全文获取类型
收费全文 | 7267篇 |
免费 | 1485篇 |
国内免费 | 2027篇 |
专业分类
测绘学 | 628篇 |
大气科学 | 1363篇 |
地球物理 | 1835篇 |
地质学 | 3985篇 |
海洋学 | 970篇 |
天文学 | 403篇 |
综合类 | 634篇 |
自然地理 | 961篇 |
出版年
2024年 | 52篇 |
2023年 | 130篇 |
2022年 | 443篇 |
2021年 | 426篇 |
2020年 | 380篇 |
2019年 | 526篇 |
2018年 | 494篇 |
2017年 | 443篇 |
2016年 | 474篇 |
2015年 | 455篇 |
2014年 | 469篇 |
2013年 | 559篇 |
2012年 | 524篇 |
2011年 | 471篇 |
2010年 | 449篇 |
2009年 | 423篇 |
2008年 | 402篇 |
2007年 | 370篇 |
2006年 | 298篇 |
2005年 | 235篇 |
2004年 | 190篇 |
2003年 | 180篇 |
2002年 | 221篇 |
2001年 | 230篇 |
2000年 | 209篇 |
1999年 | 254篇 |
1998年 | 227篇 |
1997年 | 171篇 |
1996年 | 167篇 |
1995年 | 145篇 |
1994年 | 112篇 |
1993年 | 123篇 |
1992年 | 114篇 |
1991年 | 70篇 |
1990年 | 64篇 |
1989年 | 56篇 |
1988年 | 53篇 |
1987年 | 28篇 |
1986年 | 29篇 |
1985年 | 19篇 |
1984年 | 20篇 |
1983年 | 16篇 |
1982年 | 8篇 |
1981年 | 9篇 |
1980年 | 5篇 |
1979年 | 7篇 |
1978年 | 6篇 |
1977年 | 8篇 |
1976年 | 4篇 |
1958年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
A modified global model for predicting the tritium concentration in precipitation has been developed using the dataset of International Atomic Energy Agency/the World Meteorological Organization (IAEA/WMO) over the period from 1960 to 2005. The tritium concentration in precipitation and its history can be estimated at any location using the model. The modified global model of tritium in precipitation (MGMTP) here presented has higher accuracy than the global model of tritium in precipitation (GMTP) developed by Doney et al. ( 1992 ). The new model is not only more appropriate for a particular station but also applicable for the un‐normalized observations directly. Another advantage of MGMTP is that it can estimate a longer history (from 1960 to 2005) of tritium content in precipitation than GMTP (from 1960 to 1986). The seasonal cycle of tritium in precipitation has also been modelled in the form of a simple cosine function with five parameters. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
992.
Chunhua Yuan Azimi-Sadjadi M.R. Wilbur J. Dobeck G.J. 《Oceanic Engineering, IEEE Journal of》2000,25(1):192-205
In this paper, new pre- and post-processing schemes are developed to process shallow-water sonar data to improve the accuracy of target detection. A multichannel subband adaptive filtering is applied to preprocess the data in order to isolate the potential target returns from the acoustic backscattered signals and improve the signal-to-reverberation ratio. This is done by estimating the time delays associated with the reflections in different subbands. The preprocessed results are then beamformed to generate an image for each ping of the sonar. The testing results on both the simulated and real data revealed the efficiency of this scheme in time-delay estimation and its capability in removing most of the competing reverberations and noise. To improve detection rate while significantly minimizing the incident of false detections, a high-order correlation (HOC) method for postprocessing the beamformed images is then developed. This method determines the consistency in occurrence of the target returns in several consecutive pings. The application of the HOC process to the real beamformed sonar data showed the ability of this method for removing the clutter and at the same time boosting the target returns in several consecutive pings. The algorithm is simple, fast, and easy to implement 相似文献
993.
An outline of the astrometric series of the ERP of their accuracy and of the results obtained from analyses of these data are given in the paper. Presently known systematic differences between the astrometric ERP series and those determined by VLBI and Lageos ranging techniques are discussed. Some geophysical applications of latitude and longitude variations determined by astrometric techniques are mentioned. 相似文献
994.
For the rising branch of Cycle 22, 1987 January—1989 November, we plot the daily total flux S at each of the five wavelengths 2.0, 3.4, 6.0, 10.7 and 21.2 cm against the apparent sunspot area of the dominant sunspot Ay and find that, for several large active areas, the locus is located below the average regression line, and the increase in the radio flux is insignificant compared to the increase in the sunspot area. 相似文献
995.
Qi-Rong Yuan Peng-Fei Yan Yan-Bin Yang Xu Zhou Department of Physics Nanjing Normal University Nanjing yuanqirong@njnu. edu. cn National Astronomical Observatories Chinese Academy of Sciences Beijing Department of Mathematics Physics Qingdao University of Science Technology Qingdao 《中国天文和天体物理学报》2005,5(2):126-136
Convincing evidence for a past interaction between the two rich clusters A399 and A401 was recently found in the X-ray imaging observations. We examine the structure and dynamics of this pair of galaxy clusters. A mixture-modeling algorithm was applied to obtain a robust partition into two clusters, which allowed us to discuss the virial mass and velocity distribution of each cluster. Assuming that these two clusters follow a linear orbit and they have once experienced a close encounter, we model the binary cluster as a two-body system. As a result, four gravitationally bound solutions are obtained. The recent X-ray observations seem to favor a scenario in which the two clusters with a true separation of 5.4h-1 Mpc are currently expanding at 583 km s-1 along a direction with a projection angle of 67.5°, and they will reach a maximum extent of 5.65 h-1 Mpc in about 1.0 h-1 Gyr. 相似文献
996.
讨论关于回转椭球静态场求解的一般方法,借助回转椭圆坐标系,静态场问题的一般解可以用实宗量和虚宗量勒让德函数以及余弦函数形式表出,使得结果更为简明和系统化。所得结果可以直接应用到椭球导体电场、尖端效应、介质椭球极化以至双极化雷达测量降水问题等,具有相当具体的实用价值。 相似文献
997.
998.
999.
ESR DATING OF FLUVIAL SEDIMENTS USING GE CENTER IN QUARTZ 总被引:3,自引:0,他引:3
Using the Ge centers of quartz sediments, the buried ages of fluvial sediments were determined by ESR technique. The ESR ages obtained from Ge centers are consistent with the TL ages, correspond with their horizons, accord with the geological background, and every ESR age is available. In this paper, determination of total dose of natural radiation (TD) and the reliability of ESR age using Ge center are also discussed. 相似文献
1000.
经典的太阳光谱观测是一维的,它有很大的局限性。从50年代起,天文工作者采用多种方法开展二维太阳光谱观测,已经研制出一系列仪器,建立完整的资料归算程序,取得优良成果。在二维观测资料的基础上,用理论方法推出深度分布,可以得出三维的立体图像,这会成为太阳研究的主要方法之一。 相似文献