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271.
D. Lauwaet N. P. M. van Lipzig N. Kalthoff K. De Ridder 《Meteorology and Atmospheric Physics》2010,107(3-4):109-122
The evolution of precipitating convective systems in West Africa has been a research topic throughout the past three decades and is considered to be influenced by surface–atmosphere interactions. This study builds on the previous research by examining the sensitivity of a mesoscale convective system (MCS) to a change in the vegetation cover by using a regional atmospheric model with a high horizontal resolution. Vegetation cover values in the region between 10 and 15°N have increased by 10–30% over the last 20 years. The effect of both an increase and a decrease in vegetation cover by 10, 20 and 30% is investigated. The MCS case selected occurred on 11 June 2006 and was observed during the African Monsoon Multidisciplinary Analysis field campaign in Dano, Burkina Faso. The model is able to reproduce the most important characteristics of the MCS and the atmospheric environment. For the investigated case, no clear precipitation response of the MCS to the applied vegetation scenarios is found. The vegetation changes do alter the surface fluxes in the days before the MCS arrives, which have a clear effect on the modelled convective available potential energy (CAPE) values. However, a link between CAPE, mesoscale circulation and rainfall amounts could not be demonstrated as a dynamical mechanism is found to counteract the CAPE signal. By using a kilometre-scale model, a change in the cold pool dynamics of the MCS could be detected which results from alterations in boundary layer moisture. The effect of vegetation changes on the MCS is thus not straightforward and a complex interaction between different processes should be taken into account. 相似文献
272.
Koen De Ridder 《Boundary-Layer Meteorology》2010,134(2):257-267
In the roughness sublayer (RSL), Monin–Obukhov surface layer similarity theory fails. This is problematic for atmospheric
modelling applications over domains that include rough terrain such as forests or cities, since in these situations numerical
models often have the lowest model level located within the RSL. Based on empirical RSL profile functions for momentum and
scalar quantities, and scaling the height with the RSL height z
*, we derive a simple bulk transfer relation that accounts for RSL effects. To verify the validity of our approach, these relations
are employed together with wind speed and temperature profiles measured over boreal forest during the BOREAS experimental
campaign to estimate momentum and heat fluxes. It is demonstrated that, when compared with observed flux values, the inclusion
of RSL effects in the transfer relations yields a considerable improvement in the estimated fluxes. 相似文献
273.
基于ARPS3DVAR+WRF (Advanced Regional Prediction and 3-dimensional variational System)快速同化模式对西南地区近几年发生的4次强降水过程进行模拟试验,对12 h降水预报结果采用升尺度方法,计算邻域平均预报、站点概率预报,最终形成邻域概率预报,并细致分析了这三种预报的特点与效果,讨论了升尺度窗区尺度给不同量级降水带来的影响,最后结合AROC评分与邻域空间检验FSS讨论业务概率预报应用的最佳尺度。结果表明:升尺度邻域平均预报在小雨与大暴雨量级降水上表现不稳定,对中雨的预报提高不明显,但是对大雨与暴雨预报有较好的改善效果;站点概率预报具有一定的误导性,而邻域概率预报可以弥补其缺憾,越高分辨率的模式有更多的降水样本,在降水不确定性上能给出更好的概率分级信息;相对邻域平均的升尺度预报TS检验结果,基于邻域概率的FSS和AROC分析有更好的预报技巧指导意义;36 km升尺度窗区既能消除一定程度的强降水预报不确定性,同时也可以保留适当的对流尺度特征,为最佳升尺度窗区。 相似文献
274.
该文根据气象灾害预警信号业务技术规范,结合实际业务中存在的问题,以暴雨为例,对气象灾害预警信号发布中涉及的发布标准、发布级别和时间选择、有效时段、后续应对、质量检验、与短时临近预报和决策服务的关系等问题进行了解读及技术性探讨,对于建立规范、严谨的气象灾害预警信号发布业务具有指导意义。 相似文献
275.
276.
Matthias Mauder Steven P. Oncley Roland Vogt Tamas Weidinger Luis Ribeiro Christian Bernhofer Thomas Foken Wim Kohsiek Henk A. R. De Bruin Heping Liu 《Boundary-Layer Meteorology》2007,123(1):29-54
The eddy-covariance method is the primary way of measuring turbulent fluxes directly. Many investigators have found that these
flux measurements often do not satisfy a fundamental criterion—closure of the surface energy balance. This study investigates
to what extent the eddy-covariance measurement technology can be made responsible for this deficiency, in particular the effects
of instrumentation or of the post-field data processing. Therefore, current eddy-covariance sensors and several post-field
data processing methods were compared. The differences in methodology resulted in deviations of 10% for the sensible heat
flux and of 15% for the latent heat flux for an averaging time of 30 min. These disparities were mostly due to different sensor
separation corrections and a linear detrending of the data. The impact of different instrumentation on the resulting heat
flux estimates was significantly higher. Large deviations from the reference system of up to 50% were found for some sensor
combinations. However, very good measurement quality was found for a CSAT3 sonic together with a KH20 krypton hygrometer and
also for a UW sonic together with a KH20. If these systems are well calibrated and maintained, an accuracy of better than
5% can be achieved for 30-min values of sensible and latent heat flux measurements. The results from the sonic anemometers
Gill Solent-HS, ATI-K, Metek USA-1, and R.M. Young 81000 showed more or less larger deviations from the reference system.
The LI-COR LI-7500 open-path H2O/CO2 gas analyser in the test was one of the first serial numbers of this sensor type and had technical problems regarding direct
solar radiation sensitivity and signal delay. These problems are known by the manufacturer and improvements of the sensor
have since been made.
The National Center for Atmospheric Research is supported by the National Science Foundation. 相似文献
277.
1730年(清雍正八年)7—8月,我国黄淮地区连续暴雨17 d,引起黄河、大运河和淮河暴涨、决堤的大范围洪涝灾害。这是小冰期中相对温暖时段气候背景下的极端气候事件。本文依据历史文献记载复原了1730年夏季暴雨时段的天气实况,绘制了暴雨区域图显示强降雨中心移动动态和水灾地域分布图,概述当年气候特点,指出暴雨事件与台风活动的关联。1730年是太阳活动周极小年的前3年、有重大火山活动,是极强的厄尔尼诺事件后的第2年。这些天气特点和背景条件与现代罕见的1975年河南“75?8暴雨”相似。 相似文献
278.
Gérald Darnis Dominique Robert Corinne Pomerleau Heike Link Philippe Archambault R. John Nelson Maxime Geoffroy Jean-éric Tremblay Connie Lovejoy Steve H. Ferguson Brian P. V. Hunt Louis Fortier 《Climatic change》2012,115(1):179-205
As part of the Canadian contribution to the International Polar Year (IPY), several major international research programs have focused on offshore arctic marine ecosystems. The general goal of these projects was to improve our understanding of how the response of arctic marine ecosystems to climate warming will alter food web structure and ecosystem services provided to Northerners. At least four key findings from these projects relating to arctic heterotrophic food web, pelagic-benthic coupling and biodiversity have emerged: (1) Contrary to a long-standing paradigm of dormant ecosystems during the long arctic winter, major food web components showed relatively high level of winter activity, well before the spring release of ice algae and subsequent phytoplankton bloom. Such phenological plasticity among key secondary producers like zooplankton may thus narrow the risks of extreme mismatch between primary production and secondary production in an increasingly variable arctic environment. (2) Tight pelagic-benthic coupling and consequent recycling of nutrients at the seafloor characterize specific regions of the Canadian Arctic, such as the North Water polynya and Lancaster Sound. The latter constitute hot spots of benthic ecosystem functioning compared to regions where zooplankton-mediated processes weaken the pelagic-benthic coupling. (3) In contrast with another widely shared assumption of lower biodiversity, arctic marine biodiversity is comparable to that reported off Atlantic and Pacific coasts of Canada, albeit threatened by the potential colonization of subarctic species. (4) The rapid decrease of summer sea-ice cover allows increasing numbers of killer whales to use the Canadian High Arctic as a hunting ground. The stronger presence of this species, bound to become a new apex predator of arctic seas, will likely affect populations of endemic arctic marine mammals such as the narwhal, bowhead, and beluga whales. 相似文献
279.
Sarbari Ghosh Utpal Kumar De Atmospheric Science Research Department of Physics Jadavpur University Calcutta India Received April revised July 《大气科学进展》1997,(1)
AComparativeStudyoftheAtmosphericLayersbelowFirstLiftingCondensationLevelforInstantaneousPre-MonsoonThunderstormOcurenceatAga... 相似文献
280.