全文获取类型
收费全文 | 9315篇 |
免费 | 1868篇 |
国内免费 | 1908篇 |
专业分类
测绘学 | 342篇 |
大气科学 | 683篇 |
地球物理 | 2532篇 |
地质学 | 5542篇 |
海洋学 | 882篇 |
天文学 | 1627篇 |
综合类 | 523篇 |
自然地理 | 960篇 |
出版年
2024年 | 53篇 |
2023年 | 138篇 |
2022年 | 295篇 |
2021年 | 333篇 |
2020年 | 321篇 |
2019年 | 419篇 |
2018年 | 341篇 |
2017年 | 332篇 |
2016年 | 378篇 |
2015年 | 430篇 |
2014年 | 557篇 |
2013年 | 533篇 |
2012年 | 588篇 |
2011年 | 546篇 |
2010年 | 481篇 |
2009年 | 659篇 |
2008年 | 645篇 |
2007年 | 761篇 |
2006年 | 633篇 |
2005年 | 531篇 |
2004年 | 486篇 |
2003年 | 448篇 |
2002年 | 378篇 |
2001年 | 314篇 |
2000年 | 345篇 |
1999年 | 293篇 |
1998年 | 338篇 |
1997年 | 272篇 |
1996年 | 239篇 |
1995年 | 176篇 |
1994年 | 157篇 |
1993年 | 118篇 |
1992年 | 138篇 |
1991年 | 71篇 |
1990年 | 92篇 |
1989年 | 75篇 |
1988年 | 64篇 |
1987年 | 30篇 |
1986年 | 30篇 |
1985年 | 13篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 7篇 |
1980年 | 9篇 |
1979年 | 1篇 |
1978年 | 5篇 |
1977年 | 2篇 |
1954年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
被动源激发极化法的野外试验结果 总被引:10,自引:0,他引:10
对被动源激发极化法场源的基本性质、激发极化效应的提取方法进行了讨论,以野外试验结果为例研究了矿体与异常的对应规律,对该方法的有效性和可行性进行了说明。 相似文献
992.
Quartz was studied with respect to its silicon isotopic composition and cathodoluminescence in micro-fine disseminated gold deposits in SW Guizhou and NW Guangxi.The results showed that quartz in wall rocks.ores and that in association with hydrothermal silicification are distinctive in silicon isotopes and cathodoluminescence characters.Quartz in association with primary silicification is non-luminescent while that in wall rocks and associated with secondary silicification exhibits striking luminescence.Based on the dynamic fractionation of silicon isotopes,it is suggested that the mineralization was accompanied by rapid transport of aprimary siliceous fluid along the major deep fault system into subordinate faults before ore components deposited in favorable strata via penetration and metasomatism.Therefore,a deep origin is implicit for gold deposits of this type. 相似文献
993.
Z. Kaymaz 《Annales Geophysicae》1998,16(4):376-387
This study presents cross-sectional vector maps of the magnetic field derived from IMP 8 magnetometer in the magnetosheath at 30 Re behind the Earth. In addition the vector patterns of the magnetosheath field for northward, southward, and east-west interplanetary magnetic field (IMF) directions are qualitatively compared with those obtained from the Spreiter-Stahara gas dynamic (GD) and Fedder-Lyon magnetohydrodynamic models (MHD). The main purpose is to display the cross-sectional differences in relation to the dayside merging with different IMF directions, allowing the reader to make direct visual comparisons of the vector patterns. It is seen that for east-west IMF directions, the data-based and MHD-based patterns differ noticeably in a similar way from the GD model, presumably reflecting the influence of dayside magnetic merging of the Earths magnetic field with the y-component of the interplanetary magnetic field. All three northward IMF cross sections show comparable field draping patterns as expected for a closed magnetosphere. For southward IMF case, on the other hand, differences between the three cross-sectional patterns are greater as seen in the field vector sizes and directions, especially closer to the magnetopause where more disturbed magneto-spheric conditions are known to be exist. The data comparisons with the MHD and GD models show that the differences result from the magnetic field-flow coupling and that the effects of dayside reconnection are present in IMP 8 magnetic field measurements. 相似文献
994.
Preliminary results of measuring the crustal deformation in Qinghai-Xizang area using GPS technique 总被引:5,自引:0,他引:5
GPS repetition measurement tbta in Qinghai-Xizatlg (Tibetan) area in 1992 and 1994 have been used to determine the change
rates of seven bascline vectors of Lhasa-Wenquan, etc. It is the first time to obtain the direct observation results of the
large-scale crustal horizontal motions in this area. Thesc preliminary results also for the first time provide the direct
observation evidence for some important geophysical and geological viewpoints, such as the northward gradual reduce of the
effect of the northward push-pressing to Eurasian continent by Indian Plate in the Qinghai-Xizang area, having a southward
strike slip movement of the Chuan-Dian diamond block, etc. 相似文献
995.
湘西新元古界—寒武系中锑砷存在相态研究 总被引:7,自引:0,他引:7
应用部分提取技术研究湘西地区新元古界-寒中武系锑和砷元素的存在相态表明,岩石中以可交换离子,与碳酸盐有关,与硫化物有关和赋存于硅酸直放物晶格的4种形式存在的锑元素分别占岩石中锑总量的18.65%,0.85%,31.41%和43.81%,砷则分别为7.05%,4.29%和56.11%和29.18%,呈易迁移相态存在锑和砷分别为55.91%和67.45%,在含硫开放体系中,岩石中元素的淋滤率与其中易迁 相似文献
996.
A magnetic anomaly map of the northern part of the Philippine Sea plate shows two conspicuous north–south rows of long-wavelength anomalies over the Izu–Ogasawara (Bonin) arc, which are slightly oblique to the present volcanic front. These anomalies are enhanced on reduced-to-pole and upward-continued anomaly maps. The east row is associated with frontal arc highs (the Shinkurose Ridge), and the west row is accompanied by the Nishi-Shichito Ridge. Another belt of long-wavelength anomalies very similar to the former two occurs over the Kyushu–Palau Ridge. To explain the similarity of the magnetic anomalies, it is proposed that after the spreading of the Shikoku Basin separated the Izu–Ogasawara arc from the Kyushu–Palau Ridge, another rifting event occurred in the Miocene, which divided the Izu–Ogasawara arc into the Nishi-Shichito and Shinkurose ridges. The occurrence of Miocene rifting has also been suggested from the geology of the collision zone of the Izu–Ogasawara arc against the Southwest Japan arc: the Misaka terrain yields peculiar volcanic rocks suggesting back-arc rifting at ~ 15 Ma. The magnetic anomaly belts over the Izu–Ogasawara arc do not extend south beyond the Sofugan Tectonic Line, suggesting a difference in tectonic history between the northern and southern parts of the Izu–Ogasawara arc. It is estimated that the Miocene extension was directed northeast–southwest, utilizing normal faults originally formed during Oligocene rifting. The direction is close to the final stage of the Shikoku Basin spreading. On a gravity anomaly relief map, northeast–southwest lineaments can be recognized in the Shikoku Basin as well as over the Nishi-Shichito Ridge. We thus consider that lines of structural weakness connected transform faults of the Shikoku Basin spreading system and the transfer faults of the Miocene Izu–Ogasawara arc rifting. Volcanism on the Nishi-Shichito Ridge has continued along the lines of weakness, which could have caused the en echelon arrangement of the volcanoes. 相似文献
997.
The thermoelastic response due to a time-dependent rectangular heat source in a semi-infinite medium is analyzed. The problem originates from studies of nuclear waste repositories in rock. Canisters containing heat-emitting nuclear waste are deposited over a large rectangular area deep below the ground surface. The solution for a time-dependent heat source is obtained from the corresponding instantaneous heat source by superposition. The thermoelastic problem for the instantaneous rectangular heat source in a infinite surrounding is solved exactly. An important step is the introduction of so-called quadrantal heat sources. The solution for the rectangle is obtained from four quadrantal solutions. The solution for the quadrantal heat source depends on the three dimelasionless coordinates only. Time occurs in the scale factors only. The condition of zero normal and shear stresses at the ground surface is fulfilled by using a mirror heat source and a boundary solution. The boundary solution accounts for the residual normal stress at the ground surface. Using a Hertzian potential, a surprisingly simple solution is obtained. The final analytical solution is quite tractable considering the complexity of the initial problem. The solution may be used to test numerical models for coupled thermoelastic processes. It may also be used in more detailed numerical simulations of the process near the heat sources as boundary conditions to account for the three-dimensional global process. 相似文献
998.
We discuss the effects of galactic spiral arms on the -coefficient, turbulent diffusivity and turbulent energy density of the interstellar turbulence. We argue that the -coefficient and the dynamo number are larger in the interarm regions, whereas the kinetic energy density of turbulence is larger in the arms; the turbulent magnetic diffusivity can be only weakly affected by the spiral pattern. 相似文献
999.
1000.
根据含超压气体裂隙震源模式讨论P波初动符号的分布 总被引:1,自引:1,他引:0
利用含超压气体裂隙震源模式[1]分析研究了P波初动符号的分布.根据理论推导,不同倾角含超压气体裂隙可分别形成P波初动符号的四象限分布图象和圆、椭圆、抛物线、双曲线等圆锥曲线形P波节线.按节线形状和失稳方式进行了地震分类.所推论的初动P波、S波振幅分布规律和地形变特征都与实际相符 相似文献