全文获取类型
收费全文 | 3011篇 |
免费 | 343篇 |
国内免费 | 395篇 |
专业分类
测绘学 | 214篇 |
大气科学 | 351篇 |
地球物理 | 844篇 |
地质学 | 1181篇 |
海洋学 | 463篇 |
天文学 | 207篇 |
综合类 | 182篇 |
自然地理 | 307篇 |
出版年
2024年 | 10篇 |
2023年 | 39篇 |
2022年 | 107篇 |
2021年 | 118篇 |
2020年 | 114篇 |
2019年 | 115篇 |
2018年 | 165篇 |
2017年 | 148篇 |
2016年 | 161篇 |
2015年 | 146篇 |
2014年 | 183篇 |
2013年 | 182篇 |
2012年 | 160篇 |
2011年 | 200篇 |
2010年 | 188篇 |
2009年 | 176篇 |
2008年 | 142篇 |
2007年 | 128篇 |
2006年 | 99篇 |
2005年 | 96篇 |
2004年 | 88篇 |
2003年 | 98篇 |
2002年 | 133篇 |
2001年 | 104篇 |
2000年 | 77篇 |
1999年 | 55篇 |
1998年 | 66篇 |
1997年 | 60篇 |
1996年 | 41篇 |
1995年 | 45篇 |
1994年 | 34篇 |
1993年 | 30篇 |
1992年 | 39篇 |
1991年 | 22篇 |
1990年 | 14篇 |
1989年 | 20篇 |
1988年 | 11篇 |
1987年 | 10篇 |
1986年 | 7篇 |
1985年 | 8篇 |
1984年 | 9篇 |
1983年 | 10篇 |
1982年 | 7篇 |
1981年 | 11篇 |
1980年 | 13篇 |
1979年 | 8篇 |
1978年 | 10篇 |
1977年 | 6篇 |
1976年 | 6篇 |
1975年 | 7篇 |
排序方式: 共有3749条查询结果,搜索用时 15 毫秒
991.
992.
993.
994.
995.
Summary This programme involves the study of the technique of using a micro-computer to control a rock drilling machine. The motion of an existing jumbo machine has been successfully analysed. The kinematic control equations are established for any given geometrical configuration. The computer software has been written to demonstrate its feasibility. The needs of hardware implementation are also discussed.The Deputy Chief Engineer at Yangzhuang Coal Mine, Hueibei Coal Mining Bureau, China. 相似文献
996.
The mechanical properties of particulate systems are studied from a micromechanics point of view. Two approaches, namely, computer simulation and micro-structural continuum modelling are used. The computer simulation method is used to study the uniformity of the strain field and effect of particle rotations. These results are then used to evaluate the applicability of the micro-structural continuum model. Potential applications of the micro-structural continuum model in the study of mechanical properties of soils are discussed. 相似文献
997.
San-Shyan Lin J. L. Hong Wei F. Lee Y. H. Chang 《Soil Dynamics and Earthquake Engineering》2004,24(11):829-838
A procedure that uses the structural damping (SD) concept for estimating the capacity of a pile based on the Statnamic (STN) pile load test results, formerly used by the authors for short piles, is extended in this paper for the STN tested long piles. Similar to segmental unloading point method procedures for long piles, the shaft length is divided into several segments and each segment is assumed to behave as a mass of a single degree of freedom. The SD concept is then applied to each segment to consider the displacement related soil damping instead of the velocity dependent damping. Instrumented strain gauge data at different levels of the shaft are required for the interpretation method. Three case studies are presented in this paper to study the validity and applicability of the present method. The predicted results are also compared to the available test or analytical data. 相似文献
998.
Characterization of liquefaction resistance in gravelly soil: large hammer penetration test and shear wave velocity approach 总被引:2,自引:0,他引:2
Ping-Sien Lin Chi-Wen Chang Wen-Jong Chang 《Soil Dynamics and Earthquake Engineering》2004,24(9-10):675
Gravelly soil is generally recognized to have no liquefaction potential. However, liquefaction cases were reported in central Taiwan in the 1999 Chi-Chi Taiwan earthquake and in the 1988 Armenia earthquake. Thus, further studies on the liquefaction potential of gravelly soil are warranted. Because large particles can impede the penetration of both standard penetration test and cone penetration test, shear wave velocity-based correlations and large hammer penetration tests (LPT) are employed to evaluate the liquefaction resistance of gravelly soils. A liquefied gravelly deposit site during the Chi-Chi earthquake was selected for this research. In situ physical properties of soil deposits were collected from exploratory trenches. Instrumented LPT and shear wave velocity (Vs) measurements were performed to evaluate the liquefaction resistance. In addition, large-scale cyclic triaxial tests on remolded gravelly soil samples (15 cm in diameter, 30 cm in height) were conducted to verify and improve LPT-based and Vs-based correlations. The results show that the LPT and shear wave velocity methods are reasonably suitable for liquefaction assessment of gravelly soils. 相似文献
999.
Abstract The Ogcheon fold belt and the Ryeongnam massif in the Korean Peninsula are made up of Precambrian igneous and sedimentary rocks that have been metamorphosed, tectonically deformed and extensively intruded by mafic to felsic plutonic rocks of Permian to Jurassic age. In the present study, we report seven new U–Pb zircon ages and Sr‐Nd‐Pb isotopic data for Permian to Jurassic plutons in the Ogcheon belt and the Ryeongnam massif. In the Ogcheon belt, these are: the Cheongsan porphyritic granite (217 ± 3.1 My), the Baegrog foliated granodiorite (206.4 ± 3.6 My), the Sani granite (178.8 ± 2.9 My) and the Yeonggwang foliated granite (173.0 ± 1.7 My). For the Ryeongnam massif, we report on the Yeongdeog foliated granodiorite (252.2 ± 2.9 My), the Sancheong gabbro (203.8 ± 3.3 My) and the Baegseogri foliated granodiorite (177.8 ± 2.4 My). All of these ages are lower concordia intercepts; the upper concordia intercepts indicate derivation from a Precambrian protolith. Sr, Nd and Pb isotopes also reveal that much of the Permian–Jurassic (252–173 Ma) plutonism in Korea was generated by recycling of Precambrian rocks. These new ages, together with other published zircon ages indicate that the plutonism in the Ogcheon fold belt is coeval with that in the Ryeongnam massif, but based on the Sr‐Nd‐Pb isotopic evidence, they are not cogenetic. In addition, zircon ages provide information on the movement along the Honam shear zone, which cuts across the whole Korean Peninsula and along most of its length provides the boundary between the Ogcheon fold belt and the Ryeongnam massif. It has a prolonged history of movement and deformation and appears to have been active from the Precambrian through to the Mesozoic, from before 1924 Ma to at least 180 Ma. The Permian–Jurassic igneous and tectonic activity in Korea is a manifestation of the more extensive orogenic activities that affected the East Asian continent at that time. In China, ultra high‐pressure rocks of the Qinling–Dabie belt formed between 210 and 230 Ma as result of the collision between the South China block and the North China block. In central Japan, corresponding plutonic activity is dated as 175 to 231 Ma. The absence of ultra high‐pressure rocks in Korea and Japan precludes a simple extension of the Qinling–Dabie belt eastwards; however, the effects of the continental collision eastwards are apparent from the igneous and tectonic activity. 相似文献
1000.
Static stress changes as a triggering mechanism of a shallow earthquake: case study of the 1999 Chi-Chi (Taiwan) earthquake 总被引:2,自引:0,他引:2
Jeng-Cheng WangChiou-Fen Shieh Tao-Ming Chang 《Physics of the Earth and Planetary Interiors》2003,135(1):17-25
The role of static stress changes in triggering an earthquake has long been debated in the fields of geophysics and fault mechanics. Valuable data sets for the study of static triggering were provided within the 1-year period following the devastating 1999 Chi-Chi (Taiwan) earthquake (MW=7.6), during which more than 20,000 aftershocks occurred. In this study, stress waves generated by the Chi-Chi earthquake were calculated using a source rupture model in conjunction with a layered elastic model. Static (permanent) stress changes were extracted from the long-period offsets in the stressgrams. Correlations between the calculated stress changes and seismicity were analyzed at different depths and over varying time intervals to ascertain the impact effects of stress changes on triggering aftershocks. Correlations between prior seismicity rates and static stress changes imposed by the Chi-Chi event were low, while correlations between late seismicity rates and static stress changes were much higher. This indicates that static stress changes did affect the occurrence of the Chi-Chi aftershock sequence. The percentage of early aftershocks at shallow depths (0-10 km) in static stress-enhanced areas within 2 weeks of the main shock was high but decreased considerably at greater depths (>10 km) and over longer time periods. It is concluded that static stress changes at depths of 0-10 km played a major role in triggering crustal aftershocks, especially those that occurred within 2 weeks of the main shock. In the deeper crust, static stress changes may have been modified by viscous flow, and at later times, perturbed by earlier, larger aftershocks. Although the correlations between seismicity rate changes and static stress changes are imperfect, a region that was anti-triggered is detected when these two results are compared. Static stress changes are presumably not the only aftershock triggering mechanism, but they definitively play a major role in triggering shallow aftershocks. 相似文献