全文获取类型
收费全文 | 8138篇 |
免费 | 1381篇 |
国内免费 | 2156篇 |
专业分类
测绘学 | 836篇 |
大气科学 | 1687篇 |
地球物理 | 1657篇 |
地质学 | 3849篇 |
海洋学 | 1496篇 |
天文学 | 400篇 |
综合类 | 736篇 |
自然地理 | 1014篇 |
出版年
2024年 | 68篇 |
2023年 | 166篇 |
2022年 | 397篇 |
2021年 | 435篇 |
2020年 | 426篇 |
2019年 | 414篇 |
2018年 | 438篇 |
2017年 | 387篇 |
2016年 | 467篇 |
2015年 | 439篇 |
2014年 | 493篇 |
2013年 | 549篇 |
2012年 | 548篇 |
2011年 | 566篇 |
2010年 | 490篇 |
2009年 | 481篇 |
2008年 | 435篇 |
2007年 | 420篇 |
2006年 | 362篇 |
2005年 | 342篇 |
2004年 | 270篇 |
2003年 | 207篇 |
2002年 | 225篇 |
2001年 | 240篇 |
2000年 | 237篇 |
1999年 | 272篇 |
1998年 | 231篇 |
1997年 | 219篇 |
1996年 | 210篇 |
1995年 | 184篇 |
1994年 | 176篇 |
1993年 | 150篇 |
1992年 | 140篇 |
1991年 | 121篇 |
1990年 | 84篇 |
1989年 | 80篇 |
1988年 | 63篇 |
1987年 | 50篇 |
1986年 | 30篇 |
1985年 | 26篇 |
1984年 | 23篇 |
1983年 | 18篇 |
1982年 | 28篇 |
1981年 | 14篇 |
1980年 | 7篇 |
1979年 | 9篇 |
1977年 | 5篇 |
1976年 | 8篇 |
1973年 | 4篇 |
1958年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
152.
INTRODUCTIONThetoxicityofheavymetalsreleasedintotheenvironmenthasrecentlytriggeredanumberofstudiesaimingattheremovalofmetalionsfromaqueoussolutions (FourestandVolesky ,1 997;FehrmannandPohl,1 993 ;KuyucakandVolesky,1 989) .Itwasfoundthattheaccumulationofheavymeta… 相似文献
153.
广东沿海牡蛎体Ni含量水平及其时空变化趋势 总被引:3,自引:0,他引:3
198 9~ 1997年间 ,为实施“南海贻贝观察”计划 ,对广东沿海 12个地点近江牡蛎体内的 Ni含量水平进行了连续监测 ,结果全部牡蛎样品均检出 Ni,含量范围为 0 .17~ 2 .37mg/kg(湿重 ) ,总平均值为0 .58mg/kg。污染评价结果显示 ,广东沿海 Ni含量总体上处于微污染—轻污染水平。牡蛎体 Ni平均含量呈珠江口海区 >粤西海区 >粤东海区的分布格局 ,其最高值出现在深圳湾、唐家湾和湛江港。 70年代后期至 1991年 ,牡蛎体的 Ni含量呈明显下降趋势 ,此后 Ni含量年际间虽有波动 ,但无显著差异 相似文献
154.
西部大地形变数据库设计与建设 总被引:1,自引:0,他引:1
介绍西部大地形变数据库的设计与建设. 相似文献
155.
Krucker Säm Christe Steven Lin R.P. Hurford Gordon J. Schwartz Richard A. 《Solar physics》2002,210(1-2):445-456
The excellent sensitivity, spectral and spatial resolution, and energy coverage down to 3 keV provided by the Reuven Ramaty
High-Energy Solar Spectroscopic Imager mission (RHESSI) allows for the first time the detailed study of the locations and
the spectra of solar microflares down to 3 keV. During a one-hour quiet interval (GOES soft X-ray level around B6) on 2 May,
1:40–2:40 UT, at least 7 microflares occurred with the largest peaking at A6 GOES level. The microflares are found to come
from 4 different active regions including one behind the west limb. At 7′′ resolution, some events show elongated sources,
while others are unresolved point sources. In the impulsive phase of the microflares, the spectra can generally be fitted
better with a thermal model plus power law above ∼ 6–7 keV than with a thermal only. The decay phase sometimes can be fitted
with a thermal only, but in some events, power-law emission is detected late in the event indicating particle acceleration
after the thermal peak of the event. The behind-the-limb microflare shows thermal emissions only, suggesting that the non-thermal
power law emission originates lower, in footpoints that are occulted. The power-law fits extend to below 7 keV with exponents
between −5 and −8, and imply a total non-thermal electron energy content between 1026–1027 erg. Except for the fact that the power-law indices are steeper than what is generally found in regular flares, the investigated
microflares show characteristics similar to large flares. Since the total energy in non-thermal electrons is very sensitive
to the value of the power law and the energy cutoff, these observations will give us better estimates of the total energy
input into the corona. (Note that color versions of figures are on the accompanying CD-ROM.)
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1022404512780 相似文献
156.
Share G.H. Murphy R.J. Dennis B.R. Schwartz R.A. Tolbert A.K. Lin R.P. Smith D.M. 《Solar physics》2002,210(1-2):357-372
The RHESSI high-resolution spectrometer detected γ-ray lines and continuum emitted by the Earth's atmosphere during impact
of solar energetic particles in the south polar region from 16:00–17:00 UT on 21 April 2002. The particle intensity at the
time of the observation was a factor of 10–100 weaker than previous events when gamma-rays were detected by other instruments.
This is the first high-resolution observation of atmospheric gamma-ray lines produced by solar energetic particles. De-excitation
lines were resolved that, in part, come from 14N at 728, 1635, 2313, 3890, and 5106 keV, and the 12C spallation product at ∼ 4439 keV. Other unresolved lines were also detected. We provide best-fit line energies and widths
and compare these with moderate resolution measurements by SMM of lines from an SEP event and with high-resolution measurements
made by HEAO 3 of lines excited by cosmic rays. We use line ratios to estimate the spectrum of solar energetic particles that
impacted the atmosphere. The 21 April spectrum was significantly harder than that measured by SMM during the 20 October 1989
shock event; it is comparable to that measured by Yohkoh on 15 July 2000. This is consistent with measurements of 10–50 MeV protons made in space at the time of the γ-ray observations. 相似文献
157.
广东2008年低温雨雪冰冻灾害及气象应急响应 总被引:16,自引:4,他引:12
2008年初我国南方遭受了百年一遇低温雨雪冰冻灾害,广东的受灾程度属80年一遇,造成了重大经济损失和严重社会影响.分析发现:灾害过程在近年来最严重的一次拉尼娜事件背景下发生的,与欧亚地区持续大气环流异常密切相关.在北脊南槽和西太平洋副高偏北偏强的形势下,冷暖气流在我国南方地区频繁交汇,使对流层中低层形成逆温层和局地经向环流产生异常,造成了此次持续低温雨雪冰冻过程.面对灾害引发的公共事件,广东省气象部门打破常规、准确预警,启动预案,通过媒体和公共事件预警信息发布平台,及时传播权威的公共预警信息,为安定民心、稳定社会、减少灾害起到积极作用.灾后反思发现,山区冰灾的监测、灾害的评估、公共信息发布等的能力和规范均亟待加强. 相似文献
158.
PENG Ji-long FENG Tao-jun SHI En-tao LI Lin YU Qian ZHANG Kai NIE Xiang-yu MA Zi-liang 《Chinese Astronomy and Astrophysics》2019,43(3):444-456
Solar Extreme Ultraviolet (EUV) imaging observation is an important measure for the researches of solar activities and coronal plasma physics. But the traditional EUV imager and spectrograph can hardly achieve simultaneously the high spectral resolution and wide field-of-view of solar imaging. This paper has designed a new type of solar EUV multi-band imager, by adopting a kind of slitless grating and grazing incidence structure, it can realize the solar full-disk imaging of high spectral and spatial resolution. The field-of-view of the imager can be as broad as 47′. The spectral resolution is 2×10?3nm per pixel, and the spatial resolution is 1.4′ per pixel. The temporal resolution of the solar full-disk is better than 60 s. The analysis of the solar full-disk spectral image and system response shows that the imager can observe the morphological evolutions of various solar activities, and can provide more comprehensive data for the researches of solar physics and space weather forecast. 相似文献
159.
Silvio Lorenzetti Yangting Lin Daode Wang Otto Eugster 《Meteoritics & planetary science》2003,38(8):1243-1253
Abstract— We determined the mineralogical and chemical characteristics and the He, Ne, and Ar isotopic abundances of 2 meteorites that fell in China and of 2 meteorites that were recovered by the 15th Chinese Antarctic Research Expedition. Guangmingshan (H5), Zhuanghe (H5), and Grove Mountain (GRV) 98002 (L5) yield cosmic ray exposure (CRE) ages of 68.7 ± 10.0 Ma, 3.8 ± 0.6 Ma, and 17.0 ± 2.5 Ma, respectively. These ages are within the range typically observed for the respective meteorite types. GRV 98004 (H5) had an extremely short parent body‐Earth transfer time of 0.052 ± 0.008 Ma. Its petrography and mineral chemistry are indistinguishable from other typical H5 chondrites. Only 3 other meteorites exist with similarly low CRE ages: Farmington (L5), Galim (LL6), and ALH 82100 (CM2). We show that several asteroids in Earth‐crossing orbits, or in the main asteroid belt with orbits close to an ejection resonance, are spectrally matching candidates and may represent immediate precursor bodies of meteorites with CRE ages ≤0.1 Ma. 相似文献
160.
Past studies of interplanetary magnetic sector boundaries have been based on the assumption that one can determine the field polarities by comparing the field directions with those of the nominal Parker spiral angles. Previous investigators have found evidence for decreases of B, the magnitude of the magnetic fieldB, and increases of , the angle betweenB and the ecliptic plane, at sector boundaries. Others have argued that the characteristic thickness of sector boundaries exceeds that of tangential discontinuities, making sector boundaries a separate class of structures.We use a simple technique for inferring the polarities of interplanetary magnetic fields based on the assumption thatE > 2 keV electrons are always flowing along the magnetic field away from the Sun. Electron data from the UC Berkeley experiment on the ISEE-3 spacecraft are used to examine periods around several apparent sector boundaries in 1978 and 1979. We compare properties of (a) boundaries with field polarity changes and (b) large-angle ( > 60°) directional discontinuities with no field polarity changes. We find no significant differences between the sector boundaries and the directional discontinuities in terms of associated decreases in B or of values of . These results suggest no significant difference between sector boundaries and directional discontinuities other than the change in field polarities. Within limited statistics we find that about half the polarity changes would not have been identified using a requirement that > 90° and that half of the > 120° discontinuities would have been misidentified as polarity changes. 相似文献