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   76779篇
  免费   960篇
  国内免费   1167篇
测绘学   2441篇
大气科学   5424篇
地球物理   14484篇
地质学   31712篇
海洋学   5624篇
天文学   13150篇
综合类   2254篇
自然地理   3817篇
  2022年   260篇
  2021年   450篇
  2020年   518篇
  2019年   601篇
  2018年   7262篇
  2017年   6519篇
  2016年   4508篇
  2015年   877篇
  2014年   1138篇
  2013年   1940篇
  2012年   2848篇
  2011年   5861篇
  2010年   5058篇
  2009年   5654篇
  2008年   4713篇
  2007年   5624篇
  2006年   1700篇
  2005年   1684篇
  2004年   1782篇
  2003年   1868篇
  2002年   1441篇
  2001年   949篇
  2000年   899篇
  1999年   745篇
  1998年   748篇
  1997年   735篇
  1996年   598篇
  1995年   579篇
  1994年   509篇
  1993年   465篇
  1992年   417篇
  1991年   428篇
  1990年   448篇
  1989年   399篇
  1988年   376篇
  1987年   402篇
  1986年   416篇
  1985年   512篇
  1984年   552篇
  1983年   549篇
  1982年   500篇
  1981年   476篇
  1980年   455篇
  1979年   414篇
  1978年   377篇
  1977年   386篇
  1976年   354篇
  1975年   359篇
  1974年   340篇
  1973年   372篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
942.
943.
944.
945.
946.
947.
Spectroscopic observations of three lenticular (S0) galaxies (NGC 1167, NGC 4150, and NGC 6340) and one SBa galaxy (NGC 2273) have been taken with the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences aimed to study the structure and kinematic properties of early-type disk galaxies. The radial profiles of the stellar radial velocities and the velocity dispersion are measured. N-body simulations are used to construct dynamical models of galaxies containing a stellar disk, bulge, and halo. The masses of individual components are estimated formaximum-mass disk models. A comparison of models with estimated rotational velocities and the stellar velocity dispersion suggests that the stellar disks in lenticular galaxies are “overheated”; i.e., there is a significant excess velocity dispersion over the minimum level required to maintain the stability of the disk. This supports the hypothesis that the stellar disks of S0 galaxies were subject to strong gravitational perturbations. The relative thickness of the stellar disks in the S0 galaxies considered substantially exceed the typical disk thickness of spiral galaxies.  相似文献   
948.
In order to provide new data on the neotectonics and geodynamic properties of western Syria, studies of marine terraces have been carried out. The most attention was paid to the lower terraces in the range of 3–5 to 30–35 m above sea level, because they have more complete distributions along the shore. The lower terraces were examined along the coastal area from Tartus to Latakia, and along the carbonate cliff on Arwad Island. Seven 230Th/U dates for these terraces are in the range of 85–130 ka, suggesting the age interval of the last interglacial (MIS 5). New dates on the lower terraces provide a basis for stratigraphical and geomorphological interpretation as well as neotectonic reconstruction. According to the geomorphological data and lithological composition of those terraces, two main uplifted blocks can be established. One coincides with the Latakia block, and another corresponds to the western margin of the Banias volcanic plateau. These blocks are divided by a subsided structure corresponding to the Nahr el Kebir graben. The amplitude of neotectonic uplifting in the Latakia and Banias blocks reaches 15–20 m for the Late Pleistocene.  相似文献   
949.
950.
Many speleothems show evidence for calcite precipitation under disequilibrium conditions. To improve the understanding of these kinetic processes, several laboratory experiments were performed to study the fractionation of stable oxygen and carbon isotopes during the precipitation of calcite. Carbonate was precipitated under controlled conditions from both a body of standing water (beaker experiments) and a solution flowing along a channel (channel experiments) at a relative humidity of 100%. Slow degassing of CO2, simulated by the beaker experiments, results in δ18O values in equilibrium with the solution. In contrast, the δ13C values show a significant enrichment, inversely proportional to the height of the solution in the beakers. Fast degassing of CO2, simulated by the channel experiments, showed an enrichment of both δ13C and δ18O and a slope of Δδ13C/Δδ18O of 1.4±0.6. These results represent experimental evidence for the Hendy effect, which is manifested in (i) a progressive increase in δ18O and δ13C away from the growth axis and (ii) a positive correlation between δ18O and δ13C along a single growth layer of a stalagmite.  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