全文获取类型
收费全文 | 9214篇 |
免费 | 1873篇 |
国内免费 | 2574篇 |
专业分类
测绘学 | 657篇 |
大气科学 | 2168篇 |
地球物理 | 2362篇 |
地质学 | 4829篇 |
海洋学 | 996篇 |
天文学 | 464篇 |
综合类 | 1057篇 |
自然地理 | 1128篇 |
出版年
2024年 | 44篇 |
2023年 | 188篇 |
2022年 | 438篇 |
2021年 | 535篇 |
2020年 | 418篇 |
2019年 | 458篇 |
2018年 | 593篇 |
2017年 | 489篇 |
2016年 | 559篇 |
2015年 | 525篇 |
2014年 | 550篇 |
2013年 | 584篇 |
2012年 | 529篇 |
2011年 | 536篇 |
2010年 | 550篇 |
2009年 | 553篇 |
2008年 | 509篇 |
2007年 | 479篇 |
2006年 | 384篇 |
2005年 | 374篇 |
2004年 | 276篇 |
2003年 | 252篇 |
2002年 | 221篇 |
2001年 | 265篇 |
2000年 | 298篇 |
1999年 | 410篇 |
1998年 | 379篇 |
1997年 | 379篇 |
1996年 | 322篇 |
1995年 | 239篇 |
1994年 | 261篇 |
1993年 | 229篇 |
1992年 | 172篇 |
1991年 | 120篇 |
1990年 | 112篇 |
1989年 | 92篇 |
1988年 | 89篇 |
1987年 | 48篇 |
1986年 | 49篇 |
1985年 | 29篇 |
1984年 | 24篇 |
1983年 | 21篇 |
1982年 | 23篇 |
1981年 | 15篇 |
1980年 | 8篇 |
1979年 | 8篇 |
1976年 | 2篇 |
1975年 | 5篇 |
1960年 | 2篇 |
1958年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
91.
浙江海岸侵蚀现象普遍存在。基岩海岸海蚀地貌发育,因其组成物质抗冲蚀能力强,岸线后退不明显;砂砾质海岸普遍发生侵蚀,尤其是无计划的人工挖沙,造成沙滩减小或消失;淤泥质海岸大多处于缓慢的淤涨状态,但由于自然条件的改变和人为作用的影响,某些岸段发生侵蚀,特别是受到台风暴潮的影响,岸线在短时间内出现大规模后退和滩面下蚀。侵蚀岸段主要见于杭州湾北岸澉浦至金丝娘桥岸段,杭州湾南岸临山至西三岸段及瓯江口北岸盘石至黄华岸段。淤泥质海岸后缘为滨海平原,组成物质为粘土质粉砂,抗冲蚀能力弱,为防止和减轻海岸侵蚀,沿岸建造各类海岸工程(海塘、丁坝、导堤等),提高防潮抗浪能力,在朝滩种植大米草,互花米草,消浪促淤明显。另外,在海岸开发活动中,应加强海岸侵蚀监测和综合管理。 相似文献
92.
本文利用最大熵谱分别计算了南极4个区海冰和西北太平洋台风发生频数的变化周期,并对前3年的南极海冰强弱和当年的台风发生频率数进行了逐月时间序列相关分析。 相似文献
93.
本文是根据南极“八五”国家攻关课题中的“南极海冰监测和预报”的考核目标,实现为南极考察船在 冰区中航行提供精确和清晰的冰图和预报。 相似文献
94.
Annual and interannual variations of large-scale circulation over the tropics as revealed from OLR data 总被引:1,自引:0,他引:1
In this study, the outgoing longwave radiation (OLR) data of eight years have been used to investigate the annual and interannual variations of large-scale circulation over the tropics. The results of EOF analysis indicate that the first three eigenvectors reflect the essential features in OLR annual variation. However, they contribute little to the interannual change. In comparison, the fourth to the sixth components have very large year-to-year variations. The pronounced anomalies are located over the tropics with east-west dipole pattern. It implies that ENSO events are related closely to the variation of the Walker circulation. 相似文献
95.
96.
97.
The steady response of the ventilated thermocline to an increase in Ekman pumping is investigated, focusing on the effect
of the mixed layer depth distribution on the subsurface density anomaly. We consider only the subtropical gyre, and the mixed
layer is assumed to be deep in the northwest and shallow elsewhere with a narrow transition zone separating the deep and shallow
mixed layer regions. At the intersection of this narrow transition zone and the outcrop line, low potential vorticity fluid
is subducted into and ventilates the thermocline. In such a situation, an enhancement of the Ekman pumping confined to the
northern subtropical gyre leads to pronounced subsurface cold anomalies in the southern subtropics, which is free of anomalous
forcing. These density anomalies are much greater than those that occur when either the mixed layer depth is zonally uniform
or the Ekman pumping is enhanced in the whole subtropical gyre. They are caused by anomalous changes in the trajectory of
the low potential vorticity fluid in response to anomalous Sverdrup flow.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
98.
The light curved in the CM field 总被引:1,自引:0,他引:1
In this paper we introduce the CM field in Sections 2 and 3 based on the paper by Wang and Peng (1985), and calculate the light curved in the CM field in Section 4. The result shows thatP makes CM larger than C at
, and smaller at
. Under a special circumstance which source, CM lens, and observer are in the same line, if we get |
0=0
,
and |
=/2
, we can determine theP(M) andQ(M) of the CM lens,M is the mass of the CM lens. 相似文献
99.
100.
Geochronological studies on the crust-derived Tianmenshan pluton were undertaken by SHRIMP zircon U-Pb dating and Ar-Ar dating of biotite, muscovite and K-feldspar, giving a petrogenetic age of 167 Ma. Owing to the closure systems in different minerals, the cooling history of the pluton can be determined with an age-temperature diagram. The late hydrothermal event has been recognized, which is related probably with mineralization. In terms of the comparative geochronological and petrologic records, it is concluded that there are some constrains on tectonic evolution and that the formation of the Tianmenshan pluton proceeded in a transition period from Indosinian post-orogeny extension to strong compressive tectonics. And the timing of the hydrothermal event matches the compressive climax of the Yanshanian orogeny. The temporal gap between granite emplacement and wolframite mineralization could last 10-20 Ma owing to the low cooling rate of the pluton. 相似文献