全文获取类型
收费全文 | 1600篇 |
免费 | 285篇 |
国内免费 | 229篇 |
专业分类
测绘学 | 98篇 |
大气科学 | 563篇 |
地球物理 | 589篇 |
地质学 | 343篇 |
海洋学 | 168篇 |
天文学 | 214篇 |
综合类 | 26篇 |
自然地理 | 113篇 |
出版年
2024年 | 4篇 |
2023年 | 8篇 |
2022年 | 25篇 |
2021年 | 39篇 |
2020年 | 24篇 |
2019年 | 41篇 |
2018年 | 32篇 |
2017年 | 45篇 |
2016年 | 54篇 |
2015年 | 57篇 |
2014年 | 74篇 |
2013年 | 87篇 |
2012年 | 65篇 |
2011年 | 153篇 |
2010年 | 142篇 |
2009年 | 146篇 |
2008年 | 147篇 |
2007年 | 99篇 |
2006年 | 107篇 |
2005年 | 81篇 |
2004年 | 86篇 |
2003年 | 60篇 |
2002年 | 76篇 |
2001年 | 65篇 |
2000年 | 56篇 |
1999年 | 52篇 |
1998年 | 42篇 |
1997年 | 39篇 |
1996年 | 35篇 |
1995年 | 20篇 |
1994年 | 29篇 |
1993年 | 24篇 |
1992年 | 21篇 |
1991年 | 14篇 |
1990年 | 18篇 |
1989年 | 14篇 |
1988年 | 10篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1954年 | 1篇 |
排序方式: 共有2114条查询结果,搜索用时 15 毫秒
91.
The surface parameters are being evaluated using a methodology which considers the vertical temperature structure of MONTBLEX
’90. For this 30 metre micrometeorological tower data are utilised. In this process, a concept of isolated layers has been
introduced. The parameters have been evaluated following two successive iterative processes to give a consistent value both
in the flux-profile relation and the related similarity relation.
The heat flux obtained using the present methodology, is then utilised to examine its interplay with the synoptic as well
as mesoscale features. The existence of such an interplay is observed. 相似文献
92.
青藏高原地区云对地面有效辐射的影响:Ⅱ.强迫作用 总被引:2,自引:0,他引:2
本文利用1982年8月-1983年7月青藏高原地面热源观测试验资料,讨论了与云对地面有效辐射强迫作用有关的参数的计算问题,并对这些参数的计算结果进行了分析。结果表明:晴空、全云条件下的地面有效辐射和云对地面有效辐射强迫作用的年平均日变化振幅有明显的地域差异;云对地面有效辐射的强迫作用春夏大,秋冬小,甘孜、拉萨、那曲和改则4站平均的年平均值为-27.2W/m^2。? 相似文献
93.
文章讨论了利用ISCCP卫星观测资料确定青藏高原地区地表反射率的方法,在无积雪地区和季节,地表反射率可以ISCCP可见光反射率为基础,在模式计算过程中,假定紫外反射率以及红外与可见光反射率的比值分别为常数。敏感性试验表明,由这两个假设所产生的误差并不显著。在有积雪地区或季节,地表平均反射率可直接由ISCCP可见光反射率表示。试验结果与地面实际观测作了比较,除沙漠区外,两者比较一致。文中还计算了高原晴天行星反射率。经与ERBE卫星观测比较,发现从5月至9月高原周围沙漠区气溶胶对辐射平衡有较显著的影响。而在其 相似文献
94.
M. A. Khan 《洁净——土壤、空气、水》1994,22(1):28-31
Libya occupies a large part of the Sahara Desert, and is a predominantly arid country with extremely scarce freshwaters. Despite aridity, a distinct higher rainfall zone exists along its mediterranean coastal belt. A lotic environment (perennial stream) in Ain-Scersciara, Tarhunãh in northwest Libya was studied for the species composition of diatom communities and their ecological characteristics. The waters are generally alkaline (pH = 7.5) and of hard-water (conductivity = 2008 μS/cm) type. The epiphytic diatom growth on benthic filamentous algae was high (32 taxa) with Amphora veneta as a very common taxon. Gomphonema parvulum var. micropus was an important taxon found in scrapings from the leaves of macrophytes and stony substratum. Nitzschia and Navicula showed high species richness (9 taxa in each) followed by Gomphonema (6 taxa). The ecological attributes of the majority of taxa show an oligohalobe status and alkaliphilous indicator. 相似文献
95.
Surface sealing as influenced by slope angle and position of simulated stones in the top layer of loose sediments 总被引:1,自引:0,他引:1
Jean Poesen 《地球表面变化过程与地形》1986,11(1):1-10
The influence of five different slope angles and two different positions of simulated stones in the top layer of a sandy and a silty sediment on surface sealing intensity is examined in the laboratory. Sealing intensity is assessed by studying changes of percolation rate through a sediment layer with simulated rainfall duration and by measuring cohesion of the 5 mm thick upper sediment layer, a measure of seal strength, by means of a torvane. Slope has a negative influence on sealing intensity. For a constant per cent of simulated stone cover, sealing intensity is lowest in the case of stones placed on the sediment surface compared to the case of stones pushed into the surface layer. Explanations for these findings are given and some implications are further discussed. 相似文献
96.
青藏高原积雪的分布特征及其对地面反照率的影响 总被引:7,自引:3,他引:7
通过对1983年7月至1990年6月青藏高原主体58个格点积雪资料进行EOF分析发现,青藏高原主体积雪分布以西部兴都库什山脉。天山山脉以及南部喜马拉雅山脉为主;高原中部唐古拉山脉、北部昆仑山脉和东部巴颜喀拉山脉的积雪相对较少,青藏高原西部、南部的积雪变化与中部、北部和东部的积雪变化趋势存在反位相关系。另外,本文还对积雪对高原地面反照率的影响作了简单分析。 相似文献
97.
Alan P. Carr 《地球表面变化过程与地形》1983,8(3):293-296
The method described involves the use of an electro-optical distance measurer mounted on a theodolite. Observations are taken onto a series of acrylic reflectors, aligned at right angles to the line of sight, and slope distances and vertical and horizontal angles are recorded. From these data it is possible to obtain surface heights to an accuracy of ±0·5 cm at 200 m and to avoid any direct disturbance of the site under investigation. 相似文献
98.
The heights of the daytime convective boundary layer (CBL), computed by a one-dimensional model for a bare soil surface at a semi-arid station,Anand, during the dry and hot summer month of May 1997, are presented. As input, the model requires surface heat flux, friction velocity and air temperature as functions of time. Temperature data at the one-metre level from a tower and sonic anemometer data at 9.5 m collected during the period 13–17 May 1997 in the Land Surface Processes Experiment (LASPEX-97) are used to compute hourly values of surface heat flux, friction velocity and Obukhov length following the operational method suggested by Holtslag and Van Ulden [J. Climate Appl. Meteorol.
22,517–529 (1983)]. The model has been tested with different values for the potential temperature gradient ( ) above the inversion. The model-estimated CBL heights comparefavourably with observed heights obtained from radiosonde ascents. 相似文献
99.
Bihong Fu Xinglin Lei Khaled Hessami Yoshiki Ninomiya Takashi Azuma Hisao Kondo 《Journal of Geodynamics》2007,44(3-5):160-172
The December 26, 2003 Mw 6.6 Bam earthquake is one of the most disastrous earthquakes in Iran. QuickBird panchromatic and multispectral satellite imagery with 61 cm and 2.4 m ground resolution, respectively provide new insights into the surface rupturing process associated with this earthquake. The results indicate that this earthquake produced a 2–5 km-wide surface rupture zone with a complex geometric pattern. A 10-km-long surface rupture zone developed along the pre-existing Bam fault trace. Two additional surface rupture zones, each 2–5 km long, are oblique to the pre-existing Bam fault in angles of 20–35°. An analysis of geometric and geomorphic features also shows that movement on the Bam fault is mainly right-lateral motion with some compressional component. This interpretation is consistent with field investigations, analysis of aftershocks as well as teleseismic inversion. Therefore, we suggest that the 2003 Bam earthquake occurred on the Bam fault, and that the surface ruptures oblique to the Bam fault are caused by secondary faulting such as synthetic shears (Reidel shears). Our fault model for the Bam earthquake provides a new tectonic scenario for explaining complex surface deformations associated with the Bam earthquake. 相似文献
100.
F. Shubitidze K. O'Neill B.E. Barrowes I. Shamatava J.P. Fernndez K. Sun K.D. Paulsen 《Journal of Applied Geophysics》2007,61(3-4):292-303
This paper presents an application of the normalized surface magnetic charge (NSMC) model to discriminate objects of interest, such as unexploded ordnance (UXO), from innocuous items in cases when UXO electromagnetic induction (EMI) responses are contaminated by signals from other objects. Over the entire EMI spectrum considered here (tens of Hertz up to several hundreds of kHz), the scattered magnetic field outside the object can be produced mathematically by equivalent magnetic charges. The amplitudes of these charges are determined from measurement data and normalized by the excitation field. The model takes into account the scatterer's heterogeneity and near- and far-field effects. For classification algorithms, the frequency spectrum of the total NSMC is proposed and investigated as a discriminant. The NSMC is combined with the differential evolution (DE) algorithm in a two-step inversion procedure. To illustrate the applicability of the DE–NSMC algorithm, blind test data are processed and analyzed for cases in which signals from nearby objects frequently overlap. The method was highly successful in distinguishing UXO from accompanying clutter. 相似文献