全文获取类型
收费全文 | 1627篇 |
免费 | 52篇 |
国内免费 | 51篇 |
专业分类
测绘学 | 153篇 |
大气科学 | 161篇 |
地球物理 | 300篇 |
地质学 | 695篇 |
海洋学 | 143篇 |
天文学 | 217篇 |
综合类 | 17篇 |
自然地理 | 44篇 |
出版年
2022年 | 17篇 |
2021年 | 21篇 |
2020年 | 17篇 |
2019年 | 15篇 |
2018年 | 39篇 |
2017年 | 53篇 |
2016年 | 73篇 |
2015年 | 33篇 |
2014年 | 58篇 |
2013年 | 118篇 |
2012年 | 55篇 |
2011年 | 62篇 |
2010年 | 46篇 |
2009年 | 63篇 |
2008年 | 48篇 |
2007年 | 46篇 |
2006年 | 59篇 |
2005年 | 43篇 |
2004年 | 36篇 |
2003年 | 30篇 |
2002年 | 40篇 |
2001年 | 42篇 |
2000年 | 37篇 |
1999年 | 44篇 |
1998年 | 30篇 |
1997年 | 29篇 |
1996年 | 29篇 |
1995年 | 17篇 |
1994年 | 23篇 |
1993年 | 20篇 |
1992年 | 19篇 |
1991年 | 18篇 |
1990年 | 27篇 |
1989年 | 18篇 |
1988年 | 22篇 |
1987年 | 27篇 |
1986年 | 24篇 |
1985年 | 27篇 |
1984年 | 29篇 |
1983年 | 26篇 |
1982年 | 24篇 |
1981年 | 22篇 |
1980年 | 22篇 |
1979年 | 22篇 |
1978年 | 16篇 |
1975年 | 16篇 |
1974年 | 14篇 |
1973年 | 23篇 |
1972年 | 16篇 |
1971年 | 22篇 |
排序方式: 共有1730条查询结果,搜索用时 15 毫秒
51.
Stiffened deep mixed (SDM) column is a new ground improvement technique to improve soft soil, which can be used to increase bearing capacity, reduce deformation, and enhance stability of soft soil. This technique has been successfully adopted to support the highway and railway embankments over soft soils in China and other countries. However, there have been limited investigations on its consolidation under embankment loading. This paper developed an analytical solution for the consolidation of embankment over soft soil with SDM column in which core pile is equal to or shorter than outer DM column. The consolidation problem was simplified as a consolidation of composite soil considering the load shear effect of core pile. The developed solution was verified by a comparison with the results computed by three-dimensional (3-D) finite element analysis. A parametric study based on the derived solution was conducted to investigate influence factors—length of core pile, diameter of core pile, diameter of SDM column, modulus of DM column, and permeability coefficient of DM column—on the consolidation behavior of SDM column-supported embankment over soft soil. The developed solution was applied to a case history of SDM column-supported embankment, and a good agreement was found between the predictions and the field measurements. 相似文献
52.
53.
54.
Riparian plants can adapt their water uptake strategies based on climatic and hydrological conditions within a river basin. The response of cold-alpine riparian trees to changes in water availability is poorly understood. The Lhasa River is a representative cold-alpine river in South Tibet and an under-studied environment. Therefore, a 96 km section of the lower Lhasa River was selected for a study on the water-use patterns of riparian plants. Plant water, soil water, groundwater and river water were measured at three sites for δ18O and δ2H values during the warm-wet and cold-dry periods in 2018. Soil profiles differed in isotope values between seasons and with the distance along the river. During the cold-dry period, the upper parts of the soil profiles were significantly affected by evaporation. During the warm-wet period, the soil profile was influenced by precipitation infiltration in the upper reaches of the study area and by various water sources in the lower reaches. Calculations using the IsoSource model indicated that the mature salix and birch trees (Salix cheilophila Schneid. and Betula platyphylla Suk.) accessed water from multiple sources during the cold-dry period, whereas they sourced more than 70% of their requirement from the upper 60–80 cm of the soil profile during the warm-wet period. The model indicated that the immature rose willow tree (Tamarix ramosissima Ledeb) accessed 66% of its water from the surface soil during the cold-dry period, but used the deeper layers during the warm-wet period. The plant type was not the dominant factor driving water uptake patterns in mature plants. Our findings can contribute to strategies for the sustainable development of cold-alpine riparian ecosystems. It is recommended that reducing plantation density and collocating plants with different rooting depths would be conducive to optimal plant growth in this environment. 相似文献
55.
56.
57.
P. C. Padhy R. K. Nayak V. K. Dadhwal M. Salim D. Mitra S. B. Chaudhury P. R. Rao K. H. Rao C.B. S. Dutt 《Journal of the Indian Society of Remote Sensing》2016,44(1):135-143
An empirical model is developed and used with remotely sensed predictors: sea surface temperature (SST) and chlorophyll-a concentration (Chl-a), to compute surface water partial pressure of carbon dioxide (pCO2w) and air-sea fluxes of CO2 in the Hooghly estuary and its adjacent coastal oceans. In situ observations used here were based on measurements carried out in this region during winter and summer periods in 2008. The estimated pCO2w compares well with the in situ observations at root mean square error ±18 μatm. In winter, estimated pCO2w ranges between 320 and 500 μatm with large values (>400 μatm) on the south-western and south-eastern flanks of the coastal domain and lower values (340–375 μatm) on the main-channel. In summer, it remained spatially uniform at 450 μatm. Extrapolation of the results over the study region based on the Moderate Imaging Specroradiometer (MODIS) measured SST and Chl-a suggests that the region is a strong source of atmospheric CO2 during the summer with net release of 0.095 Tg C year?1 (equivalent to mean flux of 90 molC m?2 year?1) and is a weak source during the winter with net release of 0.006 Tg C yr?1 (0.5 molC m?2 year?1) from the geographical extent of 6000 Km2 area. 相似文献
58.
59.
60.
Because the land requisition and demolishing became difficult more and more, the mining scheme of Luohe iron mine was changed from caving method to filling method. In order to ensure the safety of the residence and the underground tunnel cavern within the mobile belt of the underground mining, the Luohe iron mine did the blasting test on the vertical crater retreat mining method and blasting vibration monitoring. The blasting experiments use common emulsified oil explosives and non-electric initiation system. The way of caved ore adopts the cutting groove and bench side. The NUBOX-6016 intelligent vibration monitor was chosen in the blasting vibration monitoring. Twice experiments on the blasting vibration monitoring were done on the surface or in the underground refuge cavern. The first test select the three monitoring points on the ground and the second select two monitoring points on the ground and a monitoring point in the underground refuge cavern. The blasting vibration monitoring data were conducted by the regression analysis in the Sodev’s empirical formula. The vibration attenuation formula about the underground blasting vibration transmitting in three directions is derived. The blasting test on the vertical crater retreat mining method and the blasting vibration were analyzed. It is estimated if the vibration damage possibly the surface buildings and related facilities of mine. 相似文献