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   8108篇
  免费   690篇
  国内免费   541篇
测绘学   389篇
大气科学   765篇
地球物理   1934篇
地质学   3268篇
海洋学   754篇
天文学   1234篇
综合类   161篇
自然地理   834篇
  2023年   65篇
  2022年   131篇
  2021年   209篇
  2020年   199篇
  2019年   258篇
  2018年   302篇
  2017年   284篇
  2016年   357篇
  2015年   306篇
  2014年   327篇
  2013年   543篇
  2012年   368篇
  2011年   471篇
  2010年   393篇
  2009年   488篇
  2008年   431篇
  2007年   374篇
  2006年   326篇
  2005年   317篇
  2004年   295篇
  2003年   257篇
  2002年   274篇
  2001年   160篇
  2000年   189篇
  1999年   135篇
  1998年   142篇
  1997年   115篇
  1996年   109篇
  1995年   100篇
  1994年   100篇
  1993年   84篇
  1992年   102篇
  1991年   69篇
  1990年   61篇
  1989年   59篇
  1988年   59篇
  1987年   56篇
  1986年   61篇
  1985年   70篇
  1984年   65篇
  1983年   81篇
  1982年   59篇
  1981年   68篇
  1980年   57篇
  1979年   72篇
  1978年   60篇
  1977年   36篇
  1976年   30篇
  1974年   30篇
  1973年   34篇
排序方式: 共有9339条查询结果,搜索用时 314 毫秒
971.
972.
Dilatancy and contact surface damage are important phenomena affecting the behaviour of rock joints and other geological discontinuities. Effective constitutive laws that incorporate these behaviours have recently been developed but require the specification of new material parameters that govern damage of asperity surfaces. Determination of the parameters that control damage is currently a difficulty that confronts practitioners. This brief will summarize the findings of Hutson and Dowding's investigation of joint surface asperity degradation and elaborate on the implications for application.  相似文献   
973.
974.
Michael R. Rampino 《Icarus》2002,156(2):562-569
The largest explosive volcanic eruptions (supereruptions) produce >1000 km3 of ejected material and ≥1000 Mt (1015 g) of submicron atmospheric aerosols and dust. These eruptions may be capable of creating global climatic disturbances sufficient to cause severe problems for world agriculture and modern civilization. Supereruptions are estimated to occur on average about every 50,000 years, which is about twice the frequency of impacts by comets and asteroids ≥1 km diameter predicted to cause similar climatic effects. Prediction, prevention, and mitigation of global volcanic climatic disasters may be potentially more difficult than planetary protection from the threat of large impacts, so that explosive volcanism might limit the longevity of technological civilizations.  相似文献   
975.
The possibilities for detecting distant,highly reddened, cepheids as well as OB star clusters and associations in the surveys is considered and the value of such work for galactic structure problems is outlined.  相似文献   
976.
通过对新疆阿尔泰南缘地球物理场特征-深部构造-已知大型矿床分布规律的系统研究,认为该地区不同属性的地质块体受3组基底构造控制,即EW向、NE向和NW向3组基底构造系,并认为该地区已知大型-超大型矿床同样受这3组深部构造系的控制.最后对阿尔泰地区进行了大型、超大型多金属矿床成矿预测.  相似文献   
977.
A globular cluster distance scale based on Hipparcos parallaxes of subdwarfs has been used to derive estimates of M K for cluster Miras, including one in the Small Magellanic Cloud (SMC) globular cluster NGC 121. These lead to a zero-point of the Mira infrared period–luminosity (PL) relation, PL( K ), in good agreement with that derived from Hipparcos parallaxes of nearby field Miras. The mean of these two estimates together with data on LMC Miras yields a Large Magellanic Cloud (LMC) distance modulus of     in evident agreement with a metallicity-corrected Cepheid modulus     .
The use of luminous asymptotic giant branch (AGB) stars as extragalactic population indicators is also discussed.  相似文献   
978.
979.
We investigate the evolution of the star formation rate in cluster galaxies. We complement data from the Canadian Network for Observational Cosmology 1 (CNOC1) cluster survey  (0.15 < z < 0.6)  with measurements from galaxy clusters in the Two-degree Field (2dF) galaxy redshift survey  (0.05 < z < 0.1)  and measurements from recently published work on higher-redshift clusters, up to almost   z = 1  . We focus our attention on galaxies in the cluster core, i.e. galaxies with   r < 0.7  h −170 Mpc  . Averaging over clusters in redshift bins, we find that the fraction of galaxies with strong [O  ii ] emission is ≲20 per cent in cluster cores, and the fraction evolves little with redshift. In contrast, field galaxies from the survey show a very strong increase over the same redshift range. It thus appears that the environment in the cores of rich clusters is hostile to star formation at all the redshifts studied. We compare this result with the evolution of the colours of galaxies in cluster cores, first reported by Butcher and Oemler. Using the same galaxies for our analysis of the [O  ii ] emission, we confirm that the fraction of blue galaxies, which are defined as galaxies 0.2 mag bluer in the rest-frame B – V than the red sequence of each cluster, increases strongly with redshift. Because the colours of galaxies retain a memory of their recent star formation history, while emission from the [O  ii ] line does not, we suggest that these two results can best be reconciled if the rate at which the clusters are being assembled is higher in the past, and the galaxies from which it is being assembled are typically bluer.  相似文献   
980.
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