全文获取类型
收费全文 | 252篇 |
免费 | 5篇 |
专业分类
化学 | 129篇 |
晶体学 | 6篇 |
力学 | 4篇 |
数学 | 19篇 |
物理学 | 99篇 |
出版年
2023年 | 1篇 |
2021年 | 3篇 |
2020年 | 3篇 |
2019年 | 2篇 |
2018年 | 2篇 |
2017年 | 2篇 |
2016年 | 6篇 |
2015年 | 1篇 |
2014年 | 3篇 |
2013年 | 13篇 |
2012年 | 11篇 |
2011年 | 17篇 |
2010年 | 11篇 |
2009年 | 10篇 |
2008年 | 19篇 |
2007年 | 16篇 |
2006年 | 18篇 |
2005年 | 15篇 |
2004年 | 14篇 |
2003年 | 15篇 |
2002年 | 13篇 |
2001年 | 11篇 |
2000年 | 3篇 |
1999年 | 6篇 |
1998年 | 4篇 |
1997年 | 11篇 |
1996年 | 8篇 |
1995年 | 2篇 |
1994年 | 5篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有257条查询结果,搜索用时 15 毫秒
191.
Tomohiko Sakaguchi Kouji Kashiwa Masayuki Matsuzaki Hiroaki Kouno Masanobu Yahiro 《Central European Journal of Physics》2008,6(1):116-121
We test the stability of the mean field solution in the Nambu-Jona-Lasinio model in a semi-quantitative manner. For stable
solutions with respect to both the σ and π directions, we investigate effects of the mesonic loop corrections of 1/N
c
, which correspond to the next-to-leading order in the 1/N
c
expansion, on the high density chiral phase transition. The corrections weaken the first order phase transition and shift
the critical chemical potential to a lower value. At N
c
= 3, however, instability of the mean field effective potential prevents us from determining the minimum of the corrected
one.
相似文献
192.
Akio Honda Hiroshi Shibata Jiro Gyoba Kouji Saitou Yukio Iwaya Yôiti Suzuki 《Applied Acoustics》2007,68(8):885-896
Transfer effects of playing an auditory game with a virtual auditory display (VAD) were investigated. Furthermore, we analyzed the effects of playing the VAD game on sound localization performance under subjects’ own head-related transfer functions (HRTFs) and HRTFs fitted from those of 16 other adults. Participants performed sound localization tasks initially and 2 weeks later to show the effects. The VAD game players were of three groups, using own HRTFs, fitted HRTFs, and no playing (control). The VAD game-playing results revealed that: (1) the hit rate of the sound localization task for real sound sources increased approximately 20%; (2) the vertical and horizontal localization error decreased significantly; (3) sound localization performance using fitted HRTFs was similar to performance using own HRTFs. Follow-up tests revealed that transfer effects persisted more than 1 month, suggesting that the effects of playing the VAD game transfer to sound localization performance. 相似文献
193.
We investigate the manifestation of stripes in the in-plane resistivity anisotropy in untwinned single crystals of La2-xSrxCuO4 ( x = 0.02-0.04) and YBa(2)Cu(3)O(y) ( y = 6.35-7.0). It is found that both systems show strongly temperature-dependent in-plane anisotropy in the lightly hole-doped region and that the anisotropy in YBa(2)Cu(3)O(y) grows with decreasing y below approximately 6.60 despite the decreasing orthorhombicity, which gives most direct evidence that electrons self-organize into a macroscopically anisotropic state. The transport is found to be easier along the direction of the spin stripes already reported, demonstrating that the stripes are intrinsically conducting in cuprates. 相似文献
194.
This digest overviews successful synthetic approaches to natural dimeric 1,4-naphthoquinones. Several natural dimeric 1,4-naphthoquinone derivatives have been isolated from natural sources including plants, bacteria, and fungi. They have diverse structures and attractive biological activities. However, it is difficult to construct the dimeric scaffolds efficiently and selectively, because 1,4-naphthoquinones and their derivatives are highly reactive. Efficient and attractive synthetic methodologies to construct unique dimeric 1,4-naphthoquinone skeletons are reviewed. 相似文献
195.
K. Sakai T. Yoshida K. Kuba Y. Kato Y. Ichioka 《International Journal of Infrared and Millimeter Waves》1987,8(3):307-316
Methods based on the Stark effect are described for dither-free frequency stabilization of the optically pumped submm laser. The CO2 pump laser was stabilized using a Stark Lamb dip signal of the submm lasant in an external Stark cell. An estimated frequency stability (f/f) better than ±1.4×10–8, for one hour recording, was obtained by this method. The frequency of the submm laser was stabilized using the d.c. and a.c. Stark effects for a metal-dielectric rectangular waveguide laser. An estimated frequency stability of ±6×10–8 was obtained for 119 m line of CH3OH laser for one hour recording. 相似文献
196.
Jyunichi Koyanagi Masayuki Ogawa Katsumi Yamamoto Kouji Nakayama Akira Tanaka 《Journal of heterocyclic chemistry》1998,35(2):301-305
2-Chloronaphtho[2,3-b]furan-4,9-dione 4 was allowed to react with pyrrolidine to produce 2-(1-pyrrolidinyl)naphtho[2,3-b]furan-4,9-dione 8 in 64% yield. In a similar manner, the reaction of 4 with cyclic amines (piperidine, morpholine, 4-substituted piperazines, etc.) gave the desired compounds. 2-Dimethylaminonaphtho[2,3-b]furan-4,9-dione 20 and 2-propylaminonaphtho[2,3-b]furan-4,9-dione 23 were obtained from the reactions of 4 with amines in 67% and 48% yields, respectively. Furthermore, the reactions of 4 with acyclic amines (diethylamine, dipropylamine, isopropylamine, butylamine, etc.) gave the desired compound. Compound 4 was treated with sodium azide to give 2-azidonaphtho[2,3-b]furan-4,9-dione 28 in 42% yield. All these nucleophilic substitutions were carried out at room temperature. It was found that 4 showed high reactivity for amines. Unexpectedly, 2-morpholinonaphtho[2,3-b]furan-4,9-dione 13 was obtained from the reaction of 4 with 1-morpholino-1-cyclohexene. 相似文献
197.
Jyunichi Koyanagi Katsumi Yamamoto Kouji Nakayama Akira Tanaka 《Journal of heterocyclic chemistry》1995,32(4):1289-1291
Reaction of the parent naphtho[2,3-b]furan-4,9-dione 2 with various electrophilic reagents was difficult, and only nitration of 2 gave small amounts of 2-nitronaphtho[2,3-b]furan-4,9-dione 4 . Then 2-acetylnaphtho[2,3-b]furan-4,9-dione 1 was not obtained by the acetylation of 2 . On the other hand, compound 1 that is isolated from Tabebuia Cassinoides and has cytotoxic activity, was obtained from 3-lithiofuran in five steps. 相似文献
198.
Catalytic C-C bond cleavage of acetonitrile and C-Si bond formation have been attained in the photoreaction of MeCN with Et3SiH in the presence of an iron complex, Cp(CO)2FeMe. This catalytic system can be applied for arylnitrile C-C bond cleavage. 相似文献
199.
The radical addition of enolizable carbonyl compounds such as malonates and malononitrile to alkenes was successfully achieved through a catalytic process using the Mn(II)/Co(II)/O(2) system to afford the corresponding adducts in fair to good yields. Dimethyl malonate added to 1,5-cyclooctadiene to produce a fused bicycle compound. 相似文献
200.
Maezaki N Yagi S Yoshigami R Maeda J Suzuki T Ohsawa S Tsukamoto K Tanaka T 《The Journal of organic chemistry》2003,68(14):5550-5558
Unprecedented Pd-catalyzed sulfinylzincation with 1-alkynyl sulfoxide as a sulfinyl source was developed. Bis-sulfinyl alkenes were formed in good yields on treatment of 1-alkynyl sulfoxides with Et(2)Zn in the presence of a Pd-catalyst, wherein zinc sulfenate (or sulfinylzinc) species would be generated in situ to undergo highly syn-selective conjugate addition to the 1-alkynyl sulfoxides. By using 3,3-dimethyl-1-butynyl sulfoxides, formation of the bis-sulfinyl alkenes was completely suppressed and the sulfinylzincation of activated alkynes was accomplished. The reaction tolerates various functionalities, and was promoted considerably by the neighboring group participation of the heteroatom at the delta-position in the alkynoates. Stereodivergent synthesis of two diastereomeric vinylic sulfoxides and reaction of the resulting vinylzinc species with electrophiles were also described. 相似文献