全文获取类型
收费全文 | 22855篇 |
免费 | 4725篇 |
国内免费 | 6335篇 |
专业分类
测绘学 | 2298篇 |
大气科学 | 4080篇 |
地球物理 | 5489篇 |
地质学 | 12919篇 |
海洋学 | 2792篇 |
天文学 | 853篇 |
综合类 | 2403篇 |
自然地理 | 3081篇 |
出版年
2024年 | 121篇 |
2023年 | 434篇 |
2022年 | 1213篇 |
2021年 | 1380篇 |
2020年 | 1159篇 |
2019年 | 1362篇 |
2018年 | 1537篇 |
2017年 | 1298篇 |
2016年 | 1459篇 |
2015年 | 1466篇 |
2014年 | 1598篇 |
2013年 | 1636篇 |
2012年 | 1701篇 |
2011年 | 1780篇 |
2010年 | 1708篇 |
2009年 | 1540篇 |
2008年 | 1389篇 |
2007年 | 1302篇 |
2006年 | 1069篇 |
2005年 | 886篇 |
2004年 | 707篇 |
2003年 | 648篇 |
2002年 | 642篇 |
2001年 | 610篇 |
2000年 | 612篇 |
1999年 | 699篇 |
1998年 | 532篇 |
1997年 | 538篇 |
1996年 | 455篇 |
1995年 | 373篇 |
1994年 | 446篇 |
1993年 | 323篇 |
1992年 | 257篇 |
1991年 | 194篇 |
1990年 | 154篇 |
1989年 | 115篇 |
1988年 | 138篇 |
1987年 | 78篇 |
1986年 | 59篇 |
1985年 | 62篇 |
1984年 | 39篇 |
1983年 | 39篇 |
1982年 | 44篇 |
1981年 | 34篇 |
1980年 | 13篇 |
1979年 | 23篇 |
1978年 | 6篇 |
1958年 | 16篇 |
1957年 | 7篇 |
1954年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
141.
The effects of different lateral confinement stress on the fatigue behavior of and cumulative damage to plain concrete are investigated experimentally. Eighty 100 mm x 100 mm x 100 mm specimens of ordinary strength concrete are tested under constant- or variable-amplitude fatigue loading and lateral confinement pressure in two orthogonal directions. A fatigue equation is developed by modifying the classical Aas-Jakobsen S-N equation for taking into account the effect of the confined stress on fatigue strength of plain concrete. The results of variable-amplitude fatigue tests indicate that the linear damage theory proposed by Palmgren and Miner is unreasonable in the biaxial stress state. A nonlinear cumulative damage model that could model the effects of the magnitude and sequence of variable-amplitude fatigue loading and lateral confinement pressure is proposed on the basis of the evolution laws of the residual strains in the longitudinal direction during fatigue tests. The residual fatigue life predic 相似文献
142.
Using meteorological data of field observation in 1990 - 2000, especially polar orbit high-resolution NOAA satellite cloud maps received from the Antarctic expedition vessel since 1997, the formation and development of the Prydz Bay cyclone are studied in this paper. Some new viewpoints are suggested such as: when surround-polar cyclone enters the Prydz Bay, it can also intensify and develop in summer; cyclone can also develop in the easterlies in this bay. These view points revise old uncom-plete view point that the Prydz Bay is a burial ground of cyclone, and also further consummate formation-development theory of surround-cyclone in the Antarctic westerlies and cyclone in the Antarctic easterlies. In this paper, the mechanism of ice-air-sea interaction in the Prydz Bay is studied, and the physical process of cyclone formation-development is explained. By use of wholly dynamic transportation method, an energy exchange case of a cyclone, which explosively developed after entering the Prydz Bay, is calcu 相似文献
143.
Ocean surface waves are strongly forced by high wind conditions associated with winter storms in the Sea of Japan. They are also modulated by tides and storm surges. The effects of the variability in surface wind forcing, tides and storm surges on the waves are investigated using a wave model, a high-resolution atmospheric mesoscale model and a hydrodynamic ocean circulation model. Five month-long wave model simulations are inducted to examine the sensitivity of ocean waves to various wind forcing fields, tides and storm surges during January 1997. Compared with observed mean wave parameters, results indicate that the high frequency variability in the surface wind filed has very great effect on wave simulation. Tides and storm surges have a significant impact on the waves in nearshores of the Tsushima-kaihyō, but not for other regions in the Sea of Japan. High spatial and temporal resolution and good quality surface wind products will be crucial for the prediction of surface waves in the JES and other marginal seas, especially near the coastal regions. 相似文献
144.
The interaction of a solitary wave with an array of surface-piercing vertical circular cylinders is investigated numerically. The wave motion is modeled by a set of generalized Boussinesq equations. The governing equations are discretized using a finite element method. The numerical model is validated against the experimental data of solitary wave reflection from a vertical wall and solitary wave scattering by a vertical circular cylinder respectively. The predicted wave surface elevation and the wave forces on the cylinder agree well with the experimental data. The numerical model is then employed to study solitary wave scattering by arrays of two circular cylinders and four circular cylinders respectively. The effect of wave direction on the wave forces and the wave runup on the cylinders is quantified. 相似文献
145.
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
146.
在连云港近岸海域计算潮流场基础上建立拉格朗日余流模型,并对连云港市两大堤建成前后的拉格朗日余流变化进行了分析,且选择有代表性的排污口进行了数值跟踪。 相似文献
147.
崂山花岗岩地区含锶、偏硅酸矿泉水的形成机理 总被引:1,自引:0,他引:1
报道了崂山花岗岩地区矿泉水的特征。指出其矿泉类型为含锶、偏硅酸型,并讨论了其形成机理。 相似文献
148.
Discussion on Coastal Erosion Near Xizhuang, Penglai, China 总被引:1,自引:0,他引:1
Wu Guiqiu Li Wei Professor First Institute of Oceanography State Oceanic Administration Qingdao Associate Researcher 《中国海洋工程》1994,(2)
-In this work, on the basis of the characteristics of coastal erosion near Xizhuang (Penglai, Shandong, China) and the in-situ measured data and theoretical calculation, the causes of coastal erosion there are obtained: (1) natural erosion, (2) beach sand borrowing, and (3) sand borrowing at the Dengzhou shoal near Xizhuang, which results in the loss of the function of the wave force resistance of the shoal. Since the wave energy is increased, the longshore sediment transport rate is increased. Coastal erosions are more and more serious. A scientific basis to reduced the calamity of coastal erosion in local area is presented. Some experiences are accumulated for studying coastal erosion. 相似文献
149.
作者用聚类分析法划分浅海水团,目的在于克服大洋水团分析法进行分析所遇到的一些困难,它在根据不同海区特点确定临界值与检验值时有较大的灵活性。本文讨论了浅海变性水团与中心渔场的关系。结果表明,东海底层冷水、东海表层水和大陆沿岸水对渔业生产有重要影响。 相似文献
150.
本文研究模糊矩阵传递闭包的化简问题。通过定义 1类典型阵 ,给出传递闭包能够进一步化简的充要条件 ,为网络最大流分析提供了 1种新的模式。 相似文献