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141.
142.
Veronica?FelliEmail author Francesco?UguzzoniEmail author 《Annali di Matematica Pura ed Applicata》2004,183(4):469-493
We prove some existence results for the Webster scalar curvature problem on the Heisenberg group and on the unit sphere of n+1, under the assumption of some natural symmetries of the prescribed curvatures. We use variational and perturbation techniques. Mathematics Subject Classification (2000) 35J20, 35H20, 35J60, 43A80 相似文献
143.
Blanksby SJ Ellison GB Bierbaum VM Kato S 《Journal of the American Chemical Society》2002,124(13):3196-3197
The reaction of F(-) with CH(3)OOH has been studied in the gas phase using a tandem flowing afterglow-selected ion flow tube apparatus. The reaction is rapid (k = 1.23 x 10(-9) cm(3) s(-1), 49% efficiency), and formation of HO(-) + CH(2)O + HF is the major reaction channel observed (85%). Isotopic labeling, reactions of F(-) with larger alkyl hydroperoxides, and computational studies demonstrate that the major product ion, HO(-), is formed via a concerted elimination mechanism that appears to be general to all alkyl hydroperoxides possessing an alpha-hydrogen. This mechanism represents a base-mediated decomposition of alkyl hydroperoxides in the gas phase that may have important implications for solution and biochemical reactions. The reverse reaction, CH(3)OO(-) + HF is also efficient (k = 2.43 x 10(-9) cm(3) s(-1)). The major product ensemble HO(-) + CH(2)O + HF (81%) is identical to that of the forward reaction, and represents a novel neutral-catalyzed decomposition of the anion. 相似文献
144.
Grant CV Frydman V Harwood JS Frydman L 《Journal of the American Chemical Society》2002,124(16):4458-4462
Although magnesium fulfills several essential biochemical roles, direct studies on this ion are complicated by its unfavorable spectroscopic characteristics. This contribution explores the possibility of monitoring magnesium-nucleic acid binding via a combination of [Co(NH3)6]3+ as surrogate for [Mg(H2O)6]2+, and of high-resolution solid-state 59Co NMR as a spectroscopic probe. Such strategy quenches fast cationic exchanges between bound and free states, while exploiting the superior NMR properties of the 59Co spin. Experiments on relatively small amounts of tRNA can then discern resonances corresponding to different metal binding environments. These characterizations were assisted by studies on model compounds and by multinuclear 31P-59Co recoupling experiments. 相似文献
145.
Daniel M. Beagan Dr. Nicholas A. Maciulis Dr. Maren Pink Dr. Veronica Carta I. J. Huerfano Dr. Chun-Hsing Chen Dr. Kenneth G. Caulton 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(45):11676-11681
The reaction chemistry of the bis-tetrazinyl pyridine ligand (btzp) towards nitrogen oxyanions coordinated to zinc is studied in order to explore the reduction of the NOx− substrates with a redox-active ligand in the absence of redox activity at the metal. Following syntheses and characterization of (btzp)ZnX2 for X=Cl, NO3 and NO2, featuring O−Zn linkage of both nitrogen oxyanions, it is shown that a silylating agent selectively delivers silyl substituents to tetrazine nitrogens, without reductive deoxygenation of NOx−1. A new synthesis of the highly hydrogenated H4btzp, containing two dihydrotetrazine reductants is described as is the synthesis and characterization of (H4btzp)ZnX2 for X=Cl and NO3, both of which show considerable hydrogen bonding potential of the dihydrotetrazine ring NH groups. The (H4btzp)ZnCl2 complex does not bind zinc in the pincer pocket, but instead H4btzp becomes a bridge between neighboring atoms through tetrazine nitrogen atoms, forming a polymeric chain. The reaction of AgNO2 with (H4btzp)ZnCl2 is shown to proceed with fast nitrite deoxygenation, yielding water and free NO. Half of the H4btzp reducing equivalents form Ag0 and thus the chloride ligand remains coordinated to the zinc metal center to yield (btzp)ZnCl2. To compare with AgNO2, experiments of (H4btzp)ZnCl2 with NaNO2 result in salt metathesis between chloride and nitrite, highlighting the importance of a redox-active cation in the reduction of nitrite to NO. 相似文献
146.
Nyamweru Bugusu Celestine Kaale Eliangiringa Mugoyela Veronica Chambuso Mhina 《平面色谱法杂志一现代薄层色谱法》2013,26(3):226-231
JPC – Journal of Planar Chromatography – Modern TLC - Analysis of fixed dose combination products can present daunting challenges to the analytical chemist. This paper presents a... 相似文献
147.
Jenelle Fortunato Jack W. Jordan Graham N. Newton Darren A. Walsh Veronica Augustyn 《Current Opinion in Electrochemistry》2022
The nanoconfinement of electrochemically-active guest species in host solid state electrode materials provides opportunities to tune mass transport between the bulk electrolyte and inner surface of the electrode, enhance electron-transfer rates, and/or improve the stability and dispersion of active material. This review summarizes recent experimental and theoretical electrochemical studies of three types of nanoconfined guest species: (1) ion adsorption of electrolyte ions, (2) confined redox-active molecules, and (3) electrocatalytic reactions of confined ions/solvents and catalytic particles. The examples discussed in this review illustrate how the confinement of guest species within enclosed spaces with nanoscale dimensions – such as pores, pockets, channels, and interlayers – can lead to improved electrochemical performance. 相似文献
148.
Azomethine Ylides from Nitrones: Using Catalytic nBuLi for the Totally Stereoselective Synthesis of trans‐2‐Alkyl‐3‐oxazolines
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Veronica Juste‐Navarro Dr. Ignacio Delso Prof. Tomás Tejero Prof. Pedro Merino 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(33):11527-11532
The cycloaddition of azomethine ylide N‐oxides (nitrone ylides) with aldehydes provides 3‐oxazolines in a completely stereoselective manner in the presence of a catalytic amount of n‐butyllithium. The process involves an initial nucleophilic attack on the aldehyde, followed by intramolecular oxygen addition to the nitrone moiety and lithium‐assisted elimination of water, regenerating the catalytic species. Various Li‐based catalytic systems are possible and the in situ generated water is required for continuing the catalytic cycle. The best results are observed with 20 mol % of n‐butyllithium, whereas the use of stoichiometric amounts inhibit the rate of catalysis. Experimental, spectroscopic, and computational mechanistic studies have provided evidence of lithium‐ion catalysis and rationalized several competing catalytic pathways 相似文献
149.
150.
Filippo Samperi Salvatore Battiato Concetto Puglisi Andrea Scamporrino Veronica Ambrogi Laura Ascione Cosimo Carfagna 《Journal of polymer science. Part A, Polymer chemistry》2011,49(16):3615-3630
Linear–hyperbranched hybrid poly(butylene adipate) (HPBA) copolymers were synthesized through a branching reaction between the linear tailored prepolymer terminated with methyl ester groups and different mol percents of the 1,1,1‐tris(hydroxymethyl) propane (TMP) as branching agent, using the titanium(IV) isopropoxide as catalyst, at 180 °C under vacuum for different times. All samples were characterized by NMR and matrix assisted laser desorption/ionization time of flight mass spectrometry (MALDI‐TOF MS). In particular, MALDI‐TOF mass spectra of the unfractionated and size exclusion chromatography (SEC)‐fractionated hyperbranched (HB) samples gave information on their composition, on the end groups as well as on the TMP units present in each family of HB macromolecules. HB chains containing cyclic branches and ether bonds formed by intermolecular transesterification and intramolecular and intermolecular transetherification side reactions, respectively, were also revealed by MALDI‐TOF MS analysis. All samples were also investigated by SEC. The average molar masses (MMs) evaluated by SEC calibrated with the polystyrene (PS) narrow standards were overestimated with respect to those calculated by the SEC/MALDI‐TOF MS self‐ calibration method, which gave reliable values. Moreover, it also showed that the hydrodynamic volume of the HPBA polymers was higher than that of the linear PSs with similar MMs. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献