全文获取类型
收费全文 | 1867篇 |
免费 | 22篇 |
国内免费 | 3篇 |
专业分类
化学 | 1155篇 |
晶体学 | 16篇 |
力学 | 17篇 |
数学 | 333篇 |
物理学 | 371篇 |
出版年
2022年 | 18篇 |
2021年 | 25篇 |
2020年 | 19篇 |
2019年 | 26篇 |
2017年 | 20篇 |
2016年 | 30篇 |
2015年 | 22篇 |
2014年 | 37篇 |
2013年 | 64篇 |
2012年 | 76篇 |
2011年 | 57篇 |
2010年 | 42篇 |
2009年 | 37篇 |
2008年 | 63篇 |
2007年 | 66篇 |
2006年 | 67篇 |
2005年 | 61篇 |
2004年 | 52篇 |
2003年 | 37篇 |
2002年 | 29篇 |
2001年 | 27篇 |
2000年 | 30篇 |
1999年 | 18篇 |
1998年 | 19篇 |
1997年 | 31篇 |
1996年 | 26篇 |
1995年 | 33篇 |
1994年 | 34篇 |
1993年 | 46篇 |
1992年 | 41篇 |
1991年 | 30篇 |
1990年 | 28篇 |
1989年 | 42篇 |
1988年 | 13篇 |
1987年 | 20篇 |
1986年 | 13篇 |
1985年 | 25篇 |
1984年 | 30篇 |
1983年 | 20篇 |
1982年 | 20篇 |
1981年 | 28篇 |
1980年 | 23篇 |
1979年 | 35篇 |
1978年 | 30篇 |
1977年 | 29篇 |
1976年 | 25篇 |
1975年 | 30篇 |
1974年 | 18篇 |
1973年 | 26篇 |
1970年 | 12篇 |
排序方式: 共有1892条查询结果,搜索用时 15 毫秒
951.
With HOD initially in its vibrational ground state, we present a new detailed interpretation of the OD/OH branching ratio (approximately 3) in the photoinduced process D+OH<--HOD-->H+OD, in the first absorption band. Using semiclassical arguments, we show that the branching ratio has little to do with the initial distribution of configurations, but the initial momentum distribution plays a key role in determination of the branching ratio. The formation of D+OH arises from initial situations where OD is stretching, and it stretches faster than OH, whereas all other motions lead to H+OD. This picture is confirmed by quantum wave-packet calculations. 相似文献
952.
Marlene Kolter Prof. Dr. Konrad Koszinowski 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(44):15744-15750
The reduction of PdII precatalysts to catalytically active Pd0 species is a key step in many palladium‐mediated cross‐coupling reactions. Besides phosphines, the stoichiometrically used organometallic reagents can afford this reduction, but do so in a poorly understood way. To elucidate the mechanism of this reaction, we have treated solutions of Pd(OAc)2 and a phosphine ligand L in tetrahydrofuran with RMgCl (R=Ph, Bn, Bu) as well as other organometallic reagents. Analysis of these model systems by electrospray‐ ionization mass spectrometry found palladate(II) complexes [LnPdR3]? (n=0 and 1), thus pointing to the occurrence of transmetallation reactions. Upon gas‐phase fragmentation, the [LnPdR3]? anions preferentially underwent a reductive elimination to yield Pd0 species. The sequence of the transmetallation and reductive elimination, thus, constitutes a feasible mechanism for the reduction of the Pd(OAc)2 precatalyst. Other species of interest observed include the PdIV complex [PdBn5]?, which did not fragment via a reductive elimination but lost BnH instead. 相似文献
953.
Tobias Parchomyk Prof. Dr. Konrad Koszinowski 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(44):15609-15613
Iron‐catalyzed cross‐coupling reactions have an outstanding potential for sustainable organic synthesis, but remain poorly understood mechanistically. Here, we use electrospray‐ionization (ESI) mass spectrometry to identify the ionic species formed in these reactions and characterize their reactivity. Transmetalation of Fe(acac)3 (acac=acetylacetonato) with PhMgCl in THF (tetrahydrofuran) produces anionic iron ate complexes, whose nuclearity (1 to 4 Fe centers) and oxidation states (ranging from ?I to +III) crucially depend on the presence of additives or ligands. Upon addition of iPrCl, formation of the heteroleptic FeIII complex [Ph3Fe(iPr)]? is observed. Gas‐phase fragmentation of this complex results in reductive elimination and release of the cross‐coupling product with high selectivity. 相似文献
954.
Urs Schreiber Christoph Schweigert Konrad Waldorf 《Communications in Mathematical Physics》2007,274(1):31-64
The Wess-Zumino term in two-dimensional conformal field theory is best understood as a surface holonomy of a bundle gerbe.
We define additional structure for a bundle gerbe that allows to extend the notion of surface holonomy to unoriented surfaces.
This provides a candidate for the Wess-Zumino term for WZW models on unoriented surfaces. Our ansatz reproduces some results
known from the algebraic approach to WZW models.
manche meinen
lechts und rinks
kann man nicht velwechsern
werch ein illtum
Ernst Jandl [Jan95]
K.W. is supported with scholarships by the German Israeli Foundation (GIF) and by the Rudolf und Erika Koch–Stiftung. 相似文献
955.
S. Borneis A. Dax T. Engel C. Holbrow G. Huber T. Kühl D. Marx P. Merz W. Quint F. Schmitt P. Seelig M. Tomaselli H. Winter K. Beckert B. Franzke F. Nolden H. Reich M. Steck 《Hyperfine Interactions》2000,127(1-4):305-310
Laser spectroscopy of highly charged heavy ions in the storage ring provides an excellent tool for a test of QED in ultra-high
electric and magnetic fields. Discrepancies between experimental and theoretical values are so far mainly explained by uncertainties
of nuclear properties. New experimental possibilities can avoid these problems by additional measurements in lithium-like
systems.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
956.
957.
958.
R. Engel 《Zeitschrift fur Physik C Particles and Fields》1995,66(1-2):203-214
In the framework of the Dual Parton Model an approximation scheme to describe high energy photoproduction processes is presented. Based on the distinction between direct, resolved soft, and resolved hard interaction processes we construct effective impact parameter amplitudes. In order to treat low mass diffraction within the eikonal formalism in a consistent way a phenomenological ansatz is proposed. The free parameters of the model are determined by fits to high energy hadro- and photoproduction cross sections. We calculate the partial photoproduction cross sections and discuss predictions of the model at HERA energies. Using hadro- and photoproduction data together, the uncertainties of the model predictions are strongly reduced. 相似文献
959.
L. W. Engel C. -C. Li D. Shahar D. C. Tsui M. Shayegan 《Physica E: Low-dimensional Systems and Nanostructures》1998,1(1-4)
The conductivity of the high magnetic field insulating phases of two-dimensional electron and hole systems (2DES and 2DHS) of sufficiently low disorder exhibits a resonance at microwave frequency. We present and compare results on this resonance in a moderate disorder 2DES and in a high quality 2DHS. The 2DES exhibits the resonance even though the high-
insulator is not reentrant around the
fractional quantum Hall effect. The resonance in the 2DHS is much sharper than that in the 2DES, and appears to be inconsistent with the standard model of a two-dimensional harmonic oscillator in a magnetic field. 相似文献
960.