全文获取类型
| 收费全文 | 2221篇 |
| 免费 | 421篇 |
| 国内免费 | 682篇 |
专业分类
| 测绘学 | 166篇 |
| 大气科学 | 399篇 |
| 地球物理 | 435篇 |
| 地质学 | 1534篇 |
| 海洋学 | 245篇 |
| 天文学 | 125篇 |
| 综合类 | 152篇 |
| 自然地理 | 268篇 |
出版年
| 2024年 | 13篇 |
| 2023年 | 48篇 |
| 2022年 | 77篇 |
| 2021年 | 117篇 |
| 2020年 | 115篇 |
| 2019年 | 112篇 |
| 2018年 | 85篇 |
| 2017年 | 96篇 |
| 2016年 | 121篇 |
| 2015年 | 111篇 |
| 2014年 | 140篇 |
| 2013年 | 138篇 |
| 2012年 | 128篇 |
| 2011年 | 121篇 |
| 2010年 | 125篇 |
| 2009年 | 138篇 |
| 2008年 | 141篇 |
| 2007年 | 145篇 |
| 2006年 | 147篇 |
| 2005年 | 125篇 |
| 2004年 | 122篇 |
| 2003年 | 96篇 |
| 2002年 | 101篇 |
| 2001年 | 99篇 |
| 2000年 | 105篇 |
| 1999年 | 83篇 |
| 1998年 | 67篇 |
| 1997年 | 63篇 |
| 1996年 | 69篇 |
| 1995年 | 49篇 |
| 1994年 | 38篇 |
| 1993年 | 32篇 |
| 1992年 | 38篇 |
| 1991年 | 29篇 |
| 1990年 | 25篇 |
| 1989年 | 21篇 |
| 1988年 | 21篇 |
| 1987年 | 5篇 |
| 1986年 | 5篇 |
| 1985年 | 5篇 |
| 1984年 | 3篇 |
| 1983年 | 2篇 |
| 1982年 | 2篇 |
| 1978年 | 1篇 |
排序方式： 共有3324条查询结果，搜索用时 609 毫秒
81.
Kevin Hall 《地球表面变化过程与地形》2004,29(1):43-57
Discussions regarding weathering in cold environments generally centre on mechanical processes and on the freeze–thaw mechanism in particular. Despite the almost ubiquitous assumption of freeze–thaw weathering, unequivocal proof of interstitial rock water actually freezing and thawing is singularly lacking. Equally, many studies have used the crossing of 0 °C, or values close to that, as the basis for determining the number of ‘freeze–thaw events’. In order to assess the weathering regime at a site in northern Canada, temperatures were collected at the surface, 1 cm and 3 cm depth for sets of paving bricks, with exposures both vertical and at 45°, orientated to the four cardinal directions. Temperature data were collected at 1 min intervals for 1 year. These data provide unequivocal proof for the occurrence of the freezing and thawing of water on and within the rock (freeze–thaw events). The freeze event is evidenced by the exotherm associated with the release of latent heat as the water actually freezes. This is thought to be the ?rst record of such events from a ?eld situation. More signi?cantly, it was found that the temperature at which freezing occurred varied signi?cantly through the year and that on occasion the 1 cm depth froze prior to the rock surface. The change in freeze temperature is thought to be due to the chemical weathering of the material (coupled with on‐going salt inputs via the melting of snowfall), which, it is shown, could occur throughout the winter despite air temperatures down to ?30 °C. This ?nding regarding chemical weathering is also considered to be highly signi?cant. A number of thermal stress events were also recorded, suggesting that rock weathering in cold regions is a synergistic combination of various chemical and mechanical weathering mechanisms. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
82.
Crack widths and rock temperatures were monitored on an andestic bedrock cliff in the summit area of the Daisetsu Mountains, Hokkaido, northern Japan. Sequential data recorded the gradual widening of a crack to the point of critical crack extension, which resulted in catastrophic rock breakage. The data indicate that a combination of liquid water in?ltration into crack tip and subsequent freezing is the most signi?cant factor contributing to critical crack extension. The recorded sub‐critical crack movements involved a number of minor crack extensions and contractions, the timing of which correlates well with the magnitude of the reconstructed thermal stresses at the crack tip derived from thermal deformation of the plate‐shaped rock fragment. Larger crack extensions occurred when stress at the crack tip exceeded a threshold value, possibly re?ecting the control of rock fracture mechanics by which cracks are thought to propagate when the stress intensity factor at the crack tip exceeds the threshold values for stress corrosion cracking and the fracture toughness of the material. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
83.
CAPPS1和CAPPS2数值预报模式对比分析 总被引：6，自引：0，他引：6
对CAPPS1模式和CAPPS2模式预报广西污染物进行了对比分析。主要对比了其污染扩散原理、气象预报模式、操作系统、运行时间、预报时效及预报效果。分析表明：CAPPS1和CAPPS2模式对各种污染物预报的相关系数均在0．44以上，两种模式预报广西空气污染都是可行的；两种模式均对SO2的预报效果最好，NO2次之，PM10相对最差；CAPPS2模式对各种污染物的预报值与实测值相关系数均比CAPPS1高，其中NO2的相关系数提高幅度最大；CAPPS2模式对NO2和PM10的预报准确率比CAPPS1偏高，而对SO2的预报准确率比CAPPS1偏低；CAPPS2预报首要污染物正确率比CAPPS1高出11个百分点，而预报首要污染物等级正确率则高出9个百分点。 相似文献
84.
85.
Crustal Growth by Magmatic Accretion Constrained by Metamorphic P-T Paths and Thermal Models of the Kohistan Arc, NW Himalayas 总被引：2，自引：0，他引：2
Magmatic accretion is potentially an important mechanism inthe growth of the continental crust and the formation of granulites.In this study, the thermal evolution of a magmatic arc in responseto magmatic accretion is modeled using numerical solutions ofthe one-dimensional heat conduction equation. The initial andboundary conditions used in the model are constrained by geologicalobservations made in the Kohistan area, NW Himalayas. Takingconsideration of the preferred intrusion locations for basalticmagmas, we consider two plausible modes of magmatic accretion:the first involves the repeated intrusion of basalt at mid-crustaldepths (‘intraplate model’), and the second evaluatesthe simultaneous intrusion of basalt and picrite at mid-crustaldepths and the base of the crust respectively (‘double-platemodel’). The results of the double-plate model accountfor both the inferred metamorphic P–T paths of the Kohistanmafic granulites and the continental geotherm determined frompeak P–T conditions observed for granulite terranes. Thedouble-plate model may be applicable as a key growth processfor the production of thick mafic lower crust in magmatic arcs. KEY WORDS: thermal model; magmatic underplating; P–T path; granulite; lower crust 相似文献
86.
87.
88.
89.
90.