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901.
Veselá A Barros AS Synytsya A Delgadillo I Copíková J Coimbra MA 《Analytica chimica acta》2007,601(1):77-86
The combination of the near infrared (NIR) and Fourier-transform infrared (FTIR) absorbance spectra (1100-2500 nm and 4000-600 cm−1) of 100 cocoa powder samples was used to build calibration models for the determination of the content of fat, nitrogen, and moisture. The samples that comprised the dataset had an average composition of 13.51% of fat, 3.77% nitrogen, and 3.98% moisture. The fat content ranged from 2.42 to 22.00%, the nitrogen from 0.88 to 4.48%, and moisture from 1.60 to 7.80%. For NIR, the relative root mean square error of cross-validation (RMSECV) was 7.0% (R2 = 0.96) for fat, 1.7% (R2 = 0.98) for nitrogen, and 5.2% (R2 = 0.94) for moisture. For FTIR, the relative RMSECV was 10.4% (R2 = 0.94) for fat and 3.9% (R2 = 0.95) for nitrogen. However, for moisture, it was not possible to build a calibration model with suitable predictability. The combination of the NIR and FTIR domains (data fusion) by outer product analysis PLS1 allowed to predict these parameters and to characterise frequencies in one domain based on the information of the other domain. This work allows to conclude that the second derivative of NIR is the recommended procedure to quantify fat, nitrogen, and moisture content in cocoa powders by infrared spectroscopy. 相似文献
902.
Structural correlation in a series of eight silver(I) complexes bearing substituted phenylethynide ligands was systematically investigated through variation of the position or steric bulk of substituents on the aromatic ring. All coordination frameworks are constructed with the supramolecular synthon Ar--C triple bond C superset Ag(n) (Ar=4-MeC6H4, 3-MeC6H4, 2-MeC6H4, 4-tBuC6H4, 3,5-(CF3)2C6H3; n=4, 5), and the presence of coexisting ligands was found to influence the supramolecular assembly. The role of pi-pi stacking, C--Hpi and Ag-C(aromatic) interactions in stabilizing the coordination networks is also discussed. 相似文献
903.
Cheng WD Wu DS Shen J Huang SP Xie Z Zhang H Gong YJ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(18):5151-5159
The dependence of the optical properties of [C(12)H(12)N(4)O(2)AgPF(6)](2) (dimer-1) and [C(28)H(28)N(6)O(3)AgPF(6)](2) (dimer-2) on the arrangement of the oxime moieties in the molecule and in bulk crystals was investigated by means of time-dependent density functional theory. Dimer-1 with simple pyridine oxime ligands and a wavy arrangement has a smaller dipole moment and larger transition energy between the two states, and thus smaller third-order polarizabilities and two-photon absorption cross sections. Dimer-2 with extended pyridine oxime ligands and a ladder arrangement has a larger dipole moment and smaller transition energy between the two states, and thus larger third-order polarizabilities and two-photon absorption cross sections. The lowest energy absorption band is red-shifted for dimer-2 as compared with dimer-1, due to more pronounced pi-pi delocalization interactions and weaker hydrogen bonding in dimer-2. The electronic absorption spectra, frequency-dependent third-order polarizabilities, and two-photon absorption cross sections involve significant contributions from charge transfers from pi/pi* orbitals of the pyridine oxime ligands but no contribution from PF(6) (-) ions or H(2)O molecules in the wavelength range studied for the monomers and dimers of the C(12)H(12)N(4)O(2)AgPF(6) and C(28)H(28)N(6)O(3)AgPF(6) molecules. The third-order susceptibilities and two-photon absorption coefficients of bulk solids were estimated on the basis of the optical properties of the corresponding dimers, and the bulk material constructed from dimer-2 has the larger optical parameters of the two. 相似文献
904.
Raabe I Antonijevic S Krossing I 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(26):7510-7522
In an earlier publication (J. Am. Chem. Soc. 2002 , 124, 7111) we showed that polymeric cationic [Ag(P4S3)n]+ complexes (n=1, 2) are accessible if partnered with a suitable weakly coordinating counterion of the type [Al(ORF)4]? (ORF: poly‐ or perfluorinated alkoxide). The present work addresses the following questions that could not be answered in the initial report: How many P4S3 cages can be bound to a Ag+ ion? Why are these complexes completely dynamic in solution in the 31P NMR experiments? Can these dynamics be frozen out in a low‐temperature 31P MAS NMR experiment? What are the principal binding sites of the P4S3 cage towards the Ag+ ion? What are likely other isomers on the [Ag(P4S3)n]+ potential energy surface? Counterion influence: Reactions of P4S3 with Ag[Al{OC(CH3)(CF3)2}4] (Ag[hftb]) and Ag[{(CF3)3CO}3Al‐F‐Al{OC(CF3)3)}3] (Ag[al‐f‐al]) gave [(P4S3)Ag[hftb]]∞ ( 7 ) as a molecular species, whereas [Ag2(P4S3)6]2+[al‐f‐al]?2 ( 8 ) is an isolated 2:1 salt. We suggest that a maximum of three P4S3 cages may be bound on average to an Ag+ ion. Only isolated dimeric dications are formed with the largest cation, but polymeric species are obtained with all other smaller aluminates. Thermodynamic Born–Haber cycles, DFT calculations, as well as solution NMR and ESI mass spectrometry indicate that 8 exhibits an equilibrium between the dication [Ag2(P4S3)6]2+ (in the solid state) and two [Ag(P4S3)3]+ monocations (in the gas phase and in solution). Dynamics: 31P MAS NMR spectroscopy showed these solid adducts to be highly dynamic, to an extent that the 2JP,P coupling within the cages could be resolved (J‐res experiment). This is supported by DFT calculations, which show that the extended PES of [Ag(P4S3)n]+ (n=1–3) and [Ag2(P4S3)2]+ is very flat. The structures of α‐ and γ‐P4S3 were redetermined. Their variable‐temperature 31P MAS NMR spectra are discussed jointly with those of all four currently known [Ag(P4S3)n]+ adducts with n=1, 2, and 3. 相似文献
905.
Synthetic oligopeptides with a tryptophan residue at the C-terminus have been used for the synthesis of gold and silver nanoparticles at pH 11. The tryptophan residue in the peptides is responsible for the reduction of metal ions to the respective metals, possibly through electron transfer. A mechanistic pathway has been proposed to explain the reductive properties of the tryptophan moiety of the peptide based on some spectroscopic techniques, such as UV-visible and fluorescence spectroscopy. This study reveals that some of the peptide molecules are converted to its corresponding ditryptophan, kynurenine form and some cross-linked products, all of which are highly fluorescent species. The resultant peptide-functionalized metal nanoparticles have also been characterized by UV-visible spectroscopy, transmission electron microscopy, and Fourier transform IR spectroscopy and thermogravimatric analysis. 相似文献
906.
Godet T Vaxelaire C Michel C Milet A Belmont P 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(19):5632-5641
An efficient and versatile tandem process of acetalization and cycloisomerization reactions has been developed for the reactions of 1-alkynyl-2-carbonylquinoline substrates. The reaction occurs thanks to Au(I) and Ag(I) catalysis. Silver(I) catalysis has been extensively studied (11 different silver species) on a broad range of quinoline derivatives (variation of alkyne substituent, of carbonyl function and of nucleophiles), leading to a variety of furoquinoline and pyranoquinoline moieties. An insight is given for the presumed mechanism along with DFT-B3 LYP/6-31G** calculations to address the 6-endo and 5-exo regioselectivities observed. 相似文献
907.
Ternary compounds M6Ni16Si7 (M=Ti, Zr, Hf) have been investigated by X-ray powder/single crystal and neutron powder diffraction. Compounds with Zr and Hf crystallize in the ordered Th6Mn23 type (Mg6Cu16Si7-type, space group ), whereas Ti6Ni16.7Si7 contains an additional Ni atom partially occupying the 24e site (M2 site, x=0.4637,0,0; occ.=0.119) inside a Ti octahedron; Ti atoms occupy a split position. Ti6Ni16.7Si7 represents a new variant of the filled Th6Mn23 type structure. Ab initio calculations confirm the structural difference: additional Ni atoms favour the 24e site for Ti6Ni16.7Si7, however, for the Zr and Hf-based compounds the unoccupied site renders an energetically lower ground state. Enthalpies of formation of Ti6Ni17Si7, Zr6Ni16Si7, and Hf6Ni16Si7 were calculated to be −68.65, −74.78, and −78.59 kJ/(mol of atoms), respectively. 相似文献
908.
研究了炸药爆轰合成的纳米金刚石粉在高温(约1 600 K)、高压(5.2 GPa)条件下的行为。将纳米金刚石粉与粉末合金(Ni70Mn25Co5、100#)混合、压制成圆片,与合金片 (Ni70Mn25Co5)和人造石墨片一起交替放入高温高压合成腔体内,进行高温高压实验。实验结果表明:在高温高压条件下,纳米金刚石粉不能长大,反而石墨化了;在相同的高压和保温时间条件下,随着温度的降低,纳米金刚石粉的石墨化程度减弱,纳米金刚石粉的纳米颗粒长大,可长成0.1 mm尺寸的金刚石颗粒(温度为1 070 K左右)。而在此条件下,人造石墨不能合成金刚石,一般金刚石晶体要变成石墨相。这进一步表明,纳米金刚石颗粒表面的活性使得它可以在较低的温度下长成较大颗粒的金刚石。 相似文献
909.
910.
本文利用吸附曲线及电化学的方法,研究了一系列抑制剂在银及溴化银上的吸附行为,将这些吸附性质与显影过程中相应的抑制剂存在时的显影结果对比,实验表明:只有当抑制剂在银上为中等的吸附,而在溴化银上吸附很小时,才可能利用抑制剂达到高反差。相应的机理及抑制剂在银上的吸附性质在文中也作了讨论。 相似文献