全文获取类型
收费全文 | 95392篇 |
免费 | 16496篇 |
国内免费 | 21342篇 |
专业分类
测绘学 | 10416篇 |
大气科学 | 11391篇 |
地球物理 | 19341篇 |
地质学 | 52604篇 |
海洋学 | 12028篇 |
天文学 | 5820篇 |
综合类 | 6881篇 |
自然地理 | 14749篇 |
出版年
2024年 | 365篇 |
2023年 | 989篇 |
2022年 | 2753篇 |
2021年 | 3337篇 |
2020年 | 3358篇 |
2019年 | 4247篇 |
2018年 | 3194篇 |
2017年 | 3806篇 |
2016年 | 3890篇 |
2015年 | 4337篇 |
2014年 | 5424篇 |
2013年 | 5339篇 |
2012年 | 5875篇 |
2011年 | 6194篇 |
2010年 | 5235篇 |
2009年 | 6417篇 |
2008年 | 6188篇 |
2007年 | 6774篇 |
2006年 | 6606篇 |
2005年 | 5937篇 |
2004年 | 5547篇 |
2003年 | 5088篇 |
2002年 | 4316篇 |
2001年 | 3864篇 |
2000年 | 3635篇 |
1999年 | 3330篇 |
1998年 | 2914篇 |
1997年 | 2426篇 |
1996年 | 2138篇 |
1995年 | 1798篇 |
1994年 | 1751篇 |
1993年 | 1451篇 |
1992年 | 1150篇 |
1991年 | 839篇 |
1990年 | 662篇 |
1989年 | 629篇 |
1988年 | 420篇 |
1987年 | 274篇 |
1986年 | 187篇 |
1985年 | 124篇 |
1984年 | 60篇 |
1983年 | 47篇 |
1982年 | 44篇 |
1981年 | 33篇 |
1980年 | 38篇 |
1979年 | 40篇 |
1978年 | 51篇 |
1977年 | 27篇 |
1976年 | 8篇 |
1954年 | 34篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
271.
I.IN~crIOXLocatedinthecoddlepatofTallmBasin,withanareaof33.76X104klnZ,theTaldirnakan~isinthehinterlandofEurasia.Blockedbythehighmountainsaround,vapourofoceancanhardlyreachthedesert.APartfromthis,asthedeSertisinthesinkingcompensationareaoftheascensionalaircurrentaamstheQinghal-XIZangPlateau,itSprecipitationisrareandtheevaporationcapacityisintensealltheyearround.Allthesecontributetotheformationsofthetypifydrydesertclimate.Theacidityindexofthedesertandthearoundregionisashighasmorethan50,w… 相似文献
272.
Aimed at promoting regional coalitions and expanding the approach to economic links, this paper puts forward some new concepts
such as link intensity and receiving coefficient, expounds the indexes of quantitative analysis of economic links and establishes
the quantitative-analysis model of economic links. With help of the model, this paper calculates the values of the link intensities
between Su-Xi-Chang (Suzhou-Wuxi-Changzhou) region and Shanghai, and analyzes the regional difference of the economic links. 相似文献
273.
274.
Vertical measurements of , and N2O concentrations, and uptake, and oxidation rates were measured at 5 sites in western Cook Strait, New Zealand, between 31 March and 3 April 1983. Nitrate increased with depth at all stations reaching a maximum of 10.5 μg-atom at the most strongly stratified station whereas was relatively constant with depth at all stations (~0.1 μg-atom ). The highest rates of oxidation generally occurred in the near surface waters and decreased with depth. N2O levels were near saturation with respect to the air above the sea surface and showed no obvious changes during 24 h incubation. oxidation by nitrifying bacteria may account for about 30% of the total utilization (i.e. bacterial+agal) and, assuming oxidation through to , may supply about 40% of the algal requirements of in the study area. These results suggest that bacterial nitrification is of potential importance to the nitrogen dynamics of the western Cook Strait, particularly with respect to the nitrogen demands of the phytoplankton. 相似文献
275.
Galileo系统及其在中国的应用 总被引:9,自引:0,他引:9
较详细地介绍了Galileo系统的全面体系结构、频率设计、服务内容及其广泛的应用范围,指出了它与GPS系统相比的优点,并对开发和增强Galileo系统在我国多层次、全方位的应用提出了建议。 相似文献
276.
277.
278.
Geoff Kite 《水文研究》1993,7(2):227-233
Using current meters to estimate flows in fast mountain streams is difficult and inaccurate. The salt dilution method offers an easier and more accurate alternative. The method has been used for many years but is time consuming and messy because of the need to mix chemical solutions and measure chemical concentrations in the field. A computer program has been developed which uses a laptop computer to calculate the mixing length and the mass of salt needed. The program controls the conductivity measurements and calculates the streamflow directly in the field. The development of this program is described and examples are presented of the application of the method in the Rocky Mountains of Alberta and British Columbia. 相似文献
279.
Erosion of man-made, forestry drainage channels occurs when the plough cuts through the surface peat layer into the underlying erodible mineral soil. A procedure is developed, based on hydraulic considerations, which will allow the drainage engineer to design stable drainage networks in upland forestry plantations. An example design chart is given for an erodible sandy loam type soil. 相似文献
280.