全文获取类型
收费全文 | 5192篇 |
免费 | 383篇 |
国内免费 | 268篇 |
专业分类
测绘学 | 234篇 |
大气科学 | 237篇 |
地球物理 | 1676篇 |
地质学 | 1207篇 |
海洋学 | 815篇 |
天文学 | 53篇 |
综合类 | 190篇 |
自然地理 | 1431篇 |
出版年
2024年 | 19篇 |
2023年 | 47篇 |
2022年 | 112篇 |
2021年 | 159篇 |
2020年 | 230篇 |
2019年 | 195篇 |
2018年 | 174篇 |
2017年 | 249篇 |
2016年 | 245篇 |
2015年 | 188篇 |
2014年 | 211篇 |
2013年 | 511篇 |
2012年 | 148篇 |
2011年 | 182篇 |
2010年 | 158篇 |
2009年 | 224篇 |
2008年 | 302篇 |
2007年 | 278篇 |
2006年 | 272篇 |
2005年 | 243篇 |
2004年 | 193篇 |
2003年 | 169篇 |
2002年 | 147篇 |
2001年 | 119篇 |
2000年 | 144篇 |
1999年 | 135篇 |
1998年 | 119篇 |
1997年 | 117篇 |
1996年 | 81篇 |
1995年 | 80篇 |
1994年 | 69篇 |
1993年 | 77篇 |
1992年 | 46篇 |
1991年 | 34篇 |
1990年 | 26篇 |
1989年 | 29篇 |
1988年 | 29篇 |
1987年 | 15篇 |
1986年 | 19篇 |
1985年 | 9篇 |
1984年 | 10篇 |
1983年 | 4篇 |
1982年 | 12篇 |
1981年 | 9篇 |
1980年 | 2篇 |
1954年 | 2篇 |
排序方式: 共有5843条查询结果,搜索用时 15 毫秒
51.
为探求黄东海平滑真刺水蚤(Euchaeta plana)是否存在分化,对南黄海、东海2个海域平滑真刺水蚤进行ISSR分析。利用筛选出的4个ISSR引物对平滑真刺水蚤进行PCR扩增。共获得18个扩增位点,其中多态性位点14个,所占比例为77.78%。利用POPGENE软件计算遗传距离为0.071 8,遗传相似系数为0.930 7,从而说明2个群体之间遗传分化很小,并推断为黄海暖流影响其分布的结果。 相似文献
52.
Numerical modelling of deep sea air-lift 总被引:2,自引:0,他引:2
Deep sea air-lifting of solid particles from depth of 1600 m is simulated with a mathematical model of the three-phase flow in an upward pipe. The computations are carried out for an axisymmetric domain in a transient way. Phase distributions, pressure and velocity profiles together with flow rates for all phases are presented and analysed. The influence of the pipe diameter on the air-lift efficiency was studied for air-lift pipes of different lengths and found to be significant. The lifting efficiency increases with the increase of the pipe diameter due to the reduction of the wall friction influence on the flow. In addition, the efficiency also increases with the increase of the solid particles volume fraction at the inlet. The presented numerical model can be utilized during various stages of the design of the air-lift pumps to help answer fundamental questions on the process, and during their operation to select optimal process parameters and to address possible problems. 相似文献
53.
54.
Rosalind C. King Guillaume Backé Christopher K. Morley Richard R. Hillis Mark R.P. Tingay 《Marine and Petroleum Geology》2010
Recent GPS measurements demonstrate that NW Borneo undergoes 4–6 mm of plate-scale shortening a year, which is not accommodated by plate-scale structures. The only geological structure in NW Borneo described to accommodate on-going shortening is the Baram Delta System located on the outer shelf to basin floor. Delta toe fold-thrust belts are commonly thought to be caused by margin-normal compressional stresses generated by margin-parallel upslope gravitational extension. 相似文献
55.
Lapo Ragionieri Stefano Cannicci Christoph D. Schubart Sara Fratini 《Estuarine, Coastal and Shelf Science》2010
Most marine organisms are characterized by at least one planktonic phase during their life history, potentially allowing interconnection of populations separated by several hundred kilometers. For many years, the idea that marine species are genetically homogenous throughout their range of distribution, due to passive larval transport, has been a paradigm. Nowadays, a growing number of studies underline the existence of boundaries in the marine realm and highlight how larval dispersal is a complex process depending on biotic as well as abiotic factors. Marine fragmented habitats, such as atolls, mangroves and estuaries, are optimal systems for investigating the marine dispersion process under a metapopulation approach, since populations can be geographically defined a priori as opposed to those occupying open marine environments. Within this frame, the present paper investigates the population genetic structure and the demographic history of the mangrove crab Neosarmatium meinerti within the western Indian Ocean by partial sequences of the mitochondrial DNA cytochrome oxidase subunit I. A total of 167 specimens were sampled from six mangrove sites distributed along the East African coast, from Kenya to South Africa, also including a mangrove forest located on Mahé Island, Seychelles. A sharp genetic break between the mainland and the Seychelles is recorded, revealing the existence of two historically distinct groups that can be defined as independent evolutionary units. Gene flow along the East African coast appears to be high enough to form a single metapopulation, probably by means of stepping stone populations. Otherwise, this mainland metapopulation is currently under expansion through a gradual moving front from the subtropical toward the equatorial populations. 相似文献
56.
Despite substantial rural-urban migration, 38.1 percent of the population of Poland still live in the countryside and the
total numbers are only 0.9mln fewer than in 1946. At present the rural population is increasing and the rate of natural increase
(though falling) is higher than in the towns though the productive age group is smaller. However, these human resources are
not being properly used and the results can be seen in terms of economic inefficiency, low living standards and a high level
of state support. Loss of jobs in factories and state farms results in welfare payments by the state and considerable 'hidden
unemployment' on small family farms where profitability is constrained by inefficient use of labour. Poverty among the rural
population is evident through a collapse of house building and considerable domestic overcrowding. However, conditions vary
considerably across the country and this must be reflected in the economic and social policies drawn up for the new administrative
regions introduced in 1999.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
57.
S. K. Chaulya R. S. Singh M. K. Chakraborty B. K. Srivastava 《Geotechnical and Geological Engineering》2000,18(3):193-207
An integrated study on biological stabilisation of a dump slope has indicated that biological reclamation with grass and tree species should be considered for long term stability of this coal mine dump in India. The grasses have greater soil binding capacity and help to control soil erosion and improve dump stability. Native grasses such as Bamboo (Dendrocalmus strictus) and Kashi (Saccharum spontaneum) are the important constituents of grass species which can stabilise the dump slopes. Field observation of growth performance of grasses have indicated that mean grass height, root depth and below-ground root biomass are 185 cm (±68), 45 cm (±5) and 467 g m–2 (±170), respectively after three years of grass growth on Mudidih overburden dump slope in India. The growth performance of tree species, namely Sisum (Dalbergia sisoo) and Subabool (Leucena lecocephala), in terms of height, diameter increment, below-ground biomass and root depth have shown mean values of 219 cm (±94), 48 mm (±6), 4.0 kg m–2 (±1.5) and 1 m (±0.1), respectively. This acts as biological fertility which helps in root proliferation and enhancement of dump stability. From the numerical modelling it is suggested that roots of these grass and tree species have significantly enhanced the factor of safety of dump from 1.4 to 1.8 and therefore have a positive role in maintaining long term stability. 相似文献
58.
59.
Pierre Strzerzynski Stéphane Guillot Gabriel Courrioux Patrick Ledru 《Comptes Rendus Geoscience》2005,337(14):1284-1292
The structural analysis and the 3D modelling of Stephanian granites of the Pelvoux Massif characterize an emplacement along sinistral NW–SE- and dextral NE–SW-trending shear zones in the Pelvoux and in the Aiguilles Rouges–Mont Blanc Massifs, respectively. This Carboniferous shear system is consistent with a north–south extension direction known in the whole Variscan belt at this time. To cite this article: P. Strzerzynski et al., C. R. Geoscience 337 (2005). 相似文献
60.