全文获取类型
收费全文 | 12345篇 |
免费 | 2345篇 |
国内免费 | 3277篇 |
专业分类
测绘学 | 1203篇 |
大气科学 | 2686篇 |
地球物理 | 3020篇 |
地质学 | 6124篇 |
海洋学 | 1780篇 |
天文学 | 537篇 |
综合类 | 1131篇 |
自然地理 | 1486篇 |
出版年
2024年 | 32篇 |
2023年 | 195篇 |
2022年 | 605篇 |
2021年 | 705篇 |
2020年 | 579篇 |
2019年 | 695篇 |
2018年 | 715篇 |
2017年 | 632篇 |
2016年 | 764篇 |
2015年 | 717篇 |
2014年 | 771篇 |
2013年 | 908篇 |
2012年 | 797篇 |
2011年 | 796篇 |
2010年 | 728篇 |
2009年 | 830篇 |
2008年 | 730篇 |
2007年 | 628篇 |
2006年 | 566篇 |
2005年 | 474篇 |
2004年 | 353篇 |
2003年 | 346篇 |
2002年 | 315篇 |
2001年 | 319篇 |
2000年 | 363篇 |
1999年 | 491篇 |
1998年 | 372篇 |
1997年 | 373篇 |
1996年 | 357篇 |
1995年 | 300篇 |
1994年 | 249篇 |
1993年 | 220篇 |
1992年 | 183篇 |
1991年 | 139篇 |
1990年 | 118篇 |
1989年 | 125篇 |
1988年 | 107篇 |
1987年 | 57篇 |
1986年 | 62篇 |
1985年 | 43篇 |
1984年 | 40篇 |
1983年 | 23篇 |
1982年 | 22篇 |
1981年 | 26篇 |
1980年 | 17篇 |
1979年 | 15篇 |
1978年 | 9篇 |
1976年 | 6篇 |
1973年 | 7篇 |
1958年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 215 毫秒
31.
32.
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
33.
Yi-Zhong Fan Zi-Gao Dai Yong-Feng Huang Tan Lu Department of Astronomy Nanjing University Nanjing 《中国天文和天体物理学报》2002,2(5):449-453
The optical flash accompanying GRB 990123 is believed to be powered by the reverse shock of a thin shell. With the best-fit physical parameters for GRB 990123 and the assumption that the parameters in the optical flash are the same as in the afterglow, we show that: 1) the shell is thick rather than thin, and we have provided the light curve for the thick shell case which coincides with the observation; 2) the theoretical peak flux of the optical flash accounts for only 3×10~-4 of the observed. In order to remove this discrepancy, the physical parameters, the electron energy and magnetic ratios, εe and εB, should be 0.61 and 0.39, which are very different from their values for the late afterglow. 相似文献
34.
基于GIS的印度洋大眼金枪鱼延绳钓钓获率与水温关系的研究 总被引:3,自引:0,他引:3
采用GIS定性分析和数值分析的方法,研究了印度洋大眼金枪鱼延绳钓钓获率与水温的 关系。结果表明,大眼金枪鱼延绳钓高钓获率的出现与印度洋加权水温大面分布存在明显的相互 关系,大眼金枪鱼的渔获适温在14~17℃间。建议测量200m水深处的水温作为海上生产时的参 考。 相似文献
35.
STUDY ON GIS FOR YIELD ESTIMATION BY REMOTE SENSING IN JILIN MAIZE BELTSTUDYONGISFORYIELDESTIMATIONBYREMOTESENSINGINJILINMAIZ... 相似文献
36.
A new algorithm of order five is presented for the solution of the initial value problem where the system of ordinary differential equations is of second order and does not contain the first derivative. 相似文献
37.
Afforestation has been suggested as a means of improving soil and water conservation in north‐western China, especially on the Loess Plateau. Understanding of the hydrological responses to afforestation will help us develop sustainable watershed management strategies. A study was conducted during the period of 1956 to 1980 to evaluate runoff responses to afforestation in a watershed on the Loess Plateau with an area of 1·15 km2, using a paired watershed approach. Deciduous trees, including locust (locusta L.), apricot (praecox L.) and elm (ulmus L.), were planted on about 80% of a treated watershed, while a natural grassland watershed remained unchanged. It was estimated that cumulative runoff yield in the treated watershed was reduced by 32% as a result of afforestation. A significant trend was also observed that shows annual runoff reduction increases with the age of the trees planted. Reduction in monthly runoff occurred mainly from June to September, which was ascribed to greater rainfall and utilization by trees during this period. Afforestation also resulted in reduction in the volume and peak flow of storm runoff events in the treated watershed with greater reduction in peak flow. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
38.
Gamma-ray burst remnants become trans-relativistic typically in days to tens of days, and they enter the deep Newtonian phase in tens of days to months, during which the majority of shock-accelerated electrons will no longer be highly relativistic. However, a small portion of electrons are still accelerated to ultra-relativistic speeds and are capable of emitting synchrotron radiation. The distribution function for electrons is re-derived here so that synchrotron emission from these relativistic electrons can be calculated. Based on the revised model, optical afterglows from both isotropic fireballs and highly collimated jets are studied numerically, and compared to analytical results. In the beamed cases, it is found that, in addition to the steepening due to the edge effect and the lateral expansion effect, the light curves are universally characterized by a flattening during the deep Newtonian phase. 相似文献
39.
40.
CORROSION AND ADHERENCE AT SEA OIL-PLATFORM 总被引:1,自引:0,他引:1
Measurements of the adhesive corrosion and protective potentials of 3 Bohai Sea oilplatforms under different cathodic protection showed corrosion still occurred on these platforms undertheir designed protective potentials. Preliminary conclusions from indoor experiments on the relation betweenadhesive corrosion and cathodic protection showed adhering organisms caused the corrosion onthese platforms. 相似文献