全文获取类型
收费全文 | 2408篇 |
免费 | 73篇 |
国内免费 | 10篇 |
专业分类
化学 | 1542篇 |
晶体学 | 69篇 |
力学 | 56篇 |
数学 | 207篇 |
物理学 | 617篇 |
出版年
2023年 | 29篇 |
2022年 | 56篇 |
2021年 | 48篇 |
2020年 | 66篇 |
2019年 | 59篇 |
2018年 | 35篇 |
2017年 | 40篇 |
2016年 | 79篇 |
2015年 | 60篇 |
2014年 | 92篇 |
2013年 | 196篇 |
2012年 | 137篇 |
2011年 | 182篇 |
2010年 | 92篇 |
2009年 | 87篇 |
2008年 | 143篇 |
2007年 | 165篇 |
2006年 | 87篇 |
2005年 | 80篇 |
2004年 | 64篇 |
2003年 | 38篇 |
2002年 | 41篇 |
2001年 | 31篇 |
2000年 | 19篇 |
1999年 | 9篇 |
1998年 | 13篇 |
1997年 | 11篇 |
1996年 | 17篇 |
1995年 | 20篇 |
1994年 | 23篇 |
1993年 | 28篇 |
1992年 | 21篇 |
1991年 | 9篇 |
1990年 | 11篇 |
1989年 | 13篇 |
1988年 | 21篇 |
1987年 | 21篇 |
1986年 | 20篇 |
1985年 | 23篇 |
1984年 | 22篇 |
1983年 | 26篇 |
1982年 | 25篇 |
1981年 | 21篇 |
1980年 | 19篇 |
1979年 | 18篇 |
1978年 | 28篇 |
1977年 | 16篇 |
1976年 | 22篇 |
1974年 | 19篇 |
1973年 | 12篇 |
排序方式: 共有2491条查询结果,搜索用时 0 毫秒
81.
Hard sphere diameters of liquid alkali metal alloys (Na-Cs and K-Rb) are calculated at 373 K ensuring the minimum Helmholtz
free energy of the system. These diameters are then used to fix the packing density of the alloy. On alloying, the hard sphere
diameters of Na in Na-Cs and K in K-Rb alloys expand whereas those of Cs and Rb contract. 相似文献
82.
We have experimentally demonstrated vibration analysis of a reflecting object in time-average mode using shearing interferometry and interferometric grating. Experimental results show that time-average moiré fringes, formed between fringe pattern reflected from object and sinusoidal grating are modulated spatially by the amplitude of vibrating tilt. From the experimental results, information regarding tilt of vibrating objects can be determined. 相似文献
83.
84.
Theac anddc electroluminescence in CaS:Cu, Sm have been investigated. The luminescence spectra show three peaks in the visible region.
The brightness-voltage dependence satisfies the relationB=B
0 exp (−b/V
1/2) with two modes of variation. The nature of this dependence indc andac at different frequencies is discussed. The electroluminescence brightness also depends on the temperature of the phosphors
and shows a peak around 80.0;C. The electroluminescence efficiency increases with applied voltage up to 2200 V and this dependence
on V is explained on the basis of a transport process of the Schottky emission type. 相似文献
85.
Ujjal Debnath Narayan Chandra Chakraborty Subenoy Chakraborty 《General Relativity and Gravitation》2008,40(4):749-763
We investigate exact solution in higher dimensional Husain model for a null fluid source with pressure p and density ρ are related by the following relations (i) p = kρ, (ii) (variable modified Chaplygin) and (iii) p = kρα (polytropic). We have studied the nature of singularity in gravitational collapse for the above equations of state and also
for different choices of the of the parameters k and B namely, (i) k = 0, B = constant (generalized Chaplygin), (ii) B = constant (modified Chaplygin). It is found that the nature of singularity is independent of these choices of different
equation of state except for variable Chaplygin model. Choices of various parameters are shown in tabular form. Finally, matching
of Szekeres model with exterior Husain space–time is done. 相似文献
86.
Laboratory formation of four isomers of C5H2 molecule is reported and detection of the ring-chain isomer (isomer 1) of C5H2 in cosmic objects has been suggested. For identification of a molecule in cosmic objects, one of the required input data
is EinsteinA-coefficients (radiative transition probabilities) for the molecule. Here, we report EinsteinA-coefficients for electric dipole transitions in the ring-chain isomer of C5H2 among the rotational levels of the ground electronic and ground vibrational states up to 21 cm−1. 相似文献
87.
When a crystal is fractured impulsively by the impact of a moving piston, then initially the mechanoluminescence (ML) intensity increases quadratically with time, attains a peak value and later on it decreases with time. Considering that the solid state ML and gas discharge ML are excited due to the charging and subsequent production of electric field near the tip of moving cracks, expressions are derived for the transient ML intensity I, time tm and intensity Im corresponding to the peak of ML intensity versus time curve, respectively, the total ML intensity IT, and for fast and slow decays of the ML intensity. It is shown that the decay time for the fast decrease of the ML intensity after tm, is related to the decay time of the strain rate of crystals, and the decay time of slow decay of ML, only observed in phosphorescent crystals, is equal to the decay time of phosphorescence. The value of tm decreases with the increasing impact velocity, Im increases with the increasing impact velocity, and IT initially increases and then it tends to attain a saturation value for higher values of the impact velocity. The values of tm, Im and IT increase linearly with the thickness, area of cross-section and volume of the crystals, respectively. So far as the rise, attainment of ML peak, and fast decay of ML are concerned, there is no any significant difference in the time-evolution of solid state ML, gas discharge ML, and the ML emission consisting of both the solid state ML and gas discharge ML. From the time-dependence of ML, the values of the time-constant for decrease of the surface area created by the movement of a single crack, the time-constant for the decrease of strain rate of crystals, and the decay time of phosphorescence of crystals can be determined. A good agreement is found between the theoretical and experimental results. The importance of fracto ML induced by impulsive deformation of crystals is discussed. 相似文献
88.
Kalyanmoy Jana Somnath Das Tithi Maity Maidul Hossain Subhas Chandra Debnath 《Journal of Coordination Chemistry》2018,71(10):1497-1509
A new Co(II) complex of general formula [Co(L)2] has been synthesized from a NNO tridentate Schiff base ligand, 2-[(piperidin-2-ylmethylimino)-methyl]-phenol (L). The title complex is characterized by elemental, spectroscopic, antibacterial, and single crystal X-ray structural studies. X-Ray crystallography reveals that the complex shows a distorted octahedral geometry around the Co(II) ion. The complex was tested against several bacteria and shows good antibacterial activities against almost all of the bacteria. The interactions of the title complex with calf thymus deoxyribonucleic acid (CT-DNA) have been investigated by electronic absorption and fluorescence spectroscopy, showing that the complex interacts with CT-DNA via partial intercalation. Thermogravimetric analysis (TGA) of the complex has also been reported and the result shows that the complex is thermally stable up to 134 °C. 相似文献
89.
Transition metal complexes of Mn(II) and Ni(II) have been synthesized with novel bioactive Schiff's base ligand. Schiff's base ligand i.e. benzoylacetone‐bis(2‐amino‐4‐methylbenzothioazole) has been synthesized via condensation reaction between 2‐amino‐4‐methylbenzothioazole and benzoylacetone in 2:1 ratio, respectively. Synthesized ligand has been characterized using elemental analysis, infra‐red, 1H–NMR and mass spectroscopy techniques. Characterization of complexes was based on magnetic moment, molar conductance, elemental analysis, electronic spectra, infra‐red and EPR spectroscopic techniques. Molar conductance data suggest that metal complexes are non‐electrolytic in nature. Therefore, these complexes are formulated as [M(L)X2], where M = Mn(II), Ni(II), L = Schiff's base ligand, X = Cl?, CH3COO?, NO3?. Data of characterization study suggest octahedral geometry for Mn(II) and Ni(II) complexes. Geometry of metal complexes was also optimized with the help of computational study i.e. molecular modelling. Computational study also suggests octahedral geometry for complexes. Free ligand as well as its all metal complexes have been screened against the growth of pathogenic bacteria (E.coli, S.aureus) and fungi (C.albicans, C.krusei, C.parapsilosis, C.tropicalis) to assess their inhibition potential. The inhibition data revealed that metal complexes exhibit higher inhibition potential against the growth of bacteria and fungi microorganisms than free ligand. 相似文献
90.
Manganese(II) complexes having the general composition Mn(L)2X2 (where L = 3‐bromoacetophenone semicarbazone, 3‐bromoacetophenone thiosemicarbazone, 1‐tetralone semicarbazone, 1‐tetralone thiosemicarbazone, flavanone semicarbazone or flavanone thiosemicarbazone and X = Cl? or ½SO42?) were synthesized. All the complexes were characterized using elemental analyses, molar conductance and magnetic moment measurements, and mass, 1H NMR, infrared, electron paramagnetic resonance and electronic spectral studies. The molar conductance of the complexes in dimethylsulfoxide lies in the range 10–20 Ω?1 cm2 mol?1 indicating their non‐electrolytic nature. All the complexes show magnetic moments corresponding to five unpaired electrons. The possible geometries of the complexes were assigned on the basis of electron paramagnetic resonance, electronic and infrared spectral studies. Some of the synthesized ligands and their complexes were screened for their antifungal activities against fungi Macrophomina phaseolina, Botrytis cinerea and Phoma glomerata using the food poison technique and their antibacterial activities against Xanthomonas campestris pv. campestris and Ralstonia solanacearum using the paper disc diffusion method. They showed appreciable activities. 相似文献