全文获取类型
收费全文 | 15748篇 |
免费 | 2495篇 |
国内免费 | 4744篇 |
专业分类
测绘学 | 2139篇 |
大气科学 | 3056篇 |
地球物理 | 3437篇 |
地质学 | 6396篇 |
海洋学 | 3322篇 |
天文学 | 1389篇 |
综合类 | 1339篇 |
自然地理 | 1909篇 |
出版年
2024年 | 123篇 |
2023年 | 284篇 |
2022年 | 565篇 |
2021年 | 630篇 |
2020年 | 807篇 |
2019年 | 897篇 |
2018年 | 668篇 |
2017年 | 806篇 |
2016年 | 806篇 |
2015年 | 941篇 |
2014年 | 919篇 |
2013年 | 1088篇 |
2012年 | 1006篇 |
2011年 | 998篇 |
2010年 | 820篇 |
2009年 | 940篇 |
2008年 | 1051篇 |
2007年 | 1209篇 |
2006年 | 1188篇 |
2005年 | 1040篇 |
2004年 | 862篇 |
2003年 | 714篇 |
2002年 | 673篇 |
2001年 | 502篇 |
2000年 | 623篇 |
1999年 | 604篇 |
1998年 | 466篇 |
1997年 | 337篇 |
1996年 | 277篇 |
1995年 | 216篇 |
1994年 | 193篇 |
1993年 | 179篇 |
1992年 | 150篇 |
1991年 | 92篇 |
1990年 | 55篇 |
1989年 | 83篇 |
1988年 | 44篇 |
1987年 | 34篇 |
1986年 | 35篇 |
1985年 | 16篇 |
1984年 | 13篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 5篇 |
1977年 | 2篇 |
1954年 | 4篇 |
1877年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
依据黄、东海环流的的动力学模型 ,运用“流速分解法”对黄、东海正压环流进行了数值模拟。计算结果表明冬季黄海正压环流主要受风应力影响 ,基本形态为黄海暖流由济州岛西南进入南黄海中部 ,其东西两侧分别为两支向南流动的沿岸流 ;夏季主要受到潮致体力的影响 ,为一逆时针涡旋。东海环流主要是边界力作用驱动的结果 ,东海黑潮、台湾暖流和对马暖流较稳定。冬季风应力对东海环流表层流场有消弱作用 ,在夏季则有一定增强作用。 相似文献
102.
梭鱼标准代谢、内源氮排泄与体重和温度的关系 总被引:5,自引:0,他引:5
在 13.5 ,18,2 1.5 ,2 4和 2 7℃ 5个温度条件下测定了梭鱼 (体重范围 1.88~ 14.0 2 g)的标准代谢率和内源氮排泄率。梭鱼标准代谢率随体重的增加而增加 ,二者的关系为幂函数关系 ;随温度的升高而增加 ,二者的关系为指数关系 ;标准代谢率与体重和温度的关系可用如下方程表示 :RS=0 .12 4 6 W0 .9954 e0 .0 84 1T(r2 =0 .92 2 0 )。梭鱼的氨氮、尿素、总氮及能量的排泄率随体重和温度的增加而增加 ,与体重为幂函数关系 ,与温度的关系为多项式形式。梭鱼氨氮和尿素日排泄率的变幅分别为 0 .15~ 0 .88mg N/d和 0 .0 3~ 0 .2 9mg N/d。不同温度下 ,尿素排泄量占总氮比例在 9.9%~2 2 .4 9%之间 ,随温度升高该值有逐渐增大的趋势。 相似文献
103.
104.
The distribution of dissolved and participate concentrations of As, Cr and V was investigated in the mixing area of the Po river in five surveys over the period March 1992-March 1995. The data obtained indicate noticeable contamination of coastal waters of the northern Adriatic with Cr but not As or V. Total dissolved concentrations for As and V were comparable with oceanic levels but were higher by a factor of 4 for Cr. These results suggest either low anthropogenic inputs of As and V, from terrigenous and atmospheric sources, or efficient removal mechanisms. The investigated metals had low reactivity during freshwater-seawater mixing and the distribution of concentrations in the dissolved and solid phases suggests that the dilution process is the main factor controlling the transport of these metals to the sea in low-to-medium solid transport conditions. Further investigations are required to elucidate the behavior of these metals during high solid transport conditions. Significant changes in the speciation of As occurred during the transition between the two end-member matrices. In the coastal waters of the northern Adriatic, the arsenite fraction in winter, and the arsenite and dimethylarsinate fractions in summer increased with respect to riverine waters. Changes in the speciation of chromium were minor, but also showed a small increase in reduced species in marine waters. 相似文献
105.
应用边界拟合坐标系统,解决了闽江河口河道曲折汊道多造成的计算方向与河底走向交角过大的难点;针对闽江河口长宽比相差较大的特点,移植了通常用于河道计算的沿纵向求解大尺度矩阵问题转化为沿横向小尺度矩阵求逆的水流方程求解方法,采用全隐差分格式,使闽江口数模网格步长最小控制在50m左右,时步长达3min,潮位、流场与实测拟合良好。 相似文献
106.
Abstract. Monthly changes in the community structure of hypoxic soft-bottom macrobenthos have been studied at a station at 34 m depth in Ancón Bay (Peru) before and during two El Niño (EN) events. Of these events, 1982-83 is considered the strongest, and 1991–93 one of the most prolonged in the 20th century. On the oceanographic scale, EN 1982–83 ranges as "very strong", whereas EN 1991–93 ranges as "moderate".
The thermal anomalies at the station during EN 1982–83 (+ 7.8 °C) were almost twice those of EN 1991–93 (+ 4.1 °C). However, the community changes were not in all cases proportional to the extent of warming. Species numbers increased in a similar way (up to 24 species from near zero in each of the two events), but maximum faunal density was five times higher, and mean biomass was twice as high in 1982–83 compared with the event a decade later. Species diversity was slightly higher during EN 1982–83, whereas successional and trophic changes occurred on a broader scale during EN 1991–93. On the whole, the impact of the long-lasting event on the small soft-bottom macrofauna was not much weaker than that of the exceptionally strong event.
The authors discuss the mechanisms which may be responsible for the differences and similarities encountered in the benthic community dynamics during these two events. Both in the unusually strong and the unusually long EN, the community revealed a pattern of early biological response several months ahead of the onset of local warming which marks the official begin of EN. The question is addressed to what extent the increase of certain parameters in the benthic community could be used for predictive purposes. 相似文献
The thermal anomalies at the station during EN 1982–83 (+ 7.8 °C) were almost twice those of EN 1991–93 (+ 4.1 °C). However, the community changes were not in all cases proportional to the extent of warming. Species numbers increased in a similar way (up to 24 species from near zero in each of the two events), but maximum faunal density was five times higher, and mean biomass was twice as high in 1982–83 compared with the event a decade later. Species diversity was slightly higher during EN 1982–83, whereas successional and trophic changes occurred on a broader scale during EN 1991–93. On the whole, the impact of the long-lasting event on the small soft-bottom macrofauna was not much weaker than that of the exceptionally strong event.
The authors discuss the mechanisms which may be responsible for the differences and similarities encountered in the benthic community dynamics during these two events. Both in the unusually strong and the unusually long EN, the community revealed a pattern of early biological response several months ahead of the onset of local warming which marks the official begin of EN. The question is addressed to what extent the increase of certain parameters in the benthic community could be used for predictive purposes. 相似文献
107.
鳗弧菌(Vibrio anguillarum)M3菌株生长条件及其对蛋白酶产量的影响 总被引:2,自引:5,他引:2
采用体外测定细菌浓度、胞外产物(ECP)蛋白含量和蛋白酶活力的方法,进行了鳗弧菌M3菌株在2216E培养基中的培养条件研究。结果表明,该菌株用固体培养基培养至24h左右,可得到较高的菌体浓度、ECP蛋白含量和蛋白酶活力。采用响应面分析方法设计实验,用SAS统计软件分析数据,得到NaCl浓度、pH值和温度对菌体生长及蛋白酶产量影响的回归模型。在2216E培养基的基础上,添加不同氮源、碳源物质以及不同浓度蛋白胨进行生长研究。结果表明,胰大豆蛋白胨能促进菌体生长及ECP蛋白分泌;NH4Cl与酪蛋白水解物可抑制蛋白酶的产生;牙鲆肌肉匀浆对菌体、ECP蛋白产量和蛋白酶产生有不同程度的促进作用;培养基中蛋白胨浓度为4%时菌体量与ECP蛋白含量达最高值,在蛋白胨浓度为2%时蛋白酶分泌量已稳定;1%的葡萄糖、蔗糖、甘油均能显著地提高菌体及ECP蛋白产量,却抑制了蛋白酶的产生。 相似文献
108.
Practical implementation of Hilbert-Huang Transform algorithm 总被引:12,自引:0,他引:12
Hilbert-Huang Transform (HHT) is a newly developed powerful method for nonlinear and non-stationary time series analysis. The empirical mode decomposition is the key part of HHT, while its algorithm was protected by NASA as a US patent, which limits the wide application among the scientific community. Two approaches, mirror periodic and extrema extending methods, have been developed for handling the end effects of empirical mode decomposition. The implementation of the HHT is realized in detail to widen the application. The detailed comparison of the results from two methods with that from Huang et al. (1998, 1999), and the comparison between two methods are presented. Generally, both methods reproduce faithful results as those of Huang et al. For mirror periodic method (MPM), the data are extended once forever. Ideally, it is a way for handling the end effects of the HHT, especially for the signal that has symmetric waveform. The extrema extending method (EEM) behaves as good as MPM, and it is better t 相似文献
109.
In order to clarify the formation and circulation of the Japan/East Sea Intermediate Water (JESIW) and the Upper portion of
the Japan Sea Proper Water (UJSPW), numerical experiments have been carried out using a 3-D ocean circulation model. The UJSPW
is formed in the region southeast off Vladivostok between 41°N and 42°N west of 136°E. Taking the coastal orography near Vladivostok
into account, the formation of the UJSPW results from the deep water convection in winter which is generated by the orchestration
of fresh water supplied from the Amur River and saline water from the Tsushima Warm Current under very cold conditions. The
UJSPW formed is advected by the current at depth near the bottom of the convection and penetrates into the layer below the
JESIW. The origin of the JESIW is the low salinity coastal water along the Russian coast originated by the fresh water from
the Amur River. The coastal low salinity water is advected by the current system in the northwestern Japan Sea and penetrates
into the subsurface below the Tsushima Warm Current region forming a subsurface salinity minimum layer.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
110.
对1999年9~10月采自北太平洋亚热带环流区的19份表层海水样品的Ra同位素分析表明。研究海域表层水中的^226Ra、^228Ra放射性比度分别介于0.67~0.92、0.08~0.30Bq/m^3之间,平均值分别为0.74、0.11Bq/m^3.^226Ra/^228Ra)A.R.活度比的变化范围为0.11~0.44,平均值为0.19.上述数值明显低于近岸海域水体的相应值,表现为典型的开阔大洋水的特征.从空间分布的特征看,研究海域Ra同位素含量与^226Ra/^228Ra)A.R.值均呈均匀分布态势.将本研究结果与历史数据进行对比后发现,本研究获得的^226Ra、^228Ra放射性比度比20世纪60~80年代得到的数据来得低,可能与水体层化作用加强导致的Ra补充量的减少以及生物生产力升高导致的Ra迁出量的增加有关.北太平洋亚热带环流区表层水中Ra同位素的时间变化与文献报道的该海域叶绿素a、硅酸盐、磷酸盐含量与初级生产力的历史变化趋势相吻合. 相似文献