全文获取类型
收费全文 | 2993篇 |
免费 | 489篇 |
国内免费 | 712篇 |
专业分类
测绘学 | 149篇 |
大气科学 | 603篇 |
地球物理 | 742篇 |
地质学 | 1461篇 |
海洋学 | 413篇 |
天文学 | 202篇 |
综合类 | 324篇 |
自然地理 | 300篇 |
出版年
2024年 | 17篇 |
2023年 | 41篇 |
2022年 | 131篇 |
2021年 | 160篇 |
2020年 | 128篇 |
2019年 | 155篇 |
2018年 | 122篇 |
2017年 | 144篇 |
2016年 | 161篇 |
2015年 | 118篇 |
2014年 | 179篇 |
2013年 | 142篇 |
2012年 | 135篇 |
2011年 | 150篇 |
2010年 | 167篇 |
2009年 | 176篇 |
2008年 | 166篇 |
2007年 | 140篇 |
2006年 | 105篇 |
2005年 | 116篇 |
2004年 | 72篇 |
2003年 | 87篇 |
2002年 | 92篇 |
2001年 | 96篇 |
2000年 | 121篇 |
1999年 | 159篇 |
1998年 | 118篇 |
1997年 | 110篇 |
1996年 | 114篇 |
1995年 | 88篇 |
1994年 | 91篇 |
1993年 | 68篇 |
1992年 | 74篇 |
1991年 | 44篇 |
1990年 | 35篇 |
1989年 | 45篇 |
1988年 | 38篇 |
1987年 | 20篇 |
1986年 | 19篇 |
1985年 | 13篇 |
1984年 | 10篇 |
1983年 | 9篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1979年 | 4篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1958年 | 2篇 |
1954年 | 1篇 |
排序方式: 共有4194条查询结果,搜索用时 625 毫秒
941.
中国海区及邻域的地磁场分析 总被引:3,自引:1,他引:3
戴勤奋 《海洋地质与第四纪地质》1997,17(2):63-72
本文根据中国海区及邻城的地磁场分布特征,给地质及其它物探资料,对陆块碰撞过渡带的存在性问题,东沙-澎湖磁力高带的来源问题,东亚陆缘盆地磁异常分异的原因问题进行了讨论,最后将中国海区及邻域的基底划分为六大基底岩相区。 相似文献
942.
943.
Zhou Xireng Duan Xudong Sang Xuezhu Zhang Rui Dai Jialu Professor Tianjin University Tianjin
Engineer Xiamen Port Office Fujian
Lecturer Tianjin University Tianjin
Senior Engineer Tianjin Port Office Tianjin 《中国海洋工程》1992,(2)
A method of coupled BEM-FEM analysis for the elastic spatial structure system is presented. It can be applied to the calculation of the stress and deformation of the large-diamater cylinder structure system and it is suitable for symmetric or non-symmetric structures under the distributed or concentrated load. Numerical examples show that the proposed method and computer program BEFEM are quite efficient in the analysis of the large-diameter cylinder structure problems in ocean engineering. 相似文献
944.
An automatic flow analysis system with on-line liquid nitrogen trap, hydride generation and flame-less atomic absorption spectrophotometry was presented for the determination of inorganic arsenic and antimony in seawater. The experimental conditions such as acidity of reduction reaction, the amount of sodium borohydride , the flow rate of carry gas (high purity of nitrogen) were tested and selected optimally. The limit detection of the method presented was 0. 15 ug/L for arsenic and 0. 24 μ/L for antimony . During the determination of seawater samples with levels microgram arsenic and antimony pa litre th?variation coefficient would be ±4% for arsenic and ±10% for antimony. The volume needed for one measurement was 9 mL for arsenic and 12 mL for antimony. The frequency of sample determination reached 20 times per hour for arsenic and 15 times per hour for antimony. 相似文献
945.
白沙河平原区为青岛市蔬菜基地,农业为主要用水户,根据本区未来菜粮比例进一步提高、城乡生活水平不断提高、乡镇工业迅速发展、节水意识有所提高等特点.设计了包括工业、农业和生活需水的需水预测模型,预测结果表明,工业及生活用水比例将不断提高,农业用水仍占主要地位,但增幅不大。预测结果为管理模型设计提供了信息. 相似文献
946.
Genetical study on the parthenogenesis in Laminaria japonica 总被引:3,自引:0,他引:3
The parthenogenesis and natural doubling of chromosomes in wild type female gametophytes of Laminaria japonica were studied. The results indicate that not all the female gametophytes from the wild type hybrid parent can propagate through parthenogenesis. Most parthenosporophytes can mature, their spores germinate into gametophytes, the latter then developed into female sporophytes. To form these parthenosporophytes the natural doubling of chromosomes occurred mainly at the first and second cell divisions of the spores. It is thus considered that the parthenogenesis of L. japonica is inheritable and the relative genes link closely with the genes controlling the natural doubling of chromosomes and the female determination. 相似文献
947.
本文应用地震地层学的解释方法,简述了珠江口盆她中中新世三角洲相前积结构的分布特征,探讨了造成这种特殊分布现象的地质原因,提出原始倾斜的沉积基面、生长断层的存在和断层面不同的倾斜方向是控制前积结构分布的主要因素。 相似文献
948.
949.
黄渤海蓝点马鲛繁殖生物学的研究 总被引:11,自引:0,他引:11
根据1960-1993年在渤海,黄海及东海渔业生产和调查中收集的19096尾蓝点马鲛样品,进行繁殖生物研究。结果表明,卵巢成熟度依据外部形态观察、切片镜检、卵内结构分析、卵径测量和成熟系数计算等分为Ⅰ-Ⅵ期;性腺周年内成熟一次,并存在发育、成熟产卵后和恢复阶段。 相似文献
950.
Zhenfeng Qiu Junjie Wang Yulong Chen Yang Yang Yongsuo Li 《Marine Georesources & Geotechnology》2020,38(7):867-875
AbstractSandstone-mudstone particle mixture (SMPM) is one of the main materials, which has been widely used for filling in and around reservoirs for water conservation projects. During the periodic rising and falling of the water level, the fill material for the embankments, dam, and other waterfront features will also undergo drainage-saturation cycles. The deformation and coefficient of lateral pressure at rest K0 may be affected by periodic saturation. In this study, a device is modified for testing the K0 for gravel-soil under periodic saturation. In order to investigate the effects of periodic saturation on K0, a series of experiments were performed for SMPM under different vertical stress and saturation cycling. K0N values of SMPM containing 20% mudstone particles under periodic saturation were obtained. The results shows that the K0N initially increased, but eventually reached a stable value with the increasing number of periodic saturation cycles. The magnitude of the coefficient increment was also found to be related to the stress condition. K0N is a logarithmic function of the saturation cycling time. By calculating K0N with the proposed empirical formula, the deformation and stress distribution of the SMPM filler in waterfront engineering works can be calculated with greater precision. 相似文献