全文获取类型
收费全文 | 10240篇 |
免费 | 1094篇 |
国内免费 | 3585篇 |
专业分类
测绘学 | 535篇 |
大气科学 | 1698篇 |
地球物理 | 3613篇 |
地质学 | 5708篇 |
海洋学 | 1115篇 |
天文学 | 407篇 |
综合类 | 698篇 |
自然地理 | 1145篇 |
出版年
2024年 | 65篇 |
2023年 | 178篇 |
2022年 | 122篇 |
2021年 | 203篇 |
2020年 | 95篇 |
2019年 | 129篇 |
2018年 | 187篇 |
2017年 | 66篇 |
2016年 | 156篇 |
2015年 | 151篇 |
2014年 | 262篇 |
2013年 | 259篇 |
2012年 | 341篇 |
2011年 | 416篇 |
2010年 | 221篇 |
2009年 | 299篇 |
2008年 | 379篇 |
2007年 | 485篇 |
2006年 | 531篇 |
2005年 | 619篇 |
2004年 | 602篇 |
2003年 | 409篇 |
2002年 | 478篇 |
2001年 | 504篇 |
2000年 | 533篇 |
1999年 | 262篇 |
1998年 | 198篇 |
1997年 | 212篇 |
1996年 | 193篇 |
1995年 | 257篇 |
1994年 | 225篇 |
1993年 | 421篇 |
1992年 | 366篇 |
1991年 | 461篇 |
1990年 | 413篇 |
1989年 | 436篇 |
1988年 | 450篇 |
1987年 | 371篇 |
1986年 | 269篇 |
1985年 | 357篇 |
1984年 | 300篇 |
1983年 | 222篇 |
1982年 | 173篇 |
1981年 | 124篇 |
1980年 | 179篇 |
1964年 | 89篇 |
1960年 | 52篇 |
1959年 | 109篇 |
1958年 | 122篇 |
1957年 | 130篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Juan Zhao Yan-Ben Han Zhi-An LiDepartment of Astronomy Beijing Normal University Beijing zj@bnu.edu.cnNational Astronomical Observatories Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2004,4(2):189-197
Using continuous wavelet transform, we examine the relationship between solar activity and the annual precipitation in the Beijing area. The results indicate that the annual precipitation is closely related to the variation of sunspot numbers, and that solar activity probably plays an important role in influencing the precipitation on land. 相似文献
52.
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
53.
现在正是科学技术高速发展的时期,它必然引起劳动地域分工和生产地域组织的变化。研究经济问题的所有学科的研究对象也因而随着变化。促成这些变化的经济因素是。生产系统和非生产系统的形成;生产和非生产领域的高速发展;生产集中和地域集中;引用新工艺和新的劳动手段. 相似文献
54.
对天区0112-35的UKST物端棱镜底片上的11个类星体候选者进行了光谱观测,证实为类星体,给出了它们的红移值、证认图及光谱图。11个类星体中有6个属于角距小于4角分的3对类星体;1个类星体-星系对。 相似文献
55.
引言农田灌溉是一种最易提高干旱地区农业产量的方法。灌溉农业与旱作农业相比,谷物产量可提高6倍,根块植物产量可提高4—5倍。因此,农田灌溉在渴望得到更多粮食的干旱地区,可以发挥巨大的作用。农田灌溉使这些地区获得高产稳产,同时减轻了干旱和沙漠化的威胁。 相似文献
56.
根据波尔近似,借助于波动积分方程,近似求解半无限弹性空间中平面SH波由圆形空腔和刚性包体所散射的问题。获得了空腔表面上的散射位移、作用于被包体上的剪应力、半空间表面形变以及远场位移的近似公式。在数值计算中,ka(k=波数,a=空腔或被包体的半径)取为1.0,γ(SH波的入射角,从垂向方向起算)取为π/4。 相似文献
57.
58.
Isabella A. Abbott 《中国海洋湖沼学报》1995,(4)
A new species of Liagora,L.perennis sp.nov.from Hawai’i,is described.Unlike dpecies of this genus in China,it is carpotetrasporangial,and at the place of expected carposporangia bears cruciately di-vided tetrasporangia,a detail which differentiates it from the usual species of Liagora without tetraspores that have been reported in China.Notes are provided on other Liagora species that have an impact on the taxonomy of species found in China. 相似文献
59.
Theoretical rotational excitation rates were computed for C3H2 in collisions with He atoms at temperatures from 30 to 120 K. The intermolecular forces were obtained from accurate self-consistent field and perturbation theory calculations, and collision dynamics were treated within the infinite-order sudden approximation. The accuracy of the latter was examined by comparing with the more exact coupled states approximation. 相似文献
60.
Ram S 《Population geography : a journal of the Association of Population Geographers of India》1987,9(1-2):37-44
The period of highest migration from India to England was 1955-1975. In 1981, the Bradford metropolitan district had about 13,000 Indians. 46% were Punjabis and 43.3% were from Gujarat. Using a 10% sample of Indian households in the Bradford district in 1984 and secondary information, this study examines the impact of the following reasons on decision to migrate: 1) push factors in the area of origin, 2) the 1947 partition of India, 3) strong economic attraction of the destination, and 4) "cultural ethos" and "status competition" among the migrant communities in the areas of emigration. Findings show that 1) Punjab and Gujarat do not have high poverty levels nor very high population densities; 2) the partition of India did not influence migration decisions; 3) the economic well-being of returning migrants and the high conversion rate of English currency did attract migrants to England (39% of surveyed migrants emigrated to England for purely economic reasons); and 4) 60% of the Punjabis and over 50% of the Gujaratis state that local status competition had a significant influence on their decisions to migrate. Thus, the economic attraction of England and the status competition among local families and the community were the dominant factors in migration decision making. 相似文献