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   26010篇
  免费   508篇
  国内免费   463篇
测绘学   654篇
大气科学   2097篇
地球物理   5567篇
地质学   9187篇
海洋学   2127篇
天文学   5446篇
综合类   149篇
自然地理   1754篇
  2020年   161篇
  2019年   165篇
  2018年   340篇
  2017年   322篇
  2016年   457篇
  2015年   321篇
  2014年   461篇
  2013年   1214篇
  2012年   547篇
  2011年   832篇
  2010年   685篇
  2009年   957篇
  2008年   868篇
  2007年   837篇
  2006年   846篇
  2005年   740篇
  2004年   768篇
  2003年   728篇
  2002年   743篇
  2001年   605篇
  2000年   620篇
  1999年   604篇
  1998年   579篇
  1997年   585篇
  1996年   480篇
  1995年   465篇
  1994年   460篇
  1993年   429篇
  1992年   392篇
  1991年   342篇
  1990年   388篇
  1989年   301篇
  1988年   344篇
  1987年   384篇
  1986年   329篇
  1985年   485篇
  1984年   528篇
  1983年   532篇
  1982年   426篇
  1981年   418篇
  1980年   437篇
  1979年   381篇
  1978年   396篇
  1977年   348篇
  1976年   376篇
  1975年   341篇
  1974年   380篇
  1973年   365篇
  1972年   233篇
  1971年   186篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
An analytical relative orientation of a stereo-pair of photographs was computed in an unusual system of co-ordinates. The disparity in the widely mismatched photographs, their tilts and narrow angles subtended resulted in a rather weak solution from which sections of the lunar surface have been plotted. The results were not good but were better than expected. The main outcome of the work is a, probably unique, demonstration of the versatility of analytical photogrammetry.  相似文献   
42.
43.
44.
Mössbauer measurements on synthetic iron orthosilicate Fe2SiO4 (fayalite) were carried out in the antiferromagnetic spin state below T N 65 K. The Mössbauer parameters isomer shift , inner magnetic field H(0), angle between H(0) and the z-component of the electric field gradient (efg), quadrupole splitting QS and asymmetry parameter were determined as a function of temperature. These parameters could be attributed to the two crystallographic sites M1 and M2.The smaller isomer shift on M1 with respect to M2 displays the more covalent character of the Fe-O bond on M1, which is supported by previous neutron diffraction experiments. H(0) shows a Brillouin-type behaviour with different fields on the two crystallographic sites (stronger on M1) and a small discontinuity at T = 23 K which corresponds with previous magnetic measurements. The quadrupole splitting is equal on both sites within error bars, in agreement with previous theoretical results and in contradiction to previous Mössbauer refinements published elsewhere.  相似文献   
45.
A catalogue of galactic novae and an atlas of finding charts are under preparation and will be published in 1984. The status of the project is described.Paper presented at the Lembang-Bamberg IAU Colloquium No. 80 on Double Stars: Physical Properties and Generic Relations, held at Bandung, Indonesia, 3–7 June, 1983.  相似文献   
46.
47.
The Siljan Ring is a 362-Ma-old impact structure formed in 1700-Ma-old I-type granites. A 6.8-km-deep borehole provides a vertical profile through granites and isolated horizontal diabase sills. Fluid-inclusion thermometry, and oxygen-isotope compositions of vein quartz, granite, diabase, impact melt, and pseudotachylite, reveal a complex history of fluid activity in the Siljan Ring, much of which can be related to the meteorite impact. In granites from the deep borehole, 18O values of matrix quartz increase with depth from near 8.0 at the surface to 9.5 at 5760 m depth. In contrast, feldspar 18O values decrease with depth from near 10 at the surface to 7.1 at 5760 m, forming a pattern opposite to the one defined by quartz isotopic compositions. Values of 18O for surface granites outside the impact structure are distinct from those in near-surface samples from the deep borehole. In the deep borehole, feldspar coloration varies from brick-red at the surface to white at 5760 m, and the abundances of crack-healing calcite and other secondary minerals decrease over the same interval. Superimposed on the overall decrease in alteration intensity with depth are localized fracture zones at 4662, 5415, and 6044 m depth that contain altered granites, and which provided pathways for deep penetration of surface water. The antithetic variation of quartz and feldspar 18O values, which can be correlated with mineralogical evidence of alteration, provides evidence for interaction between rocks and impact-heated fluids (100–300° C) in the upper 2 km of the pluton. Penetration of water to depths below 2 km was restricted by a general decrease in impact-fracturing with depth, and by a 60-m-thick diabase sill at 1500 m depth that may have been an aquitard. At depths below 4 km in the pluton, where water/rock ratios were low, oxygen isotopic compositions preserve evidence for limited high-temperature (>500° C) exchange between alkali feldspar and fluids. The high-temperature exchange may have been a post-impact event involving impact-heated fluids, or a post-magmatic event.  相似文献   
48.
49.
50.
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