全文获取类型
收费全文 | 11084篇 |
免费 | 1464篇 |
国内免费 | 2148篇 |
专业分类
测绘学 | 880篇 |
大气科学 | 2033篇 |
地球物理 | 2421篇 |
地质学 | 4638篇 |
海洋学 | 2073篇 |
天文学 | 696篇 |
综合类 | 781篇 |
自然地理 | 1174篇 |
出版年
2024年 | 51篇 |
2023年 | 121篇 |
2022年 | 381篇 |
2021年 | 450篇 |
2020年 | 434篇 |
2019年 | 461篇 |
2018年 | 551篇 |
2017年 | 493篇 |
2016年 | 575篇 |
2015年 | 509篇 |
2014年 | 635篇 |
2013年 | 753篇 |
2012年 | 681篇 |
2011年 | 757篇 |
2010年 | 663篇 |
2009年 | 663篇 |
2008年 | 597篇 |
2007年 | 589篇 |
2006年 | 504篇 |
2005年 | 463篇 |
2004年 | 373篇 |
2003年 | 301篇 |
2002年 | 314篇 |
2001年 | 316篇 |
2000年 | 315篇 |
1999年 | 326篇 |
1998年 | 273篇 |
1997年 | 261篇 |
1996年 | 234篇 |
1995年 | 218篇 |
1994年 | 193篇 |
1993年 | 165篇 |
1992年 | 159篇 |
1991年 | 139篇 |
1990年 | 102篇 |
1989年 | 91篇 |
1988年 | 77篇 |
1987年 | 74篇 |
1986年 | 45篇 |
1985年 | 40篇 |
1984年 | 51篇 |
1983年 | 47篇 |
1982年 | 49篇 |
1981年 | 31篇 |
1980年 | 32篇 |
1979年 | 20篇 |
1977年 | 21篇 |
1976年 | 13篇 |
1975年 | 18篇 |
1974年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
91.
High-resolution underway temperature and conductivity measurements collected by R/V Knorr during winter and spring 2003 are used to characterize errors associated with spatial aliasing in the northern and central Adriatic Sea. During winter, 99th percentile temperature, salinity and density errors were 0.62 °C, 0.25 and 0.12 kg/m3 (0.25 °C, 0.10 and 0.05 kg/m3) for sampling at 10 km (5 km) horizontal resolution, respectively. The corresponding values in spring were 1.31 °C, 0.50 and 0.40 kg/m3 (0.93 °C, 0.25 and 0.22 kg/m3) for the 10 km (5 km) sample spacing, respectively. The largest errors were associated with energetic regions over the shallow, western Adriatic, in front of the Po River mouth and off the tip of the Istrian peninsula. The deeper eastern basin exhibited smaller errors. The variability of errors in time and space reflected the variability of small-scale density features, characterized by wavelengths as small as 2 km in winter and 1 km in spring and being more pronounced in the western and northern parts of the Adriatic. As these results indicate that errors associated with undersampling can be considerable, they should be taken into account while planning future CTD measurements in the region. 相似文献
92.
Ching-Hui Tsai Shu-Kun Hsu Yi-Ching Yeh Chao-Shing Lee Kanyuan Xia 《Marine Geophysical Researches》2004,25(1-2):63-78
Magnetic data suggest that the distribution of the oceanic crust in the northern South China Sea (SCS) may extend to about 21 °N and 118.5 °E. To examine the crustal features of the corresponding continent–ocean transition zone, we have studied the crustal structures of the northern continental margin of the SCS. We have also performed gravity modeling by using a simple four-layer crustal model to understand the geometry of the Moho surface and the crustal thicknesses beneath this transition zone. In general, we can distinguish the crustal structures of the study area into the continental crust, the thinned continental crust, and the oceanic crust. However, some volcanic intrusions or extrusions exist. Our results indicate the existence of oceanic crust in the northernmost SCS as observed by magnetic data. Accordingly, we have moved the continent–ocean boundary (COB) in the northeastern SCS from about 19 °N and 119.5 °E to 21 °N and 118.5 °E. Morphologically, the new COB is located along the base of the continental slope. The southeastward thinning of the continental crust in the study area is prominent. The average value of crustal thinning factor of the thinned continental crust zone is about 1.3–1.5. In the study region, the Moho depths generally vary from ca. 28 km to ca. 12 km and the crustal thicknesses vary from ca. 24 km to ca. 6 km; a regional maximum exists around the Dongsha Island. Our gravity modeling has shown that the oceanic crust in the northern SCS is slightly thicker than normal oceanic crust. This situation could be ascribed to the post-spreading volcanism or underplating in this region. 相似文献
93.
Experimental study of strong reflection of regular water waves over submerged breakwaters in tandem 总被引:3,自引:0,他引:3
A series of laboratory experiments was carried out to investigate the strong reflection of regular water waves over a train of submerged breakwaters. Rectangular and trapezoidal shapes of submerged breakwaters are employed and compared for reflecting capability of incident waves. Measured reflection coefficients of regular waves over impermeable submerged breakwaters are verified by comparing with those of the eigenfunction expansion method. A very good agreement is observed. Reflection coefficients of permeable submerged breakwaters are less than those of impermeable breakwaters. The trapezoidal shape is recommended for a submerged breakwater in terms of reflecting capability and practical application. 相似文献
94.
95.
本文介绍一种声遥测海底平面层系声阻抗分布的模拟实验结果。实验在油漆厂冷却水池中进行,采用取样平均迭代的反演方法,对三介质层系的遥测结果与实测值较好地接近。 相似文献
96.
An extrapolated version of a time-dependent nonreflecting boundary condition is developed for use at artificial boundaries to truncate infinite/semi-infinite domains for transient water wave problems. Test examples include single- and multiple-frequency flap wavemaker problems and free vibrations of a floating circular cylinder. The finite element results compare favorably to analytical solutions. It is shown that with the proposed boundary condition the numerical simulations have little reflections from the artificial boundaries. 相似文献
97.
An analytical solution for the coupling problem of a two-dimensional tension leg structure interacting with a monochromatic linear wave train in an inviscid and incompressible fluid is presented. The tension legs are considered to be linearly elastic. The flow is further assumed to be irrotational and single-valued velocity potentials can then be defined.The boundary value problem is incorporated into a scattering and a radiation problem. The boundary value problems are then solved separately and combined to resolve all unknowns. The complete solutions of the velocity potentials are represented by the series of eigen-functions, and the surge motion of the structure is described in terms of the incident wave properties.The analytical solution is compared with a computer-coded numerical solution utilizing the boundary element method. The solutions agree very well, and both predict a resonant frequency for a specific structure which is different from the natural frequency of the structure due to the presence of the evanescent waves caused by the structure. 相似文献
98.
An extensive experimental and computational investigation of the combined and separate effects of free surface and body on the lift characteristics of a pair of fins attached to a strut and fin alone is conducted. The results reveal that the free-surface effect becomes significant when the depth of submergence to chord ratio (H/c) is less than three. The effect of the strut is also realized for shallower depth of submergence of the fins through free-surface deformation leading to a significant change in the incidence angle of the flow to the fins. The numerical results based on the Higher Order Boundary Element Method with the linearized free-surface condition show good agreement with the experimental results for fin (foil) alone even at shallow submergence, but some discrepancies appear for the fin attached to the strut at higher speeds mostly due to the neglect of the nonlinear free-surface effect. 相似文献
99.
100.
本文研究了虾蟹海产品香味的前体物质在加热前后的变化。实验结果表明:对虾和蟹肌肉中的糖原和不饱和脂肪酸在加热前后含量下降,糖原是Maillard反应的基础物质.不饱和脂肪酸是虾蟹肌肉香味中羰基化合物的前体物质。虾蟹肌肉中主要积累的核苷酸成分AMP在加热后减少,而肌肉提取物中的游离氨基酸和结合氨基酸,特别是疏水氨基酸含量均增加。 相似文献