全文获取类型
收费全文 | 52955篇 |
免费 | 5811篇 |
国内免费 | 8151篇 |
专业分类
测绘学 | 2801篇 |
大气科学 | 8666篇 |
地球物理 | 11900篇 |
地质学 | 26282篇 |
海洋学 | 4573篇 |
天文学 | 3080篇 |
综合类 | 5084篇 |
自然地理 | 4531篇 |
出版年
2024年 | 98篇 |
2023年 | 449篇 |
2022年 | 1318篇 |
2021年 | 1547篇 |
2020年 | 1316篇 |
2019年 | 1448篇 |
2018年 | 5928篇 |
2017年 | 5143篇 |
2016年 | 4019篇 |
2015年 | 1676篇 |
2014年 | 1913篇 |
2013年 | 1707篇 |
2012年 | 2581篇 |
2011年 | 4201篇 |
2010年 | 3618篇 |
2009年 | 3889篇 |
2008年 | 3244篇 |
2007年 | 3631篇 |
2006年 | 1272篇 |
2005年 | 1287篇 |
2004年 | 1233篇 |
2003年 | 1221篇 |
2002年 | 1114篇 |
2001年 | 884篇 |
2000年 | 1088篇 |
1999年 | 1515篇 |
1998年 | 1288篇 |
1997年 | 1339篇 |
1996年 | 1122篇 |
1995年 | 1020篇 |
1994年 | 911篇 |
1993年 | 810篇 |
1992年 | 648篇 |
1991年 | 461篇 |
1990年 | 314篇 |
1989年 | 351篇 |
1988年 | 298篇 |
1987年 | 207篇 |
1986年 | 165篇 |
1985年 | 120篇 |
1984年 | 107篇 |
1983年 | 81篇 |
1982年 | 80篇 |
1981年 | 76篇 |
1980年 | 64篇 |
1979年 | 29篇 |
1978年 | 16篇 |
1977年 | 7篇 |
1976年 | 12篇 |
1958年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
411.
A geomorphological and statistical analysis of slope canyons from the northern KwaZulu-Natal continental margin is documented
and compared with submarine canyons from the Atlantic margin of the USA. The northern KwaZulu-Natal margin is characterized
by increasing upslope relief, concave slope-gradient profiles and features related to upslope growth of the canyon forms.
Discounting slope-gradient profile, this morphology is strikingly similar to canyon systems of the New Jersey slope. Several
phases of canyon incision indicate that downslope erosion is also an important factor in the evolution of the northern KwaZulu-Natal
canyon systems. Despite the strong similarities between the northern KwaZulu-Natal and New Jersey slope-canyon systems, key
differences are evident: (1) the concavity of the northern KwaZulu-Natal slope, contrasting with the ∼linear New Jersey slope;
(2) the relative isolation of the northern KwaZulu-Natal canyons, rather than the dense clustering of the New Jersey canyons;
and (3) the absence of strongly shelf-breaching canyons along the northern KwaZulu-Natal margin. In comparison with the New
Jersey margin, we surmise a more youthful stage of canyon evolution, a result of either the canyons themselves being younger
or the formative processes being less active. Less complicated patterns of erosion resulting from reduced sediment availability
have developed in northern KwaZulu-Natal. The reduction in slope concavity on the New Jersey margin may be the result of grading
of the upper slope by intensive headward erosion, a process more subdued—or less evident—on the KwaZulu-Natal margin. 相似文献
412.
413.
Comparison among four kinds of data of sea surface wind stress in the South China Sea 总被引:1,自引:0,他引:1
By using remote sensing (ERS) data, FSU data, COADS data and Hellerman & Rosen-stein objective analysis data to analyze the sea surface wind stress in the South China Sea, it is found that the remote sensing data have higher resolution and more reasonable values. Therefore we suggest that remote sensing data be chosen in the study of climatological features of sea surface wind stress and its seasonal variability in the South China Sea, especially in the study of small and middle scale eddies. 相似文献
414.
In this paper, the numerical modelling of the tidal level and current in the Bohai Sea was carried out with ADI method, by taking the sum of four main tidal components M2,S2K2,O1 as the open boundary condition. The calculated values were consistent with the predicted ones (the observed values in the case of calm) in the Tidal Table. On the basis of the modelling of the tide, the sea level and current fields under the effects of strong wind were simulated. The calculated results were also quite satisfactory. 相似文献
415.
416.
417.
In this paper, the irregular wave force on a cylindrical pier group is calculated by the method of spectrum analysis, and the coefficients of the group effect of piers in the pier group are given here. The calculated results, using P-M and Bretshneider's. (B's) spectra, are obtained for the cases of 2 piers, 3 piers and 4 piers. To compare these results with those obtained for regular waves, we can come to some significant conclusions. Under the action of the irregular wave, when the distance between the piers in the pier group increases, the coefficient of the group effect decreases and tends rapidly to the case of a single pier. In general, when the ratio of the distance between the piers to the diameter of the pier is greater than 4, the group effect can be neglected. 相似文献
418.
419.
ComparativeresearchonkaryotypeinthreespeciesofArcidaeZhengJiasheng;WangMeilin;GuoDanhong;XuXimindandGaoQinglanAbstract:Byair-... 相似文献
420.
长岛养殖扇贝丰,欠原因的初步探讨 总被引:1,自引:0,他引:1
通过对长岛扇贝养殖环境两年(1989、1990)监测及历史资料的初步分析研究,得出了影响长岛养殖扇贝丰欠的主要因子有:1)长岛地区的降水量;2)海水中浮游植物含量;3)海水盐度。建立了适合长岛水域的模糊综合评判关系式用以综合评判长岛的扇贝养殖环境及其与养殖扇贝丰、欠之间的关系。 相似文献