全文获取类型
收费全文 | 8985篇 |
免费 | 1378篇 |
国内免费 | 1567篇 |
专业分类
测绘学 | 1749篇 |
大气科学 | 1050篇 |
地球物理 | 1979篇 |
地质学 | 4052篇 |
海洋学 | 1006篇 |
天文学 | 432篇 |
综合类 | 727篇 |
自然地理 | 935篇 |
出版年
2024年 | 25篇 |
2023年 | 75篇 |
2022年 | 232篇 |
2021年 | 276篇 |
2020年 | 339篇 |
2019年 | 388篇 |
2018年 | 282篇 |
2017年 | 346篇 |
2016年 | 362篇 |
2015年 | 405篇 |
2014年 | 501篇 |
2013年 | 594篇 |
2012年 | 592篇 |
2011年 | 615篇 |
2010年 | 471篇 |
2009年 | 557篇 |
2008年 | 522篇 |
2007年 | 618篇 |
2006年 | 657篇 |
2005年 | 519篇 |
2004年 | 470篇 |
2003年 | 375篇 |
2002年 | 325篇 |
2001年 | 353篇 |
2000年 | 309篇 |
1999年 | 271篇 |
1998年 | 221篇 |
1997年 | 211篇 |
1996年 | 208篇 |
1995年 | 166篇 |
1994年 | 131篇 |
1993年 | 112篇 |
1992年 | 88篇 |
1991年 | 54篇 |
1990年 | 56篇 |
1989年 | 59篇 |
1988年 | 31篇 |
1987年 | 32篇 |
1986年 | 13篇 |
1985年 | 12篇 |
1984年 | 6篇 |
1982年 | 4篇 |
1980年 | 7篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1977年 | 7篇 |
1975年 | 3篇 |
1973年 | 5篇 |
1972年 | 6篇 |
1971年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
A.F. Velegrakis M.I. VousdoukasA.M. Vagenas Th. KarambasK. Dimou Th. Zarkadas 《Coastal Engineering》2007
This short contribution reports the results of a field study on the nearshore characteristics of waves generated by both conventional and high speed passenger ferries. The field observations took place in the late summer of 2005, at a beach close to the port of Mytilene (Island of Lesbos, Greece), and involved the visual observation of ship waves, using digital video recordings and image processing techniques. The results showed that passage of the fast ferry was associated with a longer, more complex and energetic nearshore event; this event not only did include higher nearshore waves (up to 0.74 m) and was organised in different wave packets, but it was also an order of magnitude longer (∼ 680 s) than the conventional ferry event. Regarding the effects on beach sediment dynamics, the fast ferry waves were estimated to be very efficient in mobilising the nearshore sediments in contrast to those of the conventional ferry. The fast ferry service appears to generate daily prolonged nearshore events, which contain waves with higher energy than those expected from the normal summer wind wave regime of the area; these events also include some high and very steep waves, which can be particularly erosive. Therefore, fast ferry wakes may have considerable impacts on the seasonal beach sediment dynamics/morphodynamics and the nearshore benthic ecology, as well as they may pose significant risks to bathers, affecting the recreational use of the beaches exposed to fast ferry traffic. Finally, the study has shown that satisfactory field observations of the nearshore characteristics of ship-generated (and wind) waves can be obtained using inshore deployments of calibrated poles, digital video cameras and appropriate image processing algorithms. 相似文献
52.
Toru?Iwata Keiko?Yoshikawa Katsutoshi?Nishimura Yoshihisa?Higuchi Takao?Yamashita Shigeru?Kato Eiji?OhtakiEmail author 《Journal of Oceanography》2004,60(6):995-1000
The measurements of the vertical transport of CO2 were carried out over the Sea of Japan using the specially designed pier of Kyoto University on September 20 to 22, 2000. CO2 fluxes were measured by the eddy correlation and aerodynamic techniques. Both techniques showed comparable CO2 fluxes during sea breeze conditions: −0.001 to −0.08 mg m−2s−1 with the mean of −0.05 mg m−2s−1. This means that the measuring site satisfies the fetch requirement for meteorological observations under sea breeze conditions. Moreover, the eddy diffusivity coefficient used in the aerodynamic technique is found to be consistent with the coefficient used in the eddy correlation technique. The present result leads us to conclude that the aerodynamic technique may be applicable to underway CO2 flux measurements over the ocean and may be used in place of the bulk technique. The important point is the need to maintain a measuring accuracy of CO2 concentration difference of the order of 0.1 ppmv on the research vessels or the buoys. 相似文献
53.
54.
55.
56.
本文报道了1987年夏、冬两个航次在26°50′~32°30′N,124°30′~131°30′E海区中可溶性无机磷酸盐的调查结果,阐明了磷的分布特征和形成机制。结果表明陆架区表层测值较高,大洋区为低值区,底层则相反。大洋水常年分层,中层水有爬坡涌升现象,其浓度与Aou呈正相关,与pH和S呈负相关。夏、冬两季底层磷与Aou呈正相关,其浓度变化主要依赖于生物过程。 相似文献
57.
58.
点带石斑鱼人工育苗技术 总被引:21,自引:0,他引:21
通过58批次的人工育苗试验,总结点带石斑鱼人工育苗技术;阐述了育苗池、育苗的环境条件、鱼苗不同生长阶段的饵料及投喂方法、育苗水质管理及生产中的操作方法等;讨论了如何解决开口饵料问题和出现3个危险期的原因等。 相似文献
59.
You Yage
YuZhi Associated Professor Guangzhou Institute of Energy Conversion Chinese Academy of Sciences Guangzhou
. Professor Guangzhou Institute of Energy Conversion Chinese Academy of Sciences Guangzhou 《中国海洋工程》1995,(4)
In this paper, the extreme wave loads on an on-shore wave power device are investigated. First, boundary element method is applied to solve the three dimensional potential problem based on the small amplitude wave assumption. Then the motion of the Oscillating Water Column (OWC) inside the device and its laods on the device are calculated in time domain. Several protective techniques often applied are simulated by changing the constraint of the upper end of the chamber of the device. Numerical results are used to judge the effectiveness of these techniques. The investigation shows that damping can not effectively restrain the motion of OWC when the period of incident wave is long, which may cause dangerous loads on the structure. The shut chamber can effectively restrain the motion of OWC, but alternatively cause high pressure in the chamber. A Contracting opening with a Taper (CT) can exhaust a great amount of kinetic energy of OWC, and significantly decrease the loads. It is a promising protective tec 相似文献
60.
根据大量田间试验和调查资料分析,作者提出烟单14号玉米生长过程中,小喇叭口期土壤中全氮、大喇叭口期土壤中速效磷的含量与产量相关密切。并据此建立了产量及构成三因素与土壤养分间的最优相关模型。 相似文献