全文获取类型
收费全文 | 37933篇 |
免费 | 6393篇 |
国内免费 | 8042篇 |
专业分类
测绘学 | 2816篇 |
大气科学 | 7357篇 |
地球物理 | 9943篇 |
地质学 | 18107篇 |
海洋学 | 4189篇 |
天文学 | 1719篇 |
综合类 | 3773篇 |
自然地理 | 4464篇 |
出版年
2024年 | 175篇 |
2023年 | 579篇 |
2022年 | 1489篇 |
2021年 | 1775篇 |
2020年 | 1397篇 |
2019年 | 1661篇 |
2018年 | 2202篇 |
2017年 | 1993篇 |
2016年 | 2161篇 |
2015年 | 1820篇 |
2014年 | 2170篇 |
2013年 | 2034篇 |
2012年 | 2505篇 |
2011年 | 2362篇 |
2010年 | 2174篇 |
2009年 | 2051篇 |
2008年 | 1901篇 |
2007年 | 1792篇 |
2006年 | 1435篇 |
2005年 | 2027篇 |
2004年 | 1784篇 |
2003年 | 1558篇 |
2002年 | 1066篇 |
2001年 | 1008篇 |
2000年 | 1125篇 |
1999年 | 1495篇 |
1998年 | 1193篇 |
1997年 | 1141篇 |
1996年 | 1048篇 |
1995年 | 910篇 |
1994年 | 789篇 |
1993年 | 712篇 |
1992年 | 565篇 |
1991年 | 459篇 |
1990年 | 340篇 |
1989年 | 315篇 |
1988年 | 271篇 |
1987年 | 154篇 |
1986年 | 143篇 |
1985年 | 97篇 |
1984年 | 99篇 |
1983年 | 76篇 |
1982年 | 65篇 |
1981年 | 59篇 |
1980年 | 44篇 |
1979年 | 34篇 |
1978年 | 12篇 |
1977年 | 12篇 |
1976年 | 9篇 |
1958年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
102.
103.
Frequency-selective attenuation of sound propagaion and reverberation in shallow waterTXFrequency-selectiveattenuationofsoundp... 相似文献
104.
105.
Despite the fact that BaP is a carcinogen, mammalian immunosuppressant, and ubiquitous aquatic pollutant, knowledge regarding the effects of BaP on the immune system of fish is still lacking. To begin to fill this gap, studies were conducted in medaka to examine the effects and mechanisms by which BaP exposure might alter host immunocompetence. Fish, exposed by IP injection of BaP (2-600 microg/g BW), were examined after 48 h for effects upon immune function and CYP1A expression/activity. Benzo[a]pyrene, at a concentration below that which increased levels of CYPIA expression/activity (2 microg BaP/g BW) suppressed lymphocyte proliferation. Concentrations of BaP at 20 and 200 microg/g BW. suppressed antibody-forming cell (AFC) numbers, superoxide production, and host resistance against bacteria. In contrast, exposure to the low affinity aryl hydrocarbon receptor (AhR) agonist, benzo[e]pyrene (BeP), neither induced CYP1A expression nor altered immune function. Given the lack of immunosuppressive effects produced by BeP, and the fact that exposure to the AhR antagonist (and CYP1A inhibitor) alpha-naphthoflavone (ANF) ameliorated the suppressive effects of BaP upon AFC numbers, the AhR pathway (including CYP1A-mediated production of reactive BaP metabolites) appears important in mediating BaP-induced immunotoxicity in fish, as in mammals. In the past, the medaka has proven a successful model for assessing carcinogenic agents. These studies have demonstrated its utility for also determining the immunosuppressive effects of an important aquatic contaminant. 相似文献
106.
107.
SeaWiFS航空模拟器(SAS)是专门为在水面之上测量水体表观光学参数的现场设备。文章在介绍SAS现场测量以及数据处理基本方法的基础上,分析了2002年黄海试验SAS的应用效果,并与剖面法测量数据进行了比对。 相似文献
108.
Beach profiles have been observed to change over a range of spatial and temporal scales; however techniques for quantifying this variability have not been fully established. In this paper, a wavelet technique is introduced as a method to study the multi-scale variability of beach profiles. The beach profile data comprising a 22-year time series surveyed at the US Army Corps of Civil Engineers Field Research Facility (FRF) at Duck are analysed using the adapted maximal overlap discrete wavelet transform (AMODWT). The analysis successfully identifies strong local features in the variability of beach profiles in time and space separately that cannot be isolated by traditional statistical methods. The analysis of spatial wavelet variances provides a new means of investigating the depth of closure. Analysis of variances by temporal scales shows that the combined effects of several temporal scales with one or two dominant scales can be seen at particular points across profiles whilst the dominant temporal scales are different at different portions of the profiles. The method allows for the extremely nonstationary behaviour of beach profile to be analysed into separate frequency bands that can facilitate the interpretation of morphological changes in terms of physical processes. 相似文献
109.
Li Naisheng 《海洋学报(英文版)》1994,13(2):285-296
NotesTheOceanDrillingProgram(ODP)mNowadays,withpopulationincreasingandnaturalresourcesforhumanbeingsdecreasing,scientistsmust... 相似文献
110.
A Preliminary Study of Shear Wave in Seafloor Surface Sediments 总被引:1,自引:0,他引:1
This article preliminarily reports and analyses the transmission characteristics and behaviors of shear wave in the offshore seafloor surface sediments in China, discusses the relationships between the physical and mechanical features of the shear wave and the compression wave, and compares the testing results with that of Hamilton and Chen et al. The result shows that the shear wave can be tested if the seafloor surface sediment has tangent modulus. The shear wave velocity ranges from 50-600 m/s and the measuring frequency from 50-200 kHz. The sound velocity rate of shear wave and compression wave can be used to appraise the stress-strain feature of seafloor surface sediments. This study provides a basis for further describing and appraising the seafloor sedimentary acoustic-mechanical feature and building a geological-acoustic model on China's offshore sea area. 相似文献