全文获取类型
收费全文 | 629篇 |
免费 | 17篇 |
国内免费 | 1篇 |
专业分类
化学 | 514篇 |
晶体学 | 5篇 |
力学 | 7篇 |
数学 | 25篇 |
物理学 | 96篇 |
出版年
2023年 | 3篇 |
2022年 | 3篇 |
2021年 | 9篇 |
2020年 | 11篇 |
2019年 | 8篇 |
2018年 | 8篇 |
2017年 | 8篇 |
2016年 | 13篇 |
2015年 | 9篇 |
2014年 | 16篇 |
2013年 | 31篇 |
2012年 | 39篇 |
2011年 | 40篇 |
2010年 | 23篇 |
2009年 | 26篇 |
2008年 | 42篇 |
2007年 | 46篇 |
2006年 | 34篇 |
2005年 | 32篇 |
2004年 | 41篇 |
2003年 | 29篇 |
2002年 | 19篇 |
2000年 | 9篇 |
1999年 | 6篇 |
1998年 | 9篇 |
1997年 | 3篇 |
1996年 | 8篇 |
1995年 | 8篇 |
1994年 | 13篇 |
1993年 | 5篇 |
1992年 | 9篇 |
1990年 | 3篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1973年 | 4篇 |
1972年 | 3篇 |
1970年 | 2篇 |
1969年 | 2篇 |
1968年 | 3篇 |
1964年 | 3篇 |
1928年 | 2篇 |
1910年 | 2篇 |
1909年 | 2篇 |
1885年 | 2篇 |
排序方式: 共有647条查询结果,搜索用时 906 毫秒
591.
Zenjiro Osawa Takao Kimura Yoshitaka Ogiwara Noriyuki Matsubayashi 《Journal of polymer science. Part A, Polymer chemistry》1971,9(7):2039-2049
Polymerization of methyl methacrylate with Grignard reagent in toluene–dioxane mixed solvent was carried out under ultrasonic irradiation. The effects of ultrasonic irradiation and the order of catalyst addition on Grignard reagent and the microstructure in the reacting sites were examined on the basis of the stereoregularity of polymers and oligomers produced. The formation of oligomers was also discussed on the basis of the consumption of initiator. The stereoregularity of the polymers in series A (no ripening of catalyst with solvent) is higher than that in series B (ripening of catalyst with solvent). The effect of ultrasonic irradiation on the stereoregularity was completely reversed in series A and B; it increased in the former and decreased in the latter with ultrasonic irradiation. Similar results were obtained for the stereoregularity of the oligomers, but the stereoregularity of the oligomers was lower than that of polymers. 相似文献
592.
Jianhua Liu Yoshitaka Masuda Eiichi Sekido Shin-Ichi Wakida Kazuo Hiiro 《Analytica chimica acta》1989
An ion-selective coated-wire/field-effect transistor electrode responding to dihydrogenphosphate is described. The device consists of a coated-platinum wire electrode connected to the gate of a conventional field-effect transistor. Cobalt phthalocyanine is used as ion-exchange electroactive substance and poly(vinyl chloride) as the membrane matrix. The characteristics of the device are investigated and its response is studied by two methods, the linear dependence of the square root of the drain current in the saturated region on the logarithm of ion activity for sodium dihydrogenphosphate, and the dependence of the gate-source potential on the logarithm of ion activity of the same ion. A linear response is obtained in the range of ion activity 10?5-10?1 mol dm?3 and the response slope is 45 mV per decade change of H2PO4? ion activity; the selectivity coefficients are discussed. 相似文献
593.
Tadashi Ii Yoko Ohashi Yuji Matsuzaki Tomoya Ogawa Yoshitaka Nagai 《Journal of mass spectrometry : JMS》1993,28(11):1340-1344
The structural characterization of large synthetic oligosaccharides and related glycoconjugates performed by the use of electrospray ionization mass spectrometry (ESIMS) is described. The largest molecules described here are unprotected and protected pentaantennary pentacosasaccharides 2 and 5 with average molecular masses of 4441 and 9416, respectively. The straight-chain neutral ceramide decasaccharide (d18:1/c24:0) 6 and the disialoganglioside GD2 (d18:1/c24:0) 7 were also successfully analyzed by ESIMS. In addition to exact mass determination, collision-induced dissociation (CID) spectrometry of these compounds provided saccharide chain sequence information. 相似文献
594.
595.
Nishida H Miyazaki Y Mukaihira T Shimada H Suzuki K Saitoh F Mizuno M Matsusue T Okamoto A Hosaka Y Matsumoto M Ohnishi S Mochizuki H 《Chemical & pharmaceutical bulletin》2004,52(4):459-462
Compounds containing an ethylenediamine structure in place of the piperazine ring of M55113 (1) and M55551 (2) were synthesized to investigate the effects of a piperazine moiety and evaluated for activity as factor Xa (FXa) inhibitors. Most such compounds, however, exhibited lower activity (1/10-1/100) than that of M55113 and M55551 as FXa inhibitors. 相似文献
596.
Susumu Iwabuchi Takayuki Nakahira Yoshitaka Fukushima Osamu Saito Kuniharu Kojima 《Journal of polymer science. Part A, Polymer chemistry》1981,19(3):785-793
Macroreticular redox resins with hydroquinone and catechol units as pendant groups were prepared by the Friedel-Crafts reaction of macroreticular styrene/divinylbenzene copolymer with 2,5- and 3,4-dimethoxybenzyl chlorides, followed by removal of the methyl groups with hydrobromic acid. The redox capacity of the macroreticular resins was determined by oxidation of hydrazobenzene with resins in oxidized form. Resins with 1,4-benzoquinone units were capable of oxidizing hydrazobenzene, whereas those with 1,2-benzoquinone (catechol quinone) units exhibited no apparent oxidative ability; this seems to be due to a complex formation between azobenzene and the catechol units in the reduced resins. Adsorption of metallic ions onto catechol-containing resins showed a high selectivity for Hg2+ ion. The effects of pH, reaction time, and ion concentration on the adsorption were also studied. 相似文献
597.
The chemically modified silica, obtained by reacting 2-mercaptobenz-imidazole with 3-chloropropyl silica gel, was used to adsorb Cu(II), Zn(II), Cd(II) and Pb(II) from aqueous solutions at various pH. Between pH 3–5, the order of selectivity was Hg(II) > Cd(II) Cu(II) Zn(II) Pb(II). Under batch conditions retentions of 100% were achieved for all metals except for Pb(II) where 93% was attained. Under column conditions recoveries of 100% were obtained for all metals. 相似文献
598.
Lilian L. Lorencetti Yoshitaka Gushikem Lauro T. Kubota Graciliano de Oliveira Neto João R. Fernandes 《Mikrochimica acta》1995,117(3-4):239-244
A potentiometric sensor for the perchlorate anion was developed by mixing chemically modified silicagel with pyridinium perchlorate, with an epoxy polymer and graphite. The electrode showed Nernstian response between 1.0 × 10–2 and 1.0 × 10–3
M perchlorate concentrations. The electrode showed high selectivity to this ion at solutions pH between 5.5 and 8.0. The presence of IO
4
–
, NO
3
–
,Br–, IO
3
–
, Cl– and SO
4
2–
ions in the solutions, had only small interference in the electrode response in the range mentioned. 相似文献
599.
Nishida H Mukaihira T Saitoh F Harada K Fukui M Matsusue T Okamoto A Hosaka Y Matsumoto M Shiromizu I Ohnishi S Mochizuki H 《Chemical & pharmaceutical bulletin》2004,52(4):406-412
In the course of development of factor Xa (FXa) inhibitor in an investigation involving the synthesis of 1-arylsulfonyl-3-piperazinone derivatives, we found new compounds containing a unique spiro skeleton. Among such compounds, (-)-7-[(6-chloro-2-naphthalenyl)sulfonyl]tetrahydro-8a-(methoxymethyl)-1'-(4-pyridinyl)-spiro[5H-oxazolo[3,2-a]pyrazine-2(3H),4'-piperidin]-5-one (28, M55529) had activity more favorable than those of previously reported compounds. The inhibitory activity of M55529 for FXa is IC(50)=2 nM, with high selectivity for FXa over thrombin and trypsin. 相似文献
600.
Molecular structures of diffusible amyloid intermediates, commonly observed in misfolding of amyloid proteins into fibrils, have attracted broad interest because the intermediates may be potent neurotoxins responsible for amyloid diseases such as Alzheimer's disease (AD) and because the intermediate structures provide an experimental basis for defining the misfolding pathway. However, owing to the intrinsically unstable and noncrystalline nature of the systems, traditional approaches such as X-ray crystallography and solution NMR have been ineffective for elucidating molecular-level structures of the amyloid intermediates. We present a novel approach using solid-state NMR (SSNMR) that permitted the first site-resolved structural measurement of an intermediate species in fibril formation for a 40-residue Alzheimer's beta-amyloid peptide, Abeta(1-40). In this approach, we combined detection of conformation and morphology changes by fluorescence spectroscopy and electron microscopy and quantitative structural examination for freeze-trapped intermediates by SSNMR. The results provide the initial evidence that a spherical amyloid intermediate of 15-30 nm in diameter exists prior to fibril formation of Abeta(1-40) and that the intermediate involves well-ordered beta-sheets in the C-terminal and hydrophobic core regions. The SSNMR-based approach presented here could be applied to intermediate species of diverse amyloid proteins. 相似文献