全文获取类型
收费全文 | 5153篇 |
免费 | 196篇 |
国内免费 | 35篇 |
专业分类
化学 | 3345篇 |
晶体学 | 17篇 |
力学 | 148篇 |
数学 | 882篇 |
物理学 | 992篇 |
出版年
2023年 | 43篇 |
2022年 | 67篇 |
2021年 | 97篇 |
2020年 | 115篇 |
2019年 | 126篇 |
2018年 | 91篇 |
2017年 | 96篇 |
2016年 | 182篇 |
2015年 | 107篇 |
2014年 | 153篇 |
2013年 | 266篇 |
2012年 | 331篇 |
2011年 | 409篇 |
2010年 | 243篇 |
2009年 | 175篇 |
2008年 | 301篇 |
2007年 | 370篇 |
2006年 | 304篇 |
2005年 | 235篇 |
2004年 | 213篇 |
2003年 | 173篇 |
2002年 | 142篇 |
2001年 | 61篇 |
2000年 | 62篇 |
1999年 | 71篇 |
1998年 | 50篇 |
1997年 | 61篇 |
1996年 | 56篇 |
1995年 | 40篇 |
1994年 | 32篇 |
1993年 | 38篇 |
1992年 | 46篇 |
1991年 | 23篇 |
1990年 | 19篇 |
1989年 | 30篇 |
1988年 | 26篇 |
1987年 | 17篇 |
1986年 | 20篇 |
1985年 | 34篇 |
1984年 | 28篇 |
1983年 | 15篇 |
1982年 | 24篇 |
1981年 | 36篇 |
1980年 | 32篇 |
1979年 | 21篇 |
1978年 | 33篇 |
1977年 | 22篇 |
1976年 | 23篇 |
1975年 | 14篇 |
1974年 | 19篇 |
排序方式: 共有5384条查询结果,搜索用时 15 毫秒
941.
942.
Erik Heigel 《Nachrichten aus der Chemie》2000,48(2):194-195
Im November 1999 fand im Biozentrum der Johann Wolfgang Goethe Universität in Frankfurt a.M. die Erste Frankfurter Kontaktbörse statt. Die JCF‐Regionalgruppe Frankfurt a.M. hatte sie zusammen mit dem Hochschulteam des Arbeitsamtes Frankfurt and der Fachschaft Biologie der Frankfurter Universität organisiert und durchgeführt. 相似文献
943.
Jianrong Feng Mitchell A. Winnik Alex Siemiarczuk 《Journal of Polymer Science.Polymer Physics》1998,36(7):1115-1128
Immiscible polymer blend films were formed by air drying aqueous dispersions containing mixtures of a high-Tg latex, poly(methyl methacrylate), and a film-forming low-Tg latex, poly(butyl methacrylate-co-butyl acrylate). Fluorescence energy transfer experiments were used to characterize the interfaces in these films, in which one component was labeled with a donor dye and the other with an acceptor. The quantum efficiency of energy transfer (ΦET) between the donors and acceptors is influenced by the interfacial contact area between the two polymer phases. As the amount of soft component in the blend is increased, ΦET approaches an asymptotic value, consistent with complete coverage of the hard polymer surface with soft polymer. This limiting extent of energy transfer is very sensitive to the total surface area in the film, with correspondingly more energy transfer at constant volume fraction for small hard particles. Some of the details of the energy transfer are revealed through a fluorescence lifetime distribution analysis. The presence of ionic surfactant (sodium dodecyl sulfate) in the dispersion from which the latex blend film is prepared reduces the cross-boundary energy transfer by 30%, which implies that in these films the surfactant decreases the interfacial contact. After annealing the surfactant-free blends above 100°C, we observe an increase in energy transfer, consistent with a broader interface between the two polymers. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1115–1128, 1998 相似文献
944.
Chunlin Zhou Erik K. Hobbie B. J. Bauer Charles C. Han 《Journal of Polymer Science.Polymer Physics》1998,36(15):2745-2750
Deuterium-labeled polystyrene modified by random distributions of the comonomer p-(1,1,1,3,3,3-hexaflouro-2-hydroxyisopropyl)-α-methyl-styrene [DPS(OH)] has been blended with poly(butyl methacrylate) (PBMA) and studied with small-angle neutron scattering (SANS). Miscibility is induced via hydrogen bonding between the DPS(OH) hydroxyl group and PBMA carbonyl groups. The data suggest that the nature of the miscible-phase structure in these blends differs from that of the usual homopolymer blends at small scattering angles, which we attribute to the short-range site specific nature of the hydrogen bond interaction. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2745–2750, 1998 相似文献
945.
946.
947.
VladimirN. Barai AnatoliI. Zinchenko LudmillaA. Eroshevskaya ElenaV. Zhernosek Erik DeClercq IgorA. Mikhailopulo 《Helvetica chimica acta》2002,85(7):1893-1900
9‐(3‐Deoxy‐β‐D ‐erythro‐pentofuranosyl)‐2,6‐diaminopurine ( 6 ) was synthesized by an enzymatic transglycosylation of 2,6‐diaminopurine ( 2 ) with 3′‐deoxycytidine ( 1 ) as a donor of 3‐deoxy‐D ‐erythro‐pentofuranose moiety. This transformation comprises i) deamination of 1 to 3′‐deoxyuridine ( 3 ) under the action of whole cell (E. coli BM‐11) cytidine deaminase (CDase), ii) the phosphorolytic cleavage of 3 by uridine phosphorylase (UPase) giving rise to the formation of uracil ( 4 ) and 3‐deoxy‐α‐D ‐erythro‐pentofuranose‐1‐O‐phosphate ( 5 ), and iii) coupling of the latter with 2 catalyzed by whole cell (E. coli BMT‐4D/1A) purine nucleoside phosphorylase (PNPase). Deamination of 6 by adenosine deaminase (ADase) gave 3′‐deoxyguanosine ( 7 ). Treatment of 6 with NaNO2 afforded 9‐(3‐deoxy‐β‐D ‐erythro‐pentofuranosyl)‐2‐amino‐6‐oxopurine (3′‐deoxyisoguanosine; 8 ). Schiemann reaction of 6 (HF/HBF4+NaNO2) gave 9‐(3‐deoxy‐β‐D ‐erythro‐pentofuranosyl)‐2‐fluoroadenine ( 9 ). 相似文献
948.
Alessandro Dondoni Alessandro Massi Erik Minghini Valerio Bertolasi 《Helvetica chimica acta》2002,85(10):3331-3348
The use of glycosylated reagents in Hantzsch‐type cyclocondensation reactions leading to C‐glycosylated dihydropyridines (DHPs) has been investigated. A three‐component approach with an anomeric sugar aldehyde (galacto, manno, and ribo derivatives), a β‐keto ester, and an aminocrotonate afforded C(4)‐glycosylated DHPs in high yield (70–90%). A two‐component cyclocondensation approach based on different glycosylated β‐amino acrylates (sugar enamines) and an enone derived from the Knoevenagel condensation between benzaldehyde and ethyl acetoacetate was followed for the preparation of C(6)‐glycosylated 4‐phenyl‐substituted DHPs in fair yields (60–70%). The latter compounds were obtained as mixtures of diastereoisomers owing to the asymmetric induction of the sugar moiety in the formation of the C(4)‐stereogenic center of the DHP ring. The diastereomer excess of the major products varied from 30 to 60%. The structure of selected compounds was determined by X‐ray crystallography and by chiroptical measurements. The two‐component cyclocondensation method was also employed for the preparation of a C(6)‐ribofuranosyl‐containing analogue of the well‐known hypotensive agent nifedipine. 相似文献
949.
950.