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51.
52.
lINTR0DUCTIONSoiler0si0ncanbeaseriousproblemonsl0pinguplands0fthes0uthemUnitedStatesthatareintensivelycr0pped.Conservati0nprovisionsofthel985U.S.FarmBillmandateddevelopmentofaconservati0nplanonhighlyer0diblelands.Researchwasinitiatedinl9870na28-haareaattheA-E.Nels0nFarrninn0rthernMississippit0determineiftheconservati0nprovisionscouldbeachievedwhileprofitablygr0wingrowcropsincludingcott0n(GosSyPiumhirsutumL.),soybean(GlyciDemax(L.)Merr.),sorghum(SOrghumbicolor(L.)Moench),c0rn(Zeam… 相似文献
53.
llNTRODUCTIONIrrigationisimp0rtanttof00dpr0ducti0nthr0ughoutthew0rld.Irrigati0nisused0naboutl5theworld'scropland(KendalIandPimentel,l994)and5%ofthew0rld'sfoodproductionland,whichincludesrangelandandpermanentcr0pland(FAO,l998).However,irrigatedlandproducesmorethan30%ofthew0rld'sf0od(Tribe,1994),whichis2l/2timesasmuchperunitareacomparedt0n0n-irrigatedproducti0n(KendallandPimentel,1994).IntheUnitedStates,approximatelyl5theharvestedcr0plandisirrigated,butalmost40thet0talcr0pvalue… 相似文献
54.
以采自贺兰山的5个采样点的树轮宽度资料为基础,建立区域标准化年表和差值年表,发现区域差值年表中包含的年径流总量信息多于标准化年表,并最终用区域差值年表序列重建了贺兰山东麓过去259 a的年径流量。相关分析发现降水和温度变化对于树木年轮生长及贺兰山东麓河流年径流总量的形成均有重要影响,是本文从树木年轮重建年径流量的气候水文学基础。校准方程的相关系数为0.638,可解释校准期内年径流总量变化总方差的40.8%,交叉检验的误差缩减值达0.328。分析259 a重建年径流量的变化特征发现:(1)重建流量经历了12个枯水期(1751—1759年,1765—1771年,1788—1802年,1809—1820年,1835—1840年,1847—1855年,1860—1866年,1877—1884年,1899—1908年,1924—1932年,1962—1967年,1980—1994年)和位于其间及1995—2004年的14个丰水期,以平水年份出现最多,但259 a来年径流量的变化较为剧烈。(2)年径流总量出现了持续≥10 a的4次持续枯水期和4次持续丰水期;持续枯水期中以1788—1802年的枯水期强度最大(平均距平百分率-14.9%),而强度第二的持续枯水期(平均距平百分率-10.4%),持续时间也长达15 a(1980—1994年);持续丰水期中以1867—1876年的丰水期强度最大(平均距平百分率+17.9%)。 相似文献
55.
Based on previous research results on river re-distribution models, a modification on the effects of topographic slopes for a runoff parameterization was proposed and implemented to the NCAR's land sur face model (LSM). This modification has two aspects: firstly, the topographic slopes cause outflows from higher topography and inflows into the lower topography points; secondly, topographic slopes also cause decrease of infiltration at higher topography and increases of infiltration at lower topography. Then changes in infiltration result in changes in soil moisture, surface fluxes and then in surface temperature, and eventual ly in the upper atmosphere and the climate. This mechanism is very clearly demonstrated in the point bud gets analysis at the Andes Mountains vicinities. Analysis from a regional scale perspective in the Mackenzie GEWEX Study (MAGS) area, the focus of the ongoing Canadian GEWEX program, shows that the modi fied runoff parameterization does bring significant changes in the regional surface climate. More important ly, detailed analysis from a global perspective shows many encouraging improvements introduced by the modified LSM over the original model in simulating basic atmospheric climate properties such as thermodynamic features (temperature and humidity). All of these improvements in the atmospheric climate simulation illustrate that the inclusion of topographic effects in the LSM can force the AGCM to produce a more realistic model climate. 相似文献
56.
F. J. P. M. Kwaad 《地球表面变化过程与地形》1991,16(7):653-662
Monthly runoff and soil loss data of three fallow experimental plots are presented, comprising a summer and following winter season. The fallow plots were only tilled once, at the end of April. Summer runoff appeared to be controlled by rainfall intensity and conforms to the Horton model of overland flow generation. Winter runoff was primarily controlled by rainfall amount and conforms to the saturation or storage control model of runoff generation. Summer runoff volume was one fourth of winter runoff volume. Summer soil loss was twice as high as winter soil loss and was caused by high intensity, high energy rainfall. Winter soil loss was due to detachment limited erosion, caused by low intensity, low energy rainfall. Mean sediment concentration of winter runoff was one seventh of that of summer runoff. Implications for runoff and erosion of climatic change, involving increased rainfall amounts or intensities in summer or winter, are given. 相似文献
57.
A. Yair 《地球表面变化过程与地形》1990,15(7):597-609
This paper presents the results of sprinkling experiments conducted over the lower part of vegetated and crusted linear dunes as well as over flat playa surfaces that appear in the interdune corridors. Data obtained show that these two surface units respond quickly to rainstorms. Runoff generation can be expected for any storm exceeding 2-3 mm and runoff coefficients are high. When the topsoil algal crust, 1 to 2 mm thick, is removed from the surface of the dune, infiltration increases drastically and eliminates any possibility of runoff generation under present-day rainfall conditions. This data may be of great help in the understanding of the geomorphology and sedimentary sequence of the corridors separting linear dunes. 相似文献
58.
由于车由岛周海域水比较浅,上下层混合得比较充分,营养盐的垂直分布较均匀,但在水平方向上差别较大。各种营养盐受生物活动、降雨和陆地经流的影响,有明显的季节变化。活性磷、硝酸盐和亚硝酸盐的浓度在冬季最高,春季最低;氨氮和活性硅的浓度则相反,夏季最高,秋季最低。 相似文献
59.
不同来源水沙对黄河入海泥沙通量的影响 总被引:6,自引:2,他引:6
文中研究了黄河入海泥沙通量与流域上、中游不同来源区的水沙量之间的关系 ,并以年系列和洪水系列水文泥沙资料 ,建立了表达这一关系的经验统计模型。所建立的模型表明 ,来自不同来源区的泥沙 ,对于入海泥沙通量的影响是不同的。来自多沙细沙区的每 1t泥沙 ,输送入海的为 0 .85t(年系列 )和 0 .72t(洪水系列 ) ;而来自多沙粗沙区的每 1t泥沙 ,输送入海的仅为 0 .34t(年系列 )和 0 .2 1t(洪水系列 )。 70年代以来入海泥沙通量的减少 ,与多沙细沙区水土保持工作的开展有密切关系。将文中的模型与已建立的黄河流域水土保持减水、减沙模型相耦合 ,可以用来预测未来因人类活动和气候变化而使不同来源区的水沙进一步减少时 ,黄河入海泥沙通量的变化 相似文献
60.
Remote sensing is an important source of snow‐cover extent for input into the Snowmelt Runoff Model (SRM) and other snowmelt models. Since February 2000, daily global snow‐cover maps have been produced from data collected by the Moderate Resolution Imaging Spectroradiometer (MODIS). The usefulness of this snow‐cover product for streamflow prediction is assessed by comparing SRM simulated streamflow using the MODIS snow‐cover product with streamflow simulated using snow maps from the National Operational Hydrologic Remote Sensing Center (NOHRSC). Simulations were conducted for two tributary watersheds of the Upper Rio Grande basin during the 2001 snowmelt season using representative SRM parameter values. Snow depletion curves developed from MODIS and NOHRSC snow maps were generally comparable in both watersheds: satisfactory streamflow simulations were obtained using both snow‐cover products in larger watershed (volume difference: MODIS, 2·6%; NOHRSC, 14·0%) and less satisfactory streamflow simulations in smaller watershed (volume difference: MODIS, −33·1%; NOHRSC, −18·6%). The snow water equivalent (SWE) on 1 April in the third zone of each basin was computed using the modified depletion curve produced by the SRM and was compared with in situ SWE measured at Snowpack Telemetry sites located in the third zone of each basin. The SRM‐calculated SWEs using both snow products agree with the measured SWEs in both watersheds. Based on these results, the MODIS snow‐cover product appears to be of sufficient quality for streamflow prediction using the SRM in the snowmelt‐dominated basins. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献