全文获取类型
收费全文 | 4141篇 |
免费 | 982篇 |
国内免费 | 1512篇 |
专业分类
测绘学 | 87篇 |
大气科学 | 29篇 |
地球物理 | 864篇 |
地质学 | 4851篇 |
海洋学 | 231篇 |
天文学 | 26篇 |
综合类 | 348篇 |
自然地理 | 199篇 |
出版年
2024年 | 29篇 |
2023年 | 57篇 |
2022年 | 171篇 |
2021年 | 178篇 |
2020年 | 169篇 |
2019年 | 236篇 |
2018年 | 184篇 |
2017年 | 190篇 |
2016年 | 219篇 |
2015年 | 238篇 |
2014年 | 292篇 |
2013年 | 239篇 |
2012年 | 327篇 |
2011年 | 275篇 |
2010年 | 214篇 |
2009年 | 277篇 |
2008年 | 252篇 |
2007年 | 252篇 |
2006年 | 294篇 |
2005年 | 220篇 |
2004年 | 248篇 |
2003年 | 234篇 |
2002年 | 190篇 |
2001年 | 212篇 |
2000年 | 232篇 |
1999年 | 188篇 |
1998年 | 185篇 |
1997年 | 143篇 |
1996年 | 119篇 |
1995年 | 135篇 |
1994年 | 85篇 |
1993年 | 88篇 |
1992年 | 63篇 |
1991年 | 45篇 |
1990年 | 43篇 |
1989年 | 37篇 |
1988年 | 16篇 |
1987年 | 25篇 |
1986年 | 15篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1979年 | 6篇 |
1978年 | 1篇 |
1973年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有6635条查询结果,搜索用时 517 毫秒
231.
232.
233.
Ryo Sugimoto Akihide Kasai Toshihiro Miyajima Kouichi Fujita 《Journal of Oceanography》2008,64(1):39-48
Temporal changes in nitrogen isotopic composition (δ15N) of the NO3
− pool in the water column below the pycnocline in Ise Bay, Japan were investigated to evaluate the effect of nitrification
on the change in the δ15N in the water column. The δ15N of NO3
− in the lower layers varied from −8.5‰ in May to +8.4‰ in July in response to the development of seasonal hypoxia and conversion
from NH4
+ to NO3
−. The significantly 15N-depleted NO3
− in May most likely arose from nitrification in the water column. The calculated apparent isotopic discrimination for water
column nitrification (ɛnit = δ15Nsubstrate − δ15Nproduct) was 24.5‰, which lies within the range of previous laboratory-based estimates. Though prominent deficits of NO3
− from hypoxic bottom waters due to denitrification were revealed in July, the isotopic discrimination of denitrification in
the sediments was low (ɛdenit = ∼1‰). δ15NNO3 in the hypoxic lower layer mainly reflects the isotopic effect of water column nitrification, given that water column nitrification
is not directly linked with sedimentary denitrification and the effect of sedimentary denitrification on the change in δ15NNO3 is relatively small. 相似文献
234.
On tectonic movement in the South China Sea during the Cenozoic 总被引:1,自引:1,他引:0
The tectonic movement taking place at the end of Cretaceous and the beginning of Cenozoic had opened the Cenozoic phase of polycyclic tectonic movements, then the whole crust of the South China Sea had been mainly subjected to the regional stress field of tectonic tension, which was characterized by rifting depression. Seven times of regional tectonic movement and sedimentation had been assembled into a geological development history of polycyclic oscillation. Especially, the tectonic movements were strongly intensified at the end of Cretacious and the beginning of Paleagene, between Late Eocene and MidOligocene, during Mid and Late Miocene. These three times of tectonic movement had built the most important regional tectonic interfaces in the South China Sea. Crust movements of the South China Sea were the result and epitome of interaction of the Eurasia, Pacific and IndoAustralia plates, that is, they were introduced by polycyclic changes of directions, rates and strengths of lithospheric movements and asthenospheric flows across the Pacific and IndoAustralia plates. 相似文献
235.
The geological-geophysical map series of the eastern China seas and adjacent region (1:1 000 000) will be published in the late half year of 2009. The regional tectonic map is one of the main professional maps. The Mapping methods, the division method of geological tectonic units and the main geological tectonic units are mainly discussed. The strata from Pliocene to Holocene are peeled off so as to display the Pre-Pliocene structures. In basins, isopaches are drawn for the Cenozoic deposits. The plate tectonic theory and present tectonic pattern are adopted as the priorities in tectonic division. As to the division of intraplate tectonic units, it is a revision, complement and improvement of previous dividing systems, and the nomenclature for each tectonic unit follows the current system in China. The first-order tectonic unit is plate (Pacific Plate, Eurasian Plate and Philippine Sea Plate). The second-order tectonic unit is tectonic domain (East Asian continental tectonic domain,East Asian continental margin tectonic domain and west Pacific tectonic domain). The Philippine Sea Plate and the west part of the Pacific Plate are called the West Pacific tectonic domain. The part of the Eurasian Plate involved in this study area can be further divided into East Asian continental tectonic domain and East Asian continental margin tectonic domain. The East Asian continental margin domain is composed of the Ryukyu island arc, the Okinawa Trough back-arc basin and the back-arc basin of Sea of Japan. The East Asian continental tectonic domain in this study area is composed of the Sino-Korea Massif, the Changjiang River (Yangtze) Massif and South China Massif. In turn, these massifs consist of basins, folded belts or uplift zones. The basins,the folded belts or the uplift zones are further divided into uplifts and depressions made up of sags and swells. 相似文献
236.
����������Դ���ƽ����ִ�����Ӧ�����о� 总被引:3,自引:0,他引:3
?о???1996??2005??????????52????С?????????????6????????????????????????????????????????????????????????????P???????NW????300??320???????У??????????????????????????????????????????????????????????????????????????????????仯?????????????????????????????????????NNW????????????總?????????????NWW????EW???? 相似文献
237.
���ϵ�������Ӧ������ǿ����ϵ�о� 总被引:1,自引:0,他引:1
???????????????????????????鹹???????????????????????о?????????????????????GPS?????????????????????????,?????????????????????????????????????????????????????6??????????????????????????????????????????????????????????????????????????????н???????, ??????????????3????????Σ?????? 相似文献
238.
耿达短水准异常与汶川8.0级地震 总被引:2,自引:1,他引:1
结合龙门山断裂带其他跨断层资料,对耿达短水准在汶川8.0级地震前后的观测资料进行了重新分析,发现耿达短水准在汶川地震前后的异常为当地居民修建生活小区所致,不应视为地震前兆异常。 相似文献
239.
方国敏 《成都信息工程学院学报》2008,23(4):460-463
研究基于垄断厂商收益最大化的特定折扣率的定价问题,给出解的具体表达式,同时解决原有文献中需求函数为非线性函数时,最优固定折扣率的解的问题。 相似文献
240.
�봨8������ر����Ѵ��������乹������ 总被引:7,自引:2,他引:5
???ò??GPS????8????????????????????????????????????????????????????????:?????????-?????????γ?????200 km???????????????????????-????????????γ?????75 km?????????????????????????????????????????????????????????????????????????????????????????????? 相似文献