全文获取类型
收费全文 | 2531篇 |
免费 | 433篇 |
国内免费 | 462篇 |
专业分类
测绘学 | 509篇 |
大气科学 | 181篇 |
地球物理 | 447篇 |
地质学 | 1283篇 |
海洋学 | 307篇 |
天文学 | 20篇 |
综合类 | 253篇 |
自然地理 | 426篇 |
出版年
2024年 | 11篇 |
2023年 | 26篇 |
2022年 | 110篇 |
2021年 | 125篇 |
2020年 | 120篇 |
2019年 | 145篇 |
2018年 | 113篇 |
2017年 | 143篇 |
2016年 | 138篇 |
2015年 | 149篇 |
2014年 | 157篇 |
2013年 | 216篇 |
2012年 | 159篇 |
2011年 | 208篇 |
2010年 | 174篇 |
2009年 | 170篇 |
2008年 | 152篇 |
2007年 | 150篇 |
2006年 | 155篇 |
2005年 | 112篇 |
2004年 | 96篇 |
2003年 | 87篇 |
2002年 | 82篇 |
2001年 | 70篇 |
2000年 | 63篇 |
1999年 | 59篇 |
1998年 | 34篇 |
1997年 | 31篇 |
1996年 | 43篇 |
1995年 | 21篇 |
1994年 | 32篇 |
1993年 | 16篇 |
1992年 | 10篇 |
1991年 | 3篇 |
1990年 | 16篇 |
1989年 | 12篇 |
1988年 | 2篇 |
1987年 | 6篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1982年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有3426条查询结果,搜索用时 15 毫秒
1.
探讨用遗传算法对数学模型进行优化。考虑到控制系统稳健性的要求 ,用遗传算法寻找出控制系统最佳稳定域 ,实现控制系统数学模型的寻优。阐述了用遗传算法求解问题的步骤和参数的取值 ,并用仿真实验对优化结果进行了检验。结果表明 :在控制系统数学模型的优化中 ,遗传算法具有其他算法无可比拟的优越性。 相似文献
2.
优化发电能源结构的初探 总被引:1,自引:0,他引:1
程地卫 《成都信息工程学院学报》2001,16(1):41-45
从我国电力工业发展的角度,浅析了国内外发电能源结构及其变化趋势,作者认为优化我国发电能源结构、采取必要的技术措施,是实现我国电力 工业可持续发的重要途径。 相似文献
3.
Boli basin, between Yishu fracture belt and Dunmi fracture belt, is the biggest Mesozoic coal basin in the east of Heilongjiang Province. Now it is a fault - fold remnant basin. The basin' s shape is generally consistent with the whole distribution of the cover folds, an arc protruding southwards. The basement of the basin can be divided into three fault blocks or structural units. The formation and evoluation of the basin in Mesozoic was determined by the basement fault blocks' displacement features rusulted from by the movement of the edge faults and the main basement faults. 相似文献
4.
Prediction of Stellar Atmospheric Parameters using Instance-Based Machine Learning and Genetic Algorithms 总被引:1,自引:0,他引:1
In this article we present a method for the automated prediction of stellar atmospheric parameters from spectral indices.
This method uses a genetic algorithm (GA) for the selection of relevant spectral indices and prototypical stars and predicts
their properties, using the k-nearest neighbors method (KNN). We have applied the method to predict the effective temperature,
surface gravity, metallicity, luminosity class and spectral class of stars from spectral indices. Our experimental results
show that the feature selection performed by the genetic algorithm reduces the running time of KNN up to 92%, and the predictive
accuracy error up to 35%.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
5.
基于可靠度理论的黄土高边坡优化设计 总被引:11,自引:2,他引:9
对黄土高边坡进行可靠性分析,应用数学原理和优化原理,建立了黄土高边坡的优化模型,对铜黄一级公路黄土高边坡进行分析验证。结果表明,该方法计算的结果与实际较接近.应用中易操作。 相似文献
6.
国家重大科学工程项目LAMOST总控系统的程序设计是一个庞大的软件工程.其总控系统下共包括8个既相互独立又互有关联的子系统.如何通过良好的软件设计方法来处理好这8个子系统之间的关系使其协调运转,以及如何确保软件开发的可维护性、可持续性是研究重点. 相似文献
7.
8.
A modified method of mine tremors location used in Lubin Copper Mine is presented in the paper. In mines where an intensive exploration is carried out a high accuracy source location technique is usually required. The effect of the flatness of the geophones array, complex geological structure of the rock mass and intense exploitation make the location results ambiguous in such mines. In the present paper an effective method of source location and location's error evaluations are presented, combining data from two different arrays of geophones. The first consists of uniaxial geophones spaced in the whole mine area. The second is installed in one of the mining panels and consists of triaxial geophones. The usage of the data obtained from triaxial geophones allows to increase the hypocenter vertical coordinate precision. The presented two-step location procedure combines standard location methods: P-waves directions and P-waves arrival times. Using computer simulations the efficiency of the created algorithm was tested. The designed algorithm is fully non-linear and was tested on the multilayered rock mass model of the Lubin Copper Mine, showing a computational better efficiency than the traditional P-wave arrival times location algorithm. In this paper we present the complete procedure that effectively solves the non-linear location problems, i.e. the mine tremor location and measurement of the error propagation. 相似文献
9.
10.
Fuzzy Optimum Model of Semi-Structural Decision for Lectotype Optimization of Offshore Platforms 总被引:8,自引:0,他引:8
In the process of concept design of offshore platforms, it is necessary to select the best from feasible alternatives through comparison and filter. The criterion set, used to evaluate and select the satisfying alternative, consists of many qualitative and quantitative factors. Therefore, the selection is a problem of multicriteria and semi- structural decision- making. Different from traditional methods in semi- structural decision- making, a new framework and methodology is presented in this paper for evaluation of offshore platform alternatives. First, the criterion set is established for the evaluation of alternatives. Next, the approach is studied to construct the relative membership degree matrix, in which both qualitative and quantitative factors are consistent with the uniform calculating standard. And then a new weight-assessing method is developed for calculation of the weights based on the relative membership degree matrix. Finally, a multi-hierarchy fuzzy optimum model is adopted to select t 相似文献