全文获取类型
收费全文 | 63699篇 |
免费 | 22767篇 |
国内免费 | 47141篇 |
专业分类
测绘学 | 5235篇 |
大气科学 | 25846篇 |
地球物理 | 18974篇 |
地质学 | 48917篇 |
海洋学 | 18521篇 |
天文学 | 2225篇 |
综合类 | 7685篇 |
自然地理 | 6204篇 |
出版年
2024年 | 311篇 |
2023年 | 872篇 |
2022年 | 1938篇 |
2021年 | 2490篇 |
2020年 | 3233篇 |
2019年 | 6649篇 |
2018年 | 7086篇 |
2017年 | 6647篇 |
2016年 | 6986篇 |
2015年 | 6098篇 |
2014年 | 5949篇 |
2013年 | 6450篇 |
2012年 | 6038篇 |
2011年 | 5939篇 |
2010年 | 5912篇 |
2009年 | 5182篇 |
2008年 | 4384篇 |
2007年 | 4355篇 |
2006年 | 3737篇 |
2005年 | 3575篇 |
2004年 | 3508篇 |
2003年 | 3223篇 |
2002年 | 2931篇 |
2001年 | 2806篇 |
2000年 | 2569篇 |
1999年 | 2953篇 |
1998年 | 2749篇 |
1997年 | 2727篇 |
1996年 | 2271篇 |
1995年 | 2101篇 |
1994年 | 1878篇 |
1993年 | 1753篇 |
1992年 | 1445篇 |
1991年 | 1137篇 |
1990年 | 978篇 |
1989年 | 846篇 |
1988年 | 736篇 |
1987年 | 511篇 |
1986年 | 446篇 |
1985年 | 331篇 |
1984年 | 354篇 |
1983年 | 225篇 |
1982年 | 243篇 |
1981年 | 181篇 |
1980年 | 141篇 |
1979年 | 126篇 |
1978年 | 54篇 |
1977年 | 51篇 |
1971年 | 53篇 |
1958年 | 46篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
IntroductionThe area of eastern Liaoning is an importantmetal and nonmetal metallogenetic district in China,and the Liaohe group is one of the most importantstrata that hosts Pb, Zn, Au, B and Mg etcstratabound deposits. Up to now many geo1ogistssuch as Z… 相似文献
92.
93.
本文讨论了河西走廊东部地区早二叠世地层研究的有关问题,认为甘肃山丹青羊泉下二叠统剖面是北祁连山—河西走廊地区的重要代表剖面之一。以该剖面研究为依据,提出走廊东部地区下二叠统的进一步划分方案,分析该区早二叠世地层岩性特征差异的原因,并与走廊西部地区同期地层进行对比,进一步明确了大黄沟组的含意。 相似文献
94.
PALEOSOLSOFSANDYLANDSANDENVIRONMENTALCHANGESINTHEWESTERNPARTOFNORTHEASTPLAINOFCHINAWESTERNDURINGHOLOCENE¥QiuShanwen(裘善文)LiQus... 相似文献
95.
Formation of saline groundwaters in the Baltic region through freezing of seawater during glacial periods 总被引:1,自引:0,他引:1
Typical Ca---Cl brines occur in crystalline and metamorphic rocks below freshwater horizons at various localities in Sweden and Finland. Total dissolved solids (TDS) range in concentration between 2 and 120 gl−1 and have long been thought to derive from water-rock interactions. The relationships between Na, Cl and Br in these brines suggest, however, that they were derived from freezing of seawater during glacial periods. The brines were subsequently diluted by meteoric waters and their Ca/Mg ratio was increased through water-rock interactions in the subsurface. The hydrogeological model for both the formation of freeze-derived marine brines and their lateral intrusion involves restricted inland marine basins in recent and subrecent polar climatic belts. Seawater in such basins gradually freezes in response to glaciation. The solutes which concentrate in the remaining water body are residual after precipitation of a sequence of minerals which include carbonates, mirabilite and hydrohalite. Hydraulic pressure of the growing ice sheet over the frozen seas is gradually added to the ambient hydrostatic pressure exerted on the brines. This, together with their increased density, increases the intrusional potential of the brines. As the land ice cannot exert hydraulic pressure on continental groundwater in the aquifers, the balance of pressure favours deep landward intrusion of brines. Post-glacial processes cause the subsurface dilution and replacement of the brines both by seawater and fresh waters. The presence of such brines also far from present-day coastal settings reflects the shifting of coastlines as a result of isostatic movements and eustatic sea-level changes associated with glaciation and deglaciation. 相似文献
96.
THE SIMULATED STORAGE CAPACITY OF FLOOD AND WATERLOGGING IN THE TYPICAL AGRICULTURAL REGION IN JIANGHAN PLAIN 总被引:2,自引:0,他引:2
1INTRODUCTIONJianghanPlainisoneoftheimportantbasesofChina′sagriculturalproductivitylocatedinthemiddleChangjiangRivervalleyofcentralChina.TheJianghanplainapproximately6.6×104km2inareaandover30millioninpopulationistherenowned“countryoffishandrice"in… 相似文献
97.
Li Chongyin 《大气科学进展》1993,10(1):41-53
In a simple semi-geostropic model on the equatorialβ-plane, the theoretical analysis on the 30-60 day oscillation in the tropical atmosphere is further discussed based on the
wave-CISK mechanism. The convection heat-ing can excite the CISK-Kelvin wave and CISK-Rossby wave in the tropical atmosphere
and they are all the low-frequency modes which drive the activities of 30-60 day oscillation in the tropics. The most favorable
conditions to excite the CISK-Kelvin wave and CISK-Rossby wave are indicated: There is convection heating but not very strong
in the atmosphere and there is weaker disturbance in the lower troposphere.
The influences of vertical shearing of basic flow in the troposphere on the 30-60 day oscillation in the tropics are also
discussed. 相似文献
98.
应用显微光度术、显微傅立叶红外光谱(Micro-FT.IR)和飞行时间二次离子质谱(TOF-SIMS)等原位微分析技术并结合均一温度测量对胜利油气区下第三系沙河街组沙三段中有机包裹体进行了研究。区分出两类有机包裹体,即原生有机包裹体和次生有机包裹体。结果表明两类有机包裹体特征不同,二者物质组成、有机质成分及化学结构、热演化程度等差别也较大。结合地质分析表明原生有机包裹体是沙三段烃源岩生成烃类运移产物,具“自生自储”特点,而次生有机包裹体是沙四段烃源岩生成的烃类二次运移的产物。沙三段是沙河街组油气运移和聚集的主要层位,因而是寻找油气资源的主要目标层。研究表明,有机包裹体是研究油气生成、运移、聚集和演化等成藏系统最有效的手段之一,在油气勘探中有重要的应用意义。 相似文献
99.
In this paper, we idealize the actual solar atmosphere as a multi-isothermal-layer system so as to obtain the energy transmittance of the linear Alfvén wave that propagates through such a system in presence of a uniform oblique magnetic filed. The results indicate that the two-layer model is essentially different to the three-layer one. In the two-layer model, the temperature jump acts as a high pass filter. In the three-layer model, resonant transfer will take place and the transmittance undergoes oscillation as the trigonometric function terms dominate its behavior. For actual solar atmosphere, the result reveals that the lower parts of solar atmosphere are more suitable for those Alfvén waves with period of seconds to transfer their energy. 相似文献
100.
Shi Zhi-dong Li Zhong-yuanUniversity of Science Technology of China Hefei PRC Advanced Centre for Earth Science Astronomy Third World Academy of Science 《紫金山天文台台刊》1996,(2)
Areview about K-H instability related to comet tail is presented.The effect of dust graing on KHI is theoretically analysed and relations of critical shear to excit KHI with the properties of dust grains both for sheared ion flow and for sheared dust flow re put out.Their possible application in comet tail is suggested. 相似文献