全文获取类型
收费全文 | 5384篇 |
免费 | 703篇 |
国内免费 | 1223篇 |
专业分类
测绘学 | 675篇 |
大气科学 | 454篇 |
地球物理 | 660篇 |
地质学 | 2948篇 |
海洋学 | 538篇 |
天文学 | 51篇 |
综合类 | 373篇 |
自然地理 | 1611篇 |
出版年
2024年 | 28篇 |
2023年 | 54篇 |
2022年 | 198篇 |
2021年 | 222篇 |
2020年 | 219篇 |
2019年 | 233篇 |
2018年 | 174篇 |
2017年 | 235篇 |
2016年 | 226篇 |
2015年 | 285篇 |
2014年 | 329篇 |
2013年 | 402篇 |
2012年 | 320篇 |
2011年 | 362篇 |
2010年 | 303篇 |
2009年 | 341篇 |
2008年 | 331篇 |
2007年 | 394篇 |
2006年 | 345篇 |
2005年 | 323篇 |
2004年 | 310篇 |
2003年 | 217篇 |
2002年 | 200篇 |
2001年 | 183篇 |
2000年 | 180篇 |
1999年 | 159篇 |
1998年 | 127篇 |
1997年 | 126篇 |
1996年 | 76篇 |
1995年 | 59篇 |
1994年 | 70篇 |
1993年 | 63篇 |
1992年 | 52篇 |
1991年 | 33篇 |
1990年 | 27篇 |
1989年 | 24篇 |
1988年 | 24篇 |
1987年 | 13篇 |
1986年 | 12篇 |
1985年 | 6篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1978年 | 4篇 |
1977年 | 1篇 |
排序方式: 共有7310条查询结果,搜索用时 23 毫秒
21.
本文对北部湾三维潮波进行了数值研究,并将所得结果与现有观测资料作了比较。通过比较发现两者相当一致。文中还绘制了M_2和K_1分潮的同潮图,并对其作了讨论。可以断定,北部湾的日潮优势是由日潮共振所引起的。M_2和K_1分潮流的水平分布表明,强流区位于它们各自的蜕化无潮点附近。还讨论了分潮流的铅直结构,可以看出这种结构十分接近实际分潮流场的特征。 相似文献
22.
23.
根据地形地貌、地质构造、水文地质条件将青岛市划分为6个工程地质亚区,论述了各亚区地质环境特征,结合不同城市建筑工程特点,进行了工程场地适应性和选择性分析评价,为充分合理利用城市地质环境提供良好依据 相似文献
24.
本文介绍了南极中山锚地的选择条件,勘测实施过程及水文、气象特点,并对测量区域作了分析研究与评价,科学地确定了适合科考船抛锚的锚地,致使“雪龙”船首次在中山锚地抛锚试抛成功,结束了中山站附近海域无锚地的历史。 相似文献
25.
三传感器波浪水槽二次反射主动吸收方法是加拿大科学院水力中心最近开发的一种水槽反射波控制技术。该法在造波板前 1~ 2倍波长处布置 3个传感器 ,通过入反射波分离方法得到准确的入反射波参数 ,以此调整造波信号 ,有效地吸收由建筑物反射回到造波板的二次反射波。文中在分析波浪水槽二次反射吸收方法研究现状的基础上 ,介绍了加拿大水力中心对现有方法的改进及其效果 相似文献
26.
Recruitment patterns of Serpula vermicularis L. (Polychaeta, Serpulidae) in Loch Creran, Scotland 总被引:1,自引:0,他引:1
Nicola D. Chapman Colin G. Moore Dan B. Harries Alastair R. Lyndon 《Estuarine, Coastal and Shelf Science》2007,73(3-4):598-606
This study aimed to contribute to conservation management of reefs of Serpula vermicularis by increasing understanding of the factors influencing larval settlement. The study was carried out in Loch Creran, which supports the most extensive known development of S. vermicularis reefs in the world. Settlement plates were deployed to examine the influence of season, depth, reef density, substrate type and orientation. Monthly deployment of plates revealed settlement of S. vermicularis to occur predominantly from mid-June to mid-October, peaking in late August to early September. Settlement of Pomatoceros spp. peaked much earlier, in late May to early June. Deployment of plates at different depths revealed a marked reduction in S. vermicularis settlement intensity between 6 and 12 m. As this corresponds with the deeper limit of the peripheral fringe of serpulid reefs in the loch, it is suggested that this limit is imposed by a depth-correlated settlement response, rather than reduction in available substrata. Comparisons of various substrata showed a preference by S. vermicularis larvae for a slate over a scallop substrate and no evidence of enhanced recruitment to occupied or unoccupied tubes of S. vermicularis, suggesting that gregarious attraction is unlikely to be a factor causing reef formation. Settlement onto the upper side of a horizontal scallop substrate was found to be insignificant in comparison with the underside or a vertically orientated scallop. Evidence for the role of light in controlling the depth and substrate-orientation preferences of S. vermicularis larvae is discussed. Based on the results of this study, recommendations are made regarding remediation of areas suffering reef damage. 相似文献
27.
28.
以上海市向阳圩海塘围堰主堤为工程背景,在大量原位实测的基础上通过对各测试结果的统计分析研究了软土海滩围堰堤坝及地基沉降位移特性。结果表明:围堰堤坝及地基沉降具有显著的时效特性,沉降与时间的相关关系可用负指数时效特性曲线拟合;各测点位移值随时间具有明显突变变化,整个沉降时域可分为快速沉降时域区及缓慢沉降时域区。同时,在充分考察了沉降速率随时间变化特性的前提下提出了用该参量预测堤坝稳定时间及最终沉降位移的建议。 相似文献
29.
The photochemical instability of several related pteridines in seawater was investigated by aseptic incubation of solutions at 20–22°C under illumination from cool-white light of intensity 6 kerg cm−2 sec−1, and the chemical changes were spectrophotometrically monitored. All the pteridines showed markedly accelerated degradation from this illumination relative to their behaviour in total darkness.Pterin and lumazine were degraded very slowly with zero-order reaction kinetics, while the other pteridines photolysed rapidly (according to first-order kinetics) with decomposition rates increasing in the order dioxylumazine (2,4,6,7-tetrahydroxypteridine) < leucopterin < isoxanthopterin < xanthopterin < oxylumazine (2,4,6-trihydroxypteridine). Excepting leucopterin and dioxylumazine, the photolysis rates were attributable to the pH of seawater and not its salt content; this was also the case with oxylumazine which required the salt content of seawater for decomposition in darkness. Leucopterin and dioxylumazine (both 6,7-dihydroxylated pteridines) gave evidence of complexation with the major divalent cations (Ca2+, Mg2+) of seawater, by virtue of which their photolytic degradation rates were enhanced to magnitudes obtained in pH-10 buffer without seawater. It is proposed that such complexation produces structural forms of these pteridines analogous to their normal ionic forms at pH 10–12.The photolysis of the 6-hydroxylated pteridines (xanthopterin, oxylumazine) proceeded via intermediate formation of their corresponding 7-hydroxylated derivatives (leucopterin, dioxylumazine). 相似文献
30.