全文获取类型
收费全文 | 1299篇 |
免费 | 87篇 |
国内免费 | 11篇 |
专业分类
化学 | 964篇 |
晶体学 | 5篇 |
力学 | 30篇 |
综合类 | 1篇 |
数学 | 194篇 |
物理学 | 203篇 |
出版年
2023年 | 15篇 |
2022年 | 17篇 |
2021年 | 42篇 |
2020年 | 59篇 |
2019年 | 49篇 |
2018年 | 30篇 |
2017年 | 33篇 |
2016年 | 64篇 |
2015年 | 61篇 |
2014年 | 48篇 |
2013年 | 89篇 |
2012年 | 69篇 |
2011年 | 99篇 |
2010年 | 38篇 |
2009年 | 38篇 |
2008年 | 64篇 |
2007年 | 54篇 |
2006年 | 56篇 |
2005年 | 47篇 |
2004年 | 56篇 |
2003年 | 33篇 |
2002年 | 29篇 |
2001年 | 11篇 |
2000年 | 8篇 |
1998年 | 16篇 |
1997年 | 14篇 |
1996年 | 14篇 |
1995年 | 7篇 |
1994年 | 12篇 |
1993年 | 10篇 |
1992年 | 13篇 |
1991年 | 6篇 |
1990年 | 6篇 |
1989年 | 8篇 |
1988年 | 10篇 |
1987年 | 6篇 |
1986年 | 9篇 |
1985年 | 12篇 |
1984年 | 8篇 |
1983年 | 10篇 |
1982年 | 7篇 |
1981年 | 14篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 12篇 |
1976年 | 10篇 |
1975年 | 8篇 |
1974年 | 9篇 |
1973年 | 9篇 |
1971年 | 6篇 |
排序方式: 共有1397条查询结果,搜索用时 31 毫秒
941.
A general linear response theory is presented to calculate the zero-wavevector and zero-frequency reaction rate coefficient for particles diffusing into absorbing spheres. Allowance is made for possible incomplete particle absorption. A Faxén-like theorem for chemical reactions is derived. The problem is solved completely for a simple regular array of sinks. Exact analytic expressions for the rate coefficient as a function of sink volume fraction are obtained for the sc and fcc lattices. The case of a disordered array of sinks is also considered and the leading order nonanalytic density dependence of the rate coefficient is calculated. In both cases an increase in the rate coefficient with sink density in a local region of the system is found. The general formalism is extended to examine the modification to the particle diffusion coefficient due to the presence of the spheres. For regular arrays of spheres, the mean field result is reproduced.Research supported in part by a grant from the National Research Council of Canada. 相似文献
942.
The mercury-photosensitized oxidation of CO was studied at 275°C over a wide range of [O2]/[CO] ratios in the absence and presence of the oxygen atom scavenger 2-trifluoromethylpropene (TMP) and at 25°C at low [O2]/[CO] ratios in the presence of TMP. By following the quantum yield of CO2 production, Φ {CO2}, as a function of the [O2]/[CO] ratio, the reactions of vibrationally excited CO (v υ 9) and electronically excited O2, probably in the c1Σ?u state, were studied. At low [O2]/[CO] ratios the predominant reactions are of vibrationally excited CO (v υ 9). Relative rate constants for chemical reaction versus deactivation of CO (v υ 9) were obtained. At higher [O2]/[CO] ratios, the principal reactions are of electronically excited O2. Relative rate constants for chemical reactions and deactivation of this electronically excited O2 with CO, O2, and TMP were obtained. From the effect of total pressure on Φ {CO2}, it is proposed that an intermediate CO3 is formed in the reaction of electronically excited O2 with CO. 相似文献
943.
The reaction of O(3P), prepared from the Hg photosensitization of N2O, with C2HCl3 was studied at 25°C. The products of the reaction in the absence of O2 were CO, CHCl3, and polymer (as well as N2 from the N2O). The quantum yields of CO and CHCl3 were 0.23 ± 0.01 and 0.14 ± 0.05, is respectively independent of reaction conditions. The reaction mechanism is with k14a/k14 = 0.23, where k14a + k14b. Most of the HCl and CCl2 combine to form CHCl3, but some other products must also be formed to account for the difference in the CO and CHCl3 quantum yields. The C2HCl3O* adduct polymerizes without involving additional C2HCl3 molecules, since the quantum yield of C2HCl3 disappearance, ? Φ{C2HCl3}, was about 1.0 at high values of [N2O]/[C2HCl3]. The rate coefficient for the reaction of O(3P) with C2HCl3 is 0.10 that for the reaction of O(3P) with C2F4. In the presence of O2 the free radical chain oxidation occurs because of the reaction The main product is CHCl2CCl(O) with smaller amounts of CO and CCl2O, and some CO2. The chain lengths were long and values of ? Φ {C2HCl3} up to 90 were observed. 相似文献
944.
S. Jha H. M. Seyoum Sherif Yehia Charilaos Mitros G. M. Julian R. A. Dunlap A. Vasquez J. G. M. Da Cunha S. M. M. Ramos 《Hyperfine Interactions》1986,28(1-4):491-494
We have investigated the systematics of hyperfine magnetic field on a fixed probe at the Z-site in Heusler alloys Rh2MnZ as the valence of Z (sp element) is varied. The hmf on119Sn in Rh2MnIn.98
119Sn02 has been measured at 293K and 77K. In Rh2Mn1.12Sb.86
119Sn.02 the hmf on121Sb has been measured at 77 K, and on119Sn at 293 K and 77 K. The results are compared with the hmf on119Sn in Rh2Mn Ge.98
119Sn.02 Rh2Mn Sn, and Rh2Mn Pb.98
119Sn.02.Supported by the University Research Council, University of CincinnatiSupported by the Natural Sciences and Engineering Research Council of Canada 相似文献
945.
The reactions of O3 with ethylene, allene, 1,3-butadiene, and trans-1,3-pentadiene have been studied in the presence of excess O2 over the temperature range 232 to 298 K. The initial O3 pressure was varied from 4–18 mtorr, and the olefin pressure was varied from 0.1 to 4.5 torr (ethylene), 2.8 to 39.6 torr (allene), 52.7 to 600 mtorr (1,3-butadiene) or 26.2 to 106 mtorr (trans-1,3-pentadiene). The O3 decay was monitored by ultraviolet absorption. The reactions are first order in both O3 and olefin, and the rate coefficients are independent of the O2 pressure. For the O3-ethylene system, various diluent gases (O2, N2, air) were used and the rate coefficients were found to be independent of the nature of the diluent gas. The various rate coefficients fit the Arrhenius expressions (k in cm3 s?1): where the reported uncertainties are one standard deviation and R is in cal/mol K. 相似文献
946.
947.
948.
Note on group consistency in analytic hierarchy process 总被引:1,自引:0,他引:1
Robert Lin Jennifer Shu-Jen Lin Jason Chang Didos Tang Henry Chao Peter C Julian 《European Journal of Operational Research》2008,190(3):672-678
We study the paper of Xu [Z. Xu, On consistency of the weighted geometric mean complex judgement matrix in AHP, European Journal of Operational Research 126 (2000) 683–687] for the group consistency in analytic hierarchy process of multicriteria decision-making. The purpose of this note is threefold. First, we point out the questionable results in this paper. Second, for three by three comparison matrices, we provide a patchwork for his method. Third, we constructed a counter example to show that in general his method is wrong. Numerical examples are provided to illustrate our findings. If there are four or more alternatives, then we may advise researchers to ignore his results to avoid questionable estimation of group consistency. 相似文献
949.
950.
Julian Freydl 《Monatshefte für Chemie / Chemical Monthly》1887,8(1):580-583
Ohne Zusammenfassung 相似文献