全文获取类型
收费全文 | 49912篇 |
免费 | 8679篇 |
国内免费 | 11886篇 |
专业分类
测绘学 | 4195篇 |
大气科学 | 5090篇 |
地球物理 | 11259篇 |
地质学 | 30511篇 |
海洋学 | 5572篇 |
天文学 | 2183篇 |
综合类 | 3677篇 |
自然地理 | 7990篇 |
出版年
2024年 | 166篇 |
2023年 | 457篇 |
2022年 | 1276篇 |
2021年 | 1462篇 |
2020年 | 1584篇 |
2019年 | 1968篇 |
2018年 | 1567篇 |
2017年 | 1757篇 |
2016年 | 1907篇 |
2015年 | 2082篇 |
2014年 | 2594篇 |
2013年 | 2654篇 |
2012年 | 2885篇 |
2011年 | 3169篇 |
2010年 | 2700篇 |
2009年 | 3275篇 |
2008年 | 3203篇 |
2007年 | 3636篇 |
2006年 | 3547篇 |
2005年 | 3114篇 |
2004年 | 2912篇 |
2003年 | 2812篇 |
2002年 | 2464篇 |
2001年 | 2167篇 |
2000年 | 2036篇 |
1999年 | 1894篇 |
1998年 | 1649篇 |
1997年 | 1517篇 |
1996年 | 1405篇 |
1995年 | 1170篇 |
1994年 | 1186篇 |
1993年 | 1004篇 |
1992年 | 799篇 |
1991年 | 557篇 |
1990年 | 497篇 |
1989年 | 388篇 |
1988年 | 301篇 |
1987年 | 194篇 |
1986年 | 141篇 |
1985年 | 92篇 |
1984年 | 40篇 |
1983年 | 33篇 |
1982年 | 31篇 |
1981年 | 24篇 |
1980年 | 23篇 |
1979年 | 34篇 |
1978年 | 37篇 |
1977年 | 29篇 |
1975年 | 4篇 |
1954年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 468 毫秒
361.
砂质海岸岸滩侵蚀演变模式探讨——以山东南部海岸侵蚀岸段的岸滩演变为例 总被引:5,自引:0,他引:5
在分析山东南部海岸几十年来的地形观测资料的基础上,运用砂质海岸等深线变化预测理论,建立该区的岸滩侵蚀演变预测模型,研究了该区域岸滩演变规律。实测资料验证表明:预测结果合理,基本反映了本区岸滩演变的特征。 相似文献
362.
1 .IntroductionTomeasurethereflectionofincidentwavesproducedbyaphysicalmodelinawaveflumeisacommonproblemwithphysicaltestsofwaveactiononcoastalstructures .Wavesgeneratedbythewave makerpropagateforwardinthewaveflumeandarereflectedbythephysicalmodel,andthe… 相似文献
363.
若把河口潮位时间序列简单地看为单输入和输出线性系统模型的输入输出信号,借助频谱分析可以将它们在频域内的关系建立起来,用来进行潮位序列的插补,带通滤波技术的应用可使模型的计算精度大大提高 相似文献
364.
365.
366.
Abstract. The distribution of Ibla cumingi DARWIN on different types of hard substrata along 30 km of coast in the Gulf of Elat was studied. I. cumingi was found among and underneath Tetraclita squamosa rufotincta , in oyster beds, underneath slabs of beachrock, and in fissures in igneous rocks. In the Tetraclita belt, I. cumingi is most frequent in empty shells of dead Tetraclita while in the oyster bed it is common inside the meshwork made by the oysters. The distribution is regarded as clustered distribution. The density and size of the clusters of I. cumingi is determined by the available sheltered space within the midlittoral zone. The form of the habitat determines the shape of the animals. Those found in the oyster bed and fissures are usually longer than those found in the Tetraclita belt due to the depth of the fissures or to the bigger spaces within the oyster bed. I. cumingi is orientated so that the capitulum with the cirri is projecting towards the open water, and the water current. It is concluded that I. cumingi can withstand the physical stress encountered in a tropical intertidal zone, but that the distribution pattern is caused by predation. 相似文献
367.
在采用回收法治理锯条厂氰化物污水中,通过改造生产工艺,减少污水量,提高氰化物浓度及污水经除油后减压蒸馏,可回收50%~90%的氰化铂,其他盐分也可全部回收,从污水中蒸出的蒸馏水能在系统内循环使用。 相似文献
368.
本文介绍了国家标准《潜水员水下用电安全技术规范》的研究、编制过程,以及编者对该标准性质、适用范围、总体结构、电气安全数值取舍等的基本认识,并就该标准制定实施后的经济、社会效益进行了初步预测。 相似文献
369.
We present magnetic field data collected over the Mid-Atlantic Ridge in the vicinity of the Atlantis Fracture Zone and extending out to 10 Ma-old lithosphere. We calculated a magnetization distribution which accounts for the observed magnetic field by performing a three-dimensional inversion in the presence of bathymetry. Our results show the well-developed pattern of magnetic reversals over our study area. We observe a sharp decay in magnetization from the axis out to older lithosphere and we attribute this decay to progressive low temperature oxidation of basalt. In crust which is 10 Ma, we observe an abrupt increase in magnetic field intensity which could be due to an increase in the intensity of magnetization or thickness of the magnetic source layer. We demonstrate that because the reversal epoch was of unusually long duration, a two-layer model comprised of a shallow extrusive layer and a deeper intrusive layer with sloping polarity boundaries can account for the increase in the amplitude of anomaly 5. South of the Atlantis Fracture Zone, high magnetization is correlated with bathymethic troughts at segment end points and lower magnetization is associated with bathymetric highs at segment midpoints. This pattern can be explained by a relative thinning of the magnetic source layer toward the midpoint of the segment. Thickening of the source layer at segment endpoints due to alteration of lower oceanic crust could also cause this pattern. Because we do not observe this pattern north of the fracture zone, we suggest it is a result of the nature of crustal formation process where mantle upwelling is focused. South of the fracture zone, reversals along discontinuity traces only continue to crust 2 Ma old. In crust >2 Ma, we observe bands of high, positive magnetization along discontinuity traces. We suggest that within the discontinuity traces, a high, induced component of magnetization is produced by serpentinized lower crust/upper mantle and this masks the contribution of basalts to the magnetic anomaly signal. 相似文献
370.
IwrincrIONOn the evolution of palcoenvironment, salt-water encroachmnt and the distributionof subsurface brine in the LaizhOu Bay area, many researches had been carried out, and muchknowledge abeut the gcolOgical features in this area since Late QUaternary was aCquired' ) (H8nand Wu, l992; Han and Meng, l994; Wen et al. l989). However there was IittIe studyon the sediment geOChemical characteristics since Quaternary. In this Paper, the element strati-graphic characteristics and evolut… 相似文献