全文获取类型
收费全文 | 256127篇 |
免费 | 2726篇 |
国内免费 | 997篇 |
专业分类
化学 | 139209篇 |
晶体学 | 3780篇 |
力学 | 10327篇 |
综合类 | 2篇 |
数学 | 29359篇 |
物理学 | 77173篇 |
出版年
2020年 | 1938篇 |
2019年 | 2198篇 |
2018年 | 2631篇 |
2017年 | 2526篇 |
2016年 | 4094篇 |
2015年 | 2798篇 |
2014年 | 4156篇 |
2013年 | 11804篇 |
2012年 | 8672篇 |
2011年 | 10808篇 |
2010年 | 6956篇 |
2009年 | 6822篇 |
2008年 | 9626篇 |
2007年 | 9832篇 |
2006年 | 9085篇 |
2005年 | 8489篇 |
2004年 | 7621篇 |
2003年 | 6783篇 |
2002年 | 6680篇 |
2001年 | 7381篇 |
2000年 | 5528篇 |
1999年 | 4355篇 |
1998年 | 3703篇 |
1997年 | 3745篇 |
1996年 | 3493篇 |
1995年 | 3280篇 |
1994年 | 3101篇 |
1993年 | 3125篇 |
1992年 | 3428篇 |
1991年 | 3460篇 |
1990年 | 3256篇 |
1989年 | 3202篇 |
1988年 | 3280篇 |
1987年 | 3143篇 |
1986年 | 3024篇 |
1985年 | 4163篇 |
1984年 | 4343篇 |
1983年 | 3536篇 |
1982年 | 3943篇 |
1981年 | 3810篇 |
1980年 | 3701篇 |
1979年 | 3731篇 |
1978年 | 3941篇 |
1977年 | 3762篇 |
1976年 | 3963篇 |
1975年 | 3521篇 |
1974年 | 3653篇 |
1973年 | 3956篇 |
1972年 | 2394篇 |
1971年 | 1834篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
881.
882.
Michael Andrec James H. Prestegard 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,130(2):217-232
The Bayesian perspective on statistics asserts that it makes sense to speak of a probability of an unknown parameter having a particular value. Given a model for an observed, noise-corrupted signal, we may use Bayesian methods to estimate not only the most probable value for each parameter but also their distributions. We present an implementation of the Bayesian parameter estimation formalism developed by G. L. Bretthorst (1990,J. Magn. Reson.88, 533) using the Metropolis Monte Carlo sampling algorithm to perform the parameter and error estimation. This allows us to make very few assumptions about the shape of the posterior distribution, and allows the easy introduction of prior knowledge about constraints among the model parameters. We present evidence that the error estimates obtained in this manner are realistic, and that the Monte Carlo approach can be used to accurately estimate coupling constants from antiphase doublets in synthetic and experimental data. 相似文献
883.
The magnetic phase diagrams of a two-sublattice ferrimagnet with a magnetically unstable subsystem are calculated taking account
of the susceptibility. Analytic expressions are obtained for the phase-transition fields and critical values of the parameters
of the ferrimagnet. The evolution of the magnetic phase diagrams as the susceptibility of the unstable sublattice increases
is analyzed. 相似文献
884.
K.J. Liu M. Miyake P.E. James H.M. Swartz 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,133(2):291-298
Carbon based paramagnetic materials are frequently used for EPR oximetry, especiallyin vivo,but the EPR spectra of these materials often have more than one paramagnetic center and/or relatively low signal intensity. To determine whether the multi-components of carbon based materials could be separated and enriched in the active component, we used density gradient centrifugation to separate the materials into several fractions. We studied two types of coals, gloxy and Pocahontas, and found these materials to have large density distribution. The separated density fractions had very different EPR spectra and intensities. The active component from the coal material had a more homogeneous EPR signal and significantly increased EPR signal intensity, whereas for India ink, only slight changes were observed. This result can be very useful in the development of better probes for EPR oximetry. 相似文献
885.
T.R. Saitoh N. Hashimoto G. Sletten R.A. Bark S. Törmänen M. Bergström K. Furuno K. Furutaka G.B. Hagemann T. Hayakawa T. Komatsubara A. Maj S. Mitarai M. Oshima J. Sampson T. Shizuma P.G. Varmette 《The European Physical Journal A - Hadrons and Nuclei》1998,3(3):197-199
High-spin states in 181Ta have been studied via the 176Yb(11B,α2n) reaction at 52 MeV using the PEX array and at 57 MeV using the NORDBALL array, with α-particle detection. The previously
known, Kπ=(7/2)+ ground state band and Kπ=(9/2)− band have been extended to spins (29/2)+ and (31/2)−, respectively. Two new one-quasiparticle bands, the Kπ=(5/2)+ band built on the known (5/2)+ isomer and a Kπ=((1/2)−) band have been observed. Two other rotational bands with three-quasiparticle structure, Kπ=(15/2)− and ((19/2)+ with π(7/2)[404]ν2(1/2)[510](9/2)[624] and π(9/2)[514]ν2(1/2)[510](9/2)[624] configurations, respectively, have been newly observed. The half-life of the Kπ=((19/2)+) bandhead which decays to the head of the (15/2)− band has been measured to be 140(36) ns. However, transitions from the ((19/2)+) state to the (15/2)− band have not been observed.
Received: 26 August 1998 相似文献
886.
R. Cressely V. Hartmann 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(1):57-62
In this experimental work we carefully investigate the rheological behaviour and in particular the shear thickening exhibited
by aqueous micellar solutions of CTAB with NaSal as added counterion. We are particularly interested in the evolution of the
critical shear rate (at which shear thickening occurs) versus
C
D
, the surfactant concentration. We show that , at fixed salt concentration C
S
, increases with C
D
following a power law evolution with a positive exponent of + 5.8. On the other hand we show that if the ratio C
D
/ C
S
is fixed, decreases with C
D
with a negative exponent of -2.0. Nevertheless investigations of the zero shear viscosity indicate that in all situations (implying variation of the surfactant concentration C
D
, or the salt concentration C
S
or the temperature) is a decreasing function of the length of the micelles. All these evolutions are compatible with a gelation mechanism which
could possibly be associated with entanglement effects of large interacting flowing structures.
Received: 3 March 1998 / Revised: 16 June 1998 / Accepted: 3 July 1998 相似文献
887.
The optical absorption of GaAs crystals with thicknesses d=0.4−4.4 μm is measured in the exciton-polariton resonance region at a temperature of 1.7 K. As the thickness is reduced,
both a broadening of the exciton line and increased absorption with a negligible Stark shift are observed. The way the absorption
spectra vary with crystal thickness is examined in terms of a competition between two regions for light-exciton interactions
in the crystal: in the field of surface charges and electric-field free.
Fiz. Tverd. Tela (St. Petersburg) 40, 869–871 (May 1998) 相似文献
888.
S.F. Lienin R. Brüschweiler R.R. Ernst 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,131(2):184-190
The viscosity-dependent retarding effect of a polymeric solvent on the rotation of small solute molecules is investigated by13C NMR relaxation measurements. It is found that the relaxation data of 1,3-dibromoadamantane in highly viscous polymeric chlorotrifluoroethene can be explained neither by isotropic nor by realistic anisotropic tumbling in a single environment. The experimental data are rationalized in terms of fast exchange between at least two environments with correlation times differing by up to two orders of magnitude. The study shows that a uniform retardation of molecular tumbling by a polymeric solvent, desirable for shifting the NMR observation window in studies of intramolecular mobility, is not always feasible. 相似文献
889.
The motion of a relaxing system can be revealed by its optical properties. the computed emission spectrum of an excited solid-state impurity in a crystal, which relaxes towards the equilibrium position, exhibits a series of peaks revealing the stops at the classical turning points. Detection limits are discussed. 相似文献
890.
A review of otoacoustic emissions 总被引:32,自引:0,他引:32
R Probst B L Lonsbury-Martin G K Martin 《The Journal of the Acoustical Society of America》1991,89(5):2027-2067
Otoacoustic emissions measured in the external ear canal describe responses that the cochlea generates in the form of acoustic energy. For the convenience of discussing their principal features, emitted responses can be classified into several categories according to the type of stimulation used to evoke them. On this basis, four distinct but interrelated classes can be distinguished including spontaneous, transiently evoked, stimulus-frequency, and distortion-product otoacoustic emissions. The present review details the findings that have been described for each emission type according to this classification schema. Additionally, the known features of emitted responses are discussed for both normally hearing and hearing-impaired humans and experimental animals, and with respect to their potential clinical applications. The findings reviewed here clearly indicate that future studies of otoacoustic emissions will significantly increase our understanding of the basic mechanisms of cochlear function while, at the same time, provide a new and important clinical tool. 相似文献