全文获取类型
收费全文 | 2556篇 |
免费 | 602篇 |
国内免费 | 1600篇 |
专业分类
测绘学 | 127篇 |
大气科学 | 15篇 |
地球物理 | 464篇 |
地质学 | 3559篇 |
海洋学 | 429篇 |
天文学 | 12篇 |
综合类 | 91篇 |
自然地理 | 61篇 |
出版年
2024年 | 9篇 |
2023年 | 35篇 |
2022年 | 72篇 |
2021年 | 79篇 |
2020年 | 125篇 |
2019年 | 142篇 |
2018年 | 143篇 |
2017年 | 93篇 |
2016年 | 184篇 |
2015年 | 191篇 |
2014年 | 225篇 |
2013年 | 222篇 |
2012年 | 231篇 |
2011年 | 274篇 |
2010年 | 240篇 |
2009年 | 275篇 |
2008年 | 246篇 |
2007年 | 239篇 |
2006年 | 296篇 |
2005年 | 232篇 |
2004年 | 239篇 |
2003年 | 170篇 |
2002年 | 138篇 |
2001年 | 110篇 |
2000年 | 121篇 |
1999年 | 121篇 |
1998年 | 73篇 |
1997年 | 64篇 |
1996年 | 47篇 |
1995年 | 22篇 |
1994年 | 39篇 |
1993年 | 17篇 |
1992年 | 11篇 |
1991年 | 12篇 |
1990年 | 6篇 |
1989年 | 10篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1984年 | 1篇 |
排序方式: 共有4758条查询结果,搜索用时 15 毫秒
971.
ALOCATIONALCOMPARATIVESTUDYONHIGH-TECHINDUSTRIALZONESINCHINAWeiXinzhen魏心镇;ShiYonghui史永辉(DepartmentofGeography.PekingUniversit... 相似文献
972.
王晓颖 《测绘与空间地理信息》2017,(3)
BP神经网络模型是一种经典的预测模型,被广泛应用于变形分析预测的各个领域。本文采用一定方法以进一步改进BP神经网络模型,并通过灰色Verhulst-BP模型分析软基处理地基的实例数据,结合Matlab语言,编程比较分析预测及实测的数据,得出结果证明改进灰色Verhulst-BP模型的分析预测精度较高,比较适合于建筑地基变形的预测分析。 相似文献
973.
A new method for calculation of head displacement and rotation of laterally loaded rigid monopiles and poles in multilayered heterogeneous elastic soil is presented. The analysis considers the soil as a layered elastic continuum in which the modulus vary linearly with depth within each layer. Rational pile and soil displacement fields are assumed, and the interaction between the pile and soil is taken into account by using the principle of virtual work. Two sets of equilibrium equations, one describing the pile displacement and rotation and the other describing the displacements in the soil, are obtained and solved analytically and numerically following an iterative algorithm. The new method produces pile responses as accurate as those obtained from three-dimensional finite element analysis but does not require any elaborate input for geometry and mesh. 相似文献
974.
本文在现场实验研究的基础上,提出了饱和两相介质在爆炸动载下排水固结机理的一维简化模型。数值计算结果表明在强动载作用下,土层中两相介质由于运动惯性不同,两者会出现分离运动,土体的排水速度与两相介质的运动有关。动载作用后两相介质仍具有较大的惯性,继续排水,这与静载下是不同的。土中孔隙压力的变化与两相介质运动有关,计算值与实测值在量级上有可比性。 相似文献
975.
The concept of essential fish habitats (EFHs) is widely accepted for conservational and management purposes. EFHs are often considered as high quality habitats for fisheries species and subsequently of high values for society. In this study, fish and Substrate-Associated Prey (SAP) were sampled during the productive summer season 1998 (fish) and 2003 and 2004 (SAP) in shallow coastal rocky- and soft-bottom habitats on the Swedish west coast. The aim was to study the spatial and monthly variation of SAP as well as abundance and biomass of fish, and to examine if food items found in the diet of the fish assemblage were derived from SAP. We also examined if the diet of Ctenolabrus rupestris, a resident and abundant fish species in the shallow coastal habitats, and the diet of four seasonally abundant and commercially important fish species (Gadus morhua, Pleuronectes platessa, Salmo trutta and Scomber scombrus) were derived from SAP. There were significantly higher mean species number and abundance of the SAP assemblage on rocky compared to soft bottoms and the highest values were found on the rocky bottoms in August and in the shallowest (0–3 m) depth strata. There were no significant differences in number of fish species caught in the two habitats, although mean number of fish and mean biomass were significantly higher on rocky bottoms. Both habitats showed the same seasonal variation and the highest values of number of fish species, abundance and biomass were observed in June. On rocky bottoms, gastropods and amphipods were the most frequent food items in the diet of the entire fish assemblage and these items were also the most abundant SAP in this habitat. The dominant food items of the soft-bottom fish assemblage were decapods and fish, which were not common SAP. However, except for S. scombrus, the diet of the selected fish species showed a strong association to the SAP availability. Gadus morhua displayed the strongest association to SAP on rocky bottoms and P. platessa and C. rupestris to SAP on soft bottoms. Further, for C. rupestris, multivariate statistical analysis showed a significant association to the SAP assemblage on both rocky and soft bottoms. These results provide vital new information for the management and conservation of Essential Fish Habitats on the Swedish west coast. 相似文献
976.
Seungshic Yum Seonock Woo Man Chang Taek-Kyun Lee Jun-Im Song 《Ocean Science Journal》2005,40(1):55-59
We cloned the complete cDNA of the β-tubulin from the soft coral,Scleronephthya gracillimum (Kükenthal) (Alcyonacea, Octocorallia, Anthozoa, Cnidaria), via the random sequencing of a cDNA library and the 5′-rapid
amplification of cDNA end (RACE) technique. The full-length cDNA of theS. gracillimum β-tubulin comprised 1541 bp, not including the poly (A)+ stretch, also contained a complete open reading frame, which codes for a total of 445 amino acids. The amino acid residues
16-402 appeared to be in a state of conservation in a variety of animals. Northern blot analysis clearly demonstrated that
the sequence we have obtained is, indeed, the full-length cDNA of the β-tubulin gene inS. gracillimum. 相似文献
977.
Hong-Jian Liao Li-Jun Su Wu-Chuan Pu Jian-Hua Yin 《Marine Georesources & Geotechnology》2003,21(3):183-200
A kind of diatomaceous soft rock and its constitutive model are studied in this article. Based on Yin and Graham's (1999) 3-D elastic viscoplastic constitutive model, the formulation under a triaxial stress state is established, and it is used to simulate the time-dependent stress-strain behavior and effective stress path of consolidated undrained triaxial tests of both normally consolidated and overconsolidated soft rock. The comparison between the model predictions and measured results shows that their agreement is good. This demonstrates that the constitutive equation established here can be used to simulate the time-dependent stress-strain behavior of the soft rock under triaxial stress condition. 相似文献
978.
Chai Changqing Chief Engineer First Navigational Engineering Bureau Ministry of Communications of China Jianjin 《中国海洋工程》1994,(1)
-The construction of breakwaters in China in more than 40 years since the founding of the People's Republic of China is reviewed. The construction of two main types of breakwater, upright breakwaters and rubble mound breakwaters, and the way in which they are built are expounded. Recommendations to improve the technology for future breakwater construction are presented. 相似文献
979.
980.
首钢京唐钢铁联合有限责任公司是一个在曹妃甸岛上吹填砂造地形成的场地上新建的大型现代化精品钢铁基地。分析了该建筑场地的地质环境情况和常用的基坑支护、降水方法,对该建筑场地上的建(构)筑物的基坑支护、降水设计及方案选择提出建议。 相似文献