全文获取类型
收费全文 | 5211篇 |
免费 | 861篇 |
国内免费 | 966篇 |
专业分类
测绘学 | 1783篇 |
大气科学 | 358篇 |
地球物理 | 673篇 |
地质学 | 2573篇 |
海洋学 | 570篇 |
天文学 | 91篇 |
综合类 | 507篇 |
自然地理 | 483篇 |
出版年
2024年 | 19篇 |
2023年 | 73篇 |
2022年 | 195篇 |
2021年 | 271篇 |
2020年 | 281篇 |
2019年 | 310篇 |
2018年 | 161篇 |
2017年 | 308篇 |
2016年 | 272篇 |
2015年 | 315篇 |
2014年 | 374篇 |
2013年 | 362篇 |
2012年 | 408篇 |
2011年 | 392篇 |
2010年 | 349篇 |
2009年 | 328篇 |
2008年 | 295篇 |
2007年 | 297篇 |
2006年 | 291篇 |
2005年 | 270篇 |
2004年 | 227篇 |
2003年 | 248篇 |
2002年 | 198篇 |
2001年 | 170篇 |
2000年 | 124篇 |
1999年 | 89篇 |
1998年 | 94篇 |
1997年 | 60篇 |
1996年 | 47篇 |
1995年 | 35篇 |
1994年 | 40篇 |
1993年 | 26篇 |
1992年 | 23篇 |
1991年 | 17篇 |
1990年 | 19篇 |
1989年 | 9篇 |
1988年 | 11篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 10篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1981年 | 1篇 |
1971年 | 1篇 |
1954年 | 2篇 |
排序方式: 共有7038条查询结果,搜索用时 328 毫秒
11.
本文报告一种用半导体激光器作光源,用子脉冲宽度100ns,长度为511的周期伪随机码对半导体激光器的输出作幅度调制;APD作光电检测器,高速数字信号处理器TMS320C25作信号处理的激光雷达组成方案和试作样机的实验结果。 相似文献
12.
吴秋凤 《广东海洋大学学报》2003,23(5):94-98
在阐述西部大开发中科技主导地位的基础上 ,从科技应用成效二重性的视角 ,探讨了关注西部科技伦理的必要性 ,并初步提出了西部大开发战略的科技伦理调控机制 相似文献
13.
基于CTI技术的守时系统故障报警实现 总被引:2,自引:0,他引:2
介绍了计算机电话集成(CTI-Computer Telephony Integration)技术在守时系统故障自动报警中的应用。简要介绍了构成报警系统的两个关键产品,电话语音卡和TTS(Text-To-Speech),详细讨论了ActiveX控件(Phonic.OCX)编程接口的一系列事件和方法以及由此而开发的故障报警模块。该模块不仅用于守时主系统的故障报警,也将用于电源系统、钟房环境监控系统的故障报警。 相似文献
14.
介绍了 2 0 0 1- 2 0 0 2年上海天文台卫星激光测距观测概况和亚厘米级精度的测距实验 相似文献
15.
EM技术在我国水环境保护中的应用研究进展 总被引:4,自引:0,他引:4
对EM技术在我国水环境保护中的应用情况进行了综述,重点介绍了EM技术应用于废水处理领域的研究进展,同时还展望了将来的应用及研究前景. 相似文献
16.
Techniques to measure grain-size distributions of loamy sediments: a comparative study of ten instruments for wet analysis 总被引:2,自引:0,他引:2
DIRK GOOSSENS 《Sedimentology》2008,55(1):65-96
Ten instruments for measuring the grain‐size distribution of loamy sediments in water were tested in a comparative study. Instruments tested were: the Malvern Mastersizer S, the Coulter LS 200, the Fritsch Analysette 22 (version C), the Horiba Partica LA‐950, the Sedigraph 5100, the Atterberg cylinder, the Coulter Multisizer 3, the CIS‐100, the EyeTech and the image analysis software Histolab. The first four instruments use laser diffraction. The Sedigraph and Atterberg cylinder are based on sedimentation. The Coulter Multisizer 3 uses impedance measurements and the last three instruments use optical techniques. Grain‐size analyses were carried out on four sediments with median grain diameters of approximately 35, 30, 12 and 9 μm, respectively, and with no particles >90 μm. The laser diffraction instruments produced the best results for the various criteria considered in this study, followed by the Coulter Multisizer 3 (electrical sensing zone technique), the sedimentation techniques and the optical methods. However, the study also showed that there is no such thing as an ‘ideal’ method because techniques may score differently according to the criterion tested. An appropriate evaluation thus requires that various criteria be considered. Issues to be taken into account are: type of sediment, quantity of sediment available, speed of measurement, complexity of the measurement protocol, processing of the data, reproducibility of the results and the specific aims of the study undertaken. 相似文献
17.
激光拉曼光谱法分析多种显微组分荧光变化及其应用 总被引:1,自引:1,他引:0
利用激发488 nm激光的氩离子激光器作为RENISHAW inVia型激光拉曼光谱仪的光源,建立了多种显微组分荧光变化(FAMM)分析方法,并对镜质体反射率明显抑制的东营凹陷有效烃源岩进行了测定。结果表明,东营凹陷有效烃源岩的有机质类型越好,镜质体反射率抑制程度越高,有效烃源岩的真实成熟度应主要处于0.64%~1.30%,而不是实测镜质体反射率所反映的0.37%~1.10%。 相似文献
18.
A. Wendy Russell 《Geoforum》2008,39(1):213-222
In this paper, I argue that genetically modified organisms (GMOs) have inherent potential to contribute to socially and environmentally sustainable agriculture by virtue of their ‘biological embeddedness’. Their actual ‘performance’ and how this contributes to sustainability depends on the ‘mutual shaping’ of technology and context. While much attention has been given to the design context of GMOs, this paper considers the influence of the application context and of users. A case study investigating the use of insect-resistant and herbicide-tolerant GM cotton in the cotton-growing region of New South Wales in Australia is presented. The study was based on focus groups with farmers and other stakeholders in a cotton-growing community. It demonstrated a range of direct and indirect effects of GM cotton use, both positive and negative for sustainability, and the ways in which these effects were influenced by the local social context. The influences of the biotechnology industry context, in limiting the contributions that gene technologies can make to sustainability, were also considered, and remedies suggested. I argue that the polarity of the GM debate is hindering progress on these issues, and that a more balanced approach to our analysis of GMOs is necessary in order to fully understand, and to influence, their role in the future of rural spaces. 相似文献
19.
Rosa Nappi Giuliana Alessio Giovanni Bronzino Carlo Terranova Giuseppe Vilardo 《Natural Hazards》2008,45(1):73-85
In this article the implementation and potential of the Seismotectonic Information System of the Campania Region (SISCam)
are described, in particular an application of this Web-based GIS system to the seismotectonic analysis of the Sannio area
(Southern Apennines) is performed. WEB-GIS technologies greatly contribute to both the environmental monitoring and the disaster
management of areas affected by high natural risks. Specifically the SISCam system has been developed with the aim of providing
easy access and fast diffusion, through Internet technology, of the most significant geological, geophysical, and territorial
data relative to the Campania Region. The Sannio area has been selected as our application example because it is among the
most active seismic regions in Italy. This portion of the Southern Apennines which was hit by the June 5, 1688 strong earthquake
(M
W = 6.7, CPTI 1999) and by some low- and moderate-energy seismic sequences (1990–1992, 1997), is characterized by a complex
inherited tectonic setting and low-tectonic deformation rates that hide the seismogenic sources position. Since this case
study turned out to be complicated, the use of the SIScam WEB-GIS has become indispensable because it allowed us to visualize,
integrate and analyze all the data available, in order to obtain an accurate and direct picture of the seismotectonic setting
of the area. Moreover, a different approach of data analysis was necessary, due to the lack of up-to-date neotectonic and
structural data; therefore, the operation of this GIS system enabled us to process and generate some original informative
layers, through image analysis, such as new structural lineaments represented on a map of the potential active faults of the
area, which has been the final result of our application, as a contribution to new knowledge about the local seismic risk
parameters. 相似文献
20.
激光粒度仪的广泛应用带来了与历史数据的对比问题,因此需要建立激光粒度仪与早期分析结果之间的关系。根据江苏海岸潮滩沉积物样品的激光粒度仪和移液管-筛析法分析,对粒度参数、粒度组分等进行了对比,对两种方法的差异进行了分析。结果表明,对于江苏潮滩沉积物粒度参数中平均粒径的激光粒度仪与移液管-筛析分析结果之间有良好的线性关系;筛分法测得的粗颗粒物质较激光法偏少,而移液管法法测得的细颗粒物质较激光法偏多;将样品分类之后再进行两种方法所获粒度参数的回归分析,相关性得以提高,说明不同粒度组成的沉积物对分析结果的对比有不同的影响。两种方法之间的换算关系不仅与研究区域有关,而且与沉积物本身的粒度组成有关。 相似文献