全文获取类型
收费全文 | 12545篇 |
免费 | 2663篇 |
国内免费 | 2844篇 |
专业分类
测绘学 | 1066篇 |
大气科学 | 2313篇 |
地球物理 | 5989篇 |
地质学 | 5208篇 |
海洋学 | 1428篇 |
天文学 | 425篇 |
综合类 | 847篇 |
自然地理 | 776篇 |
出版年
2024年 | 61篇 |
2023年 | 160篇 |
2022年 | 336篇 |
2021年 | 461篇 |
2020年 | 434篇 |
2019年 | 550篇 |
2018年 | 424篇 |
2017年 | 451篇 |
2016年 | 510篇 |
2015年 | 582篇 |
2014年 | 682篇 |
2013年 | 716篇 |
2012年 | 735篇 |
2011年 | 744篇 |
2010年 | 705篇 |
2009年 | 762篇 |
2008年 | 716篇 |
2007年 | 917篇 |
2006年 | 866篇 |
2005年 | 780篇 |
2004年 | 734篇 |
2003年 | 668篇 |
2002年 | 583篇 |
2001年 | 525篇 |
2000年 | 486篇 |
1999年 | 528篇 |
1998年 | 473篇 |
1997年 | 418篇 |
1996年 | 417篇 |
1995年 | 403篇 |
1994年 | 297篇 |
1993年 | 234篇 |
1992年 | 163篇 |
1991年 | 132篇 |
1990年 | 99篇 |
1989年 | 90篇 |
1988年 | 82篇 |
1987年 | 35篇 |
1986年 | 19篇 |
1985年 | 9篇 |
1984年 | 20篇 |
1983年 | 7篇 |
1982年 | 4篇 |
1980年 | 3篇 |
1979年 | 9篇 |
1978年 | 5篇 |
1977年 | 7篇 |
1973年 | 2篇 |
1971年 | 2篇 |
1954年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
李刚 《海洋地质与第四纪地质》2003,23(1):125-129
归一化层速度是对任意深度处的层速度进行归一化处理的一种速度形式,归一化处理的目的是把任意深度处的层速度转换为与深度无关的格式,归一化后层速度的横向变化主要取决于地层岩性,孔隙度等物性的变化,利用这一特点可以方便地利用已知钻井资料对其进行标定,比较简单地进行地层岩性,孔隙度等特性的预测。实际应用表明,其预测结果与钻井揭示吻合较好,预测效果令人满意。 相似文献
92.
Full-range equation covering all the flow regimes in a wave boundary layer is proposed for the boundary layer thickness. The results are compared with the available experimental data and good agreement has been found. In case of wave boundary layers, there are three definitions of boundary layer thickness in use. Therefore, the full-range equation is derived for three of the definitions. The findings of this study may be useful in calculating suspended sediment transport in coastal environments and studying wave–current combined motion. 相似文献
93.
辽东湾地区下第三系地震速度—岩性预测模型研究 总被引:9,自引:1,他引:9
地震速度-岩性预测模型由四个子模型组成:即(1)砂泥岩压实模型;(2)地震层速度转换模型;(3)速度校正模型;(4)砂岩指数转换模型。辽东湾地区的实际资料证明,上述四个子模型不但决定了岩性预测的具体方法,而且严格控制岩性预测的精度。 相似文献
94.
根据二维流体动力学方程和深度平均盐度扩散方程在河口径流量以及蒸发和降水之差为已知情况下构成的闭合方程组,预报出深度平均盐度,然后利用底层盐度与深度平均盐度、水深和时间(月)之间的经验关系,给出底层盐度的二维预报。为了检验试报结果的可靠性,文中将黄渤海底层盐度的试报结果(1979年7月11日,时效为3d)与标准断面观测资料(7月4—14日观测,124.5°E以西,共104站)作一粗略比较。比较表明,试报结果与实测值的相关系数为0.96,均方误差为α=0.26,绝对误差小于0.2和0.3的站数分别占总站数的63.5%和77.0%,而总均绝差为0.19。由此可见,试报的效果是令人满意的。 相似文献
95.
本文概述了东白令海形成刺黄盖鲽渔场的海洋学特征,并结合现场调查的标样侧重分析了刺黄盖鲽的渔业生物学特征,本文还概略地讨论了该鱼与渔业资源的关系。 相似文献
96.
Viability theory for an ecosystem approach to fisheries 总被引:1,自引:1,他引:1
97.
The determination of the drag and inertia coefficients, which enter into the wave force model given by Morison's equation, is particularly uncertain and difficult when a linear spectral model is used for ocean waves, and the structure is compliant and has nonlinear dynamic response. In this paper, a nonlinear System Identification method, called Reverse Multiple Inputs–Single Output (R–MISO) is applied to identify the hydrodynamic coefficients as well as the nonlinear stiffness parameter for a compliant single-degree-of-freedom system. Four different types of problems have been identified for use in various situations and the R–MISO has been applied to all of them. One of the problems requires iterative solution strategy to identify the parameters. The method has been found to be efficient in predicting the parameters with reasonable accuracy and has the potential for use in the laboratory experiments on compliant nonlinear offshore systems. 相似文献
98.
-The North Channel in the Yangtze Estuary is one of sea-leading waterways of Shanghai Harbour, in which yearly dredging volume reaches over ten million cubic meters, and it tends to increase year by year. Based on the channel regime similarity and through the relational grade, a GM (2, 1) is set up. It reveals the course of development of channel regime similarity under the action of various factors, and predicts the siltation volume in the nearest future which is the basis of dredging planning for relevant dredging departments. 相似文献
99.
A novel method for prediction of the load carrying capacity of a corroded reinforced concrete beam (CRCB) is presented in the paper. Nine reinforced concrete beams, which had been working in an aggressive environment for more than 10 years, were tested in the laboratory. Comprehensive tests, including flexural test, strength test for corroded concrete and rusty rebar, and pullout test for bond strength between concrete and rebar, were condueted. The flexural test results of CRCBs reveal that the distribution of surface cracks on the beams shows a fractal behavior. The relationship between the fractal dimensions and mechanical properties of CRCBs is then studied. A prediction model based on artificial neural network (ANN) is established by the use of the fractal dimension as the corrosion index, together with the basic intbrmation of the beam. The validity of the prediction model is demonstrated through the experimental data, and satisfactory resuits are achieved. 相似文献
100.