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41.
42.
研究了发酵不同阶段鸟苷发酵液的紫外吸收光谱,结果表明,鸟苷发酵不同阶段发酵液紫外吸收光谱会呈现相应的特征光谱。发酵前期除了275nm处的波峰外,在249nm又出现了一个新峰,并且随着发酵时间增加新峰逐渐升高成为主峰;发酵中期275nm处的波峰逐渐减弱并最后消失;发酵后期249nm处的波峰成为发酵液的特征波峰,并随时间的增加逐渐上升;发酵末期的显著特征为发酵液λmax的吸光值基本不变。鸟苷发酵不同阶段发酵液特征光谱研究为人们认识鸟苷发酵的动态过程提供了一种新的技术和途径,对于鸟苷发酵生产具有一定的指导意义。 相似文献
43.
Yu‐Yang Liu Xiao‐Dong Fan YA‐Bing Zhao 《Journal of polymer science. Part A, Polymer chemistry》2005,43(16):3516-3524
A novel linear poly(N‐isopropylacrylamide) (PNIPA) with β‐cylodextrin (β‐CD) moiety (PNIPA‐β‐CD) was synthesized by the conjugation of β‐CD carrying amino groups (EDA‐β‐CD) onto PNIPA with epoxy groups (P(NIPA‐co‐GMA), Mn = 3.86 × 104), and the related reaction conditions are investigated. PNIPA‐β‐CD was characterized by means of IR, NMR and UV spectroscopes, element analysis, and differential scanning calorimetry (DSC). The number‐average molecular weight (Mn) and the β‐CD content of the obtained PNIPA‐β‐CD are 4.87 × 104 and 18.8 wt %, respectively. PNIPA‐β‐CD can not only respond to temperature stimuli but also include guest molecules. Lower critical solution temperature (LCST) of aqueous PNIPA‐β‐CD solution is similar to that of PNIPA. The association constant (Ka) for PNIPA‐β‐CD with methyl orange (MO) is 2.4 × 103 L mol?1 at pH 1.4, which is comparable to that of EDA‐β‐CD (Ka = 2.9 × 103 L mol?1). © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3516–3524, 2005 相似文献
44.
将纳米金(NG)电沉积在有序介孔碳(OMC)修饰玻碳电极表面,并将L-半胱氨酸(L-Cys)自组装至OM C/NG修饰电极表面,制备了OM C/NG/L-Cys修饰电极。采用透射电子显微镜考察了OM C的结构,扫描电子显微镜研究了OMC/NG/L-Cys修饰电极的表面形貌。考察了Cu2+在该修饰电极上的电化学行为,优化了Cu2+的测定条件。在最优条件下,溶出峰峰电流与Cu2+浓度在0.05~6.0μmol/L范围内呈良好线性关系,检出限为0.03μmol/L(S/N=3)。方法用于河水样品分析,其加标回收率在92.7%~101.6%之间。 相似文献
45.
Jeilani YA Cardelino BH Ibeanusi VM 《Journal of the American Society for Mass Spectrometry》2011,22(11):1999-2010
This is the first ab initio study of the energetics of the fragmentation mechanisms of phthalate, by mass spectrometry, leading
to protonated phthalic anhydride (m/z 149). Phthalates fragment by two major pathways; namely, the McLafferty + 1 rearrangement and the loss of alkoxy. Both pathways
involve a carbonyl oxygen attack to the ortho-carbonyl carbon leading to structures with tetrahedral carbon intermediates that eventually give m/z 149. These pathways were studied by collision induced dissociation (CID) using triple quadrupole mass spectrometry. The proposed
McLafferty + 1 pathway proceeds through a distonic M•+, leading to the loss of an allylic-stabilized alkene radical. The McLafferty rearrangement step proceeds through a six-membered
ring transition state with a small activation energy ranging 0.4–6.2 kcal/mol; the transfer of a second H from the distonic
ion of the rearrangement step proceeds through a radical cation molecule complex. Based on quantum chemical modeling of the
cation molecule complexes, two kinds of cation molecule complexes were identified as radical cation molecule complex and hyperconjugated
cation molecule complex. This distinction is based on the cation and simplifies future modeling of similar complexes. Optimization
of important fragments in these pathways showed cyclized and hydrogen-bonded structures to be favored. An exception was the
optimized structure of the protonated phthalic anhydride (m/z 149) that showed a structure with an open anhydride ring. 相似文献
46.
The X-band ( x ; 9.4 v GHz) electron spin resonance (ESR) spectra of the un-doped isotopically enriched lithium tetraborate (LTB) Li 2 B 4 O 7 single crystals, irradiated by thermal neutrons (fluences | n =2.74 ‐ 10 15 1 1.79 v ‐ 10 18 v cm m 2 ) were investigated at 300 and 77 v K. The LTB crystals of high chemical purity and optical quality with different isotope compositions ( 6 Li 2 10 B 4 O 7 , 6 Li 2 11 B 4 O 7 , 7 Li 2 10 B 4 O 7 and 7 Li 2 11 B 4 O 7 ) were grown by Czochralski technique. The thermal neutrons (the total quantity >90%) with fluence near 10 18 v cm m 2 induce at least 4 different types of stable paramagnetic centers in the Li and B isotopically enriched LTB crystals. The ESR spectra, electron structure and efficiency of generation for centers, induced by thermal neutrons, essentially depend on neutron fluence and isotope composition of the LTB crystals. The local symmetry and the spin Hamiltonian parameters of the observed paramagnetic centers were determined and their electron structure were established. The possible models and formation mechanism of the radiation defects, induced by thermal neutrons in the LTB lattice, are proposed. 相似文献
47.
Statistical distributions of the frequencies of OH vibrations calculated from the experimental Raman spectra of HOD molecules over the temperature range of 10–200 C using the recently developed deconvolution technique have been analysed in the framework of fluctuation theory of hydrogen bonding. Two temperature independent functions that are the basis of the Zhukovsky theory for describing the temperature transformation of frequency distribution functions of OH vibrations in a statistical ensemble of O—H…O bonds were established and analytically approximated. This made it possible to reconstruct the entire set of initial spectra and to extrapolate their forms to a wider temperature range. These results support the continuum model of liquid water structure. 相似文献
48.
HAN Guo-qiang YA O Hai-lou 《数学季刊》2014,(2):244-246
Let K be an algebraically closed field and A be a finite dimensional algebra over K. In this paper we give a classification of biserial incidence algebras with quiver methods. 相似文献
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50.