全文获取类型
收费全文 | 505篇 |
免费 | 5篇 |
国内免费 | 5篇 |
专业分类
化学 | 261篇 |
晶体学 | 14篇 |
力学 | 5篇 |
数学 | 46篇 |
物理学 | 189篇 |
出版年
2021年 | 4篇 |
2019年 | 3篇 |
2018年 | 9篇 |
2017年 | 3篇 |
2015年 | 4篇 |
2014年 | 10篇 |
2013年 | 15篇 |
2012年 | 16篇 |
2011年 | 26篇 |
2010年 | 17篇 |
2009年 | 11篇 |
2008年 | 18篇 |
2007年 | 24篇 |
2006年 | 20篇 |
2005年 | 23篇 |
2004年 | 14篇 |
2003年 | 8篇 |
2002年 | 10篇 |
2001年 | 13篇 |
2000年 | 10篇 |
1999年 | 8篇 |
1998年 | 4篇 |
1997年 | 8篇 |
1996年 | 6篇 |
1995年 | 3篇 |
1994年 | 7篇 |
1993年 | 14篇 |
1992年 | 10篇 |
1991年 | 12篇 |
1990年 | 7篇 |
1989年 | 8篇 |
1988年 | 7篇 |
1987年 | 12篇 |
1986年 | 3篇 |
1985年 | 10篇 |
1984年 | 13篇 |
1983年 | 6篇 |
1982年 | 10篇 |
1981年 | 10篇 |
1980年 | 10篇 |
1979年 | 5篇 |
1978年 | 11篇 |
1977年 | 3篇 |
1976年 | 8篇 |
1975年 | 7篇 |
1973年 | 6篇 |
1969年 | 3篇 |
1917年 | 2篇 |
1895年 | 2篇 |
1880年 | 4篇 |
排序方式: 共有515条查询结果,搜索用时 31 毫秒
501.
Douglas Onyancha Vincent Nyamori Christopher Imrie Thomas I.A. Gerber 《Journal of organometallic chemistry》2009,694(2):207-1132
The efficient and simple routes for the synthesis of various ferrocenyl derivatives from ferrocenylcarbinols and N,N′-thiocarbonyldiimidazole (TCDI) are described. It involves grinding the two substrates in a Pyrex tube with a glass rod at room temperature. The reaction of ferrocenylmethanol (1a) provided S,S-bis(ferrocenylmethyl)dithiocarbonate (1b), whose crystal structure and a plausible mechanism for its formation are also reported. The reaction of 1-ferrocenyl-1-phenylmethanol (2a) and 1-ferrocenylbutanol (2b) gave the products 2c and 2d, respectively. The reaction of ω-ferrocenyl alcohols 4-ferrocenylphenol (3a) and 6-ferrocenylhexan-1-ol (3b) yielded the products 3c and 3d, respectively. Reaction of 1,1′-ferrocenedimethanol (3e) afforded 3f in moderate yield, and by contrast, it was not similar to 1b. Reaction of [4-(trifluoromethyl)phenyl]methanol (4a) provided the thiocarbonate 4b in good yield. 相似文献
502.
A hyphenated ion-pair (tetrabutylammonium chloride—TBACl) reversed phase (C18) HPLC-ICP-MS method (High Performance Liquid Chromatography Inductively Coupled Plasma Mass Spectroscopy) for anionic Rh(III) aqua chlorido-complexes present in an HCl matrix has been developed. Under optimum chromatographic conditions it was possible to separate and quantify cationic Rh(III) complexes (eluted as a single band), [RhCl3(H2O)3], cis-[RhCl4(H2O)2]−, trans-[RhCl4(H2O)2]− and [RhCln(H2O)6−n]3−n (n = 5, 6) species. The [RhCln(H2O)6−n]3−n (n = 5, 6) complex anions eluted as a single band due to the relatively fast aquation of [RhCl6]3− in a 0.1 mol L−1 TBACl ionic strength mobile phase matrix. Moreover, the calculated t1/2 of 1.3 min for [RhCl6]3− aquation at 0.1 mol kg−1 HCl ionic strength is significantly lower than the reported t1/2 of 6.3 min at 4.0 mol kg−1 HClO4 ionic strength. Ionic strength or the activity of water in this context is a key parameter that determines whether [RhCln(H2O)6−n]3−n (n = 5, 6) species can be chromatographically separated. In addition, aquation/anation rate constants were determined for [RhCln(H2O)6−n]3−n (n = 3-6) complexes at low ionic strength (0.1 mol kg−1 HCl) by means of spectrophotometry and independently with the developed ion-pair HPLC-ICP-MS technique for species assignment validation. The Rh(III) samples that was equilibrated in differing HCl concentrations for 2.8 years at 298 K was analyzed with the ion-pair HPLC method. This analysis yielded a partial Rh(III) aqua chlorido-complex species distribution diagram as a function of HCl concentration. For the first time the distribution of the cis- and trans-[RhCl4(H2O)2]− stereoisomers have been obtained. Furthermore, it was found that relatively large amounts of ‘highly’ aquated [RhCln(H2O)6−n]3−n (n = 0-4) species persist in up to 2.8 mol L−1 HCl and in 1.0 mol L−1 HCl the abundance of the [RhCl5(H2O)]2− species is only 8-10% of the total, far from the 70-80% as previously proposed. A 95% abundance of the [RhCl6]3− complex anion occurs only when the HCl concentration is above 6 mol L−1. The detection limit for a Rh(III) species eluted from the column is below 0.147 mg L−1. 相似文献
503.
Florence Popowycz Sandrine Gerber‐Lemaire Eliazar Rodriguez‐García Catherine Schütz Pierre Vogel 《Helvetica chimica acta》2003,86(6):1914-1948
The synthesis of 46 derivatives of (2R,3R,4S)‐2‐(aminomethyl)pyrrolidine‐3,4‐diol is reported (Scheme 1 and Fig. 3), and their inhibitory activities toward α‐mannosidases from jack bean (B) and almonds (A) are evaluated (Table). The most‐potent inhibitors are (2R,3R,4S)‐2‐{[([1,1′‐biphenyl]‐4‐ylmethyl)amino]methyl}pyrrolidine‐3,4‐diol ( 3fs ; IC50(B)=5 μM , Ki=2.5 μM ) and (2R,3R,4S)‐2‐{[(1R)‐2,3‐dihydro‐1H‐inden‐1‐ylamino]methyl}pyrrolidine‐3,4‐diol ( 3fu ; IC50(B)=17 μM , Ki=2.3 μM ). (2S,3R,4S)‐2‐(Aminomethyl)pyrrolidine‐3,4‐diol ( 6 , R?H) and the three 2‐(N‐alkylamino)methyl derivatives 6fh, 6fs , and 6f are prepared (Scheme 2) and found to inhibit also α‐mannosidases from jack bean and almonds (Table). The best inhibitor of these series is (2S,3R,4S)‐2‐{[(2‐thienylmethyl)amino]methyl}pyrrolidine‐3,4‐diol ( 6o ; IC50(B)=105 μM , Ki=40 μM ). As expected (see Fig. 4), diamines 3 with the configuration of α‐D ‐mannosides are better inhibitors of α‐mannosidases than their stereoisomers 6 with the configuration of β‐D ‐mannosides. The results show that an aromatic ring (benzyl, [1,1′‐biphenyl]‐4‐yl, 2‐thienyl) is essential for good inhibitory activity. If the C‐chain that separates the aromatic system from the 2‐(aminomethyl) substituent is longer than a methano group, the inhibitory activity decreases significantly (see Fig. 7). This study shows also that α‐mannosidases from jack bean and from almonds do not recognize substrate mimics that are bulky around the O‐glycosidic bond of the corresponding α‐D ‐mannopyranosides. These observations should be very useful in the design of better α‐mannosidase inhibitors. 相似文献
504.
May BL Gerber J Clements P Buntine MA Brittain DR Lincoln SF Easton CJ 《Organic & biomolecular chemistry》2005,3(8):1481-1488
alpha-Cyclodextrin, beta-cyclodextrin, N-(6(A)-deoxy-alpha-cyclodextrin-6(A)-yl)-N'6(A)-deoxy-beta-cyclodextrin-6(A)-yl)urea and N,N-bis(6(A)-deoxy-beta-cyclodextrin-6(A)-yl)urea (alphaCD, betaCD, 1 and 2) form inclusion complexes with E-4-tert-butylphenyl-4'-oxyazobenzene, E-3(-). In aqueous solution at pH 10.0, 298.2 K and I = 0.10 mol dm(-3)(NaClO(4)) spectrophotometric UV-visible studies yield the sequential formation constants: K(11) = (2.83 +/- 0.28) x 10(5) dm(3) mol(-1) for alphaCD.E-(-), K(21) = (6.93 +/- 0.06) x 10(3) dm(3) mol(-1) for (alphaCD)(2).E-3(-), K(11) = (1.24 +/- 0.12) x 10(5) dm(3) mol(-1) for betaCD.E-(-), K(21) = (1.22 +/- 0.06) x 10(4) dm(3) mol(-1) for (betaCD)(2).E-(-), K(11) = (3.08 +/- 0.03) x 10(5) dm(3) mol(-1) for .E-3(-), K(11) = (8.05 +/- 0.63) x 10(4) dm(3) mol(-1) for .E-3(-) and K(12) = (2.42 +/- 0.53) x 10(4) dm(3) mol(-1) for .(E-3(-))(2). (1)H ROESY NMR studies show that complexation of E-3(-) in the annuli of alphaCD, betaCD, 1 and 2 occurs. A variable-temperature (1)H NMR study yields k(298 K)= 6.7 +/- 0.5 and 5.7 +/- 0.5 s(-1), DeltaH = 61.7 +/- 2.7 and 88.1 +/- 4.2 kJ mol(-1) and DeltaS = -22.2 +/- 8.7 and 65 +/- 13 J K(-1) mol(-1) for the interconversion of the dominant includomers (complexes with different orientations of alphaCD) of alphaCD.E-3(-) and (alphaCD)(2).E-3(-), respectively. The existence of E-3(-) as the sole isomer was investigated through an ab initio study. 相似文献
505.
通过离子液体氯化1-苄基-3-甲基咪唑(BenzMeIm-Cl)与PtCl2的反应,合成了配合物(BenzMeIm)2[PtCl4],并用元素分析、红外光谱、紫外-可见光谱、1H NMR、13C NMR和单晶X射线衍射对其进行了表征。单晶X射线分析表明,配合物结构属于P21/c空间群,晶胞参数和结构解析参数为:a=0.981 80(5)nm,b=0.861 47(3)nm,c=0.144 332(7)nm,β=92.480(2)°,V=121.96(1)nm3,R1=0.014 4,wR2=0.038 8。 相似文献
506.
Flarakos J Luo W Aman M Svinarov D Gerber N Vouros P 《Journal of chromatography. A》2004,1026(1-2):175-183
A robust and validated LC-MS-MS quantitative method, using column switching and mutiple reaction monitoring was developed for the analysis of risperidone (RIS) and 9-hydroxyrisperidone in human plasma and saliva. The analytical range was 1-100 ng/ml. The method used 25 microl of sample precipitated with 75 microl of acetonitrile containing internal standard (R068808). Analyses were conducted on a PE Sciex API-III + triple quadrupole mass spectrometer fitted with a Turbo IonSpray source. The method was validated for human plasma using EDTA as the anticoagulant and cross-validated to heparinized human plasma and saliva. The recoveries of risperidone and 9-hydroxyrisperidone were 90-93 and 89-93%, respectively. The validated method was applied to clinical samples to study risperidone and 9-hydroxyrisperidone concentrations in plasma and saliva. Risperidone and 9-hydroxyrisperidone appear in the saliva of patients treated with risperidone. Their detection/quantification in saliva provides evidence for recent adherence with therapy. 相似文献
507.
In this study experimental single-pulse, time-resolved laser-induced incandescence (TIRE-LII) signal intensity profiles acquired during transient Diesel combustion events at high pressure were processed. Experiments were performed between 0.6 and 7 MPa using a high-temperature high-pressure constant volume cell and a heavy-duty Diesel engine, respectively. Three currently available LII sub-model functions were investigated in their performance for extracting ensemble mean soot particle diameters using a least-squares fitting routine, and a “quick-fit” interpolation approach, respectively. In the calculations a particle size distribution as well as the temporal and spatial intensity profile of the heating laser was taken into account. For the poorly characterized sample environments of this work, some deficiencies in these state-of-the-art data evaluation procedures were revealed. Depending on the implemented model function, significant differences in the extracted particle size parameters are apparent. We also observe that the obtained “best-fit” size parameters in the fitting procedure are biased by the choice of their respective “first-guess” initial values. This behavior may be caused by the smooth temporal profile of the LII cooling curve, giving rise to shallow local minima on the multi-parameter least squares residuals, surface sampled during the regression analysis procedure. Knowledge of the gas phase temperature of the probed medium is considered important for obtaining unbiased size parameter information from TIRE-LII measurements. PACS 42.62.-b; 51.30.+i; 82.20.Wt 相似文献
508.
In the Poisson case there is a well known formula that relates the probability of ruin to the distribution function of aggregate claims. It is shown how this formula can be generalized to the mixed Poisson case. 相似文献
509.
At high magnetic fields the 128.8 MHz (195)Pt NMR of all the species in the series [PtCl(n)(H(2)O)(6-n)](4-n) (n = 2-6) display unique (35/37)Cl isotope effects resulting in a unique 'fine-structure' of each individual resonance, which constitutes an unambiguous spectroscopic 'fingerprint' characteristic of the structure of the octahedral platinum(iv) complex, provided (195)Pt NMR are recorded at optimum magnetic field homogeneity and carefully controlled temperature (293 ± 0.1 K). The detailed (195)Pt resonance fine-structure observed experimentally can readily be accounted for by an isotopologue and isotopomer model for each complex, showing particularly noticeable differences between stereoisomer pairs such as the cis/trans- and fac/mer-complexes. Moreover partial isotopic (18)O enrichment of the coordinated water molecules in the series [Pt(35/37)Cl(n)(H(2)(16/18)O)(6-n)](n-2) (n = 2-6) confirms this model. This technique can thus be considered a novel, direct spectroscopic method of chemical speciation of appropriate platinum(iv) complexes in solution without reference to accurate chemical shifts of authentic members of such a series. These effects are interpreted qualitatively in terms of the high sensitivity of (195)Pt NMR shielding to very small and subtle Pt-(35/37)Cl and Pt-(16/18)OH(2) bond displacements. Preliminary work shows this also applied to the corresponding bromido-complexes. 相似文献
510.
J. Mannhart D. Anselmetti J. G. Bednorz A. Catana Ch. Gerber K. A. Müller D. G. Schlom 《Zeitschrift für Physik B Condensed Matter》1992,86(2):177-181
Electric transport properties of sputtered YBa2Cu3O7– films were studied as a function of screw dislocation density, ranging from 5·107 cm–2 to 1.3·109 cm–2 as determined at the film surface. A correlation was found between the number of screw dislocations and the critical current density (J
c
). Films with higher screw dislocation densities have higher critical current densities and a slower drop ofJ
c
as a function of applied magnetic fieldH. 相似文献