全文获取类型
收费全文 | 5315篇 |
免费 | 709篇 |
国内免费 | 721篇 |
专业分类
测绘学 | 432篇 |
大气科学 | 666篇 |
地球物理 | 952篇 |
地质学 | 1999篇 |
海洋学 | 471篇 |
天文学 | 1489篇 |
综合类 | 204篇 |
自然地理 | 532篇 |
出版年
2024年 | 11篇 |
2023年 | 36篇 |
2022年 | 89篇 |
2021年 | 84篇 |
2020年 | 107篇 |
2019年 | 139篇 |
2018年 | 102篇 |
2017年 | 164篇 |
2016年 | 137篇 |
2015年 | 155篇 |
2014年 | 277篇 |
2013年 | 296篇 |
2012年 | 334篇 |
2011年 | 213篇 |
2010年 | 228篇 |
2009年 | 351篇 |
2008年 | 351篇 |
2007年 | 435篇 |
2006年 | 444篇 |
2005年 | 367篇 |
2004年 | 309篇 |
2003年 | 304篇 |
2002年 | 271篇 |
2001年 | 247篇 |
2000年 | 164篇 |
1999年 | 197篇 |
1998年 | 138篇 |
1997年 | 120篇 |
1996年 | 124篇 |
1995年 | 96篇 |
1994年 | 89篇 |
1993年 | 96篇 |
1992年 | 58篇 |
1991年 | 41篇 |
1990年 | 35篇 |
1989年 | 32篇 |
1988年 | 14篇 |
1987年 | 23篇 |
1986年 | 15篇 |
1985年 | 10篇 |
1984年 | 10篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 5篇 |
1978年 | 1篇 |
1977年 | 7篇 |
1976年 | 3篇 |
1975年 | 1篇 |
1954年 | 3篇 |
排序方式: 共有6745条查询结果,搜索用时 78 毫秒
101.
102.
As a new method, the ultraviolet spectrum technique is applied to studying the connectivity of biode-gradable heavy oil reservoirs. The similarity of crude oils can be judged according to the extinction coefficient (E) because aromatic hydrocarbons and non-hydrocarbons have conjugated bonds and obvious absorption in the ultraviolet range, and different materials have different characteristics and additives. The relationship diagram is made in terms of the extinction coefficients (E) of the samples by taking E as the Y-axis and wavelength as the X-axis. The connectivity of oil reservoirs is estimated according to the curve positions and characteristic fingerprints of the sampies. The connectivity of part of the reservoirs in the western part of the QHD32-6 oilfield was studied with this method. The results showed that the connectivity of samples from wells F7 and F8 in the Nm-2 oil reservoir zone is good, that of samples from wells F17 and F20 in the Nm-1 oil reservoir zone also is good, and that of samples from wells F17, F19, and F20 is poor. 相似文献
103.
104.
Yanming Feng 《Journal of Geodesy》2008,82(12):847-862
This paper presents a general modeling strategy for ambiguity resolution (AR) and position estimation (PE) using three or
more phase-based ranging signals from a global navigation satellite system (GNSS). The proposed strategy will identify three
best “virtual” signals to allow for more reliable AR under certain observational conditions characterized by ionospheric and
tropospheric delay variability, level of phase noise and orbit accuracy. The selected virtual signals suffer from minimal
or relatively low ionospheric effects, and thus are known as ionosphere-reduced virtual signals. As a result, the ionospheric parameters in the geometry-based observational models can be eliminated for
long baselines, typically those of length tens to hundreds of kilometres. The proposed modeling comprises three major steps.
Step 1 is the geometry-free determination of the extra-widelane (EWL) formed between the two closest L-band carrier measurements,
directly from the two corresponding code measurements. Step 2 forms the second EWL signal and resolves the integer ambiguity
with a geometry-based estimator alone or together with the first EWL. This is followed by a procedure to correct for the first-order
ionospheric delay using the two ambiguity-fixed widelane (WL) signals derived from the integer-fixed EWL signals. Step 3 finds
an independent narrow-lane (NL) signal, which is used together with a refined WL to resolve NL ambiguity with geometry-based
integer estimation and search algorithms. As a result, the above two AR processes performed with WL/NL and EWL/WL signals
respectively, either in sequence or in parallel, can support real time kinematic (RTK) positioning over baselines of tens
to hundreds of kilometres, thus enabling centimetre-to-decimentre positioning at the local, regional and even global scales
in the future. 相似文献
105.
在城区化过程中,由于人口快速成长且集中,随之而来的建筑物、道路等不透水面密度增加,导致地下水补给减少及破坏水文循环。为了解土地利用方式改变对长期水文量影响,建立一个适宜的城区水循环模式是非常重要的。选定台湾台北的六馆抽水站集水区进行分析,模式参数经过敏感度分析、率定与验证。采用改变不同透水铺面设置比例的方案,评估其对径流量、入渗量、蒸发散量的改变。并分析设置不同比例屋顶雨水贮集系统对地表径流量及供水量的改变。所建立的城区水循环模式是评估土地利用改变造成水文量的改变的一个有效工具,并可提供决策者做为城区土地利用决策的参考。 相似文献
106.
安徽池州铜山铜矿深部找矿实践与启示 总被引:4,自引:0,他引:4
铜山铜矿资源储量日益枯竭。危机矿山接替资源勘查中,采用地质、物探综合手段圈定异常区,经深部钻探验证,取得突破。 相似文献
107.
108.
Cluster correspondence analysis examines the spatial autocorrelation of multi-location events at the local scale. This paper
argues that patterns of cluster correspondence are highly sensitive to the definition of operational neighborhoods that form
the spatial units of analysis. A subset of multi-location events is examined for cluster correspondence if they are associated
with the same operational neighborhood. This paper discusses the construction of operational neighborhoods for cluster correspondence
analysis based on the spatial properties of the underlying zoning system and the scales at which the zones are aggregated
into neighborhoods. Impacts of this construction on the degree of cluster correspondence are also analyzed. Empirical analyses
of cluster correspondence between paired vehicle theft and recovery locations are conducted on different zoning methods and
across a series of geographic scales and the dynamics of cluster correspondence patterns are discussed.
相似文献
109.
利用大地电磁测深法(MT)反映地质体的电性差异,首先可以确定地质体的空间展布、地质结构和构连;而由于地质体电阻率受地热水影响而降低,进而据此圈定地热水的分布范围;并在此基础上可以进一步探讨地热形成机制。在华北地台地热勘探中MT法取得了较好的勘探效果。 相似文献
110.