全文获取类型
收费全文 | 243篇 |
免费 | 4篇 |
专业分类
化学 | 146篇 |
力学 | 4篇 |
数学 | 48篇 |
物理学 | 49篇 |
出版年
2018年 | 2篇 |
2016年 | 3篇 |
2015年 | 5篇 |
2014年 | 6篇 |
2013年 | 10篇 |
2012年 | 12篇 |
2011年 | 22篇 |
2010年 | 7篇 |
2009年 | 3篇 |
2008年 | 16篇 |
2007年 | 12篇 |
2006年 | 12篇 |
2005年 | 8篇 |
2004年 | 8篇 |
2003年 | 9篇 |
2002年 | 12篇 |
2001年 | 5篇 |
2000年 | 4篇 |
1999年 | 7篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 5篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 5篇 |
1974年 | 1篇 |
1973年 | 8篇 |
1972年 | 2篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1967年 | 1篇 |
1965年 | 1篇 |
1961年 | 1篇 |
1959年 | 2篇 |
1954年 | 1篇 |
排序方式: 共有247条查询结果,搜索用时 31 毫秒
121.
Zeev Nutov 《Discrete Mathematics》2008,308(12):2533-2543
Let G be a minimally k-connected graph with n nodes and m edges. Mader proved that if n?3k-2 then m?k(n-k), and for n?3k-1 an equality is possible if, and only if, G is the complete bipartite graph Kk,n-k. Cai proved that if n?3k-2 then m?⌊(n+k)2/8⌋, and listed the cases when this bound is tight.In this paper we prove a more general theorem, which implies similar results for minimally k-outconnected graphs; a graph is called k-outconnected from r if it contains k internally disjoint paths from r to every other node. 相似文献
122.
123.
Zeev B. Alfassi 《辐射效应与固体损伤》2013,168(6):229-231
The relative efficiency of various chlorinated compounds as solvents for color transition temperatures lowering due to radiolysis is shown to be due to the C-Cl bond strength in the solvent. 相似文献
124.
The synthesis and full characterization of the first tungsten corrole reveal that it is a binuclear trioxo-bridged complex of tungsten(VI), a coordination motif without precedence for tungsten chelated by other ligands. 相似文献
125.
Lipovsky A Levitski L Tzitrinovich Z Gedanken A Lubart R 《Photochemistry and photobiology》2012,88(1):14-20
Photoexcited TiO(2) has been found to generate reactive oxygen species, yet the precise mechanism and chemical nature of the generated oxy species especially regarding the different crystal phases remain to be elucidated. Visible light-induced reactions of a suspension of titanium dioxide (TiO(2)) in water were investigated using electron paramagnetic resonance (EPR) coupled with the spin-trapping technique. Increased levels of both hydroxyl (˙OH) and superoxide anion (˙O(2)(-)) radicals were detected in TiO(2) rutile and anatase nanoparticles (50 nm). The intensity of signals assigned to the ˙OH and ˙O(2)(-) radicals was larger for the anatase phase than that originating from rutile. Moreover, illumination with visible (nonUV) light enhanced ˙O(2)(-) formation in the rutile phase. Singlet oxygen was not detected in water suspension of TiO(2) neither in rutile nor in anatase nanoparticles, but irradiation of the rutile phase with visible light revealed a signal, which could be attributed to singlet oxygen formation. The blue part of visible spectrum (400-500 nm) was found to be responsible for the light-induced ROS in TiO(2) nanoparticles. The characterization of the mechanism of visible light-induced oxy radicals formation by TiO(2) nanoparticles could contribute to its use as a sterilization agent. 相似文献
126.
Alfassi ZB 《Journal of the American Society for Mass Spectrometry》2004,15(3):385-387
It is indicated that for comparison of two mass-spectra the normalization of each ion current should be done such that each spectrum will form a unit vector, i.e., SigmaXi2 = 1, where Xi are the various components of the mass spectrum. 相似文献
127.
Kumar A Goldberg I Botoshansky M Buchman Y Gross Z 《Journal of the American Chemical Society》2010,132(43):15233-15245
A series of five free-base corroles were metalated and brominated to form 10 manganese(III) corroles. Two of the free-base corroles and six manganese(III) corroles were analyzed by X-ray crystallography, including one complex that may be considered a transition-state analogue of oxygen atom transfer (OAT) from (oxo)manganese(V) to thioansisole. Oxidation by ozone allowed for isolation of the 10 corresponding (oxo)manganese(V) corroles, whose characterization by (1)H and (19)F NMR spectroscopy and electrochemistry revealed a low-spin and triply bound manganese-oxygen moiety. Mechanistic insight was obtained by investigating their reactivity regarding stoichiometric OAT to a series of p-thioanisoles, revealing a magnitude difference on the order of 5 between the β-pyrrole brominated (oxo)manganese(V) corroles relative to the nonbrominated analogues. The main conclusion is that the (oxo)manganese(V) corroles are legitimate OAT agents under conditions where proposed oxidant-coordinated reaction intermediates are irrelevant. Large negative Hammett ρ constants are obtained for the more reactive (oxo)manganese(V) corroles, consistent with expectation for such electrophilic species. The least reactive complexes display very little selectivity to the electron-richness of the sulfides, as well as a non-first-order dependence on the concentration of (oxo)manganese(V) corrole. This suggests that disproportionation of the original (oxo)manganese(V) corrole to (oxo)manganese(IV) and (oxo)manganese(VI) corroles, followed by substrate oxidation by the latter complex, gains importance when the direct OAT process becomes progressively less favorable. 相似文献
128.
With a background in mass spectrometric studies of gas-phase ion chemistry the atmospheric pressure technology of ion mobility
spectrometry (IMS) presented me with challenges and opportunities. Fundamental studies of the parameters that influence the
mobility of ions in a low electric field yielded insights about the effects of temperature, drift gas composition and the
conformation of ions on the collision cross section. The inadequacy of current rigid-sphere, polarization limit and hard-core
models to predict the mobility of ions particularly at low temperature and in heavy drift gases, led to inclusion of additional
terms to the hard-core model to account for these effects. These studies eventually resulted in the two monographs entitled
“Ion Mobility Spectrometry” and “Ion Mobility Spectrometry –Second Edition” co-authored with Prof. Gary Eiceman and published
by Taylor & Francis, CRC Press in 1994 and 2005, respectively. Novel applications for biological and medical applications
were developed on the basis of measurement of biogenic amines by IMS, in particular the rapid, accurate and inexpensive diagnosis
of vaginal infections. 相似文献
129.
130.
Gabi Cohen Mordi Laloush Zeev Karpas 《International Journal for Ion Mobility Spectrometry》2014,17(3-4):125-129
Elevated levels of biogenic amines (trimethylamine, putrescine and cadaverine), measured by ion mobility spectrometry (IMS) were found in a sample of “dark rye” bread that had a pungent odor but not in other bread samples. The odorless breads included three types of rye bread, whole wheat, pita bread and a baguette. Sample preparation was simple and consisted of extraction of the biogenic amines into water followed by filtering the solution. The biogenic amines were measured from a single drop (50 μL) of the extract solution. The progress of spoilage was also monitored in the odorous and odorless “dark rye”. Volatile trimethylamine, readily monitored by IMS, was the main compound responsible for the offensive odor in the spoilt bread. The samples were classified by an automatic algorithm as “fresh”, “intermediate” or “spoilt” on the basis of the total biogenic amine level. Thus, we report the development of a fast and objective method to distinguish between spoilt bread and bread that is suitable for consumption. 相似文献