全文获取类型
收费全文 | 21327篇 |
免费 | 4540篇 |
国内免费 | 5716篇 |
专业分类
测绘学 | 1025篇 |
大气科学 | 5464篇 |
地球物理 | 5216篇 |
地质学 | 10768篇 |
海洋学 | 3887篇 |
天文学 | 124篇 |
综合类 | 1519篇 |
自然地理 | 3580篇 |
出版年
2024年 | 135篇 |
2023年 | 309篇 |
2022年 | 694篇 |
2021年 | 971篇 |
2020年 | 958篇 |
2019年 | 1149篇 |
2018年 | 950篇 |
2017年 | 984篇 |
2016年 | 974篇 |
2015年 | 1119篇 |
2014年 | 1423篇 |
2013年 | 1717篇 |
2012年 | 1468篇 |
2011年 | 1567篇 |
2010年 | 1341篇 |
2009年 | 1440篇 |
2008年 | 1396篇 |
2007年 | 1556篇 |
2006年 | 1464篇 |
2005年 | 1303篇 |
2004年 | 1169篇 |
2003年 | 1022篇 |
2002年 | 899篇 |
2001年 | 802篇 |
2000年 | 731篇 |
1999年 | 633篇 |
1998年 | 592篇 |
1997年 | 501篇 |
1996年 | 398篇 |
1995年 | 400篇 |
1994年 | 353篇 |
1993年 | 289篇 |
1992年 | 205篇 |
1991年 | 158篇 |
1990年 | 100篇 |
1989年 | 122篇 |
1988年 | 76篇 |
1987年 | 47篇 |
1986年 | 29篇 |
1985年 | 40篇 |
1984年 | 23篇 |
1983年 | 16篇 |
1982年 | 11篇 |
1981年 | 14篇 |
1980年 | 12篇 |
1979年 | 2篇 |
1978年 | 11篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1971年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
31.
32.
张晓晖 《成都信息工程学院学报》2002,17(3):166-169
通过对影响能见度的因素的分析,提出了一种能见度预报方法-综合分析法,极大地提高了能见度的预报准确率。 相似文献
33.
IMPACTS OF FUTURE SEA LEVEL RISE ON SALT WATER INTRUSION IN THE CHANGJIANG RIVER ESTUARY 总被引:1,自引:0,他引:1
杨桂山 《中国地理科学(英文版)》1992,2(1):30-41
Sea level rise could increase the salinity of an estuary by altering the balance between fresh water and salt water. The implications of sea level rise for increasing salinity have been examined in the Changjiang (Yangtze) River estuary. By correlative analysis of chlorinity, discharge and tidal level and calculation of two-dimensional chlorinity, distribution of the Changjiang River estuary, the changes of the intensity and lasting hours of salt water intrusion at Wusong Station and the changes of chlorinity distribution in the South Branch of the Changjiang River estuary have been estimated when future sea level rises 50-100 cm. The intensity of salt water intrusion in the future will be far more serious than current trend. 相似文献
34.
研究油藏内部油水渗流方向时,主要考虑渗透率影响,引入两个水平方向渗透率比、水平与垂向渗透率比参数来分析。前者反映样品所在储层平面上两个水平方向渗流能力的差异,后者反映样品所在储层水平与垂向渗流能力的差异,并经小柱样测试和全岩心测试两种方法确定两个参数。通过对塔中4号油藏CⅠ油组9口井2306个样品两种渗透率比值分布直方图分析,研究了CⅠ油组渗透率的非均质性及其渗流方向:CI油组储层在水平方向的渗流能力有很大差异,具有明显的方向性。储层垂向渗流能力明显小于水平方向的渗流能力。 相似文献
35.
The magnitude and spatial distribution of snow on sea ice are both integral components of the ocean–sea‐ice–atmosphere system. Although there exists a number of algorithms to estimate the snow water equivalent (SWE) on terrestrial surfaces, to date there is no precise method to estimate SWE on sea ice. Physical snow properties and in situ microwave radiometry at 19, 37 and 85 GHz, V and H polarization were collected for a 10‐day period over 20 first‐year sea ice sites. We present and compare the in situ physical, electrical and microwave emission properties of snow over smooth Arctic first‐year sea ice for 19 of the 20 sites sampled. Physical processes creating the observed vertical patterns in the physical and electrical properties are discussed. An algorithm is then developed from the relationship between the SWE and the brightness temperature measured at 37 GHz (55°) H polarization and the air temperature. The multiple regression between these variables is able to account for over 90% of the variability in the measured SWE. This algorithm is validated with a small in situ data set collected during the 1999 field experiment. We then compare our data against the NASA snow thickness algorithm, designed as part of the NASA Earth Enterprise Program. The results indicated a lack of agreement between the NASA algorithm and the algorithm developed here. This lack of agreement is attributed to differences in scale between the Special Sensor Microwave/Imager and surface radiometers and to differences in the Antarctic versus Arctic snow physical and electrical properties. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
36.
以小杂鱼或低值鱼为原料 ,采用常温溶剂萃取法进行脱脂 ,研究了不同溶剂、溶剂混合比、流速和萃取时间对鱼类脱脂的影响。结果表明 ,在常温下用等体积的异丙醇和乙酸乙酯混合溶剂 ,以流速 4~ 8mL/min连续萃取 4~ 6h ,脱脂鱼肉的脂肪平均含量w为 0 .19%,脱脂率高达96 .2 6 %。该方法的溶剂损耗量为加热溶剂萃取法的 1/3倍。 相似文献
37.
张和庆 《广东海洋大学学报》2003,23(5):15-23
介绍了我国海洋倾废的历史、发展过程和管理现状 ,分析了海洋倾倒的现状和面临的困难。文章还提出通过高新技术把疏浚泥迅速转化为再生资源进行利用和污染土无害化处理技术 ,从根本上减少疏浚泥海洋倾倒的数量和缓减海洋倾倒区紧张的状况 ,减少对海洋环境的污染 相似文献
38.
Gopal C. Kilambi Praveen Nagar N. Kameswara Rao 《Journal of Astrophysics and Astronomy》1992,13(2):175-194
Mid-ultraviolet and optical photometric analysis of helium stars are presented. A linear relation exists between the effective
temperature derived from model atmospheres and (1965-V)0 index. The effective temperatures derived from (1965-V)0 index are somewhat higher than that of MK spectral type estimates especially for late B-type helium objects. 相似文献
39.
In 1903 the Swiss Federal Research Institute WSL started its first forest hydrology measurements with the aim to deliver a sound scientific basis for the implementation of new forest legislation introduced in Switzerland in 1876. This legislation was triggered by several large floods that occurred in Switzerland, for which a major cause was widely seen as the poor condition of forests at that time. Consequently, hydrologic research at WSL first focused on the influence of forests on floods. In the second half of the 20th century, other hydrological issues such as water quality, snow hydrology and sediment transport complemented the hydrologic research at WSL. Some recent results of this work are presented in three papers joining this introductory paper to mark the 100th anniversary of hydrologic research at WSL. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
40.
This study on the distribution features of petroleum hydrocarbon in water and sedi-ment off the Fujian shore using data obtained from the baseline research on oceanic contamination in Fujian showed that:during the research preiod,petroleum hydrocarbon concentrations in water varied from 5.77μg/L to 37.28μg/L,averaged 14.48 μg/L;was lower in the wet seasson than in the dry season;and was highest in the Minjiang Estuary and Jiulong Estuary in both seasons ,The petorleum hydrocarbon concentrations in shore sediment varied from 14.48 mg/kg to 784.36 mg/kg,averaged 133.3 mg/kg ,and was closely related to sediment types (granularity). 相似文献