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   249篇
  免费   1篇
测绘学   5篇
大气科学   18篇
地球物理   125篇
地质学   57篇
海洋学   3篇
天文学   23篇
综合类   1篇
自然地理   18篇
  2017年   4篇
  2016年   6篇
  2015年   8篇
  2014年   10篇
  2013年   10篇
  2012年   9篇
  2011年   9篇
  2010年   8篇
  2009年   8篇
  2008年   5篇
  2007年   7篇
  2004年   4篇
  2003年   5篇
  2001年   8篇
  2000年   7篇
  1999年   5篇
  1998年   3篇
  1997年   6篇
  1996年   3篇
  1993年   4篇
  1992年   4篇
  1990年   5篇
  1987年   2篇
  1986年   2篇
  1983年   3篇
  1982年   3篇
  1981年   3篇
  1980年   6篇
  1979年   3篇
  1977年   2篇
  1976年   4篇
  1975年   4篇
  1974年   2篇
  1972年   2篇
  1971年   3篇
  1970年   4篇
  1969年   3篇
  1968年   5篇
  1967年   2篇
  1966年   5篇
  1965年   3篇
  1964年   2篇
  1963年   3篇
  1962年   2篇
  1961年   2篇
  1960年   4篇
  1959年   4篇
  1958年   3篇
  1957年   2篇
  1956年   2篇
排序方式: 共有250条查询结果,搜索用时 15 毫秒
161.
Summary An analytico-numerical computation of the transfer function of the sensing system of a vibrational magnetometer is presented. In discussing the results, the properties of the method are pointed out and a proposal for the sensing system is made with regard to the required sensitivity of the instrument.  相似文献   
162.
Hydrologic data derived from digital elevation models (DEM) has been regarded as an effective method in the spatial analysis of geographical information systems (GIS). However, both DEM resolution and terrain complexity has impacts on the accuracy of hydrologic derivatives. In this study, a multi-resolution and multi-relief comparative approach was used as a major methodology to investigate the accuracy of hydrologic data derived from DEMs. The experiment reveals that DEM terrain representation error affects the accuracy of DEM hydrological derivatives (drainage networks and watershed etc.). Coarser DEM resolutions can usually cause worse results. However, uncertain result commonly exists in this calculation. The derivative errors can be found closely related with DEM vertical resolution and terrain roughness. DEM vertical resolution can be found closely related with the accuracy of DEM hydrological derivatives, especially in the smooth plain area. If the mean slope is less than 4 degrees, the derived hydrologic data are usually unreliable. This result may be helpful in estimating the accuracy of the hydrologic derivatives and determining the DEM resolution that is appropriate to the accuracy requirement of a particular user. By applying a threshold value to subset the cells of a higher accumulation flow, a stream network of a specific network density can be extracted. Some very important geomorphologic characteristics, e.g., shallow and deep gullies, can be separately extracted by means of adjusting the threshold value. However, such a flow accumulationbased processing method can not correctly derive those streams that pass through the working area because it is hard to accumulate enough flow direction values to express the stream channels at the stream's entrance area. Consequently, errors will definitely occur at the stream’s entrance area. In addition, erroneous derivatives can also be found in deriving some particular rivers, e.g., perched (hanging up) rivers, anastomosing rivers and braided rivers. Therefore, more work should be done to develop and perfect the algorithms.  相似文献   
163.
A continuously operated gas monitoring station was emplaced within the epicentral area of the NW Bohemian swarm earthquakes overlying directly the active Mariánské Lázně fault. The recordings of 8-month continuous monitoring period are presented. The variations in radon concentrations are similarly to variations in CO2, i.e. CO2 is considered to be the carrier gas for radon. Very small diurnal variations in gas concentration are caused by the earth tides, as daily variations in meteorological conditions cannot explain a short daily minimum at midday times. Sudden changes in gas concentration, which clearly exceed these diurnal variations occur and are always linked with seismic activities. Decreased gas concentration may indicate compression resulting in reduced fault permeability as is implied by negative peaks following local earthquake swarms. A sudden increase in CO2 and Rn concentration may indicate an increased fault permeability caused by stress redistribution, giving rise to opening of migration pathways. This implies a repeatedly sudden rise in gas concentration before local earthquake swarms. Several variations in gas concentration were monitored linked with remote earthquakes of ground motion amplitudes  >1 μm. These seismic events are accompanied by an interference of the diurnal gas concentration–stress-cycle along the Mariánské Lázně fault. However, if shocks of remote earthquake can alter properties of the migrating fluids or the fault properties it can be suggested that these are able to trigger local seismicity, as indicated in the case of the Slovenia earthquake on 12th July 2004.  相似文献   
164.
Резюме В статье приводится описание методики измерений искусственной радиоактивности осадков. В результате измерений более 90 образцов бЫло доказано, что здесь мЫ имеем дело с искусственной радиоактивностью, вЫзЫваемой наличием продуктов распада образующихся в результате опЫтов с атомнЫм оружием. Доказательством этого служит прежде всего убЫвание активности испарений с временем. Абсолютная оценка показала, что здесь речь идет об активности порядка 10−10–10−9 кюру/л. в воде осадков. ПроведеннЫе работЫ показали, насколько важнЫми могут бЫть подобнЫе измерения для метеорологических целей, но в особенности для фпзики облаков и осадков.

Address: Vojenská lékařská akademie J. Ev. Purkynê, Hradec Králové.

Address: Geofysikální ústav ĈSAV, odd. meteorologie, Hradec Králové 8.  相似文献   
165.
166.
167.
Gypsum: a review of its role in the deterioration of building materials   总被引:2,自引:0,他引:2  
The deterioration of buildings and monuments by gypsum is the result of crystallization cycles of this salt. Although gypsum can dehydrate to a hemihydrate, the mineral bassanite, and to an anhydrate, the mineral anhydrite, this reaction occurs in nature on a geological time scale and therefore it is unlikely to occur when gypsum is found on and in building materials. The CaSO4–H2O system appears deceptively simple, however there are still discrepancies between the experimental and thermodynamically calculated data. The reason for the latter can be attributed to the slow crystallization kinetics of anhydrite. Apart from this, the large numbers of studies carried out on this system have focused on industrially important metastable phases, such as the hemihydrate and soluble anhydrite. The paper presents a review of the studies dealing with the phase equilibria of the CaSO4–H2O system as well as the influence of other salts on the solubility of gypsum. It tries to glean out the relevant information that will serve to explain the deterioration observed on building materials by the crystallization of gypsum and thus allows developing improved conservation methods.  相似文献   
168.
    
Time‐lapse photography provides an attractive source of information about snow cover characteristics, especially at the small catchment scale. The objective of this study was to design and test a monitoring system, which allows multi‐resolution observations of snow cover characteristics. The main aim was to simultaneously investigate the spatio‐temporal patterns of snow cover, snow depth and snowfall interception in the area very close to the camera, and the spatio‐temporal patterns of snow cover in the far range. The multi‐resolution design was tested at three sites in the eastern part of the Austrian Alps (Hochschwab‐Rax region). Digital photographs were taken at hourly time steps between 6:00 and 18:00 in the period November, 2004 to December, 2006. The results showed that the time‐lapse photography allows effective mapping of the snow depths at high temporal resolution in the region close to the digital camera at many snow stake locations. It is possible to process a large number of photos by using an automatic procedure for accurate snow depth readings. The digital photographs can also be used to infer the settling characteristics of the snow pack and snow interception during the day. Although it is not possible to directly estimate the snow interception mass, the photos may indeed give very useful information on the snow processes on and beneath the forest canopy. The main advantage of using time‐lapse photography in the far range of the digital camera is to observe the spatio‐temporal patterns of snow cover over different landscape configurations. The results illustrate that digital photographs can be very useful for parameterising processes such as sloughing on steep slopes, snow deposition in gullies and snow erosion on mountain ridges in a distributed snow model. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   
169.
170.
Zusammenfassung In Systemen mit vorwiegend heteropolarer Bindung ist (jedenfalls weit unterhalb des Schmelzpunktes) die Freie Energie des Gesamtsystems vor allem durch die elektrostatischen Gitterenergien bestimmt. Ihre Diskussion ermöglicht somit das Verständnis für das Auftreten oder Nicht-Auftreten der formal möglichen Kristallphasen. Bei überschlagsweisen Betrachtungen genügt es, für die zu erwartenden Phasen die Möglichkeit der Erfüllung der Paulingschen Regeln zu verlangen; dann ist das Gitter gut elektrostatisch abgesättigt und die elektrostatische Gitterenergie ist groß.  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