全文获取类型
收费全文 | 947篇 |
免费 | 33篇 |
国内免费 | 23篇 |
专业分类
测绘学 | 37篇 |
大气科学 | 47篇 |
地球物理 | 180篇 |
地质学 | 600篇 |
海洋学 | 32篇 |
天文学 | 64篇 |
综合类 | 6篇 |
自然地理 | 37篇 |
出版年
2023年 | 4篇 |
2022年 | 34篇 |
2021年 | 37篇 |
2020年 | 33篇 |
2019年 | 24篇 |
2018年 | 77篇 |
2017年 | 85篇 |
2016年 | 63篇 |
2015年 | 42篇 |
2014年 | 64篇 |
2013年 | 79篇 |
2012年 | 41篇 |
2011年 | 51篇 |
2010年 | 37篇 |
2009年 | 40篇 |
2008年 | 33篇 |
2007年 | 21篇 |
2006年 | 24篇 |
2005年 | 24篇 |
2004年 | 18篇 |
2003年 | 16篇 |
2002年 | 16篇 |
2001年 | 8篇 |
2000年 | 11篇 |
1999年 | 11篇 |
1998年 | 3篇 |
1997年 | 4篇 |
1996年 | 5篇 |
1995年 | 6篇 |
1994年 | 7篇 |
1993年 | 5篇 |
1992年 | 6篇 |
1991年 | 3篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 7篇 |
1985年 | 8篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 8篇 |
1981年 | 3篇 |
1978年 | 4篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1973年 | 3篇 |
1970年 | 2篇 |
1969年 | 2篇 |
1963年 | 1篇 |
排序方式: 共有1003条查询结果,搜索用时 0 毫秒
131.
Rehman Sufia Sahana Mehebub Hong Haoyuan Sajjad Haroon Ahmed Baharin Bin 《Natural Hazards》2019,96(2):975-998
Natural Hazards - Floods have always been associated with widespread devastation and destruction since the emergence of human civilization. The intensity of this disaster has been increasing due to... 相似文献
132.
Station-keeping for a translunar communication station 总被引:1,自引:0,他引:1
John V. Breakwell Ahmed A. Kamel Martin J. Ratner 《Celestial Mechanics and Dynamical Astronomy》1974,10(3):357-373
A translunar communication station is to be kept close to a nominal unstable periodic ‘Halo’ orbit, visible at all times from Earth. The analytically computed nominal orbit is not perfect, requiring an average control acceleration of about 10?6 g's for tight control. An adjustable quadratic combination of position deviation and control acceleration is minimized to provide an (adjustable) control law with period feedback gains and a periodic bias. The average control acceleration can be reduced to less than 10?8 g's with an error settling time of less than 21/2 months. The resulting limiting motion provides, in turn, an improved nominal, permitting the same low control cost with much tighter control, corresponding to settling times of the order of one day. 相似文献
133.
Luís André Magaia Tada-nori Goto Alaa Ahmed Masoud Katsuaki Koike 《Natural Resources Research》2018,27(3):275-298
Exploring for groundwater in crystalline rocks in semiarid areas is a challenge because of their complex hydrogeology and low potential yields. An integrated approach was applied in central western Mozambique, in an area covered by Precambrian crystalline basement rocks. The approach combined a digital elevation model (DEM), remote sensing, and a ground-based geophysical survey. The aim was to identify groundwater zones with high potential and to identify geological structures controlling that potential. Lineaments were extracted from the DEM that had been enhanced using an adaptive-tilt, multi-directional, shading technique and a non-filtering technique to characterize the regional fracture system. The shallowness and amount of stored groundwater in the fracture zones was assessed using vegetation indices derived from Landsat 8 OLI images. Then, 14 transient electromagnetic (TEM) survey profiles were taken in different geological settings across continuous lineaments that were considered to be aligned along inferred faults. In the central lineament zones, the TEM soundings gave resistivity values of less than 300 Ωm at a depth of 20–80 m. The values varied with location. Conversely, values greater than 400 Ωm were observed at the sites away from the central zones. This contrast is probably caused by the differences in permeability and degree of weathering along the fractured zones. These differences could be key factors in determining groundwater occurrence. By integrating five water-related factors (lineament density, slope, geology, vegetation index, and proximity to lineaments), high groundwater potential zones were located in the vicinity of the lineaments. In these zones, vegetation remains active regardless of the season. 相似文献
134.
Zeinab SALAH Ahmed SHALABY Allison L.STEINER Ashraf S.ZAKEY Ritesh GAUTAM Mohamed M.ABDEL WAHAB 《大气科学进展》2018,35(2):182-194
This study assesses the direct and indirect effects of natural and anthropogenic aerosols(e.g., black carbon and sulfate)over West and Central Africa during the West African monsoon(WAM) period(June–July–August). We investigate the impacts of aerosols on the amount of cloudiness, the influences on the precipitation efficiency of clouds, and the associated radiative forcing(direct and indirect). Our study includes the implementation of three new formulations of auto-conversion parameterization [namely, the Beheng(BH), Tripoli and Cotton(TC) and Liu and Daum(R6) schemes] in Reg CM4.4.1,besides the default model's auto-conversion scheme(Kessler). Among the new schemes, BH reduces the precipitation wet bias by more than 50% over West Africa and achieves a bias reduction of around 25% over Central Africa. Results from detailed sensitivity experiments suggest a significant path forward in terms of addressing the long-standing issue of the characteristic wet bias in Reg CM. In terms of aerosol-induced radiative forcing, the impact of the various schemes is found to vary considerably(ranging from-5 to-25 W m~(-2)). 相似文献
135.
Fahimi Farzad Yaseen Zaher Mundher El-shafie Ahmed 《Theoretical and Applied Climatology》2017,127(3-4):875-889
Theoretical and Applied Climatology - Snow is a key element for many socioeconomic activities in mountainous regions. Due to the sensitivity of the snow cover to variations of temperature and... 相似文献
136.
The Cairo earthquake (12 October 1992; m b = 5.8) is still and after 25 years one of the most painful events and is dug into the Egyptians memory. This is not due to the strength of the earthquake but due to the accompanied losses and damages (561 dead; 10,000 injured and 3000 families lost their homes). Nowadays, the most frequent and important question that should rise is “what if this earthquake is repeated today.” In this study, we simulate the same size earthquake (12 October 1992) ground motion shaking and the consequent social-economic impacts in terms of losses and damages. Seismic hazard, earthquake catalogs, soil types, demographics, and building inventories were integrated into HAZUS-MH to produce a sound earthquake risk assessment for Cairo including economic and social losses. Generally, the earthquake risk assessment clearly indicates that “the losses and damages may be increased twice or three times” in Cairo compared to the 1992 earthquake. The earthquake risk profile reveals that five districts (Al-Sahel, El Basateen, Dar El-Salam, Gharb, and Madinat Nasr sharq) lie in high seismic risks, and three districts (Manshiyat Naser, El-Waily, and Wassat (center)) are in low seismic risk level. Moreover, the building damage estimations reflect that Gharb is the highest vulnerable district. The analysis shows that the Cairo urban area faces high risk. Deteriorating buildings and infrastructure make the city particularly vulnerable to earthquake risks. For instance, more than 90 % of the estimated buildings damages are concentrated within the most densely populated (El Basateen, Dar El-Salam, Gharb, and Madinat Nasr Gharb) districts. Moreover, about 75 % of casualties are in the same districts. Actually, an earthquake risk assessment for Cairo represents a crucial application of the HAZUS earthquake loss estimation model for risk management. Finally, for mitigation, risk reduction, and to improve the seismic performance of structures and assure life safety and collapse prevention in future earthquakes, a five-step road map has been purposed. 相似文献
137.
Nisar Ahmed Perveiz Khalid Hafiz Muhammad Bilal Shafi Patrick Connolly 《Acta Geophysica》2017,65(5):991-1007
The use of seismic direct hydrocarbon indicators is very common in exploration and reservoir development to minimise exploration risk and to optimise the location of production wells. DHIs can be enhanced using AVO methods to calculate seismic attributes that approximate relative elastic properties. In this study, we analyse the sensitivity to pore fluid changes of a range of elastic properties by combining rock physics studies and statistical techniques and determine which provide the best basis for DHIs. Gassmann fluid substitution is applied to the well log data and various elastic properties are evaluated by measuring the degree of separation that they achieve between gas sands and wet sands. The method has been applied successfully to well log data from proven reservoirs in three different siliciclastic environments of Cambrian, Jurassic, and Cretaceous ages. We have quantified the sensitivity of various elastic properties such as acoustic and extended elastic (EEI) impedances, elastic moduli (K sat and K sat–μ), lambda–mu–rho method (λρ and μρ), P-to-S-wave velocity ratio (V P/V S), and Poisson’s ratio (σ) at fully gas/water saturation scenarios. The results are strongly dependent on the local geological settings and our modeling demonstrates that for Cambrian and Cretaceous reservoirs, K sat–μ, EEI, V P/V S, and σ are more sensitive to pore fluids (gas/water). For the Jurassic reservoir, the sensitivity of all elastic and seismic properties to pore fluid reduces due to high overburden pressure and the resultant low porosity. Fluid indicators are evaluated using two metrics: a fluid indicator coefficient based on a Gaussian model and an overlap coefficient which makes no assumptions about a distribution model. This study will provide a potential way to identify gas sand zones in future exploration. 相似文献
138.
The paper intends to study the propagation of horizontally polarized shear waves in an elastic medium with void pores constrained between a vertically inhomogeneous and an anisotropic magnetoelastic semi-infinite media. Elasto-dynamical equations of elastic medium with void pores and magnetoelastic solid have been employed to investigate the shear wave propagation in the proposed three-layered earth model. Method of separation of variables has been incorporated to deduce the dispersion relation. All possible special cases have been envisaged and they fairly comply with the corresponding results for classical cases. The role of inhomogeneity parameter, thickness of layer, angle with which the wave crosses the magnetic field and anisotropic magnetoelastic coupling parameter for three different materials has been elucidated and represented by graphs using MATHEMATICA. 相似文献
139.
Saliha Najib Khalid Mehdi Joëlle Riss Ahmed Fadili Antonio Pulido-Bosch Hakima Guessir 《水文科学杂志》2017,62(5):749-759
L’aquifère libre de la Chaouia côtière constitue un exemple des aquifères les plus exploités au Maroc. Ce travail est consacré à l’étude des processus de la salinisation des eaux souterraines par l’analyse physico-chimique de 39 puits répartis dans la zone. Deux types de faciès ont été révélés, l’un est chloruré-sodique dans la frange côtière ; l’autre faciès est de type chloruré bicarbonaté-calcique caractérisant les eaux exploitées dans les calcaires marneux du Crétacé. L’influence marine (aérosols et intrusion marine), la dissolution/précipitation de la roche aquifère et l’infiltration des eaux d’irrigation, sont parmi les causes de l’augmentation de la salinité des eaux souterraines, en plus de l’exploitation excessive de l’eau souterraine. 相似文献
140.
The authors investigated the impact of the extension of the El Kantra Channel on the composition and structure of macrobenthic assemblages in Boughrara Lagoon (Gulf of Gabes, Tunisia along with the use of 4 biotic indices (AMBI, BENTIX, M-AMBI and TUBI). Thirteen stations were sampled seasonally in 2012–2013. Forty-one species were found in 2012–2013 not recorded in 2009–2010, including 20 species of polychaetes belonging to the trophic groups of deposit-feeders and carnivores which are expected to increase in areas disturbed by organic pollution. During the survey, we recorded a high fish mortality, essentially caused by the development of harmful algal blooms (HAB) which increased organic matter deposition, thus inducing polychaete development. This seems to weaken the bio-indicating power of biotic indices used here which, paradoxically, classified all sampled stations at a high ecological status. A review of these indices and their applicability to all marine environments is recommended. 相似文献