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101.
Sitharam G. Thallak Sireesh Saride Sujit Kumar Dash 《Geotechnical and Geological Engineering》2007,25(5):509-524
This paper presents the results of laboratory model tests carried out to develop an understanding of the behaviour of geocell-reinforced
soft clay foundations under circular loading. Natural silty clay was used in this study. The geocells were prepared using
biaxial polymer grid. The performance of the reinforced bed is quantified using non-dimensional factors i.e., Bearing capacity
improvement factor (If) and Percentage reduction in footing settlement (PRS). The test results demonstrate that the geocell mattress redistributes
the footing load over a wider area thereby improving the performance of the footing. The load carrying capacity of the clay
bed is increased by a factor of up to about 4.5 times that of unreinforced bed. From the pressure-settlement responses, it
is observed that the geocell-reinforced foundation bed behaves as a much stiffer system compared to the unreinforced case
indicating that a substantial reduction in footing settlement can be achieved by providing geocell reinforcement in the soft
clay bed. The maximum reduction in footing settlement obtained with the provision of geocell mattress of optimum size placed
close to the footing is around 90%. Further improvement in performance is obtained with provision of an additional planar
geogrid layer at the base of the geocell mattress. 相似文献
102.
Kishor Panjabi Pradeep Goel Prasad Daggupati Narayan Kumar Shrestha Rituraj Shukla 《水文科学杂志》2020,65(13):2224-2232
ABSTRACT In humid regions, surface runoff is often generated by saturation-excess runoff mechanisms from relatively small variable source areas (VSAs). However, the majority of the current hydrologic models are based on infiltration-excess mechanisms. In this study, the AGricultural Non-Point Source Pollution (AGNPS) model was used to integrate the VSA concept using topographic wetness index (TWI). Both the original and AGNPS-VSA models were evaluated for a small agricultural field in Ontario, Canada. The results indicate that the AGNPS-VSA model performed better than original model. The AGNPS-VSA model predicted that only the saturated portion of the field with higher TWI values produced runoff, whereas the original AGNPS model showed uniform hydrologic response from the entire field. The results of this study are important for accurately mapping the locations of VSAs. This new model could be a powerful tool in identifying critical source areas for applying targeted best management practices to minimize pollutant loads to receiving waters. 相似文献
103.
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105.
S. Sridharan P. Vishnu Prasanth Y. Bhavani Kumar Geetha Ramkumar S. Sathishkumar K. Raghunath 《Journal of Atmospheric and Solar》2009,71(5):575-582
Resonance lidar observations of sodium density in the upper mesosphere region over Gadanki (13.5°N, 79.2°E) rarely show complex structures with rapid enhancements of sodium density, completely different from normal sporadic sodium structures. The hourly averaged meteor radar zonal winds over Trivandrum (8.5°N, 76.5°E) show an eastward shear with altitude during the nights, when these events are formed. As suggested by Kane et al. [2001. Joint observations of sodium enhancements and field-aligned ionospheric irregularities. Geophysical Research Letters 28, 1375–1378], our observations show that the complex structures may be formed due to Kelvin–Helmholtz instability, which can occur in the region of strong wind shear. 相似文献
106.
S. Abhilash Someshwar Das S. R. Kalsi M. Das Gupta K. Mohankumar John P. George S. K. Banerjee S. B. Thampi D. Pradhan 《Pure and Applied Geophysics》2007,164(8-9):1491-1509
Pre-monsoon rainfall around Kolkata (northeastern part of India) is mostly of convective origin as 80% of the seasonal rainfall
is produced by Mesoscale Convective Systems (MCS). Accurate prediction of the intensity and structure of these convective
cloud clusters becomes challenging, mostly because the convective clouds within these clusters are short lived and the inaccuracy
in the models initial state to represent the mesoscale details of the true atmospheric state. Besides the role in observing
the internal structure of the precipitating systems, Doppler Weather Radar (DWR) provides an important data source for mesoscale
and microscale weather analysis and forecasting. An attempt has been made to initialize the storm-scale numerical model using
retrieved wind fields from single Doppler radar. In the present study, Doppler wind velocities from the Kolkata Doppler weather
radar are assimilated into a mesoscale model, MM5 model using the three-dimensional variational data assimilation (3DVAR)
system for the prediction of intense convective events that occurred during 0600 UTC on 5 May and 0000 UTC on 7 May, 2005.
In order to evaluate the impact of the DWR wind data in simulating these severe storms, three experiments were carried out.
The results show that assimilation of Doppler radar wind data has a positive impact on the prediction of intensity, organization
and propagation of rain bands associated with these mesoscale convective systems. The assimilation system has to be modified
further to incorporate the radar reflectivity data so that simulation of the microphysical and thermodynamic structure of
these convective storms can be improved. 相似文献
107.
Prediction and monitoring of monsoon intraseasonal oscillations over Indian monsoon region in an ensemble prediction system using CFSv2 总被引:1,自引:0,他引:1
S. Abhilash A. K. Sahai N. Borah R. Chattopadhyay S. Joseph S. Sharmila S. De B. N. Goswami Arun Kumar 《Climate Dynamics》2014,42(9-10):2801-2815
An ensemble prediction system (EPS) is devised for the extended range prediction (ERP) of monsoon intraseasonal oscillations (MISO) of Indian summer monsoon (ISM) using National Centers for Environmental Prediction Climate Forecast System model version 2 at T126 horizontal resolution. The EPS is formulated by generating 11 member ensembles through the perturbation of atmospheric initial conditions. The hindcast experiments were conducted at every 5-day interval for 45 days lead time starting from 16th May to 28th September during 2001–2012. The general simulation of ISM characteristics and the ERP skill of the proposed EPS at pentad mean scale are evaluated in the present study. Though the EPS underestimates both the mean and variability of ISM rainfall, it simulates the northward propagation of MISO reasonably well. It is found that the signal-to-noise ratio of the forecasted rainfall becomes unity by about 18 days. The potential predictability error of the forecasted rainfall saturates by about 25 days. Though useful deterministic forecasts could be generated up to 2nd pentad lead, significant correlations are found even up to 4th pentad lead. The skill in predicting large-scale MISO, which is assessed by comparing the predicted and observed MISO indices, is found to be ~17 days. It is noted that the prediction skill of actual rainfall is closely related to the prediction of large-scale MISO amplitude as well as the initial conditions related to the different phases of MISO. An analysis of categorical prediction skills reveals that break is more skillfully predicted, followed by active and then normal. The categorical probability skill scores suggest that useful probabilistic forecasts could be generated even up to 4th pentad lead. 相似文献
108.
Vulnerability and adaptation to climate variability and water stress in Uttarakhand State, India 总被引:1,自引:0,他引:1
Ulka Kelkar Kapil Kumar Narula Ved Prakash Sharma Usha Chandna 《Global Environmental Change》2008,18(4):564
This paper presents a participatory approach to investigate vulnerability and adaptive capacity to climate variability and water stress in the Lakhwar watershed in Uttarakhand State, India. Highly water stressed microwatersheds were identified by modelling surface runoff, soil moisture development, lateral runoff, and groundwater recharge. The modelling results were shared with communities in two villages, and timeline exercises were carried out to allow them to trace past developments that have impacted their lives and livelihoods, and stimulate discussion about future changes and possible adaptation interventions. 相似文献
109.
The Indian subcontinent witnessed a severe monsoon drought in 2002, which largely resulted from a major rainfall deficiency
in the month of July. While moderate El Nino conditions prevailed during this period, the atmospheric convective activity
was anomalously enhanced over northwest and north-central Pacific in the 10–20°N latitude belt; and heavy rainfall occurred
over this region in association with a series of northward moving tropical cyclones. Similar out-of-phase rainfall variations
over the Indian region and the northwest (NW) Pacific have been observed during other instances of El Nino/Southern Oscillation
(ENSO). The dynamical linkage corresponding to this out-of-phase rainfall variability is explored in this study by conducting
a set of numerical experiments using an atmospheric general circulation model. The results from the model simulations lend
credence to the role of the tropical Pacific sea surface temperature anomalies in forcing the out-of-phase precipitation variability
over the NW Pacific and the Indian monsoon region. It is seen that the ENSO induced circulation response reveals an anomalous
pattern comprising of alternating highs and lows which extend meridionally from the equatorial region into the sub-tropic
and mid-latitude regions of west-central Pacific. This meridional pattern is associated with an anomalous cyclonic circulation
over NW Pacific, which is found to favor enhanced tropical cyclonic activity and intensified convection over the region. In
turn, the intensified convection over NW Pacific induces subsidence and rainfall deficiency over the Indian landmass through
anomalous east-west circulation in the 10–20°N latitude belt. Based on the present findings, it is suggested that the convective
activity over NW Pacific is an important component in mediating the ENSO-monsoon teleconnection dynamics. 相似文献
110.