全文获取类型
收费全文 | 2615篇 |
免费 | 105篇 |
国内免费 | 6篇 |
专业分类
化学 | 1980篇 |
晶体学 | 33篇 |
力学 | 45篇 |
数学 | 188篇 |
物理学 | 480篇 |
出版年
2023年 | 14篇 |
2022年 | 120篇 |
2021年 | 90篇 |
2020年 | 56篇 |
2019年 | 57篇 |
2018年 | 46篇 |
2017年 | 57篇 |
2016年 | 102篇 |
2015年 | 78篇 |
2014年 | 82篇 |
2013年 | 157篇 |
2012年 | 138篇 |
2011年 | 186篇 |
2010年 | 123篇 |
2009年 | 104篇 |
2008年 | 168篇 |
2007年 | 127篇 |
2006年 | 110篇 |
2005年 | 118篇 |
2004年 | 84篇 |
2003年 | 64篇 |
2002年 | 55篇 |
2001年 | 33篇 |
2000年 | 41篇 |
1999年 | 18篇 |
1998年 | 21篇 |
1997年 | 27篇 |
1996年 | 24篇 |
1995年 | 32篇 |
1994年 | 28篇 |
1993年 | 35篇 |
1992年 | 30篇 |
1991年 | 10篇 |
1990年 | 13篇 |
1989年 | 21篇 |
1988年 | 19篇 |
1987年 | 16篇 |
1986年 | 7篇 |
1985年 | 14篇 |
1984年 | 15篇 |
1983年 | 10篇 |
1982年 | 11篇 |
1981年 | 12篇 |
1980年 | 20篇 |
1979年 | 17篇 |
1978年 | 14篇 |
1977年 | 10篇 |
1976年 | 9篇 |
1974年 | 6篇 |
1973年 | 9篇 |
排序方式: 共有2726条查询结果,搜索用时 171 毫秒
131.
Energy density, magnetomechanical coupling factor and a dimensionless sensing gage factor of 〈1 0 0〉 oriented single crystal iron-gallium alloys with 16, 17.5, 19, 24.7 and 29 at% gallium were studied as functions of stress and magnetic field. To estimate these quantities, the samples were characterized under different quasi-static stress and magnetic field conditions. The experimental behavior was modeled using an energy-based non-linear approach. Both the experimental data and the model simulations were used to calculate material parameters such as magnetic permeability, piezo-magnetic strain coefficient (d33), inverse piezo-magnetic coefficient (stress sensitivity, d*33) and Young's modulus in the material. These quantities were used to obtain energy density, magnetomechanical coupling factor and sensing gage factor as functions of magnetomechanical conditions. Maximum energy density of around 3 kJ/m3, magnetomechanical coupling factor higher than 0.75 and sensing gage factor on the order of 103 were calculated. 相似文献
132.
133.
Orientational order parameter S is evaluated in the nematic phase of six liquid crystal compounds, N-(p-n-propyl benzylidene)-p-n-alkoxy anilines, 3.Om and N-(p-n-propyloxy benzylidene)-p-n-alkoxy anilines, 3O.Om compounds with m = 6, 7 and 8, using different methods. The techniques employed are S from birefringence δn, Haller's approximation from (1?T/Tc) β, effective geometry parameter αg and Vuks’ scaling factor SC. The values of S obtained using the above methods are compared with one another and with the results on a number of liquid crystals; the liquid crystals favor isotropic Vuks’ method. 相似文献
134.
Monika Karpierz Jan Suchanicz Krzysztof Konieczny Dorota Sitko Pascal Marchet Urszula Lewczuk 《Phase Transitions》2015,88(7):662-667
The 0.5K0.5Bi0.5TiO3–0.5PbTiO3 ceramics were prepared by following a standard solid-state method. The Raman, thermal and dielectric properties of these ceramics were investigated. The X-ray measurements showed that samples have single perovskite-type structure with tetragonal symmetry. Dielectric study revealed that the dielectric behaviour of the investigated ceramics is rather of normal ferroelectrics with large thermal hysteresis. The transition temperature observed by means of differential scanning calorimetry measurements is in good agreement with that obtained from dielectric study. 相似文献
135.
Mrityunjoy Datta Alan J. Buglass 《Phosphorus, sulfur, and silicon and the related elements》2013,188(6):691-700
Abstract The hydrolysis of some N,N-dibenzylalkanesulfinamides (RSONH(CH2Ph)2; 1, R = Me; 2, R = iPr; 3, R = tBu; 4, R = 1-adamantyl) has been studied in 50% (v:v) acetonitrile–water solutions of hydrobromic and hydrochloric acids, mainly at 44.8 °C, using ultraviolet (UV) spectrophotometry to determine pseudo first-order rate constants. The compounds were found to hydrolyze by concurrent bimolecular neutral, acid-catalyzed, and acid-dependent nucleophilic (halide ion) catalysis pathways. The last-named is predominant in reactions in HBr solutions, but in HCl solutions, the acid-catalyzed pathway is predominant. The results indicate that both steric and electronic effects are important in these reactions. There appears to be no mechanistic switchover in the series 1→4. 相似文献
136.
Moamen S. Refat Sulekh Chandra Monika Tyagi 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1):22-33
Mn(II), Co(II), Ni(II), and Cu(II) complexes have been synthesized with benzil bis(thiosemicarbazone) (L) and characterized by elemental analyses, molar conductance measurements, magnetic susceptibility measurements, thermogravimetric studies, infrared (IR), electronic, and electron paramagnetic resonance (eEPR) spectral studies. The molar conductance measurements of the complexes in DMF correspond to the non-electrolytic nature of the complexes. Thus these complexes may be formulated as [M(L)X2] (where M = Mn(II), Co(II), Ni(II), Cu(II) and X = Cl? and NO3 ?). On the basis of IR, electronic, and EPR spectral studies, an octahedral geometry has been assigned for Mn(II), Co(II), and Ni(II) complexes, whereas a tetragonal geometry for the Cu(II) complexes is presumed. The free ligand and its metal complexes were tested against the phytopathogenic fungi (i.e., Rhizoctonia baticola, Alternaria alternata) in vitro. 相似文献
137.
Thermal stability of PbO was studied. Reactivity of oxides in the systems PbO–M2O3 (M = In, Fe) was investigated up to 650 °C. Using the DTA and XRD methods, parts of investigated ternary oxide systems, labelled by compounds: V2O5, Pb8V2O13 and M2O3 (M = In, Fe), have been divided into partial ternary systems. IR spectra of compounds Pb2MV3O11 (M = In, Fe) have been compared. 相似文献
138.
Monika Michel Luke Chimuka Tomasz Kowalkowski Ewa M. Cukrowska Bogusław Buszewski 《Journal of separation science》2013,36(5):986-991
An artificial neural network model of supported liquid membrane extraction process with a stagnant acceptor phase is proposed. Triazine herbicides and phenolic compounds were used as model compounds. The model is able to predict the compound extraction efficiency within the same family based on the octanol–water partition coefficient, water solubility, molecular mass and ionisation constant of the compound. The network uses the back‐propagation algorithm for evaluating the connection strengths representing the correlations between inputs (octanol–water partition coefficients logP, acid dissociation constant pKa, water solubility and molecular weight) and outputs (extraction efficiency in dihexyl ether and undecane as organic solvents). The model predicted results in good agreement with the experimental data and the average deviations for all the cases are found to be smaller than ±3%. Moreover, standard statistical methods were applied for exploration of relationships between studied parameters. 相似文献
139.
Timo Stark Sandra Marxen Andrea Rütschle Genia Lücking Siegfried Scherer Monika Ehling-Schulz Thomas Hofmann 《Analytical and bioanalytical chemistry》2013,405(1):191-201
A fast and robust high-throughput ultra-performance liquid chromatography/time-of-flight mass spectrometry (UPLC–TOF MS) profiling method was developed and successfully applied to discriminate a total of 78 Bacillus cereus strains into no/low, medium and high producers of the emetic toxin cereulide. The data obtained by UPLC–TOF MS profiling were confirmed by absolute quantitation of cereulide in selected samples by means of high-performance liquid chromatography with tandem mass spectrometry (HPLC–MS/MS) and stable isotope dilution assay (SIDA). Interestingly, the B. cereus strains isolated from four vomit samples and five faeces samples from patients showing symptoms of intoxication were among the group of medium or high producers. Comparison of HEp-2 bioassay data with those determined by means of mass spectrometry showed differences, most likely because the HEp-2 bioassay is based on the toxic action of cereulide towards mitochondria of eukaryotic cells rather than on a direct measurement of the toxin. In conclusion, the UPLC–electrospray ionization (ESI)–TOF MS and the HPLC–ESI–MS/MS–SIDA analyses seem to be promising tools for the robust high-throughput analysis of cereulide in B. cereus cultures, foods and other biological samples. Figure
Score plot (comp[1] vs. comp[2]) of UPLC‐TOF MS full scan analysis (50–1,300 Da) of 78 B. cereus strains with color‐coded signal intensity of the accurate mass of pseudo molecular ion of cereulide (m/z 1175.6608, [M+Na]+), from group 1 with the lowest up to group 5 with the highest signal intensity 相似文献
140.
Amitabha Datta Jui-Hsien Huang Jack K. Clegg Pei-Hsin Liu Sheng-Jie Chuang 《Central European Journal of Chemistry》2013,11(1):116-122
A tridentate hydrazone precursor, N′-[1-(pyridin-2-yl)ethylidene]acetohydrazide (L) (1:1 refluxed product of acetichydrazide and 2-acetylpyridine), produced two octahedral CuII and NiII derivatives, [CuL2]·NO3 (1) and [NiL2]·ClO4·H2O (2). Both are subjected to X-ray diffraction system, and structural investigation shows that the central metal atom (CuII or NiII) adopts a distorted octahedral geometry with N4O2 donor sets by coordination of a pair of independent hydrazone precursors. Besides X-ray study, IR and UV-vis spectra, thermal analysis and room temperature magnetic moments are utilized for establishing significant characteristics of both complexes. It is apparent that the M-Npyridine bonds are slightly longer than the M-Nimino bonds, Cu1-N1 and Cu1-N4 [2.300(2) and 2.038(2) ?] for 1 and Ni1-N1 and Ni1-N4 [2.075(2) and 2.084(1) ?] for 2, Cu1-N2 and Cu1-N5 [2.062(1) and 1.932(1) ?] for 1 and Ni1-N2 and Ni1-N5 [2.008(2) and 1.975(2) ?] for 2, respectively. As per our observation, the effective magnetic moment value (μeff) is found to be 1.77 B.M. for 1 and 3.06 BM for 2, respectively. 相似文献