全文获取类型
收费全文 | 3738篇 |
免费 | 107篇 |
国内免费 | 755篇 |
专业分类
化学 | 4219篇 |
晶体学 | 69篇 |
力学 | 18篇 |
综合类 | 33篇 |
数学 | 6篇 |
物理学 | 255篇 |
出版年
2023年 | 22篇 |
2022年 | 49篇 |
2021年 | 53篇 |
2020年 | 71篇 |
2019年 | 54篇 |
2018年 | 86篇 |
2017年 | 103篇 |
2016年 | 99篇 |
2015年 | 75篇 |
2014年 | 134篇 |
2013年 | 420篇 |
2012年 | 172篇 |
2011年 | 198篇 |
2010年 | 148篇 |
2009年 | 198篇 |
2008年 | 214篇 |
2007年 | 266篇 |
2006年 | 257篇 |
2005年 | 250篇 |
2004年 | 242篇 |
2003年 | 200篇 |
2002年 | 157篇 |
2001年 | 120篇 |
2000年 | 114篇 |
1999年 | 102篇 |
1998年 | 72篇 |
1997年 | 73篇 |
1996年 | 82篇 |
1995年 | 88篇 |
1994年 | 86篇 |
1993年 | 77篇 |
1992年 | 69篇 |
1991年 | 33篇 |
1990年 | 25篇 |
1989年 | 29篇 |
1988年 | 28篇 |
1987年 | 11篇 |
1986年 | 24篇 |
1985年 | 8篇 |
1984年 | 7篇 |
1983年 | 6篇 |
1982年 | 9篇 |
1981年 | 12篇 |
1980年 | 15篇 |
1979年 | 12篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1976年 | 4篇 |
1974年 | 3篇 |
1972年 | 3篇 |
排序方式: 共有4600条查询结果,搜索用时 15 毫秒
1.
Prof. Dr. Frank Glorius 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(22):8047-8051
A general and efficient methodology for the direct transition metal free trifluoromethylthiolation of a broad range of biologically relevant N‐heteroarenes is reported employing abundant sodium chloride as the catalyst. This method is operationally simple, exhibits high functional group tolerance, and does not require protecting groups. 相似文献
2.
A simple, efficient and highly chemoselective method for tetrahydropyranylation of alcohols and phenols has been developed by their reaction with 3,4-dihydro-2H-pyran at room temperature in the presence of a catalytic amount of polystyrene supported AlCl3. The method is also highly selective for monoprotection of symmetrical diols. 相似文献
3.
H. Kaczmarek J. Kowalonek Z. Klusek S. Pierzgalski S. Datta 《Journal of Polymer Science.Polymer Physics》2004,42(4):585-602
The photooxidative degradation of blends (in a full range of compositions) of amorphous poly(vinyl chloride) (PVC) with semicrystalline poly(ethylene oxide) (PEO) in the form of thin films is investigated using absorption spectroscopy (UV–visible and Fourier transform infrared) and atomic force microscopy (AFM). The amount of insoluble gel formed as a result of photocrosslinking is estimated gravimetrically. It is found that the PVC/PEO blendsí susceptibility to photooxidative degradation differs from that pure of the components and depends on the blend composition and morphology. Photoreactions such as degradation and oxidation are accelerated whereas dehydrochlorination is retarded in blends. The photocrosslinking efficiency in PVC/PEO blends is higher than in PVC; moreover, PEO is also involved in this process. AFM images showing the lamellar structure of semicrystalline PEO in the blend lead to the conclusion that the presence of PVC does not disturb the crystallization process of PEO. The changes induced by UV irradiation allow the observation of more of the distinct PEO crystallites. This is probably caused by recrystallization of short, more mobile chains in degraded PEO or by partial removal of the less stable amorphous phase from the film surface. These results confirm previous information on the miscibility of PVC with PEO. The mechanism of the interactions between the components and the blend photodegradation are discussed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 585–602, 2004 相似文献
4.
Three N-3-phenyl-2-propenoyl amino acids were synthesized through interaction between 3-phenyl-2-propenoyl chloride and amino acids in alkaline with a high Yield.Structure of the products were identified by elemental analysis,IR and NMR spectroscopy. 相似文献
5.
PinHuaLI LeiWANG MinWANG JinCanYAN 《中国化学快报》2004,15(11):1295-1298
A Glaser coupling reaction of terminal alkynes in the presence of nickel chloride withoutany organics and bases in hot water has been developed, which produces the correspondinghomo-coupling products in good yields. 相似文献
6.
8.
T. Peprnicek A. Kalendova J. Simonik J.F. Gerard 《Polymer Degradation and Stability》2006,91(12):3322-3329
The paper concentrates on poly(vinyl chloride) - PVC - from the point of nanocomposite characterisation through thermal degradation of samples, evolution of the changes caused by elevating temperature using TGA, FTIR and Congo Red methods combined with morphological characterisation by XRD and TEM analyses. A novel method of PVC-paste/nanocomposite preparation while processing was used. During preparation, PVC plasticizer was mixed with clay, both natural and organophilic, and the suspension was then compounded with the other components. Two factors were followed: effect of shearing alone, and in combination with temperature. As is presented, the type of nano-filler and its chemical modifier have obvious influence on final properties either thermal or morphological. Presented contribution follows previous part of investigation and brings further information from PVC-paste/nanocomposite field. 相似文献
9.
The stannous chloride dihydrate-mediated deprotection-bicyclisation of a range of amides possessing a pendant acetal group is reported. These mild reaction conditions have been used to prepare a number of ring-fused heterocyclic compounds, some in enantiomerically pure form, which should be of interest both in their own right and as building blocks for the production of more complex target molecules. 相似文献
10.
L. Villa P. D' Agati C. Mansueto C. Pellerito M. Scopelliti T. Fiore L. Nagy L. Pellerito 《应用有机金属化学》2003,17(2):106-112
Ascidia malaca gametes before fertilization incubated in 10?5 or 10?7 M solutions of tributyltin(IV) chloride, TBTCl, for 3 h appear highly damaged under transmission electron microscopy observation. Also, the fertilization process is affected by the compound: the damaged spermatozoa are present in the vitelline coat and the egg does not cleave. An increase of microbodies, structurally similar to peroxisomes, have been detected in the egg peripheral cytoplasm, probably in relation to their role in alleviating damage to some cellular components. The results have shown that the reproduction of ascidians under unfavourable environmental conditions is prevented. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献