全文获取类型
收费全文 | 617篇 |
免费 | 5篇 |
国内免费 | 11篇 |
专业分类
化学 | 245篇 |
力学 | 47篇 |
数学 | 120篇 |
物理学 | 221篇 |
出版年
2022年 | 7篇 |
2021年 | 10篇 |
2020年 | 10篇 |
2019年 | 8篇 |
2018年 | 6篇 |
2016年 | 14篇 |
2015年 | 7篇 |
2014年 | 6篇 |
2013年 | 19篇 |
2012年 | 29篇 |
2011年 | 17篇 |
2010年 | 13篇 |
2009年 | 15篇 |
2008年 | 23篇 |
2007年 | 20篇 |
2006年 | 21篇 |
2005年 | 26篇 |
2004年 | 21篇 |
2003年 | 14篇 |
2002年 | 21篇 |
2001年 | 31篇 |
2000年 | 17篇 |
1999年 | 9篇 |
1998年 | 10篇 |
1997年 | 9篇 |
1996年 | 16篇 |
1995年 | 8篇 |
1994年 | 16篇 |
1993年 | 8篇 |
1992年 | 26篇 |
1991年 | 18篇 |
1990年 | 12篇 |
1989年 | 12篇 |
1988年 | 7篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 10篇 |
1984年 | 15篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1980年 | 10篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1976年 | 5篇 |
1975年 | 11篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1971年 | 5篇 |
1968年 | 5篇 |
1967年 | 4篇 |
排序方式: 共有633条查询结果,搜索用时 15 毫秒
91.
Mordecai B. Rubin 《Tetrahedron letters》1982,23(44):4615-4618
Irradiation of benzophenone in alcohol solutions produces unsymmetrical pinacols and para-coupled products as well as benzpinacol; the product composition depends on light intensity. 相似文献
92.
Clark AP Cadby AJ Shen CK Rubin Y Tolbert SH 《The journal of physical chemistry. B》2006,110(44):22088-22096
We have synthesized a conjugated amphiphilic polyelectrolyte, a poly(phenylene ethynylene) (PPE), and the structurally analogous neutral polymer. The solution-phase aggregation of the uncharged PPE can be reversibly controlled by varying the solvent polarity and concentration, while the charged polymer appears to self-assemble at any concentration in compatible solvents. These conclusions are based on a combination of absorption and photoluminescence spectroscopy and dynamic light scattering. Photoinduced absorption spectroscopy was also employed to investigate interchain electronic communication and the photoinduced production of free charge carriers. The uncharged PPE had a relatively high polaron yield, indicating pi-stacking of adjacent PPE chains and efficient exciton splitting, while the charged polymer did not produce polarons, indicating that the polymers are not pi-stacked despite their tendency to form aggregates. This is most likely due to the presence of the cationic trimethylammonium side chains which force neighboring polymer chains too far apart to achieve effective pi-orbital overlap. Polarons were observed in both polymers after chemical doping with iodine. The ability to control aggregation and interchain electronic communication could be a useful tool in designing nanostructured electronic materials. 相似文献
93.
Rosner JL Adam NE Alexander JP Berkelman K Cassel DG Duboscq JE Ecklund KM Ehrlich R Fields L Galik RS Gibbons L Gray R Gray SW Hartill DL Heltsley BK Hertz D Jones CD Kandaswamy J Kreinick DL Kuznetsov VE Mahlke-Krüger H Meyer TO Onyisi PU Patterson JR Peterson D Phillips EA Pivarski J Riley D Ryd A Sadoff AJ Schwarthoff H Shi X Stroiney S Sun WM Wilksen T Weinberger M Athar SB Avery P Breva-Newell L Patel R Potlia V Stoeck H Yelton J Rubin P Cawlfield C Eisenstein BI Karliner I Kim D Lowrey N 《Physical review letters》2006,96(9):092003
We determine the dielectron widths of the Gamma(1S), Gamma(2S), and Gamma(3S) resonances with better than 2% precision by integrating the cross section of e+e- -->Gamma over the e+e- center-of-mass energy. Using e+e- energy scans of the Gamma resonances at the Cornell Electron Storage Ring and measuring Gamma production with the CLEO detector, we find dielectron widths of 1.252+/-0.004(sigma(stat))+/-0.019(sigma(syst)) keV, 0.581+/-0.004+/-0.009 keV, and 0.413+/-0.004+/-0.006 keV for the Gamma(1S), Gamma(2S), and Gamma(3S), respectively. 相似文献
94.
Adam NE Alexander JP Berkelman K Cassel DG Crede V Duboscq JE Ecklund KM Ehrlich R Fields L Galik RS Gibbons L Gittelman B Gray R Gray SW Hartill DL Heltsley BK Hertz D Jones CD Kandaswamy J Kreinick DL Kuznetsov VE Mahlke-Krüger H Meyer TO Onyisi PU Patterson JR Peterson D Phillips EA Pivarski J Riley D Ryd A Sadoff AJ Schwarthoff H Shi X Shepherd MR Stroiney S Sun WM Urner D Wilksen T Weaver KM Weinberger M Athar SB Avery P Breva-Newell L Patel R Potlia V Stoeck H Yelton J Rubin P Cawlfield C 《Physical review letters》2006,96(8):082004
We observe signals for the decays psi(3770) --> XJ/psi from data acquired with the CLEO detector operating at the CESR e+ e- collider with square root of s = 3773 MeV. We measure the following branching fractions Beta(psi(3770) --> XJ/psi and significances: (189 +/- 20 +/- 20) x 10(-5) (11.6sigma) for X = pi+ pi-, (80 +/- 25 +/- 16) x 10(-5) (3.4sigma) for X = pi0 pi0, and (87 +/- 33 +/- 22) x 10(-5) (3.5sigma) for X = eta, where the errors are statistical and systematic, respectively. The radiative return process e+ e- --> gamma psi(2S) populates the same event sample and is used to measure Gamma ee[psi(2S)] = (2.54 +/- 0.03 +/- 0.11) keV. 相似文献
95.
Rubin P Cawlfield C Eisenstein BI Karliner I Kim D Lowrey N Naik P Sedlack C Selen M White EJ Wiss J Shepherd MR Besson D Pedlar TK Cronin-Hennessy D Gao KY Gong DT Hietala J Kubota Y Klein T Lang BW Poling R Scott AW Smith A Dobbs S Metreveli Z Seth KK Tomaradze A Zweber P Ernst J Severini H Dytman SA Love W Mehrabyan S Savinov V Aquines O Li Z Lopez A Mendez H Ramirez J Xin B Huang GS Miller DH Pavlunin V Sanghi B Shipsey IP Adams GS Anderson M Cummings JP Danko I Napolitano J He Q Insler J 《Physical review letters》2006,96(8):081802
Using of data collected with the CLEO-c detector, we report on first observations and measurements of Cabibbo-suppressed decays of D mesons in the following six decay modes: pi+ pi- pi0 pi0, pi+ pi+ pi- pi- pi0, pi+ pi0 pi0, pi+ pi+ pi- pi0, eta pi0, and omega pi+ pi-. Improved branching fraction measurements in eight other multipion decay modes are also presented. The measured D --> pi pi rates allow us to extract the ratio of isospin amplitudes A(DeltaI = (3/2) / A(DeltaI = (1/2)) = 0.420 +/- 0.014(stat) +/- 0.016(syst) and the strong phase shift of delta1 = (86.4 +/- 2.8 +/- 3.3) degrees, which is quite large and now more precisely determined. 相似文献
96.
Rosner JL Adam NE Alexander JP Berkelman K Cassel DG Duboscq JE Ecklund KM Ehrlich R Fields L Gibbons L Gray R Gray SW Hartill DL Heltsley BK Hertz D Jones CD Kandaswamy J Kreinick DL Kuznetsov VE Mahlke-Krüger H Meyer TO Onyisi PU Patterson JR Peterson D Phillips EA Pivarski J Riley D Ryd A Sadoff AJ Schwarthoff H Shi X Stroiney S Sun WM Wilksen T Weinberger M Athar SB Avery P Breva-Newell L Patel R Potlia V Stoeck H Yelton J Rubin P Cawlfield C Eisenstein BI Karliner I Kim D Lowrey N Naik P 《Physical review letters》2006,96(12):121801
We present the first experimental limits on high-q2 contributions to charmless semileptonic decays of the form expected from the weak annihilation (WA) decay mechanism. Such contributions could bias determinations of /Vub/ from inclusive measurements of B-->Xulupsilon. Using a wide range of models based on available theoretical input we set a limit of GammaWA/Gammab-->u<7.4% (90% confidence level) on the WA fraction, and assess the impact on previous inclusive determinations of /Vub/. 相似文献
97.
Complete saturation of a single six-membered ring on fullerene C60 has been achieved. The critical step in this first synthesis of a fully characterized 1,2,3,4,5,6-hexaadduct consisted of a remarkable double 5-exo-trig addition of alkoxyl radicals promoted by lead tetraacetate. Two possible opening pathways ([2 + 2 + 2] retrocycloadditions) for the newly synthesized compound were explored using quantum mechanical calculations. We found that the oxa bridges in the hexaadduct prevent ring opening through the retro[2 + 2 + 2] mechanism due to the high activation barrier and endothermicity of the reaction. 相似文献
98.
Jacques L. Rubin 《Foundations of Physics》2010,40(2):158-178
On the basis of the Woodhouse causal axiomatics, we show that conformal proper times and an extra variable in addition to
those of space and time, together give a physical justification for the ‘chronometric hypothesis’ of general relativity. Indeed, we show that, with a lack of these latter two ingredients and of this hypothesis, clock paradoxes
exist for which the unparadoxical asymmetry cannot be recovered when using the ‘clock and message functions’ only. These proper times originate from a given conformal structure of the spacetime when ascribing different compatible
projective structures to each Woodhouse particle, and then, each defines a specific Weylian ‘sheaf structure’. In addition, the proper time parameterizations are defined via path-dependent conformal scale factors, which act like sockets
for any kind of physical interaction and also represent the values of the variable associated with the extra dimension. 相似文献
99.
[Structure: see text] The regioselective functionalization of C60 with a trans-4,trans-4,trans-4 trisaddition pattern is not feasible directly. We have found an indirect approach taking advantage of the modified electronic reactivity of cis-1 bisadducts. The cis-1 addition pattern electronically activates three trans-4 C=C bonds on the opposite hemisphere of C60, allowing further highly regioselective additions at these positions. Thermal removal of the cis-1 blocking unit results in a trans-4,trans-4,trans-4 trisadduct with C3v symmetry. 相似文献
100.
Alexander V. Aksenov Igor Yu. Grishin Nicolai A. Aksenov Vladimir V. Malyuga Dmitrii A. Aksenov Mezvah A. Nobi Michael Rubin 《Molecules (Basel, Switzerland)》2021,26(14)
Nitroalkanes activated with polyphosphoric acid serve as efficient electrophiles in reactions with various nucleophilic amines. Strategically placed second functionality allows for the design of annulation reactions enabling preparation of various heterocycles. This strategy was employed to develop an innovative synthetic approach towards 3,4-dihydroquinazolines from readily available 2-(aminomethyl)anilines. 相似文献