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621.
Soil column experiments showed that a surficial sodic soil is efficiently reclaimed using freshwater, after the addition of
saturated gypsum solution. Gypsum application in the field was beneficial in terms of maintaining high soil permeability,
increased water infiltration and neutral pH after a rainfall event. In the present paper, two different reclamation techniques for the plough layer of a sandy loam sodic
soil were tested in laboratory columns, 25 cm long and 10 cm in diameter; the first using freshwater alone and the second
using a saturated gypsum solution. The dynamics of salt removal were studied by continuous analysis of the water drained from
the bottom of the columns. When freshwater was used, sodium presented the lower removal rate and adversely affected soil permeability.
When gypsum solution was used, calcium was present in the flushing solution and the effect of sodium dominance on clay dispersion
and soil clogging was limited. The results presented in this study are of practical importance with respect to the reclamation
of sodic soils found in the coastal area of the east Nestos Delta, Greece, where freshwater is limited, due to seawater intrusion,
and saline groundwater is used for irrigation. 相似文献
622.
The measurement of surface energy balance over a land surface in an open area in Bangalore is reported. Measurements of all
variables needed to calculate the surface energy balance on time scales longer than a week are made. Components of radiative
fluxes are measured while sensible and latent heat fluxes are based on the bulk method using measurements made at two levels
on a micrometeorological tower of 10m height. The bulk flux formulation is verified by comparing its fluxes with direct fluxes
using sonic anemometer data sampled at 10Hz. Soil temperature is measured at 4 depths. Data have been continuously collected
for over 6 months covering pre-monsoon and monsoon periods during the year 2006. The study first addresses the issue of getting
the fluxes accurately. It is shown that water vapour measurements are the most crucial. A bias of 0.25% in relative humidity,
which is well above the normal accuracy assumed by the manufacturers but achievable in the field using a combination of laboratory
calibration and field intercomparisons, results in about 20W m−2 change in the latent heat flux on the seasonal time scale. When seen on the seasonal time scale, the net longwave radiation
is the largest energy loss term at the experimental site. The seasonal variation in the energy sink term is small compared
to that in the energy source term. 相似文献
623.
624.
625.
高空槽对9711号台风变性加强影响的数值研究 总被引:26,自引:9,他引:26
9711号台风Winnie是一个在中国大陆长久维持(2—3 d)并产生强降水的热带气旋(TC),在其深入内陆过程中变性加强为一个温带气旋。用MM5V3对不同强度高空槽影响下Winnie的变性加强过程进行了数值研究。结果表明:(1)Winnie变性加强过程表现为强锋面侵入台风内部、冷空气包裹台风中心、一个温带气旋在近地层锋面上强烈发展的过程;(2)Winnie在陆上的变性加强与西风带高空槽的强度密切相关。TC与不同强度高空槽相互作用过程中,较深槽携带较强冷平流、正涡度平流以及较强的槽前高空辐散,从而有利于TC的维持和变性发展。数值试验中,高空槽越强,Winnie变性加强越明显,温带气旋的发展越快;(3)模拟结果的位涡分析表明,Winnie的温带变性发展与对流层高层正位涡下传、低层锋区和TC低压环流三者之间的相互作用有关。 相似文献
626.
Tomoko Kyuka Satomi Yamaguchi Yusuke Inoue Kattia Rubi Arnez Ferrel Hideto Kon Yasuyuki Shimizu 《地球表面变化过程与地形》2021,46(7):1225-1237
Previous studies have demonstrated that riparian vegetation leads to channel transformation from a multi-bar to a single-thread channel planform. However, it still remains unclear how the presence of pioneer and mature vegetation affects the morphodynamics of single-thread meandering rivers. In this study, we therefore investigated the effects of vegetation strength on the morphodynamic evolution of an experimental meandering channel. Three physical laboratory experiments were conducted using alfalfa sprouts in different life stages – no vegetation, immature vegetation, and mature vegetation – to simulate different floodplain vegetation strengths. Our results demonstrate that vegetation plays a key role in mediating bank erosion and point-bar accretion, and that this is reflected in both the evolution of the channel bed as well as the sediment flux. The presence of mature vegetation maintained a deep, single-thread channel by reducing bank erosion, thereby limiting both channel widening and sediment storage capacity. Conversely, an unvegetated floodplain led to channel widening and high sediment storage capacity. Channel evolution in the unvegetated scenario showed that the active sediment supply from outer bank erosion led to slightly delayed point-bar accretion on the inner banks due to helical flow, deflecting the surface flow toward the outer banks and causing further erosion. In contrast, in the immature vegetation scenario, the outer banks were also initially eroded, but point-bar accretion did not clearly progress. This led to a greater width-to-depth ratio, resulting in a transition from a single- to a multi-thread channel with minor flow paths on the floodplain. The experimental results suggest that the eco-morphodynamic effects of young (low-strength) and mature (high-strength) vegetation are different. Notably, low-strength, early-stage vegetation increases channel complexity by accelerating both channel widening and branching, and therefore might promote the coexistence of multi-bars and pioneer vegetation. 相似文献
627.
增温对华北冬小麦生产影响的试验研究 总被引:8,自引:0,他引:8
为了探索和验证未来地表气温升高对中国冬小麦生产的影响,了解冬小麦生长发育和产量对增温响应的基本特征,在田间条件下采用红外辐射器增温的方法(FATI)对冬小麦全生育期进行昼夜增温处理,分析了增温对冬小麦生长发育和产量构成及其耗水量的影响。结果表明,全生育期增温使冬小麦返青期显著提前,冬后生育阶段整体前移10d以上,全生育期天数减少,但营养生长时间大幅增加,开花至乳熟时间延长,乳熟至成熟时间缩短;在偏冷年份,增温处理保障了小麦的正常分蘖和生长,株高显著提高,有效穗数比对照增加27.4%,籽粒产量比对照大幅增加;在偏暖年份,增温导致小麦穗分化时间延长,穗粒数增加,灌浆中后期遭受高温危害,千粒重显著降低,产量下降;增温致使冬小麦生产耗水量增加。就华北冬小麦而言,冬季及早春一定幅度的升温有利于小麦生产,但增幅过大可能会导致不利结果;而春末夏初升温对小麦生产是不利的。 相似文献
628.
F. Nozzoli 《Astroparticle Physics》2011,35(4):165-169
DAMA and CoGeNT annual modulation data and, CDMS-II, EDELWEISS-II, CRESST excesses of events over the expected background are reanalyzed in terms of a dark matter particle signal considering the case of a rotating halo. It is found that the configurations of very high mass dark matter particles in a corotating cold flux are favored by data. A similar high-mass/low-velocity solution could be of interest in the light of the positron/electron excess measured by PAMELA and Fermi LAT in cosmic rays. 相似文献
629.
New evidences on the climatic causes of the formation of the spring persistent rains over southeastern China 总被引:2,自引:0,他引:2
The spring persistent rains (SPR) over southeastern China (SEC) are a unique synoptic and
climatic phenomenon in East Asia. A former study has found that the southwesterly flow which lies on
the southeastern flank of the Tibetan Plateau (TP) is one of the deflected westerly flows of the TP,
and it is suggested to be the direct climatic cause of SPR. This study found that the southwesterly
flow is also highly correlated with the sensible heating of the southeastern TP in interannual
variability, in addition to having a high correlation in seasonal variability. These facts suggest
that the thermal forcing of the TP is another important climatic cause of SPR. Numerical sensitivity
experiments further prove that the mechanical and thermal forcings of the TP are the climatic causes
of the formation of the SPR. On the other hand, the Nanling Mountains and Wuyi Mountains (NWM) over
southeastern China not only increase the SPR precipitation amount evidently, but also make the SPR
rain belt move to the south by blocking the strong southwesterly flow. 相似文献
630.
Stuart Crampin 《Geophysical Journal International》1991,107(1):185-189
b
Current earthquake prediction experiments investigate behaviour before potentially large earthquakes. There is some evidence that comparatively small typical events in isolated swarms of earthquakes may have precursory behaviour similar to that before much larger earthquakes in more complicated areas of seismicity. Such typical events in isolated swarms frequently recur with similar magnitudes in similar locations with repetition times sometimes as little as a few days. It is argued that monitoring such typical events in isolated swarms could be an effective way to gain experience of precursory activity, and might well be a good guide for investigations of precursors to large earthquakes. 相似文献
Current earthquake prediction experiments investigate behaviour before potentially large earthquakes. There is some evidence that comparatively small typical events in isolated swarms of earthquakes may have precursory behaviour similar to that before much larger earthquakes in more complicated areas of seismicity. Such typical events in isolated swarms frequently recur with similar magnitudes in similar locations with repetition times sometimes as little as a few days. It is argued that monitoring such typical events in isolated swarms could be an effective way to gain experience of precursory activity, and might well be a good guide for investigations of precursors to large earthquakes. 相似文献