全文获取类型
收费全文 | 340篇 |
免费 | 40篇 |
国内免费 | 30篇 |
专业分类
测绘学 | 44篇 |
大气科学 | 59篇 |
地球物理 | 58篇 |
地质学 | 67篇 |
海洋学 | 61篇 |
天文学 | 14篇 |
综合类 | 24篇 |
自然地理 | 83篇 |
出版年
2024年 | 2篇 |
2022年 | 11篇 |
2021年 | 7篇 |
2020年 | 4篇 |
2019年 | 7篇 |
2018年 | 9篇 |
2017年 | 13篇 |
2016年 | 13篇 |
2015年 | 15篇 |
2014年 | 19篇 |
2013年 | 12篇 |
2012年 | 18篇 |
2011年 | 27篇 |
2010年 | 19篇 |
2009年 | 27篇 |
2008年 | 22篇 |
2007年 | 23篇 |
2006年 | 17篇 |
2005年 | 12篇 |
2004年 | 13篇 |
2003年 | 13篇 |
2002年 | 10篇 |
2001年 | 11篇 |
2000年 | 17篇 |
1999年 | 12篇 |
1998年 | 9篇 |
1997年 | 7篇 |
1996年 | 10篇 |
1995年 | 4篇 |
1994年 | 5篇 |
1993年 | 10篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有410条查询结果,搜索用时 218 毫秒
91.
Variations in the abundance of fisheries resources and ecosystem structure in the Japan/East Sea 总被引:1,自引:0,他引:1
Chang Ik Zhang Jae Bong Lee Young Il Seo Sang Cheol Yoon Suam Kim 《Progress in Oceanography》2004,61(2-4):245
Evidence supports the hypothesis that two climatic regime shifts in the North Pacific and the Japan/East Sea, have affected the dynamics of the marine ecosystem and fisheries resources from 1960 to 2000. Changes in both mixed layer depth (MLD) and primary production were detected in the Japan/East Sea after 1976. The 1976 regime shift appears to have caused the biomass replacement with changes in catch production of major exploited fisheries resources, including Pacific saury, Pacific sardine and filefish. Both fisheries yield and fish distribution are reflected in these decadal fluctuations. In the 1960s and 1990s, common squid dominated the catches whereas in the 1970s and 1980s, it was replaced by walleye pollock. In the post-1988 regime shift, the distribution of horse mackerel shifted westward and southward and its distributional overlap with common mackerel decreased. The habitat of Pacific sardine also shifted away from mackerel habitats during this period. To evaluate changes in the organization and structure of the ecosystem in the Japan/East Sea, a mass-balanced model, Ecopath, was employed. Based on two mass-balanced models, representing before (1970–75) and after (1978–84) the 1976 regime shift, the weighted mean trophic level of catch increased from 3.09 before to 3.28 after. Total biomass of species groups in the Japan/East Sea ecosystem increased by 15% and total catch production increased by 48% due to the 1976 regime shift. The largest changes occurred at mid-trophic levels, occupied by fishes and cephalopods. The dominant predatory species shifted from cephalopods to walleye pollock due to the 1976 regime shift. It is concluded that the climatic regime shifts caused changes in the structure of the ecosystem and the roles of major species, as well as, large variations in biomass and production of fisheries resources. 相似文献
92.
用EOF分析方法对北太平洋及赤道太平洋地区1949~1979年31年海表面温度距平场进行分解,得到几个主要距平海温模态(EOF1~3),分析了EOF1~3的时空分布特征。得到海温距平场的EOF1和EOF2~3模态分别对E1—Nino事件和黑潮大弯曲有很显著的相关性,指出SST第三模态场对黑潮大弯曲的影响具有很好的持续性,持续时间为1~2年。最后讨论了相互的影响过程,为黑潮大弯曲和E1—Nino事件的预报的可能性提供了依据。 相似文献
93.
94.
Functional roles of interzonal migrating mesozooplankton in the western subarctic Pacific 总被引:1,自引:0,他引:1
Grazing experiments and production estimation based on life-history analysis of Neocalanus copepods (N. cristatus, N. plumchrus and N. flemingeri) were carried out in the Oyashio region to understand the carbon flows associated with the interzonal migrating copepods. These copepods, and also Eucalanus bungii, fed on nano- and micro-sized organisms non-selectively throughout the season. However, diatoms were the dominant food resource until May and organisms, such as ciliates were the major resource after May. Daily growth rate was estimated from the Ikeda–Motoda, Huntley–Lopez and Hirst–Sheader models. Since the growth rates were considered to be overestimates for the Huntley–Lopez model and underestimates for the other two models, we applied the weight-specific growth rates previously reported for these species in the Bering Shelf. Surface biomass of Neocalanus increased rapidly in June during the appearance of C5, and a successive increase of overwintering stock was evident in the deeper layer. The deep biomass decreased gradually from September to May during the dormant and reproduction period. N. cristatus has the largest annual mean biomass (2.3 gC m−2), followed by N. plumchrus (1.1) and N. flemingeri (0.4). Daily production rate of Neocalanus varied from 0.4 to 363.4 mgC m−2 day−1, to which N. cristatus was the largest contributor. Annual production was estimated as 11.5 gC m−2 year−1 for N. cristatus, 5.7 for N. plumchrus and 2.1 for N. flemingeri, yielding annual P/B ratio of 5 for each species. The annual production of Neocalanus accounted for 13.2% of the primary production in the Oyashio region. Their fecal pellets were estimated to account for 14.9% (0.7 gC m−2 year−1) of sinking flux of organic carbon at 1000-m depth. Moreover, their export flux by ontogenetic vertical migration, which is not measured by sediment trap observations, is estimated to be 91.5% (4.3 gC m−2 year−1) of carbon flux of sinking particles at 1000-m depth. These results suggest the important role of interzonal migrating copepods in the export flux of carbon. 相似文献
95.
《Norsk geografisk tidsskrift. Norwegian journal of geography》2012,66(3):199-206
Outdoor recreation policy and management have largely been occupied by questions related to use patterns: who participates in which activities, where and when? However, it is commonly held that ideas and practices mutually influence each other. In outdoor recreation, it could be expected that the observable use patterns are influenced by the meaning recreationists ascribe to their activities. In this study 14 narratives of outdoor recreation practices are analyzed, in order to broaden the traditional understanding of the meaning of outdoor recreation. 相似文献
96.
Production and R&D networks of foreign ventures in China: Implications for technological dynamism and regional development 总被引:2,自引:0,他引:2
This paper analyzes the nature of FDI local networks in production and R&D activities in China and discusses their implications for technological dynamism and regional development. We investigate foreign ventures (or foreign-invested enterprises, FIEs) in the information and communication technology (ICT) industry, based on a large-scale survey of ICT firms conducted in three mega-city regions of China: Beijing, Shanghai-Suzhou, and Shenzhen-Dongguan. Our data show that FIEs in China are gradually localizing their production, but the extent of local embeddedness is contingent upon home country effects, local specific contexts and FDI-host region relationships. We have also found significant influence of industrial agglomeration on FDI location and network decisions. Beijing tends to have broader FDI sources and better integrated global-local networks, while in those regions dominated by FDI such as Suzhou and Dongguan, FIEs are thinly embedded with local economies and tend to establish global-local networks among themselves; local embeddedness is limited by a series of technological, institutional, spatial, and structural mismatches. Shanghai and Shenzhen are in between. More efforts are still needed to better integrate FDI with local economies and strengthen China’s local innovative capacities. 相似文献
97.
Solar flare gamma-ray emissions from energetic ions and electrons have been detected and measured to GeV energies since 1980. In addition, neutrons produced in solar flares with 100 MeV to GeV energies have been observed at the Earth. These emis-sions are produced by the highest energy ions and electrons accelerated at the Sun and they provide our only direct (albeit secondary) knowledge about the properties of the acceler-ator(s) acting in a solar flare. The solar flares, which have direct evidence for pion-decaygamma-rays, are unique and are the focus of this paper. We review our current knowl-edge of the highest energy solar emissions, and how the characteristics of the acceleration process are deduced from the observations. Results from the RHESSI, INTEGRAL and CORONAS missions will also be covered. The review will also cover the solar flare ca-pabilities of the new mission, FERMI GAMMA RAY SPACE TELESCOPE, launched on 2008 June 11. Finally, we discuss the requirements for future missions to advance this vital area of solar flare physics. 相似文献
98.
SEASONAL VARIATIONS OF CONVECTIVE ACTIVITIES OVER THE SOUTH CHINA SEA AND ITS NEIGHBORHOOD AND THEIR COMPARATIVE ANALYSES IN THE STRONG AND WEAK CONVECTION YEARS* 下载免费PDF全文
The seasonal variations of convective activities over the South China Sea(SCS) and its neighborhood.as well as the similarities and differences of convection in the different key regions during the strong and weak convection years are analyzed by using the pentad data of TBB from 1980 to 1993.The results show that in winter and summer the seasonal variations of the convective activities are synchronous over the SCS and its neighborhood,the anomalous convection amplitudes are obviously different in different regions.The significant extents of convective activities have somewhat seasonal differences in the strong and weak convection years.In the strong convection years,it is in winter,spring and autumn that the convection anomaly is more evident than that in the normal years,however,after the summer monsoon onset the convection is sustained.stable and similar to that in the normal years.In the weak convection years.the convection weakens greatly in each season.but the primary weakening occurs in spring.summer and autumn.No matter in the strong or the weak convection years.the convective activities are somewhat of difference in the Bay of Bengal.the Indochina Peninsula.the SCS and the Philippines.In addition.the convective activities are also different over the south and the north parts of the SCS.the convection variation in the strong year is similar to that in the weak year over the north part of the SCS.but over the south part there are great differences. 相似文献
99.
最优子集回归在青藏高原冬季降水、气温预报中的应用及改进 总被引:2,自引:1,他引:2
最优子集回归预测方法在天气预报等领域得到了越来越广泛的应用,方法本身没有涉及到图形处理。我们对方法、原理及过程进行深入细致的研究后,重新编写了程序的头部、中部、尾部语句及子过程调用函数,经多次调试试验,实现了入口资料调用灵活、多变、计算模拟结果屏幕绘图显示等,提高了预测方法的整体实用性和预测信息的可视化程度。检验得知:该方法对青藏高原冬季降水、气温的定性、定量预报均具有较高的预报精度。 相似文献
100.
华南沿海4省区城市分类探析 总被引:6,自引:1,他引:6
采用城市就业人口的统计资料,运用城市经济基础分析、多变量聚类与统计分析相结合的方法,对东南沿海粤、闽、琼、桂4省区40个地级以上的城市进行综合职能分类、共分出5个大类9个亚类。分类结果对认识我国东南沿海主要城市的职能结构和职能特点有着重要的意义,也为本区域城市之间的比较研究提供了参照基础。 相似文献