全文获取类型
收费全文 | 63022篇 |
免费 | 12218篇 |
国内免费 | 16477篇 |
专业分类
测绘学 | 5118篇 |
大气科学 | 12373篇 |
地球物理 | 15067篇 |
地质学 | 33666篇 |
海洋学 | 8078篇 |
天文学 | 2685篇 |
综合类 | 6723篇 |
自然地理 | 8007篇 |
出版年
2024年 | 313篇 |
2023年 | 1094篇 |
2022年 | 2984篇 |
2021年 | 3542篇 |
2020年 | 2980篇 |
2019年 | 3354篇 |
2018年 | 3769篇 |
2017年 | 3377篇 |
2016年 | 3719篇 |
2015年 | 3409篇 |
2014年 | 3963篇 |
2013年 | 4022篇 |
2012年 | 3932篇 |
2011年 | 4089篇 |
2010年 | 4063篇 |
2009年 | 3846篇 |
2008年 | 3548篇 |
2007年 | 3239篇 |
2006年 | 2705篇 |
2005年 | 2490篇 |
2004年 | 1906篇 |
2003年 | 1848篇 |
2002年 | 1824篇 |
2001年 | 1847篇 |
2000年 | 1917篇 |
1999年 | 2546篇 |
1998年 | 2054篇 |
1997年 | 2116篇 |
1996年 | 1833篇 |
1995年 | 1587篇 |
1994年 | 1474篇 |
1993年 | 1283篇 |
1992年 | 1089篇 |
1991年 | 733篇 |
1990年 | 579篇 |
1989年 | 551篇 |
1988年 | 469篇 |
1987年 | 327篇 |
1986年 | 263篇 |
1985年 | 196篇 |
1984年 | 146篇 |
1983年 | 128篇 |
1982年 | 127篇 |
1981年 | 88篇 |
1980年 | 73篇 |
1979年 | 67篇 |
1978年 | 46篇 |
1977年 | 23篇 |
1976年 | 17篇 |
1958年 | 45篇 |
排序方式: 共有10000条查询结果,搜索用时 500 毫秒
441.
对类比路段进行连续模拟试验,进行现场调查,给出汽车尾气主要污染物的排污强度,预测了汽车尾气中CO、C_nH_m和NO_x的扩散范围。 相似文献
442.
443.
关于东海浮游植物,虽然国内、外都有人进行过一些调査研究,取得一些成果,但因调查时间较短或调查范围較小所获资料不全,都未能代表东海浮游植物的全貌。中国科学院海洋研究所继全国海洋综合调査之后,自1976年夏季又在东海陆架区进行了综合调查。这次调查,分析了东海浮游植物的个体数量和种数的分布状况,讨论了其主要种类的生态性质、群落组成和它们与水文环境的关系,对东海浮游植物的生态状况有了进一步了解。
1976年夏季在东海陆架区进行了两次(6月25日至7月23日和8月27日至9月21日)调查,调查范围南到北纬26°30′,东到东经127°,在沿纬度安排的6个断面共44个测站上(第一航次还在黄海南部增加一斜断面),分別进行了水文观测,并用网目为64平方微米的小型浮游生物网(Juday phytoplankton net),从水底到表面垂直拖网进行浮游植物采样,以个体计数法计数分析。 相似文献
444.
Recently, multi-layered targets have become commonplace in both military and civilian applications, such as marine hulls, armored vehicle bodies, outside structures of bulletproof cars, and aerospace vessels. This paper studies the resistant performance of perforation in multi-layered targets. An estimation procedure is established based on the concepts of the conservation of momentum, impulse-momentum law, and conservation of energy. Experimental results of the test of Almohandes et al. are adopted to check the residual velocity of multi-layered targets. The results of the verification are good in terms of agreement for impact velocities ranging from 700 to 800 m/s, when the ratio of the projectile length to the projectile diameter (i.e. L/D) is 4.2, and the average residual velocity error of single, double- or triple-layered targets range approximately from 4.42 to 8.40%. The ballistic performance is best for the double target when the ratio of the first layer thickness to the total thickness (i.e. t1/(t1+t2)) is about 0.75, and the worse performance occurs when the ratio t1/(t1+t2) is 0.5. An air gap slightly influences the resistant performance of perforation in multi-layered targets. These results may serve as a useful reference for designers. 相似文献
445.
DGPS RTK技术在无验潮水下地形测量中的应用初探 总被引:5,自引:0,他引:5
本文简要介绍了DGPS RTK技术的基本原理和作业流程,阐明了该技术在无验潮水下地形测量中的适用性,并以除六泾水文大断面的测量为例介绍了利用该技术进行工程实测的过程,通过对实测数据成果的分析,得出一些有益的结论。 相似文献
446.
447.
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
448.
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
449.
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
450.
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