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91.
92.
Saldanha Bay is a narrow-mouth bay on the west coast of South Africa linked to the southern Benguela upwelling system. Bay productivity was investigated by use of the conventional light-and-dark bottle oxygen method, and, for comparison, through assimilation of the stable isotope tracer 13C. Gross community production GCP and net community production NCP, as determined from the oxygen method, were respectively 2.6 and 2.4 times higher than estimates determined from the stable isotope method. Chlorophyll a (Chl a) concentrations increased with the onset of spring and well-defined subsurface maxima developed in association with increasingly stratified conditions (mean water column Chl a concentrations ranged from 5.4 to 31.5?mg m?3 [mean 15.5?mg m?3; SD 7.6]). A sharp decline in photosynthetic rates P* (GCP normalised to Chl a concentration) with depth was attributed to light limitation, as demonstrated by the high vertical attenuation coefficients for downward irradiance Kd, which varied from 0.29 to 0.70?m?1 (mean 0.48?m?1; SD 0.12). Productivity maxima were consequently near-surface despite the presence of deeper subsurface biomass maxima. The community compensation depth Zcc, where gross community production balances respiratory carbon loss for the entire community, ranged from 2.9 to 9.2?m (mean 5.8?m; SD 2.2), and was typically shallower than the 1% light depth for PAR (photosynthetically available radiation), Z1%PAR, which is traditionally assumed to be the depth of the euphotic zone and which ranged from 6.6 to 15.9?m (mean 9?m; SD 2.6). Autotrophic communities, where organic matter is produced in excess of respiratory demand, were confined on average to the upper 5.8?m of the water column, and often excluded the bulk of the phytoplankton community, where light limitation is considered to lead to heterotrophic community metabolism. Estimates of integrated water column productivity ranged from 0.84 to 8.46?g C m–2 d?1 (mean 3.35?g C m?2 d?1; SD 1.9). 相似文献
93.
根据帕尔默干旱模式的基本思路,建立动态的能反应旱涝持续特征的适合于天目山地区的旱涝指数。对采自天目山的柳杉树轮进行交叉定年后,测得树轮的δ^13C年序列,将δ^13C去除大气CO2趋势影响后的高频变化与不同时段的旱涝指数进行相关分析,结果显示:春夏季的旱涝指数与当年和滞后一年的δ^13C序列有着比较显著的相关性,表明树轮δ^13C对春夏季旱涝的发生有着比较好的响应。根据此显著相关性,利用多元回归方程重建了历史时期的春夏季旱涝指数,分析表明天目山地区春夏季旱涝的发生具有比较明显的年代际变化特征,为研究该地区气候变化特征提供了较可靠的参考依据。 相似文献
94.
通过对比IPCC历次评估报告中全球碳循环的收支发现,尽管评估报告在估算各主要碳库及其间的通量时差别不大,但表层至中深层海水间溶解无机碳通量却存在巨大差异。利用δ13C的收支平衡检验了这一通量的适用范围,结果表明:IPCC 1996年和2007年评估报告对此通量估计过大,而1990年和2001年评估报告估计偏小。 相似文献
95.
Keiji Horikawa Masafumi Murayama Masao Minagawa Yoshihisa Kato Takuya Sagawa 《Quaternary Research》2010,73(3):573-582
The n-alkane C31/(C29 + C31) ratios from surface sediments in the eastern equatorial Pacific (EEP) exhibit higher values to the north and lower values to the south across the southern edge (2–4°N) of the Intertropical Convergence Zone (ITCZ). Since plants tend to synthesize longer chain length n-alkanes in response to elevated temperature and/or aridity, the higher C31/(C29 + C31) ratios at northern sites suggest a higher contribution of vegetation under hot and/or dry conditions. This is consistent with the observation that northern sites receive higher levels of plant waxes transported by northeasterly trade winds from northern South America, where hot and dry conditions prevail. Furthermore, from a sediment core covering the past 750 ka (core HY04; 4°N, 95°W) we found that C31/(C29 + C31) ratios exhibit a long-term decrease from MIS (marine oxygen isotope stage) 17 to 13. During this period, the zonal SST (sea-surface temperature) gradient in the equatorial Pacific increased, suggesting an increase in Walker circulation. Such intensified Walker circulation may have enhanced moisture advection from the equatorial Atlantic warm pool to the adjacent northern South America, causing arid regions in northern South America to contract, which may explain long-term decrease in n-alkane chain lengths. 相似文献
96.
琼东南盆地崖13-1气田陵三段沉积微相对储层非均质性及流动单元划分的影响 总被引:6,自引:2,他引:4
崖13-1气田陵三段是河控与潮控的辫状三角洲,主要储层沉积微相为分流河道、水下分流河道、河口坝、远砂坝及席状砂,其中河口坝的储层物性比分流河道和水下分流河道微相好,席状砂与远砂坝的物性相对较差,而各类正韵律河道与反韵律的砂坝决定了各垂向流动单元储层韵律特征。气田内的隔夹层与不同规模的海泛面相关,隔层以前三角洲泥为主,分布稳定,而夹层以分流间湾与水下分流间湾泥为主,分布较局限。结合沉积微相分布、储层非均质性及断层的分布,可以把气田区分为两个大区及6个流动单元,而南II、南III区仍可有较好的储层,但由于构造上处于低部位,含气前景还需进一步论证。 相似文献
97.
98.
We have conducted elemental, isotopic, and Rock-Eval analyses of Cenomanian–Santonian sediment samples from ODP Site 1138 in the southern Indian Ocean to assess the origin and thermal maturity of organic matter in mid-Cretaceous black shales found at this high-latitude location. Total organic carbon (TOC) concentrations range between 1 and 20 wt% in black to medium-gray sediments deposited around the Cenomanian–Turonian boundary. Results of Rock-Eval pyrolysis indicate that the organic matter is algal Type II material that has experienced modest alteration. Important contributions of nitrogen-fixing bacteria to the amplified production of organic matter implied by the high TOC concentrations is recorded in δ15N values between −5 and 1‰, and the existence of a near-surface intensified oxygen minimum zone that favored organic carbon preservation is implied by TOC/TN ratios between 20 and 40. In contrast to the marine nature of the organic matter in the Cenomanian–Turonian boundary section, deeper sediments at Site 1138 contain evidence of contributions land-derived organic matter that implies the former presence of forests on the Kerguelen Plateau until the earliest Cenomanian. 相似文献
99.
陈宝 《地震地磁观测与研究》1993,14(2):67-73
计算机 I/O 端口病毒破坏并行口和 RS232串行口,致使打印机无法工作,双机通讯无法进行。本文据处理邯郸台网286微机 I/O 端口病毒的实践,剖析了该病毒的机理,提供了快速诊断和消除该病毒的方法,对于保障台网特别是华北遥测台网联网系统的正常运行具有实用意义。 相似文献
100.