全文获取类型
收费全文 | 217篇 |
免费 | 10篇 |
国内免费 | 9篇 |
专业分类
化学 | 48篇 |
力学 | 8篇 |
综合类 | 3篇 |
数学 | 43篇 |
物理学 | 134篇 |
出版年
2019年 | 1篇 |
2018年 | 2篇 |
2017年 | 1篇 |
2016年 | 1篇 |
2015年 | 2篇 |
2014年 | 7篇 |
2013年 | 34篇 |
2012年 | 3篇 |
2011年 | 4篇 |
2010年 | 1篇 |
2008年 | 2篇 |
2007年 | 2篇 |
2006年 | 2篇 |
2005年 | 2篇 |
2004年 | 3篇 |
2003年 | 2篇 |
2002年 | 6篇 |
2001年 | 6篇 |
2000年 | 4篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1997年 | 11篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 5篇 |
1993年 | 7篇 |
1992年 | 7篇 |
1991年 | 10篇 |
1990年 | 24篇 |
1989年 | 15篇 |
1988年 | 6篇 |
1987年 | 10篇 |
1986年 | 7篇 |
1985年 | 8篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 5篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1971年 | 2篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1958年 | 1篇 |
1955年 | 1篇 |
1948年 | 1篇 |
排序方式: 共有236条查询结果,搜索用时 31 毫秒
71.
The movement of a particular component along an HPLC column is studied on the ba-sis of equilibrium equations. Numerical simulation of multi--step gradient elution HPLC isperformed by means o? a personal computer program. The location x, as a fraction of thecolumn length, for a given time t o? each compound is calculated, the velocity and corre-sponding acceleration are given as well. Diagrams for x,dx/dt and d~2x/dt~2 versus t display themovement process of the different components along the HPLC column during gradient elu-tion. The prediction of the retention time and peak width, and the optimization for the multi-step gradient elution HPLC are all based on such simulation and the molecular structure ofthe. components is separated as well. 相似文献
72.
Alexandreas DE Allen GE Berley D Biller S Burman RL Cavalli-Sforza M Chang CY Chen ML Chumney P Coyne D Dion C Dion GM Dorfan D Ellsworth RW Goodman JA Haines TJ Harmon M Hoffman CM Kelley L Klein S Nagle DE Schmidt DM Schnee R Sinnis C Shoup A Stark MJ Weeks DD Williams DA Wu JP Yang T Yodh GB Zhang WP 《Physical review letters》1993,71(16):2524-2527
73.
Abstract— Photoreactivation in the extreme halophilic archaebacterium Halobacterium cutirubrum was studied both in vivo and in vitro. Cells irradiated with ultraviolet (UV)-fluences up to 350 J/m2 could be completely photoreactivated, indicating very efficient repair of pyrimidine dimers in UV-irradiated DNA. Dark repair is apparently absent in Halobacterium since liquid holding under non-growth conditions did not influence the survival of UV-irradiated cells, while cells remained completely photoreactivable with no change in the kinetics of photoreactivation. Experiments with Halobacterium isolates of different carotenoid content indicated that carotenoids do not influence either UV-inactivation or photoreactivation. Small differences in the rates of UV-inactivation and photoreactivation could be assigned to the occurrence of gas vesicles. Flash experiments and the temperature dependence of photoreactivation indicated an enzymatical reaction. This was confirmed by in vitro experiments with partially purified photoreactivating enzyme. The in vivo action spectrum of photoreactivation showed a main band in the 400-470 nm region with a maximum at 440 nm. Comparison with action spectra of other microorganisms classified the Halobacterium enzyme as a 8-hydroxy-5-deazaflavin type photoreactivating enzyme. 相似文献
74.
75.
We present results of Monte Carlo simulations measuring the coherent structure function of a chain moving through an ordered lattice of fixed topological obstacles. Our computer experiments use chains up to 320 beads and cover a large range of wave vectors and a time range exceeding the reptation time. For additional information we also measured the coherent structure function of internal pieces of the chain. We compare our results i) to the predictions of the primitive chain model, ii) to an approximate form resulting from Rouse motion in a coiled tube, and iii) to our recent evaluation of the full reptation model. i) The primitive chain model can fit the data for times
, where T
2 is the Rouse time of the chain. Besides some phenomenological amplitude factor this fit involves the reptation time T
3 as a second fit parameter. For the chain lengths measured, the asymptotic behavior
is not attained. ii) The model of Rouse motion in a tube, which we have criticized before on theoretical grounds, is shown to fail also on the purely phenomenological level. iii) Our evaluation of the full reptation model yields an excellent fit to the data for both total chains and internal pieces and for all wave vectors and all times, provided specific micro-structure effects of the MC dynamics are negligible. Such micro-structure effects show up for wave vectors of the order of the inverse segment size and enforce the introduction of some phenomenological, wave-vector-dependent prefactor. For the dynamics of the total chain our data analysis based on the full reptation model shows the importance of tube length fluctuations. Universal (Rouse-type) internal relaxation, however, is unimportant. It can be observed only in the form of the diffusive motion of a short central subchain in the tube. Finally, we present a fit formula which in a large range of wave vectors and chain lengths reproduces the numerical results of our theory for the scattering from the total chain.Received: 9 July 2003, Published online: 11 November 2003PACS:
83.10.Kn Reptation and tube theories - 82.35.Lr Physical properties of polymers - 83.10.Rs Computer simulation of molecular and particle dynamics 相似文献
76.
M. Piccolo I. Peruzzi P.A. Rapidis A. Barbaro-Galtieri J.M. Feller D. Lüke V. Vuillemin J.M. Dorfan R. Ely G.J. Feldman A. Fong B. Gobbi G. Hanson J.A. Jaros B.P. Kwan P. Lecomte A.M. Litke R.J. Madaras D.E. Yount 《Physics letters. [Part B]》1979,86(2):220-224
We present measurements of the cross section for inclusive D and K meson production in e+e? annihilation in the center of mass energy range 3.6 to 5.8 GeV. D production accounts for most of the increase in the total cross section for hadron production in e+e? annihilation at energies above 4 GeV. 相似文献
77.
A. Roussarie D.L. Burke G.S. Abrams M.S. Alam C.A. Blocker A. Blondel A.M. Boyarski M. Breidenbach W.C. Carithers W. Chinowsky M.W. Coles S. Cooper W.E. Dieterle J.B. Dillon J. Dorenbosch J.M. Dorfan M.W. Eaton G.J. Feldman H. Zaccone 《Physics letters. [Part B]》1981,105(4):304-308
We report a measurement of the cross section for the process γγ→π+π? at invariant masses 500 MeV/c2 < mππ<2000 MeV/c2. A value for the radiative width of the f(1270) tensor meson Γf→γγ = 3.6 ± 0.3 ± 0.5 KeV (helicity λ = 2) has been obtained from a fit to the observed ππ mass spectrum. 相似文献
78.
P.A. Rapidis G.J. Feldman G.S. Abrams M.S. Alam A. Barbaro-Galtieri A.M. Boyarski M. Breidenbach W. Chinowsky J.M. Dorfan R. Ely J.M. Feller A. Fong B. Gobbi G. Goldhaber G. Hanson J.A. Jaros J.A. Kadyk B.P. Kwan D.E. Yount 《Physics letters. [Part B]》1979,84(4):507-510
Inclusive momentum and energy spectra of neutral and charged D-mesons produced in e+e? annihilation at energies near 7 GeV are presented. The slope of the energy spectrum is similar to the charged pion spectrum at the same energy. The inclusive cross section σ(e+e?→ D or + anything) at 7 GeV is 4.8±1.3 nb. 相似文献
79.
80.
The properties of silver-silicon interfaces formed by cleaving n-type silicon in ultra high vacuum (UHV) in a stream of evaporating silver atoms were studied. The barrier heights of these contacts were measured at different temperatures by using C-V techniques. All measurements were performed in UHV. The dependence of the barrier height upon temperature did not follow the temperature dependence of the Si band gap as it is usually found. The measured temperature behavior depended on the roughness of the Si surface. The temperature behavior can be explained by assuming a specific band structure of the interface states. For Ag contacts on atomically smooth n-type Si, the interface states were found to be arranged in two bands, one band 4 × 10?3 eV wide with acceptor type states 0.18 eV below the intrinsic level Ei and a density of 1017 states/cm2 eV, and the other 1 eV wide with donor type states with its upper edge 0.28 eV below Ei, and a density of 4 × 1014 states/cm2eV. 相似文献