全文获取类型
收费全文 | 7979篇 |
免费 | 218篇 |
国内免费 | 315篇 |
专业分类
测绘学 | 220篇 |
大气科学 | 639篇 |
地球物理 | 1675篇 |
地质学 | 2954篇 |
海洋学 | 649篇 |
天文学 | 1900篇 |
综合类 | 32篇 |
自然地理 | 443篇 |
出版年
2023年 | 43篇 |
2022年 | 58篇 |
2021年 | 70篇 |
2020年 | 72篇 |
2019年 | 85篇 |
2018年 | 247篇 |
2017年 | 204篇 |
2016年 | 284篇 |
2015年 | 171篇 |
2014年 | 272篇 |
2013年 | 431篇 |
2012年 | 253篇 |
2011年 | 424篇 |
2010年 | 298篇 |
2009年 | 472篇 |
2008年 | 371篇 |
2007年 | 329篇 |
2006年 | 342篇 |
2005年 | 314篇 |
2004年 | 296篇 |
2003年 | 282篇 |
2002年 | 260篇 |
2001年 | 219篇 |
2000年 | 206篇 |
1999年 | 183篇 |
1998年 | 175篇 |
1997年 | 164篇 |
1996年 | 157篇 |
1995年 | 142篇 |
1994年 | 116篇 |
1993年 | 94篇 |
1992年 | 79篇 |
1991年 | 91篇 |
1990年 | 80篇 |
1989年 | 86篇 |
1988年 | 60篇 |
1987年 | 104篇 |
1986年 | 64篇 |
1985年 | 65篇 |
1984年 | 70篇 |
1983年 | 71篇 |
1982年 | 72篇 |
1981年 | 68篇 |
1980年 | 53篇 |
1979年 | 52篇 |
1977年 | 49篇 |
1976年 | 47篇 |
1975年 | 35篇 |
1974年 | 30篇 |
1973年 | 41篇 |
排序方式: 共有8512条查询结果,搜索用时 921 毫秒
271.
Zircon fission track dating and track length analysis in the high‐grade part of the Asemigawa region of the Sanbagawa belt demonstrates a simple cooling history passing through the partial annealing zone at 63.2 ± 5.8 (2 σ) Ma. Combining this age with previous results of phengite and amphibole K–Ar and 40Ar/39Ar dating gives a cooling rate of between 6 and 13 °C Myr?1, which can be converted to a maximum exhumation rate of 0.7 mm year?1 using the known shape of the P–T path. This is an order of magnitude lower than the early part of the exhumation history. In contrast, zircon fission track analyses in the low‐grade Oboke region show that this area has undergone a complex thermal history probably related to post‐orogenic secondary reheating younger than c. 30 Ma. This event may correlate with the widespread igneous activity in south‐west Japan around 15 Ma. The age of subduction‐related metamorphism in the Oboke area is probably considerably older than the generally accepted range of 77–70 Ma. 相似文献
272.
We perform a global statistical investigation into the problem of Coulomb stress triggering of earthquakes by using the Harvard CMT catalogue of shallow earthquakes from 1976 to 2001. We consider ‘earthquake pairs’, i.e., pairs of successive earthquakes occurring near each other with similar focal mechanisms, and address the problem of whether or not the change of the Coulomb failure stress (CFS) produced by the first earthquake of the pair ‘encourages’ the occurrence of the second one. An interesting feature is that such a Coulomb stress-triggering phenomenon has an apparent focal mechanism dependence: for thrust earthquakes, a more evident triggering effect can be observed. 相似文献
273.
Y. Ali Z. Aslam M. Y. Ashraf G. R. Tahir 《International Journal of Environmental Science and Technology》2004,1(3):221-225
Salt tolerance in eighteen advanced rice genotypes was studied under an artificially salinized (EC=8.5 dSm?1) soil conditions after 90 days of transplanting. The results showed that the yield per plant, chlorophyll concentrations, fertility percentage, and number of productive tillers, panicle length and number of primary braches per panicle of all the genotypes were reduced by salinity. However, genotypes viz. Jhona-349 x Basmati-370, NR-1, DM-59418, DM-63275, DM-64198 and DM-38-88 showed better salinity tolerance than others. 相似文献
274.
Asynchronous Holocene climatic change across China 总被引:1,自引:0,他引:1
A review of Holocene climatic variations in different parts of China shows that they were asynchronous. Proxy data from ice cores, pollen, loess, lacustrine sediments, and changes of sea and lake levels demonstrate that many warm and cold oscillations have occurred in China during the Holocene, including a most important climatic event known as the “Holocene optimum,” a milder and wetter period, and that the duration and amplitude of the optimum period, as well as its start and end times, differed in different parts of China. Uplift of the Tibetan plateau over the past millions of years led to the development of the monsoon climate and to complex atmospheric circulation over continental China during the Holocene. As a result, the Holocene optimum began and terminated earlier in high-altitude regions of western China than at lower elevations in eastern China, and the amplitude of the variations was lower in the east. This suggests that the western higher-altitude areas were more sensitive to climatic change than were the eastern lower-altitude areas. Holocene climatic records in the Dunde and Guliya ice cores do not correspond. Inverse δ18O variations between the two cores indicate that the effects of climate and atmospheric processes on the stable isotopes at the two sites differed. The correlation between the isotopic composition of carbonates in lake deposits in western China and climatic variations is similar to that in the ice cores. The climatic resolution in ice cores and lake sediments is higher than that in other media. The lack of precise correspondence of climatic records constructed on the basis of proxy data from different parts of China is a result of the different locations and elevations of the sampling sites, the different resolutions of the source material, and the varied climatic conditions within China. Further work is needed to confirm both the conclusions and the inferences presented here. 相似文献
275.
Carlos Marquardt Alain Lavenu Luc Ortlieb Estanislao Godoy Diana Comte 《Tectonophysics》2004,394(3-4):193-219
Neotectonic observations allow a new interpretation of the recent tectonic behaviour of the outer fore arc in the Caldera area, northern Chile (27°S). Two periods of deformation are distinguished, based on large-scale Neogene to Quaternary features of the westernmost part of the Coastal Cordillera: Late Miocene to Early Pliocene deformations, characterized by a weak NE–SW to E–W extension is followed by uppermost Pliocene NW–SE to E–W compression. The Middle Pleistocene to Recent time is characterized by vertical uplift and NW–SE extension. These deformations provide clear indications of the occurrence of moderate to large earthquakes. Microseismic observations, however, indicate a lack of shallow crustal seismicity in coastal zone. We propose that both long-term brittle deformation and uplift are linked to the subduction seismic cycle. 相似文献
276.
Rural Hong Kong contains culturally protected enclaves of remnant woodlands that provide sanctuary for vegetation, wildlife and soil. This study focuses on the influence of natural and cultural factors on soil properties in woodlands with different human activities. At each of the nine selected sites, two pits were dug to collect soil samples for analysis of 24 physical and chemical properties. Analyses of variance between soil attributes and site factors suggest the prominence of woodland size, and important contribution of topography, aspect and parent material. Soil indicators of human impacts and the tenacity of woodland soil towards anthropogenic disturbance were demonstrated. 相似文献
277.
278.
279.
Imaging the Dead Sea Transform with scattered seismic waves 总被引:2,自引:0,他引:2
280.