全文获取类型
收费全文 | 90550篇 |
免费 | 942篇 |
国内免费 | 579篇 |
专业分类
测绘学 | 2327篇 |
大气科学 | 6837篇 |
地球物理 | 16873篇 |
地质学 | 33785篇 |
海洋学 | 7223篇 |
天文学 | 19603篇 |
综合类 | 285篇 |
自然地理 | 5138篇 |
出版年
2020年 | 511篇 |
2019年 | 527篇 |
2018年 | 3896篇 |
2017年 | 3703篇 |
2016年 | 2962篇 |
2015年 | 1161篇 |
2014年 | 1703篇 |
2013年 | 3446篇 |
2012年 | 2694篇 |
2011年 | 4825篇 |
2010年 | 4465篇 |
2009年 | 5203篇 |
2008年 | 4385篇 |
2007年 | 4968篇 |
2006年 | 2478篇 |
2005年 | 2631篇 |
2004年 | 2457篇 |
2003年 | 2417篇 |
2002年 | 2128篇 |
2001年 | 1771篇 |
2000年 | 1665篇 |
1999年 | 1537篇 |
1998年 | 1499篇 |
1997年 | 1504篇 |
1996年 | 1201篇 |
1995年 | 1168篇 |
1994年 | 1101篇 |
1993年 | 992篇 |
1992年 | 961篇 |
1991年 | 907篇 |
1990年 | 1008篇 |
1989年 | 905篇 |
1988年 | 828篇 |
1987年 | 988篇 |
1986年 | 838篇 |
1985年 | 1103篇 |
1984年 | 1253篇 |
1983年 | 1202篇 |
1982年 | 1116篇 |
1981年 | 1070篇 |
1980年 | 982篇 |
1979年 | 929篇 |
1978年 | 936篇 |
1977年 | 843篇 |
1976年 | 810篇 |
1975年 | 747篇 |
1974年 | 796篇 |
1973年 | 780篇 |
1972年 | 492篇 |
1971年 | 461篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
A. Bhatnagar R. M. Jain J. T. Burkepile I. M. Chertok A. Magun H. Urbarz P. Zlobec 《Astrophysics and Space Science》1996,243(1):209-213
The powerful cosmic ray flare of Sept. 29, 1989 occurred behind the limb and was observed over a wide spectral range. The analysis of optical, radio, and other relevant data suggest two phases of energy release. After an impulsive phase a prolonged post eruption energy release occurred in an extended region of the corona following the eruption of a large coronal mass ejection (CME). This phase is responsible for numerous coronal and interplanetary phenomena including the ground-level increase of cosmic rays. 相似文献
52.
Theoretical studies have shown the possibility of high-temperature ('high enthalpy') geothermal reservoirs in the pre-Tertiary rocks at 4–5 km depth range within the Pannonian Basin. This expectation was proven by the hotwater/steam blowout of Fábiánsebestyén-4 borehole (16.12.85–31.1.86). Exploration efforts carried out during 1987–88 in the broad vicinity of the borehole proved that reservoirs of this type can be found with the combination of seismic reflection, silica-thermometry and magnetotelluric sounding methods. Deliberate prospection should be continued in all suitable areas within the basin, since high enthalpy reservoirs promise profitable operation of geothermal power stations. 相似文献
53.
R. G. Langebartel 《Astrophysics and Space Science》1985,115(1):39-41
The average radial and angular velocity components are obtained for a rotating two-dimensional self-gravitating system near an equilibrium state. First-order perturbation configurations of flaring straight bars emanating from the center provide examples of such systems. In these systems the average velocity field to first order is incompressible and irrotational. The second-order effects on the product of the average velocity components with the spatial density are essentially independent of the angular coordinate. 相似文献
54.
F. M. F. El-Sabaa 《Celestial Mechanics and Dynamical Astronomy》1985,37(1):71-79
The equation of motion of a rigid body in Kovaleveskaya case is reduced to a plane motion. By using the method of small parameters introduced by Poincaré, the existence of a periodic solution is established. 相似文献
55.
Alan M Bond Julie R Bradbury Henry A Hudson John S Garnham Peter J Hanna Stanley Strother 《Marine Chemistry》1985,16(1):1-9
Evidence was found that uptake of lead from seawater in both model and natural systems by the leaves of the seagrass Zostera muelleri does occur for live, dead and scraped leaves at all the lead concentrations tested. Positive uptake of lead was measured using the three analytical techniques of radio-tracer, differential pulse anodic stripping voltammetry and atomic absorption spectrometry; similar uptake profiles were obtained for each technique. Profiles always showed an initial rapid uptake phase followed by a gradual transition to a plateau phase at which an approximate equilibrium between lead attached to seagrass and free ionic lead in seawater was reached. The presence of active lead uptake processes was indicated in experiments which attempted to remove lead from leaves by a chelating agent. 相似文献
56.
An HF radar called the Coastal Ocean Dynamics Applications Radar (CODAR) is presently being used in several forms to measure ocean surface parameters. The original version was developed by the National Oceanic and Atmospheric Administration (NOAA) and utilizes a four-element receive array. The array consists of four equally spaced elements arranged on a circle with a radius of 0.2151 wavelengths (at 25.4 MHz). It was designed to measure ocean currents using a direction-finding technique based on an extension to a simple two-element interferometer. The problem of determining the bearing of a radiating source can be readily shown to be equivalent to that incurred in spectral estimation. In an attempt to improve upon the processing of existing data, modern nonlinear spectral estimation techniques are applied in a beam-forming bearing estimation procedure and compared against several direction-finding algorithms. Enhancement of bearing estimators via analysis of the eigenstructure of a spatial correlation matrix is included. Antenna response patterns are calculated and used to investigate properties of direction-finding algorithms. Simulated data are used for a comparison of direction finding and beam forming. The asymmetrical bias of each method is investigated to determine its effect on the error in estimating the angle of arrival of a radar target. 相似文献
57.
Measurements of salinity perturbations in a partially mixed estuary have been used to evaluate the usefulness of an inductive salinometer and to determine some of the characteristics of the salinity perturbations. The salinometer performed satisfactorily under most conditions. Although internal wave like effects were present, the turbulence fluctuations were dominant. The salinity fluctuations and the turbulent fluxes and were found to behave in a manner similar to the density fluctuations in a thermally stratified atmospheric boundary layer and a laboratory open channel flow. A quadrant analysis suggested that the contribution of each quadrant to the turbulent flux changed with Ri. The turbulence parameters ν and cγ were found to decrease and increase respectively as Ri increases. 相似文献
58.
Recently, exact spatially-homogeneous solutions have been found for a conformally invariant massless scalar fieldS(t) coupled to a Robertson-Walker geometry. We investigate extending these solutions to inhomogeneous scalar fieldsS(t, x
l
). For an isotropic scalar fieldS(t, r) we find a solution satisfying three of the five field equations. If we use REDUCE, we show that the remaining equations forceS=S(t). 相似文献
59.
J. CAMPSIE M. H. RASMUSSEN L. C. KOVACS F. DITTMER J. C. BAILEY N. O. HANSEN J. LAURSEN L. JOHNSON 《Polar research》1990,8(2):237-243
New aeromagnetic data, K-Ar age determinations of dredged marine igneous rocks, as well as other geophysical evidence have shed light on the chronology, nature and evolution of the northern Iceland Plateau. Correspondence between seismic refraction profiles taken on the Jan Mayen Ridge and westward through Jan Mayen Island, suppressed aeromagnetic anomalies, earthquake surface wave studies, and ages of dredged igneous rocks suggest these strata may form an extended region of thickened crust, possibly of Caledonian age, extending westward toward the Kolbeinsey Ridge and northwest to the south wall of the Jan Mayen Fracture Zone. 相似文献
60.