全文获取类型
收费全文 | 764篇 |
免费 | 30篇 |
国内免费 | 17篇 |
专业分类
化学 | 568篇 |
晶体学 | 4篇 |
力学 | 10篇 |
数学 | 38篇 |
物理学 | 191篇 |
出版年
2023年 | 5篇 |
2022年 | 3篇 |
2021年 | 5篇 |
2020年 | 11篇 |
2019年 | 19篇 |
2018年 | 16篇 |
2017年 | 7篇 |
2016年 | 20篇 |
2015年 | 14篇 |
2014年 | 23篇 |
2013年 | 31篇 |
2012年 | 34篇 |
2011年 | 33篇 |
2010年 | 29篇 |
2009年 | 27篇 |
2008年 | 37篇 |
2007年 | 37篇 |
2006年 | 39篇 |
2005年 | 48篇 |
2004年 | 41篇 |
2003年 | 26篇 |
2002年 | 26篇 |
2001年 | 26篇 |
2000年 | 19篇 |
1999年 | 12篇 |
1998年 | 4篇 |
1997年 | 18篇 |
1996年 | 13篇 |
1995年 | 6篇 |
1994年 | 23篇 |
1993年 | 8篇 |
1992年 | 9篇 |
1991年 | 9篇 |
1990年 | 7篇 |
1989年 | 5篇 |
1988年 | 7篇 |
1987年 | 4篇 |
1986年 | 11篇 |
1985年 | 8篇 |
1984年 | 16篇 |
1983年 | 3篇 |
1982年 | 8篇 |
1981年 | 9篇 |
1980年 | 3篇 |
1979年 | 14篇 |
1977年 | 8篇 |
1976年 | 11篇 |
1975年 | 3篇 |
1973年 | 6篇 |
1971年 | 2篇 |
排序方式: 共有811条查询结果,搜索用时 31 毫秒
31.
A facile and efficient synthesis of N-tert-butoxycarbonyl-O-cyclohexyl-L-tyrosine [Boc-Tyr(Chx)-OH] is described. Boc-Tyr-OH was treated with NaH in dimethylformamide and then with 3-bromocyclohexene to give N-Boc-O-(cyclohex-2-enyl)-L-tyrosine [Boc-Tyr(Che)-OH] in 70% yield. Hydrogenation of Boc-Tyr(Che)-OH over PtO2 afforded Boc-Tyr(Chx)-OH in almost quantitative yield. The highest yield was achieved when a side product in the synthesis of Boc-Tyr-OH, Boc-Tyr(Boc)-OH, was not removed, because it was also converted to Boc-Tyr(Che)-OH without any additional manipulations. The new synthetic method described here is convenient for practical use, and would facilitate the widespread use of the Chx group for the hydroxy-protection of Tyr. 相似文献
32.
Xiao‐Feng Wang Yang Lv Zhi Su Taka‐aki Okamura Gang Wu Wei‐Yin Sun Prof. Dr. Norikazu Ueyama 《无机化学与普通化学杂志》2007,633(15):2695-2700
The metal complexes [Hg2(tbim)2Br4]·2DMF ( 1 ) and [Hg2(tbim)I4]·1.5DMF ( 2 ) were prepared by reactions of 1,3,5‐tris(benzimidazol‐1‐ylmethyl)‐2,4,6‐trimethylbenzene (tbim) with HgBr2, HgI2, respectively, and [Hg2(tbim)I4]·0.5(FeCp2)·H2O ( 3 ) was obtained by the same method with addition of ferrocene (FeCp2) as additive. Their structures were determined by X‐ray crystallographic analyses. Complex 1 has a macrocyclic binuclear structure with one benzimidazole arm of the ligand free of coordination and the binuclear units are further connected by C‐H···N hydrogen bonds to give an infinite zigzag chain. Complexes 2 and 3 have a 2D network structure in which tbim serves as a tridentate ligand. The results showed that the halides of bromide and iodide have remarkable impact on the structure of the complexes. The FeCp2 molecules are trapped in the voids of framework 3 . 相似文献
33.
Kaoru Suzuki Iwao Nishiyama Yasushi Ozaki Kozo Kuchitsu 《Chemical physics letters》1978,58(1):145-148
Light emission from Cl(5p) atoms (near 440 nm) produced in the reaction of HCl in a discharged flow of argon was investigated with a flowing-afterglow apparatus. Ionic species, most probably argon ions in metastable states, Ar+M, were found to be responsible for the Cl(5p) production in the dissociative excitation of HCl. 相似文献
34.
Reactions of two new tripodal ligands 1,3,5-tris(1-imidazolyl)benzene (4) and 1,3-bis(1-imidazolyl)-5-(imidazol-1-ylmethyl)benzene (5) with metal [Ag(I), Cu(II), Zn(II), Ni(II)] salts lead to the formation of novel two-dimensional (2D) metal-organic frameworks [Ag(2)(4)(2)][p-C(6)H(4)(COO)(2)].H(2)O (6), [Ag(4)]ClO(4) (7), [Cu(4)(2)(H(2)O)(2)](CH(3)COO)(2).2H(2)O (8), [Zn(4)(2)(H(2)O)(2)](NO(3))(2) (9), [Ni(4)(2)(N(3))(2)].2H(2)O (10), and [Ag(5)]ClO(4) (11). All the structures were established by single-crystal X-ray diffraction analysis. Crystal data for 6: monoclinic, C2/c, a = 23.766(3) A, b = 12.0475(10) A, c = 13.5160(13) A, beta = 117.827(3) degrees, Z = 4. For compound 7: orthorhombic, P2(1)2(1)2(1), a = 7.2495(4) A, b = 12.0763(7) A, c = 19.2196(13) A, Z = 4. For compound 8: monoclinic, P2(1)/n, a = 8.2969(5) A, b = 12.2834(5) A, c = 17.4667(12) A, beta = 96.5740(10) degrees, Z = 2. For compound 9: monoclinic, P2(1)/n, a =10.5699(3) A, b = 11.5037(3) A, c = 13.5194(4) A, beta = 110.2779(10) degrees, Z = 2. For compound 10: monoclinic, P2(1)/n, a = 9.8033(3) A, b = 12.1369(5) A, c = 13.5215(5) A, beta = 107.3280(10) degrees, Z = 2. For compound 11: monoclinic C2/c, a = 18.947(2) A, b = 9.7593(10) A, c = 19.761(2) A, beta = 97.967(2) degrees, Z = 8. Both complexes 6 and 7 are noninterpenetrating frameworks based on the (6, 3) nets, and 8, 9 and 10 are based on the (4, 4) nets while complex 11 has a twofold parallel interpenetrated network with 4.8(2) topology. It is interesting that, in complexes 6,7, and 11 with three-coordinated planar silver(I) atoms, each ligand 4 or 5 connects three metal atoms, while in the case of complexes 8, 9, and 10 with six-coordinated octahedral metal atoms, each ligand 4 only links two metal atoms, and another imidazole nitrogen atom of 4 did not participate in the coordination with the metal atoms in these complexes. The results show that the nature of organic ligand and geometric needs of metal atoms have great influence on the structure of metal-organic frameworks. 相似文献
35.
Fukushima S Miyata K Nishiyama N Kanayama N Yamasaki Y Kataoka K 《Journal of the American Chemical Society》2005,127(9):2810-2811
An A-B-C type triblock copolymer, tandemly aligning two types of polycations with different pKa values in a single polymer strand, was developed for the construction of novel polyplex micelles, satisfying a high DNA condensing ability as well as a proton buffering activity directed to elevating gene transfection. The micelle might feature the distinctive three-layered structure, where an inner polyplex layer of condensed pDNA with poly(l-lysine) (pKa approximately 9.4) as the C segment is successively wrapped with an intermediate layer of poly[(3-morpholinopropyl)aspartamide] (B segment) with a comparatively low pKa of approximately 6.2, to provide a buffering effect, and an outer PEG layer (A segment) as a biocompatible palisade. 相似文献
36.
Tomihiro Nishiyama Yasushi Nakai Masataka Kushiyama Etsuo Ikemoto Fukiko Yamada 《Journal of heterocyclic chemistry》1982,19(5):1223-1226
The mass spectral fragmentation of 4-, 5-, and 4,8-disubstituted derivatives of 6-aryl-5,6,7,8-tetrahydro-4H-1,3,2,6-dioxathiazocine 2-oxides is reported. 相似文献
37.
[60]-Fullerene functionalized amino acids with 4-6 methylene spacers from α-carbon to the nitrogen atom of fulleropyrolidine and corresponding multifullerene peptides have been synthesized. 相似文献
38.
Spirobenzopyran 1 , with the 3-(diethoxymethylsilyl)-propyl group at the N atom, was synthesized. The condensation reaction of the spiropyran 1 and diethoxydimethylsilane gave oligomeric poly(dimethylsiloxane) with the spiropyran moiety in the side chain. The oligomer was photochromic; its colour changed from colorless to purple-red on uv irradiation and the color faded on visible irradiation or on standing in the dark. The half-decay time of the thermal decoloration was about twice that of monomeric spiropyran dissolved in the dimethylsiloxane oligomer. Photochromic poly(dimethylsiloxane) with the spirooxazine moiety in the side chain was also prepared. 相似文献
39.
40.
Four 6-phenyl-5,6,7,8-tetrahydro-4H-1,3,2,6-dioxathiazocine 2-oxides were synthesized by the reaction of the corresponding N,N-bis(2-hydroxyethyl)aniline with thionyl chloride in the presence of triethylamine. 相似文献