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   44359篇
  免费   728篇
  国内免费   367篇
测绘学   1375篇
大气科学   3308篇
地球物理   9045篇
地质学   15132篇
海洋学   3764篇
天文学   10468篇
综合类   136篇
自然地理   2226篇
  2021年   327篇
  2020年   362篇
  2019年   448篇
  2018年   1293篇
  2017年   1217篇
  2016年   1294篇
  2015年   736篇
  2014年   1198篇
  2013年   2031篇
  2012年   1372篇
  2011年   1705篇
  2010年   1479篇
  2009年   2034篇
  2008年   1800篇
  2007年   1814篇
  2006年   1706篇
  2005年   1719篇
  2004年   1933篇
  2003年   1597篇
  2002年   1252篇
  2001年   1089篇
  2000年   1016篇
  1999年   892篇
  1998年   883篇
  1997年   888篇
  1996年   710篇
  1995年   665篇
  1994年   624篇
  1993年   543篇
  1992年   474篇
  1991年   484篇
  1990年   465篇
  1989年   484篇
  1988年   433篇
  1987年   502篇
  1986年   456篇
  1985年   534篇
  1984年   658篇
  1983年   568篇
  1982年   557篇
  1981年   504篇
  1980年   440篇
  1979年   432篇
  1978年   445篇
  1977年   379篇
  1976年   335篇
  1975年   342篇
  1974年   321篇
  1973年   362篇
  1972年   252篇
排序方式: 共有10000条查询结果,搜索用时 21 毫秒
201.
A complex of channels underlying the Baginton-Lillington Gravel (Baginton Formation) at Waverley Wood Quarry, Warwickshire is described. Fossil pollen and plant macrofossils, Coleoptera, Ostracoda, Mollusca and Mammalia are described from the channel-fill deposits. Consideration of all the evidence allows the identification of four separate stages of channel fill which largely occurred under a cool temperate climate. At the top of Channel 2 evidence for a cold, continental climatic episode can be recognised, suggesting that the whole complex was deposited under a fluctuating climate at the end of a temperate stage. At two levels in the channels human artefacts were recovered confirming the presence of Palaeolithic people in Warwickshire during the deposition of the sediments. Amino-acid geochronology suggests an age within the ‘Cromerian Complex’ Stage for the channels. The small vertebrate and molluscan faunas indicate that the deposits are no older than the latter part of the ‘Cromerian Complex’ Stage of East Anglia. The regional stratigraphic significance of the Waverley Wood succession is outlined.  相似文献   
202.
203.
204.
205.
206.
Radio emission of the historical supernovae remnants Tycho (SNR1572) and Kepler (SNR1604) and evolution of their luminosity are considered. Measurement data of secular luminosity decrease rate, obtained earlier by the authors, were corrected with account of variation in time of the flux density of the reference sources. As a result, it is found that the SNR1604 luminosity at 1667 MHz is weakening with an annual mean rate equal to (0.2 ± 0.07)%. The corresponding rate for SNR1572 is (0.47 ± 0.05)%. Since the radio luminosity evolution, as well as energy densities of magnetic field and relativistic electrons inside SNR1604 and SNR1572 are essentially different, these remnants should be considered as different types of supernovae. Bandiera classified SN1604 as type SNIb or SNII.  相似文献   
207.
208.
We present observations of a sample of Herbig AeBe stars, as well as the FU Orionis object V1057 Cygni. Our K-band (2.2μm) observations from the Palomar Testbed Interferometer (PTI) used baselines of 110 m and 85 m, resulting in fringe spacings of ∼4 mas and 5 mas, respectively. Fringes were obtained for the first time on V1057 Cygnias well as V594 Cas. Additional measurements were made of MWC147, while upper limits to visibility-squared are obtained for MWC297, HD190073, and MWC614. These measurements are sensitive to the distribution of warm, circumstellar dust in these sources. If the circumstellar infrared emission comes from warm dust in a disk, the inclination of the disk to the line of sight implies that the observed interferometric visibilities should depend upon hour angle. Surprisingly, the observations of Millan-Gabet, Schloerb and Traub (2001)(hereafter MST) did not show significant variation with hour angle. However, limited sampling of angular frequencies on the sky was possible with the IOTA interferometer, motivating us to study a subset of their objects to further constrain these systems. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
209.
210.
We present radio interferometric observations of the Algol-type binary system RZ Cassiopeiae made with the VLA and MERLIN arrays at 6 cm over an incomplete orbital cycle of the system (1.195 d). We detected RZ Cas with both instruments. The images were unresolved in both cases, with angular extents comparable to the synthesized beams. The peak flux density in the VLA image was 1.14 mJy beam−1 and in the MERLIN image it was 0.93 mJy beam−1. The derived brightness temperatures are  4.02 × 108  and  4.35 × 108 K  and the effective electron energies are 0.347 and 0.346 MeV for the MERLIN and VLA data respectively. The radio light curve shows an interesting modulation centred close to the primary eclipse which seems to correlate with ASCA SIS observations of the system. The results can be interpreted as an emitting region on the outer hemisphere of the cool component aligned along the centroid axis of the binary system.  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