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21.
TG and DTA have been carried out on new anhydrous rare-earth selenites R2SeaO3+2a (a=3.5,4) in order to establish their stability. Decomposition occurs in three steps attributed to successive losses of SeO2. The first process gives rise to other new group of selenites of composition R2Se3O9, which crystallize in two different forms depending on the rare-earth element. The second process leads to isomorphous compounds R2SeO5. The final product of thermal degradation is R2O3. All products were characterized by chemical analysis and X-ray powder diffraction methods. 相似文献
22.
S. V. Belaya D. Yu. Naumov N. V. Podberezskaya I. G. Vasilieva N. V. Pervukhina 《Journal of Structural Chemistry》2003,44(6):1011-1017
A series of experiments have been carried out to synthesize holmium polysulfides at temperatures from 600 to 840°C and sulfur vapor pressures of (2.1, 6.5, 16.7)á105 Pa. Polysulfide crystals sized up to 2 mm and micron-sized powders were investigated thereafter by powder diffractometry. Powder diffraction patterns were calculated based on our previous X-ray structural data. Characteristic reflections have been revealed for the individual monoclinic and tetragonal phases, and X-ray phase analysis (XRPA) has been performed for all batches of the synthesis. The monoclinic phase is shown to prevail irrespective of the synthetic conditions. The tetragonal phase was found in amounts of up to 10 wt.%. 相似文献
23.
Pasynskii A. A. Semenova N. I. Torubaev Yu. V. Belousov P. V. Lyssenko K. A. Dobrokhotova Zh. V. 《Russian Chemical Bulletin》2001,50(11):2215-2220
Transmetallation of the Fe3(3-X)2(CO)9 clusters (X = S, Se, or Te) under the action of (-C8H12)PtCl2 afforded new heterometallic clusters (-C8H12)Pt(3-X)2Fe2(CO)6 (2—4, respectively), which were characterized by X-ray diffraction analysis. The (-C8H12)Pt fragment in these clusters is bound to two 3-bridging chalcogen atoms X. The iron atoms are linked to each other. The coordination environment about the Pt atom is planar-square; the Pt...Fe distance is larger than 3.2 . In the synthesis of cluster 4, a new Pt complex was also obtained for which the structure (CO)2Pt(-Te)2Pt(CO)2 (5) was proposed. According to the results of differential scanning calorimetry, thermal decomposition of complex 5 gave rise only to PtTe, whereas complexes 1—4 gave products with the empirical formula Fe2PtX2C2O2. The influence of the steric effects on the geometry of the clusters is discussed. 相似文献
24.
Vlastimil Matějec Ivan Kašík Daniela Berková Miloš Hayer Jiří Kaňka 《Journal of Sol-Gel Science and Technology》1998,13(1-3):617-621
Optical cores of preforms for drawing optical fibers doped with Er3+ and Yb3+ were fabricated by the sol-gel method with the aim of increasing the thickness of glass layers coated in a single coating cycle and to determine the relation between the preparation conditions and optical properties of the fibers. Al2O3-P2O5-SiO2 and TiO2-P2O5-SiO2 glasses have been studied as matrices for entrapping the rare-earth elements. Input sols have been prepared from silicon and titanium alkoxides, AlCl3, ErCl3, YbCl3, POCl3, water and a modifier under acidic catalysis of HCl. The sols were coated on the inner wall of a silica substrate tube and the gel layers were sintered at high temperatures up to 2000°C after which the tube was collapsed into the preform. Continuous and homogenous glass films with the maximum thickness of about 8 m were fabricated. The influence of high-temperature heat treatment of the layers on their composition and optical attenuation was observed. The amplified stimulated emission of Er3+ around 1.55 m was measured under the excitation of the fibers by an Nd : YAG laser at 1.064 m. 相似文献
25.
Pasynskii A. A. Grigoriev V. N. Torubaev Yu. V. Blokhin A. I. Shapovalov S. S. Dobrokhotova Zh. V. Novotortsev V. M. 《Russian Chemical Bulletin》2003,52(12):2689-2700
Transmetallation of the dichalcogenide complexes [CpMn(CO)2]2(-X2) (X = S or Se) with M(CO)5(thf) (M = Cr or W) afforded new heterometallic complexes CpMn(CO)2(-Se2)Cr(CO)5, CpMn(CO)2(-Se2)[Cr(CO)5]2, CpMn(CO)2(-X2)[W(CO)5]2 (X = S or Se), and CpMn(CO)2(-Se2)[Cr(CO)5][W(CO)5]. According to the X-ray diffraction data, their molecular structures contain the cyclic MnX2 fragments coordinated by one or two M(CO)5 groups via the X atoms. Study of thermal decomposition of the manganese complexes with different Mn : M : X ratios (M = Cr, W; X = S, Se, Te) by differential scanning calorimetry (DSC) and thermogravimetry demonstrated that this process took place at rather low temperatures (100—400 °C) and was accompanied by complete elimination of the CO groups followed by elimination of the Cp groups. At any metal to chalcogen ratio, the resulting inorganic chalcogenides contained no impurities of metal oxides and carbides. 相似文献
26.
Electron transitions in divinyl chalcogenides (CH2=CHXCH=CH2, where X is S, Se, or Te) have been analyzed using UV absorption spectra of dialkyl and alkyl vinyl chalcogenides. The following relations for the orbital energies are found: * < * < * < * for Te and * < * < * < * for S and Se. For chalcophenes, a correlation between the energy of the excited state (E
*) of specific symmetry, the ionization potential (I) and the electron affinity (EA) is obtained:E
*=const+(I+EA)/2. The electron affinity of divinyl chalcogenides is estimated. The correlation between the excited * states of divinyl chalcogenides and chalcophenes is discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 831–835, May, 1994. 相似文献
27.
28.
Potential dependences of the angle of contact between perfluorodecaline C10F18 and copper, copper(I) sulfide, and copper telluride Cu4Te3 in 0.1 M CH3COONa are measured. The data are in good agreement with the metal hardness measured in 1 M KOH. The uncharged-surface potentials (USP) for copper, copper(I) sulfide, and copper telluride equal 0.05–0.07, –0.02 to –0.04, and 0.05–0.07 V (NHE) in 0.1 M CH3COONa. Studying the effect of Br– ions shows that USP for copper and Cu2S shift in, respectively, the negative and positive directions with an increase in [Br–]. For copper telluride, USP shifts in the positive direction at low Br– concentrations, and at NaBr concentrations in excess of 0.04 M, in the negative direction. 相似文献
29.
Virginia Lea Miller Wei-li Lee Nai-Phuan Ong 《Journal of solid state chemistry》2005,178(5):1508-1512
We report the synthesis and elementary properties of the Co7Se8−xSx (x=0-8) and Ni7Se8−xSx (x=0-7) solid solutions. Both systems form a NiAs-type structure with metal vacancies. In general, the lattice parameters decrease with increasing x, but in the Ni7Se8−xSx system c increases on going from x=5 to 7. Magnetic susceptibility measurements show that all samples exhibit temperature-independent paramagnetism from 25-250 K. Samples within the Co7Se8−xSx system, as well as Ni7Se8 and Ni7SeS7, were found to be poor metals with resistivities of ∼0.20 and ∼0.06 mΩ cm at 300 K, respectively. The Sommerfeld constant (γ) was determined from specific heat measurements to be ∼13 mJ/molCoK2 and ∼7 mJ/molNiK2 for Co7Se8−xSx and Ni7Se8−xSx, respectively. 相似文献
30.
The ternary rare-earth nickel arsenides R3Ni7As5 (R=La, Ce, Pr, Nd, Sm) were prepared by arc melting the elemental components and subsequent annealing at T=1070 K. The crystal structure of Ce3Ni7As5 was determined from single-crystal X-ray data: space group Pmmn, Z=2; a=1.24210(6), b=0.40797(2), c=0.96436(5) nm, RF=0.037 (Rw=0.044); 596 independent reflections; 53 variable parameters. It is a new structure type, which belongs to the family of BaAl4-related structures. The magnetic properties are as follows: La3Ni7As5 is a Pauli-type paramagnet above 4.2 K, Pr3Ni7As5 remains paramagnetic in the temperature range investigated and Nd3Ni7As5 undergoes a ferromagnetic ordering at TC=24 K. Sm3Ni7As5 orders antiferromagnetically at a Néel temperature of TN=18 K followed by a spin flip towards parallel spin-alignment below TC=6 K. Ce3Ni7As5 reveals a strong deflection of the linear temperature dependence of the inverse susceptibility due to an intermediate valence behavior. The temperature dependence of the electrical resistivities for the La, Pr, Nd, Sm containing samples corroborates with the metallic state of the non-magnetic (La) and the magnetically ordered compounds, whereas in case of Ce3Ni7As5 the resistivity seems to be determined by an interplay of Kondo scattering and crystalline field effects. LIII X-ray absorption spectra confirm the demagnetization effects owing from valence fluctuations, the actual valence thereby changes from ν=3.10-3.14 at room temperature and 10 K, respectively. 相似文献