全文获取类型
收费全文 | 6340篇 |
免费 | 1107篇 |
国内免费 | 1754篇 |
专业分类
测绘学 | 666篇 |
大气科学 | 1253篇 |
地球物理 | 1432篇 |
地质学 | 3131篇 |
海洋学 | 987篇 |
天文学 | 227篇 |
综合类 | 591篇 |
自然地理 | 914篇 |
出版年
2024年 | 21篇 |
2023年 | 90篇 |
2022年 | 214篇 |
2021年 | 277篇 |
2020年 | 179篇 |
2019年 | 282篇 |
2018年 | 300篇 |
2017年 | 269篇 |
2016年 | 345篇 |
2015年 | 305篇 |
2014年 | 365篇 |
2013年 | 391篇 |
2012年 | 447篇 |
2011年 | 455篇 |
2010年 | 431篇 |
2009年 | 435篇 |
2008年 | 387篇 |
2007年 | 448篇 |
2006年 | 342篇 |
2005年 | 354篇 |
2004年 | 326篇 |
2003年 | 259篇 |
2002年 | 409篇 |
2001年 | 330篇 |
2000年 | 279篇 |
1999年 | 255篇 |
1998年 | 153篇 |
1997年 | 139篇 |
1996年 | 103篇 |
1995年 | 104篇 |
1994年 | 104篇 |
1993年 | 66篇 |
1992年 | 62篇 |
1991年 | 55篇 |
1990年 | 44篇 |
1989年 | 28篇 |
1988年 | 30篇 |
1987年 | 29篇 |
1986年 | 14篇 |
1985年 | 11篇 |
1984年 | 18篇 |
1983年 | 8篇 |
1982年 | 12篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1977年 | 3篇 |
1972年 | 2篇 |
1971年 | 3篇 |
1958年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有9201条查询结果,搜索用时 156 毫秒
961.
Hong Sik Yun 《Solar physics》1979,63(1):31-33
The physical meaning of the convection efficiency parameter of Öpik's theory is clarified by relating it to that of the mixing-length theory. A compact comparison of both theories is presented to explain the earlier findings of Gough and Weiss (1976), that Öpik's theory becomes indistinguishable from the mixing-length theory when the value of Öpik's cell depth is taken as being equal to 2.44 times the local pressure scale height for the solar convective envelope. 相似文献
962.
963.
964.
本文提出了一个划分冬麦农业气候北界的数学模型,它包括:1.气候-冬麦越冬死亡率方程;2.空间-气候方程;3.将所研究地区划分网格,利用上述两组方程推算出每个网格的冬麦越冬死亡率,并根据死亡率的多少,通过电子计算机划出安全种植北界和可能种植北界.这个数学模型对农业气候区划的方法有一定参考意义. 相似文献
965.
966.
A numerical application to the extreme cases of high and low degree of ionization of the binary collision theory of Burgers (1960) and the multiple collision theory of Shkarofsky (1960) shows very good agreement in the values of the magnetic tensor components for solar electrical conductivity. It is pointed out that the inclusion of ion motions in Burgers theory favors its use in the future evaluation of the solar thermal conductivity tensor.The research reported in this paper was sponsored by the Air Force Cambridge Research Laboratories, AFSC, under Contract F19628-70-C-0192-P00001, but the report does not necessarily reflect endorsement by the sponsor. 相似文献
967.
Analysis of stomach contents of samples of clupeid fishes (Japanese anchovy, half-fin anchovy, zunas' scaled sardine, rednosed
glassnose and tapertail anchovy) collected from the catches of a 1982–1984 fishery resource survey showed they are zooplanktonivorous.
Similar food groups, such as copepoda. Chaetognatha, Amphipoda and Mysidacea were found in the stomach. Dietary similarity
coefficients were studied to evaluate the degree of similarity in the dietary species-pairs. Seasonal variation is discussed.
Contribution No.2050 from the Institute of Oceanology, Academia Sinica. 相似文献
968.
信号的时频分布具有比时间尺度分布更高的描述和刻画非稳态地震波信号的能力,进一步提高信号的时频聚集性和尽可能减小交叉项干扰是时频分析发展的方向。基于高阶矩时频分布理论,本首次提出了将其应用于数字化地震波形资料分析和处理的技术途径和方法。通过对仿真信号的Choi-Willams各阶矩时频分布与Wigner各阶矩时频分布的对比和交叉项干扰的理论分析,认为Choi-willams高阶矩时频分布具有时频聚集性高和交叉干扰项小的特点,在提高处理数字化地震波特性参数精度和地震应急技术系统的智能化程度等方面具有潜在应用前景。 相似文献
969.
Preliminary study on PAH degradation by bacteria from contaminated sediments in Xiamen Western Sea,Fujian, China 总被引:1,自引:0,他引:1
In order to estimate the biodegradation of three polycyclic aromatic hydrocarbons (PAHs) compounds, bacterial strains were isolated from marine sediments in three heavily contaminated sites (Yuandang Lake, Dongdu Port and Aquacultural zones in Maluan Bay) in Xiamen Western Sea. The results show three bacterial strains, which used pyrene as the sole carbon source, were identified as strains of Aureobacterium sp.,Arthrobacter sp., Rhodococcus sp. The PAH-degrading bacteria isolated had a strong ability to degrade phenanhrene, fluoranthene and pyrene at different degradation rates. The highest degradation rate was observed when three PAH compounds were mixed with an individual strain in the medium. The three PAHs were degraded after one week with a degradation rate of 89.94 % for phenanthrene and 93.4 % for both of fluoranthene and pyrene.In addition, after 25 days of incubation, the degradation rate was 99.98 % for phenanthrene and 99.97 % for both of fluoranthene and pyrene. Optical density was measured to estimate bacterial growth during the degradation of PAHs. Highest levels of bacterial growth were observed with a three PAH mixture in the culture, suggesting that the concentration of PAHs influenced bacterial growth and the highest levels of degradation for most series were detected after one week of incubation. 相似文献
970.
一种基于网络拓扑关系的地图匹配算法 总被引:3,自引:0,他引:3
地图匹配是车辆导航定位系统中提高定位精度的一种方法,其精度受定位数据、地图数据质量及坐标系转换关系的影响.在分析现有算法的基础上,提出了一种基于网络拓扑关系的地图匹配算法.该算法只需将GPS定位数据和GIS 数据相结合,即可用算法的形式解决地图匹配中一些常见的问题.实验证明:该算法是一种精度高、效率好、实用性强的地图匹配算法,具有较好的实用价值. 相似文献