全文获取类型
收费全文 | 1618篇 |
免费 | 287篇 |
国内免费 | 232篇 |
专业分类
测绘学 | 98篇 |
大气科学 | 582篇 |
地球物理 | 591篇 |
地质学 | 344篇 |
海洋学 | 169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 | 9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 | 75篇 |
2013年 | 87篇 |
2012年 | 65篇 |
2011年 | 153篇 |
2010年 | 142篇 |
2009年 | 148篇 |
2008年 | 148篇 |
2007年 | 99篇 |
2006年 | 108篇 |
2005年 | 83篇 |
2004年 | 86篇 |
2003年 | 61篇 |
2002年 | 77篇 |
2001年 | 67篇 |
2000年 | 58篇 |
1999年 | 53篇 |
1998年 | 43篇 |
1997年 | 40篇 |
1996年 | 35篇 |
1995年 | 22篇 |
1994年 | 31篇 |
1993年 | 25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 | 2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2137条查询结果,搜索用时 234 毫秒
101.
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
102.
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
103.
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
104.
J.-F. Girard M. Boucher A. Legchenko J.-M. Baltassat 《Journal of Applied Geophysics》2007,63(3-4):103-116
Karstic conduits play a crucial role for water supply in many parts of the world. However, the imaging of such targets is generally a difficult task for most geophysical methods. Magnetic Resonance Sounding (MRS) is a geophysical method designed for imaging of water bearing structures. Initially, MRS was developed for characterizing horizontally stratified aquifers. However, when applying a 1D MRS measuring setup to the imaging of 2D–3D targets, the size of which may be much smaller than the loop, the accuracy and the lateral resolution may not be sufficient. We have studied the possibility of simultaneously processing several MRS aligned along a profile to perform a Magnetic Resonance Tomography (MRT). This work emphasizes the gain of resolution for 2D–3D imagery of MRT versus the interpolation of 1D inversion results of MRS along the same profile. Numerical modelling results show that the MRT response is sensitive to the size and location of the 2D target in the subsurface. Sensitivity studies reveal that by using the coincident transmitting/receiving (TX/RX) setup and shifting the loop around the anomaly area, the depth, section and position of a single karstic conduit with a size smaller than the MRS loop size can be resolved. The accuracy of the results depends on the noise level and signal level, the latter parameter being linked to the depth and volume of the karstic conduit and the water content in the limestone matrix. It was shown that when applying MRT to the localization of 2D anomalies such as karstic conduits, the inclination of the geomagnetic field, the orientation of the MRT profile and the angle of crossover of the conduit by the MRT profile must be taken into account. Otherwise additional errors in interpretation should be expected. A 2D inversion scheme was developed and tested. Both numerical and experimental results confirm the efficiency of the developed approach. 相似文献
105.
O'Leary González Leonardo Alvarez Mariangela Guidarelli Giuliano F. Panza 《Pure and Applied Geophysics》2007,164(10):1985-2007
An overview of the crust and upper mantle structure of Central America and the Caribbean region is presented as a result of
the processing of more than 200 seismograms recorded by digital broadband stations from SSSN and GSN seismic networks. Group
velocity dispersion curves are obtained in the period range from 10s to 40s by FTAN analysis of the fundamental mode of the
Rayleigh waves; the error of these measurements varies from 0.06 and 0.09 km/s. From the dispersion curve, seven tomographic
maps at different periods and with average spatial resolution of 500 km are obtained. Using the logical combinatorial classification
techniques, eight main groups of dispersion curves are determined from the tomographic maps and eleven main regions, each
one characterized by one kind of dispersion curves, are identified. The average dispersion curves obtained for each region
are extended to 150s by adding data from a larger-scale tomographic study (Vdovin et al., 1999) and inverted using a nonlinear procedure. A set of models of the S-wave velocity vs. depth in the crust and upper
mantle is found as a result of the inversion process. In six regions we identify a typically oceanic crust and upper mantle
structure, while in the other two the models are consistent with the presence of a continental structure. Two regions, located
over the major geological zones of the accretionary crust of the Caribbean region, are characterized by a peculiar crust and
upper mantle structure, indicating the presence of lithospheric roots reaching, at least, about 200 km of depth. 相似文献
106.
The diurnal structure of the boundary layer during Indian summer monsoon period is studied using a one-dimensional meteorological
boundary layer model and the observations collected from the Monsoon Trough Boundary Layer Experiment conducted in 1990 at
Jodhpur, India. The model was initialized with the observed temperature profiles at 0530 LST on 17 July, 1990 at Jodhpur and
was run for 26 hours. The study is carried out with a geostrophic wind speed of 9.5 m s−1 corresponding to the strong wind simulation. The mean thermodynamic and wind structure simulated by the model are in good
agreement with those observed from 30 m tower. The computed surface layer characteristics such as the surface fluxes, TKE
and standard deviations of velocity components are found to be reasonably in good agreement with those based on turbulence
measurements. The shear and buoyancy budget computed from the model are also compared with the turbulence measurements. The
integrated cooling budget in the nocturnal boundary layer is examined. 相似文献
107.
On May 28, 1998, a moderate size earthquake of mb 5.5 occurred offshore the northwestern part of Egypt (latitude 31.45°N and
longitude 27.64°E). It was widely felt in the northern part of Egypt. Being the largest well-recorded event in the area for
which seismic data from the global digital network are available, it provides an excellent opportunity to study the tectonic
process and present day stress field occurring along the offshore Egyptian coast. The source parameters of this event are
determined using three different techniques: modeling of surface wave spectral amplitudes, regional waveform inversion, and
teleseismic body waveform inversion. The results show a high-angle reverse fault mechanism generally trending NNW–SSE. The
P-axis trends ENE–WSW consistently with the prevailed compression stress along the southeastern Hellenic arc and southwestern
part of the Cyprean arc. This unexpected mechanism is most probably related to a positive inversion of the NW trending offshore
normal faults and confirms an extension of the back thrusting effects towards the African margin. The estimated focal depth
ranges from 22 to 25 km, indicating a lower crustal origin earthquake owing to deep-seated tectonics. The source time function
indicates a single source with rise time and total rupture duration of 2 and 5 s, respectively. The seismic moment (M
o) and the moment magnitude (M
w) determined by the three techniques are 1.03 × 1017 Nm, 5.28; 1.24 × 1017 Nm, 5.33; and 1.68 × 1017 Nm, 5.42; respectively. The calculated fault radius, stress drop, and the average dislocation assuming a circular fault model
are 7.2 km, 0.63 Mpa, and 0.11 m, respectively. 相似文献
108.
109.
中国北方干旱区地表湿润状况的趋势分析 总被引:85,自引:3,他引:85
利用 1 95 1~ 1 997年中国 1 6 0站月降水和平均气温资料 ,通过计算的地表湿润指数 Hi =PPe(P为观测的月降水总量 ,Pe为月最大潜在蒸发 ) ,对比分析了中国华北、西北两个典型干旱区区域平均地表湿润指数的年代年际变化特征及季节性差异 ,并讨论了它与降水和气温的联系。最后 ,给出了地表湿润指数年及各季节变化趋势的地理分布。研究表明 :西北西部和华北地区的年际及年代际变化趋势基本相反 ,前者地表为变湿趋势 ,后者为变干趋势。华北地区的干化趋势主要发生在夏秋季节 ,而西北除东部的秋季和西部的夏季外 ,其它季节均存在变湿趋势 相似文献
110.
广州中尺度模式局地要素预报性能分析 总被引:7,自引:2,他引:7
该文简要介绍了华南中尺度模式的地表要素的预报诊断方案, 站点要素时间序列预报情况.用适合站点要素时间序列预报的检验方法, 检验并分析了各要素时间序列预报的性能.表明该中尺度模式的地表要素时间序列预报方案是有效的, 预报具有较高的准确性和应用价值. 相似文献