全文获取类型
收费全文 | 17245篇 |
免费 | 3462篇 |
国内免费 | 5066篇 |
专业分类
测绘学 | 1927篇 |
大气科学 | 3568篇 |
地球物理 | 3795篇 |
地质学 | 9660篇 |
海洋学 | 2575篇 |
天文学 | 568篇 |
综合类 | 1644篇 |
自然地理 | 2036篇 |
出版年
2024年 | 74篇 |
2023年 | 318篇 |
2022年 | 873篇 |
2021年 | 1044篇 |
2020年 | 865篇 |
2019年 | 1020篇 |
2018年 | 1016篇 |
2017年 | 1000篇 |
2016年 | 1031篇 |
2015年 | 1019篇 |
2014年 | 1109篇 |
2013年 | 1227篇 |
2012年 | 1157篇 |
2011年 | 1205篇 |
2010年 | 1199篇 |
2009年 | 1083篇 |
2008年 | 1087篇 |
2007年 | 915篇 |
2006年 | 883篇 |
2005年 | 754篇 |
2004年 | 584篇 |
2003年 | 615篇 |
2002年 | 700篇 |
2001年 | 580篇 |
2000年 | 554篇 |
1999年 | 599篇 |
1998年 | 488篇 |
1997年 | 472篇 |
1996年 | 415篇 |
1995年 | 357篇 |
1994年 | 315篇 |
1993年 | 243篇 |
1992年 | 204篇 |
1991年 | 148篇 |
1990年 | 109篇 |
1989年 | 109篇 |
1988年 | 103篇 |
1987年 | 68篇 |
1986年 | 52篇 |
1985年 | 43篇 |
1984年 | 25篇 |
1983年 | 24篇 |
1982年 | 13篇 |
1981年 | 14篇 |
1980年 | 17篇 |
1979年 | 14篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1958年 | 15篇 |
1954年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
112.
The natural human female hormones oestrone and 17β-oestradiol have been implicated in the disruption of endocrine systems in some wildlife adjacent to sewage effluents. The sorption behaviour of these two compounds under estuarine conditions was studied by spiking either 2.55 μg of oestrone or 2.65 μg of 17β-oestradiol in kinetic experiments. In equilibrium experiments, 3 ng of oestrone or 3.2 ng of 17β-oestradiol was added in each of the centrifuge tubes. Sorption onto sediment particles was relatively slow, with sorption equilibrium being reached in about 70 and 170 h for oestrone and 17β-oestradiol, respectively. The effects of a variety of environmental parameters on sorption were studied including salinity, sediment concentration (SC), the presence of a third phase, particle size and, also, surfactant concentrations. Results show that although salinity did not induce any statistically significant effect on the sorption of 17β-oestradiol, it did statistically enhance the sorption of oestrone, and a salting constant of 0.3 l mol−1 was derived. The partition coefficient for both compounds decreased with increasing sediment concentration, a phenomenon that has been widely reported and attributed to the presence of colloids (which could enhance dissolved concentrations). In this paper, the true partition coefficients for sediment particles (Kptrue) and colloidal particles (Kctrue) have been calculated, and a Kptrue value of 141 and 102 ml g−1 was obtained for oestrone and 17β-oestradiol, respectively. In addition, Kctrue values for oestrone (222×102 ml g−1) and 17β-oestradiol (135×102 ml g−1) were two orders of magnitude higher than their respective Kptrue values, suggesting that the colloidal particles are significantly stronger sorbents for natural oestrogens than sediment particles. Particles of different sizes were found to have different partition coefficients due to the strong relationships between partition coefficients for the two compounds and particulate organic carbon (POC) contents and specific surface areas (SSAs). The presence of a surfactant was shown to reduce the partition coefficients for the two compounds, although its concentrations being used were higher than those normally found in the natural environment. 相似文献
113.
本文通过研究区5个钻孔松散沉积岩心磁性地层的划分对比,获知布容与松山极性带的界线,南黄海和陆区北部位于80.0—99.5m。陆区的南部此界线于270.4m深处。松山和高斯极性带的界线,海区未揭露到,其沉积起始时间都小于1.7Ma。而陆区的南、北部分别位于117m和328.2m。高斯和吉尔伯特极性带的界线,陆区北部为140m,而南部区为460.15m。沉积起始时间为3.4Ma。吉尔伯特底界仅北部陆区所揭示,为190.5m。松散沉积层与下伏白垩纪(?)石灰岩接触面位于400.35m,沉积起始时间约17.0Ma。 相似文献
114.
提出一种合成Methomyl的改良法。该方法的特点是反应可在常压下进行。对常压反应的优宜条件作了系统研究,并讨论了反应机理。 相似文献
115.
应用勘探层分析及石油资源专家系统对XH凹陷下第三系勘探目的层的三个勘探层烃资源量作出了综合预测,结果表明,凹陷内各勘探层,尤其是渐新统勘探层,烃资源量相当可观。提出在渐新统内的地层圈闭中可进一步作详细的勘探工作。 相似文献
116.
117.
118.
119.
The sway, heave and roll added masses of three uniform cylinders with semi-circular, rectangular and triangular cross-sectional shapes in shallow and narrow water are numerically analysed. The method is based on simulation of the potential flow induced by the cylinder's mode of motion. The effects of shallow and narrow water on added mass are analysed and presented. It is concluded that the shallow and narrow water effects on added mass depend on the different cross-section shapes of the cylinders. In particular, the water depth effect on sway added mass is stronger than that on heave added mass while the narrow water effect on sway is weaker than that on heave. The shallow water effect on added mass tends to weaken the narrow water effect. Lastly the effect of shallow and narrow water on added mass on a rectangular cylinder is the strongest while that on a triangular cylinder is the weakest. 相似文献
120.
考虑应用系统中如何安全、高效的进行统一的人员管理及权限管理问题,研究基于微软活动目录构建通用中间件并以WebService方式发布的解决方案。具体内容包括把活动目录作为统一的人员库;构建通用授权管理平台统一管理用户在不同的软件系统中的角色和权限;该管理平台以WebService的方式向其它的应用系统提供接口。文中示例表明该方案切实可行,应用范围广。 相似文献