全文获取类型
收费全文 | 9543篇 |
免费 | 1100篇 |
国内免费 | 3543篇 |
专业分类
测绘学 | 493篇 |
大气科学 | 1672篇 |
地球物理 | 3224篇 |
地质学 | 5561篇 |
海洋学 | 1016篇 |
天文学 | 394篇 |
综合类 | 697篇 |
自然地理 | 1129篇 |
出版年
2024年 | 65篇 |
2023年 | 179篇 |
2022年 | 101篇 |
2021年 | 199篇 |
2020年 | 85篇 |
2019年 | 135篇 |
2018年 | 186篇 |
2017年 | 66篇 |
2016年 | 153篇 |
2015年 | 148篇 |
2014年 | 259篇 |
2013年 | 248篇 |
2012年 | 304篇 |
2011年 | 386篇 |
2010年 | 220篇 |
2009年 | 296篇 |
2008年 | 333篇 |
2007年 | 439篇 |
2006年 | 489篇 |
2005年 | 576篇 |
2004年 | 553篇 |
2003年 | 374篇 |
2002年 | 443篇 |
2001年 | 482篇 |
2000年 | 512篇 |
1999年 | 235篇 |
1998年 | 190篇 |
1997年 | 195篇 |
1996年 | 174篇 |
1995年 | 219篇 |
1994年 | 196篇 |
1993年 | 380篇 |
1992年 | 336篇 |
1991年 | 447篇 |
1990年 | 390篇 |
1989年 | 438篇 |
1988年 | 447篇 |
1987年 | 375篇 |
1986年 | 264篇 |
1985年 | 357篇 |
1984年 | 295篇 |
1983年 | 218篇 |
1982年 | 171篇 |
1981年 | 121篇 |
1980年 | 174篇 |
1964年 | 89篇 |
1960年 | 52篇 |
1959年 | 109篇 |
1958年 | 120篇 |
1957年 | 127篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
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
62.
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
63.
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
64.
65.
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
66.
Hausladen G 《Soviet geography》1987,28(2):71-89
Future trends in urbanization in the USSR east of the Urals are considered using official Soviet data from 1959 to 1985. "Absolute and relative growth and growth rates are calculated for economic regions, oblast-level administrative entities, and individual cities, as well as for city-size categories. The nature of Siberian growth suggests that in addition to serving as centers of resource exploitation, Siberian cities also function as growth poles for more integrated development. The analysis serves as the preliminary stage for proposed future research on the extent of Siberian urban development and the integration of Siberia into the Soviet economy." 相似文献
67.
We have obtained velocity-resolved spectra of the 12C II 157.8 microns 2P3/2-2P1/2 fine structure line in the M42 region of Orion. Observations at 0.8 km s-1 resolution with a laser heterodyne spectrometer show multiple velocity components in some locations, with typical linewidths of 3-5 km s-1. Spectra of theta 1C and BN-KL also show weak emission from the F = 2-1 hyperfine component of the equivalent 13C II line. From the observed 12C II/13C II line intensity ratios, we deduce that the 12C II emission is optically thick with tau approximately 5 at both positions. Excitation temperatures of 128 K and 90 K, together with column densities of approximately 1 x 10(19) cm-2 and approximately 4 x 10(18) cm-2, are derived for theta 1C and BN-KL, respectively. 相似文献
68.
本文着重描述了SGR钻孔处冰盖上的积雪在密实化过程中的特征变化,并对该过程进行了分段的和全面的回归分析.结果表明,冰盖密度随深度增大,但增长幅度随深度减小.作者提出密度变化减小度的概念.计算得出的所研究冰芯钻取点的密度变化减小度为-0.15kg/m~3·m~2,粒雪成冰前的密实速率平均值为4.08kg/m~3·a.本文得到的冰盖密度变化“临界点”与以往报道的有所不同.分析这一现象时,作者强调当积雪还在活动层时冰盖温度的影响,并以此解释密度剖面的异常变化以及离差的回升.特别指出,积雪的密度变化具有气候学意义,它在一定程度上能够反映出积雪形成及变化过程中气候变化的某些信息.本文由密度变化确定的钻孔点雪冰转化深度为50米. 相似文献
69.
We have used observations of the rare isotopes of HCN and HNC to determine the relative abundance of these two chemical isomers along the central ridge of the Orion molecular cloud. The abundance ratio [HCN]/[HNC] decreases by more than an order of magnitude from the relatively warm plateau and hot core sources toward the KL nebula to the colder, more quiescent clouds to the north and south. Even in the cooler regions, however, the ratio is an order of magnitude larger than that found in previous investigations of cold dark clouds. We determine the kinetic temperature in the regions we have studied from new observations of methylacetylene (CH3CCH), together with other recent estimates of the gas temperature near KL. The results suggest that the warmer portions of the cloud are dominated by different chemical pathways than those in the general interstellar cloud material. 相似文献
70.
"An attempt is made in the light of an analysis of population changes occurring in several sub-districts of Greater Santiago in the period between the last population censuses of 1970 and 1982, based on small-area census units (distritos and communas) to draw attention to the effects on the spatial growth of the city resulting from changed conditions in the political and juridical sphere since the change of power in 1973." The effect of changes in government policy concerning the liberalization of the property market and the illegal occupation of land are noted. (summary in ENG) 相似文献