe2(III)(HCOO)10(C6H7N6)n, (1) exhibits a neutral two-dimensional layer network of alternating iron(II) and iron(III) ions, bridged equatorially by formate groups. All iron atoms are octahedrally coordinated, with iron(III) coordinating axially to one gamma-picoline and one formate group, while the iron(II) centers interact axially with two gamma-picoline groups, above and below the layer plane. The complex crystallizes in the triclinic space group P1 at all studied temperatures [at 120 K, the cell dimensions are: a = 10.228(1), b = 12.071(1), c = 12.072(1) A, alpha = 89.801(2), beta = 71.149(2), gamma = 73.371(2) degrees]. An intralayer antiferromagnetic exchange interaction of J = -2.8 cm(-1) between iron(II) and iron(III) was observed in the magnetic studies. Decreasing the temperature to close to 20 K causes a magnetic-ordering phenomenon to occur and a low-temperature phase with a long-range antiferromagnetic spin orientation appears. The magnetic phase transition was confirmed by M?ssbauer spectroscopic studies at temperatures above and below the critical temperature. Structural information of 1 from synchrotron X-ray diffraction data collected at room temperature and 16 K suggests that the antiferromagnetic ordering is caused by an enhanced pi-pi interaction between chi-picoline groups from adjacent layers. 相似文献
103.
WenXiangHU XueJunHOU QingTaoPENG 《中国化学快报》2002,13(12):1199-1202
In this paper,a new HPLC method was established to determine the earbonyl compounds in air.As the absorbent,2,4-dinitrophenylhydrazint(2,4-DNPH)reaeted with earbonyls specifieally,which form the corresponding 2,4-dinitrophenylhydrazones,then analyzed by HPLC.The chromatographic conditions,the recovery rate,stability of samples,reagent blank,sampling efficiency were all studied systematically.The results showed that this established method had high sensitivity and good selectivity compared with other analytical methods,and it can detemine ten earbonyl compounds in air in 26 min simultancously. 相似文献
104.
Ibragimov A. G. Khafizova L. O. Zagrebel"naya I. V. Parfenova L. V. Sultanov R. M. Khalilov L. M. Dzhemilev U. M. 《Russian Chemical Bulletin》2001,50(2):292-296
A new method for the synthesis of dialkyl(ethyl)alanes by the reaction of EtAlCl2 with -olefins in the presence of Mg and a catalytic amount of Cp2TiCl2 (Ti(OPri)4, Ti(OBun)4) in THF was developed. 相似文献
105.
New spirocyclic heterocycles 8, 16, 19/20, 25, 27 , and 30 derived from pyrimido[4,5‐b][1,4]diazepin]‐8′(9′H)‐one were synthesised by a tandem nitroso‐ene/Diels–Alder reaction of 4‐(alkenoylamino)‐5‐nitrosopyrimides. The crystal structure of 16 was established by X‐ray analysis. It is characterised by four pairs of intermolecular H‐bonds linking every two molecules in the unit cell. Sequential imine reduction and intramolecular condensation of the C(4′)‐(acylamino)‐pyrimido[4,5‐b][1,4]diazepines 27 and 30 led to the [1,4]diazepino[1,2,3‐gh]purines 28 / 29 and 31 , respectively. 相似文献
106.
Le Guennic B Neugebauer J Reiher M Autschbach J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(5):1677-1686
The experimental 13C NMR chemical shift of the central carbon atom in the octahedral [(Ph3PAu)6C]2+ cluster was investigated on the basis of relativistic density functional calculations. In order to arrive at independent model conclusions regarding the value of the chemical shift, a systematic study of the dependence of the cluster structure on the phosphine ligands, the chosen density functionals, and the basis set size was conducted. The best structures obtained were then used in the NMR calculations. Because of the cage-like cluster structure a pronounced deshielding of the central carbon nucleus could have been expected. However, upon comparison with the 13C NMR properties of the related complex [C{Au[P(C6H5)2(p-C6H4NMe2)]}6]2+, Schmidbaur et al. have assigned a signal at delta=135.2 ppm to the interstitial carbon atom. Our calculations confirm this value in the region of the aromatic carbon atoms of the triphenylphosphine ligands. The close-lying signals of the 108 phenyl carbon atoms can explain the difficulties of assigning them experimentally. 相似文献
107.
108.
109.
Published data of the last 10-15 years on the use of the reactions of sulfur dichloride with various unsaturated compounds for the synthesis of oxathia- and thiacrown compounds and study of their extraction characteristics toward various transition and heavy metals are reviewed. Some previously unpublished results and associated experimental data are also included. 相似文献
110.