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991.
992.
Twenty-two isomers/conformers of C3H6S+√ radical cations have been identified and their heats of formation (ΔHf) at 0 and 298 K have been calculated using the Gaussian-3 (G3) method. Seven of these isomers are known and their ΔHf data are available in the literature for comparison. The least energy isomer is found to be the thioacetone radical cation (4+) with C2v symmetry. In contrast, the least energy C3H6O+√ isomer is the 1-propen-2-ol radical cation. The G3 ΔHf298 of 4+ is calculated to be 859.4 kJ mol−1, ca. 38 kJ mol−1 higher than the literature value, ≤821 kJ mol−1. For allyl mercaptan radical cation (7+), the G3 ΔHf298 is calculated to be 927.8 kJ mol−1, also not in good agreement with the experimental estimate, 956 kJ mol−1. Upon examining the experimental data and carrying out further calculations, it is shown that the G3 ΔHf298 values for 4+ and 7+ should be more reliable than the compiled values. For the five remaining cations with available experimental thermal data, the agreement between the experimental and G3 results ranges from fair to excellent.
Cation CH3CHSCH2+√ (10+) has the least energy among the eleven distonic radical cations identified. Their ΔHf298 values range from 918 to 1151 kJ mol−1. Nevertheless, only one of them, CH2=SCH2CH2+√ (12+), has been observed. Its G3 ΔHf298 value is 980.9 kJ mol−1, in fair agreement with the experimental result, 990 kJ mol−1.
A couple of reactions involving C3H6S+√ isomers CH2=SCH2CH2+√ (12+) and trimethylene sulfide radical cation (13+) have also been studied with the G3 method and the results are consistent with experimental findings. 相似文献
993.
Crystalline [Y(OH2)3(NCMe)(benzo-15-crown-5)][ClO4]3·benzo-15-crown-5-CH3CN can be obtained by slowly cooling a reaction mixture of Y(ClO4)3·n H2O with benzo-15-crown-5 in a solution of acetonitrile and methanol (3 : 1) from 60°C to room temperature. The crystal structure of this complex has been determined at –150 and 20°C. The complex is triclinic,P
. At –150°C the cell parameters area = 11.986(4),b = 12.071(7),c = 16.364(5) Å, = 93.56(3), = 98.68(3), = 109.68(4)°, vol = 2187 Å3, andD
calc = 1.61 g cm–3 forZ = 2 formula units. 3633 independently observed [F
o 5(F
o)] reflections were used in the final least-squares refinement leading to an agreement index ofR = 0.048. The Y(III) ion coordination geometry approximates a tricapped trigonal prism with three water molecules and three benzo-15-crown-5 oxygen atoms forming the prism, with the two remaining benzo-15-crown-5 oxygen atoms and the acetonitrile molecule completing the coordination as capping atoms. The three water molecules hydrogen bond a second crown ether molecule and two of the perchlorate anions. The two acetonitrile molecules have contacts with perchlorate oxygen atoms close enough for some weak interaction. One perchlorate is ordered, one is partially disordered as is the coordinated solvent molecule, and the third anion is totally disordered. The two unique crown ether molecules have distinctively different conformations.For Part 20, see reference [1]. 相似文献
994.
A theorem of Deza asserts that ifH
1, ...,H
m
ares-sets any pair of which intersects in exactlyd elements and ifm ≧s
2 −s+2, then theH
i
form aΔ-system, i.e.
. In other words, every large equidistant (0, 1)-code of constant weight is trivial. We give a (0, +1, −1) analogue of this
theorem. 相似文献
995.
Jumina Ratnaningsih Eko Sarjono Brajna Paramitha Ika Hendaryani Dwi Siswanta Sri Juari Santosa Chairil Anwar Hardjono Sastrohamidjojo Keisuke Ohto Tatsuya Oshima 《中国化学会会志》2007,54(5):1167-1178
A study on the adsorption characteristics of Pb(II) and Cr(III) cations onto C‐4‐methoxyphenylcalix‐[4]resorcinarene (CMPCR) in batch and fixed bed column systems has been conducted. CMPCR was produced by one step synthesis from resorcinol, 4‐methoxybenzaldehyde, and HCl. The synthesis was carried out at 78 °C for 24 hours and afforded the adsorbent in 85.7% as a 3:2 mixture of C4ν:C2ν isomer. Most parameters in batch and fixed bed column systems confirm that CMPCR is a good adsorbent for Pb(II) and Cr(III), though Pb(II) adsorption was more favorable than that of Cr(III). The adsorption kinetic of Pb(II) and Cr(III) adsorptions in batch and fixed bed column systems followed a pseudo 2n order kinetics model. The rate constant of Pb(II) was higher than that of Cr(III) in the batch system, but this result was contrary to the result obtained in a fixed bed column system. Desorption studies to recover the adsorbed Pb(II) and Cr(III) were performed sequentially with distilled water and HCl, and the results showed that the adsorption was dominated by chemisorption. 相似文献
996.
Ivan panik Jan Krupcik Ivan Skacani Jaap De Zeeuw Mario Galli Pat Sandra 《Journal of separation science》1997,20(12):688-692
The separation of isomers and enantiomers of branched C10-C12 phenylalkanes by gas chromatography on fused silica capillary columns coated with some modified β- and γ-cyclodextrins was studied. It was shown that the separation of positional isomers of C10-C12 phynylalkanes on modified cyclodextrin capillary columns is not better than that on a column coated with modified polyethylene glycol. Differences were found in the enantioselectivity of modified β- and γ-cyclodextrins for the separation of C10-C12 secondary phenylalkane enantiomers. While alkylderivatives of β-CDs resolve enantiomers of 3-phenylalkanes, alkyl derivatives of γ-CD resolve enantiomers of 2-phenylalkanes. Since shape selectivity factors of modified cyclodextrins have indicated no inclusion of the considered solutes in cyclodextrin cavities, enantioselective interactions most probably occur on the outer sphere of cyclodextrins. 相似文献
997.
Anthony Fratiello Vicki Kubo-Anderson Soheil Azimi Thomas Flores Eric Marinez Dennis Matejka Richard Perrigan Michael Vigil 《Journal of solution chemistry》1990,19(8):811-829
A coordination study of Lu(III) has been carried out for the nitrate and perchlorate salts in aqueous mixtures of acetone-d6 and Freon-12 by1H,15N and35Cl NMR spectroscopy. At temperatures lower than –90°C, proton and ligand exchange are slow enough to permit the direct observation of1H resonance signals for coordinated and free water molecules, leading to an accurate measure of the Lu(III) hydration number. In perchlorate solution, in the absence of inner-shell ion-pairing, Lu(III) exhibits a maximum coordination number of six over the allowable concentration range of study, contrasting markedly with the report of values of six to nine or greater as determined by a similar NMR method. The absence of contact ion-pairing was confirmed by35Cl NMR chemical shift and linewidth measurements. Extensive ion-pairing was observed in the nitrate solutions as reflected by the lower Lu(III) hydration numbers of two to three in these systems, the observation of two coordinated water signals, and15N NMR signals for two complexes. The1H and15N NMR spectra and the hydration number could be accounted for by the presence of (H2O)4Lu(NO3)2+ and (H2O)2Lu(NO3)
2
1+
. 相似文献
998.
K. Laihia A. Valkonen E. Kolehmainen A. Antonov D. Zhukov I. Fedosov V. Nikiforov 《Journal of Molecular Structure》2006,800(1-3):100-105
Three spiro[pyrrolidine-2,3′-oxindoles], 1,1′,2,2′,5′,6′,7′,7′a-octahydro-2-oxo-1′-phenyl-spiro[3H-indole-3,3′-[3H]-pyrrolizine]-2′-carboxylic acid methyl ester (1), 1,1′,2,2′,5′,6′,7′,7′a-octahydro-2-oxo-1′-nitro-2′-phenyl-spiro[3H-indole-3, 3′-[3H]-pyrrolizine] (2) and 1,1′,2,2′,5′,6′,7′,7′a-octahydro-2-oxo-1′-nitro-2′-(4″-chlorophenyl)-spiro[3H-indole-3,3′-[3H]-pyrrolizine] (3) have been synthesized and their 1H, 13C and 15N spectra assigned. The chemical shift assignments are based on Pulsed Field Gradient (PFG) Double Quantum Filter (DQF) 1H, 1H correlation spectroscopy (COSY), PFG 1H, 13C Heteronuclear Multiple Quantum Coherence (HMQC) and PFG 1H,X (X = 13C and 15N) Heteronuclear Multiple Bond Correlation (HMBC) experiments. The single crystal X-ray structures of 1–3 have been determined. Compounds 1 and 2 crystallized in monoclinic space group C2/c and compound 3 in monoclinic space group P21/c, respectively. Also the ESI-TOF MS data of 1–3 are given. 相似文献
999.
The new triterpene glycoside cycloorbicoside C was isolated from the aerial parts of Astragalus orbiculatus Ledeb. (Leguminosae) and was identified as (23R,24S)-16,23;16,24-diepoxycycloartan-3,25-diol 3-O--D-xylopyranoside 25-O--D-glucopyranoside. 相似文献
1000.
Hiroshi Hata Dr. Shigeru Yamaguchi Goro Mori Satomi Nakazono Taisuke Katoh Keishi Takatsu Satoru Hiroto Hiroshi Shinokubo Prof. Dr. Atsuhiro Osuka Prof. Dr. 《化学:亚洲杂志》2007,2(7):849-859
Highly regioselective and efficient borylation of a variety of porphyrins has been achieved by reaction with bis(pinacolato)diboron through C? H bond activation under iridium catalysis on the basis of the synthetic protocol developed by Miyaura, Hartwig, and Smith. A boryl group can be selectively introduced at sterically uncongested positions in the peripheral aryl groups of porphyrin substrates whose peripheral β‐positions are sterically hindered. Curiously, β substituents adjacent to the aryl group to be borylated have unexpectedly large effects on the regioselectivity, because the iridium catalyst can discriminate between subtle steric differences. Chemoselective borylation was also achieved for several functionalized porphyrins. This borylation protocol can be applied to various monomeric and oligomeric functional porphyrins, hence offering an efficient route to elaborate multiporphyrin‐based molecular constructs. 相似文献