全文获取类型
收费全文 | 9323篇 |
免费 | 250篇 |
国内免费 | 337篇 |
专业分类
测绘学 | 265篇 |
大气科学 | 764篇 |
地球物理 | 1904篇 |
地质学 | 3508篇 |
海洋学 | 763篇 |
天文学 | 2120篇 |
综合类 | 40篇 |
自然地理 | 546篇 |
出版年
2023年 | 54篇 |
2022年 | 58篇 |
2021年 | 75篇 |
2020年 | 84篇 |
2019年 | 97篇 |
2018年 | 267篇 |
2017年 | 218篇 |
2016年 | 315篇 |
2015年 | 186篇 |
2014年 | 305篇 |
2013年 | 484篇 |
2012年 | 291篇 |
2011年 | 478篇 |
2010年 | 361篇 |
2009年 | 572篇 |
2008年 | 436篇 |
2007年 | 420篇 |
2006年 | 413篇 |
2005年 | 389篇 |
2004年 | 341篇 |
2003年 | 321篇 |
2002年 | 304篇 |
2001年 | 260篇 |
2000年 | 249篇 |
1999年 | 208篇 |
1998年 | 194篇 |
1997年 | 184篇 |
1996年 | 174篇 |
1995年 | 157篇 |
1994年 | 135篇 |
1993年 | 109篇 |
1992年 | 95篇 |
1991年 | 101篇 |
1990年 | 94篇 |
1989年 | 90篇 |
1988年 | 71篇 |
1987年 | 109篇 |
1986年 | 75篇 |
1985年 | 79篇 |
1984年 | 81篇 |
1983年 | 93篇 |
1982年 | 89篇 |
1981年 | 82篇 |
1980年 | 66篇 |
1979年 | 60篇 |
1977年 | 56篇 |
1976年 | 62篇 |
1975年 | 43篇 |
1973年 | 55篇 |
1972年 | 41篇 |
排序方式: 共有9910条查询结果,搜索用时 15 毫秒
901.
H.-C. Kuo D.-F. Juang L. Yang W.-C. Kuo Y.-M. Wu 《International Journal of Environmental Science and Technology》2014,11(6):1661-1668
The purpose of this study was to investigate the effect of phytoremediation on soils contaminated with heavy crude oil using plants infected by mycorrhizal fungi. Five plant species, Vetiveria zizanioides, Bidens pilosa, Chloris barbata, Eleusine indica, and Imperata cylindrica, infected with the species of mycorrhizal fungi Glomus mosseae, were selected for this study. The degradation of total petroleum hydrocarbons in soils and several physiological parameters of plants such as shoot length and biomass were analyzed. Out of the 5 plant species tested, only V. zizanioides, B. pilosa, and E. indica could take up the G. mosseae. Out of these three, V. zizanioides showed the greatest growth (biomass) in soils with 100,000 mg kg?1 total petroleum hydrocarbons. In addition, B. pilosa infected with G. mosseae was found to be able to increase degradation by 9 % under an initial total petroleum hydrocarbons concentration of 30,000 mg kg?1 in soils after 64 days. We conclude that plants infected with mycorrhizal fungi can enhance the phytoremediation efficiency of soils contaminated with high concentrations of heavy oil. 相似文献
902.
903.
1IntroductionDuringthe past several years,concern hasincreasedover the potential pollution of watershed by estrogeniccompounds,including steroidal hormones fromhumanand ani mal sources.Effluents from wastewater treat-ment plants are sources of endocrine-d… 相似文献
904.
R. L. McKenzie W. A. Matthews Y. Kondo R. Zander Ph. Demoulin P. Fabian D. G. Murcray F. J. Murcray O. Lado-Bordowsky C. Camy-Peyret H. K. Roscoe J. A. Pyle R. D. McPeters 《Journal of Atmospheric Chemistry》1988,7(4):353-367
Column measurements of nitric oxide were made using several techniques during the MAP/GLOBUS campaign in France in September 1985. The data sets are nearly co-located and simultaneous, therefore allowing a valid intercomparison of the various measurement methods. The range of altitudes sampled differs from instrument to instrument. This complicates the comparison because the data sets are to some extent complementary. The NO distributions apparently vary significantly from day to day, and possibly over shorter timescales. Changes in dynamics may be responsible for these variations. The results from the instruments which measure in the infrared and the ultraviolet are self-consistent, and show good agreement with photochemical predictions. On 19 September, when the intercomparison was made, the profile measured by the in-situ chemiluminescent instrument differed significantly from the predicted profile, and the measured columns were generally higher. 相似文献
905.
Rocky desertification and its causes in karst areas: a case study in Yongshun County,Hunan Province,China 总被引:9,自引:0,他引:9
Y.?J.?Xiong G.?Y.?QiuEmail author D.?K.?Mo H.?Lin H.?Sun Q.?X.?Wang S.?H.?Zhao J.?Yin 《Environmental Geology》2009,57(7):1481-1488
Rocky desertification, a process of land degradation characterized by soil erosion and bedrock exposure, is one of the most
serious land degradation problems in karst areas, and is regarded as an obstacle to local sustainable development. It is well
known that human activities can accelerate rocky desertification; however, the effects of climate change on rocky desertification
in karst areas are still unclear. This study focused on the effects of temperature and precipitation changes and human activities
on rocky desertification in karst areas to determine the impacts of climate change and human disturbances on rocky desertification.
Areas of different level of rocky desertification were obtained from Landsat TM (1987) and Landsat ETM+ (2000) images. The
results show that, although the total desertification area increased by only 1.27% between 1987 and 2000, 17.73% of the slightly
desertified land had degraded to a moderate or intense level, 2.01 and 15.71%, respectively. Meanwhile, between 1987 and 2000,
the air temperature increased by 0.7°C, and precipitation increased by 170 mm. Statistical results indicate that the increase
in precipitation was caused by heavy rainfall. In addition, under the interactive influences of heavy rainfall and temperature,
the average karst dissolution rate was about 87 m3 km−2 a−1 during the 14 years in the study area. Further analysis indicated that rocky desertification was positively related with
the increase in temperature and precipitation and especially with the heavy rainfall events. Climate change accelerated rocky
desertification in the karst areas.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
906.
Y. M. Pihlstrm J. E. Conway R. S. Booth P. J. Diamond B. Koribalski 《New Astronomy Reviews》1999,43(8-10)
We report on observations, with sub-parsec resolution, of neutral hydrogen seen in absorption in the λ=21 cm line against the nucleus of the active spiral galaxy NGC 5793. The absorption line consists of three components separated in both location as well as velocity. We derive HI column densities of 2×1022 cm−2 assuming a gas spin temperature of 100 K. For the first time we are able to reliably estimate the HI cloud sizes (≈15 pc) and atomic gas densities (≈200 cm−3). Our results suggest that the HI gas is not associated with the <10 pc region which presumably contains the H2O masers, but it is more distant from the nucleus, and is probably associated with the r1 kpc gas seen in CO. 相似文献
907.
908.
Kerstin S. Treydte David C. Frank Gerhard Helle Jan Esper 《Geochimica et cosmochimica acta》2009,73(16):4635-7303
We present one millennium-long (1171-year), and three 100 year long annually resolved δ13C tree-ring chronologies from ecologically varying Juniperus stands in the Karakorum Mountains (northern Pakistan), and evaluate their response to climatic and atmospheric CO2 changes. All δ13C records show a gradual decrease since the beginning of the 19th century, which is commonly associated with a depletion of atmospheric δ13C due to fossil fuel burning. Climate calibration of high-frequency δ13C variations indicates a pronounced summer temperature signal for all sites. The low-frequency component of the same records, however, deviates from long-term temperature trends, even after correction for changes in anthropogenic CO2. We hypothesize that these high-elevation trees show a response to both climate and elevated atmospheric CO2 concentration and the latter might explain the offset with target temperature data. We applied several corrections to tree-ring δ13C records, considering a range of potential CO2 discrimination changes over the past 150 years and calculated the goodness of fit with the target via calibration/verification tests (R2, residual trend, and Durbin-Watson statistics). These tests revealed that at our sites, carbon isotope fixation on longer timescales is affected by increasing atmospheric CO2 concentrations at a discrimination rate of about 0.012‰/ppmv. Although this statistically derived value may be site related, our findings have implications for the interpretation of any long-term trends in climate reconstructions using tree-ring δ13C, as we demonstrate with our millennium-long δ13C Karakorum record. While we find indications for warmth during the Medieval Warm Period (higher than today’s mean summer temperature), we also show that the low-frequency temperature pattern critically depends on the correction applied. Patterns of long-term climate variation, including the Medieval Warm Period, the Little Ice Age, and 20th century warmth are most similar to existing evidence when a strong influence of increased atmospheric CO2 on plant physiology is assumed. 相似文献
909.
KADIK A.; PINEAU F.; LITVIN Y.; JENDRZEJEWSKI N.; MARTINEZ I.; JAVOY M. 《Journal of Petrology》2004,45(7):1297-1310
Studies of iron-bearing silicate melt (ferrobasalt) + iron metallicphase + graphite + hydrogen equilibria show that carbon andhydrogen solubilities in melts are important for the evolutionof the upper mantle. In a series of experiments conducted at3·7 GPa and 15201600°C, we have characterizedthe nature (oxidized vs reduced) and quantified the abundancesof C- and H-compounds dissolved in iron-bearing silicate melts.Experiments were carried out in an anvil-with-hole apparatuspermitting the achievement of equal chemical potentials of H2in the inner Pt capsule and outer furnace assembly. The fO2for silicate meltiron equilibrium was 2·32 ±0·04 log units below ironwüstite (IW). Theferrobasalt used as starting material experienced a reductionof its iron oxides and silicate network. The counterpart wasa liberation of oxygen reacting with the hydrogen entering thecapsule. The amount of H2O dissolved in the glasses was measuredby ion microprobe and by step-heating and was found to be between1 and 2 wt %. The dissolved carbon content was found to be 1600ppm C by step-heating. The speciation of C and H componentswas determined by IR and Raman spectroscopy. It was establishedthat the main part of the liberated oxygen was used to formOH and to a much lesser extent H2O, and only traces ofH2, CO2 and 相似文献
910.
The Main Zone of the Hidaka Metamorphic Belt is an uplifted crustal section of island-arc type. The crust was formed during early Tertiary time, as a result of collision between two arc–trench systems of Cretaceous age. The crustal metamorphic sequence is divided into four metamorphic zones (I–IV), in which zone IV is in the granulite facies. A detailed study of the evolution of the Hidaka Belt, based on a revised P–T–t analysis of the metamorphic rocks, notably a newly found staurolite-bearing granulite, confirms a prograde isobaric heating path, after a supposed event of tectonic thickening of accretionary sedimentary and oceanic crustal rocks. During the peak metamorphic event (c. 53 Ma), the regional geothermal gradient attained 33–40° C km?1, and the highest P–T condition obtained from the lowest part of the granulite unit is 830° C, 7 kbar. In this part, XH2O of Gt–Opx–Cd gneiss is about 0.15 and that of Gt–Cd–Bt gneiss is 0.4. The P–T–XH2O condition of the granulite unit is well within a field where fluid-present partial melting of pelitic and greywacke metamorphic rocks takes place. This is in harmony with the restitic nature of the Gt–Opx–Cd gneiss in the lowest part of the granulite unit. The possibility that partial melting took place in the Main Zone is significant for the genesis of the peraluminous (S-type) granitic rocks within it. The S-type granitic rocks in this zone are Opx–Gt–Bt tonalite in the granulite zone, Gt–Cd–Bt tonalite in the amphibolite zone, and Cd–Bt–Mus tonalite in the Bt–Mus gneiss zone. The mineralogical and chemical nature of these strongly peraluminous tonalitic rocks permit them to be regarded as having been derived from S-type granitic magma generated by crustal anatexis of pelitic metamorphic rocks in deeper crust. 相似文献