首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   439篇
  免费   15篇
  国内免费   5篇
测绘学   6篇
大气科学   39篇
地球物理   77篇
地质学   107篇
海洋学   131篇
天文学   75篇
综合类   5篇
自然地理   19篇
  2021年   2篇
  2020年   5篇
  2019年   8篇
  2018年   7篇
  2017年   16篇
  2016年   21篇
  2015年   9篇
  2014年   16篇
  2013年   24篇
  2012年   10篇
  2011年   15篇
  2010年   13篇
  2009年   21篇
  2008年   21篇
  2007年   25篇
  2006年   20篇
  2005年   24篇
  2004年   26篇
  2003年   17篇
  2002年   13篇
  2001年   12篇
  2000年   14篇
  1999年   15篇
  1998年   15篇
  1997年   8篇
  1996年   9篇
  1995年   8篇
  1994年   7篇
  1993年   3篇
  1992年   2篇
  1991年   8篇
  1990年   3篇
  1989年   4篇
  1988年   3篇
  1987年   4篇
  1986年   5篇
  1985年   2篇
  1984年   3篇
  1983年   10篇
  1982年   2篇
  1981年   3篇
  1980年   1篇
  1978年   1篇
  1976年   2篇
  1972年   1篇
  1970年   1篇
排序方式: 共有459条查询结果,搜索用时 15 毫秒
151.
Scientific visualization is an integral part of the modeling workflow, enabling researchers to understand complex or large data sets and simulation results. A high-resolution stereoscopic virtual reality (VR) environment further enhances the possibilities of visualization. Such an environment also allows collaboration in work groups including people of different backgrounds and to present results of research projects to stakeholders or the public. The requirements for the computing equipment driving the VR environment demand specialized software applications which can be run in a parallel fashion on a set of interconnected machines. Another challenge is to devise a useful data workflow from source data sets onto the display system. Therefore, we develop software applications like the OpenGeoSys Data Explorer, custom data conversion tools for established visualization packages such as ParaView and Visualization Toolkit as well as presentation and interaction techniques for 3D applications like Unity. We demonstrate our workflow by presenting visualization results for case studies from a broad range of applications. An outlook on how visualization techniques can be deeply integrated into the simulation process is given and future technical improvements such as a simplified hardware setup are outlined.  相似文献   
152.
In Kamchatka, Central Koryak, Central Kamchatka and East Kamchatka metallogenic belts are distributed from northwest to southeast. K–Ar age, sulfur isotopic composition of sulfide minerals, and bulk chemical compositions of ores were analyzed for 13 ore deposits including hydrothermal gold‐silver and base metal, in order to elucidate the geological time periods of ore formation, relationship to regional volcanic belts, type of mineralization, and origin of sulfur in sulfides. The dating yielded ore‐forming ages of 41 Ma for the Ametistovoe deposit in the Central Koryak, 17.1 Ma for the Zolotoe deposit and 6.9 Ma for the Aginskoe deposit in the Central Kamchatka, and 7.4 Ma for the Porozhistoe deposit and 5.1 Ma for the Vilyuchinskoe deposit in the East Kamchatka metallogenic belt. The data combined with previous data of ore‐forming ages indicate that the time periods of ore formation in these metallogenic belts become young towards the southeast. The averaged δ34SCDT of sulfides are ?2.8‰ for the Ametistovoe deposit in Central Koryak, ?1.8‰ to +2.0‰ (av. ?0.1‰) for the Zolotoe, Aginskoe, Baranievskoe and Ozernovskoe deposits in Central Kamchatka, and ?0.7 to +3.8‰ (av. +1.7‰) for Bolshe‐Bannoe, Kumroch, Vilyuchinskoe, Bystrinskoe, Asachinskoe, Rodnikovoe, and Mutnovskoe deposits in East Kamchatka. The negative δ34SCDT value from the Ametistovoe deposit in Central Koryak is ascribed to the contamination of 32S‐enriched sedimentary sulfur in the Ukelayat‐Lesnaya River trough of basement rock. Comparison of the sulfur isotope compositions of the mineral deposits shows similarity between the Central Koryak and Magadan metallogenic belts, and East Kamchatka and Kuril Islands belts. The Central Kamchatka belt is intermediate between these two groups in term of sulfur isotopic composition.  相似文献   
153.
We describe a catalogue of solar flares observed by the three instruments (SOT, XRT, EIS) onboard the Hinode satellite. From the launch of the Hinode satellite in September 2006 until late 2011, about 5000 solar flares (larger than A-class in the GOES classification) occurred during the five-year period of Hinode observations, and more than half of them were captured by the Hinode telescopes. Observation information for RHESSI and Nobeyama Radioheliograph are also included in the catalogue. This catalogue is distributed to users through the Internet. It will be useful and helpful for scientists in surveying flares to be analyzed, facilitate access to Hinode data, and help advance data analysis activities among the world solar community.  相似文献   
154.
In integrated systems for accurate positioning, which consist of GNSS, INS, and other sensors, the GNSS positioning accuracy has a decisive influence on the performance of the entire system and thus is very important. However, GNSS usually exhibits poor positioning results in urban canyon environments due to pseudorange measurement errors caused by multipath creation, which leads to performance degradation of the entire positioning system. For this reason, in order to maintain the accuracy of an integrated positioning system, it is necessary to determine when the GNSS positioning is accurate and which satellites can have their pseudorange measured accurately without multipath errors. Thus, the objective of our work is to detect the multipath errors in the satellite signals and exclude these signals to improve the positioning accuracy of GNSS, especially in an urban canyon environment. One of the previous technologies for tackling this problem is RAIM, which checks the residual of the least square and identifies the suspicious satellites. However, it presumes a Gaussian measurement error that is more common in an open-sky environment than in the urban canyon environment. On the other hand, our proposed method can estimate the size of the pseudorange error directly from the information of altitude positioning error, which is available with an altitude map. This method can estimate even the size of non-Gaussian error due to multipath in the urban canyon environment. Then, the estimated pseudorange error is utilized to weight satellite signals and improve the positioning accuracy. The proposed method was tested with a low-cost GNSS receiver mounted on a test vehicle in a test drive in Nagoya, Japan, which is a typical urban canyon environment. The experimental result shows that the estimated pseudorange error is accurate enough to exclude erroneous satellites and improve the GNSS positioning accuracy.  相似文献   
155.
A ground-penetrating radar (GPR) survey was conducted at the end of August 2009 in the suburb region of Ulaanbaatar, Honhor basin, Mongolia, in combination with conventional methods such as borehole drilling and measurement of ground temperatures. The interface of frozen and unfrozen sediment was distinctly resolved in the interpreted GPR images, verified by the borehole drilling records and 6-month measurement of ground temperatures. The location of the permafrost table was assessed to be at the depth of 2?C4?m in the study region. A conspicuous ice-saturated soil layer (massive ground ice) was detected in the interpreted GPR images with a thickness of 2?C5?m. The GPR investigation results were consistent with the borehole drilling records and ground temperatures observation. The borehole logs and ground temperatures profile in the borehole indicates that permafrost at Honhor basin is characterized by high ground temperature and high ice content, which implies that ongoing climatic warming would have great influence on permafrost dynamics. The research results are of great importance to further assess permafrost dynamics to climatic change in the boundary of discontinuous and sporadic permafrost regions in Mongolia in the future.  相似文献   
156.
157.
The response of phytoplankton to the Beaufort shelf-break eddies in the western Arctic Ocean is examined using the eddy-resolving coupled sea ice–ocean model including a lower-trophic marine ecosystem formulation. The regional model driven by the reanalysis 2003 atmospheric forcing from March to November captures the major spatial and temporal features of phytoplankton bloom following summertime sea ice retreat in the shallow Chukchi shelf and Barrow Canyon. The shelf-break warm eddies spawned north of the Barrow Canyon initially transport the Chukchi shelf water with high primary productivity toward the Canada Basin interior. In the eddy-developing period, the anti-cyclonic rotational flow along the outer edge of each eddy moving offshore occasionally traps the shelf water. The primary production inside the warm eddies is maintained by internal dynamics in the eddy-maturity period. In particular, the surface central area of an anti-cyclonic eddy acquires adequate light, nutrient, and warm environment for photosynthetic activity partly attributed to turbulent mixing with underlying nutrient-rich water. The simulated biogeochemical properties with the dominance of small-size phytoplankton inside the warm eddies are consistent with the observational findings in the western Arctic Ocean. It is also suggested that the light limitation before autumn sea ice freezing shuts down the primary production in the shelf-break eddies in spite of nutrient recovery. These results indicate that the time lag between the phytoplankton bloom in the shelf region following the summertime sea ice retreat and the eddy generation along the Beaufort shelf break is an important index to determine biological regimes in the Canada Basin.  相似文献   
158.
The nucleus of the Comet 73P/Schwassmann–Wachmann had been split into many fragments at least past two returns. Since the related dense dust trail has been detected in the space infrared observation, the strong activity of the meteor shower is highly expected in the future. We applied the so-called dust-trail theory to this interesting object, and obtained several results on the future encounter with the dust trail. In this paper we introduce our results on the forecasts.  相似文献   
159.
We explored the substantial spatial spread of the Quadrantid stream, based on the backward integration of orbital motions of the Quadrantids, impulsively perturbed by Jupiter. We found that the Jovian impulses can widely spread out them in the early twentieth century, especially their perihelia extended by a factor of ∼90 than those at the observed epoch. We regarded the spread as the intrinsic one of the Quadrantid stream itself.  相似文献   
160.
N2O concentration and its isotopomer ratios were measured over a wide area from San Diego to Honolulu in the eastern subtropical North Pacific (ESNP). Waters in the study area had an N2O maximum (38.2–50.5 nmol kg?1) at 600–1000 m depth, which is similar to the profiles obtained previously in other areas in the North Pacific. We separated the seawater into five water masses (two for the surface layer, two for the middle layer, and one for the deep layer) and deduced N2O production–consumption mechanisms in each water body by use of N2O isotopomer ratios. The results showed that the mechanisms differ slightly among water masses. In the “coastal” surface layer, N2O is produced by nitrification (NH2OH oxidation). In the “open ocean” surface layer, it is produced mainly by nitrifier denitrification and to a lesser extent by nitrification under substrate-limited conditions. In both “upwelling” and “open ocean” middle layers it is produced mainly by denitrification and to a lesser extent by nitrifier denitrification. It is also partly reduced. In the deep layer, it is produced predominantly by denitrification with partial reduction. In this way, isotopomers aid elucidation of production–consumption mechanisms of N2O in the sea even though the mechanisms cannot always be ascertained.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号