全文获取类型
收费全文 | 1499篇 |
免费 | 202篇 |
国内免费 | 267篇 |
专业分类
测绘学 | 82篇 |
大气科学 | 407篇 |
地球物理 | 248篇 |
地质学 | 276篇 |
海洋学 | 99篇 |
天文学 | 628篇 |
综合类 | 67篇 |
自然地理 | 161篇 |
出版年
2024年 | 5篇 |
2023年 | 26篇 |
2022年 | 27篇 |
2021年 | 39篇 |
2020年 | 37篇 |
2019年 | 46篇 |
2018年 | 44篇 |
2017年 | 38篇 |
2016年 | 36篇 |
2015年 | 63篇 |
2014年 | 71篇 |
2013年 | 84篇 |
2012年 | 81篇 |
2011年 | 74篇 |
2010年 | 68篇 |
2009年 | 102篇 |
2008年 | 83篇 |
2007年 | 88篇 |
2006年 | 88篇 |
2005年 | 91篇 |
2004年 | 62篇 |
2003年 | 74篇 |
2002年 | 85篇 |
2001年 | 68篇 |
2000年 | 92篇 |
1999年 | 80篇 |
1998年 | 55篇 |
1997年 | 37篇 |
1996年 | 31篇 |
1995年 | 43篇 |
1994年 | 36篇 |
1993年 | 16篇 |
1992年 | 14篇 |
1991年 | 13篇 |
1990年 | 14篇 |
1989年 | 15篇 |
1988年 | 12篇 |
1987年 | 11篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1982年 | 4篇 |
1981年 | 3篇 |
排序方式: 共有1968条查询结果,搜索用时 15 毫秒
11.
Understanding the oil distribution characteristics in unconventional tight reservoirs is crucial for hydrocarbon evaluation and oil/gas extraction from such reservoirs. Previous studies on tight oil distribution characteristics are mostly concerned with the basin scale. Based on Lucaogou core samples, geochemical approaches including Soxhlet extraction, total organic carbon (TOC), and Rock-Eval are combined with reservoir physical approaches including mercury injection capillary pressure (MICP) and porosity-permeability analysis, to quantitatively evaluate oil distribution of tight reservoirs on micro scale. The emphasis is to identify the key geological control factors of micro oil distribution in such tight reservoirs. Dolomicrites and non-detrital mudstones have excellent hydrocarbon generation capacity while detritus-containing dolomites, siltstones, and silty mudstones have higher porosity and oil content, and coarser pore throat radius. Oil content is mainly controlled by porosity, pore throat radius, and hydrocarbon generation capacity. Porosity is positively correlated with oil content in almost all samples including various lithologies, indicating that it is a primary constraint for providing storage space. Pore throat radius is also an important factor, as oil migration is inhibited by the capillary pressure which must be overcome. If the reservoir rock with suitable porosity has no hydrocarbon generation capacity, pore throat radius will be decisive. As tight reservoirs are generally characterized by widely distributed nanoscale pore throats and high capillary pressure, hydrocarbon generation capacity plays an important role in reservoir rocks with suitable porosity and fine pore throats. Because such reservoir rocks cannot be charged completely. The positive correlation between hydrocarbon generation capacity and oil content in three types of high porosity lithologies (detritus-containing dolomites, siltstones, and silty mudstones) supports this assertion. 相似文献
12.
渤海海冰中太阳辐射的光谱特征观测研究 总被引:7,自引:2,他引:5
通过采用多光谱仪器,对渤海营口港一带的近岸固定冰进行了3个站位11个谱段的入射辐射、反射辐射和透射辐射随时间变化过程的观测和研究。结果表明,发生在海冰中的反射辐射和透射辐射与入射太阳辐射的谱分布有明显差别,而且有显著的日变化。文章确立了入射辐射、反射辐射和透射辐射随时间的变化与太阳高度角的正弦成精确的线性关系,海冰的积分反照率与太阳高度角的正弦满足二次函数关系,可将不同时刻的观测值归算到正午时刻的辐射值,使不同时刻的观测结果具有可比性。计算结果表明,海冰只衰减特定强度的辐射,衰减量与入射辐射光谱分布以及辐射的强度无关,导致绿光的透射辐射最强。该文是对渤海海冰透射辐射的初步尝试,所获得的结果对未来大范围海冰光学观测打下了基础。 相似文献
13.
14.
In this work, enhanced poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) bulk-heterojunction photovoltaic devices are achieved via slow-solvent-vapour treatment. The correlations between the morphology of the active layer and the photovoltaic performance of polymer-based solar cell are investigated. The active layers are characterized by atomic force microscopy and optical absorption. The results show that slow-solvent-vapour treatment can induce P3HT self-organization into an ordered structure, leading to the enhanced absorption and efficient charge transport. 相似文献
15.
基于地理信息系统的太阳直接辐射与冰川物质平衡的关系 总被引:3,自引:1,他引:3
基于冰川微地形对冰川物质平衡重要影响的认识,在考虑朝向、坡度、地形遮蔽等因素的条件下,以地理信息系统为手段,对乌鲁木齐河源1号冰川冰面太阳可能直接辐射进行了理论计算.在此基础上,建立了计算冰面任意一点物质平衡的B=f(T,R)(气温-辐射)模型.比较了该模型与B=f(T)(气温)模型、B=f(P,T)(降水-气温)模型及B=f(Q)(能量平衡)模型之间的优缺点,表明该模型具有物理意义明确、计算精度较高、参数易于获得等优点,从而为计算冰川物质平衡提供了新的途径. 相似文献
16.
王水 《紫金山天文台台刊》1994,13(3):181-188
Basic processes of magnetic reconnection and observations of coronal mass ejection are introduced. A possible mechanism of CME caused by magnetic rcconnection in the current sheet of solar corona is suggested. 相似文献
17.
Thierry Montmerle Jean-Charles Augereau Marc Chaussidon Mathieu Gounelle Bernard Marty Alessandro Morbidelli 《Earth, Moon, and Planets》2006,98(1-4):39-95
The solar system, as we know it today, is about 4.5 billion years old. It is widely believed that it was essentially completed 100 million years after the formation of the Sun, which itself took less than 1 million years, although the exact chronology remains highly uncertain. For instance: which, of the giant planets or the terrestrial planets, formed first, and how? How did they acquire their mass? What was the early evolution of the “primitive solar nebula” (solar nebula for short)? What is its relation with the circumstellar disks that are ubiquitous around young low-mass stars today? Is it possible to define a “time zero” (t 0), the epoch of the formation of the solar system? Is the solar system exceptional or common? This astronomical chapter focuses on the early stages, which determine in large part the subsequent evolution of the proto-solar system. This evolution is logarithmic, being very fast initially, then gradually slowing down. The chapter is thus divided in three parts: (1) The first million years: the stellar era. The dominant phase is the formation of the Sun in a stellar cluster, via accretion of material from a circumstellar disk, itself fed by a progressively vanishing circumstellar envelope. (2) The first 10 million years: the disk era. The dominant phase is the evolution and progressive disappearance of circumstellar disks around evolved young stars; planets will start to form at this stage. Important constraints on the solar nebula and on planet formation are drawn from the most primitive objects in the solar system, i.e., meteorites. (3) The first 100 million years: the “telluric” era. This phase is dominated by terrestrial (rocky) planet formation and differentiation, and the appearance of oceans and atmospheres. 相似文献
18.
Gong-liang Zhang 《Chinese Astronomy and Astrophysics》1996,20(4):482-486
Observed instances are given in this paper to show that sub-Alfvénic flow can be formed in the quiet and recurrent low-speed solar wind streams. This kind of flow appears in regions with abnormal enhancement of Alfvénic speed and is associated with a specific type of magnetic configuration. 相似文献
19.
Hari Om Vats 《Journal of Astrophysics and Astronomy》2006,27(2-3):227-235
Examples of extreme events of solar wind and their effect on geomagnetic conditions are discussed here. It is found that there
are two regimes of high speed solar wind streams with a threshold of ∼ 850 km s-1. Geomagnetic activity enhancement rate (GAER) is defined as an average increase in Ap value per unit average increase in
the peak solar wind velocity (Vp) during the stream. GAER was found to be different in the two regimes of high speed streams
with +ve and-ve IMF. GAER is 0.73 and 0.53 for solar wind streams with +ve and -ve IMF respectively for the extremely high
speed streams (< 850 km s-1). This indicates that streams above the threshold speed with +ve IMF are 1.4 times more effective in enhancing geomagnetic
activity than those with -ve IMF. However, the high speed streams below the threshold with -ve IMF are 1.1 times more effective
in enhancing geomagnetic activity than those with +ve IMF. The violent solar activity period (October–November 2003) of cycle
23 presents a very special case during which many severe and strong effects were seen in the environment of the Earth and
other planets; however, the z-component of IMF (Bz) is mostly positive during this period. The most severe geomagnetic storm
of this cycle occurred when Bz was positive. 相似文献
20.
A statistical analysis of the contemporary (1954-1975) solar flare particle events has been made for the parametersF (integrated, proton fluence in cm-2 in an event with kinetic energy above 10 MeV) andR
0 (the characteristic rigidity). These data are compared with the long-term averaged values determined from stable- and radio-nuclide
measurements of lunar samples. The analysis shows that the ancient solar flare proton spectrum was harder (higher R0 values) compared to that observed in contemporary flares. A similar analysis can not be made for the mean long-term averaged
flux (ˉJ, cm-2 S-1), since the contemporary averages suffer from an uncertainty due to the statistics of a single event. However, the average
flux estimates for time durations 〈T〉 exceeding 103 yr, are free from such uncertainties. The long-term averaged ˉJ values obtained over different time scales (104 - 106 yr) suggest a possible periodic variation in solar flare activity, with enhanced flux level during the last 105 yr. The available data rule out the occurrence of giant flares, with proton fluence exceeding 1015 cm-2 during the last million years. 相似文献