全文获取类型
收费全文 | 207188篇 |
免费 | 2163篇 |
国内免费 | 1022篇 |
专业分类
化学 | 104254篇 |
晶体学 | 2749篇 |
力学 | 9590篇 |
综合类 | 19篇 |
数学 | 28512篇 |
物理学 | 65249篇 |
出版年
2021年 | 1068篇 |
2020年 | 1170篇 |
2019年 | 1171篇 |
2018年 | 3141篇 |
2017年 | 3408篇 |
2016年 | 3339篇 |
2015年 | 2666篇 |
2014年 | 3083篇 |
2013年 | 8528篇 |
2012年 | 9723篇 |
2011年 | 10466篇 |
2010年 | 6661篇 |
2009年 | 6640篇 |
2008年 | 7988篇 |
2007年 | 7965篇 |
2006年 | 7692篇 |
2005年 | 12413篇 |
2004年 | 11312篇 |
2003年 | 8191篇 |
2002年 | 5488篇 |
2001年 | 6266篇 |
2000年 | 4662篇 |
1999年 | 3640篇 |
1998年 | 2743篇 |
1997年 | 2693篇 |
1996年 | 2621篇 |
1995年 | 2318篇 |
1994年 | 2212篇 |
1993年 | 2064篇 |
1992年 | 2501篇 |
1991年 | 2453篇 |
1990年 | 2140篇 |
1989年 | 2096篇 |
1988年 | 2109篇 |
1987年 | 2017篇 |
1986年 | 1911篇 |
1985年 | 2811篇 |
1984年 | 2788篇 |
1983年 | 2234篇 |
1982年 | 2415篇 |
1981年 | 2301篇 |
1980年 | 2245篇 |
1979年 | 2211篇 |
1978年 | 2276篇 |
1977年 | 2228篇 |
1976年 | 2214篇 |
1975年 | 2155篇 |
1974年 | 2065篇 |
1973年 | 2154篇 |
1972年 | 1238篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
881.
882.
We have determined the temperature from SRS spectra of N2-N2, N2-CO2, O2-O2, and CO2-CO2 recorded in wide pressure and temperature ranges. The fitting procedure takes simultaneously into account the Dicke effect and motional narrowing. We have quantified the accuracy of the MEG and ECS-P models for rotational relaxation. The temperature extracted from each model is compared with thermocouple measurements. The influence of vibrational broadening and shifting is discussed in detail. 相似文献
883.
We study the propagation of phase space singularities for the time dependent Schrödinger equation with potential having Coulomb-type singularities in space dimension equal tothree. We prove that the singularities (frequency set) of the solution are reflected by a Coulomb center exactly as in the classical problem, i.e. the frequency set follows theregularized trajectories of Classical Mechanics after a collision. 相似文献
884.
885.
超重元素(新核素)合成研究进展情况分析和展望 总被引:2,自引:0,他引:2
本文在介绍和分析国际、国内在超重元素(新核素)合成实验研究与理论研究进展情况的基础上对我国今后如何从理论与实验的结合上开展超重元素(核)合成研究工作提出一些看法和建议,提供讨论。 相似文献
886.
H.G.C. Human N.P. Ferreira C.J. Rademeyer P.K. Faure 《Spectrochimica Acta Part B: Atomic Spectroscopy》1982,37(7):593-602
A method and computer program were developed for calculating the temperature of any part of a graphite furnace tube at any instant of time after onset of the heating cycle. Results for tubes of the Massman design show large differences in spatial temperature distributions during and at the end of the heating cycle when equilibrium is reached. When constant current is applied to contoured tubes, greater heating rates at the tube centres are obtained than with standard tubes. 相似文献
887.
Unconventional antiferromagnetic correlations of the doped Haldane gapsystem Y 2 BaNi 1 - x Zn x O 5
V. Villar R. Mélin C. Paulsen J. Souletie E. Janod C. Payen 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(1):39-51
We make a new proposal to describe the very low temperature susceptibility of the doped Haldane gap compound Y2BaNi1-xZnxO5. We propose a new mean field model relevant for this compound. The ground state of this mean field model is unconventional
because antiferromagnetism coexists with random dimers. We present new susceptibility experiments at very low temperature.
We obtain a Curie-Weiss susceptibility χ(
T
) ∼
C
/(Θ +
T
) as expected for antiferromagnetic correlations but we do not obtain a direct signature of antiferromagnetic long range order.
We explain how to obtain the “impurity” susceptibility
(
T
) by subtracting the Haldane gap contribution to the total susceptibility. In the temperature range [1 K, 300 K] the experimental
data are well fitted by T
(
T
) =
C
imp
1 +
T
imp
/
T
. In the temperature range [100 mK, 1 K] the experimental data are well fitted by T
(
T
) =
A
ln(
T
/
T
c
), where T
c
increases with x. This fit suggests the existence of a finite Néel temperature which is however too small to be probed directly in our experiments.
We also obtain a maximum in the temperature dependence of the ac-susceptibility
(
T
) which suggests the existence of antiferromagnetic correlations at very low temperature.
Received 17 July 2001 相似文献
888.
H.O.U. Fynbo Y. Prezado J. Äystö U.C. Bergmann M.J.G. Borge P. Dendooven W. Huang J. Huikari H. Jeppesen P. Jones B. Jonson M. Meister G. Nyman M. Oinonen K. Riisager O. Tengblad I.S. Vogelius Y. Wang L. Weissman K.W. Rolander 《The European Physical Journal A - Hadrons and Nuclei》2002,15(1-2):135-138
889.
Keith Warren Julien C. Sprott Raymond C. Hawkins 《Nonlinear dynamics, psychology, and life sciences》2002,6(1):55-70
In recent years there has been considerable interest in the construction of nonlinear models of the dynamics of human behavior. In this exploratory article we argue that attempts at controlling problematic thoughts, emotions, or behaviors can lead to nonlinearity in mental/behavioral dynamics. We illustrate our model by fitting threshold autoregression models to self-recorded time series of the daily highs in intensity of anxiety and obsessive ruminations, kept by an individual in therapy for this problem. In our discussion, we raise the possibility that bifurcations that occur in this nonlinear model may offer insight into mental control paradoxes. 相似文献
890.
The general features of two series of sol-gel derived materials, designatedurethanesils (Ut), have been investigated by infrared and Raman spectroscopies with the goal of elucidating the chemical environment of
the Eu3+ cations.
The host frameworks of the two families of ormolytes studied have been represented by m-Ut(350) and d-Ut(300), where m stands
for mono, d stands for di, 350 and 300 are the average molecular weights of the organic precursors (poly(ethylene glycol)
methyl ether, PEGME, and poly(ethylene glycol), PEG, respectively).
The hybrid matrix of the mono-xerogels is composed by a siliceous backbone bonded by means of urethane linkages (-NHC (=O)O-)
to pendant methyl end capped oligopolymer chains with approximately 7 oxyethylene units, whereas that of the di-xerogels is
based on a siliceous network grafted through urethane groups to both ends of poly(oxyethylene) segments containing about 6
(OCH2CH2) repeat units.
Both classes of materials have been doped with europium triflate (Eu(CF3SO3)3). The doped samples have been identified by m-Ut(350)nEu(CF3SO3)3 and d-Ut(300)nEu(CF3SO3), where n is the molar ratio of (OCH2CH2) repeat units per Eu3+ ion. Materials with n ranging from ∞ to 5 have been analyzed. The spectral data obtained provide evidence that the cations
begin to coordinate to the ether oxygen atoms of the oligopolymer chains at n=40 in the mono-urethanesils and at n=10 in the
di-urethanesils. In mono-urethanesils samples with n>40 and in di-urethanesils materials with n>10, the Eu3+ coordinate exclusively to the carbonyl oxygen atoms of the urethane linkages.
Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16–22, 2001. 相似文献