全文获取类型
收费全文 | 3318篇 |
免费 | 536篇 |
国内免费 | 451篇 |
专业分类
测绘学 | 1333篇 |
大气科学 | 304篇 |
地球物理 | 863篇 |
地质学 | 816篇 |
海洋学 | 328篇 |
天文学 | 35篇 |
综合类 | 419篇 |
自然地理 | 207篇 |
出版年
2024年 | 8篇 |
2023年 | 33篇 |
2022年 | 115篇 |
2021年 | 133篇 |
2020年 | 138篇 |
2019年 | 231篇 |
2018年 | 126篇 |
2017年 | 214篇 |
2016年 | 186篇 |
2015年 | 197篇 |
2014年 | 189篇 |
2013年 | 218篇 |
2012年 | 242篇 |
2011年 | 243篇 |
2010年 | 168篇 |
2009年 | 215篇 |
2008年 | 217篇 |
2007年 | 231篇 |
2006年 | 220篇 |
2005年 | 165篇 |
2004年 | 156篇 |
2003年 | 124篇 |
2002年 | 102篇 |
2001年 | 72篇 |
2000年 | 70篇 |
1999年 | 61篇 |
1998年 | 53篇 |
1997年 | 36篇 |
1996年 | 30篇 |
1995年 | 25篇 |
1994年 | 23篇 |
1993年 | 15篇 |
1992年 | 14篇 |
1991年 | 4篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1954年 | 2篇 |
排序方式: 共有4305条查询结果,搜索用时 15 毫秒
911.
912.
Akihiko Tanaka Motoaki Kishino Roland Doerffer Helmut Schiller Tomohiko Oishi Tadashi Kubota 《Journal of Oceanography》2004,60(3):519-530
An algorithm is presented to retrieve the concentrations of chlorophyll a, suspended pariclulate matter and yellow substance
from normalized water-leaving radiances of the Ocean Color and Temperature Sensor (OCTS) of the Advanced Earth Observing Satellite
(ADEOS). It is based on a neural network (NN) algorithm, which is used for the rapid inversion of a radiative transfer procedure
with the goal of retrieving not only the concentrations of chlorophyll a but also the two other components that determine the water-leaving radiance spectrum. The NN algorithm was tested using the
NASA's SeaBAM (SeaWiFS Bio-Optical Mini-Workshop) test data set and applied to ADEOS/OCTS data of the Northwest Pacific in
the region off Sanriku, Japan. The root-mean-square error between chlorophyll a concentrations derived from the SeaBAM reflectance data and the chlorophyll a measurements is 0.62. The retrieved chlorophyll a concentrations of the OCTS data were compared with the corresponding distribution obtained by the standard OCTS algorithm.
The concentrations and distribution patterns from both algorithms match for open ocean areas. Since there are no standard
OCTS products available for yellow substance and suspended matter and no in situ measurements available for validation, the result of the retrieval by the NN for these two variables could only be assessed
by a general knowledge of their concentrations and distribution patterns.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
913.
自适应遗传算法解决集装箱装载问题的方法探讨 总被引:8,自引:0,他引:8
集装箱装箱问题是1个有很强应用背景的组合优化问题,约束条件多,求解极为困难。本文探讨了自适应遗传算法在复杂集装箱装载问题中的应用,算法中采用跨世纪精英选择策略保持了群体的多样性,并给出了有效的解码算法。实例仿真结果显示出很好的效果,同等条件下求解结果比使用启发式算法高出近10个百分点,表明该算法是行之有效的。 相似文献
914.
作者讨论矩阵方程 ATX+ XTA=B。该方程在 Hamilton力学研究中有用。首先利用L yapunov方程证明了极小 Frobenius范数解的存在性和惟一性。然后用奇异值分解给出了求解最小范数解的一种方法。最后讨论极小范数解的向前扰动分析和最佳向后扰动分析 相似文献
915.
Identification of modal parameters of a linear structure with output-only measurements has received much attention over the past decodes. In the paper, the Natural Excitation Technique (NEXT) is used for acquisition of the impulse signals from the structural responses. Then Eigensystem Realization Algorithm (ERA) is utilized for modal identification.For disregarding the fictitious ‘computational modes’, a procedure, Statistically Averaging Modal Frequency Method (SAMFM), is developed to distinguish the true modes from noise modes, and to improve the precision of the identified modal frequencies of the structure. An offshore platform is modeled with the finite element method. The theoretical modal parameters are obtained for a comparison with the identified values. The dynamic responses of the platform under random wave loading are computed for providing the output signals used for identification with ERA. Results of simulation demonstrate that the proposed method can determine the system modal frequency with high precision. 相似文献
916.
917.
本文提出了一种基于 TMS32 0 C31串行接口的双通道实时数据采集处理系统的设计与实现方案 ,该设计以 TMS32 0 C31和 TL C32 0 AD5 0 C为核心器件 ,具有两个独立的 A/D,D/A通道 ,能够实现 32位浮点计算和 16位数据采集与回放。应用该系统进行归一化最小均方误差 (Normal-ized L east Mean Square,NLMS)算法实时自适应噪声抵消实验 ,实验结果表明 ,该系统能够实现实时的自适应噪声抵消 ,可广泛应用于实时语音信号处理等领域。 相似文献
918.
凸包计算是计算几何研究中的基本问题之一 ,在许多领域均有应用。本文对求解空间点集凸包的卷包裹算法的实现问题进行了讨论。提出了 2点优化措施 ,并解决了实现中可能出现的共面点及由此带来的退化问题。 相似文献
919.
The concept of candidate particle set is introduced in the MPS gridless numerical method to generate neighboring particle set matrix, which can reduce the CPU time to 1/11 of that before introduction. The Bi-CGSTAB (bi-conjugate gradient stabilized) algorithm is applied to solving the Poisson pressure equation, by which the solving speed is significantly accelerated. The process of solitary waves propagating over a numerical flume and interacting with a vertical wall is simulated. The simulated results of water surface elevation are in good agreement with the analytical solution as well as the measured data. The predicted maximum values of the run-up of solitary waves with various relative incident wave heights agree well with the measured results. 相似文献
920.
In conventional slowness-time coherence(STC)method,slowness and time need to be searched at the same time,which limits the precision and lowers the efficiency.The dichotomy method combined with slowness-time coherence algorithm aims to enhance the efficiency of data processing and to improve the precision.The algorithm changes the searching pattern of conventional slowness-time coherence method to acquire the slowness of component waves in array acoustic logging data.Based on energy ratio of short time window versus long time window and slowness-time coherence method,the algorithm first acquires the arrivals of the component waves using energy ratio of short time window versus long time window method.It then uses the calculated results as the arrivals in conventional slowness-time coherence method,so the slowness-time two-dimensional searching process is simplified to slowness searching process.Based on dichotomy method,the searching pattern is further optimized in replace of the ergodic searching pattern in conventional slowness-time coherence method,which means that as the iteration proceeds,the current searching interval is reduced to half of the former,so the number of searching times is decreased.The dichotomy method combined with slowness-time coherence algorithm is applied to well L in the data processing.Compared with conventional slowness-time coherence method,for compressional wave,the searching efficiency of the algorithm is 4.53 times better,while for Stoneley wave,the searching efficiency is 1.85 times better.Compared with conventional logging data,the average absolute error of the results of the dichotomy method combined with slowness-time coherence algorithm is 1.14μs/ft smaller than that of the conventional method,while the average relative error is 1.2 percent lower.The dichotomy method combined with slowness-time coherence algorithm shows good results in its application,which can enhance the processing efficiency remarkably while getting reliable results at the same time. 相似文献