全文获取类型
收费全文 | 1277篇 |
免费 | 38篇 |
国内免费 | 8篇 |
专业分类
化学 | 501篇 |
晶体学 | 29篇 |
力学 | 61篇 |
数学 | 394篇 |
物理学 | 338篇 |
出版年
2023年 | 9篇 |
2022年 | 23篇 |
2021年 | 27篇 |
2020年 | 14篇 |
2019年 | 19篇 |
2018年 | 26篇 |
2017年 | 37篇 |
2016年 | 34篇 |
2015年 | 22篇 |
2014年 | 42篇 |
2013年 | 98篇 |
2012年 | 66篇 |
2011年 | 86篇 |
2010年 | 68篇 |
2009年 | 54篇 |
2008年 | 62篇 |
2007年 | 54篇 |
2006年 | 44篇 |
2005年 | 39篇 |
2004年 | 34篇 |
2003年 | 35篇 |
2002年 | 24篇 |
2001年 | 17篇 |
2000年 | 18篇 |
1999年 | 18篇 |
1998年 | 11篇 |
1996年 | 17篇 |
1995年 | 7篇 |
1994年 | 10篇 |
1993年 | 14篇 |
1992年 | 10篇 |
1991年 | 13篇 |
1990年 | 7篇 |
1988年 | 8篇 |
1987年 | 10篇 |
1986年 | 7篇 |
1985年 | 20篇 |
1984年 | 13篇 |
1983年 | 15篇 |
1982年 | 20篇 |
1981年 | 10篇 |
1980年 | 19篇 |
1979年 | 18篇 |
1978年 | 10篇 |
1977年 | 11篇 |
1976年 | 13篇 |
1975年 | 11篇 |
1974年 | 7篇 |
1973年 | 11篇 |
1972年 | 7篇 |
排序方式: 共有1323条查询结果,搜索用时 15 毫秒
31.
Vapor phase catalytic oxidation of toluene over perovskites viz., LaCoO3, LaCrO3 and LaFeO3 has been studied. The maximum activity was observed at 450°C. The oxidation is first order. The order of catalytic reactivity is LaCoO3>LaFeO3>LaCrO3. The activation energy (Ea) values for LaCoO3, LaFeO3 and LaCrO3 are 13.4, 23.93 and 25.31 kJ/mol, respectively. 相似文献
32.
Summary A study of the Cd(CN)2 +x X– [Cd(CN)2X
x
]
x–
equilibrium (where X = Cl, Br or CNS) has been carried out at 18° and 38° by measuring the solubility of cadmium cyanide in potassium chloride, bromide and thiocyanate at various concentrations, and at a high ionic strength (6 M) maintained with sodium perchlorate to minimise the effect of activity coefficients. Equilibrium constants forx = 1 and 2 have been calculated and clearly favour the situation wherex = 1. H values for the dissociation of [Cd(CN)2X]– have also been calculated. 相似文献
33.
Study of EPR, optical properties and electrical conductivity of vanadyl doped Bi2O3.PbO.B2O3 glasses
Gahlot PS Agarwal A Seth VP Sanghi S Gupta SK Arora M 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(6):1189-1194
Heavy metal based oxide glasses having composition xBi(2)O(3).(0.30 - x)PbO.0.70B(2)O(3) have been prepared (0.00 < or = x < or = 0.15, mol%) containing 2.0mol% of V(2)O(5) by normal melt-quenching technique. Electron paramagnetic resonance (EPR), optical spectra and dc conductivity of these glasses have been studied. Spin Hamiltonian parameters (SHP) of VO(2+) ions, dipolar hyperfine parameter, P and Fermi contact interaction parameter, K, molecular orbital coefficients (alpha(2) and gamma(2)) and optical band gap have been calculated. It is observed that in these glasses, the tetragonal nature of V(4+)O(6) complex increases with Bi(2)O(3) content. Increase in Bi(2)O(3):PbO ratio results in the contraction of 3d(xy) orbit of the unpaired electron in the vanadium ion, and the SHP are dependent on the theoretical optical basicity, Lambda(th). In present glasses, the conductivity (activation energy) first decreases (increases) with increase in mol% of Bi(2)O(3) content upto x = 0.08 and then shows a maxima (minima) at x = 0.10 and then starts decreasing (increasing) upto x < or = 0.15 with mol% of Bi(2)O(3) content. 相似文献
34.
Renu Sharma Santosh K. Agarwal Shikha Rawat Meena Nagar 《Transition Metal Chemistry》2006,31(2):201-206
The synthesis and characterization of some transition metal cis-3,7-dimethyl-2,6-octadiensemicarbazone (CDOSC) complexes are reported. The ligand CDOSC yields: [ML2 Cl2] and [ML2 Cl2] Cl type complexes, where M = CrIII, MnII, FeIII, CoII, NiII, CuII, ZnII, CdII and HgII, L = CDOSC. Structures of the complexes were determined using elemental analysis, molar conductivity, magnetic measurements,
i.r. and electronic, as well as n.m.r spectra. CDOSC acts as a bidentate ligand in all the complexes. All the newly synthesized
metal complexes, as well as the ligand, were screened for their antibacterial activity. All the complexes exhibit strong inhibitory
action against Gram (+) bacteria Staphylococcus aureus and Gram (−) bacteria Escherichia coli. The antibacterial activities of the complexes are stronger than those of the ligand CDOSC itself. 相似文献
35.
A new series of complexes of 5,6-benzoquinoline (Benzqn) with lanthanide perchlorates with the general composition Ln(ClO4)3·7Benzqn (Ln = La, Ce, Pr, Nd, Sm, Gd, Tb, Dy or Ho) were synthesised and characterised by elemental analysis, conductance, molecular weight and infrared spectra. The thermal behaviour of these complexes have also been studied. 相似文献
36.
37.
38.
Ravinder Agarwal V. R. Singh M. M. Pradhan Ved Singh 《International Journal of Infrared and Millimeter Waves》1991,12(2):115-123
The occurance of the urinary stones varies according to the geographical regions. The presence of stones in the urinary system causes pain and discomfort. These generate colics and hence are sometimes life threatening. In the present study, infrared measurements have been made on several stone samples. It has been found that calcium oxalate, calcium phosphate, magnesiunm ammonium phosphate, calcium carbonate, uric acid, -cystine and xanthin are present, as expected. Also, silicon dioxide is found to be present in some of the stones but in small quantity, in addition to the above constituents. This constituent is responsible to exhibit piezoelectricity in the urinary calculi. 相似文献
39.
Sushma Agarwal 《Journal of solution chemistry》1978,7(10):795-798
The excess volume of mixing of some electron-donating aromatic hydrocarbons like benzene, toluene,p-xylene, and mesitylene with an electronaccepting liquid 1,2,4-trichlorobenzene have been measured at 30°C. The results indicate that the interaction between the components increases as the electron-donating power of the hydrocarbons increases. The V
m
e
values are related to the ionization potentials of the hydrocarbons. 相似文献
40.
In this paper we establish some new dynamic inequalities on time scales which contain in particular generalizations of integral and discrete inequalities due to Hardy, Littlewood, P′olya, D'Apuzzo, Sbordone and Popoli. We also apply these inequalities to prove a higher integrability theorem for decreasing functions on time scales. 相似文献