全文获取类型
收费全文 | 2416篇 |
免费 | 429篇 |
国内免费 | 741篇 |
专业分类
测绘学 | 89篇 |
大气科学 | 857篇 |
地球物理 | 568篇 |
地质学 | 1222篇 |
海洋学 | 495篇 |
天文学 | 110篇 |
综合类 | 121篇 |
自然地理 | 124篇 |
出版年
2024年 | 12篇 |
2023年 | 33篇 |
2022年 | 66篇 |
2021年 | 96篇 |
2020年 | 96篇 |
2019年 | 118篇 |
2018年 | 84篇 |
2017年 | 113篇 |
2016年 | 82篇 |
2015年 | 120篇 |
2014年 | 120篇 |
2013年 | 172篇 |
2012年 | 124篇 |
2011年 | 144篇 |
2010年 | 111篇 |
2009年 | 163篇 |
2008年 | 163篇 |
2007年 | 156篇 |
2006年 | 137篇 |
2005年 | 144篇 |
2004年 | 120篇 |
2003年 | 105篇 |
2002年 | 101篇 |
2001年 | 123篇 |
2000年 | 109篇 |
1999年 | 105篇 |
1998年 | 120篇 |
1997年 | 95篇 |
1996年 | 74篇 |
1995年 | 54篇 |
1994年 | 67篇 |
1993年 | 60篇 |
1992年 | 29篇 |
1991年 | 30篇 |
1990年 | 23篇 |
1989年 | 18篇 |
1988年 | 16篇 |
1987年 | 7篇 |
1986年 | 5篇 |
1985年 | 9篇 |
1984年 | 10篇 |
1983年 | 6篇 |
1982年 | 12篇 |
1981年 | 8篇 |
1980年 | 11篇 |
1979年 | 2篇 |
1978年 | 8篇 |
1977年 | 5篇 |
排序方式: 共有3586条查询结果,搜索用时 296 毫秒
191.
192.
北极海冰面积变化与大气遥相关型 总被引:4,自引:0,他引:4
本文综述了北极海注面积变化与大气遥相关型研究工作中的一些主要结果。诊断分析表明,北极海冰面积变化具有3-4年的振荡周期,大气中的遥相关型不仅与海冰面积变化的区域有关,还与海冰面积的振荡频率有关。海冰面积变化与大气遥相关型是互相维持的,一方的加强有利于另一方的加强,本文最后还对北极海冰和赤道中,东太平洋海温对北半年冬半年中纬度大气环流影响的相似性等问题进行了讨论。 相似文献
193.
Rocket-borne ultraviolet photometers operating at =0.31 m have been used at Thumba (8°33N, 76°52E) to make measurements of atmospheric scattering at tropospheric and lower stratospheric altitudes. Measurements could be made of the amplitude of the scattered fluxes and the angular distribution up to an altitude of about 24 km on three rocket flights conducted as part of the 16 February 1980 solar eclipse campaign. These measurements have been used to study the size distribution as well as the number densities of aerosols in the troposphere and lower stratosphere over Thumba. 相似文献
194.
E. O. Oladiran 《Pure and Applied Geophysics》1982,120(4):673-681
Streamers were injected into a large population of small droplets, of radii about 20 m, confined to a given region of pre-determined shape on a photographic film, and situated in a gap between which a variable electric field can be applied. Results showed that the droplet region behaves like a dipole discharging from both ends if its inclination to the electric field is less than 45° and the field is not less than –230 kV/m at atmospheric pressure.We deduced that streamer intensification will occur at relatively low fields if there exists pockets of large number density of small droplets. 相似文献
195.
John D. Zambakas 《Pure and Applied Geophysics》1982,120(4):691-697
A recently developed data presentation technique, the rectangular wind frequency isopleth diagram, has been applied to examine the effect of wind speed and direction, acting simultaneously, on ambient air negative ion densities. The large negative ion concentration decreases in the majority of directions and wind speed intervals, while that of the small ions increases, as the wind speed increases. The local maxima and minima, occurring in some sectors, are properly discussed. 相似文献
196.
Further Studies Of Atmospheric Turbulence In Layers Near The Surface: Scaling The Tke Budget Above The Roughness Sublayer 总被引:2,自引:0,他引:2
The second of two experimental studies of the TKE budget conducted on sites of different roughness is described, and results are compared. The first took place within a shallow layer above a small field of mostly bare, cultivated soil; the second was carried out above a roughness sublayer of significant depth on an extensive plain of tall dry grass. Budget terms observed in the second study were scaled with a modified u which compensated for effects of an unusually large stress gradient and ensured that the m functions would be collinear. By showing that the modification becomes negligible in smaller gradients, it is demonstrated that in normal conditions, budgets observed above significant roughness sublayers should be normalized by scaling in terms of the unreduced Reynolds stress at the sublayer's upper surface. This procedure is shown to be consistent with the expectation that TKE budgets in layers near the surface all scale in fundamentally the same way.Other findings include: (1) the fact that most m functions previously reported are not quite collinear is attributed to a type of overspeeding known to affect three-cup anemometers; (2) revised m functions, collinear and largely free of the effects of overspeeding, are determined from a well-established characteristic of the linear m relation for the stable case; (3) data that define collinear m functions can also be represented with single hyperbolic curves; (4) dissipation is found to be 10 to 15% too small to balance total TKE production in unstable and neutral conditions and to decrease with increasing z/L in thestable regime; and (5) new relations for based on the observed behaviour of the dissipation deficit provide an improved closure for the set of equations that express the budget terms as functions of m and z/L. 相似文献
197.
A fingernail clam (Sphaerium simile, Sphaeriidae) from Science Lake, a small watershed located in Allegany State Park, New York, USA and a zebra mussel (Dreissena polymorpha, Dreissenidae) from Keuka Lake, New York, the third largest Finger Lake of central New York, were selected to evaluate the applicability of using 18O(CaCO3) and 13O(CaCO3) values for sub-weekly climate records. Seasonal variation in 18O(CaCO3) values was compared with predicted equilibrium values to test the hypothesis that lacustrine molluscs produce shell aragonite according to environmental variables. For the purpose of comparison, aragonite temperature-fractionation equations determined by Grossman& Ku (1986) and Patterson et al. (1993) were used. Sphaerium simile appears to produce 18O(CaCO3) values predicted by Patterson et al. (1993), while Dreissena polymorpha produces 18O(CaCO3) values in agreement with Grossman & Ku (1986). We attribute the difference to family-specific temperature-fractionation relationships. Because both types of mollusc record climate variables with a high degree of integrity, they should each serve as excellent paleoclimate proxies.The fingernail clam collected from a small watershed exhibits higher variation about the seasonal pattern than did the zebra mussel collected from a large watershed. This is attributed to the increased sensitivity of the small watershed to storm perturbation. Analysis of fossil molluscs from such watersheds might be useful in discerning paleo-storminess. 相似文献
198.
地幔氧逸度的研究进展 总被引:13,自引:0,他引:13
通过对目前国际上诸多有关地幔氧逸度的研究结果的系统分析和总结 ,提出了地幔中自由氧对地幔物质的性质、状态及运动过程产生影响的基本作用方式 ;介绍了目前地幔氧逸度研究的主要研究手段 ,包括本征氧逸度的实验室测量、模拟氧逸度的实验室测量、地幔氧逸度计及理论计算等及其优缺点 ;定性探讨了地幔氧逸度的时空分布规律 ,获得了地幔随时间的推移变得愈来愈氧化 ,随深度的增加变得愈来愈还原 ,以及在横向上不同大地构造部位的地幔区域具有不同的氧逸度等诸多结论。结合目前人们对地幔物质组成、性质、状态、运动过程及地球的起源与演化历史等的认识 ,初步提出了地幔不同圈层氧逸度的约束机制。最后 ,针对目前地幔氧逸度的研究现状 ,为今后提出了一些参考性的研究方向。 相似文献
199.
青藏高原北缘哈拉湖近800年来 湖泊沉积及其环境意义* 总被引:5,自引:5,他引:5
文章以青藏高原北缘高山祁连山湖泊——哈拉湖作为研究对象,利用放射性核素210 Pb和137 Cs测年资料,通过对此高海拔湖泊沉积碳酸盐氧碳同位素、碳酸盐含量、总有机碳含量、磁化率等环境代用指标的分析,揭示了这一地区近800年来的气候环境变化过程。分析表明哈拉湖记录的气候环境变化经历了3个阶段:1206~1700A.D.环境较为寒冷、湿润,并有持续变湿的趋势;1700~1920A.D.环境由冷湿的状况趋向温暖干旱,1771年之后,环境保持相对稳定;1920~2002A.D.是自1206年以来最为温暖干旱的阶段。 相似文献
200.
C. Panneerselvam C. Selvaraj K. Jeeva K. U. Nair C. P. Anilkumar S. Gurubaran 《Journal of Earth System Science》2007,116(3):179-186
Surface measurements of the atmospheric electrical parameters like Maxwell current, electric field and conductivity studied
at the Indian station, Maitri (70.75° S, 11.75° E, 117 m above mean sea level), Antarctica, during austral summer have been
analyzed for the years 2001 to 2004. A total of 69 days were selected which satisfied the ‘fairweather’ conditions, i.e.,
days with absence of high winds, drifting or falling snow, clouds, and fog effects. The diurnal variation curve of electric
field and vertical current averaged for 69 fairweather days is a single periodic with a minimum at 03:00 UT and a maximum
near 19:00 UT, which is very similar to the Carnegie curve. The correlation coefficient between these measured parameters
has a high value (more than 0.9) for all the days. During fairweather days the measured current and field variations are similar
and hence it is clear that the conductivity is more or less stable. During magnetically disturbed days, the dawn-dusk potential
drop has clear influences on the diurnal variation and it modifies the conductivity. Apart from the day-to-day variation in
low latitude thunderstorm activity, there are diurnal, seasonal, inter-annual variations in the electric potential and the
currents, as well as solar influences on the measured parameters. This study will help us to examine the impact of solar and
geophysical phenomena like solar flares, geomagnetic storms and substorms on the global electric circuit. 相似文献