全文获取类型
收费全文 | 11097篇 |
免费 | 2095篇 |
国内免费 | 2702篇 |
专业分类
测绘学 | 626篇 |
大气科学 | 2066篇 |
地球物理 | 2800篇 |
地质学 | 5494篇 |
海洋学 | 1752篇 |
天文学 | 643篇 |
综合类 | 1295篇 |
自然地理 | 1218篇 |
出版年
2024年 | 64篇 |
2023年 | 169篇 |
2022年 | 559篇 |
2021年 | 614篇 |
2020年 | 508篇 |
2019年 | 589篇 |
2018年 | 660篇 |
2017年 | 620篇 |
2016年 | 666篇 |
2015年 | 552篇 |
2014年 | 676篇 |
2013年 | 636篇 |
2012年 | 726篇 |
2011年 | 678篇 |
2010年 | 680篇 |
2009年 | 639篇 |
2008年 | 555篇 |
2007年 | 543篇 |
2006年 | 433篇 |
2005年 | 385篇 |
2004年 | 282篇 |
2003年 | 306篇 |
2002年 | 277篇 |
2001年 | 312篇 |
2000年 | 375篇 |
1999年 | 486篇 |
1998年 | 371篇 |
1997年 | 414篇 |
1996年 | 345篇 |
1995年 | 308篇 |
1994年 | 293篇 |
1993年 | 245篇 |
1992年 | 208篇 |
1991年 | 148篇 |
1990年 | 126篇 |
1989年 | 103篇 |
1988年 | 78篇 |
1987年 | 44篇 |
1986年 | 41篇 |
1985年 | 28篇 |
1984年 | 30篇 |
1983年 | 35篇 |
1982年 | 18篇 |
1981年 | 20篇 |
1980年 | 9篇 |
1979年 | 5篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1958年 | 12篇 |
1954年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
本文对Osherovich的黑子返回磁通量模型作了适当的修改,使用黑子中心作为边界条件,用五种观测结果,导出了理论模型所需的五个主要参量,用半经验方法求得了黑子静力学模型的磁场、压力和温度等物理量.将此模型应用于一个中等大小的圆形对称黑子,可得到一个特解,结果发现我们的模型既能满足黑子的磁性质,同时又能满足合理的热力学量分布. 相似文献
2.
Vertical drains are usually installed in subsoil consisting of several layers. Due to the complex nature of the problem, over the past decades, the consolidation properties of multi‐layered ground with vertical drains have been analysed mainly by numerical methods. An analytical solution for consolidation of double‐layered ground with vertical drains under quasi‐equal strain condition is presented in this paper. The main steps for the computation procedure are listed. The convergence of the series solution is discussed. The comparisons between the results obtained by the present analytical method and the existing numerical solutions are described by figures. The orthogonal relation for the system of double‐layered ground with vertical drains is proven. Finally, some consolidation properties of double‐layered ground with vertical drains are analysed. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
3.
TANGYa XIEJiasui SUNHui 《山地科学学报》2004,1(1):38-45
Dry valleys are a striking geographic landscape in Hengduan Mountains Region and are characterized by low rainfall, desert type of vegetation and fragile environment. Past efforts and resources have been concentrated mainly on rehabilitation of degraded ecosystem and fragile environment, particularly reforestation, while socio-economic development has been largely overlooked. Despite successes in pocket areas, the overall trend of unsustainability and environmental deterioration are continuing. It is important to understand that uplift of the Tibetan Plateau is the root cause of development of dry valleys, and development and formation of dry valleys is a natural process. Human intervention has played a secondary role in development of dry valleys and degradation of dry valleys though human intervention in many cases has speeded up environmental degradation of the dry valleys. It is important to understand that dry valleys are climatic enclaves and an integrated approach that combines rehabilitation of degraded ecosystems and socio-economic development should be adopted if the overall goal of sustainable development of dry valleys is to be achieved. Promotion of niche-based cash crops, rural energy including hydropower, solar energy, biogas and fuelwood plantation is recommended as the priority activities. 相似文献
4.
Baolin Tan Haisheng Ji Guangli Huang Tuanhui Zhou Qiwu Song Yu Huang 《Solar physics》2006,239(1-2):137-148
Using one-minute cadence vector magnetograms from Big Bear Solar Observatory (BBSO), we analyze the temporal behavior of derived
longitudinal electric currents associated with two flares on July 26, 2002. One of the events is an M1.0 flare which occurred
in active region NOAA 10044, while the other is an M8.7 flare in the adjacent region 10039. Rapid changes of magnetic fields
in the form of flux emergence are found to be associated with both of these events. However, the temporal behavior of electric
currents are very different. For the M1.0 flare, the longitudinal electric current density drops rapidly near the flaring
neutral line; while for the M8.7 flare, the current density rapidly increases, confirming the picture of the current-carrying
flux emergence. We offer a possible explanation for such a difference: magnetic reconnection at different heights for the
two events, near the photosphere for the M1.0 flare, and higher up for the M8.7 flare. 相似文献
5.
6.
A. Quirrenbach J. Larkin M. Barczys T. Gasaway C. Iserlohe A. Krabbe M. McElwain I. Song J. Weiss S. Wright 《New Astronomy Reviews》2006,49(10-12):639
OSIRIS (OH-Suppressing Infra-Red Integral-field Spectrograph) is a new facility instrument for the Keck Observatory. After seeing first light in February 2005, OSIRIS is currently undergoing commissioning. OSIRIS provides the capability of performing three-dimensional spectroscopy in the near-infrared z, J, H, and K bands at the resolution limit of the Keck II telescope, which is equipped with adaptive optics and a laser guide star. The science case for OSIRIS is summarized, and the instrument and associated data reduction software are described. 相似文献
7.
A synthesis of Holocene pollen records from the Tibetan Plateau shows the history of vegetation and climatic changes during the Holocene. Palynological evidences from 24 cores/sections have been compiled and show that the vegetation shifted from subalpine/alpine conifer forest to subalpine/alpine evergreen sclerophyllous forest in the southeastern part of the plateau; from alpine steppe to alpine desert in the central, western and northern part; and from alpine meadow to alpine steppe in the eastern and southern plateau regions during the Holocene. These records show that increases in precipitation began about 9 ka from the southeast, and a wide ranging level of increased humidity developed over the entire of the plateau around 8-7 ka, followed by aridity from 6 ka and a continuous drying over the plateau after 4-3 ka. The changes in Holocene climates of the plateau can be interpreted qualitatively as a response to orbital forcing and its secondary effects on the Indian Monsoon which expanded northwards 相似文献
8.
针对多通道滤光器太阳磁场望远镜的磁场观测定标及掌握(所采用的)谱线特征之需要,取VAL宁静太阳大气模型计算了7条Fel光球线的Stokes轮廓、形成深度、贡献函数分布,从而较为系统地对多条反常及正常Zeeman线的特征及性质作出了分析与总结,解释了在磁光效应影响下Stokes Q,U参量的形成深度曲线在近线心区域处出现陡峭峰值的原因。 相似文献
9.
10.
韩崇德 《地球科学与环境学报》1992,(4)
洛坝铅锌矿床位于黄诸关韧脆性变形带所波及的范围内,断裂、褶皱、劈理、节理等形态构造类型均很发育,经对小型构造的统计及应力场分析证明,矿区变形主要是在海西—印支期长期存在的南北向古应力场持续作用下形成的。 相似文献