全文获取类型
收费全文 | 33760篇 |
免费 | 18230篇 |
国内免费 | 43587篇 |
专业分类
测绘学 | 2785篇 |
大气科学 | 21209篇 |
地球物理 | 12505篇 |
地质学 | 35607篇 |
海洋学 | 16108篇 |
天文学 | 812篇 |
综合类 | 4399篇 |
自然地理 | 2152篇 |
出版年
2024年 | 134篇 |
2023年 | 262篇 |
2022年 | 376篇 |
2021年 | 648篇 |
2020年 | 1856篇 |
2019年 | 5291篇 |
2018年 | 5475篇 |
2017年 | 5209篇 |
2016年 | 5265篇 |
2015年 | 4670篇 |
2014年 | 4088篇 |
2013年 | 4666篇 |
2012年 | 4395篇 |
2011年 | 4651篇 |
2010年 | 4416篇 |
2009年 | 3931篇 |
2008年 | 2841篇 |
2007年 | 2843篇 |
2006年 | 2673篇 |
2005年 | 2617篇 |
2004年 | 3193篇 |
2003年 | 2749篇 |
2002年 | 2384篇 |
2001年 | 2137篇 |
2000年 | 1670篇 |
1999年 | 1663篇 |
1998年 | 1801篇 |
1997年 | 1864篇 |
1996年 | 1415篇 |
1995年 | 1357篇 |
1994年 | 1219篇 |
1993年 | 1358篇 |
1992年 | 1171篇 |
1991年 | 809篇 |
1990年 | 711篇 |
1989年 | 613篇 |
1988年 | 495篇 |
1987年 | 420篇 |
1986年 | 330篇 |
1985年 | 245篇 |
1984年 | 280篇 |
1983年 | 166篇 |
1982年 | 203篇 |
1981年 | 142篇 |
1980年 | 109篇 |
1979年 | 111篇 |
1978年 | 54篇 |
1977年 | 56篇 |
1971年 | 53篇 |
1970年 | 45篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
481.
杆状病毒感染越冬亲虾(Penaeus chenesis)的研究——越冬亲虾感染及其垂直传播的可能性 总被引:2,自引:0,他引:2
在中国对虾越冬亲虾中检出杆状病毒。经对病虾鳃、前中肠、卵巢组织进行电镜观察,在这些组织中发现大量有囊膜的杆状病毒。病毒粒子大小约为367nm×128nm,核衣壳为324nm×92nm。病毒在细胞内不形成包涵体,在核内或在细胞质的发生基质中装配。从病毒的形态特征、感染组织以及典型的发病症状和病理变化,初步认为亲虾感染的病毒与近年广泛报道的造成养殖对虾大规模流行病的主要原因——中国对虾杆状病毒为同一种。卵巢组织也是病毒的主要靶器官之一,亲虾卵巢组织的被感染暗示着该病毒有可能通过生殖细胞而垂直传播 相似文献
482.
483.
Zuo Qihua Yang Zhengji .
Senior Engieer River Harbour Department Nanjing Hydraulic Research Institute Nanjing 《中国海洋工程》1996,(3)
- The variation of the amplitude of waves with varying incident angles when waves propagate through a typical approach channel is discussed by a numerical calculation method, the result of which shows that the influence of the channel on wave propagation is obvious. When the wave propagation direction is in coincidence with the channel axis, the wave amplitude ratio will decrease with the increase of propagation distance. When the incident angle is 15 - 30 , there appears an area of larger wave amplitude ratio on the side slope facing the waves, but at the another side, the wave amplitude ratio is generally small, indicating that the channel has a shielding effect. When waves propagate across the channel perpendicularly, the wave amplitude ratio can be calculated with the shallow water coefficient. 相似文献
484.
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
485.
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
486.
In this paper, a new theoretical expression of dissipation term is presented on the basis of statistical model of breaking wave, which is an improvement to LAGFD-WAM wave model. The computational results in three typical wind fields show a good improvement to LAGFD-WAM model and a better accuracy in comparison with the observed data in the South China Sea. 相似文献
487.
海水中痕量硅酸盐常用硅钼黄法测定[1-4].本文进一步研究酸度对硅钼黄形成反应的影响,采用合理的高酸度以获得较高的灵敏度和稳定性,使盐效应校正系数降低至4%.试验用人工海水工作曲线,结果免除了盐效应校正手续.试验将反应试剂事先混合后一次加入,简化了分析操作,缩短了工作时间,减少了船上的工作量.监于硅酸盐可能有聚合及水解反应,曾试验本方法制备的硅标准溶液的稳定性,结果可稳定一年之久. 相似文献
488.
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
489.
Following Bagnold's approach, a relationship between sediment transport and energy dissipation is developed. The major assumption made in the study is that the near bed velocity plays a dominant role in the process of sediment transport. A general relationship between energy dissipation and sediment transport is first proposed. Then the equations for total sediment transport are derived by introducing the appropriate expression of energy dissipation rate under different conditions, such as open channel flows, combination of wave and current, as well as longshore sediment transport. Within the flows investigated, the derived relationships are fairly consistent with the available data over a wide range of conditions. 相似文献
490.