全文获取类型
收费全文 | 1478篇 |
免费 | 25篇 |
国内免费 | 4篇 |
专业分类
化学 | 1153篇 |
晶体学 | 9篇 |
力学 | 6篇 |
数学 | 53篇 |
物理学 | 286篇 |
出版年
2022年 | 18篇 |
2021年 | 19篇 |
2020年 | 15篇 |
2019年 | 20篇 |
2018年 | 17篇 |
2017年 | 13篇 |
2016年 | 18篇 |
2015年 | 16篇 |
2014年 | 16篇 |
2013年 | 54篇 |
2012年 | 53篇 |
2011年 | 74篇 |
2010年 | 45篇 |
2009年 | 40篇 |
2008年 | 84篇 |
2007年 | 85篇 |
2006年 | 70篇 |
2005年 | 75篇 |
2004年 | 79篇 |
2003年 | 48篇 |
2002年 | 50篇 |
2001年 | 24篇 |
2000年 | 31篇 |
1999年 | 23篇 |
1998年 | 19篇 |
1997年 | 24篇 |
1996年 | 12篇 |
1995年 | 12篇 |
1994年 | 18篇 |
1993年 | 22篇 |
1992年 | 26篇 |
1991年 | 26篇 |
1990年 | 30篇 |
1989年 | 29篇 |
1988年 | 26篇 |
1987年 | 17篇 |
1986年 | 15篇 |
1985年 | 27篇 |
1984年 | 24篇 |
1983年 | 14篇 |
1982年 | 22篇 |
1981年 | 16篇 |
1980年 | 9篇 |
1979年 | 24篇 |
1978年 | 13篇 |
1977年 | 15篇 |
1976年 | 18篇 |
1975年 | 14篇 |
1973年 | 6篇 |
1968年 | 6篇 |
排序方式: 共有1507条查询结果,搜索用时 15 毫秒
11.
Tsuyoshi Miura Satoshi Tsujino Kohtaro Goto Midori Noguchi Manabu Node Nobuyuki Imai 《Tetrahedron》2005,61(27):6518-6526
The use of the bisfluorous chain-type propanoyl (Bfp) group as a fluorous protective group made it possible to rapidly synthesize the Gb2 and Gb3 oligosaccharide derivatives by a simple fluorous-organic extraction purification. Furthermore, the fluorescence-labeled Gb2 and Gb3 oligosaccharides were prepared as a potential Vero Toxins detecting reagent. 相似文献
12.
13.
Yoshitane Imai Kakuhiro Kawaguchi Tomohiro Sato Michiya Fujiki Yoshio Matsubara 《Tetrahedron letters》2007,48(16):2927-2930
By using (1R,2R)-1,2-diphenylethylenediamine as a chiral molecule and 2-anthracenecarboxylic acid as a fluorescent molecule, we created a chiral supramolecular organic fluorophore having circularly polarized luminescence properties in the solid-state. 相似文献
14.
Yoshio Imai N. N. Maldar Masa-Aki Kakimoto 《Journal of polymer science. Part A, Polymer chemistry》1984,22(9):2189-2196
2,5-Bis(4-aminophenyl)-3,4-diphenylthiophene, a polyimide-forming monomer, was prepared in three steps starting from benzyl chloride and sulfur. Novel polyimides were synthesized from the diamine and pyromellitic dianhydride or 3,3′, 4,4′-benzophenonetetracarboxylic dianhydride (BTDA). Polymerization was carried out either by the usual two-step procedure that included ring-opening polyaddition giving polyamic acids, followed by cyclodehydration to polyimides, or by the direct one-pot procedure involving cyclodehydration in situ. The polyimide derived from the diamine and BTDA, especially that prepared by the one-pot procedure in m-cresol containing isoquinoline, is soluble in various organic solvents and gave a yellow, transparent, tough, and flexible film. Solubility of this polyimide varied by the preparative method and by the copolymerization with bis(4-aminophenyl) ether. All the polyimides are highly thermally stable and exhibited no appreciable decomposition up to 450°C in air and nitrogen atmospheres. 相似文献
15.
Synthesis and analgesic activity of novel heterocycles, [1]benzothiopyrano[3,4-b]pyrrole derivatives
M Hori T Kataoka H Shimizu E Imai N Iwata N Kawamura M Kurono K Nakano M Kido 《Chemical & pharmaceutical bulletin》1989,37(5):1282-1286
In order to develop analgesic compounds possessing a sulfur atom in the alicyclic ring, novel cis-fused heterocycles, [1]benzothiopyrano[3,4-b]pyrrole derivatives (II) were synthesized via a unique cyclization reaction starting from 4-(4-methoxyphenylthio)-2-butanone (1) or 6-methoxy-3,4-dihydro-2H-1-benzothiopyran-4-one (7). The analgesic effects of benzothiopyranopyrroles (16, 18) were measured by means of the writhing test. The phenolic derivative 18 completely inhibited the appearance of writhing at the dose of 50 mg/kg, but the methoxy derivative 16 had no analgesic effect. 相似文献
16.
Soto-Chinchilla JJ Gámiz-Gracia L García-Campaña AM Imai K García-Ayuso LE 《Journal of chromatography. A》2005,1095(1-2):60-67
The determination of seven sulfonamides by means of HPLC with chemiluminescence detection is proposed for the first time. The analytes are derivatized with fluorescamine, separated and subsequently they participate in the post-column chemiluminescence (CL) peroxyoxalate system using imidazole as a catalyst. Among the different peroxyoxalates tested, bis[4-nitro-2-(3,6,9-trioxadecyloxycarbonyl)phenyl] oxalate provides higher sensitivities and stabilities, avoiding precipitation problems. A rigorous optimization of the significant variables by means of experimental designs has been developed in order to reconcile the chromatographic conditions with the CL reaction. The method provides detection limits in the low microgl(-1) range and has been satisfactorily applied to the analysis of spiked raw milk samples. 相似文献
17.
Mitsuru Ueda Akira Sato Yoshio Imai 《Journal of polymer science. Part A, Polymer chemistry》1979,17(3):783-787
Catalytic actions of various additives were studied in the polycondensation of di(4-nitrophenyl) isophthalate with bis(4-aminophenyl) ether in N-methyl-2-pyrrolidone, and 1-hydroxybenzotriazole (HOBt) was found to be a highly effective catalyst that yielded high-molecular-weight polyamide. In addition to the polycondensation of the 4-nitrophenyl ester, the polymerization of negatively substituted phenyl esters like di(2,4,5-trichlorophenyl) isophthalate was also accelerated by HOBt. For the HOBt-catalyzed aminolysis of esters a bifunctional concerted mechanism that involves an eight-membered transition state was proposed. 相似文献
18.
Bile acids, such as cholic, chenodeoxycholic, deoxycholic, lithocholic and ursodeoxycholic acids, were allowed to react with hexafluoroisopropanol and tri-fluoracetic anhydride at 37 for 30 min. The resulting derivatives were gas chromatographed on QF-1, with flame ionization detection, and were identified by gas chromatography-mass spectrometry. Separation was good. By using this method, these acids were detected in samples of human duodenal fluid; the ratios of each were 24.4, 41.5, 24.9, 2.3 and 6.9%, respectively. 相似文献
19.
The reaction of the dianion of phenylsulfinylacetone with alkyl halides afforded beta-keto sulfoxides, which were first chlorinated with hexachloroethane and then treated successively with KH and t-BuLi to give carboxylic acids in three-steps in moderate overall yields from the alkyl halides. This procedure affords a good method for a synthesis of carboxylic acids from alkyl halides with three-carbon elongation. 相似文献
20.
The characteristic fragment ions and visualization of cationic starches on pulp fiber using ToF‐SIMS
Yasuyuki Matsushita Takuya Sekiguchi Kaori Saito Toshiyuki Kato Takanori Imai Kazuhiko Fukushima 《Surface and interface analysis : SIA》2007,39(6):501-505
Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) was used to investigate the distribution of cationic starch on pulp fiber. To identify the characteristic fragment ions of the cationic starches, deuterium‐labeled cationic starches were prepared and analyzed using ToF‐SIMS. The starch 2‐hydroxypropyltrimethylammonium chloride derivative generated characteristic fragments at m/z 58 and 59, which were identified as [H2C?N(CH3)2]+ and [N(CH3)3]+·, respectively. The fragmentation patterns were also suggested. From the imaging analysis, the adsorption of the cationic starch on fibers was uneven on individual fibers, as well as between fibers. This may have been on account of fiber morphology and structure. On examining scanning electron microscope (SEM) images, the quaternary ammonium starch derivative (QS) did not penetrate the fiber. No migration of cationic starch was observed under various drying conditions. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献