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   4754篇
  免费   413篇
  国内免费   844篇
测绘学   45篇
大气科学   202篇
地球物理   657篇
地质学   2038篇
海洋学   1043篇
天文学   1430篇
综合类   167篇
自然地理   429篇
  2024年   22篇
  2023年   57篇
  2022年   104篇
  2021年   130篇
  2020年   131篇
  2019年   141篇
  2018年   118篇
  2017年   126篇
  2016年   138篇
  2015年   156篇
  2014年   214篇
  2013年   179篇
  2012年   179篇
  2011年   254篇
  2010年   184篇
  2009年   379篇
  2008年   345篇
  2007年   347篇
  2006年   359篇
  2005年   289篇
  2004年   298篇
  2003年   252篇
  2002年   236篇
  2001年   216篇
  2000年   213篇
  1999年   182篇
  1998年   193篇
  1997年   96篇
  1996年   88篇
  1995年   72篇
  1994年   53篇
  1993年   37篇
  1992年   32篇
  1991年   21篇
  1990年   27篇
  1989年   26篇
  1988年   14篇
  1987年   12篇
  1986年   15篇
  1985年   29篇
  1984年   21篇
  1983年   8篇
  1982年   5篇
  1981年   9篇
  1979年   2篇
  1978年   2篇
排序方式: 共有6011条查询结果,搜索用时 390 毫秒
11.
12.
13.
14.
15.
16.
The remnant resulting from the merger of two neutron stars produces neutrinos in copious amounts. In this paper we present the neutrino emission results obtained via Newtonian, high-resolution simulations of the coalescence event. These simulations use three-dimensional smoothed particle hydrodynamics together with a nuclear, temperature-dependent equation of state and a multiflavour neutrino leakage scheme. We present the details of our scheme, discuss the neutrino emission results from a neutron star coalescence and compare them with the core-collapse supernova case where neutrino emission has been studied for several decades. The average neutrino energies are similar to those in the supernova case, but contrary to the latter, the luminosities are dominated by electron-type antineutrinos that are produced in the hot, neutron-rich, thick disc of the merger remnant. The cooler parts of this disc contain substantial fractions of heavy nuclei, which, however, do not influence the overall neutrino emission results significantly. Our total neutrino luminosities from the merger event are considerably lower than those found in previous investigations. This imposes constraints on the ability of neutron star mergers to produce a gamma-ray burst via neutrino annihilation. The neutrinos are emitted preferentially along the initial binary rotation axis, an event seen 'pole-on' would appear much brighter in neutrinos than a similar event seen 'edge-on'.  相似文献   
17.
In this study, the 14N:15N ratio of suspended particulate material collected from the Tamar river estuary, south-west England, is described. Three populations of particles, distinguishable by their 15N content, were observed. This investigation has shown that populations of estuarine particles are generated by biological transformations in situ and that the 15N content of estuarine particles does not merely reflect hydrodynamic mixing of the freshwater and seawater source particulate material.  相似文献   
18.
19.
In the coastal and estuarine waters of Goa, particulate organic carbon (POC) varied from 0.52 to 2.51 mg l?1 and from 0.28 to 5.24 mg l?1 and particulate phosphorus (PP) varied from 0.71 to 5.18 μg l?1 and from 0.78 to 20.34 μg l?1, respectively. The mean values of chlorophyll and primary productivity were 1.94 mg m?3 and 938.1 mg C m?2 day?1 in the coastal waters and 4.3 mg m?3 and 636.5 mg C m?1 day?1 in the estuarine waters, respectively.POCchl ratios were low in June and October even when POC values were quite high. The POC in surface waters was linearly correlated with the chlorophyll content. Also PP increased when chlorophyll and primary productivity remained high. The results suggest that the phytoplankton was sharply increasing and contributed to POC and PP content. The percentage of detritus calculated from the intercept values of chlorophyll on POC varied from 46 to 76% depending on season. Results indicate that the major portion of POC and PP during postmonsoon (October–January) is derived from phytoplankton production while the allochthonous matter predominate during monsoon (June–September).  相似文献   
20.
Astrophysical limits on massive dark matter   总被引:1,自引:0,他引:1  
Annihilations of weakly interacting dark matter particles provide an important signature for the possibility of indirect detection of dark matter in galaxy haloes. These self-annihilations can be greatly enhanced in the vicinity of a massive black hole. We show that the massive black hole present at the centre of our galaxy accretes dark matter particles, creating a region of very high particle density. Consequently the annihilation rate is considerably increased, with a large number of e+e pairs being produced either directly or by successive decays of mesons. We evaluate the synchrotron emission (and self-absorption) associated with the propagation of these particles through the galactic magnetic field, and are able to constrain the allowed values of masses and cross sections of dark matter particles.  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