全文获取类型
收费全文 | 13505篇 |
免费 | 1694篇 |
国内免费 | 3277篇 |
专业分类
测绘学 | 294篇 |
大气科学 | 4024篇 |
地球物理 | 1207篇 |
地质学 | 4731篇 |
海洋学 | 1641篇 |
天文学 | 5127篇 |
综合类 | 487篇 |
自然地理 | 965篇 |
出版年
2024年 | 39篇 |
2023年 | 135篇 |
2022年 | 354篇 |
2021年 | 398篇 |
2020年 | 414篇 |
2019年 | 535篇 |
2018年 | 414篇 |
2017年 | 453篇 |
2016年 | 455篇 |
2015年 | 520篇 |
2014年 | 786篇 |
2013年 | 930篇 |
2012年 | 782篇 |
2011年 | 973篇 |
2010年 | 938篇 |
2009年 | 1313篇 |
2008年 | 1245篇 |
2007年 | 1137篇 |
2006年 | 1018篇 |
2005年 | 944篇 |
2004年 | 778篇 |
2003年 | 666篇 |
2002年 | 546篇 |
2001年 | 483篇 |
2000年 | 420篇 |
1999年 | 373篇 |
1998年 | 303篇 |
1997年 | 168篇 |
1996年 | 157篇 |
1995年 | 119篇 |
1994年 | 128篇 |
1993年 | 122篇 |
1992年 | 61篇 |
1991年 | 69篇 |
1990年 | 40篇 |
1989年 | 33篇 |
1988年 | 33篇 |
1987年 | 11篇 |
1986年 | 21篇 |
1985年 | 29篇 |
1984年 | 27篇 |
1983年 | 21篇 |
1982年 | 21篇 |
1981年 | 17篇 |
1980年 | 13篇 |
1979年 | 4篇 |
1978年 | 6篇 |
1977年 | 19篇 |
1877年 | 1篇 |
1875年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
982.
哈巴特盖测区1/5万土壤地球化学测量发现了4个异常区,多元素组合异常多分布在黑云母二长花岗岩的内、外接触带上,土壤地球化学异常特征显示本区成矿是多期次的,多元素组合异常在露头矿和盲矿上方均有出现,且异常连续、浓集中心明显,异常的强度和规模大,呈带状、宽带状或面状产出。 相似文献
983.
河北西北部熔积岩特征及其地质意义 总被引:1,自引:0,他引:1
熔积岩是火山碎屑岩的一种特殊类型,由熔浆和未固结的湿沉积物两种组分掺杂混合而成。熔积岩的形成主要受炽热熔浆与未固结的湿沉积物接触时引起的淬碎或蒸汽爆炸作用以及寄主沉积物流体化作用控制,通常分布于熔岩流底部或前缘,也可分布于超浅成侵人体周围。据熔浆碎屑物的结构特征,冀西北熔积岩可分为流状和块状两种类型。流状熔积岩多是熔浆与细粒沉积物混合的结果,块状熔积岩大多与粗粒沉积物相关。正确鉴别熔积岩对确定沉积作用与岩浆作用的时序、研究盆地发展演化历史具有重要意义。 相似文献
984.
青藏高原加热对东亚地区夏季降水的影响 总被引:11,自引:4,他引:11
东亚地区降水主要集中在夏季,是亚洲夏季风系统的重要特征.本文利用NCEP再分析资料和CRU的降水资料,分析了青藏高原非绝热加热对东亚夏季降水的影响.结果表明,东亚地区夏季降水的分布形势与青藏高原非绝热加热变化有很好的相关关系.由于高原非绝热加热可在亚洲东部沿海地区强迫出类似Rossby波列的大气环流低频振荡结构,而此低频波可以影响到西太平洋副热带高压的形态和位置变化,从而使得东亚夏季降水的形势发生变化.而青藏高原非绝热加热的形态从春季到夏季有很好的持续性,春季高原加热与夏季东亚的降水形势分布也有很好的相关.本研究中采用的青藏高原非绝热加热指数可作为东亚夏季降水预测的一个指标,亚洲季风降水不仅受赤道太平洋海温的影响,青藏高原地区的非绝热加热对其也有显著的影响作用. 相似文献
985.
Thara V. Prabha Anandakumar Karipot Michael W. Binford 《Boundary-Layer Meteorology》2007,123(2):239-261
Large-eddy simulation is used to study secondary circulations in the convective boundary layer modulated as a result of horizontally
varying surface properties and surface heat fluxes over flat terrain. The presence of heat flux heterogeneity and its alignment
with respect to geostrophic wind influences the formation, strength and orientation of organized thermals. Results show boundary-attached
roll formation along heat flux maxima in the streamwise direction. The streamwise organization of the updrafts and downdrafts
formed downwind of heterogeneities leads to counter-rotating secondary circulations in the crosswind plane. The distribution
of resolved-scale pressure deviations shows large pressure gradients in the crosswind plane. Spanwise and vertical velocity
variances and heat flux profiles depict considerable spatial variability compared to a homogeneous forest simulation. Secondary
circulations are observed for various ambient wind scenarios parallel and perpendicular to heterogeneities. In the presence
of increased wind speed, thermals emerging from the heat flux heterogeneity are elongated, and organize along and downwind
of large-scale heterogeneity in the streamwise direction. Simulation with a reduced heat flux shows a shallower circulation
with a lower aspect ratio. Point measurements of heat flux inside the roll circulation could be overestimated by up to 15–25%
compared to a homogeneous case. 相似文献
986.
Based on the National Centers for Environmental Prediction and National Center for Atmospheric Research (NCEP/NCAR) reanalysis data from 1950-1999, interdecadal variability of the East Asian Summer Monsoon (EASM) and its associated atmospheric circulations are investigated. The EASM exhibits a distinct interdecadal variation, with stronger (weaker) summer monsoon maintained from 1950-1964 (1976-1997). In the former case, there is an enhanced Walker cell in the eastern Pacific and an anti-Walker cell in the western Pacific. The associated ascending motion resides in the central Pacific, which flows eastward and westward in the upper troposphere, descending in the eastern and western ends of the Pacific basin. At the same time, an anomalous East Asian Hadley Cell (EAHC) is found to connect the low-latitude and mid-latitude systems in East Asia, which strengthens the EASM. The descending branch of the EAHC lies in the west part of the anti-Walker cell, flowing northward in the lower troposphere and then ascending at the south of Lake Baikal (40°-50°N, 95°- 115°E) before returning to low latitudes in the upper troposphere, thus strengthening the EASM. The relationship between the EASM and SST in the eastern tropical Pacific is also discussed. A possible mechanism is proposed to link interdecadal variation of the EASM with the eastern tropical Pacific SST. A warmer sea surface temperature anomaly (SSTA) therein induces anomalous ascending motion in the eastern Pacific, resulting in a weaker Walker cell, and at the same time inducing an anomalous Walker cell in the western Pacific and an enhanced EAHC, leading to a weaker EASM. Furthermore, the interdecadal variation of summer precipitation over North China is found to be the south of Lake Baikal through enhancing and reducing strongly regulated by the velocity potential over the regional vertical motions. 相似文献
987.
使用中国科学院大气物理研究所大气科学和地球流体力学数值模拟国家重点实验室(LASG/IAP)发展的大气环流谱模式SAMIL(R42L9),进行了有、无青藏高原对亚洲夏季风北边缘影响的数值模拟。结果表明,青藏高原大地形对夏季风北边缘活动有重要影响。有(无)高原时,其东侧的偏南风较强(弱)、较深(浅),向北扩展偏北(南),有(不)利于引导和加强夏季风北上,使北边缘偏北(南);同时,西太平洋副热带高压偏北偏西(偏南偏东),也有(不)利于夏季风向北深入我国大陆,从而使夏季风北边缘偏北(南)。与之相对应的夏季风降水区也偏北(南)。 相似文献
988.
应用遥感技术预测油气勘探靶区具有低成本、高效率的特点。目前有直接和间接两种油气遥感方法用于预测油气勘探靶区。本文简单介绍了这两种方法的原理,重点对遥感影像中的线-环影像构造异常和烃渗漏异常所表现的特征进行了全面的总结,最后对遥感技术在预测油气勘探靶区的应用前景进行了展望。 相似文献
989.
990.
Mistreatment of the economic impacts of extreme events in the Stern Review Report on the Economics of Climate Change 总被引:1,自引:0,他引:1
The Stern Review on the Economics of Climate Change has focused debate on the costs and benefits of alternative courses of action on climate change. This refocusing has helped to move debate away from science of the climate system and on to issues of policy. However, a careful examination of the Stern Review's treatment of the economics of extreme events in developed countries, such as floods and tropical cyclones, shows that the report is selective in its presentation of relevant impact studies and repeats a common error in impacts studies by confusing sensitivity analyses with projections of future impacts. The Stern Review's treatment of extreme events is misleading because it overestimates the future costs of extreme weather events in developed countries by an order of magnitude. Because the Stern Report extends these findings globally, the overestimate propagates through the report's estimate of future global losses. When extreme events are viewed more comprehensively the resulting perspective can be used to expand the scope of choice available to decision makers seeking to grapple with future disasters in the context of climate change. In particular, a more comprehensive analysis underscores the importance of adaptation in any comprehensive portfolio of responses to climate change. 相似文献