全文获取类型
收费全文 | 27582篇 |
免费 | 3921篇 |
国内免费 | 5672篇 |
专业分类
测绘学 | 3314篇 |
大气科学 | 5469篇 |
地球物理 | 6588篇 |
地质学 | 11339篇 |
海洋学 | 3388篇 |
天文学 | 1159篇 |
综合类 | 1782篇 |
自然地理 | 4136篇 |
出版年
2024年 | 132篇 |
2023年 | 449篇 |
2022年 | 853篇 |
2021年 | 1081篇 |
2020年 | 1206篇 |
2019年 | 1475篇 |
2018年 | 1013篇 |
2017年 | 1364篇 |
2016年 | 1338篇 |
2015年 | 1389篇 |
2014年 | 1762篇 |
2013年 | 2098篇 |
2012年 | 1670篇 |
2011年 | 1858篇 |
2010年 | 1432篇 |
2009年 | 1867篇 |
2008年 | 1833篇 |
2007年 | 1867篇 |
2006年 | 1790篇 |
2005年 | 1428篇 |
2004年 | 1307篇 |
2003年 | 1123篇 |
2002年 | 867篇 |
2001年 | 761篇 |
2000年 | 678篇 |
1999年 | 637篇 |
1998年 | 636篇 |
1997年 | 540篇 |
1996年 | 462篇 |
1995年 | 400篇 |
1994年 | 339篇 |
1993年 | 329篇 |
1992年 | 228篇 |
1991年 | 182篇 |
1990年 | 137篇 |
1989年 | 131篇 |
1988年 | 107篇 |
1987年 | 62篇 |
1986年 | 57篇 |
1985年 | 51篇 |
1984年 | 30篇 |
1982年 | 25篇 |
1981年 | 19篇 |
1980年 | 21篇 |
1979年 | 14篇 |
1978年 | 14篇 |
1977年 | 19篇 |
1976年 | 25篇 |
1973年 | 17篇 |
1971年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
Zhang Furan Zhao Jun Zhang Xueqin Assistant Researcher Tianjin Research Institute of Water Transport Engineering Tianjin Assistant Engineer Tianjin Research Institute of Water Transport Engineering Tianjin 《中国海洋工程》1993,(2)
In respect of an offshore berthing pillar, the test study result of current force acting on mooring ships is described in this paper. Empirical and semi-empirical relationships of current force coefficient are given according to the angle between the flow direction and the ship's longitudinal axis, which are coincident with the result of theoretical analysis. 相似文献
142.
沿海地区城市发展及地面沉降的系统控制 总被引:9,自引:0,他引:9
郑铣鑫 《海洋地质与第四纪地质》1992,12(1):57-65
本文运用系统工程原理,系统论述了地下水合理开发、管理和地面沉降系统控制,这对沿海地区地面沉降控制起到重要的作用。 相似文献
143.
The large-diameter cylinder structure, which is made of large successive bottomless cylinders placed on foundation bed or partly driven into soil, is a recently developed retaining structure in China. It can be used in port, coastal and off-shore works. The method for stability analysis of the large-diameter cylinder structure, especially for stability analysis of the embedded large-diameter cylinder structure, is an important issue. In this paper, an idea is presented that is, em-bedded large-diameter cylinder quays can be divided into two types, i.e. the gravity wall type and the cylinder pile wall type. A method for stability analysis of the large-diameter cylinder quay of the cylinder pile wall type is developed and a method for stability analysis of the large-diameter cylinder quay of the gravity wall type is also proposed. The effect of sig-nificant parameters on the stability of the large-diameter cylinder quay of the cylinder pile wall type is investigated through numerical calculation. 相似文献
144.
145.
The spatial variability of porosity and permeability was determined for a section in the uppermost Maastrichtian chalk exposed in the Sigerslev quarry at Stevns Klint. The aims were threefold: (1) to quantify the spatial variability pattern and its link to geology by applying systematic variogram analysis procedure, (2) to detect potential cyclicity in the petrophysical properties in this pure and overtly homogeneous chalk, and (3) to compare the section with chalk reservoirs in the North Sea in order to asses to what extent this onshore sequence has a potential as an analogue of the offshore, more deeply buried chalk reservoirs. The interval is of comparable stratigraphic age to the uppermost reservoir zones in the Tor Formation of the North Sea chalk reservoirs. The variability and spatial correlation of porosity and permeability in both horizontal and vertical directions are interpreted in a geological context and show indications of small-scale heterogeneity at 15–25 cm scale, but the clear cyclic layering described from other chalk deposits is not recognised at this locality. The investigated outcrop is not a close analogue to North Sea reservoir chalk, but some aspects are common including basic material properties, porosity/permeability trends and the variability pattern. The outcrop has a potential as analogue for some of the onshore subsurface chalk successions at shallow burial depth that form important aquifers. 相似文献
146.
刘新国 《中国海洋大学学报(自然科学版)》1996,(2)
本文系统地研究具二次约束最小二乘问题的敏度分析。首先给出长期方程唯一正根的上界和下界;然后证明割线法用于计算拉格朗日乘子时全局收敛;最后给出解的扰动界。 相似文献
147.
三角褐指藻(Phaeodactylum tricornutum)和翦股颖草属禾草(A-grostis capillaris)经过处理后再用液相层析法从中提取一种金属结合多肽,极谱分析表明不同的镉结合多肽具有不同的稳定性,金属结合与金属硫蛋白不同,在电位--1.7V附近未出现氧催化峰,金属硫蛋白以及从单胞藻和禾草中提取的多肽在极谱测定过程中都在电位-520mV和-930mV附近出现双峰,在-520mV处,半波电位显示了单个镉硫醇键的还原,在-930mV处的峰是由于镉和硫多齿螯合的还原,因此这通常可用以鉴定镉螯合物。在镉浓度为5umol/dm^3和10umol/dm^3时-930mV的峰高与镉浓度之间存在着对应关系。 相似文献
148.
The modified hybrid element method (MHEM) is utilized to predict and analyze wave forces on arbitrarily shaped multiple bodies. This method can be applied to waves of all water depths, i. e. shallow, intermediate, and deep waters, on slowly varying seabed. The MHEM employs the ICCG method to save CPU and storage, thus the computation of wave forces for large multi-body systems can be carried out on microcomputers. Numerical results of the present method are compared with experimental data and other solutions. It is shown that the MHEM provides more accurate solutions of the wave forces than other numerical methods do. Therefore, the methodology presented herein can be used in the design of coastal and ocean structures. 相似文献
149.
150.
青海湖全新世植被演变及气候变迁:QH85—14C孔孢粉数值分析 总被引:20,自引:3,他引:20
本文应用青海湖QH85-14C孔取得的具有~(14)C测年数据所支持的原始孢粉资料,进行数值分析(有序聚类、主成份分析、滑动平均和回归分析)。从而对青海湖区11000年以来的植被和气候变化进一步讨论。 相似文献