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   1000篇
  免费   47篇
  国内免费   18篇
测绘学   21篇
大气科学   142篇
地球物理   216篇
地质学   373篇
海洋学   68篇
天文学   213篇
综合类   3篇
自然地理   29篇
  2023年   4篇
  2022年   5篇
  2021年   8篇
  2020年   15篇
  2019年   8篇
  2018年   41篇
  2017年   49篇
  2016年   73篇
  2015年   39篇
  2014年   63篇
  2013年   67篇
  2012年   39篇
  2011年   56篇
  2010年   52篇
  2009年   53篇
  2008年   42篇
  2007年   39篇
  2006年   19篇
  2005年   13篇
  2004年   18篇
  2003年   26篇
  2002年   26篇
  2001年   16篇
  2000年   19篇
  1999年   9篇
  1998年   26篇
  1997年   14篇
  1996年   20篇
  1995年   9篇
  1994年   5篇
  1993年   24篇
  1992年   11篇
  1991年   14篇
  1990年   19篇
  1989年   9篇
  1988年   6篇
  1987年   7篇
  1986年   8篇
  1985年   8篇
  1984年   9篇
  1983年   6篇
  1982年   4篇
  1981年   5篇
  1978年   5篇
  1977年   4篇
  1976年   4篇
  1973年   4篇
  1971年   5篇
  1969年   5篇
  1965年   4篇
排序方式: 共有1065条查询结果,搜索用时 15 毫秒
61.
62.
A statistically relevant correlation between the reaction rate coefficient, k OH, for the OH radical reaction with 161 organic compounds in the gas phase at 300 K, and the corresponding vertical ionisation energies E i,v, reveals two classes of compounds: aromatics where –log(k OH/cm3s-1)3/2E i,v(eV)–2 and aliphatics where –log(k OH/cm3s-1)4/5E i,v(eV)+3. The prediction of the rate coefficient, k OH, for the reaction of OH with organic molecules from the above equations has a probability of about 90%. Assuming a global diurnal mean of the OH radical concentration of 5×105 cm3, the upper limit of the tropospheric half-life of organic compounds and their persistence can be estimated.  相似文献   
63.
64.
65.
The rate of aftershock occurrence after the M6 Ston-Slano (Croatia) earthquake is modeled as the Epidemic Type Aftershock Sequence (ETAS). Increase of the modeled cumulative number of aftershocks with time was fitted to observations by the least-squares criterion using the combined grid-search and Monte-Carlo approach. This enabled not only the estimation of the most probable ETAS parameters, but also the determination of their confidence limits, as well as the estimation of the bias between them. It has been found that the bias is significant for some of the parameter pairs, regardless of the threshold magnitude assumed. Residual analyses revealed that all strong aftershocks (M L 4.5) occurred during the periods of normal to high aftershock activity. There were two periods of quiescence in the sequence, both of which were followed by a strong aftershock.  相似文献   
66.
Raju  K.P.  Singh  Jagdev  Srikanth  R.  Chou  Dean-Yi  Team  the Ton 《Solar physics》2001,199(1):1-11
We have obtained the temporal correlation function, Q(t), from time sequences of Caii K filtergrams and Dopplergrams from Antarctica, Taiwan Oscillation Network (TON) and Solar and Heliospheric Observatory (SOHO). Q(t) gives the time evolution of the pattern under examination, supergranulation in this case. It has been found that Q(t) shows oscillatory signals of both 5-min and long-term periods. The 5-min oscillations are suppressed by averaging the images over 10 min. An exponential decay curve which represents the lifetime trend of supergranules, is fitted to Q(t) and subtracted out. The Q(t) residuals thus obtained contain the oscillatory component and are then subjected to a periodogram analysis. Significant periodicities in the range of 1.4–10 hours have been noted. The causes of these oscillations are not fully known at present, but the instrumental and atmospheric factors can be ruled out, pointing to solar origin. Various possibilities are discussed. Some of the observed periodicities may be considered as probable candidates for long-term oscillations in the Sun, such as the elusive gravity modes.  相似文献   
67.
The lysosomal membrane destabilization and the metallothionein content in the digestive gland cells of mussels (Mytilus galloprovincialis Lam.), collected along the east coast of the North Adriatic (Istrian and Kvarnerine coast, Croatia), were examined over a period of four years (1996–1999). The lysosomal membrane stability, as a biomarker of general stress, showed that the membrane labilization period in mussels from polluted, urban- and industrial-related areas was significantly decreased (p<0.05) when compared to mussels from control, clean sea water sites. In the harbour of Rijeka, the most contaminated site, the lysosomal membrane stability was reduced by more than 70% compared to the control. This method also proved to be a useful biomarker for detection of additional stress caused by short-term hypoxia that occurred once during this study inside the polluted and periodically quite eutrophic Pula Harbour. The concentration of metallothioneins in the mussel digestive gland, as a specific biomarker of exposure to heavy metals, did not reveal significant differences (p<0.05) between sites covered by this study.  相似文献   
68.
69.
Iodine contents of soils developed over the major rock formations of the northern zone of the Eastern Pontide Tectonic Belt (Northeastern Turkey) have been investigated with respect to soil-parent rock relationship, effect of topography, elevation, and climate to construe its effect on the health of the local population. Samples were collected from the A and B horizons of the soils developed over the major stratigraphic units constituting the eastern Pontides, including the Lower Basic Complex of Jurassic-Lower Cretaceous age, the Berdiga limestone (Jurassic-lower Cretaceous), the Dagbasi granitoid (Upper Cretaceous), volcano-sedimentary sequence of Upper Cretaceous age, ore-bearing and barren dacites of Upper Cretaceous age, and Neogene alkaline basalts. Chemical analyses of soil samples indicate significantly lower iodine abundances for all the soils studied (5–28 ppm) in comparison to the average abundance of iodine in analogous soils of other parts of the world (22–93 ppm). The concentration of iodine in soils developed over the same geologic formation decrease with increasing elevation. In certain cases, this decrease may reach up to 70%. Goiter is highly common throughout this region in Turkey. The results of this study suggest that the iodine deficiency of region’s soils may be a principal underlying cause for this area of Turkey being an endemic goiter region.  相似文献   
70.
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