全文获取类型
收费全文 | 1836篇 |
免费 | 26篇 |
国内免费 | 57篇 |
专业分类
化学 | 862篇 |
晶体学 | 11篇 |
力学 | 8篇 |
数学 | 3篇 |
物理学 | 1035篇 |
出版年
2024年 | 3篇 |
2023年 | 137篇 |
2022年 | 33篇 |
2021年 | 25篇 |
2020年 | 24篇 |
2019年 | 29篇 |
2018年 | 30篇 |
2017年 | 33篇 |
2016年 | 49篇 |
2015年 | 37篇 |
2014年 | 54篇 |
2013年 | 191篇 |
2012年 | 138篇 |
2011年 | 91篇 |
2010年 | 104篇 |
2009年 | 129篇 |
2008年 | 98篇 |
2007年 | 124篇 |
2006年 | 104篇 |
2005年 | 76篇 |
2004年 | 40篇 |
2003年 | 58篇 |
2002年 | 51篇 |
2001年 | 40篇 |
2000年 | 27篇 |
1999年 | 30篇 |
1998年 | 19篇 |
1997年 | 18篇 |
1996年 | 21篇 |
1995年 | 18篇 |
1994年 | 8篇 |
1993年 | 8篇 |
1992年 | 14篇 |
1991年 | 7篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 12篇 |
1987年 | 4篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1978年 | 1篇 |
1976年 | 3篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有1919条查询结果,搜索用时 187 毫秒
111.
Scott C. Herndon David D. Nelson Jr Mark S. Zahniser 《Journal of Quantitative Spectroscopy & Radiative Transfer》2005,90(2):207-216
The spectral line strengths in the v2 band of H2CO (segments spanning 1720-) have been determined relative to two sets of spectral line groups in the v1 and v5 band, using tunable diode laser spectroscopy. Simultaneous detection using a dual-diode instrument with a absorption cell was employed to assure identical H2CO column density for the two spectral regions. The results in the selected regions of this study are in good agreement with the line positions and the relative intensities specified in an unpublished complete line listing for the v2 band prepared by Linda Brown (see full text for reference). Based upon measurements of individual groups of spectral lines in the P, Q and R branches, the absolute band strength has been determined to be . 相似文献
112.
The rate constants have been measured for deprotonation reaction of substituted N-phenacyl-pyridinium bromides, in the pyridine ring, with 1,4-diazabicyclo[2,2,2]octane in water and DMSO, and some with 1,8-diazabicyclo[5,4,0]undec-7-ene. The dependence of the rate constant, k, on pKa of substituted pyridines is made of two distinct linear branches obtained for the salts with electron-withdrawing and electron-donating substituents, respectively. The structures of four salts have been determined by the B3LYP/6-31G(d,p) level of theory and compared with the available X-ray structure. The effect of the substituent and solvent on k values has been discussed. 相似文献
113.
We analyze the role and influence of a tradition of research linked to the concept of
primary matter
in nineteenth-century studies on the nature of the elements.The suggestion of William Prout
(1785-1850) in 1816 that the atomic weights of pure chemical elements are whole numbers and
multiples of the atomic weight of hydrogen, taken as unity, was met with serious confutations,which
in turn prompted several attempts to save Prouts hypothesis.We discuss these attempts in detail
and the objections raised against them, for instance by Dmitry Ivanovich Mendeleev (1834-1907).
We pay particular attention to the use of spectroscopy as a method for proving the existence of
elementary forms of matter inside atoms. Leaders in this field of research were two English scientists,
the astrophysicist Norman Lockyer (1836-1920) and the chemist William Crookes (1832-
1919). Both of their approaches involved the idea of primary matter. However, while Crookess
approach proved to be incorrect, Lockyers ideas survived for several years and supported the discovery
of the electron by J.J.Thomson (1856-1940). 相似文献
114.
C. Lupulescu . Vajda A. Lindinger A. Merli L. Wöste 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):173-176
In this paper we present two-color pump and probe
spectroscopy on Na2F, the smallest of the
non-stoichiometric sodium-fluoride clusters
(NanFn-1), in
molecular beams by employing femtosecond laser pulses. The
molecules were pumped into the first excited state by one
photonic transition and consecutively ionized from there by the
second photon. We resolved the wavepacket oscillatory motion
involving periodical structural rearrangements in the first
excited state of Na2F with a period of
185 fs. The time-resolved
experiments show that sodium fluoride clusters provide
interesting features which can be manipulated in optimal control
experiments. 相似文献
115.
G. Durand F. Spiegelmann 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,13(2):237-243
The stability against fragmentation and possible relaxation of the lowest excited states of the Na5F4 cluster (representative of cubic non stoechiometric clusters with an excess sodium atom, also called sodium-tail) is investigated
by means of one-electron pseudopotential calculations with particular reference to photoabsorption processes from the ground
state. Whereas the equilibrium configuration of the ground state has C3v symmetry, the doubly degenerate 12E excited state is affected by a conical intersection and a Jahn-Teller effect associated with the rotation of the sodium
tail around the C3-axis. This yields a “Mexican hat" topology for the lowest sheet with three equivalent Cs minima. Alternatively the 22A1 state has a minimum retaining the C3v symmetry. The dissociation paths of the cluster along the C3-axis into respectively Na4F4 + Na and Na4F3 + NaF are also investigated. Among the former paths, the excited states are found adiabatically stable with respect to the
products. However in the A1 symmetry, fragmentation into NaF exhibits an interesting avoided crossing between configurations correlated respectively
with Na4F3
+ + NaF- and Na4F3 + NaF. Such interaction, similar to the well-known charge exchange processes in elementary molecules might induce non adiabatic
predissociation of the 22A1 state. This mechanism is invoked to explain the differences between R2PI and depletion spectra, correlated with the dissociation
or relaxation of the excited states.
Received 24 March 2000 and Received in final form 11 July 2000 相似文献
116.
N. Hori A. Furuya M. Tsuruta F. Misaizu K. Ohno 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):41-44
Photoinduced dissociation in the ultraviolet region has been investigated for Ag nF n-1
+ cluster ions. Photodissociation spectrum of
Ag2F+
in the energy of 3.8–5.6 eV exhibits several sharp bands corresponding to the transition to electronically excited states.
In this dissociation, only the Ag2
+ ion was observed as a fragment ion. Theoretical calculation indicates that the parent Ag2F+ ion has a linear Ag-F-Ag equilibrium geometries in the ground and excited states. Since conformational changes by excitation
of bending vibration are necessary for the fragmentation of an F atom, this indicates that production of Ag2
+ from Ag2F+ is a result of internal conversion and following conformational changes. 相似文献
117.
G. Leahu R. Li Voti C. Sibilia M. Bertolotti V. Golubev D. A. Kurdyukov 《Optical and Quantum Electronics》2007,39(4-6):305-310
In this paper the thermal and optical properties of the SiO2/GaN synthetic opals are studied by photothermal deflection technique. This technique, used in different configurations, allows
to determine the effective thermal diffusivity and the absorption spectra. 相似文献
118.
G. A. Miller 《The European Physical Journal A - Hadrons and Nuclei》2007,31(4):578-584
The discovery more than twenty years ago, by the EMC Collaboration, that the deep-inelastic-scattering DIS structure functions
are influenced by the nuclear environment stunned the nuclear physics community and brought quarks and gluons into the field
with great impact. A great length of time has passed, but despite a semi-infinite number of papers on the subject, there is
no explanation that is universally accepted. Many models (related in one way or another to QCD) have been successful in reproducing
data for deep inelastic scattering on nuclear targets, but fewer have described both the DIS and nuclear Drell-Yan experiments.
Although there are some positive indications, no model has been used to predict correctly and unambiguously new independent
phenomena. We review the history and discuss the best experimental prospects for future discovery. 相似文献
119.
Sulphur-headgroup organic molecules have been chemisorbed on Cu(1 0 0) as self-assembled monolayers (SAMs) in highly-ordered two-fold symmetry structures, and the electronic states induced at the interface have been measured by photoemission: a close similarity of the main interface states for methane-thiolate and mercaptobenzoxazole on Cu(1 0 0) in the same p(2 × 2)-phase is observed. The bonding states for methane-thiolate/Cu(1 0 0) in the p(2 × 2) and c(2 × 2) structures have been compared to ab-initio calculation of the total density of states (DOS) for the S/Cu(1 0 0) system in the same phases. The major role of the S-Cu bonding to determine the density of state evolution at the interface is brought to light. The observed differences in the two phases depend mainly on the charge distribution associated to the different molecular packing, with a minor role of the radical group. 相似文献
120.
An angle-dependent X-ray photoelectron spectroscopy (XPS) method used to measure the thickness of molecularly thin lubricants was developed. The method was built based on an island model of patched overlayer on a flat substrate by using the photoemission signal solely from the lubricant film. Typical molecularly thin Zdol films on the CHx overcoat of unused commercial magnetic disks were measured to verify the metrology. The lubricant thickness determined by the metrology was equal to the recent result by thermostatic high vacuum atomic force microscopy. The measured deduction in the thickness of the molecularly thin lubricant films, successively irradiated by the monochromatic source operated at 14 kV/250 W, was as low as 1 ? during the first irradiation hour. XPS spectra showed that no hydrocarbons, water or oxygen were adsorbed over the Zdol outer surfaces in the tested XPS conditions. The inelastic mean free path (IMFP) of C 1s in Zdol or in CHx was found to be independent of take off angle (TOA) when TOA < 40°. The IMFP of C 1s in Zdol was ∼63.5 ? and the lubricant island thickness was ∼35 ?. 相似文献