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991.
张明洁 《广东海洋大学学报》1993,(2)
为使船用天然丁苯橡胶绝缘电缆(CF型)剩余使用寿命达到合理利用,本文重点讨论温度对电缆绝缘热老化的影响。通过电缆结构及使用过程中对其寿命关联最大的绝缘层老化——即热老化的确定和计算,归纳出各种温度状态下电缆的剩余使用寿命。 相似文献
992.
1 INTRODUCTION The introduction of invasive marine species into new environments by ship’s ballast water, by attaching to ships’ hulls or via other vectors has been recognized as one of the four major threats to the world’s oceans by Global Environment… 相似文献
993.
Dennis G. Dye 《水文研究》2002,16(15):3065-3077
This study investigated variability and trends in the annual snow‐cover cycle in regions covering high‐latitude and high‐elevation land areas in the Northern Hemisphere. The annual snow‐cover cycle was examined with respect to the week of the last‐observed snow cover in spring (WLS), the week of the first‐observed snow cover in autumn (WFS), and the duration of the snow‐free period (DSF). The analysis used a 29‐year time‐series (1972–2000) of weekly, visible‐band satellite observations of Northern Hemisphere snow cover from NOAA with corrections applied by D. Robinson of Rutgers University Climate Laboratory. Substantial interannual variability was observed in WLS, WFS and DSF (standard deviations of 0·8–1·1, 0·7–0·9 and 1·0–1·4 weeks, respectively), which is related directly to interannual variability in snow‐cover area in the regions and time periods of snow‐cover transition. Over the nearly three‐decade study period, WLS shifted earlier by 3–5 days/decade as determined by linear regression analysis. The observed shifts in the annual snow‐cover cycle underlie a significant trend toward a longer annual snow‐free period. The DSF increased by 5–6 days/decade over the study period, primarily as a result of earlier snow cover disappearance in spring. The observed trends are consistent with reported trends in the timing and length of the active growing season as determined from satellite observations of vegetation greenness and the atmospheric CO2 record. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
994.
Losses of 15N labelled nitrogen in a Spartina alterniflora salt marsh was measured over three growing seasons. Labelled equivalent to 100 μg 15N g?1 of dry soil was added in four instalments over an eight week period. Recovery of the added nitrogen ranged from 93% 5 months after addition of the to 52% at the end of the third growing season which represented a nitrogen loss equivalent to 3·4 gNm?2. The availability of the labelled incorporated into the organic fraction was estimated by calculation of the rate of mineralization. The time required for mineralization of 1% of the tagged organic N increases progressively with succeeding cuttings of the S. alterniflora and ranged from 152 to 299 days. Only 2% of the nitrogen applied as 15N labelled plant material to the marsh surface in the fall could be accounted for in S. alterniflora the following season. 相似文献
995.
Based on surveyed data from seven coastal sections and the collected data of wind, sea level, tide, nearshore suspended sediment
concentration and river flux from adjacent stations, this paper deals with regressive correlation between monthly average
flat elevation and monthly average figures of the influential factors. All sections except one which is located within the
river mouth showed negative correlation between flat elevation and sea level and between flat elevation and tidal range, with
correlation coefficients being −0.53 – −0.91 (−0.77 on the average) in the former condition and −0.56 – −0.97 (−0.80 on the
average) under the latter. Each of the sections with available suspended sediment concentration (SSC) data shows a positive
correlation between flat elevation and SSC, with correlative coefficients being 0.35 – 0.97 (0.66 on the average). Only two
sections (one in the Changjiang River Estuary and the other in the Hangzhou Bay) which are similar to beaches in sediment
grain-size and slope gradient showed a negative correlation between flat elevation and onshore wind frequency and between
flat elevation and average wind velocity, with correlative coefficients being respectively −0.57 and −0.69 (−0.63 on the average)
in the former situation and −0.61 and −0.75 (−0.68 on the average) in the latter. Other sections did not show uniform relationship
between flat elevation and wind conditions. Due to local marine factors the nearshore SSC in the studied area is negatively
correlated with the Changjiang River sediment flux (r=−0.78), which results in false negative correlation between flat elevation
and river sediment flux. The paper also gives sediment dynamic and morphodynamic explanation for the above correlations. Sea
level rise results in the spread of breaker zone from subtidal area to intertidal area and then increases the intertidal water
energy. The larger the tidal range, the stronger the tide currents and the easier for the flat to be eroded. The higher the
SSC of flood water, the easier for the sediment to deposit down. Because of correlations among the influential factors, it
is difficult to give the prime one which dominates the erosion and accretion processes in tidal flats. 相似文献
996.
CARBON CYCLE OF MARSH IN THE SANJIANG PLAIN 总被引:1,自引:0,他引:1
Peat~hisaprocessofbeinghelpfulfordecreasingtheincrementofopcontentintheair,whichiscausedbycombustionofdineralfuelsandhumanactivitiesinterrestrialecosystem.But,exploitingrnaxsh,eSPeCiallyPeatedtObefuels,impliesthatorgbocsubstanceaccUInulatedfroma~hereduringthepastthousandsofyearsisrapidlyOxidized.aamthemarShplaysanimPOrtantroleinthecycleofbiogaxhdristry.TheSanjiangPlainisalowplainformedbythecommonreactionoftheHeilongRiver,SonghuaherandWUSuliabover.Thetotalareais10.89X104klnZandmarsharea… 相似文献
997.
桂东南和桂西南地区中生代三叠纪和白垩纪的火山活动活跃。近年来通过对这些火山岩研究,根据目前普遍采用的火山活动旋回划分的基本原则,将该地区中生代火山活动划分出上、下2个火山岩系,4个火山活动旋回 相似文献
998.
周年采集环沟格特蛤(Katelysiarimularis)分别测定生长指标(总重、软体部重、性腺重、肝重和软体部干重等)并用组织切片观察性腺发育的状况,以确定性腺发育的周期和时间。组织的光镜研究说明环沟格特蛤雌雄性腺发育均可分为增殖期、生长期、成熟期、排放期和休止期。在厦门吴冠镇环沟格特蛤1月开始其性腺发育,3月进入生长期,5~6月成熟,5~11月都有产卵,每年7月11月各有一次排卵高峰期。 相似文献
999.
1000.
The past achievements, benefits and future opportunities of human spaceflight are discussed from a European perspective. Earlier work performed on the Skylab, Salyut, Shuttle, Spacelab, and Mir orbital facilities is reviewed, together with the prospects for new research on the International Space Station (ISS). Major scientific benefits are expected from the ISS in the areas of life science research (including human physiology and medicine) physical sciences, and fundamental physics. 相似文献