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   19497篇
  免费   3670篇
  国内免费   5734篇
测绘学   697篇
大气科学   6901篇
地球物理   3245篇
地质学   7241篇
海洋学   2138篇
天文学   5215篇
综合类   916篇
自然地理   2548篇
  2024年   125篇
  2023年   306篇
  2022年   713篇
  2021年   754篇
  2020年   871篇
  2019年   963篇
  2018年   777篇
  2017年   805篇
  2016年   792篇
  2015年   947篇
  2014年   1294篇
  2013年   1423篇
  2012年   1410篇
  2011年   1564篇
  2010年   1387篇
  2009年   1772篇
  2008年   1600篇
  2007年   1668篇
  2006年   1534篇
  2005年   1340篇
  2004年   1123篇
  2003年   973篇
  2002年   774篇
  2001年   676篇
  2000年   621篇
  1999年   509篇
  1998年   435篇
  1997年   272篇
  1996年   247篇
  1995年   217篇
  1994年   211篇
  1993年   197篇
  1992年   111篇
  1991年   99篇
  1990年   62篇
  1989年   65篇
  1988年   60篇
  1987年   23篇
  1986年   27篇
  1985年   31篇
  1984年   24篇
  1983年   21篇
  1982年   17篇
  1981年   12篇
  1980年   16篇
  1979年   4篇
  1978年   6篇
  1977年   17篇
  1877年   1篇
  1875年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
V838 Mon is the prototype of a new class of objects. Understanding the nature of its multistage outburst and similar systems is challenging. So far, several scenarios have been invoked to explain this group of stars. In this work, the planets-swallowing model for V838 Mon is further investigated, taking into account the findings that the progenitor is most likely a massive B-type star. We find that the super-Eddington luminosity during the eruption can explain the fast rising times of the three peaks in the optical light curve. We used two different methods to estimate the location where the planets were consumed. There is a nice agreement between the values obtained from the luminosities of the peaks and from their rising time-scale. We estimate that the planets were stopped at a typical distance of one solar radius from the centre of the host giant star. The planets-devouring model seems to give a satisfying explanation to the differences in the luminosities and rising times of the three peaks in the optical light curve of V838 Mon. The peaks may be explained by the consumption of three planets or alternatively by three steps in the terminal falling process of a single planet. We argue that only the binary merger and the planets-swallowing models are consistent with the observations of the new type of stars defined by V838 Mon.  相似文献   
122.
123.
用电测深研究地电断面、寻找隐伏多金属矿体时,以往采用ρ_s(或η_s)等值线断面图进行地质推断解释,因受浅源信号的干扰,效果差。本文提出了采用ρ_s(或η_s)差值法,能排除浅源干扰信号,反映出地电断面的相对变化,突出了深部微弱信息,取得了较好的地质解释效果。  相似文献   
124.
125.
126.
127.
Erosion of man-made, forestry drainage channels occurs when the plough cuts through the surface peat layer into the underlying erodible mineral soil. A procedure is developed, based on hydraulic considerations, which will allow the drainage engineer to design stable drainage networks in upland forestry plantations. An example design chart is given for an erodible sandy loam type soil.  相似文献   
128.
The main reasons for the high content of inorganic N and its increase by several times in the Changjiang River and its mouth during the last 40 years were analysed in this work. The inorganic N in precipitation in the Changjiang River catchment mainly comes from gaseous loss of fertilizer N, N resulting from the increases of population and livestock, and from high temperature combustions of fossil fuels. N from precipitation is the first N source in the Changjiang River water and the only direct cause of high content of inorganic N in the Changjiang River and its mouth. The lost N in gaseous form and from agriculture non-point sources fertilizer comprised about 60% of annual consumption of fertilizer N in the Changjiang River catchment and were key factors controlling the high content of inorganic N in the Changjiang River mouth. The fate of the N in precipitation and other N sources in the Changjiang River catchment are also discussed in this paper.  相似文献   
129.
130.
We have observed the eclipsing low-mass X-ray binary MS 1603.6+2600 with Chandra for 7 ks. The X-ray spectrum is well fit with a single absorbed power law with an index of ∼2. We find a clear sinusoidal modulation in the X-ray light curve with a period of  1.7 ± 0.2 h  , consistent with the period of 1.85 h found before. However, no (partial) eclipses were found. We argue that if the X-ray flare observed in earlier X-ray observations was a type I X-ray burst, then the source can only be an accretion disc corona source at a distance of ∼11–24 kpc (implying a height above the Galactic disc of ∼8–17 kpc). It has also been proposed in the literature that MS 1603.76+2600 is a dipper at ∼75 kpc. We argue that, in this dipper scenario, the observed optical properties of MS 1603.6+2600 are difficult to reconcile with the optical properties one would expect on the basis of comparisons with other high-inclination, low-mass X-ray binaries, unless the X-ray flare was not a type I X-ray burst. In that case, the source can be a nearby soft X-ray transient accreting at a quiescent rate, as was proposed by Hakala et al., or a high-inclination source at ∼15–20 kpc.  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