全文获取类型
收费全文 | 1674篇 |
免费 | 49篇 |
国内免费 | 3篇 |
专业分类
化学 | 1320篇 |
晶体学 | 16篇 |
力学 | 19篇 |
数学 | 48篇 |
物理学 | 323篇 |
出版年
2023年 | 7篇 |
2021年 | 21篇 |
2020年 | 17篇 |
2019年 | 26篇 |
2018年 | 14篇 |
2017年 | 15篇 |
2016年 | 15篇 |
2015年 | 28篇 |
2014年 | 27篇 |
2013年 | 78篇 |
2012年 | 78篇 |
2011年 | 87篇 |
2010年 | 46篇 |
2009年 | 38篇 |
2008年 | 91篇 |
2007年 | 103篇 |
2006年 | 82篇 |
2005年 | 102篇 |
2004年 | 90篇 |
2003年 | 69篇 |
2002年 | 67篇 |
2001年 | 48篇 |
2000年 | 37篇 |
1999年 | 31篇 |
1998年 | 30篇 |
1997年 | 22篇 |
1996年 | 30篇 |
1995年 | 17篇 |
1994年 | 20篇 |
1993年 | 26篇 |
1992年 | 29篇 |
1991年 | 22篇 |
1990年 | 15篇 |
1989年 | 25篇 |
1988年 | 7篇 |
1987年 | 9篇 |
1986年 | 21篇 |
1985年 | 22篇 |
1984年 | 23篇 |
1983年 | 11篇 |
1982年 | 25篇 |
1981年 | 17篇 |
1980年 | 12篇 |
1979年 | 21篇 |
1978年 | 13篇 |
1977年 | 17篇 |
1976年 | 14篇 |
1975年 | 16篇 |
1974年 | 12篇 |
1973年 | 11篇 |
排序方式: 共有1726条查询结果,搜索用时 15 毫秒
111.
Secondary 2-thiophenecarboxamides efficiently undergo unique triarylation accompanied by formal decarbamoylation under palladium catalysis. 3-Substituted thiophenes, especially having an electron-withdrawing group, can also be triarylated. 相似文献
112.
Electronic states of P donors in Si nanocrystals (nc-Si) embedded in insulating glass matrices have been studied by electron spin resonance. Doping of P donors into nc-Si was demonstrated by the observation of optical absorption in the infrared region due to intraconduction band transitions. P hyperfine structure (hfs) was successfully observed at low temperatures. The observed splitting of the hfs was found to be much larger than that of the bulk Si:P and depended strongly on the size of nc-Si. The observed strong size dependence indicates that the enhancement of the hyperfine splitting is caused by the quantum confinement of P donors in nc-Si. 相似文献
113.
Novel ferromagnetism in Ca(1-x)La(x)B(6) is studied in terms of the Ginzburg-Landau theory for excitonic-order parameters, taking into account symmetry of the wave functions. We found that the minima of the free energy break both inversion and time-reversal symmetries, while the product of these two remains preserved. This explains various novelties of the ferromagnetism and predicts a number of magnetic properties, including the magnetoelectric effect, which can be tested experimentally. 相似文献
114.
Applying Kontsevich's iterated integral for tangles, we get an isotopy invariant of tangles. We give a method to compute the integral of a tangle combinatorially from modified integrals of some simple tangles. We localize the integral by moving the end points of the tangle to an extreme configuration, and modify the integral so that it is convergent. By using a similar technique, we generalize Kontsevich's invariant to a framed tangle. 相似文献
115.
Dimethylaluminiun chloride has been found to cleave THP ethers selectively without any removal of t-butyldimethylsilyl ethers 相似文献
116.
117.
118.
Some of the physical and thermodynamic properties of III–V liquids can be explained by assuming that the liquids have a dual structure. The thermodynamic model which has been established for the present paper is a partially associated solution model. It was constructed on the assumption of the existence of associated complexes. The asymmetry of the liquidus curve and the amount of excess free energy determined from the phase diagram analysis can be explained by using the model. Some of the thermodynamic parameters obtained in this study are found to have important physical meanings. The interaction parameter between monoatomic species, ωA,B is in a good agreement with the theoretical value proposed by Stringfellow. The heat of formation of associated complexes can be represented explicitly in terms of the spectroscopic ionicity and the dehybridization factor. The free energy of formation is empirically evaluated to be 20-6(fi ?0.17)RT?35,000fiDcal/mol for III–V binary liquids. 相似文献
119.
Hamao Watanabe Kazuaki Higuchi Tomoko Goto Tsutomu Muraoka Jun Inose Masaaki Kageyama Yasuko Iizuka Masakatsu Nozaki Yoichiro Nagai 《Journal of organometallic chemistry》1981,218(1):27-39
In the presence of a catalytic amount of sodium methoxide, sym-dimethoxytetramethyldisilane was converted into α,ω-dimethoxypermethylpolysilanes, MeO(SiMe2)nOMe where n ? 3, at room temperature. On the other hand, similar treatment of the disilane in THF solution gave cyclic polysilanes, (Me2Si)n where n = 5–7. Decomposition of the disilane in the presence of diphenylacetylene afforded a trisilacyclopentene derivative under similar conditions. This compound was obtained also by the reaction between α,ω-dimethoxypermethylpolysilanes and diphenylacetylene in the presence of sodium methoxide. These cyclic products most likely were formed via permethyl polysilyl anion intermediates derived from α,ω-dimethoxypermethylpolysilanes. Also, the formation of α,ω-dimethoxypermethylpolysilanes could be elucidated in terms of the mechanism involving the base-assisted, concerted nucleophilic substitution or stepwise substitution by silyl anions, rather than the successive dimethylsilylene (Me2Si:) insertion reaction. 相似文献
120.
Ultrafast charge resonant (CR) dynamics between two molecules in a dimer system has been studied theoretically and experimentally using 6-fs laser pulses and a thin film of amorphous-phase phthalocyanine tin(IV) dichloride (SnPc). The modulation of the absorbance change in the bleaching spectral range of the CR absorption band was analyzed to obtain the amount of charge resonantly transferred back and forth by a dimeric vibration induced by photoexcitation. The modulation can be explained in terms of a periodic change in the cross section and a periodic energy shift, where both are induced by the change in the overlap integral caused by the accordion-type intermolecular vibration. The associated change in distance between two molecules with the intermolecular vibration was estimated to be 0.09 A, which corresponds to 2.5% of the mean distance between the two SnPc molecules in the dimeric system. 相似文献