全文获取类型
收费全文 | 5834篇 |
免费 | 163篇 |
国内免费 | 23篇 |
专业分类
化学 | 4272篇 |
晶体学 | 47篇 |
力学 | 113篇 |
数学 | 750篇 |
物理学 | 838篇 |
出版年
2024年 | 5篇 |
2023年 | 37篇 |
2022年 | 96篇 |
2021年 | 132篇 |
2020年 | 100篇 |
2019年 | 94篇 |
2018年 | 77篇 |
2017年 | 84篇 |
2016年 | 205篇 |
2015年 | 127篇 |
2014年 | 157篇 |
2013年 | 352篇 |
2012年 | 424篇 |
2011年 | 485篇 |
2010年 | 247篇 |
2009年 | 204篇 |
2008年 | 416篇 |
2007年 | 398篇 |
2006年 | 345篇 |
2005年 | 375篇 |
2004年 | 277篇 |
2003年 | 234篇 |
2002年 | 208篇 |
2001年 | 80篇 |
2000年 | 78篇 |
1999年 | 50篇 |
1998年 | 65篇 |
1997年 | 42篇 |
1996年 | 83篇 |
1995年 | 42篇 |
1994年 | 38篇 |
1993年 | 51篇 |
1992年 | 28篇 |
1991年 | 36篇 |
1990年 | 45篇 |
1989年 | 35篇 |
1988年 | 37篇 |
1987年 | 35篇 |
1986年 | 21篇 |
1985年 | 31篇 |
1984年 | 26篇 |
1983年 | 13篇 |
1982年 | 19篇 |
1981年 | 12篇 |
1980年 | 14篇 |
1979年 | 15篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1974年 | 7篇 |
1973年 | 4篇 |
排序方式: 共有6020条查询结果,搜索用时 0 毫秒
71.
J. Miguel Vadillo M. Esther Gonzalez Isabel Carretero J. Javier Laserna 《Mikrochimica acta》1995,118(3-4):273-282
Micellar liquid chromatography (MLC) and capillary zone electrophoresis (CZE) have been evaluated for the analysis of twelve banned drugs in sport including diuretics and -blockers. In MLC, a sodium dodecylsulphate aqueous solution has been used as mobile phase using an octadecylsilica column. In CZE, a pH 8 buffer solution and a silica capillary have been employed. Parameters of retention and efficiency have been compared. Limits of detection with UV detection at 254 nm and relative standard deviations for atenolol, furosemide, nadolol, spironolactone and triamterene were established and compared in both techniques. Examples of direct urine injection into the separation systems are presented. Drugs overlapping in MLC are well resolved in CZE, while the opposite is true for a limited number of drugs. Some interferences from urine may arise in CZE. The selectivity of analysis would be greatly enhanced by using both techniques, which require only filtration as pre-treatment. 相似文献
72.
73.
The photosensitized aquation of pentaammine(pyridine)ruthenium(II) by several dyes has been studied under conditions where only the sensitizers absorb light. The ratio of the quantum yields for ammine and pyridine substitution was the same as that for direct photoaquation. Sensitization was effective with singlet sensitizers Rhodamine-B (17 452 cm(-)(1)) and Safranine-T (17 690 cm(-)(1)), as well as the triplet sensitizer biacetyl (19 000 cm(-)(1)), but no reaction was observed with Neutral-Red (16 900 cm(-)(1)). The results indicate that the excited state precursor of the observed photosubstitution in the complex lies in the energy range between 17 000 and 17 700 cm(-)(1). 相似文献
74.
75.
76.
Garcia EM Sanchez MD Tonetto G Volpe MA 《Journal of colloid and interface science》2005,292(1):179-185
The preparation of different samples of vanadia supported on ultrastable zeolite (VO(x)/USY) is discussed. The samples were prepared in order to obtain highly dispersed V-species, avoiding the formation of crystalline vanadia and the destruction of the zeolite framework. Two methods were employed for preparing VO(x)/USY samples: an organic route using V(AcAc)3 and an inorganic route using NH4VO3. The characterization of the samples was performed with XRD, TPR, NH3-TPD, and N2 isotherms. From these results it is concluded that when VO(x) is supported on the surface of USY from acidic aqueous solution of ammonium metavanadate, the destruction of the zeolite framework is accomplished. For higher pH values in the impregnating solution, undesired V2O5 is formed on the USY surface. On the other hand, VO(x)/USY prepared from the organic precursor shows no destruction of the USY structure. In addition, highly dispersed VO(x) are formed, though for relatively high V loadings (6%) an obstruction of the zeolite windows takes place. The samples are tested as catalysts for gas phase dehydrogenation of n-butane to olefins. The catalysts prepared from NH4VO3 are almost inactive for the reaction. On the other hand, both samples prepared from V(AcAc)3 present initial conversion levels in the 8-12% range. However, the selectivity depends on the V loading, the catalysts with 6% loading being the most selective (75%). The catalytic patterns of the samples (activity and selectivity) are in agreement with the physicochemical features of the VO(x)/USY surface. 相似文献
77.
Íñigo X. García-Zubiri Gustavo González-Gaitano Miguel Sánchez Josér; Ramón Isasi 《Journal of inclusion phenomena and macrocyclic chemistry》2004,49(3-4):291-302
The inclusion complexes of β-cyclodextrin (β-CD) with naphthalene and some of its derivatives in the solid state have been studied by infrared spectroscopy. Digital subtraction, deconvolution and curve fitting have been used to investigate the interactions between the naphthalene derivatives andβ-CD. Several preparation methods for the solid dispersions have been tested, using FTIR as an effective tool to evaluate the interactions at the molecular level. The effects of temperature and humidity on the spectra have been also analyzed. A carbonyl moiety in the guest molecule can increase the stability of the complex by establishing specific interactions with the hydroxyl groups of the CD cavity rims. The stability of the complexes is higher for 2-naphthylacetate than that for 1-naphthyl acetate, andso is the degree of association of its carbonyl groups. On the other hand, 2-acetylnaphthaleneforms very stable inclusioncomplexes although its carbonyl groups appear to be significantly less associated. 相似文献
78.
Armentano D De Munno G Mastropietro TF Julve M Lloret F 《Journal of the American Chemical Society》2005,127(31):10778-10779
Intermolecular proton transfer in solid phase from the hydroxo bridge to a water molecule occurs in a new mu-hydroxo iron(III) compound of formula {EtNH3[Fe2(ox)2Cl2(mu-OH)].2H2O}n leading to a still crystalline compound in which the mu-oxo bridge replaces the mu-hydroxo one. Both three-dimensional compounds exhibit magnetic ordering at Tc ca. 70 K due to a spin canting. 相似文献
79.
F. Briones D. Golmayo L. González J. L. de Miguel 《Applied Physics A: Materials Science & Processing》1985,36(3):147-151
H2S gas has been used during molecular beam epitaxy (MBE) growth of GaAs and Al
x
Ga1–x
As as sulphur vector forn-type doping. Doping efficiencies are less than 10–3 at usual growth temperatures, and are limited by an incorporation competitive surface process, probably 2Ga+H2SGa2S+H2. In AlxGa1–x
As forx0.2 the doping efficiency is further reduced by carrier freeze-out at deep levels. Measured thermal activation energies depend on growth conditions and remain relatively low even up to the direct-indirect bandgap crossover for substrate temperatures in the 585–645 C range. 相似文献
80.