全文获取类型
收费全文 | 3061篇 |
免费 | 127篇 |
国内免费 | 14篇 |
专业分类
化学 | 2394篇 |
晶体学 | 48篇 |
力学 | 25篇 |
数学 | 120篇 |
物理学 | 615篇 |
出版年
2023年 | 13篇 |
2022年 | 19篇 |
2021年 | 24篇 |
2020年 | 32篇 |
2019年 | 34篇 |
2018年 | 30篇 |
2017年 | 24篇 |
2016年 | 56篇 |
2015年 | 60篇 |
2014年 | 71篇 |
2013年 | 154篇 |
2012年 | 175篇 |
2011年 | 196篇 |
2010年 | 123篇 |
2009年 | 129篇 |
2008年 | 181篇 |
2007年 | 202篇 |
2006年 | 195篇 |
2005年 | 196篇 |
2004年 | 146篇 |
2003年 | 163篇 |
2002年 | 141篇 |
2001年 | 39篇 |
2000年 | 34篇 |
1999年 | 46篇 |
1998年 | 23篇 |
1997年 | 37篇 |
1996年 | 50篇 |
1995年 | 17篇 |
1994年 | 25篇 |
1993年 | 21篇 |
1992年 | 34篇 |
1991年 | 22篇 |
1990年 | 15篇 |
1989年 | 16篇 |
1988年 | 14篇 |
1987年 | 14篇 |
1986年 | 17篇 |
1985年 | 56篇 |
1984年 | 58篇 |
1983年 | 16篇 |
1982年 | 45篇 |
1981年 | 44篇 |
1980年 | 37篇 |
1979年 | 31篇 |
1978年 | 25篇 |
1977年 | 16篇 |
1976年 | 20篇 |
1975年 | 12篇 |
1974年 | 16篇 |
排序方式: 共有3202条查询结果,搜索用时 328 毫秒
111.
Kazuyoshi Yano Hiroshi Yoshitake Uwe T. Bornscheuer Rolf D. Schmid Kazunori Ikebukuro Kenji Yokoyama Yuzo Masuda Isao Karube 《Analytica chimica acta》1997,340(1-3):41-48
Piezoelectric quartz crystal sensors were developed using lipids with various properties for highly sensitive detection of chemical vapors. Lipids with varying lengths of alkyl chains were coated onto 10 MHz AT-cut quartz crystal resonators and the response of these modified crystals to chemical vapors were measured. It was shown that hydrophilic compounds, such as ethanol and methanol, could be recognized efficiently by lipids having shorter alkyl chains, whereas lipids with longer alkyl chains showed affinity to more hydrophobic vapors, such as toluene, hexane and cyclohexane. Frequency changes caused by adsorption of alcohols could be enhanced when cholesterol was co-immobilized in the lipid layer. To confirm the assumption that the sensor-response might be affected by the properties of lipids derived from acyl chains, we have examined the effects of two types of newly synthesized unusual lipids on sensor response. When lipids having one triple bond each at different positions on their alkyl chains were coated onto quartz crystals separately, lower responses were observed compared to responses obtained for a sensor with immobilized, saturated phosphatidylcholine. Lipids containing -branched acyl chains, however, showed good affinity for organic vapors, and sensor responses improved 4–5-fold. Moreover, these sensors were shown to have sensitivity of the same order as the humans' sense of smell (10−5–10−6 w/w in liquid paraffin) when measured using standard odorants (isovaleric acid, skatole, etc.) for an olfactometry established in Japan. 相似文献
112.
Toru Takagishi Hiroshi Kozuka Nobuhiko Kuroki 《Journal of polymer science. Part A, Polymer chemistry》1983,21(2):447-455
A study was made of the formation of polyion complexes between a piperidinium cationic polymer and polyanions and of the binding of azo-dye anions (methyl, ethyl, propyl, and butyl orange) by these complexes. Sodium poly(acrylate), poly(styrenesulfonate), dextran sulfate, and carboxy-methylcellulose were used as polyanions. The resultant polyion complexes (insoluble in aqueous solutions) were compared for their ability to bind the small organic molecules in aqueous solutions, for example, of urea and an inorganic electrolyte (KCI), and exhibited a strong binding affinity toward these small anions. Polyion complexes that consisted of sodium poly(acrylate), dextran sulfate, and carboxymethylcellulose as polyanions cooperated in the binding, whereas the polyion complex of sodium poly(styrenesulfonate) did not. It was suggested that small organic anions interact with the polyion complexes primarily through electrostatic and hydrophobic forces. 相似文献
113.
Hirata K Suzuki T Noya A Takei I Hidai M 《Chemical communications (Cambridge, England)》2005,(29):3718-3720
The reactions of [Cp*MCl2]2(Cp*=eta5-C5Me5, M = Rh, Ir) with thiacalix[4]arene (TC4A(OH)4) and tetramercaptothiacalix[4]arene (TC4A(SH)4) gave the mononuclear complexes [(Cp*M){eta3-TC4A(OH)2(O)2}] and the dinuclear complexes [(Cp*M)2{eta3eta3-TC4A(S)4}] respectively, while the analogous reactions with dimercaptothiacalix[4]arene (TC4A(OH)2(SH)2) produced the tetranuclear complexes [(Cp*M)2(Cp*MCl2)2-{eta3eta3eta1eta1-TC4A(O)2(S)2}]. 相似文献
114.
Toru Takagishi Katsushige Takami Nobuhiko Kuroki 《Journal of polymer science. Part A, Polymer chemistry》1974,12(1):191-200
The binding of 4′-dibutylaminoazobenzene-4-sulfonate anion (butyl orange) by bovine serum albumin has been examined quantitatively by an equilibrium dialysis method at 5, 10, 15, 20, 25, and 35°C. The first binding constants and the thermodynamic parameters for the formation of the first dye anion-protein complex have been calculated. The peculiar temperature dependence of the first binding constant could be observed. That is, the value of the first binding constant increases with increasing temperature until it reaches a maximum value at approximately 18°C and then decreases with raising temperature. Accordingly, this binding process is exothermic above 18°C and is endothermic below 18°C. Near 18°C the process exhibits athermal reaction. From the thermodynamic data obtained, it is evident that the favorable free energy of the binding is accompanied by an entropy gain and that the enthalpies of the binding vary from a positive (unfavorable) value below 18°C to a negative (favorable) one above 18°C. Furthermore an apparent temperature dependence of the thermodynamic functions was observed. That is, ΔF° becomes larger in absolute magnitude as the temperature increases. The positive quantity of ΔS° tends to decrease with increasing temperature. All these facts can be interpreted satisfactorily in terms of hydrophobic interactions between hydrophobic portions of the dye and nonpolar parts of the albumin. 相似文献
115.
Toshinobu Higashimura Kenji Ebara Sadahito Aoshima 《Journal of polymer science. Part A, Polymer chemistry》1989,27(9):2937-2950
Living cationic polymerizations of two silicon-containing vinyl ethers, 2-(t-butyldimethyl-silyloxyl)ethyl vinyl ether (tBuSiVE) and 2-(trimethylsilyloxyl)ethyl vinyl ether (MeSiVE), have been achieved with use of the hydrogen iodide/iodine (HI/I2) initiating system in toluene at ?15 or ?40°C, despite the existence of the acid-sensitive silyloxyl pendants. The living nature of the polymerizations was demonstrated by linear increases in the number-average molecular weights (M?n) of the polymers in direct proportion to monomer conversion and by their further rise upon addition of a second monomer feed to a completely polymerized reaction mixture. The polymers obtained in these experiments all exhibited very narrow molecular weight distributions (MWD) with M?w/M?n around or below 1.1. Desilylation of the polymers under mild conditions (with H+ for MeSiVE and F? for tBuSiVE) gave poly(2-hydroxyethyl vinyl ether), a water-soluble polyalcohol with a narrow MWD. The living processes also permitted clean syntheses of amphiphilic AB block copolymers and water-soluble methacrylate-type macromonomers, all of which bear narrowly distributed segments of the polyalcohol derived from the silicon-containing vinyl ethers. 相似文献
116.
Keiichi Noguchi Hidekazu Kondo Yasushi Ichikawa Junichiro Washiyama Kenji Okuyama 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(8):o528-o530
The 20‐membered ring of the title compound, C16H24O8, adopts an approximately flat rectangular structure with three‐ and seven‐bond sides and lies across a crystallographic center of inversion. The corners of the ring occur at both ends of one of the planar ester segments. All of the carbonyl O atoms are involved in intermolecular C—H⋯O hydrogen bonds. 相似文献
117.
Carlos Rodríguez-Abreu Massimo Lazzari Dharmesh Varade Masaya Kaneko Kenji Aramaki Manuel Arturo López Quintela 《Colloid and polymer science》2007,285(6):673-680
The structure and rheological properties of a poly(dimethylsiloxane)-graft-poly(oxyethylene) copolymer at high concentrations
in block-selective solvents were studied by small-angle X-ray scattering (SAXS) and rheometry. Analysis of SAXS data indicates
that quasispherical, reverse micellar aggregates (with no ordered packing) are present in concentrated solutions of the copolymer
in nonpolar solvents, and that upon addition of water, the size of such aggregates increases due to the solubilization inside
the micellar cores. The viscosity of concentrated polymer solutions increases exponentially as water is added, and finally,
viscoelastic, gel-like behavior is found in the vicinity of the phase separation limit. It was found that small silver nanoparticles
with an average diameter of ≈3 nm can be synthesized inside the copolymer aggregates without the need of a reducing agent;
namely, particles embedded in a viscoelastic matrix are obtained. The synthesis seems to follow first-order kinetics.
Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users. 相似文献
118.
(2R,5S)-2-Methyl-5-hexanolide and its antipode were synthesized in highly optically pure state (?98–99% e.e.) starting from ethyl (S)-lactate and the enantiomers of methyl β-hydroxyisobutyrate. The specific rotations of our samples were [α]D±91.0-93.5° (CHCl3), while the reported values of the samples prepared by resolution or asymmetric synthesis were ±64.5–65.6°. 相似文献
119.
Both the enantiomers of 2,3-dihydro-2-isopropyl-2,5-dimethylfuran were synthesized employing the Sharpless asymmetric epoxidation reaction. The (R)-(—)-enantiomer of this cyclic enol ether was also synthesized starting from (R)-(—)-linalool. 相似文献
120.
Takeshi Hanamoto Yuhko Iwamoto Kenji Yamada Ryoko Anno 《Journal of fluorine chemistry》2007,128(10):1126-1130
The 1,3-dipolar cycloaddition reaction of fluoro(trimethylsilyl)acetylene prepared in situ with an excess of diazomethane smoothly proceeded to give the corresponding 4-fluoro-5-trimethylsilyl-1H-pyrazole in 84% yield. The copper iodide-catalyzed N-arylation of the fluorinated pyrazole with a variety of aryl iodides afforded N-aryl-4-fluoropyrazoles as desilylation products in good to excellent yields. 相似文献