全文获取类型
收费全文 | 14843篇 |
免费 | 3170篇 |
国内免费 | 4360篇 |
专业分类
测绘学 | 1875篇 |
大气科学 | 2330篇 |
地球物理 | 3226篇 |
地质学 | 8780篇 |
海洋学 | 2225篇 |
天文学 | 382篇 |
综合类 | 1580篇 |
自然地理 | 1975篇 |
出版年
2024年 | 103篇 |
2023年 | 319篇 |
2022年 | 864篇 |
2021年 | 1003篇 |
2020年 | 815篇 |
2019年 | 928篇 |
2018年 | 1060篇 |
2017年 | 869篇 |
2016年 | 959篇 |
2015年 | 1051篇 |
2014年 | 1087篇 |
2013年 | 1169篇 |
2012年 | 1259篇 |
2011年 | 1262篇 |
2010年 | 1231篇 |
2009年 | 1071篇 |
2008年 | 960篇 |
2007年 | 861篇 |
2006年 | 735篇 |
2005年 | 609篇 |
2004年 | 446篇 |
2003年 | 386篇 |
2002年 | 381篇 |
2001年 | 371篇 |
2000年 | 329篇 |
1999年 | 358篇 |
1998年 | 259篇 |
1997年 | 253篇 |
1996年 | 220篇 |
1995年 | 174篇 |
1994年 | 198篇 |
1993年 | 146篇 |
1992年 | 116篇 |
1991年 | 100篇 |
1990年 | 66篇 |
1989年 | 48篇 |
1988年 | 48篇 |
1987年 | 34篇 |
1986年 | 17篇 |
1985年 | 24篇 |
1983年 | 15篇 |
1982年 | 12篇 |
1981年 | 12篇 |
1980年 | 7篇 |
1979年 | 13篇 |
1965年 | 16篇 |
1958年 | 10篇 |
1957年 | 7篇 |
1954年 | 8篇 |
1933年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 390 毫秒
91.
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
92.
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
93.
Tang Rongqing Wang Daoyan Zhang Xixian Egnineer Shanghai Jiao Tong University Shanghai Associate Professor Shanghai Jiao University Shanghai 《中国海洋工程》1993,(3)
- The authors have used a low-cost ROV of observation type for underice surveying of the Nen-Jiang Cross-river oil pipe line in the Da Qing oil field. The operation method, process and the safety measures for severe cold areas are presented. The fruitful tries and experience may be useful to ROV operators in severe cold areas. 相似文献
94.
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
95.
-Based on the feasibility study of developing the navigation resources of the Guanhe River and the model test results of the mouth bar regulation, this paper presents some basic principles for the regulation of the channel on the mouth bar, for instance, the direction of navigation channel should be identical with that of the ebb tide current and the main waves, and perpendicular to the bathymetric contours. The principles for regulating mouth bars are also discussed in this paper. 相似文献
96.
Xu Shikai Wang Hongchuan Hong Guangwen
Engineer Nanjing Hydraulic Research Institute Nanjing .
Professor Research Institute of Coastal Ocean Engineering Hohai University Nanjing 《中国海洋工程》1996,(4)
To solve problems concerning wave elements and wave propagation, an effective way is the wave energy balance equation, which is widely applied in oceanography and ocean dynamics for its simple computation. The present papaer advances wave energy balance equations considering lateral energy transmission and energy loss as the governing equation for the study of wave refraction-diffraction. For the mathematical model, numerical simulation is made by means of difference method, and the result is verified with two examples. 相似文献
97.
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
98.
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
99.
在浅层工程折射地震测量中 ,通常采用相遇观测系统采集数据和相应的解释方法进行解释 ;对于单边观测采集方法由于与其相应的解释方法较少而少被采用。本文提出 1种方法简单、精度可靠、可直接利用同一点相邻 2排列 2次观测的初至折射时间并适合于海洋走航式单边连续观测系统的折射初至资料解释方法。其精度基本与同观测段的采用相遇观测的差异时距方法解释的精度十分接近。该方法即适合于人工解释又适合于计算机自动解释。 相似文献
100.