全文获取类型
收费全文 | 10913篇 |
免费 | 454篇 |
国内免费 | 109篇 |
专业分类
测绘学 | 302篇 |
大气科学 | 891篇 |
地球物理 | 2505篇 |
地质学 | 3776篇 |
海洋学 | 1060篇 |
天文学 | 1714篇 |
综合类 | 23篇 |
自然地理 | 1205篇 |
出版年
2021年 | 117篇 |
2020年 | 153篇 |
2019年 | 156篇 |
2018年 | 242篇 |
2017年 | 221篇 |
2016年 | 331篇 |
2015年 | 254篇 |
2014年 | 280篇 |
2013年 | 601篇 |
2012年 | 367篇 |
2011年 | 460篇 |
2010年 | 407篇 |
2009年 | 523篇 |
2008年 | 489篇 |
2007年 | 430篇 |
2006年 | 442篇 |
2005年 | 344篇 |
2004年 | 406篇 |
2003年 | 365篇 |
2002年 | 356篇 |
2001年 | 249篇 |
2000年 | 252篇 |
1999年 | 208篇 |
1998年 | 224篇 |
1997年 | 146篇 |
1996年 | 158篇 |
1995年 | 146篇 |
1994年 | 151篇 |
1993年 | 144篇 |
1992年 | 133篇 |
1991年 | 137篇 |
1990年 | 114篇 |
1989年 | 100篇 |
1988年 | 88篇 |
1987年 | 127篇 |
1986年 | 105篇 |
1985年 | 177篇 |
1984年 | 210篇 |
1983年 | 161篇 |
1982年 | 135篇 |
1981年 | 133篇 |
1980年 | 115篇 |
1979年 | 131篇 |
1978年 | 126篇 |
1977年 | 112篇 |
1976年 | 109篇 |
1975年 | 104篇 |
1974年 | 71篇 |
1973年 | 90篇 |
1972年 | 54篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
R. T. Schilizzi W. Aldrich B. Anderson A. Bos R. M. Campbell J. Canaris R. Cappallo J. L. Casse A. Cattani J. Goodman H. J. van Langevelde A. Maccafferri R. Millenaar R. G. Noble F. Olnon S. M. Parsley C. Phillips S. V. Pogrebenko D. Smythe A. Szomoru H. Verkouter A. R. Whitney 《Experimental Astronomy》2001,12(1):49-67
32.
Progress in the introduction of coulometry for the analysis of total carbon dioxide (TCO2) in marine waters is described. An extractor—stripper removes CO2 that is measured coulometrically by the quantity of electricity (coulombs) used to electrogenerate OH? ions for the titration of the acid formed by the reaction of CO2 and ethanolamine. The equivalence point is detected photometrically with thymolphthalein as the indicator, and Faraday's Law relates coulombs to equivalents of titrant generated and CO2 determined so that there are no standard curves needed or titrants to standardize or store. Accuracy was determined by adding gelatin capsules containing 100–1500 μg C of pure CaCO3 into the stripper, and accuracies of better than ± 1 μg C were achieved. The best precision for natural seawater (± 1 standard error) of ± 0.5 μmol l?1 was found for 17 samples of Bermuda coastal waters having a mean TCO2 of 2007.2 μmol l?1 (0.05% CV). Sources of error and precautions are discussed. This method, which has been used successfully at sea, can be used to study a variety of marine phenomena involving TCO2. 相似文献
33.
34.
35.
Ezio Caroli Natalia Auricchio Lorenzo Amati Yuriy Bezsmolnyy Carl Budtz-JøRgensen Rui M. Curado da Silva Filippo Frontera Alessandro Pisa Stefano Del Sordo John B. Stephen Giulio Ventura 《Experimental Astronomy》2005,20(1-3):341-351
The energy range above 60 keV is important for the study of many open problems in high energy astrophysics such as the role of Inverse Compton with respect to synchrotron or thermal processes in GRBs, non thermal mechanisms in SNR, the study of the high energy cut-offs in AGN spectra, and the detection of nuclear and annihilation lines. Recently the development of high energy Laue lenses with broad energy bandpasses from 60 to 600keV have been proposed for a Hard X ray focusing Telescope (HAXTEL) in order to study the X-ray continuum of celestial sources. The required focal plane detector should have high detection efficiency over the entire operative range, a spatial resolution of about 1mm, an energy resolution of a few keV at 500keV and a sensitivity to linear polarization. We describe a possible configuration of the focal plane detector based on several CdTe/CZT pixelated layers stacked together to achieve the required detection efficiency at high energy.
Each layer can operate both as a separate position sensitive detector and polarimeter or work with other layers to increase the overall photopeak efficiency. Each layer has a hexagonal shape in order to minimize the detector surface required to cover the lens field of view. The pixels would have the same geometry so as to provide the best coupling with the lens point spread function and to increase the symmetry for polarimetric studies. 相似文献
36.
Alan M Bond Julie R Bradbury Henry A Hudson John S Garnham Peter J Hanna Stanley Strother 《Marine Chemistry》1985,16(1):1-9
Evidence was found that uptake of lead from seawater in both model and natural systems by the leaves of the seagrass Zostera muelleri does occur for live, dead and scraped leaves at all the lead concentrations tested. Positive uptake of lead was measured using the three analytical techniques of radio-tracer, differential pulse anodic stripping voltammetry and atomic absorption spectrometry; similar uptake profiles were obtained for each technique. Profiles always showed an initial rapid uptake phase followed by a gradual transition to a plateau phase at which an approximate equilibrium between lead attached to seagrass and free ionic lead in seawater was reached. The presence of active lead uptake processes was indicated in experiments which attempted to remove lead from leaves by a chelating agent. 相似文献
37.
38.
The silica-scaled chrysophytes are being used increasingly in paleolimnological studies of lake acidification. This study compares the distribution of scaled chrysophytes in the surface sediment of a calibration set of lakes from the Adirondack Park and from northern New England. With the exception of two taxa, species distributions with respect to pH are similar in the two regions. The stratigraphic distribution of chrysophytes is then compared in five Adirondack and three New England lakes. All the presently acid lakes indicate recent lake acidification, with more acid tolerant chrysophytes increasing in relative frequency in the recent sediments. Because the timing of these species changes is unrelated to any watershed disturbances that may have occurred in the lakes' catchments, atmospheric deposition of acids is believed responsible for these recent pH changes.This is the seventh of a series of papers to be published by this journal which is a contribution of the Paleoecological Investigation of Recent Lake Acidification (PIRLA) project. Drs. D. F. Charles and D. R. Whitehead are guest editors for this series. 相似文献
39.
刘少明 《大地测量与地球动力学》2004,24(4):13-19
对1999年8月11日日全食阴影扫过欧洲期间,设在Annelles,Uccle,Walferdange和Bondy弹簧和超导重力仪的记录进行了分析.为了确定月亮对太阳万有引力可能的遮挡效应的极限,对超导和弹簧重力仪记录进行了比较.同时也对LCR和阿斯卡尼亚重力仪观测结果进行了讨论.结论是如果日食重力吸引效应存在,它应在超导重力仪±1 nm/s2(0.1×10-8ms-2)的观测精度范围之内.研究发现在以上情形下,弹簧和超导重力仪都在它们的精度范围内工作,并且日食引起的异常环境干扰可能使重力信号有重大的改变. 相似文献
40.