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   2089篇
  免费   73篇
  国内免费   11篇
测绘学   99篇
大气科学   124篇
地球物理   802篇
地质学   563篇
海洋学   103篇
天文学   366篇
综合类   9篇
自然地理   107篇
  2021年   40篇
  2020年   20篇
  2019年   25篇
  2018年   61篇
  2017年   63篇
  2016年   101篇
  2015年   61篇
  2014年   71篇
  2013年   106篇
  2012年   60篇
  2011年   73篇
  2010年   83篇
  2009年   94篇
  2008年   76篇
  2007年   72篇
  2006年   64篇
  2005年   35篇
  2004年   64篇
  2003年   48篇
  2002年   50篇
  2001年   44篇
  2000年   48篇
  1999年   28篇
  1998年   31篇
  1997年   24篇
  1996年   41篇
  1995年   29篇
  1994年   25篇
  1993年   40篇
  1992年   22篇
  1991年   24篇
  1990年   20篇
  1989年   25篇
  1988年   22篇
  1987年   24篇
  1986年   24篇
  1985年   20篇
  1984年   23篇
  1983年   34篇
  1982年   25篇
  1981年   19篇
  1980年   22篇
  1979年   23篇
  1978年   28篇
  1977年   28篇
  1976年   21篇
  1975年   18篇
  1974年   18篇
  1973年   19篇
  1971年   20篇
排序方式: 共有2173条查询结果,搜索用时 46 毫秒
211.

Parameterization of wave runup is of paramount importance for an assessment of coastal hazards. Parametric models employ wave (e.g., Hs and Lp) and beach (i.e., β) parameters to estimate extreme runup (e.g., R2%). Thus, recent studies have been devoted to improving such parameterizations by including additional information regarding wave forcing or beach morphology features. However, the effects of intra-wave dynamics, related to the random nature of the wave transformation process, on runup statistics have not been incorporated. This work employs a phase- and depth- resolving model, based on the Reynolds-averaged Navier-Stokes equations, to investigate different sources of variability associated with runup on planar beaches. The numerical model is validated with laboratory runup data. Subsequently, the role of both aleatory uncertainty and other known sources of runup variability (i.e., frequency spreading and bed roughness) is investigated. Model results show that aleatory uncertainty can be more important than the contributions from other sources of variability such as the bed roughness and frequency spreading. Ensemble results are employed to develop a new parametric model which uses the Hunt (J Waterw Port Coastal Ocean Eng 85:123–152, 1959) scaling parameter \(\beta \left (H_{s}L_{p}\right )^{1/2}\).

  相似文献   
212.
The western part of the Bohemian Massif has played an exceptional role in recent geodynamic activity of the region. It is characterised by repeated occurrences of earthquake swarms and by other manifestations of deep tectonic processes (CO 2 emissions, anomalous 3 He content, mineral waters, mofettes, etc.). The purpose of this paper is to introduce some other intraplate regions with earthquake swarm occurrence (French Massif Central; Colli Albani and Vulsini Mts., central Italy; Southern Apennines, Italy; the Danville and Long Valley regions, California; central Arkansas), and with artificially induced earthquake swarms (Larderello, Italy, geothermal field; Coso, California, geothermal field; NE Bavaria, Germany, deep drilling project). Although these areas represent different tectonic environments, the manifestations of recent geodynamic and/or man-made activity are similar in many aspects. This coincidence most probably issues from a common cause of both tectonic and artificially induced earthquake swarms – intrusions/injections of fluids. Since the regions with earthquake swarm occurrence of tectonic origin are situated as a rule in the close neighbourhood of Quaternary volcanoes, the intruding fluids seem to be derived from magma recently transported to upper crustal layers.  相似文献   
213.
Summary Some errors of method occurring in A. C. measurements of the electrical conductivity of rocks are discussed. It is demonstrated that the difference between A.C. and D.C. conductivities, at given frequency, depends mostly on the magnitude of the D.C. conductivity and magnitude of the dielectric constant.  相似文献   
214.
Summary The estimation of the theoretical magnitude for deep foci based on the vertica component of medium-period PKIKP waves, Earth model PREM and source spectra is presented. The given graphs are valid for period T ranging from 1·6 s to 10 s, source depth of 25 km to 600 km and distance range of 16 500 km to 19 800 km. A simplified method of representing calibration curves is used.  相似文献   
215.
216.
Summary Procedure for verifying the agreement between parameters common to the basic and connecting trigonometric net. Procedure of determining the accuracy of the connecting net. This determination concerns not only the relativized accuracy of the points of the connecting network, but also the mutual accuracy of the points of the basic net relative to the points of the connecting net and the global accuracy of the resultant net. The procedure takes into account the accuracy of the points of the basic net which remain unchanged in computing the coordinates of new points.
m¶rt; ¶rt; nu au u naam¶rt;mu u nu¶rt;u m. m¶rt; ¶rt; u mmu nu¶rt;u mu. a aam m mum nua mmu m nu¶rt; mu, ma au mmu m mu n mu ma nu¶rt;u mu ua mmu mu mu. m¶rt; umam mm m mu, m aa uu ¶rt;uam m mam uu.
  相似文献   
217.
m¶rt; amamu ¶rt;uau nma nauua ¶rt; a n amu . n ¶rt;a uu u¶rt;au,aumuu u mn nma. mam maa auum ¶rt; m u nmm u¶rt;ua n¶rt;a u a maa a umua a nam . ¶rt; nmm amuu n¶rt;m uu 3,3/ 3 , n¶rt; ¶rt;uuuau u na¶rt;uau mu a anma ¶rt; 3,2/ 3 . ¶rt; n¶rt;uu a¶rt;u aau mum nm, maumaa ¶rt;¶rt;m aama u ¶rt; amu .

Presented at the KAPG Symposium Problems of Interpretation and Construction of Physical Models of Litosphere, Liblice (CSSR), March 6–10, 1978.  相似文献   
218.
219.
Summary According to the results of the adjustments of eight trigonometric and three-dimensional networks, the a priori variance m2() of the measured vertical angle is expressed by the formula: m2() = m2(a) + [C 1/2 m(k)]2, where m(a) represents accidental observation errors; the constant C is estimated in the interval 0.5–1.5 according to the number of repreated observations and the variation of their changes with time; is the angle between the normals to the ellipsoid at the initial and final point of the line of sight, and m(k) is the mean square error of the coefficient of refraction which can be estimated for a given network from Tab. 1.Dedicated to 90th Birthday of Professor Frantiek Fiala  相似文献   
220.
Zusammenfassung Es wird der Einfluss des sogenannten Vorticity-Zentrums auf die Grenzfläche zweier Luftmassen der mittleren geographischen Breiten studiert. Zwecks Aufklärung der Rolle des Bewegungs- und Druckfeldes in diesem Prozesse wurde ein einfaches Modell konstruiert und numerisch gelöst. Die sich entwickelnde frontale Welle kann beziehungsweise als ein Anfangswert beim Lösen der mit der Stabilität der Wellen verbundenen Probleme mittels der Gleichungen, linearisiert durch die Methode der kleinen Störungen, dienen. Bei der Konstruktion des Modells wird ausser anderem von der Geometrie der Bewölkung ausgegangen, wie sie auf den Aufnahmen der meteorologischen Satelliten erfasst ist.  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