全文获取类型
收费全文 | 667篇 |
免费 | 16篇 |
国内免费 | 2篇 |
专业分类
化学 | 507篇 |
晶体学 | 6篇 |
力学 | 20篇 |
数学 | 100篇 |
物理学 | 52篇 |
出版年
2023年 | 2篇 |
2022年 | 5篇 |
2021年 | 8篇 |
2020年 | 12篇 |
2019年 | 14篇 |
2018年 | 6篇 |
2017年 | 9篇 |
2016年 | 9篇 |
2015年 | 16篇 |
2014年 | 15篇 |
2013年 | 30篇 |
2012年 | 33篇 |
2011年 | 45篇 |
2010年 | 26篇 |
2009年 | 25篇 |
2008年 | 40篇 |
2007年 | 40篇 |
2006年 | 33篇 |
2005年 | 37篇 |
2004年 | 27篇 |
2003年 | 30篇 |
2002年 | 34篇 |
2001年 | 11篇 |
2000年 | 15篇 |
1999年 | 5篇 |
1998年 | 9篇 |
1997年 | 10篇 |
1996年 | 18篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 9篇 |
1992年 | 6篇 |
1991年 | 5篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1987年 | 5篇 |
1986年 | 7篇 |
1985年 | 9篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 7篇 |
1981年 | 9篇 |
1980年 | 8篇 |
1979年 | 2篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 6篇 |
1973年 | 4篇 |
1970年 | 1篇 |
1927年 | 1篇 |
排序方式: 共有685条查询结果,搜索用时 31 毫秒
581.
Dietrich-Buchecker C Colasson B Fujita M Hori A Geum N Sakamoto S Yamaguchi K Sauvage JP 《Journal of the American Chemical Society》2003,125(19):5717-5725
Transition metal-mediated templating and self-assembly have shown powerful potentials for the synthesis of interlocked molecules. These two strategies were combined in designing and preparing a new type of coordination catenanes incorporating Cu(I) and Pd(II) metal centers. The ligand designed here contains a phenanthroline core and pyridine sidearms (compound 1). Using this phenanthroline-pyridine conjugated ligand, two approaches were examined, which were shown to be surprisingly efficient for the catenane synthesis: the entwining route (entwining of two ligands around Cu(I) followed by Pd(II) clipping) and the threading approach (Cu(I)-templated threading of a cyclic ligand on an acyclic ligand followed by the Pd(II) clipping of the second ring). In the former method, stepwise treatment of 1 with Cu(CH(3)CN)(4)PF(6) (templating center) and enPd(NO(3))(2) (assembling center) gives rise to the quantitative formation of CuPd(2) catenane 18. In the latter method, Cu(I) templates the threading of phenanthroline-containing macrocycle 2 on ligand 1, which is followed by Pd(II) clipping to give hetero catenane 20. In both approaches, the formation of catenanes is convincing thanks to the strong templating effect of Cu(I), while the ring closure steps are efficiently furnished by Pd(II)-directed self-assembly. 相似文献
582.
Christiane Reifenh?user Klaus G. Heumann 《Fresenius' Journal of Analytical Chemistry》1990,336(7):559-563
Summary A definitive method of isotope dilution mass spectrometry (IDMS) was developed to determine four different iodine species in aquatic systems (iodide, iodate and two organoiodine compounds: one of the organic species is chromatographically elutable from a column filled with an anion exchanger resin, the other one is not). The iodine species were analysed after the isotope dilution step with an enriched 129I spike and after their chromatographic separation. The total iodine concentration was measured after decomposition of organic compounds in the aquatic system by UV irradiation. Different types of natural water samples (river water, water of a pond, moorland lake water) were analysed and important water parameters like pH-value, redox potential, oxygen content and dissolved organic carbon were measured for each of these samples. The total iodine concentration in the different samples differed only slightly in the range of 2–7 g/l. In most of the moorland lake water samples only the two organoiodine species could be detected. In these samples the concentration of iodide and iodate was less than the detection limit of 0.5 g/l and 0.1 g/l, respectively. On the other hand, all four iodine species could be determined in most of the river water samples. Positive correlations were found for the oxygen content of the water samples and the iodate concentration as well as for the redox potential and the anionic organoiodine compound.In memoriam of Dr. I. Linus Barnes who died in January, 1990. Dr. Barnes was senior scientist at the National Institute of Standard and Technology in Gaithersburg, USA. He made numerous outstanding contributions to the field of mass spectrometry and IDMS 相似文献
583.
Jimenez-Molero MC Dietrich-Buchecker C Sauvage JP 《Chemical communications (Cambridge, England)》2003,(14):1613-1616
The authors describe their study of molecular systems suited to the fabrication of machines and (rotory or linear) motors at the molecular level. They indicate that a future application of these molecular'muscles'could be in the area of information storage and processing. 相似文献
584.
Eichele K Nachtigal C Jung S Mayer HA Lindner E Ströbele M 《Magnetic resonance in chemistry : MRC》2004,42(9):807-813
A comprehensive 31P solid-state NMR study of Ru(eta1-Ph2PCH2CH2OCH3)2(eta2-en)Cl2 (en = ethylenediamine) (1), by 1D (contact time variation, inversion-recovery, SPARTAN) and 2D techniques (homonuclear J-resolved, SECSY) indicated that the crystal structure of 1 should be complex. The single-crystal x-ray structure determination confirmed the presence of eight independent molecules in the asymmetric unit, with 31P isotropic chemical shifts in the range 27.3-40.1 ppm, while the spans of the phosphorus chemical shift tensors are of the order of 170 ppm. Based on unique structural features and NMR data, one molecule has been tentatively assigned. 相似文献
585.
Prélot B Villiéras F Pelletier M Razafitianamaharavo A Thomas F Poinsignon C 《Journal of colloid and interface science》2003,264(2):343-353
Relationships between structural parameters of MnO2 and their surface properties at the solid-gas interface were investigated. The studied series ranged from ramsdellite to pyrolusite and encompassed disordered gamma-MnO2 samples. The structural model used takes into account structural defects: Pr (rate of pyrolusite intergrowth in the ramsdellite network) and Tw (rate of microtwinning). Analysis of the N2 adsorption isotherm evidenced positive correlations between specific surface area and Tw for gamma-MnO2 only and between the energetic constant C and (1-Pr). No microporosity is evidenced. Water adsorption isotherms evidenced the dependence of the H2O monolayer volume on Tw and showed a positive correlation between the cross-section area of water molecules adsorbed in the first monolayer and Pr, ranging from 13.5 A2 for Pr=1 to 6.3 A2 for Pr=0.2 (12 sites/nm2). Energetic heterogeneity is quantified from Ar and N2 low-pressure adsorption isotherms with the DIS procedure and correlated with H2O adsorption. High-energy adsorption domains are quantified and assigned to the different crystal faces: (110) faces with a common 1 x 1 octahedra layer of pyrolusite and ramsdellite and the (001) face of ramsdellite with 2 x 2 octahedra on which channels and plateaus are differentiated. The specific surface area ratio of ramsdellite high-energy sites to total ramsdellite content is shown to depend on Tw. The dependence on microtwinning of low cross-sectional area of N2 and much lower cross-sectional of residual H2O molecules leads us to assume that their adsorption sites on grain boundaries are represented by the twin planes between the structured nanocrystals generated by oxygen evolution during MD synthesis. 相似文献
586.
Herv Casabianca Jean-Bernard Graff Patrick Jame Christiane Perrucchietti Maurice Chastrette 《Journal of separation science》1995,18(5):279-285
This work presents two techniques for testing for the adulteration of flavors. One uses multidimensional gas chromatography on cyclodextrin derivatives to separate chiral compounds, the other uses isotope ratio mass spectrometry coupled with gas chromatography to determine stable isotope ratios. Applications to fruits and plants for the food and perfume industry are introduced. 相似文献
587.
Bernd?HuberEmail author Hubert?Gnaser Christiane?Ziegler 《Analytical and bioanalytical chemistry》2003,375(7):917-923
Nanoporous thin films were deposited onto glass substrates by painting with a solution of nanocrystalline anatase TiO(2) particles (with a size of either 6 nm or 16 nm) suspended in an organic solvent. Upon drying in air for about 1 day, the films were tempered at 450 degrees C in air for 1 h. This procedure results in stoichiometric TiO(2) films with a thickness of several micro m and a milky whitish appearance. Scanning force microscopy of the surface revealed that the nanoparticles of the films agglomerated into structures with lateral dimensions of some 100 nm. Transmission electron microscopy was utilized to investigate the structural arrangement of the crystallites in the films. High-resolution electron diffraction and X-ray diffraction analyses demonstrated, furthermore, that the material consists exclusively of a single TiO(2) phase, namely anatase, and that the films do not exhibit any preferential texture. The elemental stoichiometry and the possible presence of impurities were monitored throughout the films by means of secondary-ion mass spectrometry depth profiling. Electrical measurements have been carried out as a function of both the sample temperature T and the ambient oxygen partial pressure p(O(2)). From these data the electrical conductivity sigma of the porous films was determined in dependence of those parameters. 相似文献
588.
Malvy DJ Guinot C Preziosi P Galan P Chapuy MC Maamer M Arnaud S Meunier PJ Hercberg S Tschachler E 《Photochemistry and photobiology》2000,71(4):466-469
A link between bone mineral density and skin color has been reported recently, and pigmentation has been shown to affect cutaneous vitamin D production. In the present study, we investigated the relationship between phototype, global self-assessed sun exposure, geographical location and vitamin D serum levels in 1191 French adults. When the factors were analyzed separately, individuals with lower phototypes as well as those with lower sun exposure showed significantly lower levels of vitamin D than those with darker phototypes or those with higher sun exposure. However, when factors were analyzed as a whole, the vitamin D status was no longer linked with the phototype, but with sun exposure and geographical location. Since phototypes and global self-assessments of sun exposure were positively linked, our data suggest that lower vitamin D levels in fair-skinned individuals are due to their sun exposure behavior. 相似文献
589.
Christiane Fernandes Eduardo Stadler Valderes Drago Carlos Jorge da Cunha Izaura Hiroko Kuwabara 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》1996,52(14):1815-1821
In this study we have investigated eight complexes of the general composition [Fe3O(OOCCH3)6(L)3]NO3, where L is a heterocyclic ligand, viz. a 4-substituted pyridine. The Mössbauer spectra of the complexes showed isomer shifts and quadrupole splittings that are characteristic of iron(III) high-spin complexes. The Mössbauer quadrupolar doublets showed asymmetries that are attributed principally to the Goldanskii-Karyagin effect. A correlation is proposed between the Mössbauer parameters, and between the energy of the charge transfer band spectra, and the pKa values of the N-heterocyclic ligands. 相似文献
590.
We report the synthesis of novel anticancer compounds based on bioreductive and DNA-alkylating properties. The strategy was to combine a benzoquinone annelated pyrrole with bioreductive properties with a set
of DNA-alkylating functionalities, thus resulting in bifunctional anticancer compounds. The biological activity of all compounds
was evaluated against a number of cancer cell lines. One of the compounds should be emphasized. 相似文献