全文获取类型
收费全文 | 13469篇 |
免费 | 1677篇 |
国内免费 | 2054篇 |
专业分类
测绘学 | 1238篇 |
大气科学 | 1112篇 |
地球物理 | 1564篇 |
地质学 | 5250篇 |
海洋学 | 1278篇 |
天文学 | 5386篇 |
综合类 | 659篇 |
自然地理 | 713篇 |
出版年
2024年 | 30篇 |
2023年 | 100篇 |
2022年 | 295篇 |
2021年 | 313篇 |
2020年 | 395篇 |
2019年 | 419篇 |
2018年 | 365篇 |
2017年 | 369篇 |
2016年 | 390篇 |
2015年 | 464篇 |
2014年 | 762篇 |
2013年 | 797篇 |
2012年 | 844篇 |
2011年 | 929篇 |
2010年 | 935篇 |
2009年 | 1203篇 |
2008年 | 1129篇 |
2007年 | 1065篇 |
2006年 | 1008篇 |
2005年 | 892篇 |
2004年 | 747篇 |
2003年 | 621篇 |
2002年 | 510篇 |
2001年 | 466篇 |
2000年 | 393篇 |
1999年 | 372篇 |
1998年 | 290篇 |
1997年 | 151篇 |
1996年 | 161篇 |
1995年 | 126篇 |
1994年 | 113篇 |
1993年 | 127篇 |
1992年 | 61篇 |
1991年 | 53篇 |
1990年 | 48篇 |
1989年 | 43篇 |
1988年 | 34篇 |
1987年 | 18篇 |
1986年 | 22篇 |
1985年 | 23篇 |
1984年 | 20篇 |
1983年 | 15篇 |
1982年 | 16篇 |
1981年 | 7篇 |
1980年 | 11篇 |
1978年 | 6篇 |
1977年 | 19篇 |
1973年 | 4篇 |
1972年 | 3篇 |
1971年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
选取2011-03-11日本MW9.3地震后全球地震台站记录的约220 h波形数据,基于一定的判断准则,筛选出质量较高的448个垂向观测数据,采用频域AR方法对0S0模态的特征频率和品质因子进行估值,并以信噪比为权重进行加权平均,得到特征频率f=0.814 658 4±5.3×10-7,品质因子Q=5 586±12。该结果与已有研究成果相比精度更高,有助于约束现有地球介质密度和衰减模型,使其更接近真实地球。 相似文献
42.
几丁质酶(chitinase)在甲壳动物的蜕皮、消化和免疫等很多生物学过程中发挥重要功能,为深入探讨几丁质酶的免疫防御机制,本实验利用RACE技术克隆了三疣梭子蟹(Portunus trituberculatus)PtCht6基因。该基因cDNA全长2736bp,开放阅读框(ORF)2103bp,编码700个氨基酸,具有几丁质酶GH18家族典型特征。利用实时荧光定量技术分析PtCht6在三疣梭子蟹不同组织、不同蜕皮阶段、不同病原感染以及低盐胁迫(11)下的表达特征,结果显示:PtCht6在各组织中均有表达且在肝胰腺中的表达量最高;在不同蜕皮时期的肝胰腺中,其表达量由蜕皮后期(A/B)、蜕皮间期(C)、蜕皮前期(D)依次递减(P0.05);人工感染WSSV和副溶血弧菌后.PtCht6的表达量在肝胰腺中分别于12h、72h达到最大值,在血细胞中均于12h达到最大值,且相较于对照组,整体显著上调表达(P0.05);低盐胁迫能够显著抑制该基因的表达,最高抑制73倍(P0.05)。同时发现,低盐环境下感染WSSV后,该基因达到峰值的时间明显延迟(至少延迟12h.P0.05)。该研究结果预示PtCht6作为免疫因子参与三疣梭子蟹的病原防御,且低盐胁迫在一定程度上抑制了该基因的免疫功能。 相似文献
43.
44.
为实现地磁台站场地勘选指标的快速计算和勘选报告的在线保存与查询,提高地磁台站勘选数据处理效率,降低人工处理数据错误率,在现有地磁数据处理软件功能的基础上设计开发地磁台站勘选数据处理系统,以提高勘选的工作效率。 相似文献
45.
Michael Dentith Randolph J. Enkin William Morris Cameron Adams Barry Bourne 《Geophysical Prospecting》2020,68(1):178-199
As mineral exploration seeks deeper targets, there will be a greater reliance on geophysical data and a better understanding of the geological meaning of the responses will be required, and this must be achieved with less geological control from drilling. Also, exploring based on the mineral system concept requires particular understanding of geophysical responses associated with altered rocks. Where petrophysical datasets of adequate sample size and measurement quality are available, physical properties show complex variations, reflecting the combined effects of various geological processes. Large datasets, analysed as populations, are required to understand the variations. We recommend the display of petrophysical data as frequency histograms because the nature of the data distribution is easily seen with this form of display. A petrophysical dataset commonly contains a combination of overlapping sub-populations, influenced by different geological factors. To understand the geological controls on physical properties in hard rock environments, it is necessary to analyse the petrophysical data not only in terms of the properties of different rock types. It is also necessary to consider the effects of processes such as alteration, weathering, metamorphism and strain, and variables such as porosity and stratigraphy. To address this complexity requires that much more supporting geological information be acquired than in current practice. The widespread availability of field portable instruments means quantitative geochemical and mineralogical data can now be readily acquired, making it unnecessary to rely primarily on categorical rock classification schemes. The petrophysical data can be combined with geochemical, petrological and mineralogical data to derive explanations for observed physical property variations based not only on rigorous rock classification methods, but also in combination with quantitative estimates of alteration and weathering. To understand how geological processes will affect different physical properties, it is useful to define three end-member forms of behaviour. Bulk behaviour depends on the physical properties of the dominant mineral components. Density and, to a lesser extent, seismic velocity show such behaviour. Grain and texture behaviour occur when minor components of the rock are the dominate controls on its physical properties. Grain size and shape control grain properties, and for texture properties the relative positions of these grains are also important. Magnetic and electrical properties behave in this fashion. Thinking in terms of how geological processes change the key characteristics of the major and minor mineralogical components allows the resulting changes in physical properties to be understood and anticipated. 相似文献
46.
We present a new approach to enhancing weak prestack reflection signals without sacrificing higher frequencies. As a first step, we employ known multidimensional local stacking to obtain an approximate ‘model of the signal’. Guided by phase spectra from this model, we can detect very weak signals and make them visible and coherent by ‘repairing’ corrupted phase of original data. Both presented approaches – phase substitution and phase sign corrections – show good performance on complex synthetic and field data suffering from severe near-surface scattering where conventional processing methods are rendered ineffective. The methods are mathematically formulated as a special case of time-frequency masking (common in speech processing) combined with the signal model from local stacking. This powerful combination opens the avenue for a completely new family of approaches for multi-channel seismic processing that can address seismic processing of land data with nodes and single sensors in the desert environment. 相似文献
47.
This paper presents an experimental study on the performance of a shear-sliding stud-type damper composed of multiple friction units with high-tension bolts and disc springs. A numerical evaluation of the response reduction effects achieved by the stud-type damper is also presented. In dynamic loading tests, the behavior of stud-type multiunit friction damper specimens was investigated. Three different full-scale damper specimens, which were composed of five, six, or seven friction units with two or four sliding surfaces, were incorporated into loading devices for testing. The stud-type friction dampers demonstrated stable rigid-plastic hysteresis loops without any remarkable decrease in the sliding force even when subjected to repetitive loading, in addition to showing no unstable behavior such as lateral buckling. The damper produced a total sliding force approximately proportional to the number of sliding surfaces and friction units. The total sliding force of the stud-type damper can thus be estimated by summing the contributions of each friction unit. In an earthquake response simulation, the control effects achieved by stud-type dampers incorporated into an analytical high-rise building model under various input waves, including long-period, long-duration and pulse-like ground motions, were evaluated. A satisfactory response reduction was obtained by installing the developed stud-type dampers into the main frame without negatively impacting usability and convenience in terms of building planning. 相似文献
48.
河北怀安朱家洼矿区位于华北板块北缘中段太古宙、元古宙、中生代金银铅锌铁硫铁矿成矿带,为火山热液型金多金属矿。为查明该区成矿规律,明确找矿方向,在区内开展了水系沉积物测量、土壤地球化学测量等工作。通过对元素分布、元素相关性、元素异常等特征研究表明,Au、Mo为本区主成矿元素;各元素异常平面分布具有分带性,高温元素W、Sn、Bi异常位于骆驼山火山机构中心,中低温元素Pb、Zn、As、Ag等异常分布于火山机构边部及周边围岩中,成矿元素Au、Mo异常主要位于火山机构西侧围岩中。异常查证发现金钼矿化体2条,金钼矿化受火山机构和北西向构造带控制。依据成矿地质条件、地球化学异常及查证成果认为,朱家洼矿区Au、Mo成矿潜力大,火山机构西侧围岩区是该区重点找矿地段。 相似文献
49.
在对渤海滨州贝壳堤岛的自由生活海洋线虫进行分类和多样性研究中,发现2个我国新纪录种并进行了描述。其中,澳洲深咽线虫Bathylaimus australis Cobb,1894主要特征为:头刚毛长约20μm,分为4节,顶端膨大;前口腔大,无齿,后口腔小,具小齿;化感器双环形,位于口腔中部位置;交接刺细长,稍向腹面弯曲,近端膨大呈头状,长32-37μm;引带宽大,肾形,长36-40μm,末端角质化,渐尖。古氏努朵拉线虫Nudora gourbaultae Vincx,1989主要特征为:体表具12列纵向排列的V型装饰;第二体环较宽,头刚毛11-15μm(为头颈的67%-81%);化感器圆形,直径4-6μm(为相应体径的29%-38%),位于第二体环上;具双咽球;交接刺细长,弯曲呈S型,长为肛径的1.3-1.5倍;引带等于或长于交接刺,镰刀型,无肛前辅器。 相似文献
50.
守初心耕海探洋七十载担使命披风踏浪砥砺行——中国科学院海洋研究所70年发展纪实 总被引:1,自引:0,他引:1
中国科学院海洋研究所是新中国第一个专门从事海洋科学研究的国立科研机构,她的70年光辉历程是我国海洋科技事业从无到有、从弱到强的发展缩影,是新中国海洋科学调查研究自主创新发展历程的真实写照。本文简要介绍中国科学院海洋研究所的主要发展历程,回顾70年来取得的主要科技成就,并围绕新形势下建设海洋大科学研究中心等改革发展举措,讨论和展望研究所的未来发展。 相似文献