全文获取类型
收费全文 | 469篇 |
免费 | 14篇 |
国内免费 | 3篇 |
专业分类
化学 | 186篇 |
晶体学 | 1篇 |
力学 | 3篇 |
数学 | 71篇 |
物理学 | 225篇 |
出版年
2023年 | 3篇 |
2021年 | 3篇 |
2019年 | 8篇 |
2018年 | 3篇 |
2017年 | 4篇 |
2016年 | 8篇 |
2015年 | 3篇 |
2014年 | 14篇 |
2013年 | 14篇 |
2012年 | 21篇 |
2011年 | 45篇 |
2010年 | 12篇 |
2009年 | 8篇 |
2008年 | 23篇 |
2007年 | 22篇 |
2006年 | 30篇 |
2005年 | 22篇 |
2004年 | 23篇 |
2003年 | 11篇 |
2002年 | 12篇 |
2001年 | 7篇 |
2000年 | 7篇 |
1999年 | 10篇 |
1998年 | 6篇 |
1997年 | 8篇 |
1996年 | 9篇 |
1995年 | 8篇 |
1994年 | 11篇 |
1993年 | 6篇 |
1992年 | 5篇 |
1991年 | 7篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 11篇 |
1987年 | 5篇 |
1986年 | 8篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1977年 | 5篇 |
1976年 | 9篇 |
1975年 | 6篇 |
1974年 | 3篇 |
1971年 | 3篇 |
1968年 | 3篇 |
1959年 | 2篇 |
1935年 | 2篇 |
1932年 | 2篇 |
排序方式: 共有486条查询结果,搜索用时 312 毫秒
61.
62.
Delanson R. Crist Chung-Hua Li Charles F. Hammer Keith A. Nelson Horst G. Adolph 《Journal of heterocyclic chemistry》1994,31(6):1525-1528
The base-promoted addition of glyoxal to 1,1,2,2-tetrakis(ethoxycarbonylamino)ethane in DMF gives a product mixture containing mostly 1,1′,3,3′-tetrakis(ethoxycarbonyl)-4,4′,5,5,'-tetrahydroxy-2,2′-biimidazolidyl. An alternate structure containing a tetraazadecalin system was considered less likely, since the most significant peak in the mass spectrum of this product and a tetraacetate derivative corresponded to half the mass of the parent ion. Two-dimensional nmr spectra on the major hplc fraction are more consistent with the biimidazolidinyl structure (very low Jvic and lack of NOE enhancement). A HETCOSY spectrum on the mixture allowed assignment of 1H nmr shifts. 相似文献
63.
In the paper the mathematical methods for dead-time and pile-up corrections are discussed. The dead-time correction formulae
for a system of two short-lived isotopes and constant component (background) are reported which mathematical problem has not
been solved so far. The new electronic circuit for simultaneous measurements of clock- and live- (or dead-) times is described.
It is shown that using this circuit one can correct the counting loss for both effects simultaneously. Finally, the advantages
and disadvantages of mathematical methods for dead-time and pile-up corrections are discussed based on the authors' several-year
laboratory practice. 相似文献
64.
Volker Gehrling J. Wolfgang Hammer Klaus -Werner Hoffmann 《Zeitschrift für Physik A Hadrons and Nuclei》1971,246(5):376-382
The electron capture decay and the positron decay of84Rb were investigated using NaJ (Tl)-detectors and a Ge (Li)-detector. Measurements of all intensities and of some informative double and triple coincidences were performed. From coincidence measurements betweenK-X-radiation and the following γ-radiation we got theK-fluorescence yield of Krypton ΩitK=0.653 ± 0.004. Taking in consideration former measurements1 one concludes a continuous behaviour of ΩitK(Z) forZ=36, 37 and 38 within an uncertainty of 1%. For the branching ratios of the decay of84Rb we obtained The half-life of84Rb was determined to beT 1/2=(34.5 ± 0.2) d. 相似文献
65.
66.
Horst-Henning Grotheer Johann Wolfgang Hammer Klaus-Werner Hoffmann 《Zeitschrift für Physik A Hadrons and Nuclei》1969,225(4):293-302
The electron capture decay of85Sr and55Y has been investigated using NaI(Tl)-detectors. Spectroscopic-coincidence techniques have been employed to examine theK-electron capture rates. The experimental results areP K ω K (Sr)=.5959 ± 0.0035 andP K ω K (Y)=0.6340± 0.0032. Using theK-capture probabilities, derived from the capture ratios ofBrysk andRose with the exchange correction ofBahcall:P K (Sr)=0.880± 0.008 andP K (Y)=0.883 ± 0.008, one can derive from these results the fluorescence yieldsω K (Rb)=0.677± 0.009 andω K (Sr)=0.712± 0.010. Functions ofω K (Z) were fitted to recent experimental data and tabulated forZ=5–90. In addition to these results the half life of the 514 keV state of85Rb and the branching ratios and the positron rate of the88Y-decay have been measured with the same techniques. The data obtained partly disagree from measurements of other authors. 相似文献
67.
Hammer NI Early KT Sill K Odoi MY Emrick T Barnes MD 《The journal of physical chemistry. B》2006,110(29):14167-14171
Size-correlated single-molecule fluorescence measurements on CdSe quantum dots functionalized with oligo(phenylene vinylene) (OPV) ligands exhibit modified fluorescence intermittency (blinking) statistics that are highly sensitive to the degree of ligand coverage on the quantum dot surface. As evidenced by a distinct surface height signature, fully covered CdSe-OPV nanostructures (approximately 25 ligands) show complete suppression of blinking in the solid state on an integration time scale of 1 s. Some access to dark states is observed on finer time scales (100 ms) with average persistence times significantly shorter than those from ZnS-capped CdSe quantum dots. This effect is interpreted as resulting from charge transport from photoexcited OPV into vacant trap sites on the quantum dot surface. These results suggest exciting new applications of composite quantum dot/organic systems in optoelectronic systems. 相似文献
68.
The adhesion properties and catalytic activity of rutile TiO(2)(110)-supported Au(7) nanoclusters in different oxidation states are investigated by means of density functional theory. The calculations cover both surface science conditions of reduced TiO(2) and real catalyst conditions of oxidized (alkaline) TiO(2) supports. Large adhesion energies of Au(7) are found only when modeling real catalysts where the cluster becomes cationic with Au(+) ions in Au-O or Au-OH bonds. The full catalytic cycle for oxidation of CO by O(2) over Au(7) on alkaline TiO(2)(110) is calculated and found to involve only small activation barriers. In the presence of the CO reductant, the Au(+) sites are capable of cycling between bonding of atomic and molecular oxygen. We confirm our findings by comparison of calculated and experimental infrared stretch frequency data for adsorbed CO. 相似文献
69.
Mark Lenkewitz Evgeny Epelbaum H. -W. Hammer Ulf-G. Meißner 《The European Physical Journal A - Hadrons and Nuclei》2013,49(2):1-11
We calculate the electromagnetic neutral pion production off tri-nucleon bound states (3H, 3He) at threshold in chiral nuclear effective field theory to fourth order in the standard heavy baryon counting. We show that the fourth-order two-nucleon corrections to the S-wave multipoles at threshold are very small. This implies that a precise measurement of the S-wave cross section for neutral pion production off 3He allows for a stringent test of the chiral perturbation theory prediction for the S-wave electric multipole $E_{0+}^{\pi^0 n}$ . 相似文献