全文获取类型
收费全文 | 18020篇 |
免费 | 3662篇 |
国内免费 | 5984篇 |
专业分类
测绘学 | 2693篇 |
大气科学 | 3389篇 |
地球物理 | 3545篇 |
地质学 | 10552篇 |
海洋学 | 2945篇 |
天文学 | 493篇 |
综合类 | 1604篇 |
自然地理 | 2445篇 |
出版年
2024年 | 95篇 |
2023年 | 342篇 |
2022年 | 936篇 |
2021年 | 1128篇 |
2020年 | 827篇 |
2019年 | 1129篇 |
2018年 | 991篇 |
2017年 | 898篇 |
2016年 | 1003篇 |
2015年 | 1117篇 |
2014年 | 1106篇 |
2013年 | 1401篇 |
2012年 | 1338篇 |
2011年 | 1355篇 |
2010年 | 1265篇 |
2009年 | 1325篇 |
2008年 | 1299篇 |
2007年 | 1241篇 |
2006年 | 1209篇 |
2005年 | 968篇 |
2004年 | 823篇 |
2003年 | 676篇 |
2002年 | 619篇 |
2001年 | 584篇 |
2000年 | 612篇 |
1999年 | 535篇 |
1998年 | 361篇 |
1997年 | 347篇 |
1996年 | 334篇 |
1995年 | 282篇 |
1994年 | 235篇 |
1993年 | 209篇 |
1992年 | 178篇 |
1991年 | 143篇 |
1990年 | 128篇 |
1989年 | 121篇 |
1988年 | 104篇 |
1987年 | 66篇 |
1986年 | 64篇 |
1985年 | 46篇 |
1984年 | 48篇 |
1983年 | 22篇 |
1982年 | 26篇 |
1981年 | 29篇 |
1980年 | 17篇 |
1979年 | 14篇 |
1978年 | 11篇 |
1976年 | 9篇 |
1973年 | 9篇 |
1957年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
91.
固定化鲅鱼乙酰胆碱酯酶的制备及部分性质测定 总被引:3,自引:0,他引:3
酶的固定化是酶传感器制备过程中重要的1个环节.研究采用直接共价法固定鲅鱼乙酰胆碱酯酶(AChE).制备方法为:0.1g CNBr活化的Sepharose 4B凝胶用1mmol/L的HCl充分溶胀后,与活力为10U的AChE溶液混合,于4℃下150r/min振荡8h.所制备的固定化酶活力回收率较高(96%),对pH值和温度变化的适应能力均优于非固定化酶;在3个月保存期内,前者的活力损失13%,而后者的活力则下降89%.这说明固定过程能够大大提高AChE的抗逆性和保持酶活力的稳定,有利于酶传感器的制备. 相似文献
92.
本文以南麂海洋站1983~1990年风、浪的实测资料为依据,建立了南麂海城春、夏、秋、冬季定常波风浪波高与风速的经验关系式。检验结果表明,曲线回归显著,计算值与实测值吻合良好。文中还对偏NNE向和偏SSW向计算波高随风速增大的快慢,同一方向在同一风速作用下计算波高的季节变化及其机理作了初浅的讨论。 相似文献
93.
94.
95.
96.
Representation of double-peaked sea wave spectra in Jiaozhou Bay 总被引:1,自引:0,他引:1
The spectrum shape characteristics of double-peaked sea wave spectia actually measured in the Jiaozhou Bay were analysed and one representation of double-peaked sea wave spectra with six-parameters which can be determined from a given sea wave spectrum is proposed in this paper. After verifying by fitting process with the data sets of double-peaked sea wave spectra measured in the Jiaozhou Bay, it can be seen from the results that the representation mentioned above may be used to express the double-peaked sea wave spectra generated in the Jiaozhou Bay under various sea states, and that the absolute values of maximum deviation index (D.I.) do not exceed 30. 0. 相似文献
97.
Study of zooplankton ecology in Zhejiang coastal upwelling system-Zooplankton biomass and abundance of major groups 总被引:1,自引:0,他引:1
He Dehu Yang Guanming Fang Shaojin Shen Weilin Liu Hongbin Gao Aigen Huang Shuxin 《海洋学报(英文版)》1988,7(4):607-620
The studied area is a shallow water area that belongs to the East China Sea continent shelf. The distribution of zooplankton biomass is higher inshore than offshore. The maximum abundance is in the inshore edge of the centre of upwelling, which is the superposed area of the salinity front and temperature front, due to the fact that the mixture of three different waters has brought about a concentration of nutrients. The herbivorous Euphausia, Copepoda and Tunicata are the major groups of the abundant area. Tunicata possess the possibility to compete against other kinds of herbivorous zooplankton. This means that there is negative correlation between the distribution of Tunicata and that of Copepoda and Euphausia. The positions of maximum areas of zooplankton biomass, phytoplankton individual and the concentration of phosphates and chlorophyll-a overlap one another. In the centre of upwelling, zooplankton can not adapt itself to the environment of lower temperature and less oxygen even with rich nutrient 相似文献
98.
A new approach to high-order Boussinesq-type equations with ambient currents is presented. The current velocity is assumed to be uniform over depth and of the same magnitude as the shallow water wave celerity. The wave velocity field is expressed in terms of the horizontal and vertical wave velocity components at an arbitrary water depth level. Linear operators are introduced to improve the accuracy of the kinematic condition at the sea bottom. The dynamic and kinematic conditions at the free surface are expressed in terms of wave velocity variables defined directly on the free surface. The new equations provide high accuracy of linear properties as well as nonlinear properties from shallow to deep water, and extend the applicable range of relative water depth in the case of opposing currents. 相似文献
99.
Cheng-Han Tsai Min-Chih Huang Fu-Ji Young Yin-Chern Lin Hsien-Wen Li 《Ocean Engineering》2005,32(10):4936-1259
Except the commonly selected pressure transfer function derived from the linear wave theory, a previous study on the pressure transfer function for recovering surface wave from underwater pressure transducer suggested that the pressure transfer function is a function of frequency parameter only. With careful analysis, this study showed that the pressure transfer function should include a transducer submergence parameter as that given by the linear theory. It was found that the previously suggested empirical formula should be restricted to measurements with the pressure transducer close to the surface; otherwise overestimation of wave height would result. Field measurements were carried out with an acoustic wave gauge and a synchronized pressure transducer located at various depths with submergence parameter close to 1 (near the sea floor). It was shown that the previous one-parameter empirical formula might overestimate the significant wave height by more than 30%. This study found that with deep-water wave bursts excluded, the transfer function based on the linear wave theory provided a fairly good estimation on the significant wave heights, with an average deviation of 3.6%. 相似文献
100.
INTRODUCTIONDissolvedorganiccarbon (DOC)makesupthesecondlargestofthebioactivepoolsofcar bonintheocean ,secondtothelargestpoolofdissolvedinorganiccarbon .Theglobaldissolvedorganiccarbonpoolisestimatedtobe 6 85Gt,avaluecomparabletothemassofCO2 intheat mosphere (Hedges,1 992 ) .Thesizeofthereservoir,aswellasitsdynamics ,indicatesthatDOCplaysacentralroleintheoceancarboncycle .AsitrelatestogreenhousegasessuchasCO2 andassociatesclimatecycle ,oceanicDOCbiogeochemicalcycleshavebeenoneoftheh… 相似文献