全文获取类型
收费全文 | 1461篇 |
免费 | 35篇 |
国内免费 | 3篇 |
专业分类
化学 | 1093篇 |
晶体学 | 20篇 |
力学 | 23篇 |
数学 | 60篇 |
物理学 | 303篇 |
出版年
2023年 | 7篇 |
2021年 | 8篇 |
2020年 | 20篇 |
2019年 | 18篇 |
2018年 | 8篇 |
2016年 | 14篇 |
2015年 | 28篇 |
2014年 | 29篇 |
2013年 | 73篇 |
2012年 | 73篇 |
2011年 | 66篇 |
2010年 | 32篇 |
2009年 | 45篇 |
2008年 | 108篇 |
2007年 | 90篇 |
2006年 | 105篇 |
2005年 | 97篇 |
2004年 | 74篇 |
2003年 | 43篇 |
2002年 | 66篇 |
2001年 | 28篇 |
2000年 | 31篇 |
1999年 | 12篇 |
1998年 | 12篇 |
1997年 | 10篇 |
1996年 | 14篇 |
1995年 | 18篇 |
1994年 | 19篇 |
1993年 | 18篇 |
1992年 | 20篇 |
1991年 | 15篇 |
1990年 | 15篇 |
1989年 | 16篇 |
1988年 | 22篇 |
1987年 | 22篇 |
1986年 | 7篇 |
1985年 | 21篇 |
1984年 | 17篇 |
1983年 | 11篇 |
1982年 | 17篇 |
1981年 | 18篇 |
1980年 | 10篇 |
1979年 | 14篇 |
1978年 | 20篇 |
1977年 | 12篇 |
1976年 | 13篇 |
1975年 | 5篇 |
1974年 | 10篇 |
1973年 | 16篇 |
1966年 | 4篇 |
排序方式: 共有1499条查询结果,搜索用时 14 毫秒
181.
Eiichi Masumoto Hiroshi Maruoka Fumi Okabe Sho Nishida Yuki Yoshimura Toshihiro Fujioka Kenji Yamagata 《Journal of heterocyclic chemistry》2011,48(1):96-104
Dihydropyridazinones 4a , 4b , N‐substituted dihydropyrazoles 5b , 5c , 5d , and O‐substituted pyrazoles 6a , 6b , 6c , 6d have been synthesized starting from spirocyclopropanepyrazole derivative 2 . Treatment of 2 with α‐chloro esters, e.g., methyl chloroacetate, ethyl chloroacetate, isopropyl chloroacetate, and tert‐butyl chloroacetate, in potassium carbonate/sodium iodide system caused ring opening and subsequent C‐ or N‐attack nucleophilic substitution to give the corresponding dihydropyridazinones 4a , 4b and N‐substituted dihydropyrazoles 5b , 5c , 5d . On the other hand, in the absence of sodium iodide, O‐substituted pyrazoles 6a , 6b , 6c , 6d were obtained from 2 via an O‐attack nucleophilic substitution. J. Heterocyclic Chem., 2011. 相似文献
182.
Ohno O Chiba T Todoroki S Yoshimura H Maru N Maekawa K Imagawa H Yamada K Wakamiya A Suenaga K Uemura D 《Chemical communications (Cambridge, England)》2011,47(46):12453-12455
Novel sesquiterpene alkaloids, halichonines A (1), B (2), and C (3), were identified from the marine sponge Halichondria okadai Kadota. By spectroscopic analyses and synthesis, their structures were revealed to include a 6,6-bicyclic ring system and two prenylated amine moieties. In addition, 2 induced apoptosis in HL60 human leukemia cells. 相似文献
183.
184.
We have investigated the pressure-induced Raman spectral changes of 1-ethyl-3-methylimidazolium tetrafluoroborate ([emim][BF4]). We found that [emim][BF4] did not crystallize up to 1.2 GPa. The Raman CH stretching spectra arising from the CH3 groups of the ethyl-chain and the CH3 group adjacent to the imidazolium-ring in [emim]+ cation largely changed against pressure. Moreover, the Raman intensity of the CH2 (N) bending band arising from the alkyl-chain drastically changes with increasing pressure, but that of the imidazolium-ring in-plane bending band arising from the imidazolium-ring is independent of pressure. Our results show that the environment around the alkyl-chain of [emim][BF4] is largely perturbed rather than that around the imidazolium-ring upon compression. 相似文献
185.
Toshihiro Yoshimura Yusuke Tamenori Nozomu Iwasaki Hiroshi Hasegawa Atsushi Suzuki Hodaka Kawahata 《Journal of synchrotron radiation》2013,20(5):734-740
Magnesium K‐edge X‐ray absorption near‐edge structure (XANES) spectra have been investigated to develop a systematic understanding of a suite of Mg‐bearing geological materials such as silicate and carbonate minerals, sediments, rocks and chemical reagents. For the model compounds the Mg XANES was found to vary widely between compounds and to provide a fingerprint for the form of Mg involved in geologic materials. The energy positions and resonance features obtained from these spectra can be used to specify the dominant molecular host site of Mg, thus shedding light on Mg partitioning and isotope fractionation in geologic materials and providing a valuable complement to existing knowledge of Mg geochemistry. 相似文献
186.
H. Wada H. Nakamura E. Fukami K. Yoshimura M. Shiga Y. Nakamura 《Journal of magnetism and magnetic materials》1987,70(1-3):17-19
The thermal expansion and low temperature and low temperature specific heat were measured for Y1−xScxMn2. The results are discussed in terms of spin fluctuations and compared with those of Y(Mn1−xAlx)2, which show al local moment character. It is revealed that Y1−xScxMn2 is a typical nearly antiferromagnet in which giant spin fluctuations are thermally excited. 相似文献
187.
We have proposed a method to control the three-dimensional electric field in the focus of an optical microscope using two non-twisted liquid crystal spatial light modulators, and to detect the molecular orientation of a single molecule. The three-dimensional electric field is generated by focusing the beam with two dimensional spatial distribution of polarization. The possibility of detection of three-dimensional single molecular orientation was shown by numerical calculations. © 2005 The Optical Society of Japan 相似文献
188.
When perfect recall is not satisfied, the informational contents of mixed and behavior strategies differ and are more than what the information partition describes. First, we consider two kinds of additional information strategies may carry, and show that such information leads to theperfect recall refinement of a given information partition. This does not, however, imply that the strategies compensate fully for the lack of perfect recall. We give a necessary and sufficient condition on an information partition, calledA-loss, for the informational content of mixed strategies to fully compensate for the lack of perfect recall. The informational content of behavior strategies never fully compensates. 相似文献
189.
Nemoto Rei Wang Li Ikoma Toshiyuki Tanaka Junzo Senna Mamoru 《Journal of nanoparticle research》2004,6(2):259-265
Hydroxyapatite (HAp) nanocrystals were prepared at room temperature by a coprecipitation method from Ca(OH)2 and H3PO4, in the presence of chemically disintegrated silk fibroin (SF). Adsorbed amounts of cations on SF and crystallinity of HAp in the composite were increased by the chemical disintegration of SF higher order structure. Preferential alignment of c-axis of HAp crystallites along the longitudinal direction of ca. 150nm SF fibril was observed. These changes due to disintegration of SF were discussed in terms of the chemical interaction between HAp and SF. The resulted composite with preferential alignment of HAp nanocrystals is a good candidate as a starting material for bone substitutes. 相似文献
190.