全文获取类型
收费全文 | 1365篇 |
免费 | 255篇 |
国内免费 | 385篇 |
专业分类
测绘学 | 11篇 |
大气科学 | 780篇 |
地球物理 | 134篇 |
地质学 | 459篇 |
海洋学 | 107篇 |
天文学 | 12篇 |
综合类 | 90篇 |
自然地理 | 412篇 |
出版年
2024年 | 3篇 |
2023年 | 19篇 |
2022年 | 23篇 |
2021年 | 27篇 |
2020年 | 30篇 |
2019年 | 45篇 |
2018年 | 37篇 |
2017年 | 28篇 |
2016年 | 43篇 |
2015年 | 58篇 |
2014年 | 60篇 |
2013年 | 80篇 |
2012年 | 62篇 |
2011年 | 76篇 |
2010年 | 74篇 |
2009年 | 72篇 |
2008年 | 95篇 |
2007年 | 129篇 |
2006年 | 98篇 |
2005年 | 99篇 |
2004年 | 97篇 |
2003年 | 94篇 |
2002年 | 84篇 |
2001年 | 86篇 |
2000年 | 83篇 |
1999年 | 59篇 |
1998年 | 64篇 |
1997年 | 58篇 |
1996年 | 50篇 |
1995年 | 40篇 |
1994年 | 33篇 |
1993年 | 26篇 |
1992年 | 18篇 |
1991年 | 19篇 |
1990年 | 5篇 |
1989年 | 12篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有2005条查询结果,搜索用时 15 毫秒
81.
赤道西太平洋末次盛冰期以来的浮游有孔虫氧碳稳定同位素记录 总被引:6,自引:0,他引:6
对西太平洋暖池核心区MD01—2386柱状样最上部5m进行了高分辨率的浮游有孔虫Globigerinoides ruber和Pulleniatina obliquiloculata的氧、碳稳定同位素分析,结合AMS^14C测年,研究表明其属于末次盛冰期-全新世的沉积。赤道西太平洋海区末次盛冰期以来δ^18O值显著降低,但有几次回返事件。表层浮游有孔虫G.ruber比次表层温跃层属种P.obliquiloculata对于环境变化的响应要快,但后者变化的幅度较大。这两个种的氧、碳同位素差值反映出温跃层深度自末次盛冰期以来逐渐加深,并存在周期性的回返事件,说明西太平洋暖池晚第四纪冰期旋回存在气候不稳定性。 相似文献
82.
83.
通过内蒙古地区近46 a降水和潜在蒸散量以及湿润度在气温突变前后的倾向率和差值变化分析,得出该区域主要植被类型干湿环境演变的时空变化特征。研究结果表明:降水在气温突变前“东增西减”,突变后呈相反的变化趋势。46 a降水倾向率增加区域主要集中在呼伦贝尔市东部和乌兰察布市以西大部地区;潜在蒸散量在气温突变前呈减少趋势,突变后有增加趋势,突变后潜在蒸散量明显小于突变前。内蒙古46 a潜在蒸散量倾向率大部地区偏小,偏大区域仅存在于中东部偏北地区,气温突变后全区大部地区存在明显的“蒸发悖论”;大兴安岭西麓和乌兰察布市以西地区突变后湿润度增加明显,暖湿的气候环境有利于当地植被建设和生态恢复,内蒙古东南部、呼伦贝尔草原和锡林郭勒盟草原区有暖干化趋势,上述草原区存在潜在退化风险。 相似文献
84.
Sandra M. Cahuin Luis A. Cubillos Miguel
iquen Rubn Escribano 《Estuarine, Coastal and Shelf Science》2009,84(4):591-597
The recruitment rate of Peruvian anchoveta, Engraulis ringens, was studied to test the hypothesis that long-term environmental variation (regime shifts) had a significant impact on density-dependent processes governing the anchovy recruitment during the period 1963–2004. On the basis of previous defined regimes and turning points for the Humboldt Current System, we identified two groups of years for increased recruitment of anchoveta (1963–1971 and 1986–2004), and one unfavorable period (1972–1985). A common intercept and significantly different slopes were found when the recruitment rate was plotted as a function of the spawning stock biomass during those groups of years, suggesting that density-dependent effects on recruitment were affected during different climate regimes. The favorable (unfavorable) regime was characterized by higher (lower) zooplankton volumes, and with a higher frequency of colder (warmer) waters. Dome-shaped relationships between recruitment rate, spawning stock biomass and SST, were detected with a Generalized Additive Model for the favorable regime. Thus, recruitment could be explained by non-linear effects of environmental variables. Ultimately, climatic regimes are affecting the density-dependent effects on recruitment of anchoveta and the mechanisms involved may be associated with changes in the carrying capacity of the spawning habitat of anchoveta off Peru, which in turn are related with the effects of cold and warm regimes. 相似文献
85.
????13??T/P???????????????????????????????????????????????????????????????????????????????????Ubari-Murzuq????????????????????????????????????????′????????????????????????С?????Ku???κ?C???ι?????????????????????????????P???????仯?????? 相似文献
86.
白银市农业气候资源特征及开发应用 总被引:4,自引:0,他引:4
白银市农业气候资源具有日照充足,降水少而变率大,气象灾害种类多、危害重的特点。提出了气候资源开发与应用的途径。 相似文献
87.
川渝地区夏季降水变化气候特征分析 总被引:2,自引:0,他引:2
利用川渝地区34站1960—2006年共计47年的逐月降水量资料,采用经验正交函数(BOF)分解、旋转经验正交函数(REOF)分解、小波分析等方法详细讨论了川渝地区夏季降水量的时空变化特征。结果表明:川渝地区夏季降水量时空分布不均,川渝地区夏季降水量可以分为3个区,分别是川西高原区、盆地中部区和盆地东部区。近50年来,川渝地区夏季降水量具有显著不同的年代际变化特征,川西高原和盆地东部夏季降水量长期变化呈增加的趋势,而盆地中部呈减少的趋势。川渝各区夏季降水量具有显著不同的多时间尺度的周期变化特征,其中川西高原具有准15年和准5年的周期变化特征,盆地中部具有准14年、准6年和准3年的周期变化,盆地东部具有准16年、准8年和准3年的周期变化特征。 相似文献
88.
Agriculture development-induced surface albedo changes and climatic implications across northeastern China 总被引:1,自引:0,他引:1
To improve the understandings on regional climatic effects of past human-induced land cover changes,the surface albedo changes caused by conversions from natural vegetation to cropland were estimated across northeastern China over the last 300 years,and its climatic effects were simulated by using the Weather Research and Forecasting (WRF) model.Essential natural vegetation records compiled from historical documents and regional optimal surface albedo dataset were used.The results show that the surface albedo decreased by 0.01-0.03 due to conversions from grassland to cropland in the Northeast China Plain and it increased by 0.005-0.015 due to conversions from forests to cropland in the surrounding mountains.As a consequence,in the Northeast China Plain,the surface net radiation increased by 4-8 W/m 2,2-5 W/m 2,and 1-3 W/m 2,and the climate was therefore warmed by 0.1℃-0.2℃、0.1℃-0.2℃、 0.1℃-0.3 ℃ in the spring,autumn and winter,respectively.In the surrounding mountain area,the net radiation decreased by less than 1.5 W/m 2,and the climate was therefore cooled too slight to be detected.In summer,effects of surface albedo changes on climate were closely associated with moisture dynamics,such as evapotranspiration and cloud,instead of being merely determined by surface radiation budget.The simulated summer climatic effects have large uncertainties.These findings demonstrate that surface albedo changes resulted in warming climate effects in the non-rainy seasons in Northeast China Plain through surface radiation processes while the climatic effects in summer could hardly be concluded so far. 相似文献
89.
Characteristics of Spatial and Temporal Variations of Monthly Mean Surface Air Temperature over Qinghai-Tibet Plateau 总被引:1,自引:0,他引:1
ZHANG Qianggong KANG Shichang YAN Yuping 《中国地理科学(英文版)》2006,16(4):351-358
1 Introduction The Qinghai-Tibet Plateau, known as the highest plateau with the most complex topography in the world, covers an area of more than 200km2, with a mean elevation of more than 4000m a.s.l. (Ye and Gao, 1979). Surrounded by the Earth’s highest mountains, such as the Himalayas, Pamir, Kunlun Mountains, the plateau plays a significant role in climate change in China even in the world, thus attracted great attention of researchers. Up to now, many achievements have been gained by… 相似文献
90.
1INTRODUCTIONIrrigated ricefieldsarecharacterizedbylargespatialandtemporalvariationsin CH4 emissiontotheatmo-sphere.Accordingly,thereisagreatuncertaintyintheestimate ofCH4 emissionsfromricefields.GreateffortshavebeenmadetoestimatetheCH4 emissionsfromricefieldsandseveralapproacheshavebeendeveloped.TherepresentativemethodsincludetheIPCC(Inter-governmentPanelofClimateChange)region-specificemissionfactormethodandthemodelcalculationmethod.Toimprovethecalculationaccuracy,theIPCCmethodreq… 相似文献