全文获取类型
收费全文 | 10351篇 |
免费 | 2362篇 |
国内免费 | 3539篇 |
专业分类
测绘学 | 563篇 |
大气科学 | 2832篇 |
地球物理 | 2786篇 |
地质学 | 5866篇 |
海洋学 | 2107篇 |
天文学 | 123篇 |
综合类 | 588篇 |
自然地理 | 1387篇 |
出版年
2024年 | 48篇 |
2023年 | 133篇 |
2022年 | 354篇 |
2021年 | 394篇 |
2020年 | 470篇 |
2019年 | 578篇 |
2018年 | 487篇 |
2017年 | 487篇 |
2016年 | 505篇 |
2015年 | 594篇 |
2014年 | 729篇 |
2013年 | 805篇 |
2012年 | 755篇 |
2011年 | 823篇 |
2010年 | 625篇 |
2009年 | 821篇 |
2008年 | 757篇 |
2007年 | 877篇 |
2006年 | 823篇 |
2005年 | 634篇 |
2004年 | 659篇 |
2003年 | 556篇 |
2002年 | 496篇 |
2001年 | 389篇 |
2000年 | 380篇 |
1999年 | 358篇 |
1998年 | 305篇 |
1997年 | 293篇 |
1996年 | 247篇 |
1995年 | 201篇 |
1994年 | 169篇 |
1993年 | 128篇 |
1992年 | 78篇 |
1991年 | 67篇 |
1990年 | 50篇 |
1989年 | 30篇 |
1988年 | 35篇 |
1987年 | 26篇 |
1986年 | 14篇 |
1985年 | 18篇 |
1984年 | 12篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 9篇 |
1980年 | 5篇 |
1979年 | 6篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1971年 | 3篇 |
1954年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
61.
本文将伴随法用于渤、黄、东海M2分潮的数值模拟,利用Topex/Poseidon高度计资料进行同化,优化海底摩擦系数。文中对底摩擦系数取常数时进行了优化,同时还对底摩擦系数的一种新的处理方法进行了研究,即在计算海区选取一些点给定底摩擦系数,海区中任意一点的底摩擦系数由这些点的底摩擦系数线性播值得到,优化后得到空间分布的底摩擦系数。针对两种不同的线性底摩擦假设分别进行了一系列的实际实验,结果表明由空间分布的底摩擦系数得到的模拟值比底摩擦系数取常数得到的模拟值更接近观测值,能有效地提高数值模拟的精度。 相似文献
62.
In order to accurately design a sand compaction pile (SCP) with low replacement area ratio, it is important to understand the mechanical interaction between the sand pile and clay ground and its mechanism during consolidation process in composite ground. In this article, therefore, a series of numerical analyses on composite ground improved by SCP with low replacement area ratio were carried out. The applicability of numerical analyses, in which an elasto-viscoplastic consolidation finite element method was applied, were confirmed by comparing the results obtained from a series of laboratory model tests with the composite ground improved by SCP. Through the results of the numerical analyses, mechanical behavior of the sand pile and clay in composite ground during consolidation is elucidated, together with a stress sharing mechanism between sand pile and clay. 相似文献
63.
The aim of this paper is to investigate the shape and tension distribution of fishing nets in current. A numerical model is developed, based on lumped mass method to simplify the net. The motion equation is set up for each lumped mass. The Runge–Kutta–Verner fifth-order and sixth-order method is used to solve these simultaneous equations, and then the displacement and tension of each lumped mass are obtained. In order to verify the validity of the numerical method, model tests have been carried out. The results by the numerical simulation agree well with the experimental data. 相似文献
64.
本文给出了满足给定数字特征和谱的随机序列的产生方法,即用无记忆非线性变换实现非正态随机信号的模拟.该法与Gujar法相比较,放宽了变量概率分布的限制,只要求变量矩的存在。同时考虑无记忆非线性变换对谱的影响,用异于Liu的方法在频域上求解输入正态分布随机序列的谱. 相似文献
65.
66.
67.
Zhang Changkuan Wang Zhen Zhang Dongsheng
Associate Professor Dept. of Navigation Ocean Engineering Hohai University Nanjing
Lecturer Dept. of Navigation Ocean Engineering Hohai University Nanjing
Professor Dept. of Navigation Ocean Engineering Hohai University Nanjing 《中国海洋工程》1995,(2)
A numerical model of shoreline change of sand beaches based on long-term field wave data is proposed, the explicit and implicit finite difference forms of the model are described, and an application of the model is presented. Results of the application indicate that the model is sensitive to the order of the input wave data, and that the effects of long-term wave series and the effects of the mean annual wave conditions on the model are different. Instead of a single wave condition, the wave series will make the calibration and the verification of the model more practical and the results of the model more reasonable. 相似文献
68.
Sediment-starved sand ridges on a mixed carbonate/siliciclastic inner shelf off west-central Florida
S. E. Harrison S. D. Locker A. C. Hine J. H. Edwards D. F. Naar D. C. Twichell D. J. Mallinson 《Marine Geology》2003,200(1-4):171-194
High-resolution side-scan mosaics, sediment analyses, and physical process data have revealed that the mixed carbonate/siliciclastic, inner shelf of west-central Florida supports a highly complex field of active sand ridges mantled by a hierarchy of bedforms. The sand ridges, mostly oriented obliquely to the shoreline trend, extend from 2 km to over 25 km offshore. They show many similarities to their well-known counterparts situated along the US Atlantic margin in that both increase in relief with increasing water depth, both are oriented obliquely to the coast, and both respond to modern shelf dynamics. There are significant differences in that the sand ridges on the west-central Florida shelf are smaller in all dimensions, have a relatively high carbonate content, and are separated by exposed rock surfaces. They are also shoreface-detached and are sediment-starved, thus stunting their development. Morphological details are highly distinctive and apparent in side-scan imagery due to the high acoustic contrast. The seafloor is active and not a relict system as indicated by: (1) relatively young AMS 14C dates (<1600 yr BP) from forams in the shallow subsurface (1.6 meters below seafloor), (2) apparent shifts in sharply distinctive grayscale boundaries seen in time-series side-scan mosaics, (3) maintenance of these sharp acoustic boundaries and development of small bedforms in an area of constant and extensive bioturbation, (4) sediment textural asymmetry indicative of selective transport across bedform topography, (5) morphological asymmetry of sand ridges and 2D dunes, and (6) current-meter data indicating that the critical threshold velocity for sediment transport is frequently exceeded. Although larger sand ridges are found along other portions of the west-central Florida inner shelf, these smaller sand ridges are best developed seaward of a major coastal headland, suggesting some genetic relationship. The headland may focus and accelerate the N–S reversing currents. An elevated rock terrace extending from the headland supports these ridges in a shallower water environment than the surrounding shelf, allowing them to be more easily influenced by currents and surface gravity waves. Tidal currents, storm-generated flows, and seasonally developed flows are shore-parallel and oriented obliquely to the NW–SE trending ridges, indicating that they have developed as described by the Huthnance model. Although inner shelf sand ridges have been extensively examined elsewhere, this study is the first to describe them in a low-energy, sediment-starved, dominantly mixed siliciclastic/carbonate sedimentary environment situated on a former limestone platform. 相似文献
69.
70.