全文获取类型
收费全文 | 1418篇 |
免费 | 44篇 |
国内免费 | 239篇 |
专业分类
化学 | 1276篇 |
晶体学 | 4篇 |
综合类 | 10篇 |
物理学 | 48篇 |
综合类 | 363篇 |
出版年
2024年 | 1篇 |
2023年 | 11篇 |
2022年 | 12篇 |
2021年 | 24篇 |
2020年 | 19篇 |
2019年 | 30篇 |
2018年 | 21篇 |
2017年 | 31篇 |
2016年 | 28篇 |
2015年 | 26篇 |
2014年 | 72篇 |
2013年 | 135篇 |
2012年 | 75篇 |
2011年 | 83篇 |
2010年 | 42篇 |
2009年 | 72篇 |
2008年 | 104篇 |
2007年 | 82篇 |
2006年 | 88篇 |
2005年 | 96篇 |
2004年 | 95篇 |
2003年 | 74篇 |
2002年 | 50篇 |
2001年 | 32篇 |
2000年 | 40篇 |
1999年 | 37篇 |
1998年 | 29篇 |
1997年 | 27篇 |
1996年 | 34篇 |
1995年 | 31篇 |
1994年 | 25篇 |
1993年 | 28篇 |
1992年 | 28篇 |
1991年 | 21篇 |
1990年 | 24篇 |
1989年 | 20篇 |
1988年 | 26篇 |
1987年 | 9篇 |
1986年 | 5篇 |
1985年 | 2篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有1701条查询结果,搜索用时 46 毫秒
61.
A novel homotrifunctional conjugation reagent, 1,3,5-tris-(N-maleimidomethyl)benzene has been synthesized in high yield with minimum purification. The reactivity of this compound was examined by using l-cysteine as a nucleophile. 相似文献
62.
Rémy Lartia 《Tetrahedron letters》2004,45(31):5949-5952
We report here a novel, simple reagent enabling the chemical incorporation of a thiophosphate or a phosphate group at the 5′-end of oligonucleotides using very mild basic deprotection conditions. This method can be useful in the case of alkali sensitive modified oligonucleotides. This reagent also gives access to the preparation of bifunctional oligonucleotides with either a thiophosphate group at the 5′-end and a phosphate at the 3′-end, or two thiophosphate groups at both the 5′- and the 3′-ends, or a 5′-thiophosphate group and a 3′-amino-containing linker. 相似文献
63.
Mikhail I. Kodess Marina A. Ezhikova Galina L. Levit Victor P. Krasnov Valery N. Charushin 《Journal of organometallic chemistry》2005,690(11):2766-2768
Experimental conditions for determination of enantiomeric composition of 1-substituted 3-aminocarboranes by 1H and 13C NMR spectroscopy using chiral shift reagent Eu(hfc)3 have been found. 相似文献
64.
Drochioiu G 《Talanta》2002,56(6):1163-1165
A very simple, accurate, fast, selective and sensitive assay of cyanide based on its reaction with 2,2-dihydroxy-l,3-indanedione at basic pH is proposed. As little as 0.01 μg ml−1 of cyanide can be determined. The molar absorptivity may reach 5.1–8.0×104 l mol−1 cm−1 depending on the reaction conditions. Thus, 1 ml of sample solution is mixed with 500 μl of 5 mg ml−1 solution of 2,2-dihydroxy-1,3-indanedione monohydrate in 2% sodium carbonate. The absorbance of the purple color is measured at 510 nm in 1-cm glass cuvettes, 10–15 min after mixing the reagents. The procedure could also be used to identify free CN− in natural waters and hydrocyanic acid in the environment. 相似文献
65.
Lei Wang Guang-ming Zhu Yue-zhong Meng Chun-mei Gao 《高分子科学》2007,(4):419-426
A novel sulfonated poly(arylene ether) containing triphenylmethane moieties was synthesized by the sulfonation of a designed parent polymer using chlorosulfonic acid as sulfonation agent. The sulfonation took place at the para position of the pendant phenyl rings because of the specially designed parent polymer. The position and degree of sulfonation were characterized by ^1H-NMR and elemental analysis. The sulfonated polymers are highly soluble in common organic solvents, such as dimethylsulfoxide, N,N'-dimethylacetamide, dimethylformamide, ethylene glycol monomethyl ether, and can be readily cast into tough and smooth films from solutions. The films showed good thermal and hydrolysis stabilities. Moreover, Fenton's reagent test revealed that the films exhibited superior stability to oxidation. The proton conductivities of the films were comparable with Nation 117 under same conditions. The membrane electrode assembly (MEA) prepared with the asmade film (706 EW, 100 μm dry thickness) shows better cell performance than Nation 115-MEA in the whole current density range. 相似文献
66.
尽管已报道了多种结构类型的手性单或双噁唑啉, 但手性多噁唑啉的合成及其应用的文献报道比较少. 本工作以多元羧酸为原料, 与手性2-氨基-1-丁醇经一步反应合成了8个手性多噁唑啉, 产率为89%~98%, 其结构经1 H NMR谱、IR谱、MS谱和元素分析确证. 相似文献
67.
Sarah C. Hubbard 《Tetrahedron》2005,61(31):7425-7430
The preparation and investigation of triplet photosensitizers designed to be preferentially soluble in room-temperature ionic liquids are reported. Photosensitizers prepared by covalent attachment of 1-methylimidazole to aryl ketones are soluble in ionic liquids and remain in the ionic liquid layer when the solution is extracted with an organic solvent. The photosensitized isomerization of trans-β-ionol to cis-β-ionol was efficiently carried out in ionic liquid solution with the product ionol being extracted and the sensitizer/ionic liquid mixture being re-used in additional photosensitization reactions. The scope and utility of the sensitizers in sensitizing other reactions are discussed. 相似文献
68.
Jungyeob Ham 《Tetrahedron letters》2005,46(39):6683-6686
A new synthesis of an agonist for the peroxisome proliferator-activated receptor δ (PPARδ) GW501516 as a potential antiobesity drug is described. The synthetic route involves the in situ protection of the phenol group with a Grignard reagent and a regio-controlled one-pot reaction for the formation of a sulfide bond as the key step. Starting from commercially available 4-iodo-2-methylphenol, this approach affords GW501516 with an overall yield of 87%. 相似文献
69.
S. I. Oshevski 《Russian Chemical Bulletin》2002,51(7):1171-1176
The possibility of specific cleavage of a single-stranded DNA fragment due to cooperative action of two oligonucleotide derivatives bearing chemical groups (at the 3"-phosphate and 5"-thiophosphate ends, respectively) located close to each other in a complementary complex is demonstrated. 相似文献
70.
本文综述了近年来不对称Diels-Alder反应中手性催化剂研究的进展,对各类手性催化剂的性能和特点作了简要介绍. 相似文献