全文获取类型
收费全文 | 3190篇 |
免费 | 563篇 |
国内免费 | 753篇 |
专业分类
测绘学 | 144篇 |
大气科学 | 641篇 |
地球物理 | 864篇 |
地质学 | 1566篇 |
海洋学 | 356篇 |
天文学 | 187篇 |
综合类 | 331篇 |
自然地理 | 417篇 |
出版年
2024年 | 12篇 |
2023年 | 59篇 |
2022年 | 131篇 |
2021年 | 147篇 |
2020年 | 117篇 |
2019年 | 158篇 |
2018年 | 162篇 |
2017年 | 136篇 |
2016年 | 164篇 |
2015年 | 162篇 |
2014年 | 170篇 |
2013年 | 186篇 |
2012年 | 188篇 |
2011年 | 180篇 |
2010年 | 152篇 |
2009年 | 196篇 |
2008年 | 183篇 |
2007年 | 140篇 |
2006年 | 146篇 |
2005年 | 123篇 |
2004年 | 104篇 |
2003年 | 84篇 |
2002年 | 65篇 |
2001年 | 98篇 |
2000年 | 112篇 |
1999年 | 171篇 |
1998年 | 128篇 |
1997年 | 154篇 |
1996年 | 117篇 |
1995年 | 84篇 |
1994年 | 106篇 |
1993年 | 82篇 |
1992年 | 57篇 |
1991年 | 33篇 |
1990年 | 48篇 |
1989年 | 25篇 |
1988年 | 30篇 |
1987年 | 19篇 |
1986年 | 16篇 |
1985年 | 11篇 |
1984年 | 8篇 |
1983年 | 7篇 |
1982年 | 13篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1965年 | 1篇 |
1958年 | 5篇 |
排序方式: 共有4506条查询结果,搜索用时 281 毫秒
941.
942.
Qinghui?Qiao Nianrong?Shi Xiaomei?FengEmail author Jie?Lu Yuqian?HanEmail author Changhu?Xue 《中国海洋大学学报(英文版)》2016,15(3):489-494
As the key point in sex hormone analysis, sample pre-treatment technology has attracted scientists' attention all over the world, and the development trend of sample preparation forwarded to faster and more efficient technologies. Taking economic and environmental concerns into account, subcritical fluid extraction as a faster and more efficient method has stood out as a sample pre-treatment technology. This new extraction technology can overcome the shortcomings of supercritical fluid and achieve higher extraction efficiency at relatively low pressures and temperatures. In this experiment, a simple, sensitive and efficient method has been developed for the determination of diethylstilbestrol(DES) in fish tissue using subcritical 1,1,1,2-tetrafluoroethane(R134a) extraction in combination with gas chromatography-mass spectrometry(GC-MS). After extraction, freezing-lipid filtration was utilized to remove fatty co-extract. Further purification steps were performed with C_(18) and NH_2 solid phase extraction(SPE). Finally, the analyte was derived by heptafluorobutyric anhydride(HFBA), followed by GC-MS analysis. Response surface methodology(RSM) was employed to optimizing the extraction condition, and the optimized was as follows: extraction pressure, 4.3 MPa; extraction temperature, 26℃; amount of co-solvent volume, 4.7 m L. Under this condition, at a spiked level of 1, 5, 10 μg kg~(-1), the mean recovery of DES was more than 90% with relative standard deviations(RSDs) less than 10%. Finally, the developed method has been successfully used to analyzing the real samples. 相似文献
943.
The perforated breakwater is an environmentally friendly coastal structure,and dissolved oxygen concentration levels are an important index to denote water quality.In this paper,oxygen transport experiments with regular waves through a vertical perforated breakwater were conducted.The oxygen scavenger method was used to reduce the dissolved oxygen concentration of inner water body with the chemicals Na_2SO_3 and Co Cl_2.The dissolved oxygen concentration and wave parameters of 36 experimental scenarios were measured with different perforated arrangements and wave conditions.It was found that the oxygen transfer coefficient through wave surface,K_1a_1,is much lower than the oxygen transport coefficient through the perforated breakwater,K_2a_2.If the effect of K_1a_1 is not considered,the dissolved oxygen concentration computation for inner water body will not be greatly affected.Considering the effect of a permeable area ratio α,relative location parameter of perforations δ and wave period T,the aforementioned data of 30 experimental scenarios,the dimensional analysis and the least squares method were used to derive an equation of K_2a_2(K_2a_2=0.0042α~(0.5)δ~(0.2)T~(-1)).It was validated with 6 other experimental scenarios data,which indicates an approximate agreement.Therefore,this equation can be used to compute the DO concentration caused by the water transport through perforated breakwater. 相似文献
944.
945.
946.
947.
948.
Ice core is an important object of the global climate change research, and can extract paleoclimate information by physical and chemical methods. As one of the major physical analysis technology, conductivity measurement technology mainly contains two methods and has been applied to many drilling project. The technology reflects the ice core electrical properties influenced by factors such as temperature, pressure, impurities and changes, and the cause of these changes can be explained from the aspects of macroscopic and microscopic. What obtained from measurement can be used to the research of dating, volcanic events, accumulation rate, biomass burning, ion concentration recovery, which systematically help us to understand the quaternary evolution of Antarctic climate since late pleistocene. This paper summarized in detail the main research achievements on electrical properties and dielectric measurement technology of ice core, and also discussed the prospect of the technology in China deep ice core project further. 相似文献
949.
950.