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101.
Giuliani JR Gjersing EL Chinn SC Jones TV Wilson TS Alviso CT Herberg JL Pearson MA Maxwell RS 《The journal of physical chemistry. B》2007,111(45):12977-12984
Thermal degradation of a filled, cross-linked siloxane material synthesized from poly(dimethylsiloxane) chains of three different average molecular weights and with two different cross-linking species has been studied by (1)H multiple quantum (MQ) NMR methods. Multiple domains of polymer chains were detected by MQ NMR exhibiting residual dipolar coupling () values of 200 and 600 Hz, corresponding to chains with high average molecular weight between cross-links and chains with low average molecular weight between cross-links or near the multifunctional cross-linking sites. Characterization of the values and changes in distributions present in the material were studied as a function of time at 250 degrees C and indicate significant time-dependent degradation. For the domains with low , a broadening in the distribution was observed with aging time. For the domain with high , increases in both the mean and the width in were observed with increasing aging time. Isothermal thermal gravimetric analysis reveals a 3% decrease in weight over 20 h of aging at 250 degrees C. Degraded samples also were analyzed by traditional solid-state (1)H NMR techniques, and off-gassing products were identified by solid-phase microextraction followed by gas chromatography-mass spectrometry. The results, which will be discussed here, suggest that thermal degradation proceeds by complex competition between oxidative chain scissioning and postcuring cross-linking that both contribute to embrittlement. 相似文献
102.
The authors time resolve molecular motion in bound state, ionic potentials that leads to bond cleavage during the interaction with intense, ultrafast laser fields. Resonances in molecular ions play an important role in dissociative ionization with ultrafast laser fields, and the authors demonstrate how these resonances evolve in time to produce dissociation after initial strong-field ionization. Exploiting such dynamic resonances offers the possibility of controlled bond breaking and characterizing time-dependent molecular structure. 相似文献
103.
We follow the evolution of a vibrational wave packet in a highly excited state of the halogenated methane CH(2)I(2). We observe how the wave packet modulates both dissociation and concerted elimination to form CH(2)I(+) and I(2) (+), respectively. We present a simple and intuitive interpretation of the molecular dynamics leading to the formation of the products. 相似文献
104.
Synthetic efforts toward the homoerythrina alkaloids 1-3 are described. Two separate model systems guided the pivotal [3 + 2] azomethine ylide cycloaddition cascade to form the A-C rings of these alkaloids. The cycloaddition precursors 63 and 68, prepared in nine and ten steps, respectively, from alkyne 47, each contain an enolizable ketone, a tethered electrophile, and an electron-poor dipolarophile. Heating 63 and 68 with the stannyl amine 17 generated demethoxyschelhammeridine 65 and demethoxyschelhammericine 70, the products of intramolecular azomethine ylide cycloadditions. Subsequent attempts to install the C-3 methoxy group of 1-3 are also described. 相似文献
105.
DC Muddiman AP Null JC Hannis 《Rapid communications in mass spectrometry : RCM》1999,13(12):1201-1204
Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICRMS) has been used to determine the mass of a double-stranded 500 base-pair (bp) polymerase chain reaction (PCR) product with an average theoretical mass of the blunt-ended (i.e. unadenylated) species of 308 859.35 Da. The PCR product was generated from the linearized bacteriophage Lambda genome which is a double-stranded template. Utilization of ethanol precipitation in tandem with a rapid microdialysis step to purify and desalt the PCR product was crucial to obtain a precise mass measurement. The PCR product (0.8 pmol/μL) was electrosprayed from a solution containing 75% acetonitrile, 25 mM piperidine, and 25 mM imidazole and was infused at a rate of 200 nL/min. The average molecular mass and the corresponding precision were determined using the charge-states ranging from 172 to 235 net negative charges. The experimental mass and corresponding precision (reported as the 95% confidence interval of the mean) was 309 406 +/- 27 Da (87 ppm). The mass accuracy was compromised due to the fact that the PCR generates multiple products when using Taq polymerase due to the non-template directed 3'-adenylation. This results in a mixture of three PCR products with nearly identical mass (i.e. blunt-ended, mono-adenylated and di-adenylated) with unknown relative abundances that were not resolved in the spectrum. Thus, the experimental mass will be a weighted average of the three species which, under our experimental conditions, reflects a nearly equal concentration of the mono- and di-adenylated species. This report demonstrates that precise mass measurements of PCR products up to 309 kDa (500 bp) can be routinely obtained by ESI-FTICR requiring low femtomole amounts. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
106.
Orde Q. Munro Nicole Pearson 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(10):m407-m412
The title salt, (1,4,7,10,13,16‐hexaoxacyclooctadecane‐κ6O)[(isothiocyanato)triphenylborato‐κS]potassium(I), [K(C19H15BNS)(C12H24O6)] or [K(SCNBPh3)(18‐crown‐6)], where 18‐crown‐6 is 1,4,7,10,13,16‐hexaoxacyclooctadecane and [SCNBPh3]− is the (isothiocyanato)triphenylborate anion, exhibits a supramolecular structure that is best described as a helical coordination polymer or molecular screw. This unusual supramolecular structure is based on a framework in which the SCN− ion bridges the chelated K+ ion and the B atom of BPh3 in a μ2 fashion. The X‐ray crystal structure of the title salt has been determined at 100 (1) and 293 (2) K. The K+ ion exhibits axial ligation by the S atom of the [SCNBPh3]− anion, with a K—S distance of 3.2617 (17) Å (100 K). The trans‐axial ligand is an unexpected η2‐bound C=C bond of a phenyl group (meta‐ and para‐C atoms) that belongs to the BPh3 moiety of a neighboring molecule. The K—C bond distances span the range 3.099 (3)–3.310 (3) Å (100 K) and are apparently retained in CDCl3 solution (as evidenced by 13C NMR spectroscopy). By virtue of the latter interaction, the supramolecular structure is a helical coordination polymer, with the helix axis parallel to the b axis of the unit cell. IR spectroscopy and semi‐empirical molecular orbital (AM1) calculations have been used to investigate further the electronic structure of the [SCNBPh3]− ion. 相似文献
107.
Glen B. Deacon Pauline Pearson Brian W. Skelton Leone Spiccia Allan H. White 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(12):m537-m539
The syntheses and crystal structure determinations of a pair of `sawhorse' dimers are reported, viz. [Ru2(C6H5CO2)2(C5H5N)2(CO)4] [a new polymorph, cf. Kepert, Deacon, Spiccia, Fallon, Skelton & White (2000). J. Chem. Soc. Dalton Trans. pp. 2867–2874] and [Ru2(CF3CO2)2(C5H5N)2(CO)4]. The Ru⋯Ru distances are 2.6724 (2) and 2.7122 (5) Å, respectively. 相似文献
108.
A comprehensive analysis is presented for the acid-base double-exchange reaction as well as the associated acid-displacement and base-displacement "half-reactions" with the goal of elucidating the meaning of the hard/soft acid/base (HSAB) principle and the conditions for its validity. When electron-transfer effects are important and other effects are negligible, the HSAB principle is driven by the surpassing stability of the soft acid/soft base product. When electrostatic effects dominate the reactivity, the HSAB principle is driven by the surpassing stability of the hard acid/hard base product. Because electron-transfer effects favor soft/soft interactions, while electrostatic effects favor hard/hard interactions, acid-base exchange reactions may be used to determine whether a reagent's reactivity is dominated by electron-transfer or by electrostatic effects. Because electron-transfer and electrostatic considerations separately favor the HSAB principle whenever the electronic chemical potentials of the acids and bases involved in the reaction are similar, our analysis provides strong support for the HSAB principle. The electronic chemical potential measures the intrinsic strength of acids and bases. 相似文献
109.
Saki Tanaka Yusuke Nakaya Kazufumi Ninomiya Hironori Nishio Junichi Onishi Robert Openshaw Matthew Pearson Yumi Totsuka Jiro Murata 《Physics of Particles and Nuclei》2014,45(1):237-240
A new experiment named MTV-G, probing a large electron spin-precession due to a possible strong gravitational field, which predicted by large extra dimension model, is started at TRIUMF from 2011. In an electron-nuclear scattering experiment, a strong gravitational field is tested as a large spin precession effect caused by geodetic precession predicted by general relativity theory as a result of a warped space-time around nuclei. Experimental design using spin polarized electron source and Mott-spin analyzer, commissioning experiment and the preliminary results are described. 相似文献
110.
We report an NMR experimental realization of a rapid quantum deletion algorithm that deletes marked states in an unsorted database.Unlike classical deletion,where search and deletion are equivalent,quantum deletion can be implemented with only a single query,which achieves exponential speed-up compared to the optimal classical analog.In the experimental realization,the GRAPE algorithm was used to obtain an optimized NMR pulse sequence,and the efficient method of maximum-likelihood has been used to reconstruct the experimental output state. 相似文献