全文获取类型
收费全文 | 2453篇 |
免费 | 97篇 |
国内免费 | 7篇 |
专业分类
化学 | 1930篇 |
晶体学 | 7篇 |
力学 | 22篇 |
数学 | 305篇 |
物理学 | 293篇 |
出版年
2023年 | 14篇 |
2022年 | 14篇 |
2021年 | 31篇 |
2020年 | 58篇 |
2019年 | 39篇 |
2018年 | 14篇 |
2017年 | 13篇 |
2016年 | 72篇 |
2015年 | 62篇 |
2014年 | 77篇 |
2013年 | 124篇 |
2012年 | 160篇 |
2011年 | 162篇 |
2010年 | 90篇 |
2009年 | 78篇 |
2008年 | 142篇 |
2007年 | 116篇 |
2006年 | 119篇 |
2005年 | 123篇 |
2004年 | 132篇 |
2003年 | 90篇 |
2002年 | 98篇 |
2001年 | 47篇 |
2000年 | 43篇 |
1999年 | 35篇 |
1998年 | 27篇 |
1997年 | 38篇 |
1996年 | 38篇 |
1995年 | 38篇 |
1994年 | 46篇 |
1993年 | 41篇 |
1992年 | 36篇 |
1991年 | 22篇 |
1990年 | 25篇 |
1989年 | 26篇 |
1988年 | 29篇 |
1987年 | 15篇 |
1985年 | 28篇 |
1984年 | 16篇 |
1983年 | 9篇 |
1982年 | 19篇 |
1981年 | 18篇 |
1980年 | 12篇 |
1979年 | 18篇 |
1978年 | 11篇 |
1977年 | 17篇 |
1976年 | 13篇 |
1975年 | 11篇 |
1973年 | 9篇 |
1970年 | 10篇 |
排序方式: 共有2557条查询结果,搜索用时 0 毫秒
61.
Uwe Klingebiel Dietrich Fischer Prof. Dr. Anton Meller 《Monatshefte für Chemie / Chemical Monthly》1975,106(2):459-471
The reaction of aminofluorsilanes of the type (R=H,F) (Me 3Si)2N?SiF2R with two moles of ammonia, or of a mono- or dialkylamine, yields the corresponding amino-compounds, e.g. (Me 3Si)2N?Si(F)R?NH2, (Me 3Si)2N?Si(F)R?NHR′ and (Me 3Si)2N?Si(F)R?NR2′ (R′=Me, Et). Analogous products are obtained by reaction of the aminofluorosilanes with lithium salts of amines with bulky organic substituents in a 1 : 1 molar ratio. Alkoxy- and aryloxyaminofluorosilanes are prepared by the reaction of sodium alcoholates and sodium phenolate with (Me 3Si)2N?Si(F2)R (R=H, C2H3, C2H5, C6H5). The i.r.-, mass-,1H- and19F-NMR spectra of the above compounds are reported. 相似文献
62.
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
63.
Müller U Rätzsch M Schwanninger M Steiner M Zöbl H 《Journal of photochemistry and photobiology. B, Biology》2003,69(2):97-105
The yellowing and IR-changes of spruce wood as a result of UV-irradiation were studied using two different types of xenon lamps (lambda>300 nm; I(o)=50 mW cm(-2) and lambda>280 nm; I(o)=17.5 mW cm(-2)). Changes in the IR spectra as well as the yellowing of the irradiated wood surfaces show the influence of UV light on the wood modules. The UV-irradiation (72 h; lambda>300 nm; I(o)=50 mW cm(-2)) decreased the lignin content on the surface by up to 20% of the original values. The colour difference of yellowing (deltaE) exhibited a systematic trend to higher values with increasing irradiation time. Our results show that the photoyellowing (UV-Vis detection) correlates very well with lignin degradation (IR detection). This result is in agreement with the quinone formation as the chromophoric reaction product of lignin decay. The degradation, yellowing, and oxidation kinetics differed only little using different light sources. The absorbed light intensity, which depends on wavelength, the intensity distribution of the light source and the absorption spectrum of lignin, influenced the degradation rate. Under the current experimental conditions, the absorption spectrum of lignin was the most important factor. Therefore, irradiation with lambda>280 nm is useful for rapidly monitoring the UV-degradation of wood 相似文献
64.
Ostash B Rix U Rix LL Liu T Lombo F Luzhetskyy A Gromyko O Wang C Braña AF Méndez C Salas JA Fedorenko V Rohr J 《Chemistry & biology》2004,11(4):547-555
A 3 kb DNA fragment from the Streptomyces globisporus 1912 landomycin E (LaE) biosynthetic gene cluster (lnd) was completely sequenced. Three open reading frames were identified, lndGT4, lndZ4, and lndZ5, whose probable translation products resemble a glycosyltransferase, a reductase, and a hydroxylase, respectively. Studies of generated mutants from disruption and complementation experiments involving the lndGT4 gene allowed us to determine that LndGT4 controls the terminal L-rhodinose sugar attachment during LaE biosynthesis and that LndZ4/LndZ5 are responsible for the unique C11-hydroxylation of the landomycins. Generation of the novel landomycins F, G, and H in the course of these studies provided evidence for the flexibility of lnd glycosyltransferases toward their acceptor substrates and a basis for initial structure-activity relationships within the landomycin family of antibiotics. 相似文献
65.
Uwe Klingebiel Dieter Bentmann Anton Meller 《Journal of organometallic chemistry》1978,144(3):381-388
Aminofluorsilanes are obtained by the reaction of fluorosilanes with the lithium salts of the corresponding amines. The reaction of aminofluorosilanes with butyllithium in a (2 + 2)cyclo addition reaction leads to the formation of fourmembered silicon-nitrogen ring compounds. The mechanism of the reaction is discussed, the mass, 1H and 19F NMR spectra of the compounds are reported. 相似文献
66.
Uwe Einmahl 《Probability Theory and Related Fields》1992,92(2):177-194
Summary In a previous paper we obtained upper and lower class type results refining the bounded LIL for sums of iid Hilbert space valued mean zero random variables, whose covariance operators satisfy certain regularity assumptions. We now establish precise convergence rates for the bounded LIL in the non-regular case. It turns out that the almost sure behavior in this case is entirely different from the behavior in the previous situation.Supported in part by NSF Grant DMS 90-05804 相似文献
67.
Normen Peulecke Andreas Ohff Wolfgang Baumann Rhett Kempe Vladimir V. Burlakov Uwe Rosenthal 《Journal of organometallic chemistry》1996,520(1-2):235-239
The reaction of Cp2Zr(L)(η2-Me3SiC2) (L = THF, py) with equimolar amounts of H2C = CMe-CHO at room temperature depends strongly on the ligands L and the solvents that are used. With L = THF, in the THF solution the insertion product 1 was isolated, whereas by conducting the reaction in n-hexane solution an alkyne substitution with 1,4-coordination of the methacrolein takes place and the binuclear complex [ 2 was obtained. In conttrast, with L = py (a stronger ligand) only a 1:1 ratio of 1 and 2 was observed in both THF and in n-hexane. At 50°C complex 1 was converted into 2 and the alkyne was eliminated quantitatively.
Complexes 1 and 2 were characterized by IR and NMR spectroscopical measurements and 1 by an additional X-ray structure determination. 相似文献
68.
Fluoro- und aminofluoro-silanes react with the lithium salt of N,O-bis(trimethylsilyl)hydroxylamine under LiF elimination and substitution. Alkyl- and amino-fluorosilanes give O-fluorosilyl-N,N-bis(trimethylsilyl)hydroxylamines, arylfluorosilanes give N-fluorosilyl-N,O-bis(trimethylsilyl)hydroxylamines. By the further reaction of O-difluorosilyl-N,N-bis(trimethylsilyl)hydroxylamine with the lithiated hydroxylamine, O,O′-fluoromethylsilyldi[N,N-bis(trimethylsilyl)hydroxylamine] is formed. On heating N-difluorophenylsilyl-N,O-bis(trimethylsilyl)hydroxylamine di[fluorophenylsilyl(methyl)amino]pentamethylsiloxane is formed by methyl group migration. The NMR and mass spectra of the compounds are reported. 相似文献
69.
Uwe Klingebiel Detlev Enterling Lutz Skoda Anton Meller 《Journal of organometallic chemistry》1977,135(2):167-172
Fluorosilyl substituted cyclosilazanes are formed by treating lithium salts of hexamethylcyclotri- and octa-methylcyclotetrasilazanes with silicon tetrafluoride and organo-substituted silicon fluorides. Disubstituted compounds are obtained by the reaction of dilithium hexamethylcyclotrisilazane with silicon fluorides or by the reaction of lithium hexamethylcyclotrisilazane with silicon fluorides at higher temperature. Cyclosilazanes with bulky ligands react with butyllithium with elimination of butane as a first step and then react further with a silicon fluoride compound, with LiF-elimination, to give a mixed substituted cyclosilazane. Ring coupling through a silicon bridge is achieved by the reaction of a fluorosilyl-substituted cyclotrisilazane with lithium hexamethylcyclotrisilazane. The mass,1H and19F NMR spectra of the compounds are reported. 相似文献
70.
Alkoxylierung von bis(trimethylsilyl)-aminofluorsilanen,sowie siloxanbildung unter äthereliminierung
Uwe Klingebiel Dietrich Fischer Anton Meller 《Journal of organometallic chemistry》1975,85(2):141-147
The reaction of bis(trimethylsilyl)aminofluorsilanes, (Me3Si)2NSiF2R (R = CH3 or F), with sodium alcoholates or sodium phenylate yields under elimination of NaF alkoxy- and aryloxy-aminofluorosilanes of the composition (Me3Si)2NSiF(R)OR′(R′ = CH3, C2H5, C3H7, C6H5). A disiloxane is formed by thermal elimination of diethyl ether from bis(trimethylsilyl)aminomethylfluoroethoxysilane. The IR, mass, 1H and 19F NMR spectra of the above-mentioned compounds are reported. ab]Die Reaktion von Bis(trimethylsilyl)-aminofluorsilanen des Typs (Me3Si)2NSiF2R (R = F, CH3) mit Natriumalkoholaten und Natriumphenolat führt unter NaF-Abspaltung zu Alkyl- und Aryloxyaminofluorsilanen der Zusammensetzung: (Me3Si)2NSiF(R)OR′ (R′ = CH3, C2H7, C6H5, C6H5). Ein Disiloxan könnte durch die thermische Eliminierung von Diäthyläther aus Bis(trimethylsilyl)aminomethyl-fluor-äthoxy-silylarnin erhalten werden.Die IR-, Massen-, 1H- und 19F-NMR-Spektren der dargestellten Verbindungen werden mitgeteilt. 相似文献