全文获取类型
收费全文 | 22772篇 |
免费 | 4762篇 |
国内免费 | 6253篇 |
专业分类
测绘学 | 2281篇 |
大气科学 | 4071篇 |
地球物理 | 5474篇 |
地质学 | 12905篇 |
海洋学 | 2777篇 |
天文学 | 828篇 |
综合类 | 2388篇 |
自然地理 | 3063篇 |
出版年
2024年 | 87篇 |
2023年 | 434篇 |
2022年 | 1213篇 |
2021年 | 1363篇 |
2020年 | 1159篇 |
2019年 | 1288篇 |
2018年 | 1536篇 |
2017年 | 1298篇 |
2016年 | 1459篇 |
2015年 | 1466篇 |
2014年 | 1598篇 |
2013年 | 1636篇 |
2012年 | 1701篇 |
2011年 | 1780篇 |
2010年 | 1708篇 |
2009年 | 1540篇 |
2008年 | 1389篇 |
2007年 | 1301篇 |
2006年 | 1069篇 |
2005年 | 886篇 |
2004年 | 707篇 |
2003年 | 648篇 |
2002年 | 642篇 |
2001年 | 610篇 |
2000年 | 612篇 |
1999年 | 699篇 |
1998年 | 532篇 |
1997年 | 538篇 |
1996年 | 455篇 |
1995年 | 373篇 |
1994年 | 446篇 |
1993年 | 323篇 |
1992年 | 257篇 |
1991年 | 194篇 |
1990年 | 153篇 |
1989年 | 115篇 |
1988年 | 138篇 |
1987年 | 78篇 |
1986年 | 59篇 |
1985年 | 62篇 |
1984年 | 39篇 |
1983年 | 39篇 |
1982年 | 44篇 |
1981年 | 34篇 |
1980年 | 13篇 |
1979年 | 23篇 |
1978年 | 6篇 |
1958年 | 16篇 |
1957年 | 7篇 |
1954年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 435 毫秒
61.
62.
我们于1989年11月30日晚对PG0027+260进行了时间分辨率为108秒的高速CCD测光,得到了一条完整的光变曲线,从而确认其为激变食变星系统,轨道周期0.146~d 相似文献
63.
We discuss the determination of membership of 42 open clusters. Our analysis shows that Vasilevskis' mathematical model can be reasonably applied to this case. Our improved version of Sanders' method and our definition of cluster member based on the principles of discriminatory analysis effectively exclude stars of low probabilities. It is important in the study of open cluster to use only those with high probabilities. The effectiveness of the statistical method is closely related to the velocity distributions of the member and field stars. For fields where the error rate is high, it is better to combine other data than proper motion in determining membership. 相似文献
64.
65.
66.
67.
APPLICATION OF GEOGRAPHICAL PARAMETER DATABASE TO ESTABLISHMENT OF UNIT POPULATION DATABASE 总被引:1,自引:1,他引:0
Now GIS is turning into a good tool in handling geographical, economical, and population data, so we can obtain more and more information from these data. On the other hand, in some cases, for a calamity, such as hurricane, earthquake, flood, drought etc., or a decision-making, such as setting up a broadcasting transmitter, building a chemical plant etc., we have to evaluate the total population in the region influenced by a calamity or a project. In this paper, a method is put forward to evaluate the population in such special region. Through exploring the correlation of geographical parameters and the distribution of people in the same region by means of quantitative analysis and qualitative analysis, unit population database (1km× 1km) is established. In this way, estimating the number of people in a special region is capable by adding up the population in every grid involved in this region boundary. The geographical parameters are obtained from topographic database and DEM database on the scale of 相似文献
68.
CORROSION AND ADHERENCE AT SEA OIL-PLATFORM 总被引:1,自引:0,他引:1
Measurements of the adhesive corrosion and protective potentials of 3 Bohai Sea oilplatforms under different cathodic protection showed corrosion still occurred on these platforms undertheir designed protective potentials. Preliminary conclusions from indoor experiments on the relation betweenadhesive corrosion and cathodic protection showed adhering organisms caused the corrosion onthese platforms. 相似文献
69.
提出一种基于负反馈权值的动态网络负载调度算法。算法主要用在多出口路由器上,其执行效率高,开销小。基于算法的多出口路由器不仅能够很好的保持出口间的负载均衡。还具有良好的出口容错性能。 相似文献
70.
Dong-Mei Qin Ping Guo Zhan-Yi Hu Yong-Heng ZhaoNational Laboratory of Pattern Recognition Laboratory Institute of Automation Chinese Academy of Sciences Beijing dmqin@nlpr.ia.ac.cnDepartment of Computer Sciences Beijing Normal University Beijing National Astronomical Observatories Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2003,3(3)
For LAMOST, the largest sky survey program in China, the solution of the problem of automatic discrimination of stars from galaxies by spectra has shown that the results of the PSF test can be significantly refined. However, the problem is made worse when the redshifts of galaxies are not available. We present a new automatic method of star/(normal) galaxy separation, which is based on Statistical Mixture Modeling with Radial Basis Function Neural Networks (SMM-RBFNN). This work is a continuation of our previous one, where active and non-active celestial objects were successfully segregated. By combining the method in this paper and the previous one, stars can now be effectively separated from galaxies and AGNs by their spectra-a major goal of LAMOST, and an indispensable step in any automatic spectrum classification system. In our work, the training set includes standard stellar spectra from Jacoby's spectrum library and simulated galaxy spectra of EO, SO, Sa, Sb types with redshift ranging from 0 to 1 相似文献