全文获取类型
收费全文 | 1959篇 |
免费 | 438篇 |
国内免费 | 512篇 |
专业分类
测绘学 | 219篇 |
大气科学 | 282篇 |
地球物理 | 566篇 |
地质学 | 1149篇 |
海洋学 | 225篇 |
天文学 | 44篇 |
综合类 | 230篇 |
自然地理 | 194篇 |
出版年
2024年 | 8篇 |
2023年 | 49篇 |
2022年 | 112篇 |
2021年 | 135篇 |
2020年 | 137篇 |
2019年 | 141篇 |
2018年 | 135篇 |
2017年 | 133篇 |
2016年 | 121篇 |
2015年 | 139篇 |
2014年 | 139篇 |
2013年 | 137篇 |
2012年 | 124篇 |
2011年 | 106篇 |
2010年 | 140篇 |
2009年 | 130篇 |
2008年 | 116篇 |
2007年 | 116篇 |
2006年 | 91篇 |
2005年 | 71篇 |
2004年 | 76篇 |
2003年 | 57篇 |
2002年 | 81篇 |
2001年 | 70篇 |
2000年 | 60篇 |
1999年 | 60篇 |
1998年 | 42篇 |
1997年 | 26篇 |
1996年 | 17篇 |
1995年 | 19篇 |
1994年 | 23篇 |
1993年 | 12篇 |
1992年 | 18篇 |
1991年 | 15篇 |
1990年 | 11篇 |
1989年 | 6篇 |
1988年 | 8篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1958年 | 1篇 |
1954年 | 3篇 |
排序方式: 共有2909条查询结果,搜索用时 7 毫秒
81.
82.
EGM96和EGM2008地球重力场模型计算弹道扰动引力的比较 总被引:2,自引:2,他引:0
给出了利用地球重力场模型计算扰动引力以及重力场模型截断误差的公式,计算了36阶、360阶、2 160阶地球重力场模型在径向和水平方向的截断误差,并对36阶、360阶的EGM96和EGM2008重力场模型计算的弹道扰动引力矢量进行了分析和比较.结果表明,采用重力场模型计算扰动引力时,模型阶数和弹道点的高度越低,模型截断误差越大;EGM96和EGM2008模型的一致性随着模型阶数的升高而逐渐降低.总体来看,EGM2008模型的精度要好于EGM96模型. 相似文献
83.
���ھ�������ʵ��۲�ȶ� 总被引:2,自引:0,他引:2
???FG5???????????????????????2008??1?????й??????????о?????3053????????????????????????о?????????????????FG5-214??FG5-232???н???????????????????????????????????????н????????????????????????????????????2~3????10 -8 ms -2?? 相似文献
84.
The pathological changes of hemocytes in the haemolymph and hepatopancreas were examined in experimentally and naturally WSSV
(white spot syndrome virus) infected Fenneropenaeus chinensis. The results showed that the pathological manifestations of hemocytes were similar among moribund shrimps infected via injection,
feeding and by nature. Firstly, the total hemocyte counts (THCs) in WSSV-infected shrimp were significantly lower than those
in healthy shrimp. Secondly, necrotic, broken and disintegrated cells were often observed, and a typical hematolysis was present
in the haemolymph smear of WSSV-infected shrimp. Thirdly, necrosis and typical apoptosis of hemocytes were detected with TEM
in the peripheral haemolymph of WSSV-infected shrimp. Hyalinocytes and semi-granulocytes with masses of WSSVs in their nuclei
often appeared, whereas no granular hemocytes with WSSV were found in the hepatopancreas of moribund infected shrimps. All
our results supported that hemocytes were the main target cells of WSSV, and hyalinocytes and semigranular hemocytes seemed
to be more favorable for WSSV infection in F. chinensis. 相似文献
85.
The calibration of sedimentary rock absolute dates is one of the difficulties in sedimentological and stratigraphic research. Since strontium(Sr) resides in seawater much longer(≈106 a) than the seawater intermixing time(≈103 a), the Sr isotopic composition of global seawater is uniform at any time and results in a stable system throughout geological history,based on which a global Sr isotope composition dating database has been established for age-calibration of marine strata.The Permian stratigraphic sections in the northern part of the Upper Yangtze block, southern China, record continuous marine sediments with clear stratigraphic boundaries and is suitable for stratigraphic dating of Sr isotopes. Based on sampling and Sr isotopic compositions of Permian carbonate strata in the northern part of the Upper Yangtze, a Permian Sr isotope evolution curve was established. According to the basic principles of Sr isotope stratigraphy, the global Strontium isotope age database can be used to calibrate the Permian stratigraphic dates in the northern Upper Yangtze. The results show that the Sr isotope evolution curves for the marine carbonate rocks in the Permian stratigraphic section of the Upper Yangtze present a decreasing trend from the mid-Qixia stage(P2) to the mid-Wujiaping stage(P3), and then rise from the middle Wujiaping stage to the end of Changxing stage(P3). When the Permian Sr-isotope evolution curve is compared with the global Sr isotope evolution curve in the northern Upper Yangtze, the two are consistent in their long-term evolutionary trend, indicating that Permian global geological events are important controlling factors for the composition and evolution of Sr isotopes. The 87 Sr/86 Sr value decreased gradually in the background of large-scale regressions at the turn of middle to late Permian period, revealing that the Emeishan basalt eruption occurred near the Maokou/Wujiaping boundary(GLB). Srisotope stratigraphy dating was performed on the boundaries of the Qixia Formation/Maokou Formation, Maokou Formation/Wujiaping Formation(GLB), Wujiaping Formation/Changxing Formation(WCB) and the Permian/Triassic(PTB) using the Global Strontium Isotope Age Database. The results are 270.4 Ma, 261.2 Ma, 254.5 Ma and 249.7 Ma,respectively. Based on this, the eruption age of the Emeishan basalts is defined at about 261.2 Ma., which is more coincident with that acquired from other previous dating methods on the eruption age of the Emeishan basalts, and therefore proves that the application of Sr isotopic stratigraphy to dating marine sedimentary units is an effective method. 相似文献
86.
87.
台湾海峡海表面温度的遥感反演及精度检验 总被引:2,自引:0,他引:2
海表面温度(SST)是海洋-大气系统中一个十分关键的物理量。SST为海洋学课题的研究提供了一种直观的指示量[1],在海洋捕捞中SST是寻找中心渔场的指标之一,可为渔业部门提供鱼类的回游路线和渔场的位置信息[2]。SST制约着海面和大气的热量、动量和水汽交换,是研究大气环流和气候变化[3]甚至台风移动路径[4]等气象学课题的一个重要因子。因此,SST在海洋学和气象学研究中占有非常重要的地位,此外SST对海洋运输、海洋污染、海上油气资源开发、海滨核电站建设等方面的影响近年来也倍受关注。 相似文献
88.
89.
90.
地磁日变改正数据的合理选取直接关系到海洋磁测的成果精度。通过在南海南部海域布放的一个4 000m长的地磁观测潜标及同步开展的磁力测量,并在收集周边陆域地磁台站数据的基础上,对水体中获得的地磁日变观测数据和水面磁测数据进行综合分析和研究,得到几点认识:(1)浅水海域获得的日变观测数据用于海洋磁测数据处理时,其测量准确度比深水海域的好,且与陆域地磁台站数据曲线的一致性要高;(2)船磁校正曲线是否对称与地磁日变观测数据的合理选取密切相关;(3)在远海区磁测时,为确保详尽记录局部磁扰,建议海底地磁日变观测站应布放于靠近工区、水深较浅的水体之中。 相似文献