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排序方式: 共有132条查询结果,搜索用时 31 毫秒
91.
92.
Solutions of iodobenzene diacetate in CH3CN, AcOH, MeOH/H2O and MeOH (with or without base) were analyzed by electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (ESI-MS/MS). The major species in CH3CN, AcOH and MeOH/H2O solutions are [PhI(OAc)2Na]+, [PhI(OAc)2K]+, [PhI]+, [PhIOAc]+, [PhIOH]+, [PhIO2Ac]+, [PhIO2H]+ and the dimer [Ph2I2O2Ac]+. On the other hand, MeOH solutions showed [PhIOMe]+ as the most abundant species. A similar result was observed adding 2, 3 or 4 equiv of KOH to MeOH solutions. However, in the presence of 10 equiv of KOH, probably occurs the formation of a polymeric material. Similarly, ESI-MS analysis of the MeOH solution of iodobenzene bis(trifluoroacetate) showed a pattern analogous to that observed for the corresponding solutions of PhI(OAc)2. However, ESI-MS spectral data of PhI(O2CCF3)2 of CH3CN suggests that the main species in solutions is iodosylbenzene, which contrasts with the results obtained for PhI(OAc)2. 相似文献
93.
94.
Limin Zhou 《Cellulose (London, England)》2006,13(2):119-129
An attempt has been made to prepare second-order nonlinear optic (NLO) materials based on cellulose diacetate and melamine
derivatives. The NLO cationic chromophore, composed of 1,3-dimethyl-2-(4′-N,N-dimethylaminophenyl)-azo-imidazole chloride and small amounts of 1,3-dimethyl-2-(4′-N,N-dimethylaminophenyl)-azo-imidazole methylsulfate, was incorporated into a crosslink network formed from the reaction of cellulose
diacetate with trimethylol melamine or hexamethylol melamine. The poled and cured NLO materials exhibited an electro-optic
coefficient (r
13) of 1.03 or 1.42 pm/V, respectively, at the laser wavelength 1550 nm and a modulation frequency of 12.7 kHz; the r
13 values decreased to 97% or 86.6%, respectively, of the initial values after 4 days. The laser transmission loss was 0.58 or
0.6 dB, respectively. The crosslinked materials showed better temporal stability than the material of the host/guest system
with a doped cationic chromophore. The results of Fourier transform infrared spectroscopy, dielectric relaxation and thermogravimetry
analyses proved the formation of a crosslink structure, and the degree of dielectric relaxation was shown to became higher
if a crosslinker of too high functionality was used. 相似文献
95.
Hironori Sato Yasumitsu Uraki Takao Kishimoto Yoshihiro Sano 《Cellulose (London, England)》2003,10(4):397-404
To explore further potential applications of acetic acid pulp, an investigation was conducted to develop a direct method for producing cellulose acetate from wood in combination with atmospheric acetic acid pulping. The process consists of delignification, totally chlorine-free bleaching, and esterification, with the concentrated acetic acid aqueous solution being used as only solvent throughout the process. The acetic acid pulp with kappa number of 30 and ISO brightness of 16 was bleached with 5% ozone on pulp to kappa number of 1.4 and brightness of 61. The resulting bleached pulp was further bleached with peracetic acid to kappa number of less than 1.0 and brightness of 68. The final bleached acetic acid pulp was acetylated with acetic anhydride in the concentrated acetic acid for 45 min to produce cellulose acetate with an apparent degree of substitution (DS) of 2.54. Although the product was lower grade compared with commercially available cellulose diacetate because it was prepared from the chemical pulp but not dissolving pulp, the product was almost soluble in acetone. Eventually, the DS of the acetone-soluble fraction was 2.62. The acetone solubility might be attributed to the original acetic acid pulp that had been partially acetylated during the pulping. 相似文献
96.
H. A. Azab 《Monatshefte für Chemie / Chemical Monthly》1992,123(12):1107-1115
Summary The complexation of Pb(II) by N-(2-acetamido) imino diacetate (ADA) has been studied polarographically (dc and ac polarographic techniques). Ac polarographic studies have been particularly helpful in deciding the reversibility of the reduction of both simple and complexed metal ions and for confirmation of the overall stability constants. A weighted least squares numerical technique has been applied for the calculation of the overall stability constants using both dc and ac techniques. The reduction of Pb(II) in N-(2-acetamido) iminodiacetate solutions has been found to be reversible and diffusion controlled, involving a two electron transfer process. Potential vs. concentration data at =0.1 mol dm–3 (KNO3) are interpreted on the basis of the formation of two complex species PbADA and Pb(ADA)2– in thepH range 6.85–8.50. The logarithms of the stability constants (calculated from ac measurements) of these complexes are 8.73±0.12, 10.86±0.18 at 25°C, 8.31±0.28, 10.31±0.09 at 35°C and 7.61±0.20, 10.10±0.11 at 45°C, respectively. The thermodynamic parameters G, H and S have been calculated at 35°C.
Polarographische Untersuchung von Zusammensetzung und Stabilitätskonstanten von Pb(II) N-(2-Acetamido)iminodiacetat-Komplexen
Zusammenfassung Es wurde die Komplexierung von Pb(II) mit N-(2-Acetamido)iminodiacetat (ADA) polarographisch mittels DC- und AC-Techniken untersucht. Insbesonders AC-Polarographie ergab eine klare Entscheidung bezüglich der Reversibilität der Reduktion von einfachen und komplexierten Metallionen und für die Bestätigung der Stabilitätskonstanten. Zur Bestimmung der Gesamtstabilitätskonstanten wurde eine gewichtete mittlere Fehlerquadrat-Methode auf Basis von DC- und AC-Messungen herangezogen. Die Reduktion von Pb(II) in N-(2-Acetamido)iminodiacetat-Lösung stellte sich als ein reversibler und diffusionskontrollierter Zweielektronen-Transferprozess heraus. Die Abhängigkeit des Potentials von der Konzentration bei =0.1 mol dm–3 (KNO3) läßt sich mit der Bildung von zwei Komplex-Spezies PbADA und Pb(ADA)2– impH-Bereich 6.85–8.50 erklären. Die Logarithmen der Stabilitätskonstanten dieser Komplexe (aus AC-Messungen) sind 8.73±0.12 und 10.86±0.18 bei 25°C, 8.3 ±0.28 und 10.31±0.09 bei 35°C bzw. 7.61±0.20 und 10.10±0.11 bei 45°C. Die thermodynamischen Parameter G, H und S wurden für eine Temperatur von 35°C berechnet.相似文献
97.
V. A. Dodonov T. I. Starostina Yu. L. Kuznetsova A. V. Gushchin 《Russian Chemical Bulletin》1995,44(1):151-153
Tri-p-tolylbismuth diacetate in the presence of a catalytic amount of a copper(II) salt (10.02, mol/mol) and tri-p-tolylbismuth in the presence of copper diacetate (1 2) replace the hydrogen atom of the hydroxyl groups of methanol and butanol with a tolyl group at 80 °C in up to 90 % yields.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 156–158, January, 1995. 相似文献
98.
Chan CP Tzang LC Sin KK Ji SL Cheung KY Tam TK Yang MM Renneberg R Seydack M 《Analytica chimica acta》2007,584(1):7-11
Advances in nanotechnology have had significant impacts in the field of biodiagnostics. In this study, we describe the novel application of dissolvable, organic and biofunctional nanocrystals for the quantitative detection of a PCR product. Fluorescein diacetate (FDA), a fluorogenic precursor of fluorescein, was milled in a solution of a polymeric surfactant to create a stable, nanosized colloid with an interface for coupling streptavidin molecules. The application of these particulate labels for the quantitative detection of biotinylated human papillomavirus (HPV) DNA, amplified in a standard PCR procedure, was demonstrated. After the affinity reaction, the FDA molecules were dissolved and concomitantly converted into fluorescein. This approach resulted in a high selectivity, short incubation times and a sensitivity up to 147 times greater than obtained from state-of-the-art, directly fluorescent-labeled streptavidins. This innovative method offers rapid detection of small amounts of nucleic acids because less target material and thus fewer PCR cycles are required. 相似文献
99.
This Letter reports new and efficient synthetic approaches for biologically interesting cannabinoid analogues. The key strategies involve ethylenediamine diacetate/triethylamine-catalyzed cyclization. As an application of this methodology, one-step synthesis of biologically active natural (−)-hexahydrocannabinol and its unnatural enantiomer (+)-hexahydrocannabinol was carried out. 相似文献
100.