全文获取类型
收费全文 | 591篇 |
免费 | 36篇 |
国内免费 | 145篇 |
专业分类
测绘学 | 13篇 |
大气科学 | 38篇 |
地球物理 | 243篇 |
地质学 | 299篇 |
海洋学 | 88篇 |
天文学 | 26篇 |
综合类 | 22篇 |
自然地理 | 43篇 |
出版年
2024年 | 3篇 |
2023年 | 5篇 |
2022年 | 6篇 |
2021年 | 11篇 |
2020年 | 3篇 |
2019年 | 7篇 |
2018年 | 9篇 |
2017年 | 6篇 |
2016年 | 8篇 |
2015年 | 13篇 |
2014年 | 22篇 |
2013年 | 14篇 |
2012年 | 17篇 |
2011年 | 37篇 |
2010年 | 12篇 |
2009年 | 15篇 |
2008年 | 47篇 |
2007年 | 31篇 |
2006年 | 38篇 |
2005年 | 42篇 |
2004年 | 42篇 |
2003年 | 29篇 |
2002年 | 34篇 |
2001年 | 21篇 |
2000年 | 39篇 |
1999年 | 26篇 |
1998年 | 17篇 |
1997年 | 8篇 |
1996年 | 8篇 |
1995年 | 17篇 |
1994年 | 15篇 |
1993年 | 27篇 |
1992年 | 15篇 |
1991年 | 14篇 |
1990年 | 13篇 |
1989年 | 19篇 |
1988年 | 10篇 |
1987年 | 6篇 |
1986年 | 9篇 |
1985年 | 10篇 |
1984年 | 11篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1980年 | 11篇 |
1957年 | 2篇 |
1954年 | 1篇 |
1939年 | 1篇 |
1935年 | 1篇 |
1924年 | 2篇 |
排序方式: 共有772条查询结果,搜索用时 15 毫秒
171.
172.
A ROBUST PLS PROCEDURE 总被引:1,自引:0,他引:1
A robust partial least squares(PLS)regression algorithm is developed.This is achieved by substitutionof the univariate regression steps in the iterative PLS2 algorithm by a robust alternative.The anglebetween loading vectors from both perturbed and unperturbed solutions is used as a measure ofrobustness.By means of a perturbation study on a structure-activity data set,it is demonstrated thatthe stability of the robust method is superior to standard PLS. 相似文献
173.
本文描述了一个高分辨率气团变性(AMT)模式。该模式试图对低层大气的温度、湿度廓线,边界层结构、边界层高度、云量进行预报。它由一个一维多层边界层模式组成,多层模式沿着轨迹从气团源区平移至接收点,轨迹是在一较大尺度(有限区域)模式中计算出。温度和湿度的初始廓线从探空仪资料获得。本文描述了此模式的物理和动力学背景。用此模式作了北海上空层积云发展的个例研究,并且我们模拟了陆上晴空的表达。把此模式的输出结果 ECMWF 模式和目前业务中用的单层气团变性模式的输出结果进行了比较。还讨论了模式对初始、边界条件的敏感性。除个例研究外,在77次常规预报中采用此模式作为业务预报工具,其结果由彼此独立的预报员作了评价,因模式执行情况良好,且不须大型计算设备,因此,对短期天气预报员该模式是一个有用的预报工具。 相似文献
174.
对地中海带研究区段内形态-运动学特征、产生的构造层次、时空关系以及推覆体形成机理的研究,可得出如下结论:(1)构造推覆体可划分为如下类型:(a)拆离的基底推覆体,包括内Carpathian推覆体(Tatricium,包括Lesser Carpathians,Veporikan,Gemerikum)、中东Garpathian推覆体、北Apuseni的Come推覆体(Bibaria和kodru推覆体体系和Arieseroi推覆体)、Rhodop地块的Crystalliihicum推覆体岩 相似文献
175.
Ю.A.KOCЬIГИH 《国外地质(北京)》1990,(1):45-47
行星的磁力和热力特性同行星的旋转之间存在着相关性,应通过专门观察和理论研究的途径来确定这一相关关系。这些研究是必要的,因为可以在实质上帮助理解在地球物理与宇宙作用的关系方面构造运动发生的原因。 相似文献
176.
BOUNDARY LAYER GROWTH AND LAPSE RATE CHANGES DETERMINED BY LIDAR AND SURFACE HEAT FLUX IN SOFIA*
下载免费PDF全文
![点击此处可从《Acta Meteorologica Sinica》网站下载免费的PDF全文](/ch/ext_images/free.gif)
In this study the results from a boundary layer experiment,conducted in autumn 1991 over a flat,build-up urban area in Southeast Sofia,together with some models for mixed layer growth rates are used to investigate the layered structure of the vertical atmospheric stability distribution in the Sofia Valley.Lidar measurements of aerosol layer heights and morning boundary layer development are combined with surface eddy correlation measurements of kinematic heat and moisture fluxes,profiles of temperature and humidity,wind speed and wind direction.A diagnostic method is presented for determining vertical lapse rates using surface meteorological measurements and lidar returns observed during the transition from nighttime stable stratification to daytime convective boundary layer after the sunrise. 相似文献
177.
Photochemistry of giant planets and their satellites is characterized by numerous reactions involving many chemical species. In the present paper, chemical systems are modeled by signal flow graphs. Such a technique evaluates the transmission of any input into the system (solar flux, electrons...) and gives access to the identification of the most important mechanisms in the chemical system. For a given chemical system, we first evaluate rate coefficients. Then, in order to obtain concentrations of each compound, we integrate the set of continuity equations by Gear's method. Gear's method is chosen rather than another classical method because it is recommended for a system of stiff equations due to the existence of greatly differing time constants. Finally, the technique of signal flow graphs is used. This method is applied to the production of hydrocarbons in the atmospheres of giant planets. In particular, the production of C2H6 in the atmosphere of Neptune from the photodissociation of CH4 is investigated. Different paths of dissociation of CH4 are possible from L alpha radiations. A chemical system containing 14 species and 30 reactions including these different paths of dissociation is integrated. The main mechanism of production of C2H6 is identified and evaluated for each model of dissociation. The importance of various reaction paths as a function of time is discussed. 相似文献
178.
"This paper analyses population change in the Belfast Urban Area (BUA) [of Northern Ireland] between 1971 and 1991 in its socio-economic context to understand the nature of urban social change. Although considering religious factors as a cause of population change, the research compares the BUA with other urban areas and relates developments in Belfast to some literature on sociospatial polarisation and the ?underclass'.... The results suggest that population change is not driven by explicitly religious factors, the relationship between religion and socio-economic well-being has changed, and that changes in religious mixing and segregation occur in many contexts. The BUA is like other urban areas, albeit with unique features arising from the influence of religion." 相似文献
179.
Induction of zona radiata and vitellogenin genes in estradiol and nonylphenol exposed male sheepshead minnows (Cyprinodon variegatus) 总被引:1,自引:0,他引:1
Several genes normally induced by estradiol (E(2)) in female fish, those for vitellogenins (VTGs) and zona radiata proteins (ZRPs), are also inducible in males exposed to estrogenic chemicals. Male sheepshead minnows (SHM) were exposed to both E(2) and para-nonylphenol (NP), at several doses and times to determine a dose-response. Quantitative real time PCR was used to measure mRNA for VTG1, VTG2, ZRP2 and ZRP3. Both E(2) and NP elicited a dose-response increase in all of the mRNAs tested. Exposure to both chemicals resulted in VTG2 expression at about a 10-fold lower level than VTG1, and ZRP2 expression at a lower level than ZRP3. 相似文献
180.
一、引言 食用海鱼乃为人类从食物中摄入汞、特别是剧毒甲基汞的重要来源。不管被捕捞的海区是否受汞污染,鱼体内常含有占总汞量80—100%的甲基汞。海洋环境中的甲基汞或来源于工业废水或由自然的甲基化作用所合成。鱼能从海水和食物中积累甲基汞,但本身并不能使无机汞甲基化。甲基汞仅在有严重汞污染历史的日本水俣湾检出过。主要是在已知受汞污染地区的一些沉积物中发现有汞,然而浓度很低。有机汞一般占沉积物中总汞的1%以下,但实际上,常常少于0.1%。有人认为沉积物 相似文献