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141.
Compounds A3M5 (A = alkaline earth, M = triel/tetrel): A Case Study on Structural and Electronic Factors Stabilizing Polar Intermetallics Starting from the non electron precise binary compounds Ca3Ga5/Sr3In5 (Hf3Ni2Si3 type) and Ba3Al5 at one hand and Ba3Pb5 (Pu3Pd5 type) at the other hand, a series of new ternary intermetallics of the general formula A3M5 (A: alkaline earth, M: triel/tetrel) has been synthesized, structurally characterized and studied by band structure calculations. The chemical substitution of M in A3M5 allows, via the continous variation of the radius ratio (rA:rM) and the valence electron number (VE/M) the detection of the geometrically and electronically determined stability ranges of the three structure types formed by the binary compounds. At values of rA:rM between 1.30 and 1.52 in the triel rich region of A3M′xM″5?x the Hf3Ni2Si3 type (orthorhombic, space group Cmcm) is formed: In Ca3Ga5 up to 1.8 Ga can be substituted by Al, in Sr3In5 similar amount of In can be replaced by either Al or Ga. The mixed trielide Sr3Al2.6Ga2.4 (a = 468.4(1), b = 1132.5(1), c = 1570.0(2) pm, R1 = 0.0261) can be obtained, although both corresponding binary phases are not known. At larger values of the ratio rA/rM as in Ba3Al3Ga2 (Ba3Al5 type, hexagonal, space group P63/mmc, a = 598.9(1), c = 1456.0(3) pm, R1 = 0.0353) layers of condensed M5 building blocks with Al‐Al partial bonds are formed. Substituting one In position in Sr3In5 against Pb results in the isotypic, but electron precise Zintl compound Sr3In4Pb (a = 506.1(1), b = 1191.8(3), c = 1650.2(4) pm, R1 = 0.0286), where the Fermi level in shifted into a distinct minimum of the density of states. Conversely, at the tetrele rich end of the series A3InxPb5?x, characterized by compounds of the Pu3Pd5 type (orthorhombic, space group Cmcm) with almost isolated nido clusters M5, a minimum of the DOS can be reached, if Pb is partially substituted by In (A3InxPb5?x with A = Sr/Ba: x = 0.7/0.6; a = 1084.6(2)/1118.6(2), b = 867.1(2)/904.4(1), c = 1104.8(2)/1133.9(2) pm, R1 = 0.0394/0.0434). 相似文献
142.
Thomas Müller 《Silicon Chemistry》2007,3(3-4):123-130
Quantum mechanical calculations at the B3LYP/6-311+G(d,p) and MP2/6-311+G(d,p) level of theory reveal that higher congeners
of the aromatic imidazolium ion, e.g. 2-E-imidazolium ions (E = Si, Ge, Sn), adopt either planar or pyramidal structures,
depending on the substituent R
2 attached to the element and on the group 14 element itsself. In the case of 2-silaimidazolium ions chemically significant
energy differences in favour of non-planar cations are predicted only for strongly σ-electron withdrawing substituents R
2 such as F or CF3. The pyramidalization computed for the germanium and tin analogues are however significant for all investigated substituents
R
2 and are accompanied by a substantial stabilization compared to the corresponding planar structures. A detailed bonding analysis
reveals that the non-planar cations are best described as complexes of monovalent group 14 element cations R
2E+ with the diazabutadiene ligand. 相似文献
143.
Darío Gmez Marina Dos Santos Fabin Fujiwara Griselda Polla Julieta Marrero Laura Dawidowski Patricia Smichowski 《Microchemical Journal》2007,85(2):276-284
A study was undertaken to evaluate the distribution of Al, As, Cr, Cu, Fe, Mn, Ni, Pb, Ti, V and Zn in fly ashes collected in the electrostatic precipitator of a thermal power plant in San Nicolás (Argentina). Five samples were collected during one week of operation. For the fractionation, the scheme applied consisted in extracting the elements in four fractions namely (i) soluble and exchangeable elements; (ii) carbonates, oxides and reducible elements; (iii) bound to sulfidic metals; and (iv) residual elements. Metals and metalloids at μg g− 1 level were determined in each fraction by inductively coupled plasma optical emission spectrometry (ICP OES). For validation, a standard reference material (SRM 1633 coal fly ash) from NIST was subjected to the same chemical sequential extraction procedure that the samples. X-ray diffraction powder (XRD) analysis and scanning electron microscopy (SEM) were used to characterize the major minerals present in the matrix. Total analyte concentration (in μg g− 1) varied from 10.6 for Pb to 17,622 for Al. Minimum and maximum concentrations (in μg g− 1) found in individual samples in the four fractions were: Al, 92.7–9668; As, < 0.3–143; Cr, 2.0–10.4; Cu, < 0.2–35.6; Fe, < 0.3–4992; Mn, < 0.1–128; Ni, < 0.3–139; Pb, < 0.5–9.1; Ti, < 0.3–2243; V, 17.0–112.9; and Zn, < 0.1–68.2. The leachability of the 11 elements under study proved to be different. Low percentages of Al (1%), V (7%) and Cr (8%) were detected in the most bioavailable fraction. Arsenic was found to be most abundant in the non-silicate phase, represented by the second and third fractions, while Cr, Fe, Ni, Pb and Zn were mostly associated to the residual fraction. 相似文献
144.
Amitava Choudhury Larisa A. Polyakova Ingo Hartenbach Thomas Schleid Peter K. Dorhout 《无机化学与普通化学杂志》2006,632(15):2395-2401
Four related quaternary compounds containing rare‐earth metals have been synthesized employing the molten flux method and metathesis. The reactions of Eu and Rb2S5 with Si and Ge in evacuated fused silica ampoules at 725 °C for 150 h yielded RbEuSiS4 ( I ) and RbEuGeS4 ( II ), respectively. On the other hand, a reaction between CeCl3 and K4Ge4Se10 at 650 °C for 148 h has yielded KCeGeSe4 ( III ) and KPrSiSe4( IV ) was obtained by the reaction of elemental Pr, Si and Se in KCl flux at 850 °C for 168 h. Crystal data for these compounds are as follows: I , orthorhombic, space group P212121 (#19), a = 6.392(1), b = 6.634(2), c = 17.001(3) Å, α = β = γ = 90°, Z = 4; II , monoclinic, space group P21/m (#11), a = 6.498(2), b = 6.689(3), c = 8.964(3) Å, β = 108.647(6)°, Z = 2; III , monoclinic, space group P21 (#4), a = 6.852(2), b = 7.025(2), c = 9.017(3) Å, β = 108.116(2)°, Z = 2; IV , monoclinic, space group P21 (#4), a = 6.736(2), b = 6.943(2), c = 8.990(1) Å, β = 108.262(2)°, Z = 2. The crystal structures of I ‐ IV contain two‐dimensional corrugated anionic layers of the general formula, [LnEQ4]? (Ln = Ce, Pr, Eu; E = Si, Ge and Q = S, Se) alternately piled upon layers of alkali cations. In addition to structural elucidation, Raman and UV‐visible spectroscopy, and magnetic measurements for compound III (KCeGeSe4) are also discussed. 相似文献
145.
Investigation of the separation of scandium and rare earth elements from red mud by use of reversed-phase HPLC 总被引:1,自引:0,他引:1
Tsakanika LV Ochsenkühn-Petropoulou MT Mendrinos LN 《Analytical and bioanalytical chemistry》2004,379(5-6):796-802
A chromatographic method has been developed for separation and determination of scandium (Sc) and rare earth elements (REEs) in samples from a red mud (RM)-utilization process. Reversed-phase high-performance liquid chromatography (RP-HPLC) with post-column derivatization using 4-(2-pyridylazo)-resorcinol (PAR) and UV–visible detection at 520 nm was tested using different gradient elution profiles and pH values to optimize separation and recovery, primarily for Sc but also for yttrium and the individual lanthanides, from iron present in the samples. The separation was performed in less than 20 min by use of a mobile phase gradient. The concentration of -hydroxyisobutyric acid (-HIBA), as eluent, was altered from 0.06 to 0.4 mol L–1 (pH 3.7) and 0.01 mol L–1 sodium salt n-octane sulfonic acid (OS) was used as modifier. Very low detection limits in the nanogram range and a good resolution for Sc and REEs except for Y/Dy were achieved. Before application of the method to the red mud samples and to the corresponding bauxites, Sc and REEs were leached from red mud with 0.6 mol L–1 HNO3
and mostly separated, as a group, from the main elements by ion exchange/selective elution (6 mol L–1
HNO3) in accordance with a pilot-plant process developed in this laboratory. After evaporation of the eluent to dryness the extracted elements were re-dissolved in the mobile phase. By use of this chromatographic method Sc, which is the most expensive of the elements investigated and occurs in economically interesting concentrations in red mud, could be separated not only from co-existing Fe but also from Y/Dy, Yb, Er, Ho, Gd, Eu, Sm, Nd, Pr, Ce and La. All the elements investigated were individually recovered. Their recoveries were found to be nearly quantitative. 相似文献
146.
为了对比野生与种植青海川西獐牙菜中微量元素的变化,分别采集野生川西獐牙菜与种植青海川西獐牙菜种子采收前后的全植株,采用原子吸收光谱仪测定了其铜、锌、铁、锰、钴等微量元素含量。结果表明,野生川西獐牙菜较种植青海川西獐牙菜中微量元素含量高,种植川西獐牙菜在成熟种子采收后较采收前(花果期)铁、锰、钴、锌等元素含量高。 相似文献
147.
微量元素叶面肥料中硼的测定 总被引:2,自引:0,他引:2
张文德 《理化检验(化学分册)》2002,38(3):137-138
研究了在 pH 6 .5乙酸铵缓冲溶液中 ,硼与 3 甲氧基 甲亚胺H的显色反应条件 ,最大吸收在 4 2 0nm处 ,摩尔吸光系数为 8.1× 10 3,硼含量在 0~ 10 μg/ 10ml范围内符合比耳定律。用于微量元素叶面肥料中硼的测定 ,获得了与国标法一致的结果 相似文献
148.
火焰原子吸收光谱法测定南湖菱中矿质元素 总被引:5,自引:0,他引:5
用火焰原子吸收光谱法测定嘉兴南湖菱中钾、钠、钙、镁、铁、铜、锌、锰、镉、铅金属元素的含量。结果表明,南湖菱中有较高的矿物质营养价值,有害元素的含量低于国家食品允许标准。 相似文献
149.
150.
Energy-adjusted pseudopotentials for the rare earth elements 总被引:1,自引:0,他引:1
Nonrelativistic and quasirelativistic energy-adjusted pseudopotentials and optimized (7s6p5d)/[5s4p3d]-GTO valence basis sets for use in molecular calculations for fixed f-subconfigurations of the rare earth elements, La through Lu, have been generated. Atomic excitation and ionization energies from numerical HF, as well as SCF pseudopotential calculations using the derived basis sets, differ by less than 0.1 eV from numerical HF all-electron results. Corresponding values obtained from CI(SD), CEPA-1, as well as density functional calculations using the quasirelativistic pseudopotentials, are in reasonable agreement with experimental data. 相似文献