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排序方式: 共有280条查询结果,搜索用时 46 毫秒
91.
Robert D. Hale Chang‐Ching Chan Carl S. Weisbecker Athula B. Attygalle 《Journal of mass spectrometry : JMS》2014,49(3):195-200
Upon collisional activation, gaseous metal adducts of lithium, sodium and potassium oxalate salts undergo an expulsion of CO2, followed by an ejection of CO to generate a product ion that retains all three metals atoms of the precursor. Spectra recorded even at very low collision energies (2 eV) showed peaks for a 44‐Da neutral fragment loss. Density functional theory calculations predicted that the ejection of CO2 requires less energy than an expulsion of a Na+ and that the [Na3CO2]+ product ion formed in this way bears a planar geometry. Furthermore, spectra of [Na3C2O4]+ and [39K3C2O4]+ recorded at higher collision energies showed additional peaks at m/z 90 and m/z 122 for the radical cations [Na2CO2]+? and [K2CO2]+?, respectively, which represented a loss of an M? from the precursor ions. Moreover, [Na3CO2]+, [39K3CO2]+ and [Li3CO2]+ ions also undergo a CO loss to form [M3O]+. Furthermore, product‐ion spectra for [Na3C2O4]+ and [39K3C2O4]+ recorded at low collision energies showed an unexpected peak at m/z 63 for [Na2OH]+ and m/z 95 for [39K2OH]+, respectively. An additional peak observed at m/z 65 for [Na218OH] + in the spectrum recorded for [Na3C2O4]+, after the addition of some H218O to the collision gas, confirmed that the [Na2OH] + ion is formed by an ion–molecule reaction with residual water in the collision cell. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
92.
93.
M. A. El-sayed 《Journal of Chemical Sciences》1991,103(3):277-282
The determination of the mechanisms of chemical and physical changes is one of the principal occupations of many chemists
today. To accomplish this, the dependence of the change being examined on a number of intensive variables such as temperature,
pressure, concentration of reactants as well as the pH is usually studied. In this account, we summarize our recent studies
on the reactivity and dynamics of niobium gaseous clusters in which their changes with size are used as a new degree of freedom
that assists in deducing the mechanism of the change studied. 相似文献
94.
《科学通报(英文版)》2004,49(Z1):79-79
The mechanism of carbon isotopic fractionation for gaseous hydrocarbons is revealed by investigating the residual liquid hydrocarbons in laboratory pyrolysates of n-octodecane. The results indicate that cracking and polymerization in the relatively low temperatures and dispropor-tionation reactions leading to light hydrocarbons and pol-yaromatic hydrocarbons at high temperatures are probably causes for the carbon isotope reversal of gaseous hydrocarbons that is commonly observed in pyrolysis experiments. This study provides significant insight for quantitative modeling of natural gas δ13C values and aid in the identification and assessment of natural gases derived from oil cracking. 相似文献
95.
Kohji Mitsubayashi Genki Nishio Masayuki Sawai Elito Kazawa Hiromichi Yoshida Takao Saito Hiroyuki Kudo Kimio Otsuka Motoharu Takao Hirokazu Saito 《Mikrochimica acta》2008,160(4):427-433
A biochemical gas-sensor (sniffer-chip) with formaldehyde dehydrogenase (FALDH) was developed for convenient analysis of gaseous
formaldehyde with high gas-selectivity. The sniffer-chip for formaldehyde in the gas phase was constructed by immobilizing
FALDH to a Pt-electrode coated hydrophilic PTFE membrane. The oxidation current of NADH produced by the enzymatic reactions
was measured by amperometric analysis. The calibration range of the sniffer-chip for formaldehyde in the gas phase was from
40 to 2000 ppb, which encountered the maximum permissible concentration of formaldehyde vapor in the residential house (80 ppb)
and formaldehyde detection limit for the human sense of smell (410 ppb). As the resident-environmental application, the sniffer-chip
was possible to measure the formaldehyde concentration from some timber materials (3 kinds of interior timber and 2 kinds
of exterior formwork timber) within 3 min. The calculated concentration value by a regression analysis was consistent with
those of a commercially available gas sensor and a gas detector tube for formaldehyde. The FALDH sniffer-tip would be effective
and convenient approach to detect and measure gaseous formaldehyde with high gas-selectivity at the residential atmosphere.
Correspondence: Kohji Mitsubayashi, Department of Biomedical Devices and Instrumentation, Institute of Biomaterials and Bioengineering,
Tokyo Medical and Dental University, 2-3-10 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-0062, Japan 相似文献
96.
针对电子教学系统人机交互的自然性和用户适应性不足的问题,研究设计了基于草图的人机交互技术的新型电子教学系统,提出了基于用户信息的草图识别方法.实验表明该方法具有很好的效果. 相似文献
97.
98.
Freneil B. Jariwala Ryan E. Wood Upul Nishshanka Athula B. Attygalle 《Journal of mass spectrometry : JMS》2012,47(4):529-538
In the negative‐ion collision‐induced dissociation mass spectra of most organic sulfonates, the base peak is observed at m/z 80 for the sulfur trioxide radical anion (SO3–·). In contrast, the product‐ion spectra of a few sulfonates, such as cysteic acid, aminomethanesulfonate, and 2‐phenylethanesulfonate, show the base peak at m/z 81 for the bisulfite anion (HSO3–). An investigation with an extensive variety of sulfonates revealed that the presence of a hydrogen atom at the β‐position relative to the sulfur atom is a prerequisite for the formation of the bisulfite anion. The formation of HSO3– is highly favored when the atom at the β‐position is nitrogen, or the leaving neutral species is a highly conjugated molecule such as styrene or acrylic acid. Deuterium‐exchange experiments with aminomethanesulfonate demonstrated that the hydrogen for HSO3– formation is transferred from the β‐position. The presence of a peak at m/z 80 in the spectrum of 2‐sulfoacetic acid, in contrast to a peak at m/z 81 in that of 3‐sulfopropanoic acid, corroborated the proposed hydrogen transfer mechanism. For diacidic compounds, such as 4‐sulfobutanoic acid and cysteic acid, the m/z 81 ion can be formed by an alternative mechanism, in which the negative charge of the carboxylate moiety attacks the α‐carbon relative to the sulfur atom. Experiments conducted with deuterium‐exchanged and deuterium‐labeled analogs of sulfocarboxylic acids demonstrated that the formation of the bisulfite anion resulted either from a hydrogen transfer from the β‐carbon, or from a direct attack by the carboxylate moiety on the α‐carbon. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
99.
The Monchick–Mason approximation for the calculation of the transport coefficients of atomic ions in diatomic gases is extended in a manner that allows comparison of theoretical and experimental mobilities of gaseous ions to serve as quantitative tests of the accuracy of the ab initio, angle- and position-dependent interaction potentials used in the calculations. The feasibility of this procedure is demonstrated with Li+ in H2. 相似文献
100.
在气泡-液柱一维耦合振动模型的基础上对刚性微管两侧声压不相等时管内柱状气泡的轴向一维受迫振动进行了理论探索. 声压不均匀分布不影响气泡线性振动时的共振频率, 但振动幅度受到有效声压幅值的影响. 利用逐级近似法分析了管内非线性振动气泡的基频、三倍频和三分之一分频振动的幅-频响应关系, 结果表明当驱动声压超过0.1 MPa时, 气泡振动处于非线性状态. 非线性声响应特征主要表现为:基频和分频振动幅值响应的多值性; 三倍频振动在低频区响应强于高频区; 三分频振动在大于共振频率的频域内出现的概率更大. 相似文献