全文获取类型
收费全文 | 2565篇 |
免费 | 108篇 |
国内免费 | 16篇 |
专业分类
化学 | 2097篇 |
晶体学 | 24篇 |
力学 | 28篇 |
数学 | 88篇 |
物理学 | 452篇 |
出版年
2023年 | 11篇 |
2022年 | 15篇 |
2021年 | 24篇 |
2020年 | 33篇 |
2019年 | 40篇 |
2018年 | 32篇 |
2017年 | 25篇 |
2016年 | 61篇 |
2015年 | 49篇 |
2014年 | 62篇 |
2013年 | 111篇 |
2012年 | 119篇 |
2011年 | 185篇 |
2010年 | 89篇 |
2009年 | 98篇 |
2008年 | 187篇 |
2007年 | 178篇 |
2006年 | 178篇 |
2005年 | 144篇 |
2004年 | 147篇 |
2003年 | 123篇 |
2002年 | 102篇 |
2001年 | 30篇 |
2000年 | 40篇 |
1999年 | 43篇 |
1998年 | 37篇 |
1997年 | 26篇 |
1996年 | 32篇 |
1995年 | 16篇 |
1994年 | 23篇 |
1993年 | 22篇 |
1992年 | 22篇 |
1991年 | 12篇 |
1990年 | 15篇 |
1989年 | 14篇 |
1988年 | 17篇 |
1987年 | 21篇 |
1985年 | 23篇 |
1984年 | 29篇 |
1983年 | 18篇 |
1982年 | 32篇 |
1981年 | 24篇 |
1980年 | 12篇 |
1979年 | 23篇 |
1978年 | 16篇 |
1977年 | 11篇 |
1975年 | 12篇 |
1974年 | 16篇 |
1973年 | 18篇 |
1967年 | 13篇 |
排序方式: 共有2689条查询结果,搜索用时 15 毫秒
61.
62.
Reaction of α-nitro olefins with secondary amines in the presence of palladium(O) catalyst affords allylic amines. 相似文献
63.
Masao Ikeda Takashi Nakamura Yu Nagase Koji Ikeda Yoshiro Sekine 《Journal of polymer science. Part A, Polymer chemistry》1981,19(10):2595-2607
For the purpose of studying the mechanism of thermal degradation of poly[(tetramethyl-p-silphenylene) Siloxane] (poly TMPS) a series of polymers with silphenylene and siloxane bonds in the main chain were prepared and subjected to thermogravimetry (TG) and pyrolysis study. Analyses of products from poly TMPS degradation (in vacuum at a constant temperature) by gas chromatography (GC), infrared (IR), nuclear magnetic resonance (NMR) spectroscopy, and gas chromatography-mass spectrometry (GC–MS) revealed that degradation occurs at the silphenylene bonds. The TG curves obtained in He for heating rates of 1,2,2.5,7.5, and 10°C/min were analyzed by the Ozawa method; activation energies of 39 ± 1 and 45 ± 2 kcal/mol were obtained respectively for the initial cleavage of the methyl side group and the later-stage scission of the main-chain silphenylene bond which leads to a major weight loss. The results agree with those obtained for other structurally similar polymers. 相似文献
64.
Koji Ishizu Satoru Minematsu Takashi Fukutomi 《Journal of polymer science. Part A, Polymer chemistry》1990,28(5):1091-1099
We have studied the structural changes on poly(2-hydroxyethyl methacrylate) (PHEMA)/polystyrene (PS) blends by means of phase growth of microheterophase pattern on a template surface composed of poly[2-hydroxyethyl methacrylate (HEMA)-g-styrene (S)] graft copolymer (lamellar shape). The PS macromonomer was synthesized by free radical polymerization of S monomer initiated by a functional initiator [2,2'-azobis(2-(2-imidazolin-2-yl)propane: VA-061] in the presence of a degradative chain transfer agent, followed by an end-capping reaction with p-chloromethylstyrene (CMS). Poly(HEMA-g-S) graft copolymers were prepared by free radical copolymerization of these vinylbenzyl-terminated PS macromonomers with HEMA comonomer. 相似文献
65.
Koji Konomi He-Sheng Li† Norihito Kuno Masaki Furuya‡ 《Photochemistry and photobiology》1993,58(6):852-857
Abstract Treatment of imbibed embryonic axes taken from seeds of Pisum sativum with N-phenylimide S-23142, a herbicide that has been suggested to inhibit protoporphyrin synthesis, or with N -methyl mesoporphyrin IX, an inhibitor of the iron chelatase for heme, resulted in a significant decrease in the amount of spectrophotometrically detectable phytochromc in the axes in both cases. However, the amount of immunochemically detectable phytochrome was not affected by either treatment. If S-23142 inhibits the synthesis of protoporphyrin IX in pea, it appears that the conversion of protoporphyrinogen IX to protoporphyrin IX is involved in the biosynthesis of the phytochrome chromophore. The conversion of protoporphyrin IX to heme (Fe-protoporpbyrin) also appears to be a step in the biosynthesis of the chromophore, since N -methyl mesoporphyrin IX prevented the synthesis of spectrophotometrically detectable phytochrome but did not affect the magnesium chelatase activity required for the synthesis of chlorophyll in pea embryonic axes. The results suggest that protoporphyrinogen IX, protoporphyrin IX and heme are intermediates in the biogenesis of the phytochromc chromophore. The pathway to phytochromobilin might become fixed after protoporphyrin IX, being directed toward the Fe branch for heme rather than to the Mg branch for chlorophyll. 相似文献
66.
Poly(ethylene oxide-)-poly(1, 1-dimethyl-2, 2-dihexyldisilene) block copolymers (PEO-b-PMHS) were synthesized by the anionic polymerization of masked disilenes initiated with the potassium alkoxide of poly(ethylene glycol). The block copolymer self-assembled into polymer micelles in water accompanied by a transition in the polysilane conformation. 相似文献
67.
Hiroji Fukui Mitsuo Sawamoto Toshinobu Higashimura 《Journal of polymer science. Part A, Polymer chemistry》1994,32(14):2699-2708
Telechelic ( 8 ) and end-functionalized four-arm star polymers ( 9 ) were synthesized through the coupling reactions of end-functionalized living poly(isobutyl vinyl ether) ( 5; DP n ~ 10) with the bi-and tetrafunctional silyl enol ethers, H4-nC? [CH2OC6H4C(OSiMe3) = CH2]n ( 3: n = 2; 4: n = 4). The precursor polymers 5 were prepared by living cationic polymerization with functionalized initiators, CH3CH(Cl)OCH2CH2X(6), in conjunction with zinc chloride in methylene chloride at ?15°C. The initiators 6 were obtained by the addition of hydrogen chloride gas to vinyl ethers bearing pendant functional groups X , including acetoxy [? OC(O)CH3], styryl (? OCH2C6H4-p-CH = CH2), and methacryloyl [? OC(O)C(CH3) = CH2]. The coupling reactions with 3 and 4 in methylene chloride at ?15°C for 24 h afforded the end-functionalized multiarmed polymers ( 8 and 9 ) in high yield (>91%), where those with styryl or methacryloyl groups are new multifunctional macromonomers. © 1994 John Wiley & Sons, Inc. 相似文献
68.
Meso and racemic isomers of 1,1′-bis(α-hydroxyalkyl)ferrocene derivatives, and trans and cis isomers of 7-oxa[3]ferrocenophanes have been isolated. The configurations of these isomers have been determined both by spectroscopy and from their reaction behavior. It has been found that the ring-closure and ring-opening interconversion reactions between 1,1′-bis(α-hydroxyalkyl)ferrocenes and 7-oxa[3]ferrocenophanes are stereospecific. PMR spectra of the diols and ethers have been examined at 100 MHz in CF3COOH, and the existence of α-[1′-(α-hydroxyalkyl)ferrocenyl]carbonium ions has been demonstrated in this acid. A mechanism for the various interconversion reactions is proposed on the basis of their stereospecific reactivity and from the PMR spectra of the carbonium ions. 相似文献
69.
Koji Kano Hirofumi Kawazumi Teiichiro Ogawa Junzo Sunamoto 《Chemical physics letters》1980,74(3):511-514
Fluorescence quenching of pyrene and pyrenedecanoic acid by various kinds of anilines has been studied in dipalmitoylphosphatidylcholine liposomes in gel phases. N,N-dimethylaniline and p-isopropyl-N,N-dimethylaniline caused anisotropic diffusional quenching, while N,N-dicetylaniline, a less mobile quencher, predominantly caused static quenching. These data suggested the location sites of both pyrenes and anilines in the membranes. 相似文献
70.
Calculation using CNDO/2 method have been performed for the crown ethers and their cation complexes. The photoelectron spectra of 18-crown-6 and 12-crown-4 are well described by the present MO calculations. The orbital interactions between the crown ligand and the cation indicate the importance of the charge transfer interaction for the complex formation. The destabilization energy due to the ring-shrinking (~ 0.5 eV) is very small compared with the complexation energy (5–8 eV). The stability of the complex was reasonably explained by the considering the hydrated species of the cation and the complex, indicating the important role of the solvation effect in the selectivity of the crown ether to the cation. 相似文献