全文获取类型
收费全文 | 7757篇 |
免费 | 1453篇 |
国内免费 | 1733篇 |
专业分类
测绘学 | 519篇 |
大气科学 | 1016篇 |
地球物理 | 864篇 |
地质学 | 5183篇 |
海洋学 | 740篇 |
天文学 | 56篇 |
综合类 | 670篇 |
自然地理 | 1895篇 |
出版年
2024年 | 62篇 |
2023年 | 179篇 |
2022年 | 313篇 |
2021年 | 383篇 |
2020年 | 351篇 |
2019年 | 340篇 |
2018年 | 297篇 |
2017年 | 337篇 |
2016年 | 352篇 |
2015年 | 324篇 |
2014年 | 495篇 |
2013年 | 524篇 |
2012年 | 485篇 |
2011年 | 507篇 |
2010年 | 512篇 |
2009年 | 482篇 |
2008年 | 429篇 |
2007年 | 476篇 |
2006年 | 544篇 |
2005年 | 412篇 |
2004年 | 389篇 |
2003年 | 374篇 |
2002年 | 360篇 |
2001年 | 332篇 |
2000年 | 320篇 |
1999年 | 245篇 |
1998年 | 216篇 |
1997年 | 173篇 |
1996年 | 147篇 |
1995年 | 124篇 |
1994年 | 108篇 |
1993年 | 81篇 |
1992年 | 79篇 |
1991年 | 47篇 |
1990年 | 24篇 |
1989年 | 21篇 |
1988年 | 25篇 |
1987年 | 17篇 |
1986年 | 11篇 |
1985年 | 12篇 |
1984年 | 8篇 |
1983年 | 3篇 |
1982年 | 6篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1978年 | 6篇 |
1977年 | 3篇 |
1971年 | 1篇 |
1954年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
The Transylvanian Basin is a mature hydrocarbon province of Romania characterized by two petroleum systems: Mesozoic (thermogenic) and Miocene (biogenic). An extensive outcrop-based sedimentological and micropaleontological study correlated to seismic and well data discusses the elements of the Miocene petroleum system. The facies associations are indicative of alluvial, fandelta, shallow- and deep-marine settings. These are grouped into four different depositional systems (evaporite, mud-carbonate, sand-mud and sand-gravel). Their evolution in time and space shows large differences between various parts of the basin that have important consequences for exploration. 相似文献
62.
Hisaaki Sato 《Marine Georesources & Geotechnology》2018,36(7):768-780
We propose a geochemical parameter, “metal flux” in evaluating hydrogenetic Co-rich ferromanganese crust deposits in the Pacific seamount area, that is based on physical, chemical, and geological characterization of the integrated growth piles of crusts. We calculated the metal flux for fifteen sites from different depths ranging between 900-6000m from different seamounts. The secular and areal variations of metal flux indicate a strong geological controls, and also can be a reliable tool for estimating an economic potential of the crusts. The Co flux decreases with increasing water depth, followed by almost constant flux of Ni and Mn. The Al and Fe fluxes vary with regions, indicating higher values in the western regions near the island arc probably related to a supply from the Asian continents. The results imply that Co, a redox sensitive metal element, is controlled by redox conditions of seawater, while Fe and Al are by terrigenous input. The metal flux reflects global and regional conditions and controls the compositional diversity of metals, thus consequently, the parameter can be a reliable powerful tool to estimate or single out more potential areas. 相似文献
63.
《Marine Policy》2016
Marine minerals such as manganese nodules, Co-rich ferromanganese crusts, and seafloor massive sulfides are commonly seen as possible future resources that could potentially add to the global raw materials supply. At present, a proper assessment of these resources is not possible due to a severe lack of information regarding their size, distribution, and composition. It is clear, however, that manganese nodules and Co-rich ferromanganese crusts are a vast resource and mining them could have a profound impact on global metal markets, whereas the global resource potential of seafloor massive sulfides appears to be small. These deep-sea mineral commodities are formed by very different geological processes resulting in deposits with distinctly different characteristics. The geological boundary conditions also determine the size of any future mining operations and the area that will be affected by mining. Similarly, the sizes of the most favorable areas that need to be explored for a global resource assessment are also dependent on the geological environment. Size reaches 38 million km2 for manganese nodules, while those for Co-rich crusts (1.7 million km2) and massive sulfides (3.2 million km2) are much smaller. Moreover, different commodities are more abundant in some jurisdictions than in others. While only 19% of the favorable area for manganese nodules lies within the Exclusive Economic Zone of coastal states or is covered by proposals for the extension of the continental shelf, 42% of the favorable areas for massive sulfides and 54% for Co-rich crusts are located in EEZs. 相似文献
64.
65.
《Marine Policy》2014
For nearly a decade, governments have been discussing the need to improve efforts to conserve and sustainably use marine biodiversity in areas beyond national jurisdiction (ABNJ). Support for a new international agreement under the United Nations Convention on the Law of the Sea (UNCLOS) – an Implementing Agreement – on the conservation and sustainable use of marine biodiversity in ABNJ has been growing. In June 2012, at the United Nations Conference on Sustainable Development held in Rio de Janeiro, Brazil, States agreed to take a decision on the development of an international instrument under UNCLOS before the end of the 69th session of the United Nations General Assembly (UNGA), which runs from September 2014 to August 2015. In follow-up to this commitment, it was agreed to consider the “scope, parameters and feasibility” of this instrument. To inform these international discussions, this article highlights some potential options for the content of a new UNCLOS Implementing Agreement. It first reviews the history of UN discussions, and then elaborates on options to address key elements identified as priorities for States in 2011: marine genetic resources, including the sharing of benefits, area-based management tools, including marine protected areas, environmental impact assessments, capacity-building and the transfer of marine technology. It addresses cross-cutting issues such as the governing principles, institutional structure as well as on other critical points such as High Seas fishing and flag State responsibilities. The article concludes with suggestions on possible next steps in order to succeed in the negotiations for an agreement. 相似文献
66.
全球三大洋海山钴结壳资源量估算 总被引:8,自引:0,他引:8
钴结壳具有Co、Ni、Cu和Mn及其他金属的潜在矿产资源和储存在结壳层中古环境信息的双重意义。与深海多金属结核和热液硫化物矿床相比,具有较高Co、Ni和Pt含量的海山钴结壳有可能成为商业勘探的潜在目标。为合理地估算出全球三大洋海山钴结壳资源量,基于我国西太平洋海山钴结壳拖网采样调查资料和对太平洋海山钴结壳资源分布规律和钴结壳矿区圈定参数指标的深入研究,按海山不同高度、不同洋壳年龄赋予不同结壳厚度,进而计算出全球三大洋海山钴结壳分布面积为3 039 452.14km2和干结壳资源量为(1 081.166 1~2 162.332 2)×108 t。太平洋海山钴结壳分布面积为2 123 087.12km2和干结壳资源量为(513.244~1 026.488)×108 t,大西洋海山钴结壳分布面积为512 509.74km2和干结壳资源量为(116.503 2~233.006 4)×108 t,印度洋海山钴结壳分布面积为403 855.28km2和干结壳资源量为(81.484 9~162.969 8)×108 t。三大洋海山钴结壳的Mn、Co、Ni和Cu金属量分别为(138.848 0~277.696 0)×108 t,(3.967 6~7.935 2)×108 t、(2.793 6~5.587 2)×108 t和(0.825 1~1.650 2)×108 t。根据钴结壳的Co含量、Co通量和厚度相关分析,所赋予的钴结壳厚度占理论推测厚度的6.10%~12.20%,这与Ku等得出"钴结壳生长时间约占其整个生命史4%"的认识非常相近。三大洋海山钴结壳实测厚度与赋值厚度对比分析表明,太平洋海山钴结壳赋值厚度平均值为1.87cm,实测厚度平均值为1.77cm,相对误差为5.35%,大西洋和印度洋相对误差分别为18.18%和23.23%。研究数据表明按海山高度和洋壳年龄所赋的钴结壳厚度基本合理,估算出的钴结壳资源量基本可靠。本文首次估算出三大洋海山钴结壳资源量,为整个海盆和三大洋海山钴结壳资源量估算提供了新方法。 相似文献
67.
基于熵权TOPSIS模型的海岛地区资源环境承载力研究——以舟山普陀区、定海区为例 总被引:2,自引:0,他引:2
随着海洋强国、"一带一路"、生态文明建设等国家战略的不断推进,海岛在国家政治、军事、经济、社会、生态中的地位不断提高,海岛开发、利用的规模越来越大,其生态保护也面临着新的挑战。本文依据资源环境承载力内涵,兼顾海岛资源环境特点,研究形成海岛地区资源环境承载力评价指标体系,综合应用熵权法、TOPSIS(逼近理想解排序方法)模型评价了典型海岛地区——普陀区与定海区2009-2015年间的资源环境承载力状况,结果表明:普陀和定海资源环境承载力水平呈稳步提升趋势,各个时期的环境保护政策和节能减排相关措施在环境保护与污染治理等方面起到了较为积极的作用。最后,在基于生态系统的海岛综合管理框架内提出了对策建议。 相似文献
68.
基于线粒体CO1基因的序列,对渔山列岛,大连獐子岛,南麂列岛,山东南隍城乡,舟山嵊泗5个野生群体的厚壳贻贝进行遗传多样性和遗传结构的分析。结果表明:在mt DNACO1基因同源片段上共检测到了39个多态位点,其中39个简约信息位点,无单突变位点,构成40个单倍型,群体遗传多样性水平为:渔山山东大连舟山南麂;然而单倍型多样性却是山东渔山南麂大连舟山。分子进化树和单倍型网络关系图构建结果显示:5个群体之间分为3个单倍型类群(A、B、C),其中A类群含15个单倍型,B类群含23个单倍型,C类群含2个单倍型(均为渔山列岛的单倍型),其中渔山列岛的单倍型在上述三个类群中都有分布。3个单倍型类群间的遗传距离为0.0099~0.0268。渔山列岛群体内遗传分化较为显著,其他4个群体间未检测到显著的遗传分化。 相似文献
69.
轴向重力流沉积是一种重要的深水储层,其形成的岩性油气藏也是目前莺歌海盆地重点勘探领域。通过钻井、测井、地震和区域地质等资料的综合研究,分析莺歌海盆地中新统轴向重力流沉积特征和演化规律,探讨轴向重力流岩性油气藏的成藏条件和控制因素。结果表明,中新统储层为重力流沉积成因的厚层细砂岩,主水道和朵叶复合体是重力流沉积有利的沉积微相;中新世海南物源供给充足、断裂坡折带发育以及盆地轴向负向地形是该区形成轴向重力流沉积的宏观地质条件,在中新世各个时期形成了一系列沿盆地轴向分布、具有前积反射结构特征的轴向重力流沉积。研究区中新统轴向重力流储层厚度大、沉积规模广、临近烃源岩、构造脊微裂隙发育、圈闭保存好,具备优越的岩性油气藏成藏条件,是盆地下一步勘探的重要领域。 相似文献
70.
For South Korea, liquefaction potential along the western coast has not been widely assessed because South Korea is considered to be a low seismic hazard. However, recent earthquake events and historical records indicate that the seismic hazard of South Korea should not be ignored. Moreover, as artificial fills are extensively used along the western coast for development, liquefaction evaluation of the soils in this area is necessary. In this paper, we present: (1) the seismic characteristics of the study area; (2) procedures for evaluating liquefaction potential, focusing on the liquefaction potential index (LPI) approach; and (3) LPI distributions at several representative locations along the western coast of South Korea under various seismic scenarios. The liquefaction potential index represents the liquefaction potential over the upper 20 m of a boring or sounding. Using cone penetration test (CPT) and standard penetration test (SPT) data from two coastal sites, we compare and discuss CPT-based and SPT-based LPI values, particularly values computed in nonplastic, silt-rich soils. In these soils, it appears that the CPT yields lower liquefaction resistance, resulting in large LPI values. Finally, discussion and suggestions are provided for CPT- and SPT-based liquefaction assessment of low plasticity and high fines content soils. 相似文献