全文获取类型
收费全文 | 3247篇 |
免费 | 130篇 |
国内免费 | 80篇 |
专业分类
测绘学 | 98篇 |
大气科学 | 289篇 |
地球物理 | 749篇 |
地质学 | 1064篇 |
海洋学 | 304篇 |
天文学 | 712篇 |
综合类 | 29篇 |
自然地理 | 212篇 |
出版年
2022年 | 22篇 |
2021年 | 48篇 |
2020年 | 63篇 |
2019年 | 53篇 |
2018年 | 93篇 |
2017年 | 91篇 |
2016年 | 119篇 |
2015年 | 91篇 |
2014年 | 79篇 |
2013年 | 173篇 |
2012年 | 120篇 |
2011年 | 138篇 |
2010年 | 149篇 |
2009年 | 145篇 |
2008年 | 156篇 |
2007年 | 132篇 |
2006年 | 123篇 |
2005年 | 114篇 |
2004年 | 134篇 |
2003年 | 127篇 |
2002年 | 158篇 |
2001年 | 148篇 |
2000年 | 98篇 |
1999年 | 68篇 |
1998年 | 54篇 |
1997年 | 49篇 |
1996年 | 43篇 |
1995年 | 49篇 |
1994年 | 46篇 |
1993年 | 31篇 |
1992年 | 22篇 |
1991年 | 30篇 |
1990年 | 35篇 |
1989年 | 21篇 |
1987年 | 19篇 |
1986年 | 20篇 |
1985年 | 30篇 |
1984年 | 40篇 |
1983年 | 26篇 |
1982年 | 22篇 |
1981年 | 23篇 |
1980年 | 14篇 |
1978年 | 20篇 |
1977年 | 13篇 |
1976年 | 19篇 |
1975年 | 20篇 |
1974年 | 26篇 |
1972年 | 21篇 |
1971年 | 17篇 |
1970年 | 13篇 |
排序方式: 共有3457条查询结果,搜索用时 93 毫秒
141.
Mountainous areas surrounding the Campanian Plain and the Somma-Vesuvius volcano (southern Italy) are among the most risky areas of Italy due to the repeated occurrence of rainfall-induced debris flows along ash-fall pyroclastic soil-mantled slopes. In this geomorphological framework, rainfall patterns, hydrological processes taking place within multi-layered ash-fall pyroclastic deposits and soil antecedent moisture status are the principal factors to be taken into account to assess triggering rainfall conditions and the related hazard. This paper presents the outcomes of an experimental study based on integrated analyses consisting of the reconstruction of physical models of landslides, in situ hydrological monitoring, and hydrological and slope stability modeling, carried out on four representative source areas of debris flows that occurred in May 1998 in the Sarno Mountain Range. The hydrological monitoring was carried out during 2011 using nests of tensiometers and Watermark pressure head sensors and also through a rainfall and air temperature recording station. Time series of measured pressure head were used to calibrate a hydrological numerical model of the pyroclastic soil mantle for 2011, which was re-run for a 12-year period beginning in 2000, given the availability of rainfall and air temperature monitoring data. Such an approach allowed us to reconstruct the regime of pressure head at a daily time scale for a long period, which is representative of about 11 hydrologic years with different meteorological conditions. Based on this simulated time series, average winter and summer hydrological conditions were chosen to carry out hydrological and stability modeling of sample slopes and to identify Intensity-Duration rainfall thresholds by a deterministic approach. Among principal results, the opposing winter and summer antecedent pressure head (soil moisture) conditions were found to exert a significant control on intensity and duration of rainfall triggering events. Going from winter to summer conditions requires a strong increase of intensity and/or duration to induce landslides. The results identify an approach to account for different hazard conditions related to seasonality of hydrological processes inside the ash-fall pyroclastic soil mantle. Moreover, they highlight another important factor of uncertainty that potentially affects rainfall thresholds triggering shallow landslides reconstructed by empirical approaches. 相似文献
142.
Molybdenum Mass Fractions and Isotopic Compositions of International Geological Reference Materials
下载免费PDF全文
![点击此处可从《Geostandards and Geoanalytical Research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Pei‐Pei Zhao Jie Li Le Zhang Zhi‐Bing Wang De‐Xin Kong Jin‐Long Ma Gang‐Jian Wei Ji‐Feng Xu 《Geostandards and Geoanalytical Research》2016,40(2):217-226
The double‐spike method with multi‐collector inductively coupled plasma‐mass spectrometry was used to measure the Mo mass fractions and isotopic compositions of a set of geological reference materials including the mineral molybdenite, seawater, coral, as well as igneous and sedimentary rocks. The long‐term reproducibility of the Mo isotopic measurements, based on two‐year analyses of NIST SRM 3134 reference solutions and seawater samples, was ≤ 0.07‰ (two standard deviations, 2s, n = 167) for δ98/95Mo. Accuracy was evaluated by analyses of Atlantic seawater, which yielded a mean δ98/95Mo of 2.03 ± 0.06‰ (2s, n = 30, relative to NIST SRM 3134 = 0‰) and mass fraction of 0.0104 ± 0.0006 μg g?1 (2s, n = 30), which is indistinguishable from seawater samples taken world‐wide and measured in other laboratories. The comprehensive data set presented in this study serves as a reference for quality assurance and interlaboratory comparison of high‐precision Mo mass fractions and isotopic compositions. 相似文献
143.
Jo Beth Mullens 《The Journal of geography》2016,115(6):244-255
Charging undergraduate geography students with the task of designing a recreational trail in their local community offers an engaging experiential opportunity with potential to advance geographic learning in a real-world setting. This article presents an assignment in which students were asked to develop a recreational trail proposal for an undeveloped local conservation area and the results of a survey that asked the students to reflect and report upon the educational value of this experience one year later. Results of the survey validated the assignment's lasting value to the students across the cognitive, psychomotor, and affective learning domains. 相似文献
144.
145.
146.
147.
148.
149.
150.
A single specimen of the pelagic shrimps, Pasiphaea japonica Omori, 1976 (Pasiphaeidae) collected in the southeastern waters of Korea is described and illustrated. Although this species occurs widely in the Indo-West Pacific including the Japanese coast of the East/Japan Sea and the middle and southern parts of the East China Sea, this is the first record of the species and the genus in Korean waters. The species is distinguished from other congeners by the following combination of characteristics: non-carinate dorsal sixth abdominal somite with a terminal tooth, rudimentary pleurobranch on the eighth thoracic somite, merus of the first pereopod with more than eight spines, and almost entirely transparent white color. 相似文献