全文获取类型
收费全文 | 2854篇 |
免费 | 44篇 |
国内免费 | 10篇 |
专业分类
化学 | 1812篇 |
晶体学 | 23篇 |
力学 | 90篇 |
数学 | 357篇 |
物理学 | 626篇 |
出版年
2021年 | 26篇 |
2019年 | 20篇 |
2018年 | 18篇 |
2016年 | 33篇 |
2015年 | 29篇 |
2014年 | 38篇 |
2013年 | 119篇 |
2012年 | 104篇 |
2011年 | 131篇 |
2010年 | 52篇 |
2009年 | 59篇 |
2008年 | 116篇 |
2007年 | 138篇 |
2006年 | 120篇 |
2005年 | 109篇 |
2004年 | 113篇 |
2003年 | 113篇 |
2002年 | 120篇 |
2001年 | 91篇 |
2000年 | 70篇 |
1999年 | 38篇 |
1998年 | 36篇 |
1997年 | 41篇 |
1996年 | 43篇 |
1995年 | 56篇 |
1994年 | 46篇 |
1993年 | 47篇 |
1992年 | 42篇 |
1991年 | 52篇 |
1990年 | 48篇 |
1989年 | 24篇 |
1988年 | 31篇 |
1987年 | 26篇 |
1986年 | 24篇 |
1985年 | 38篇 |
1984年 | 50篇 |
1983年 | 31篇 |
1982年 | 37篇 |
1981年 | 43篇 |
1980年 | 37篇 |
1979年 | 33篇 |
1978年 | 43篇 |
1977年 | 43篇 |
1976年 | 35篇 |
1975年 | 30篇 |
1974年 | 26篇 |
1973年 | 48篇 |
1972年 | 27篇 |
1971年 | 24篇 |
1969年 | 16篇 |
排序方式: 共有2908条查询结果,搜索用时 15 毫秒
41.
Ammar R Ball S Baringer P Bean A Besson D Coppage D Copty N Davis R Hancock N Kelly M Kwak N Lam H Kubota Y Lattery M Nelson JK Patton S Perticone D Poling R Savinov V Schrenk S Wang R Alam MS Kim IJ Nemati B O'Neill JJ Severini H Sun CR Zoeller MM Crawford G Daubenmier CM Fulton R Fujino D Gan KK Honscheid K Kagan H Kass R Lee J Malchow R Morrow F Skovpen Y Sung M White C Butler F Fu X Kalbfleisch G Ross WR Skubic P Snow J Wang PL Wood M Brown DN Fast J McIlwain RL Miao T Miller DH Modesitt M 《Physical review D: Particles and fields》1994,49(11):5701-5704
42.
D. Wayne Cooke Melvin Leon Michael A. Paciotti Peter F. Meier Stephen F. J. Cox Edward A. Davis Thomas L. Estle Bassam Hitti Roger L. Lichti Carolus Boekema John Lam Anny Morrobel-Sosa Jean Oostens 《Hyperfine Interactions》1994,86(1):699-704
A distinctive longitudinal magnetic field dependence of the muon polarization for anomalous muonium in polycrystalline semiconductor targets has been predicted. The polarization exhibits a cusp,i.e., a discontinuous jump in the slope from negative to positive. Measurements of the longitudinal polarization for polycrystalline silicon in fields up to 0.5 T, and temperatures 53 and 200 K have been made at LAMPF. A cusp in the field dependence indeed occurs at 0.345 T, in excellent agreement with the prediction. No cusp is observed at 200 K because Mu* has been thermally ionized. 相似文献
43.
We introduce a new spectral sequence called the p-chain spectral sequence which converges to the (co-)homology of a contravariant C-space with coefficients in a covariant C-spectrum for a small category C. It is different from the corresponding Atiyah–Hirzebruch-type spectral sequence. It can be used in combination with the Isomorphism Conjectures of Baum and Connes and Farrell and Jones to compute algebraic K- and L-groups of group rings and topological K-groups of reduced group C*-algebras. 相似文献
44.
45.
M. R. Davis 《Experiments in fluids》1988,6(5):335-343
A specially adapted schlieren system is used to generate fluctuating signals which respond strongly to large scale coherent components of a turbulent mixing jet flow and which have a relatively reduced response to random disturbances. The schlieren signals also provide a direct indication of the presence of vortex-like structures in the turbulent mixing layers by virtue of the phase relationship of the schlieren signals to the pressure field. This system gives a clear resolution of the fluctuating periodic effects associated with vortex structures in the flow from a choked convergent nozzle. It has thus been possible to determine that vortex-like eddies are associated with the feedback screech mechanism, and also generate periodic disturbances due to their passage through the diamond shaped wave structure in the flow. The regular disturbances in the flow move at 0.77 of the fully expanded flow velocity. Phase spectral observations demonstrate clearly the vortex like structure of coherent disturbances in the flow by virtue of the quadrature phase relation between the schlieren and microphone signals. Movement of the sensing microphone in the pressure field external to the flow shows disturbance propagation at the acoustic velocity, and also shows that disturbances at Strouhal numbers above 0.7 emanating from the inner mixing zone can be identified by an additional time delay to reach the microphone and only influence the microphone when it is located downstream of the flow sensing schlieren system due to confinement of pressure disturbances within Mach cones of the flow. 相似文献
46.
We consider the diffraction of a time-harmonic acoustic plane wave by a rigid half-plane in a viscous fluid medium. The linearized equations of viscous fluid flow and the no-slip condition on the half-plane are used to derive a pair of disjoint Wiener-Hopf equations for the fluid stresses and velocities. The Wiener-Hopf equations are solved in conjunction with a requirement that the stresses are integrable near the edge of the half-plane. Specific wave components of the scattered velocity field are given analytically. A Padé approximation to the Wiener-Hopf kernel function is used to derive numerical results that show the effect of viscosity on the velocity field in the immediate vicinity of the edge of the half-plane. 相似文献
47.
G. M. Luke L. P. Le B. J. Sternlieb Y. J. Uemura J. H. Brewer R. Kadono R. F. Kiefl S. R. Kreitzman T. M. Riseman C. E. Stronach M. Davis S. Uchida H. Takagi Y. Tokura Y. Hidaka T. Murakami E. A. Early J. T. Markert M. B. Maple C. L. Seaman 《Hyperfine Interactions》1991,63(1-4):311-317
We report muon spin relaxation/rotation measurements on sintered powder samples of Nd2−x
Ce
x
CuO4−y
and a large single crystal of Nd2CuO4−y
. We find an electronic phase diagram which is quite similar to that of hole-doped superconductors such as La2−x
Sr
x
CuO4−y
, although the doping of electrons into the system is less efficient in destroying the static moments on the copper spins.
Static magnetic order in Nd2CuO4−y
appears below about 250 K, and two spin reorientations are seen atT=75 K andT=35 K. Measurements of the magnetic field penetration depth have been unsuccessful due to the rare-earth paramagnetism of
these materials. 相似文献
48.
W.K. McGregor J.D. Few D.R. Keefer H.S. Lowry M.G. Davis 《Journal of Quantitative Spectroscopy & Radiative Transfer》1980,23(5):527-530
Errors in Ref. 1 are corrected. Using the new data, the collisional broadening coefficient of NO γ-band lines by N2 is 2390 (±220) atm-1-K (old value = 1270±200) and the optical collision diameter is 13.3±0.6 Å (instead of 3.5±0.3 Å). Values for argon (2150±200 atm-1-K) and CO2 (2040±200 atm-1-K) yield the optical collision diameters of 13.2 and 13.1 Å, respectively. 相似文献
49.
Silvin P. Knight Louise Newman John D. OConnor James Davis Rose Anne Kenny Roman Romero-Ortuno 《Entropy (Basel, Switzerland)》2021,23(1)
In this cross-sectional study, the relationship between noninvasively measured neurocardiovascular signal entropy and physical frailty was explored in a sample of community-dwelling older adults from The Irish Longitudinal Study on Ageing (TILDA). The hypothesis under investigation was that dysfunction in the neurovascular and cardiovascular systems, as quantified by short-length signal complexity during a lying-to-stand test (active stand), could provide a marker for frailty. Frailty status (i.e., “non-frail”, “pre-frail”, and “frail”) was based on Fried’s criteria (i.e., exhaustion, unexplained weight loss, weakness, slowness, and low physical activity). Approximate entropy (ApEn) and sample entropy (SampEn) were calculated during resting (lying down), active standing, and recovery phases. There was continuously measured blood pressure/heart rate data from 2645 individuals (53.0% female) and frontal lobe tissue oxygenation data from 2225 participants (52.3% female); both samples had a mean (SD) age of 64.3 (7.7) years. Results revealed statistically significant associations between neurocardiovascular signal entropy and frailty status. Entropy differences between non-frail and pre-frail/frail were greater during resting state compared with standing and recovery phases. Compared with ApEn, SampEn seemed to have better discriminating power between non-frail and pre-frail/frail individuals. The quantification of entropy in short length neurocardiovascular signals could provide a clinically useful marker of the multiple physiological dysregulations that underlie physical frailty. 相似文献
50.