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   37648篇
  免费   324篇
  国内免费   316篇
测绘学   737篇
大气科学   1814篇
地球物理   7164篇
地质学   14903篇
海洋学   3586篇
天文学   8819篇
综合类   120篇
自然地理   1145篇
  2022年   504篇
  2021年   727篇
  2020年   776篇
  2019年   843篇
  2018年   1722篇
  2017年   1567篇
  2016年   1665篇
  2015年   631篇
  2014年   1438篇
  2013年   2068篇
  2012年   1639篇
  2011年   1928篇
  2010年   1811篇
  2009年   2010篇
  2008年   1793篇
  2007年   1992篇
  2006年   1749篇
  2005年   912篇
  2004年   830篇
  2003年   819篇
  2002年   756篇
  2001年   776篇
  2000年   652篇
  1999年   442篇
  1998年   461篇
  1997年   498篇
  1996年   354篇
  1995年   373篇
  1994年   353篇
  1993年   289篇
  1992年   290篇
  1991年   298篇
  1990年   343篇
  1989年   279篇
  1988年   263篇
  1987年   265篇
  1986年   193篇
  1985年   305篇
  1984年   305篇
  1983年   296篇
  1982年   278篇
  1981年   248篇
  1980年   265篇
  1979年   203篇
  1978年   243篇
  1977年   204篇
  1976年   177篇
  1975年   184篇
  1974年   171篇
  1973年   206篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
251.
The first find of srilankite (very rare Zr and Ti oxide, Ti2ZrO6) in the Urals and the third find in Russia is reported. Srilankite forms very small (0.5–20 μm) inclusions in some rutile grains. These minerals are observed in the rare rock variety, corundum-bearing spinel–saphirine hornblendite forming a block in serpentinized amphibolizied peridotite of the Ilmeny–Vishnevogorsk Complex, near the village of Taiginka, Chelyabinsk oblast. Srilankite has not been observed in such an association yet. The composition of the host rock provides evidence for its deep (the lowermost crust of the Earth) origin. Srilankites of the Urals are distinguished from all others by the high concentrations of UO2, ThO2, HfO2, and Nb2O5, which provides additional evidence for their crustal origin. Srilankite may indicate high-temperature and high-pressure conditions of rock formation.  相似文献   
252.
Firms often encounter location-based impediments that hinder them from engaging with international markets. These challenges can be exacerbated for smaller firms, which often have limited resources and exposure to global markets. This article examines successful small and medium-sized exporters from Nova Scotia, a province with decreased export activity in recent years. It explores these firms’ trade-related motivations, their impediments, and the strategies that they have used to address possible location-related problems. Although geographical distance does not appear to be a competitive challenge, other issues emerge, including travel expenditures and the costs of export intelligence gathering. Successful exporters have overcome many potential impediments by using government trade programs, establishing and maintaining face-to-face contacts, and working with international partners.  相似文献   
253.
Corundum-containing and corundum-free plagioclasites localized in chromite-bearing ultramafites of the Rai-Iz Massif were explored for the composition and age. The composition of rock-forming minerals was studied, and the geochemical characteristics of the rocks were ascertained. The isotope age of plagioclasites determined by zircons using the U–Pb mode with a SHRIMP II device was equal to 398 ± 3 Ma. The age found conformed to the boundary on most of the Rai-Iz Massif took place against the background of a starting powerful collision, which caused the formation of the chromium mineralization of a high-chromic type, as well as the separation of a series of essentially plagioclase rocks of ruby mineralization at the discharge zones of the vein series.  相似文献   
254.
Milyukov  V. K.  Yeh  Hsien-Chi 《Astronomy Reports》2018,62(12):1003-1012
Astronomy Reports - A review of the achievements of space geodesy in the 21st century, represented by the successful realization of the CHAMP, GOCE, and GRACE missions, is presented. The main...  相似文献   
255.
256.
Geotectonics - The South Anyui Fold System was formed at the end of the Early Cretaceous at the site of a closed oceanic basin as a result of the collision of the Chukotka microcontinent with the...  相似文献   
257.
Ermash  A. A.  Pilipenko  S. V.  Mikheeva  E. V.  Lukash  V. N. 《Astronomy Reports》2021,65(12):1194-1210
Astronomy Reports - Within the framework of the model of the extragalactic background created earlier by the authors, the factors influencing the statistical properties of the confusion noise have...  相似文献   
258.
Doklady Earth Sciences - This paper discusses sources of significant errors that occur in the course of determination of the primary environmental standard for natural waters: the maximum...  相似文献   
259.
Solar System Research - Ionizing radiation is one of the main factors that destroy biomolecules in extraterrestrial conditions. The effects of radiation depend on the conditions of the exposure...  相似文献   
260.
It is proposed a formula for the solar energy flux including the limb darkening effect and beeing valid at any distance from the Sun.  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