全文获取类型
收费全文 | 2936篇 |
免费 | 827篇 |
国内免费 | 901篇 |
专业分类
测绘学 | 223篇 |
大气科学 | 92篇 |
地球物理 | 486篇 |
地质学 | 2479篇 |
海洋学 | 449篇 |
天文学 | 552篇 |
综合类 | 212篇 |
自然地理 | 171篇 |
出版年
2024年 | 20篇 |
2023年 | 81篇 |
2022年 | 176篇 |
2021年 | 241篇 |
2020年 | 191篇 |
2019年 | 216篇 |
2018年 | 108篇 |
2017年 | 116篇 |
2016年 | 108篇 |
2015年 | 151篇 |
2014年 | 165篇 |
2013年 | 209篇 |
2012年 | 167篇 |
2011年 | 222篇 |
2010年 | 149篇 |
2009年 | 281篇 |
2008年 | 193篇 |
2007年 | 207篇 |
2006年 | 216篇 |
2005年 | 175篇 |
2004年 | 172篇 |
2003年 | 164篇 |
2002年 | 143篇 |
2001年 | 124篇 |
2000年 | 115篇 |
1999年 | 91篇 |
1998年 | 91篇 |
1997年 | 72篇 |
1996年 | 64篇 |
1995年 | 56篇 |
1994年 | 40篇 |
1993年 | 33篇 |
1992年 | 27篇 |
1991年 | 18篇 |
1990年 | 14篇 |
1989年 | 13篇 |
1988年 | 14篇 |
1987年 | 8篇 |
1986年 | 3篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1954年 | 2篇 |
排序方式: 共有4664条查询结果,搜索用时 31 毫秒
361.
Based on combined Cloud Sat/CALIPSO detections, the seasonal occurrence of deep convective clouds(DCCs) over the midlatitude North Pacific(NP) and cyclonic activity in winter were compared. In winter, DCCs are more frequent over the central NP, from approximately 30°N to 45°N, than over other regions. The high frequencies are roughly equal to those occurring in this region in summer. Most of these DCCs have cloud tops above a 12 km altitude, and the highest top is approximately 15 km. These wintertime marine DCCs commonly occur during surface circulation conditions of low pressure, high temperature, strong meridional wind, and high relative humidity. Further, the maximum probability of DCCs,according to the high correlation coefficient, was found in the region 10°–20° east and 5°–10° south of the center of the cyclones. The potential relationship between DCCs and cyclones regarding their relative locations and circulation conditions was also identified by a case study. Deep clouds were generated in the warm conveyor belt by strong updrafts from baroclinic flows. The updrafts intensified when latent heat was released during the adjustment of the cyclone circulation current. This indicates that the dynamics of cyclones are the primary energy source for DCCs over the NP in winter. 相似文献
362.
A preliminary scuba survey of oligotrophic Lake Rotoma in 1972 revealed a vegetation mainly composed of native hydrophytes in which exotics were at an early stage of colonisation. In 1973 the presence of species was recorded in 5708 quadrats (625 cm2) at 1 m intervals along a total of 50 line transects placed systematically around the lake. Water depth was measured, and quadrat cover and substrate type were subjectively estimated. Species frequency calculations showed that the dominant vegetation pattern was a characean meadow of Chara fibrosa f. acanthopitys (A.Br.) R.D.W., Nitella leptostachys var. leonhardii (R.D.W.) R.D.W., and N. pseudoflabellata var. mucosa (Nordst.) Bailey. The charophytes extended over a depth range of 1–17.5 m on a wide variety of substrates and gradients. Native vascular plants were absent from many transects, and had a depth range only from 0 to 4.5 m, with most occurring above 3.5 m. The Low Mixed Community, found in shallow water less than 1.25 m in depth at the northeast end of the lake, provided this area with a high species diversity. Exotic hydrophytes had established in many areas around the lake. The distribution of Lagarosiphon major (Ridley) Moss and Elodea canadensis Michx. appeared to coincide with boating access and fallen submerged trees over a depth range of 0–6.0 m, although much of the available habitat had not yet been exploited. Emergent species were most abundant within the southwest inlet and also in the lagoons surrounding the lake where sheltered conditions and shallow gradients prevail. 相似文献
363.
The Tarim Basin is the only petroliferous basin enriched with marine oil and gas in China. It is presently also the deepest basin for petroleum exploration and development in the world. There are two main sets of marine Source Rocks (SRs) in the Tarim Basin, namely the high over-mature Cambrian–Lower Ordovician (∈–O1) and the moderately mature Middle–Upper Ordovician (O2–3). The characteristic biomarkers of SRs and oils indicate that the main origin of the marine petroleum is a mixed source of ∈–O1 and O2–3 SRs. With increasing burial, the hydrocarbon contribution of the ∈–O1 SRs gradually increases. Accompanied by the superposition of multi-stage hydrocarbon-generation of the SRs and various secondary alteration processes, the emergence and abnormal enrichment of terpenoids, thiophene and trimethylaryl isoprenoid in deep reservoirs indicate a complex genesis of various deep oils and gases. Through the analysis of the biofacies and sedimentary environments of the ∈–O1 and O2–3 SRs, it is shown that the lower Paleozoic high-quality SRs in the Tarim Basin were mainly deposited in a passive continental margin and the gentle slope of the platform, deep-water shelf and slope facies, which has exhibited a good response to the local tectonic-sedimentary environment. The slope of the paleo-uplift is the mutual area for the development of carbonate reservoirs and the deposition of marine SRs, which would be favorable for the accumulation of petroleum. Due to the characteristics of low ground temperature, the latest rapid and deep burial does not cause massive oil-cracking in the paleo-uplift and slope area. Therefore, it is speculated that the marine reservoirs in the slope of the Tabei Uplift are likely to be a favorable area for deep petroleum exploration, while the oil-cracking gas would be a potential reserve around the west margin of the Manjiaer Depression. Hydrocarbons were generated from various unit SRs, mainly migrating along the lateral unconformities or reservoirs and the vertical faults. They eventually brought up three major types of exploration fields: middle and lower Cambrian salt-related assemblages, dolomite inner reservoirs and Middle and Lower Ordovician oil-bearing karst, which would become the most favorable target of marine ultra-deep exploration in the Tarim Basin. 相似文献
364.
365.
366.
可控源音频大地电磁法深部找矿实验效果 总被引:5,自引:1,他引:4
为了考查电磁法在探测深部金属矿及地质构造方面的实际效果,用可控源音频大地电磁法分别在埋深为500 m和1 100 m的两个已知隐伏铁、铜矿体上进行了实验工作。实验结果表明地电异常显示了矿体、断层以及岩层接触带的分布。在矿体埋藏深度小于500 m、矿层较厚时,地电异常十分明显;若矿体埋藏深度大于1 000 m,地电异常主要反应了控矿、容矿构造。 相似文献
367.
368.
369.
370.