全文获取类型
收费全文 | 420篇 |
免费 | 19篇 |
专业分类
化学 | 269篇 |
晶体学 | 9篇 |
力学 | 7篇 |
数学 | 56篇 |
物理学 | 98篇 |
出版年
2024年 | 1篇 |
2021年 | 5篇 |
2020年 | 5篇 |
2019年 | 2篇 |
2018年 | 10篇 |
2017年 | 7篇 |
2016年 | 19篇 |
2015年 | 22篇 |
2014年 | 18篇 |
2013年 | 27篇 |
2012年 | 25篇 |
2011年 | 31篇 |
2010年 | 20篇 |
2009年 | 10篇 |
2008年 | 31篇 |
2007年 | 27篇 |
2006年 | 20篇 |
2005年 | 23篇 |
2004年 | 22篇 |
2003年 | 13篇 |
2002年 | 8篇 |
2001年 | 5篇 |
2000年 | 7篇 |
1999年 | 6篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 5篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1991年 | 5篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 8篇 |
1981年 | 7篇 |
1980年 | 1篇 |
1977年 | 2篇 |
1973年 | 1篇 |
1967年 | 1篇 |
1966年 | 1篇 |
1938年 | 1篇 |
1928年 | 2篇 |
排序方式: 共有439条查询结果,搜索用时 10 毫秒
81.
We describe a computer program that performs the Metropolis algorithm for the 3D Ising model at a peak speed of 98 million spin updates per second on a 2-pipe CDC Cyber 205. This speed is achieved using the special vector capabilities of the Cyber 205 and multispin coding techniques. 相似文献
82.
The cross section for singleW ? production ine + e ? collisions is exactly computed for an arbitraryW magnetic moment. It is found that this process may give a first look at theW Wγ vertex just below the twoW threshold. A detailed comparison is made with previous calculations that used the equivalent photon approximation. 相似文献
83.
We show that in supersymmetric SU(3) × SU(2) × U(1) it is possible to break SU(2) with an Higgs singlet and at the same time to avoid vacuum expectation values for s-fermions. With rather simple constraints we obtain important restrictions on the values of the model parameters. 相似文献
84.
Brereton Richard G. Jansen Jeroen Lopes João Marini Federico Pomerantsev Alexey Rodionova Oxana Roger Jean Michel Walczak Beata Tauler Romà 《Analytical and bioanalytical chemistry》2018,410(26):6691-6704
Analytical and Bioanalytical Chemistry - The contribution of chemometrics to important stages throughout the entire analytical process such as experimental design, sampling, and explorative data... 相似文献
85.
Araujo K Colina M Mazurek R Delgado J Ledo H Gutierrez E Herrera L 《Analytical and bioanalytical chemistry》1996,355(3-4):319-320
The mercury concentrations in wastewater and sewage sludge of a stabilization pond system have been evaluated. The system is built by three parallel facultative ponds followed by two systems of three maturation ponds in series. The samples of wastewater and sludge were digested using nitric acid and placed into a Parr-type bomb for 4 h at 110 degrees C. Mercury was measured by Cold Vapour Atomic Absorption Spectrometry (CV-AAS) at 253.7 nm with sodium tetrahydroborate as reductant. The methodologies were checked with an USEPA quality control sample, a standard reference material from NIST and with another method of mineralization (cold mineralization) showing good results. Concentrations of mercury in wastewater between 1.47 +/- 0.75 microgl(-1) have been found at the entrance of the system and 0.74 +/- 0.0 microgl(-1) at the exit, while in sludge the results were between 0.29 +/- 0.12 microgkg(-1) in the facultative pond and 0.04 +/- 0.02 microgkg(-1) in the second maturation pond (exit). 相似文献
86.
Oxidative dehydrogenation ofn-butane and propene has been studied on six Mg−Al−Fe oxide catalysts prepared by thermal decomposition of layered double hydroxides
with a hydrotalcite-like structure, possessing Mg2+ and Al3+ ions in the brucite-like layers, and hexacyanoferrate in the interlayers. In all cases, CO2 and H2O are formed, together with minor amounts of ethylene and methane. On the solids prepared from hexacyanoferrate(II), formation
of benzene is also observed. 相似文献
87.
In this paper a systematic study of four metallic oxinates (ferric, nickel, lead, and copper complexes) is carried out, determining some characteristics of the organic solutions of these complexes in reactions of reextraction by the exchange of ligands. These reactions are based on the decoloration produced in organic solutions of colored complexes when they are mixed with aqueous solutions of anions. The study of some characteristics and the qualitative tests shows that only the copper oxinate is interesting for quantitative purposes because its solutions in chloroform are decolored at very low concentrations of oxalate ethylenediamine tetraacetate, sulfide, and cyanide.The application of this study to the indirect spectrophotometric determination of cyanide is carried out. The decoloration varies linearly with the cyanide concentration between 10 and 50 ppm for a phase volume ratio 1:1. Finally, the error, reproducibility of the method, nature of the exchange reaction, and interferences of foreign ions are also established. 相似文献
88.
The eta(5)-to-eta(3) coordination shift of cyclopentadienyl (Cp=C(5)H(5)(-)) and indenyl (Ind=C(9)H(7)(-)) ligands in molybdenocene complexes, [(eta(5)-Cp')(eta(5)-Cp)Mo(CO)(2)](2+) (Cp'=Cp or Ind), driven by a two-electron reduction of those species, was studied and compared by means of molecular orbital calculations (B3LYP HF/DFT hybrid functional, DZP basis sets). The results obtained, in terms of optimized geometries, relative energies, and bond analysis parameters, compare well with the experimental data, and verify the well-known indenyl effect, that is, a significantly more facile eta(5)-to-eta(3) rearrangement for the indenyl ligand when compared to cyclopentadienyl. However, the study of the folding of free Cp and Ind, combined with the (eta(5/3)-Cp')-M bond analysis, shows that the observed difference is not the result of an intrinsic characteristic of the indenyl ligand, such as the traditionally accepted aromaticity gain in the benzene ring formed in eta(3)-Ind complexes. Instead, it is directly related to the Cp'-M bond strength. While the difference in the energy required to fold the two free ligands is negligible (< or =1 kcal mol(-1) for folding angles up to 20 degrees), the (eta(5)-Cp)-M bond is stronger than that of (eta(5)-Ind)-M; however, the opposite situation is found for the eta(3) coordination mode. The net result, for Cp'=Ind, is a destabilization of the eta(5) complexes and a stabilization of the eta(3) intermediates or transition states yielding smaller activation energies and faster reaction rates for processes in which that is the rate-determining step. 相似文献
89.
P. Román J. M. Gutiérrez-Zorrilla M. Martínez-Ripoll S. García-Blanco 《Journal of chemical crystallography》1987,17(1):109-119
The title compound, (C6H8N)4[Mo8O26], has been prepared and its crystal structure determined by X-ray crystallography. The compound is triclinic,P¯1,Z=1 witha=10.167(1),b=10.745(1),c=10.027(8) Å,=85.05(1),=106.73(3), =107.75(1)°,V=999.1(7) Å3,F(000)=748,D
x=2.59 andD
o=2.61(1) Mg/m3. The [Mo8O26]4– anion shows slight differences in several bond lengths and angles when compared with other related octamolybdates. The planar cations are connected to the polyanions through bifurcated hydrogen bonds. The MoO6 octahedra are distorted and the distortion has been evaluated using three different equations. The spectroscopic study shows that the cations are protonated and the polyanion presents the well-known infrared spectrum for octamolybdates. 相似文献
90.
S. Ribeiro Guevara M. A. Arribére S. Calvelo G. Román Ross 《Journal of Radioanalytical and Nuclear Chemistry》1995,198(2):437-448
Five species of epiphytic lichens were sampled from urban and periurban areas of Bariloche, a non industrial city located on the East side of the Nahuel Huapi National Park, North-Western Patagonia, Argentina, and from pristine areas of the Park. Each individual lichen was analyzed using Instrumental Neutron Activation Analysis. The results of the analysis showed high concentrations of lithophile elements, with very good correlations among them. The relative concentration of these elements in all lichen species is in good agreement with the elemental composition of sediments collected in the Park. Elemental concentrations which are not related to detritical inputs are also presented. 相似文献