全文获取类型
收费全文 | 4749篇 |
免费 | 106篇 |
国内免费 | 22篇 |
专业分类
化学 | 3190篇 |
晶体学 | 62篇 |
力学 | 73篇 |
数学 | 337篇 |
物理学 | 1215篇 |
出版年
2022年 | 32篇 |
2021年 | 35篇 |
2020年 | 47篇 |
2019年 | 67篇 |
2018年 | 44篇 |
2017年 | 40篇 |
2016年 | 70篇 |
2015年 | 80篇 |
2014年 | 73篇 |
2013年 | 256篇 |
2012年 | 229篇 |
2011年 | 247篇 |
2010年 | 151篇 |
2009年 | 178篇 |
2008年 | 262篇 |
2007年 | 283篇 |
2006年 | 280篇 |
2005年 | 234篇 |
2004年 | 174篇 |
2003年 | 182篇 |
2002年 | 185篇 |
2001年 | 108篇 |
2000年 | 116篇 |
1999年 | 81篇 |
1998年 | 54篇 |
1997年 | 50篇 |
1996年 | 81篇 |
1995年 | 54篇 |
1994年 | 49篇 |
1993年 | 56篇 |
1992年 | 78篇 |
1991年 | 48篇 |
1990年 | 49篇 |
1989年 | 48篇 |
1988年 | 71篇 |
1987年 | 50篇 |
1986年 | 59篇 |
1985年 | 72篇 |
1984年 | 78篇 |
1983年 | 30篇 |
1982年 | 49篇 |
1981年 | 48篇 |
1980年 | 49篇 |
1979年 | 50篇 |
1978年 | 39篇 |
1977年 | 49篇 |
1976年 | 26篇 |
1975年 | 35篇 |
1974年 | 35篇 |
1973年 | 27篇 |
排序方式: 共有4877条查询结果,搜索用时 15 毫秒
91.
Saito T Koopal LK van Riemsdijk WH Nagasaki S Tanakat S 《Langmuir : the ACS journal of surfaces and colloids》2004,20(3):689-700
The adsorption of natural organic matter (NOM) on mineral (hydr)oxide plays an important role in the evaluation of the speciation of toxic metal ions in the environment. Because both NOM and mineral oxide have variable charges that adjust upon adsorption, a good understanding of proton binding is required before the binding of metal ions can be understood. In this study, the adsorption of purified Aldrich humic acid (PAHA) on goethite was examined as a function of the environmental conditions (pH, salt concentration, and free concentration of PAHA) together with the proton adsorption to PAHA, goethite, and their mixtures. The induced charges on both components were separated on the basis of the difference between the charge/pH curves of the mixture and those of the single components. The electrostatic potential profile across the adsorbed layer was obtained as a numerical solution of the Poisson-Boltzmann equation using the charge density of the adsorbed PAHA and the goethite surface. From the quantitative evaluation of the induced charge on both components, it is revealed that the degree of the charge adjustment is related to the electrostatic affinity between the PAHA segments and the goethite surface, the electrostatic repulsion between the PAHA segments, and the electrostatic shielding by salt ions. Considering the charge distribution of the adsorbed PAHA at the goethite surface, it is concluded that the change of the charge adjustment is sensitive to that of the conformation of the adsorbed PAHA. From the detailed inspection of the assumptions made and the comparison with the reported theoretical calculations, the obtained potential profiles are considered to broadly reflect the true potential profiles. Because a charge adjustment is not frequently considered in detail in relation to the NOM adsorption on metal (hydr)oxides, the obtained results can form the basis for the further development of modeling of the adsorption of NOM on (hydr)oxide surfaces. 相似文献
92.
93.
Katsuyuki Ogura Kunio Sanada Kazumasa Takahashi Hirotada Iida 《Tetrahedron letters》1982,23(39):4035-4038
Ethyl 2-acetylalkanoate gave ethyl 2-(methyl- or phenylthio)alkanoate in high yield on treatment wiht CH3SSO2CH3, PhSSO2Ph, or PhSSPh in the presence of small excess of EtONa in EtOH. Application of the present method to synthesis of pellitorine and the queen substance is also described. 相似文献
94.
127I M?ssbauer spectra of good quality were obtained at 20 K using a Zn127mTe source produced by high flux neutron irradiation of 66Zn-126Te at reactor core. The M?ssbauer spectra for KI and some iodine(III) compounds with absorption intensity of about 5% suggest that the 127I M?ssbauer spectroscopy is useful in elucidating the bonding nature of the iodine compounds. Preparative method of the M?ssbauer source and experimental technique are reported in detail. 相似文献
95.
The effects of cation symmetry and packing on the mixed-valence state of binuclear ferrocene derivatives are discussed separately by using chiral isomers and racemic modification of 1',1' "-bis(2-phenylbutyl)-1,1' '-biferrocenium pentaiodide. The pentaiodide anion has a polymeric structure and is composed of triiodide anion and iodine molecule units. The (R,S) isomer having an inversion center shows a detrapped-valence state even at 78 K. On the other hand, the (R,R) and the (S,S) isomers having no inversion center show a trapped-valence state at room temperature. The racemic modification, however, consisting of the (R,R) and the (S,S) isomers shows a perfect detrapped-valence state at room temperature. This finding shows that the packing effect overcomes the effect of cation asymmetry. 相似文献
96.
Riki Seki Etsuko Kimura Toshiyuki Takahashi Nagao Ikeda 《Journal of Radioanalytical and Nuclear Chemistry》1990,138(1):17-31
The concentration of129I in soil in Japan was determined by neutron activation analysis. For the activation analysis, pre-irradiation chemical separation of the iodine was carried out by acid decomposition and distillation and post-irradiation treatment was performed by ion exchange and solvent extraction. The concentration of stable iodine and137Cs were also determined and compared with the behavior of129I in soil.Soil samples from Ibaraki, Fukui, Fukushima, and Nagasaki Prefectures were analyzed and129I was detected in amounts ranging from 10–7 to 10–5 Bq/g soil in uncultivated surface soil. There are apparently small variations in the129I concentrations in each of the regions analyzed.From depth profile studies in sandy soil, the iodide form of129I was found to migrate downward at a relatively rapid rate while other species remain longer in the surface soil. 相似文献
97.
Raman spectra of stilbene mono- and di-negative ions in tetrahydrofuran solution were obtained by Ar+ laser exciting lines. A considerable frequency shift was observed for several vibrations in the successive steps: stilbene → (stilbene)? → (stilbene)2?. The observed shift is discussed in a simple VB scheme, particularly in comparison with the results on anthracene negative ions. The resonance Raman effect was striking for both ions with intensity maxima at the exciting wavelengths close to the absorption maxima. 相似文献
98.
Fujitani T Nakamura I Kobayashi Y Takahashi A Haneda M Hamada H 《The journal of physical chemistry. B》2005,109(37):17603-17607
Adsorption and reactions of NO on clean and CO-precovered Ir(111) were investigated by means of X-ray photoelectron spectroscopy (XPS), high-resolution electron energy loss spectroscopy (HR-EELS), infrared reflection absorption spectroscopy (IRAS), and temperature-programmed desorption (TPD). Two NO adsorption states, indicative of fcc-hollow sites and atop sites, were present on the Ir(111) surface at saturation coverage. NO adsorbed on hollow sites dissociated to Na and Oa at temperatures above 283 K. The dissociated Na desorbed to form N2 by recombination of Na at 574 K and by a disproportionation reaction between atop-NO and Na at 471 K. Preadsorbed CO inhibited the adsorption of NO on atop sites, whereas adsorption on hollow sites was not affected by the coexistence of CO. The adsorbed CO reacted with dissociated Oa and desorbed as CO2 at 574 K. 相似文献
99.
Tetsuro Ito Toshiyuki TanakaMunekazu Iinuma Ibrahim IliyaKen-ichi Nakaya Zulfiqar AliYoshikazu Takahashi Ryuichi SawaYoshiaki Shirataki Jin MurataDedy Darnaedi 《Tetrahedron》2003,59(28):5347-5363
Five new resveratrol oligomers; pauciflorols A-C (1-3), isovaticanols B (6) and C (8), and three new oligostilbene glucosides; pauciflorosides A (11), B (13), C (14), were isolated from the stem bark of Vatica pauciflora (Dipterocarpaceae) together with known 17 resveratrol oligomers (4, 5, 7, 9, 10, 12 and 15-25) and bergenin (26). The structures of isolates were established on the basis of detailed spectroscopic analysis. The typical and characteristic spectral properties of some resveratrol oligomers were also discussed. 相似文献
100.
Hong-Ling Li Koichi Takahashi Yusuke Ujihira Mariko Ishiwatari Kurima Kobayashi Takahiko Iriyama Tokuzo Konishi 《Journal of Thermal Analysis and Calorimetry》1995,45(6):1359-1371
The Mössbauer spectra of Sm2Fe17Nx, prepared by the nitrogenation of Sm2Fe17 powders in an ammonia and hydrogen atmosphere, were observed at elevated temperatures to shed light on the thermal behavior of nitrogen in the compounds Sm2Fe17Nx. It was found that there were large differences in thermal behavior between the starting Sm2Fe17, crystalline Sm2Fe17Nx (x≈1.7) and amorphous Sm2Fe17Nx(x~7). The thermal decomposition behavior of Sm2Fe17N3.2, developed as one of the most promising hard magnetic materials, was found to be different under different atmospheres. 相似文献