全文获取类型
收费全文 | 12758篇 |
免费 | 1199篇 |
国内免费 | 1582篇 |
专业分类
测绘学 | 794篇 |
大气科学 | 984篇 |
地球物理 | 1327篇 |
地质学 | 4063篇 |
海洋学 | 1268篇 |
天文学 | 1550篇 |
综合类 | 941篇 |
自然地理 | 4612篇 |
出版年
2024年 | 36篇 |
2023年 | 110篇 |
2022年 | 363篇 |
2021年 | 350篇 |
2020年 | 356篇 |
2019年 | 434篇 |
2018年 | 316篇 |
2017年 | 370篇 |
2016年 | 405篇 |
2015年 | 417篇 |
2014年 | 539篇 |
2013年 | 677篇 |
2012年 | 634篇 |
2011年 | 574篇 |
2010年 | 509篇 |
2009年 | 712篇 |
2008年 | 759篇 |
2007年 | 820篇 |
2006年 | 829篇 |
2005年 | 719篇 |
2004年 | 679篇 |
2003年 | 616篇 |
2002年 | 608篇 |
2001年 | 592篇 |
2000年 | 578篇 |
1999年 | 540篇 |
1998年 | 432篇 |
1997年 | 314篇 |
1996年 | 240篇 |
1995年 | 197篇 |
1994年 | 157篇 |
1993年 | 151篇 |
1992年 | 102篇 |
1991年 | 84篇 |
1990年 | 80篇 |
1989年 | 56篇 |
1988年 | 49篇 |
1987年 | 48篇 |
1986年 | 24篇 |
1985年 | 16篇 |
1984年 | 12篇 |
1983年 | 3篇 |
1982年 | 9篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1972年 | 1篇 |
1954年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 988 毫秒
11.
TANGYa XIEJiasui SUNHui 《山地科学学报》2004,1(1):38-45
Dry valleys are a striking geographic landscape in Hengduan Mountains Region and are characterized by low rainfall, desert type of vegetation and fragile environment. Past efforts and resources have been concentrated mainly on rehabilitation of degraded ecosystem and fragile environment, particularly reforestation, while socio-economic development has been largely overlooked. Despite successes in pocket areas, the overall trend of unsustainability and environmental deterioration are continuing. It is important to understand that uplift of the Tibetan Plateau is the root cause of development of dry valleys, and development and formation of dry valleys is a natural process. Human intervention has played a secondary role in development of dry valleys and degradation of dry valleys though human intervention in many cases has speeded up environmental degradation of the dry valleys. It is important to understand that dry valleys are climatic enclaves and an integrated approach that combines rehabilitation of degraded ecosystems and socio-economic development should be adopted if the overall goal of sustainable development of dry valleys is to be achieved. Promotion of niche-based cash crops, rural energy including hydropower, solar energy, biogas and fuelwood plantation is recommended as the priority activities. 相似文献
12.
广西海洋资源丰富 ,品种繁多 ,为了更好开发 ,建议从法制、宣传教育、普及海洋资源有关知识 ,提高人们整体素质做起 ,进一步抓住机遇 ,合理开发 ,才能取得良好效益 ,达到预定目标 相似文献
13.
14.
芮国强 《广东海洋大学学报》2003,23(2):72-78
可持续发展作为现代化建设的两大战略之一 ,对我国政府的能力提出了挑战。可持续发展战略的实施 ,要求加强政府的作用 ,将政府建设成为强有力而又廉价的政府。为此 ,我国政府应从加强政府的财政汲取能力建设、强化中央政府协调地区发展的能力 ,加强政府调控能力建设、强化中央政府协调当前利益和长远利益、经济利益与生态效益的能力 ,并从根本上转变政府职能、精兵简政、建设廉价高效的政府等方面着手来提高我国政府推进和实施可持续发展战略的能力 相似文献
15.
Hai-Ning LiNational Astronomical Observatories Chinese Academy of Sciences Beijing lhnDepartment of Astronomy Beijing Normal University Beijing 《中国天文和天体物理学报》2003,3(5)
We present a quantitative estimate of the relativistic corrections to the thermal SZ power spectrum produced by the energetic electrons in massive clusters. The corrections are well within 10% for current experiments with working frequencies below v < 100 GHz, but become non-negligible at high frequencies v > 350 GHz. Moreover, the corrections appear to be slightly smaller at higher l or smaller angular scales. We conclude that there is no need to include the relativistic corrections in the theoretical study of the SZ power spectrum especially at low frequencies unless the SZ power spectrum is used for precision cosmology. 相似文献
16.
17.
18.
19.
We present warm dark matter (WDM) as a possible solution to the missing satellites and angular momentum problem in galaxy
formation and introduce improved initial conditions for numerical simulations of WDM models, which avoid the formation of
unphysical haloes found in earlier simulations. There is a hint, that because of that the mass function of satellite haloes
has been overestimated so far, pointing to higher values for the WDM particle mass.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
20.
The response of natural vegetation to climate change is of global concern. In this research, an aggregated Holdridge Life Zone System was used to study the possible response of life zones in China under doubled atmospheric CO2 concentration with the input climatic parameters at 0.5×0.5° resolution of longitude and latitude from NCAR regional climate model 2 (RegCM2) coupled with the CSIRO global climate model. The results indicate that the latitudinal distribution of life zones would become irregular because of the complicated climate change. In particular, new life zones, such as subtropical desert (SD), tropical desert (TDE) and tropical thorn woodland (TTW), would appear. Subtropical evergreen broadleaved forest (SEBF), tropical rainforest and monsoon forest (TRF), SD, TDE and TTW zones would appear in the northeastern China. Cool-temperate mixed coniferous and broadleaved forest (CMC) and warm-temperate deciduous broadleaved forest (WDBF) zones would appear at latitudes 25–35°N. The temperate desert (TD) in the western China would become Tibetan high-cold plateau (THP), SEBF, WDBF and temperate steppe (TS), and a large part of THP would be replaced by TRF, TDE, SEBF, TS and TTW. The relative area (distribution area/total terrestrial area) of CMC, TRF, TDE and TTW zone would increase about 3%, 21%, 3% and 6%, respectively. However, the relative area of SEBF, TS, TD and THP would decrease about 5%, 3%, 19% and 4%, respectively. In all, the relative area of forests (CCF, CMC, WDBF, SEBF, TRF) would increase about 15%, but the relative area of desert (TD, SD, TDE, and TTW) and THP would decrease about 9% and 4%, respectively. Therefore, responses of different life zones in China to climate change would be dramatic, and nationwide corridors should be considered for the conservation of migrating species under climate change. 相似文献