全文获取类型
收费全文 | 642篇 |
免费 | 27篇 |
国内免费 | 10篇 |
专业分类
测绘学 | 3篇 |
大气科学 | 17篇 |
地球物理 | 149篇 |
地质学 | 171篇 |
海洋学 | 142篇 |
天文学 | 145篇 |
综合类 | 9篇 |
自然地理 | 43篇 |
出版年
2022年 | 2篇 |
2021年 | 6篇 |
2020年 | 4篇 |
2019年 | 15篇 |
2018年 | 7篇 |
2017年 | 24篇 |
2016年 | 13篇 |
2015年 | 11篇 |
2014年 | 30篇 |
2013年 | 23篇 |
2012年 | 13篇 |
2011年 | 27篇 |
2010年 | 22篇 |
2009年 | 33篇 |
2008年 | 28篇 |
2007年 | 37篇 |
2006年 | 31篇 |
2005年 | 28篇 |
2004年 | 40篇 |
2003年 | 21篇 |
2002年 | 18篇 |
2001年 | 28篇 |
2000年 | 20篇 |
1999年 | 14篇 |
1998年 | 15篇 |
1997年 | 15篇 |
1996年 | 13篇 |
1995年 | 6篇 |
1994年 | 4篇 |
1993年 | 12篇 |
1992年 | 5篇 |
1991年 | 7篇 |
1990年 | 5篇 |
1989年 | 11篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1986年 | 8篇 |
1985年 | 5篇 |
1984年 | 7篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1977年 | 6篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1972年 | 2篇 |
1971年 | 3篇 |
排序方式: 共有679条查询结果,搜索用时 531 毫秒
561.
Yasuhito SEKINE Seiji SUGITA Takafumi SHIDO Takashi YAMAMOTO Yasuhiro IWASAWA Toshihiko KADONO Takafumi MATSUI 《Meteoritics & planetary science》2006,41(5):715-729
Abstract— Fischer‐Tropsch catalysis, by which CO and H2 are converted to CH4 on the surface of transition metals, has been considered to be one of the most important chemical reactions in many planetary processes, such as the formation of the solar and circumplanetary nebulae, the expansion of vapor clouds induced by cometary impacts, and the atmospheric re‐entry of vapor condensate due to asteroidal impacts. However, few quantitative experimental studies have been conducted for the catalytic reaction under conditions relevant to these planetary processes. In this study, we conduct Fischer‐Tropsch catalytic experiments at low pressures (1.3 times 10?4 bar ≤ P ≤ 5.3 times 10?1 bar) over a wide range of H2/CO ratios (0.25–1000) using pure iron, pure nickel, and iron‐nickel alloys. We analyze what gas species are produced and measure the CH4 formation rate. Our results indicate that the CH4 formation rate for iron catalysts strongly depends on both pressure and the H2/CO ratio, and that nickel is a more efficient catalyst at lower pressures and lower H2/CO ratios. This difference in catalytic properties between iron and nickel may come from the reaction steps concerning disproportionation of CO, hydrogenation of surface carbon, and the poisoning of the catalyst. These results suggest that nickel is important in the atmospheric re‐entry of impact condensate, while iron is efficient in circumplanetary subnebulae. Our results also indicate that previous numerical models of iron catalysis based on experimental data at 1 bar considerably overestimate CH4 formation efficiency at lower pressures, such as the solar nebula and the atmospheric re‐entry of impact condensate. 相似文献
562.
563.
564.
565.
Indicators of critical point behavior prior to rock failure inferred from pre-failure damage 总被引:4,自引:0,他引:4
To investigate possible indicators of critical point behavior prior to rock failure, the statistical properties of pre-failure damage were analyzed based on acoustic emission events (AE) recorded during the catastrophic fracture of typical rock samples under differential compression. AEs were monitored using a high-speed 32-channel waveform recording system. Time-dependent statistics, including the energy release rate, b-value of the magnitude–frequency distribution, fractal dimension and spatial correlation length (SCL) of the AE hypocenters were calculated for each data set. Each parameter is a function of the time-to-failure and thus can be treated as an indicator of the critical point. It is clear that the pre-failure damage evolution prior to catastrophic failures in several common rock-types is generally characterized by: 1) accelerated energy release, 2) a decrease in fractal dimension and SCL with a subsequent precursory increase, and 3) a decrease in b-value from 1.5 to 0.5 for hard rocks, and from 1.1 to 0.8 for soft rocks such S–C cataclasite. However, each parameter also reveals more complicated temporal evolution due to either the heterogeneity of the rock mass or the micro-mechanics of shear fracturing. This confirms the potential importance of integrated analysis of two or more parameters for successfully predicting the critical point. The decreasing b-value and increasing energy release may prove meaningful for intermediate-term prediction, while the precursory increase in fractal dimension and SCL may facilitate short-term prediction. 相似文献
566.
R. Ishikawa N. Narukage M. Kubo S. Ishikawa R. Kano S. Tsuneta 《Solar physics》2014,289(12):4727-4747
Spectro-polarimetric observations in the vacuum ultraviolet (VUV) range are currently the only means to measure magnetic fields in the upper chromosphere and transition region of the solar atmosphere. The Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) aims to measure linear polarization at the hydrogen Lyman-α line (121.6 nm). This measurement requires a polarization sensitivity better than 0.1 %, which is unprecedented in the VUV range. We here present a strategy with which to realize such high-precision spectro-polarimetry. This involves the optimization of instrument design, testing of optical components, extensive analyses of polarization errors, polarization calibration of the instrument, and calibration with onboard data. We expect that this strategy will aid the development of other advanced high-precision polarimeters in the UV as well as in other wavelength ranges. 相似文献
567.
568.
Xianghui Li Chiduru Takashima Akihiro Kano Saburo Sakai Yunhua Chen Baoliang Xu Iodp Expedition Scientists 《第四纪科学杂志》2011,26(2):178-189
Stable isotopes and element compositions of the fine‐grained matrix were measured for IODP Expedition 307 Hole U1317E drilled from the summit of Challenger Mound in Porcupine Seabight, northeast Atlantic, to explore the palaeoceanographic and palaeoclimatic background to development of the deep‐water coral mound. The 155 m long mound section was divided into two units by an unconformity at 23.6 mbsf: Unit M1 (2.6–1.7 Ma) and Unit M2 (1.0–0.5 Ma). Results from 519 specimens show a difference in δ13C value between Unit M1 (?0.6‰ to ?5.0‰) and Unit M2 (?1.0‰ to 1.0‰), but such a distinct difference was not seen in δ18O values (1.0‰–2.5‰), CaCO3 content (40–60 wt%), Sr/Ca ratio (2.0–8.0 mmol mol?1), and Mg/Ca ratio (10.0–20.0 mmol mol?1) through the mound. Positive δ18O and negative δ13C shifts at the mound base are consistent with the oceanographic changes in the northeast Atlantic at the beginning of the Quaternary. The positive δ13C regression in Unit M2 suggests a linkage to the mid Pleistocene intensified glaciation in the Northern Hemisphere. Warm Mediterranean Upper Core Water of Mediterranean Outflow Water, Eastern North Atlantic Water and cold Labrador Sea Water of North Atlantic Deep Water are key oceanographic features that cause spikes and shifts in stable isotope and element composition. However, the stable isotope values of the sediment matrix could not primarily record the glacial–interglacial eustatic/temperature change, but indirectly indicate current regimes of the intermediate oceanic layer where the coral mound grew. Similarly, elemental ratios and CaCO3 content may not represent the productivity and temperature of surface sea water, respectively, but superpose the fractions from both surface and bottom water. It is concluded that palaeoceanographic change coupled to the Pleistocene glacial/interglacial cycles is a key control on the geochemical stratigraphy of the matrix sediments of the carbonate mound developed in Porcupine Seabight. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
569.
Takako Masuda Ken Furuya Naoko Kohashi Mitsuhide Sato Shigenobu Takeda Makoto Uchiyama Naho Horimoto Takashi Ishimaru 《Journal of Oceanography》2010,66(6):801-813
Phytoplankton dynamics in the lower euphotic zone were observed by tracking a subsurface water released at 20-m depth from
Takumi, an artificial upwelling device. Takumi continually discharged seawater pumped up from a depth of 205 m: this water was mixed with 5-m depth water to adjust the
density to that of 20-m depth water of Sagami Bay, Japan. The discharged water was pulse-labeled at Takumi with uranine and tracked for 63.9 h with a drifting buoy equipped with a drogue at 20-m depth. We present a simple model
to estimate in situ phytoplankton net growth rates from temporal changes in phytoplankton abundance in the discharged water with correction for
the influence of water exchange between the discharged water and neighboring layers. Lagrangian observation showed active
growth of pico- and nanophytoplankton, especially cryptophytes and Synechococcus (Cyanobacteria), in the subsurface layer. In contrast, diatoms grew little in spite of micromolar concentrations of nutrients.
The active growth of pico- and nanophytoplankton was in good agreement with shipboard serial dilution culture experiments.
The low growth activity of diatoms was suggested to be related to low light availability in the subsurface layer. 相似文献
570.
Midori Kawabe Hiroshi Kohno Takashi IshimaruOsamu Baba Naho HorimotoReiko Ikeda Jota KandaTakafumi Kudo Masaji MatsuyamaMasato Moteki Yayoi OshimaTsuyoshi Sasaki 《Marine Policy》2009
This paper reviews the initial phase of a coastal education for sustainable development program for Edomae, the innermost reaches of Tokyo Bay. The program has been steered by a working group of Tokyo University of Marine Science and Technology faculty members from different academic backgrounds. Although the process began with conventional educational ideas, the ESD practice framework evolved to include more interactive activities. The overall goal is to pursue discussions of a plan for the sustainable use of Tokyo Bay in the coastal communities through a university–community partnership by developing Edomae ESD leaders in the coastal community. 相似文献