全文获取类型
收费全文 | 1656篇 |
免费 | 31篇 |
国内免费 | 3篇 |
专业分类
化学 | 787篇 |
晶体学 | 10篇 |
力学 | 34篇 |
数学 | 157篇 |
物理学 | 702篇 |
出版年
2021年 | 10篇 |
2020年 | 17篇 |
2019年 | 20篇 |
2018年 | 10篇 |
2017年 | 14篇 |
2016年 | 26篇 |
2015年 | 21篇 |
2014年 | 26篇 |
2013年 | 68篇 |
2012年 | 67篇 |
2011年 | 63篇 |
2010年 | 47篇 |
2009年 | 36篇 |
2008年 | 65篇 |
2007年 | 71篇 |
2006年 | 69篇 |
2005年 | 66篇 |
2004年 | 51篇 |
2003年 | 24篇 |
2002年 | 53篇 |
2001年 | 36篇 |
2000年 | 30篇 |
1999年 | 21篇 |
1998年 | 22篇 |
1997年 | 27篇 |
1996年 | 47篇 |
1995年 | 49篇 |
1994年 | 42篇 |
1993年 | 57篇 |
1992年 | 43篇 |
1991年 | 23篇 |
1990年 | 38篇 |
1989年 | 16篇 |
1988年 | 20篇 |
1987年 | 16篇 |
1986年 | 18篇 |
1985年 | 22篇 |
1984年 | 17篇 |
1983年 | 18篇 |
1982年 | 20篇 |
1981年 | 23篇 |
1980年 | 18篇 |
1979年 | 25篇 |
1978年 | 21篇 |
1977年 | 19篇 |
1976年 | 16篇 |
1975年 | 20篇 |
1974年 | 12篇 |
1973年 | 10篇 |
1972年 | 10篇 |
排序方式: 共有1690条查询结果,搜索用时 10 毫秒
81.
Dewald EL Suter LJ Landen OL Holder JP Schein J Lee FD Campbell KM Weber FA Pellinen DG Schneider MB Celeste JR McDonald JW Foster JM Niemann C Mackinnon AJ Glenzer SH Young BK Haynam CA Shaw MJ Turner RE Froula D Kauffman RL Thomas BR Atherton LJ Bonanno RE Dixit SN Eder DC Holtmeier G Kalantar DH Koniges AE Macgowan BJ Manes KR Munro DH Murray JR Parham TG Piston K Van Wonterghem BM Wallace RJ Wegner PJ Whitman PK Hammel BA Moses EI 《Physical review letters》2005,95(21):215004
The first hohlraum experiments on the National Ignition Facility (NIF) using the initial four laser beams tested radiation temperature limits imposed by plasma filling. For a variety of hohlraum sizes and pulse lengths, the measured x-ray flux shows signatures of filling that coincide with hard x-ray emission from plasma streaming out of the hohlraum. These observations agree with hydrodynamic simulations and with an analytical model that includes hydrodynamic and coronal radiative losses. The modeling predicts radiation temperature limits with full NIF (1.8 MJ), greater, and of longer duration than required for ignition hohlraums. 相似文献
82.
Busacca CA Grossbach D Campbell SJ Dong Y Eriksson MC Harris RE Jones PJ Kim JY Lorenz JC McKellop KB O'Brien EM Qiu F Simpson RD Smith L So RC Spinelli EM Vitous J Zavattaro C 《The Journal of organic chemistry》2004,69(16):5187-5195
The Boehringer-Ingelheim phosphinoimidazoline (BIPI) ligands were applied to the formation of chiral quaternary centers in the asymmetric Heck reaction. Several different substrates were examined in detail, using more than 70 members of this new ligand class. Hammett relationships were determined through systematic variation of the ligand electronics. All substrates showed essentially the same Hammett behavior, where enantioselectivity increased as the ligands were made more electron-deficient. Ligand optimization has led to catalysts which give the highest enantioselectivities reported to date for these difficult systems. 相似文献
83.
Buffer-gas cooling of NH via the beam loaded buffer-gas method 总被引:1,自引:0,他引:1
D.?Egorov W.?C.?Campbell B.?Friedrich S.?E.?Maxwell E.?Tsikata L.?D.?van?Buuren J.?M.?DoyleEmail author 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2004,31(2):307-311
NH radicals from a molecular beam are cooled using a novel beam-loaded buffer gas method. The radicals are produced in a glow discharge beam source and injected into cryogenic helium gas. Up to 1012 molecules in their ground electronic, vibrational, and rotational state are detected in the buffer gas and translational temperatures under 6 K are achieved. The cooling method presented is general and can be applied to any molecules in a molecular beam.Received: 20 July 2004, Published online: 26 October 2004PACS:
33.80.Ps Optical cooling of molecules; trapping - 34.50.Ez Rotational and vibrational energy transfer - 39.10. + j Atomic and molecular beam sources and techniquesB. Friedrich: Present address: Department of Molecular Physics, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin, Germany. 相似文献
84.
Campbell JL 《Rapid communications in mass spectrometry : RCM》2010,24(24):3527-3530
Atmospheric pressure ionization (API) sources have the ability to serve as dynamic 'reaction vessels' and this capability has been rapidly evolving over the past few years. With API sources, many different reagents and source conditions can be rapidly explored with minimal carryover or contamination of the mass spectrometer. While most API applications involve the simple protonation/deprotonation of analyte molecules, a great deal of flexibility and utility is available in almost any API source, provided the reagents and ionization conditions are judiciously selected. Here, the generation of a unique and useful class of reagent ions at atmospheric pressure is demonstrated for the first time. Within the AP gas-phase environment of a dual inlet ion source, the gas-phase synthesis of substituted N-phenylpyridinium cations is demonstrated by establishing conditions favorable to the nucleophilic substitution reaction required for their formation. The flexibility of this API source as a reaction vessel is also demonstrated. 相似文献
85.
86.
J. B. Campbell J. M. Greene E. R. Lavagnino D. N. Gardner A. J. Pike J. Snoddy E. C. Taylor 《Journal of heterocyclic chemistry》1986,23(3):669-672
New methods of preparing 2,3-diaminopyridine ( 13 ) from 2-chloro-3-nitropyridine ( 11 ) and 3,4-diaminopy-ridine ( 8 ) from 4-ethoxy-3-nitropyridine hydrochloride ( 5 ) have been explored and evaluated. 相似文献
87.
S.L. Campbell W. Marszalek 《Mathematical and Computer Modelling of Dynamical Systems: Methods, Tools and Applications in Engineering and Related Sciences》2013,19(1):18-42
The idea of the index of a differential algebraic equation (DAE) (or implicit differential equation) has played a fundamental role in both the analysis of DAEs and the development of numerical algorithms for DAEs. DAEs frequently arise as partial discretizations of partial differential equations (PDEs). In order to relate properties of the PDE to those of the resulting DAE it is necessary to have a concept of the index of a possibly constrained PDE. Using the finite dimensional theory as motivation, this paper will examine what one appropriate analogue is for infinite dimensional systems. A general definition approach will be given motivated by the desire to consider numerical methods. Specific examples illustrating several kinds of behavior will be considered in some detail. It is seen that our definition differs from purely algebraic definitions. Numerical solutions, and simulation difficulties, can be misinterpreted if this index information is missing. 相似文献
88.
Neutron irradiation of Cp2MoCl2 for 24 h afforded the radiotracer Cp299MoCl2 which was characterised by UV–Vis spectroscopy and thin layer chromatography. Binding experiments with the thiol containing protein human serum albumin (HSA) or calf thymus DNA, were monitored for 99Mo using a gamma counter. Under the conditions investigated, molar ratios of binding of 0.2:1 (Cp2MoCl2:DNA) and 9.4:1 (Cp2MoCl2:HSA) were calculated. The results are consistent with in vitro coordination studies that have shown strong preferential interaction of Cp2MoCl2 with thiols versus other donor sites in biomolecules including DNA. 相似文献
89.
Abe F Amidei D Apollinari G Atac M Auchincloss P Baden AR Bamberger A Barbaro-Galtieri A Barnes VE Bedeschi F Behrends S Belforte S Bellettini G Bellinger J Bensinger J Beretvas A Berge JP Bertolucci S Bhadra S Binkley M Blair R Blocker C Booth AW Brandenburg G Brown D Buckley E Byon A Byrum KL Campagnari C Campbell M Carey R Carithers W Carlsmith D Carroll JT Cashmore R Cervelli F Chadwick K Chiarelli G Chinowsky W Cihangir S Clark AG Connor D Contreras M Cooper J Cordelli M Crane D Curatolo M 《Physical review letters》1989,63(7):720-723
90.
Gade A Bazin D Brown BA Campbell CM Church JA Dinca DC Enders J Glasmacher T Hansen PG Hu Z Kemper KW Mueller WF Olliver H Perry BC Riley LA Roeder BT Sherrill BM Terry JR Tostevin JA Yurkewicz KL 《Physical review letters》2004,93(4):042501
The 9Be(32Ar, 31Ar)X reaction, leading to the 5/2+ ground state of a nucleus at the proton drip line, has a cross section of 10.4(13) mb at a beam energy of 65.1 MeV/nucleon. This translates into a spectroscopic factor that is only 24(3)% of that predicted by the many-body shell-model theory. We introduce refinements to the eikonal reaction theory used to extract the spectroscopic factor to clarify that this very strong reduction represents an effect of nuclear structure. We suggest that it reflects correlation effects linked to the high neutron separation energy (22.0 MeV) for this state. 相似文献