全文获取类型
收费全文 | 2538篇 |
免费 | 186篇 |
国内免费 | 522篇 |
专业分类
测绘学 | 126篇 |
大气科学 | 255篇 |
地球物理 | 1078篇 |
地质学 | 1081篇 |
海洋学 | 321篇 |
天文学 | 109篇 |
综合类 | 77篇 |
自然地理 | 199篇 |
出版年
2023年 | 27篇 |
2022年 | 20篇 |
2021年 | 16篇 |
2020年 | 46篇 |
2019年 | 40篇 |
2018年 | 43篇 |
2017年 | 9篇 |
2016年 | 23篇 |
2015年 | 17篇 |
2014年 | 56篇 |
2013年 | 54篇 |
2012年 | 112篇 |
2011年 | 163篇 |
2010年 | 45篇 |
2009年 | 57篇 |
2008年 | 141篇 |
2007年 | 119篇 |
2006年 | 135篇 |
2005年 | 157篇 |
2004年 | 120篇 |
2003年 | 95篇 |
2002年 | 111篇 |
2001年 | 96篇 |
2000年 | 125篇 |
1999年 | 45篇 |
1998年 | 56篇 |
1997年 | 50篇 |
1996年 | 58篇 |
1995年 | 66篇 |
1994年 | 66篇 |
1993年 | 88篇 |
1992年 | 97篇 |
1991年 | 120篇 |
1990年 | 97篇 |
1989年 | 91篇 |
1988年 | 111篇 |
1987年 | 75篇 |
1986年 | 50篇 |
1985年 | 66篇 |
1984年 | 48篇 |
1983年 | 44篇 |
1982年 | 31篇 |
1981年 | 25篇 |
1980年 | 54篇 |
1978年 | 10篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1975年 | 5篇 |
1974年 | 5篇 |
1964年 | 7篇 |
排序方式: 共有3246条查询结果,搜索用时 0 毫秒
1.
英国地理学家学会年会于1984年1月4日至7日在德勒姆大学召开。会址设在德勒姆大学的科学中心。这个中心包括该大学的地理系。学会的各个研究小组共计召开有33次会议,向这些会上提交的论文有170篇。 相似文献
2.
本文用完全动力学程式计算了Ⅰ型超新星爆发。这些模型是依据氦或碳和氧构成星核,部分地或全部地产生瞬时完成的核燃烧。计算中将动力学方程、核统计平衡、Rayleigh-Taylor不稳定性等物理过程联合起来求解。重点比较了Rayleigh-Taylor不稳定性的影响,现不能作出完全肯定的结论。计算结果列在表1、表2和图2—6中。 相似文献
3.
4.
引言 D.布鲁金尼的论文《可用空间时代技术进行更精确的人口普查》提出了一些有趣的问题。我们为能够在《摄影测量工程和遥感》杂志上看到这篇有关遥感在社会科学领城内的应用的论文而高兴。我们认为只有了解人口普查数据的多种用途之后,再来检验那些改进人口普查的方法才是合适的,众所周知,每十年一次的人口普查数据的精度和完备性并不是没有缺点的。无疑地,许多人口普查人员将首先承认,每次由点数 相似文献
5.
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
6.
7.
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
8.
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
9.
"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
10.
Partitioning of polycyclic aromatic hydrocarbons between water and particles compared to bioaccumulation in mussels: a harbour case 总被引:3,自引:0,他引:3
Hellou J Steller S Leonard J Langille MA Tremblay D 《Marine environmental research》2005,59(2):101-117
Water and particles from three sites located in Halifax Harbour, near and further away from combined municipal sewage effluents (CMSE) were analysed for parental and alkylated polycyclic aromatic hydrocarbons (par and alkPAH). Bioavailability of PAH was compared for inter-tidal mussels collected at the same sites in April and November. The PAH fingerprint determined over 9 sampling times covering a period of 19 months differed more between phases (water and particles) and seasons, than between sites. In the spring, more alkPAH associated with diesel and gasoline were detected in the soluble phase, along with more bioaccumulation of alkPAH in inter-tidal mussels. A broader number of parPAH were detected in mussels collected in the fall. The mean sum of dissolved alkPAH concentrations was higher in water at the site closer to raw CMSE than at the other two sites and particles of that site. However, lowest bioconcentration factors (BCF) were determined in mussels of this more contaminated site. Similar biota-particle accumulation factors (BPAF) were determined for parPAH in mussels from the three sites, all lower than the BCF of alkPAH. The study indicates that sewage treatment plants will reduce the amount of parPAH especially larger than fluoranthene and pyrene from being deposited in the harbour; that alk naphthalenes and fluorenes present in water will continue to be discharged; that the disturbance of sediments can make particle-bound PAH available to mussels. 相似文献