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161.
Leonelli F Blesi F Dirito P Trombetta A Ceccacci F La Bella A Migneco LM Marini Bettolo R 《The Journal of organic chemistry》2011,76(16):6871-6876
The problem of constructing diastereoselectively the C/D ring system of stemarane diterpenes from a bicyclo[2.2.2]octane intermediate was solved resulting in very simple synthesis of (+)-13-stemarene 1. The obtaining of the latter represents also a formal synthesis of (+)-18-deoxystemarin 2. In the key step, the epimeric mixture 10, dissolved in toluene, was converted by the action of TsOH into (+)-stemar-13-en-15-one 28. 相似文献
162.
Reviriego F Navarro P Arán VJ Jimeno ML García-España E Latorre J Yunta MJ 《The Journal of organic chemistry》2011,76(20):8223-8231
By using an improved synthetic method reported earlier, the cyclic stannoxanes obtained from RN-diethanolamine (R = Me, Bu) and dibutyltin oxide have been reacted with 1H-pyrazole-3,5-dicarbonyl dichloride to afford 26-membered diaza tetraester crowns (1, R = Me; 3, R = Bu) and 39-membered triaza hexaester crowns (2, R = Me; 4, R = Bu). The new structures were identified from their analytical and spectroscopic ((1)H and (13)C NMR, FAB-MS, and/or ESI-MS) data. Both diaza tetraester crowns (1 and 3), containing two 1H-pyrazole units, self-assemble into dimeric species through the formation of four hydrogen bonds involving the two NH pyrazole groups and the two tertiary amine groups of both crowns, as proved by X-ray crystallography and NMR analysis. Preliminary NMR, ESI-MS, MALDI-TOF-MS, and molecular modeling studies suggest that, in CDCl(3) solution, 1 interacts with ethyleneurea (ETU), affording 1:1, 2:1, and 2:2 1-ETU complexes. 相似文献
163.
Fernández N Carrillo L Vicario JL Badía D Reyes E 《Chemical communications (Cambridge, England)》2011,47(45):12313-12315
We have developed a highly efficient procedure for carrying out the catalytic enantioselective (3+2) cycloaddition between enals and stable azomethine ylides such as isoquinolinium and phthalizinium methylides. Under the optimized reaction conditions highly substituted chiral pyrroloisoquinolines and pyrrolophthalazines have been obtained in high yields and excellent diastereo- and enantioselectivities. 相似文献
164.
165.
1H longitudinal relaxation time profiles (T1) at different proton Larmor frequencies were registered for a solid-state plant tissue by using fast field cycling (FFC) nuclear magnetic resonance (NMR) spectroscopy. T1 distributions were obtained and the curves deconvoluted in order to differentiate among the different T1 components. Among the components, two were assigned to hydrophobic (e.g., fatty acid) and hydrophilic (e.g., saccharide) molecular systems, whereas the others were attributed to bulk and bound water. This paper shows for the first time solid-state FFC-NMR spectroscopy applied to plant tissue and reveals that relaxometry is a very promising technique for studying plant systems. 相似文献
166.
The intramolecular electron transfer reaction within the binuclear complex formed between tetraamminepyrazinecarboxylatocobalt(III) and aquopentacyanoferrate(II) ions is studied in various binary aqueous media at different temperatures. Results could not be explained on the basis of a primitive model. Experimental data were fitted by using a multiparameter regression which shows the important role played by specific interactions on reactivity. © 1993 John Wiley & Sons, Inc. 相似文献
167.
Jos María Miguel del Corral Marina Gordaliza Jos-Luis Lpez Esther Del Olmo M. Angeles Castro M. Luisa Lpez 《Helvetica chimica acta》1995,78(7):1793-1796
The configuration of several keto-cyclolignans related to podophyllotoxin has been reviewed. Under basic catalysis, the configuration at the C-atom in α-position to the lactone carbonyl group in podophyllotoxone is inverted instead of the C-atom in α-position to the ketone group, as it has been reported. 相似文献
168.
The system Fe(II)-5-Aphen-H2O was studied. The spectroscopic and electrochemical results show that only one stable complex between Fe(II) and 5-Aphen forms, having a 1:3 stoichiometric ratio. The spectrophotometry study allowed determination of the formation constant of the complex (log β3 = 23.42 ± 0.06). Also, the stability of the complex was evaluated as a function of pH; it was found that it decomposed at low pH values depending on the concentration and a pseudo-first order kinetics constant associated with k′ = 0.011 min−1. The results are in agreement with the electrochemical behaviour observed in the system, which indicated that at pH 1.33 the destruction of the complex [Fe(5-Aphen)3]2+ took place as a function of time; however, when the experiments were carried out at pH 6.19 the complex was stable. The thermodynamic data obtained through the use of MEDUSA allowed construction of predominance zone diagrams of the system Fe(II)-5-Aphen-H2O under the experimental conditions used. The thermodynamic results represented in the PZD describe the experimental behaviour reported in this work. 相似文献
169.
170.
Maria Luisa Dalla Chiara 《International Journal of Theoretical Physics》1995,34(8):1331-1336
The event-structure of a state-event system, containing unsharp elements, can be described either as aregular involutive bounded poset, or alternatively as anunsharp orthoalgebra (called alsodifference poset oreffect algebra). Such structures give rise to different forms ofunsharp quantum logics. 相似文献