全文获取类型
收费全文 | 90618篇 |
免费 | 1468篇 |
国内免费 | 728篇 |
专业分类
测绘学 | 2291篇 |
大气科学 | 6433篇 |
地球物理 | 17441篇 |
地质学 | 34441篇 |
海洋学 | 7487篇 |
天文学 | 19529篇 |
综合类 | 337篇 |
自然地理 | 4855篇 |
出版年
2022年 | 401篇 |
2021年 | 719篇 |
2020年 | 804篇 |
2019年 | 847篇 |
2018年 | 4125篇 |
2017年 | 3884篇 |
2016年 | 3456篇 |
2015年 | 1453篇 |
2014年 | 2238篇 |
2013年 | 3898篇 |
2012年 | 3187篇 |
2011年 | 5388篇 |
2010年 | 4717篇 |
2009年 | 5663篇 |
2008年 | 4886篇 |
2007年 | 5227篇 |
2006年 | 2988篇 |
2005年 | 2791篇 |
2004年 | 2612篇 |
2003年 | 2527篇 |
2002年 | 2200篇 |
2001年 | 1879篇 |
2000年 | 1799篇 |
1999年 | 1433篇 |
1998年 | 1526篇 |
1997年 | 1423篇 |
1996年 | 1131篇 |
1995年 | 1168篇 |
1994年 | 991篇 |
1993年 | 909篇 |
1992年 | 882篇 |
1991年 | 780篇 |
1990年 | 883篇 |
1989年 | 752篇 |
1988年 | 667篇 |
1987年 | 836篇 |
1986年 | 684篇 |
1985年 | 886篇 |
1984年 | 949篇 |
1983年 | 884篇 |
1982年 | 853篇 |
1981年 | 756篇 |
1980年 | 702篇 |
1979年 | 628篇 |
1978年 | 611篇 |
1977年 | 571篇 |
1976年 | 554篇 |
1975年 | 508篇 |
1974年 | 523篇 |
1973年 | 482篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
In astronomical photometry, the sensitivity of observations is limited by the dark counts of the photomultiplier tube. In the present work, the effect of dark count noise in photon counting systems is investigated by theory and experimental measurements. Dark counts are considered to be originating from two sources, namely: dc fluctuations and random pulses.Experimental measurements were carried out to determine noise effects in different operating regions of noise dominance. The results provide strong evidence that: in normal operating mode, where the effect of random pulses is dominant, dark counts do not follow Poisson statistics. The observed noise shows strong (1/f) power spectrum, where the observed noise power is found to increase with time of observation.The results are important in photon counting systems operating under dark count limited mode. The conclusions drawn can be useful in obtaining more accurate error estimates and in assessing astronomical photometric observations and data reduction techniques. 相似文献
32.
A highly automated moving object detection package 总被引:1,自引:0,他引:1
33.
The UBV photometric observations of RT Per, from Sanwal and Chaubey (1981), were analyzed by the Wilson and Devinney code (1971). The light curves include reflection effects that for the first time has been suggested by Dugan (1911). RT Per has a semi-detached configuration where the lower-mass component is in contact with its respective Roche surface. The higher-mass component very nearly fills its Roche lobe. It has the characteristic of an Algol type system. The absolute dimensions for the primary and secondary of this system were calculated from its spectral types and by combining the photometric solution with inferred component radial velocities (Lu, 1990). 相似文献
34.
35.
36.
V. Parro J.A. Rodríguez-Manfredi C. Compostizo E. Vez M. Moreno-Paz P. Fernández-Calvo J. Pérez-Mercader J. Gómez-Elvira 《Planetary and Space Science》2005,53(7):729-737
Recent findings by the MER rover opportunity confirming the presence of iron minerals that can only be formed in the presence of water emphasize the study of analogous environments to Mars on Earth. The study of chemolithoautotrophic communities living in acidic iron-rich habitats is highly relevant in order to identify Mars analog environment-specific biomarkers. Iron oxidizing bacteria like Leptospirillum ferrooxidans and Acidithiobacillus ferrooxidans have ways of life for which it is feasible to identify a past or present hypothetical niche on Mars. We have developed a strategy for biomarker identification based on: (i) search for biosignatures on acid and metal-rich environments; (ii) development of an immunosensor microarray; and (iii) integration into an instrument for autonomous and remote operation. The instrument that we have built, called Signs Of LIfe Detector (SOLID), is capable of processing a variety of samples for the detection of specific biomarkers. Antibodies against several bacterial strains have been developed and tested in a microarray biosensor on SOLID. Tests with field samples have been successfully performed, allowing the detection of L. ferrooxidans, A. ferrooxidans present in sediment samples. 相似文献
37.
We consider the particular solutions of the evolutionary system of equations in elements that correspond to planar and spatial circular orbits of the singly averaged Hill problem. We analyze the stability of planar and spatial circular orbits to inclination and eccentricity, respectively. We construct the instability regions of both particular solutions in the plane of parameters of the problem. 相似文献
38.
MohammedHazaea HUKe MohammedMattash CHENBing M.O.AI-JabaliAref MohammedAbdussalam 《东北亚地学研究》2004,7(2):181-184
The chemical composition of several thermal springs around Changbaishan area has been investigated. Cenozoic basaltic rocks are widely distributed in Northeast China and geothermal characteristics have been described. About one hundred hot springs exist around Changhaishan Volcano at the border between China and D.P.R.Korea with high temperature about 82~C. The pH values of the spring water range from 6.9 to 7.1 and the total flow rate is about 4.8 L/sec. The chemical composition of the thermal springs is sodium carbonate; the high-mineral contents of thermal water are believed to have medicinal properties. Bathhouses are already built along the hot springs to take the advantage of the supposed healing properties. The high quality of those hot springs is believed to be utilitized for mineral water. The chemical equilibrium temperatures were estimated at about 160℃ based on the Na-K-Ca geochemical thermometer. 相似文献
39.
40.