全文获取类型
收费全文 | 3598篇 |
免费 | 104篇 |
国内免费 | 22篇 |
专业分类
化学 | 2493篇 |
晶体学 | 31篇 |
力学 | 73篇 |
数学 | 588篇 |
物理学 | 539篇 |
出版年
2022年 | 18篇 |
2021年 | 25篇 |
2020年 | 40篇 |
2019年 | 53篇 |
2018年 | 40篇 |
2017年 | 30篇 |
2016年 | 68篇 |
2015年 | 61篇 |
2014年 | 97篇 |
2013年 | 192篇 |
2012年 | 153篇 |
2011年 | 180篇 |
2010年 | 123篇 |
2009年 | 115篇 |
2008年 | 166篇 |
2007年 | 156篇 |
2006年 | 152篇 |
2005年 | 146篇 |
2004年 | 119篇 |
2003年 | 108篇 |
2002年 | 111篇 |
2001年 | 62篇 |
2000年 | 72篇 |
1999年 | 45篇 |
1998年 | 58篇 |
1997年 | 51篇 |
1996年 | 61篇 |
1995年 | 58篇 |
1994年 | 49篇 |
1993年 | 54篇 |
1992年 | 52篇 |
1991年 | 64篇 |
1990年 | 39篇 |
1989年 | 49篇 |
1988年 | 56篇 |
1987年 | 44篇 |
1986年 | 57篇 |
1985年 | 55篇 |
1984年 | 61篇 |
1983年 | 41篇 |
1982年 | 35篇 |
1981年 | 45篇 |
1980年 | 55篇 |
1979年 | 40篇 |
1978年 | 39篇 |
1977年 | 36篇 |
1976年 | 31篇 |
1975年 | 27篇 |
1974年 | 23篇 |
1973年 | 22篇 |
排序方式: 共有3724条查询结果,搜索用时 15 毫秒
71.
An oxidation method (sulfone method) for the determination of polycyclic aromatic sulfur heterocycles (PASH) in diesel fuel is presented. The aromatic fraction of a diesel fuel, isolated by solid phase extraction, is oxidized under controlled conditions with hydrogen peroxide. The oxidation products, mainly methylated dibenzosulfone, are determined and quantified directly, without further clean-up, by HPLC with photodiode-array detection. 相似文献
72.
The addition of C6H5? to the NN' ligand (NN' = Schiff base of pyridine carbaldehyde-(2) and (S)-(—)-α-phenylethylamine) in [C5H5 Mo(CO)2 NN'] PF6 occurs stereospecific from the side opposite to the C5H5-ring. 相似文献
73.
74.
NMR spectroscopy plays an important part in the determination of the structures of organic compounds. The parameters of importance here are the chemical shifts of the 1H and 13C nuclei and the spin-spin interactions both between 1H nuclei and between 1H and 13C nuclei. Couplings between 13C nuclei were almost completely neglected until a few years ago, since they were extremely difficult to observe because of the low natural abundance of 13C. However, it is these couplings which afford information directly on the carbon-carbon connectivities in the molecule. It is now possible to use a special NMR pulse sequence to make these couplings more readily visible: the result of using this sequence is a 13C-NMR spectrum from which the carbon skeleton concerned can be directly read off. Two-dimensional spectra in particular are very easy to evaluate. The pulse sequence involved, which bears the somewhat puzzling name INADEQUATE, produces double-quantum coherences from which the NMR signals of the coupled carbon nuclei can be obtained. In this article the principle of double-quantum coherence is described and a number of examples for the application of the INADEQUATE pulse sequences to problems in synthetic organic chemistry, biosynthesis and natural products chemistry are presented; in addition, the possibility of applying the INADEQUATE method to other nuclei is considered. 相似文献
75.
The thermodynamics of water incorporation into Fe-doped SrTiO(3) was investigated by thermogravimetric measurements. Changes in valence states of redox-active dopant ions (Fe(3+)/Fe(4+)) with water vapor pressure were taken into account in the defect chemical analysis. The proton solubility was significantly enhanced by the presence of the redox centers. The hydration enthalpies and entropies were -60 kJ mol(-1) and -122 J mol(-1) K(-1). The defect chemical model was applied to describe the water vapor dependence of the electrical conductivity in mixed ionic and electronic conducting Fe-doped SrTiO(3) single crystals. 相似文献
76.
Water concentrations in dichloroacetic acid in the range of 0<C <1 % (C = percent by weight) can be determined directly by photometry at 1425 nm. The absorbance A at this maximum is described by the function A=1.267×C0.93 (cell path d=5 cm, correlation coefficient r=0.997). The variation coefficient for water concentrations of ≈0.06% was found to be V=6.5%. 相似文献
77.
Bicyclo[2.2.1]-2,5-heptadiene complexes of transition metal carbonyls have been treated with organometallic phosphines, to give the disubstituted compounds [(R3M′)3P]2M(CO)4 [R = CH3; M′ = Ge, Sn; M = Cr, Mo, W] by exchange of ligands. The chemical and spectroscopic properties of the new compounds are reported. 相似文献
78.
79.
Hans Joachim Schmid 《Numerische Mathematik》1978,31(3):281-297
Summary In this paper an approach is outlined to the two-dimensional analogon of the Gaussian quadrature problem. The main results are necessary and sufficient conditions for the existence of cubature formulae which are exact for all polynomials of degree m and which have a minimal number of 1/2k(k+1) knots,k=[m/2]+1. Ifm is odd, similar results are due to I.P. Mysovskikh ([5, 6]) which will be derived in a new way as a special case of the general characterization given here. Furthermore, it will be shown how this characterization can be used to construct minimal formulae of even degree. 相似文献
80.
Joachim Schaefer William A. Lester Donald Kouri Charles A. Wells 《Chemical physics letters》1974,24(2):185-190
Integral cross sections for pure rotational and vibrational-rotational excitation of H2(X1Σ+g) by Li+(1S) impact are computed by close-coupling methods at 0.2, 0.6, and 1.2 eV in the c.m. system using vibrational functions that are numerical solutions of the one-dimensional radial Schrödinger equation for harmonic, Morse, and adiabatically corrected Kolos-Wolniewicz (KW) potential functions. Comparison of results employing KW and Morse functions shows excellent agreement for all transitions studied. Findings using harmonic oscillator functions, however, differ noticeably from KW and Morse values for vibrational (0 → 1) and very large rotational (Δj = 10) transitions, but are satisfactory for lower order (0 → 2, 4, 6, 8) rotational transitions. 相似文献