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101.
利用2005年12月7~29日在兰州市皋兰山顶获取的地气相互作用观测资料,对比分析了冬季典型晴天和平均状态下绿化地与裸地地表辐射、能量收支及土壤温、湿度的日变化特征。结果表明:绿化地和裸地太阳总辐射、大气长波辐射很接近,地表短波和长波向上辐射因不同下垫面特征不同而差异较大;地表能量平衡绿化地、裸地均以感热输送为主,土壤热通量和潜热输送很小,尤其是潜热通量,峰值往往不超过10 W.m-2;观测发现绿化地感热比裸地高,这一反常现象值得进一步研究证实;观测期平均特征与晴天比较接近,表明云和降雪的扰动影响有限;绿化地、裸地地表日平均反照率相对稳定,绿化地日平均反照率在0.20~0.28之间变化,裸地在0.25~0.31之间变化,平均值分别为0.21和0.29。 相似文献
102.
103.
福建省兴化湾有毒重金属的输入输出 总被引:3,自引:0,他引:3
基于对兴化湾大气干、湿沉降,沉积物及河(海)水的取样分析数据,主要考虑河流输入及与外海的物质交换,大气干、湿沉降和沉积作用过程重金属物质的迁移量,估算了兴化湾重金属的输入输出量.结果表明,As、Cr、Pb主要来自于河流输入,其河流输入量分别占总输入量的76.4%,78.2%和68.9%,Hg主要来自于河流输入和与外海的物质交换,Cd主要以大气干、湿沉降为输入方式,该方式的输入量占输入总量的78.8%.沉积作用是5种有毒重金属的主要输出方式,占输出总量的88.2%~100%,潮汐作用可将部分As、Cr、Pb输向外海,但也可能将Hg带入兴化湾,兴化湾Cd污染有加剧的趋势. 相似文献
104.
105.
城市下垫面反照率变化对北京市热岛过程的影响——个例分析 总被引:13,自引:1,他引:13
随着城市的不断发展,城区地表反照率等下垫面物理特征和属性会发生明显的变化,进而会对城市热岛等大气环境形成影响。文中使用中国气象科学研究院开发的新一代数值天气预报模式(GRAPES),针对2004年10月北京一次重空气污染事件中的典型城市热岛过程,分别设计了两种数值试验方案:(1)对照试验,使用模式缺省的城区下垫面反照率参数,取值0.18;(2)敏感性试验,参考同期中国科学院大气物理研究所铁塔280m高度下垫面反照率观测事实,将北京区域城市类型下垫面反照率减小至0.15。通过对比两种试验方案在1km水平分辨率下的24h模拟结果,研究了城市下垫面反照率变化对北京地区城市热岛过程的影响。结果表明:(1)GRAPES模式可成功模拟此次热岛过程中城区和郊区近地面温度的日变化趋势;(2)城市下垫面反照率的变化对城市热岛的发展非常重要,城市反照率下降0.03会使城市热岛强度增强0.8℃左右,结果也更接近实况。这说明随着城市发展引起的地表反照率减小有利于城市热岛强度增加;(3)通过分析地表的长波辐射发现,在城市区域较小反照率情形下,城区的长波辐射始终比郊区大,有利于热岛的形成;同时也有利于城区近地层的风场辐合增加,对此次污染过程的发展是有利的。 相似文献
106.
Climatic impacts of historical wetland drainage in Switzerland 总被引:1,自引:0,他引:1
The effects of historical land-use and land-cover changes on the climate of the Swiss Plateau in the different seasons were
investigated. In the 19th century, a civil engineering project was initiated to reshape the lake and river system on the Swiss
Plateau in order to ban the frequent flooding during extreme weather events. The landscape modifications consisted primarily
of a conversion of wetlands with extended peat soils into a highly productive agricultural landscape. Historical maps (1800–1850)
served as a basis for the reconstruction of the past land use. The “Lokal-Modell” of the Consortium for Small-Scale Modelling
was used to conduct eight one-month long high-resolution simulations (1.5 × 1.5 km2) with present and past landscape conditions. The modified soil and surface properties led to distinctly altered energy and
moisture exchanges at the surface and as a consequence affected the local and regional climate. The climatic changes show
different characteristics and magnitudes in the cold (October – March) as compared to the warm season (April – September).
The landscape modifications led to an average daytime cooling between −0.12 °C (January) and −0.61 °C (April) and a night-time
warming of 0.19 °C−0.34 °C. The differences in the mean monthly temperatures show a warming of 0.1 °C−0.2 °C in the cold season
and a cooling of similar magnitude in most of the study area in the warm season. The modification of the radiation budget
and the surface energy balance distinctly affected the convective activity in the study area in the warm season, but had only
a weak effect on convectivity in the cold season. The cloud coverage in the warm season is therefore distinctly reduced compared
to the past. 相似文献
107.
中国东部水分收支的初步分析 总被引:7,自引:6,他引:7
利用中国160站降水资料、中国气象局提供的探空资料、NCEP/NCAR提供的再分析资料(简称NCEP资料)和ECMWF提供的再分析资料(简称ERA40资料), 根据水汽平衡方程, 估算了1990~1999年中国东部的陆表水分收支, 分析了华北、 长江流域和华南三个典型区域的陆表水分收支, 同时对NCEP、ERA40资料在东亚地区的陆表水分收支进行评估。结果表明, 在中国东部区域, 年平均和夏季是水汽汇区, 冬季降水与蒸发基本平衡;华北在年平均、夏季以及冬季均为水汽源区;长江流域在年平均、夏季及冬季均为水汽汇区;华南在年平均和冬季为弱水汽汇区, 夏季为水汽源区。两套再分析资料基本揭示出了上述特征。就区域平均的蒸发和降水的年际变化而言, 两套再分析资料的结果与观测都存在显著相关, 但估算的蒸发NCEP好于ERA40; 相对于气候态的定量比较而言, 由两套再分析资料得到的陆表水分收支距平(即降水减去蒸发的距平)的年际变化基本与观测一致。 相似文献
108.
As in other regions colonised from Europe within the last few centuries, Australia's vegetation and soils have been dramatically changed by clearing, cropping and grazing. In southeastern Australia, particularly on the Southern Tablelands, the impacts of European settlement are clearly manifested by channel incision. By using stratigraphic and documentary evidence, in conjunction with aerial photographs, sediment budgets for the post-settlement period have been constructed to define the fluxes and stores of sediment for each of the major geomorphic components of the 136 km2 catchment of Jerrabomberra Creek near Canberra. Using these budgets, and some plausible assumptions, it has been possible to approximate the history of both the sediment delivery ratio and sediment yield for this catchment. While the quantities estimated in this analysis are approximations, the trends through time are credible. Sediment yield increased rapidly to a peak after European settlement, and has returned to a level between the peak and the pre-European value. The delivery ratio has followed a similar trend. The most general conclusion to emerge is that in this landscape both the total sediment flux and the sediment yield of the catchment have been dominated by channel erosion. This result is contrary to the findings in many parts of the world where sheet and rill erosion dominates the fluxes. The soil conservation implication of these results is clear: to control off-site effects of erosion, the focus must be on the channels. 相似文献
109.
Estimation of groundwater recharge using the chloride mass-balance method, Pingtung Plain, Taiwan 总被引:4,自引:0,他引:4
Due to rapid economic growth in the Pingtung Plain of Taiwan, the use of groundwater resources has changed dramatically.
Over-pumping of the groundwater reservoir, which lowers hydraulic heads in the aquifers, is not only affecting the coastal
area negatively but has serious consequences for agriculture throughout the plain. In order to determine the safe yield of
the aquifer underlying the plain, a reliable estimate of groundwater recharge is desirable. In the present study, for the
first time, the chloride mass-balance method is adopted to estimate groundwater recharge in the plain. Four sites in the central
part were chosen to facilitate the estimations using the ion-chromatograph and Thiessen polygon-weighting methods. Based on
the measured and calculated results, in all sites, including the mountain and river boundaries, recharge to the groundwater
is probably 15% of the annual rainfall, excluding recharge from additional irrigation water. This information can improve
the accuracy of future groundwater-simulation and management models in the plain.
Received, April 1996 Revised, March 1997, November 1997 Accepted, March 1998 相似文献
110.
A. Y. Perelman 《Pure and Applied Geophysics》1978,116(6):1077-1088
Summary The scattering of electromagnetic radiation from soft particles has been studied by a new method which allows to transform the Mie series into a simplified form through the use of some auxiliary expansions derived in the Appendix of this article. This simplified form (eq. 1) converts into the Hulst and Rayleigh-Debye-Gans' formulae if the parameters of eq. I are properly restricted. A further simplified form (eq. II), improves the well-known Hulst approximation. 相似文献