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91.
The crystal structure of the hexahydroborite analog Ca[B(OH)4]2 · 2H2O (a = 7.9941(3) Å, b = 6.6321(2) Å, c = 7.9871(3) Å, β = 104.166(4)°, V = 410.58(3) Å3, sp. gr. P2/c, Z = 2, ρcalc = 1.891 g/cm3; Xcalibur S CCD automated diffractometer, 1196 reflections with I > 2σ(I), λMoK α), which was synthesized by the hydrothermal method via the recrystallization of calciborite CaB2O4 (M) in the M ? B2O3 ? H2O system (t = 250°C and P = 70–80 atm), was refined by the least-squares method with anisotropic displacement parameters (H atoms were located; R 1 = 0.0260). The structure of synthetic hexahydroborite consists of infinite columns running along the c axis. The columns are formed by Ca polyhedra linked together and to [B(OH)4] orthotetrahedra by sharing edges. Along the two other axes, the translationally equivalent columns are linked only by hydrogen bonds. The presence of a stronger bond between the discrete (Ca-B-O) columns along the shortest (b = 6.6 Å) axis accounts for the possibility of the shift of the columns by 1/2T b and the formation of the second modification of Ca[B(OH)4]2 · 2H2O. The crystals of synthetic hexahydroborite were studied by IR spectroscopy. A crystal-chemical analysis was performed for a series of natural metaborates with the general formula CaB2O4 · nH2O (CaO: B2O3 = 1: 1, n = 0–6), including calciborite CaB2O4 and hexahydroborite CaB2O4 · 6H2O as the end members. 相似文献
92.
Single crystals of Rb2NaAlF6, the Rb analogue of the mineral elpasolite, are obtained in the NaF-Rb2CO3-Al2O3-Rb3PO4-H2O system under hydrothermal conditions, and their structure is determined by X-ray diffraction (R = 0.0188): a = 8.3087(1) Å, space group $Fm\bar 3m$ , Z = 4, and ρcalcd = 3.88 g/cm3. The hypothesis that Rb elpasolite exists in nature in late associations of pegmatites enriched in rubidium is proposed. 相似文献
93.
The relation between the IR data and the quantum-chemical indices. calculated by the CNDO/2 method has been studied. The linear relationship between the experimentally measured °C≡N and the corresponding Wiberg bond index (WC≡N) has been found for the series of conjugated nitriles including neutral molecules. anion - radicals and dianions. The changes in the intensity of the stretching C≡N vibration on transition from a neutral molecule into anion - radical and dianion have been investigated by the CNDO/2 method. The calculated values for δμ/δQCN show that in the order: neutral molecule, anion - radical and dianion the IR intensity of the stretching C≡N vibration significantly increases. 相似文献
94.
95.
Complexes of poly(propylene imine) dendrimers D8[DAB-dendr-(NH2)8] and D32 [DAB-dendr-(NH2)32] were prepared by interaction of the dendrimers with transition metal salts such as FeCl3.6H2O; CoCl2.6H2O; CuCl2.2H2O; VOSO4.5H2O; Na2MoO4.2H2O and Na2WO4.2H2O at room temperature in aqueous solutions. The content of metal ions in the complexes was found to be from 8.2 to 69.6 mg metal ion/g polymer carrier. The complexes were characterized by using IR, UV-VIS, Moessbauer spectroscopy and EPR. The anticipated co-ordination structure of the compounds was suggested. It was found that the order of the catalytic activity of the complexes of poly(propylene imine) dendrimers D8 and D32 in the reaction of epoxidation of cyclohexene with organic hydroperoxides such as tert-butyl hydroperoxide (t-BHP), ethylbenzene hydroperoxide (EBHP) and cumene hydroperoxide (CHP) was as follows: D32-MoО22+>D32-VО2+>D32-WО22+ > D32-Co2+ > D32-Cu2+>D32-Fe3+. The order of reactivity of organic hydroperoxides in the reaction studied was: t-BHP > EBHP > CHP. 相似文献
96.
N. A. Yamnova S. M. Aksenov V. S. Mironov A. S. Volkov E. Yu. Borovikova O. A. Gurbanova O. V. Dimitrova D. V. Deyneko 《Crystallography Reports》2017,62(3):382-390
The new potassium–bismuth–nickel oxophosphate obtained by hydrothermal synthesis in the Bi(OH)3–NiCO3–K2CO3–K3PO4 system is studied by X-ray diffraction, IR spectroscopy, and Raman spectroscopy. Parameters of the orthorhombic cell are as follows: a = 13.632(1) Å, b = 19.610(2) Å, and c = 5.4377(3) Å; V = 1452.64(2) Å3; and space group Pnma. The structure is solved and refined to the final discrepancy factor R 1 = 5.76% in the anisotropic approximation of atomic displacements using 3606 reflections with I > 2σ(I). The crystal-chemical formula (Z = 4) is KBi4{Ni2O4(PO4)3}, where the composition of the layer nickel–phosphate polyanion is enclosed in braces. Theoretical calculations show that all exchange spin interactions between Ni2+ ions are antiferromagnetic and very weak (J < 0.1 cm–1) because of the polyatomic character of bridging Ni–O–P–O–Ni and Ni–O–Bi–O–Ni groups. Thus, this compound is expected to be paramagnetic with very weak antiferromagnetic exchange interactions and appreciable energy of zero-field splitting of the spin levels of Ni2+ ions. 相似文献
97.
E. L. Belokoneva S. Yu. Stefanovich O. V. Dimitrova N. N. Mochenova N. V. Zubkova 《Crystallography Reports》2009,54(5):814-821
The structures of new nonaborates, (Pb,Ba)3(OH)[B9O16][B(OH)3] (space group P31c) and Ba3Na(OH)[B9O16][B(OH)4] (space group P1), synthesized under hydrothermal conditions, have been investigated. These structures differ from the structure of the previously
studied nonaborate Pb3(OH)[B9O16][B(OH)3] (space group P31c) in the occupation of the zeolite nonaframework, which, in the case of the (Ba,Na) borate, contains a larger number of cations
and OH groups. Despite this difference, all the structures have a high trigonal or pseudotrigonal symmetry, which suggests
the existence of the structure type or the family of nonaborates. The structural similarity is violated by the presence of
B(OH)41− tetrahedra instead of neutral trigonal groups B(OH)3 in channels of the (Ba,Na) borate. The latter polyhedra are characterized by a pseudomonoclinic arrangement that corresponds
to the space group Cc with the true triclinic group P1. The ability of nonaborates to generate the optical second harmonic as a function of the specific features of their crystal
structures is discussed. 相似文献
98.
Lyudmila Kabaivanova Venelin Hubenov Lyudmila Dimitrova Ivan Simeonov Haoping Wang Penka Petrova 《Molecules (Basel, Switzerland)》2022,27(5)
Anaerobic digestion (AD) is a microbially-driven process enabling energy production. Microorganisms are the core of anaerobic digesters and play an important role in the succession of hydrolysis, acidogenesis, acetogenesis, and methanogenesis processes. The diversity of participating microbial communities can provide new information on digester performance for biomass valorization and biofuel production. In this study anaerobic systems were used, operating under mesophilic conditions that realized biodegradation processes of waste wheat straw pretreated with NaOH—a renewable source for hydrogen and methane production. These processes could be managed and optimized for hydrogen and methane separately but combining them in a two-stage system can lead to higher yields and a positive energy balance. The aim of the study was to depict a process of biohydrogen production from lignocellulosic waste followed by a second one leading to the production of biomethane. Archaeal and bacterial consortia in a two-stage system operating with wheat straw were identified for the first time and the role of the most important representatives was elucidated. The mixed cultures were identified by the molecular-biological methods of metagenomics. The results showed that biohydrogen generation is most probably due to the presence of Proteiniphilum saccharofermentans, which was 28.2% to 45.4% of the microbial community in the first and the second bioreactor, respectively. Archaeal representatives belonging to Methanobacterium formicicum (0.71% of the community), Methanosarcina spelaei (0.03%), Methanothrix soehngenii (0.012%), and Methanobacterium beijingense (0.01%) were proven in the methane-generating reactor. The correlation between substrate degradation and biogas accumulation was calculated, together with the profile of fatty acids as intermediates produced during the processes. The hydrogen concentration in the biogas reached 14.43%, and the Methane concentration was 69%. Calculations of the energy yield during the two-stage process showed 1195.89 kWh·t−1 compared to a 361.62 kWh·t−1 cumulative yield of energy carrier for a one-stage process. 相似文献
99.
Kiril Blazhev Gavazov Petya V. Racheva Nikolina P. Milcheva Vidka V. Divarova Denitsa Dimitrova Kiradzhiyska Fatma Gen Antoaneta D. Saravanska 《Molecules (Basel, Switzerland)》2022,27(15)
The hydrophobic azo dye 6-hexyl-4-(2-thiazolylazo)resorcinol (HTAR, H2L) was studied as part of a system for the centrifuge-less cloud point extraction (CL-CPE) and spectrophotometric determination of traces of cobalt. The extracted 1:2 (Co:HTAR) complex, [CoIII(HL−)(L2−)]0, shows an absorption maximum at 553 nm and contains HTAR in two different acid–base forms. Optimum conditions for its formation and CL-CPE were found as follows: 1 × 10−5 mol L−1 of HTAR, 1.64% of Triton X-114, pH of 7.8, incubation time of 20 min at ca. 50 °C, and cooling time of 30 min at ca. −20 °C. The linear range, limit of detection, and apparent molar absorptivity coefficient were 5.4–189 ng mL−1, 1.64 ng mL−1, and 2.63 × 105 L mol−1 cm−1, respectively. The developed procedure does not use any organic solvents and can be described as simple, cheap, sensitive, convenient, and environmentally friendly. It was successfully applied to the analysis of artificial mixtures and real samples, such as steel, dental alloy, rainwater, ampoules of vitamin B12, and saline solution for intravenous infusion. 相似文献
100.