全文获取类型
收费全文 | 2290篇 |
免费 | 340篇 |
国内免费 | 583篇 |
专业分类
测绘学 | 49篇 |
大气科学 | 118篇 |
地球物理 | 295篇 |
地质学 | 1483篇 |
海洋学 | 638篇 |
天文学 | 282篇 |
综合类 | 145篇 |
自然地理 | 203篇 |
出版年
2024年 | 5篇 |
2023年 | 25篇 |
2022年 | 54篇 |
2021年 | 66篇 |
2020年 | 62篇 |
2019年 | 66篇 |
2018年 | 63篇 |
2017年 | 71篇 |
2016年 | 92篇 |
2015年 | 80篇 |
2014年 | 111篇 |
2013年 | 147篇 |
2012年 | 103篇 |
2011年 | 134篇 |
2010年 | 126篇 |
2009年 | 163篇 |
2008年 | 185篇 |
2007年 | 185篇 |
2006年 | 175篇 |
2005年 | 142篇 |
2004年 | 128篇 |
2003年 | 116篇 |
2002年 | 102篇 |
2001年 | 82篇 |
2000年 | 124篇 |
1999年 | 89篇 |
1998年 | 96篇 |
1997年 | 61篇 |
1996年 | 61篇 |
1995年 | 55篇 |
1994年 | 55篇 |
1993年 | 38篇 |
1992年 | 30篇 |
1991年 | 20篇 |
1990年 | 25篇 |
1989年 | 11篇 |
1988年 | 11篇 |
1987年 | 10篇 |
1986年 | 8篇 |
1985年 | 13篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1978年 | 3篇 |
1976年 | 1篇 |
排序方式: 共有3213条查询结果,搜索用时 15 毫秒
81.
在实验室条件下,研究了温度对赤潮异弯藻生长速率、细胞体积和生化组成的影响。结果表明,赤潮异弯藻在10~30℃之间均能正常生长,25℃时生长速率最高,25℃为其最适生长温度;赤潮异弯藻的细胞体积随着温度的升高大致呈逐渐减小的趋势,10℃时细胞体积最大(823.89μm3),25℃时细胞体积最小(387.98μm3)。进一步分析表明,赤潮异弯藻生长速率与细胞体积(对数值)呈显著的负相关关系(P0.05)。在10~25℃之间,赤潮异弯藻单个细胞的碳、氮含量随着温度的升高呈逐渐减少的趋势,其单位体积细胞的碳、氮含量却呈单峰变化(15℃时结果为峰值)现象;叶绿素a含量在单个细胞和单位体积细胞两个层次上随温度的变化趋势一致,即其在整个温度区间内随着温度的升高均呈逐渐增加的趋势。赤潮异弯藻细胞C∶Chl a和N∶Chl a随着温度的升高呈先减小后增加的趋势,均在10℃时最大,在25℃时最小。 相似文献
82.
83.
提出了一种基于MDA的空间信息服务组合建模方法。该方法使用UML设计空间信息服务组合元模型,利用MDA模型转换机制生成空间信息服务链设计器,利用设计器构建空间信息服务组合模型。该建模方法能很好地描述数据流和控制流,通过引入空间信息服务本体库,实现服务资源动态组合建模。 相似文献
84.
85.
在对应用集成及其发展分析的基础上,将Web Services技术运用到空间信息应用集成,提出和建立了面向服务的空间信息应用集成框架,包括Web应用层、服务集成层、服务层和UDDI等4个组成部分。通过该框架,可以实现空间信息集成、服务集成和应用集成。论文解决了空间信息应用集成框架中的2个关键问题:(1)提出了分别从数据层次和业务层次对原有系统集成的解决方案,在数据层次上,提出了基于XML/GML的空间数据封装和基于Web服务接口的空间数据封装策略;在业务层次上,提出根据系统的功能模块和业务逻辑分别进行封装的策略;(2)提出了空间信息Web服务链接和服务组合的串联、并联和混联模式,通过三种模式服务链的设计,可以实现多个服务的链接和组合,从而完成空间信息以及应用集成。 相似文献
86.
Phytoplankton pigment patterns and community composition in the northern South China Sea during winter 总被引:1,自引:0,他引:1
Phytoplankton pigment patterns and community composition were investigated in the northern South China Sea using high-performance liquid chromatography and the CHEMTAX software from February 11 to 23, 2009. We recognized four different vertical distribution patterns of pigments: chlorophyll a (Chl a)-like type, divinyl chlorophyll a (DV Chl a) type, even distribution type, and surface type. The average value of ratios of accessory photo-protective pigments (APP) to accessory photo-synthetic pigments was 0.89±0.63 in the upper 50 m and 0.16±0.06 below 50 m depth. With increasing depth, APP decreased and photo-synthetically active radiation was attenuated. There was an obvious succession in the phytoplankton community from inshore to the open sea. Diatoms were dominant in the inshore region, while pelagophytes, Prochlorococcus, cyanobacteria and prymnesiophytes were dominant in the open sea. The vertical distribution of phytoplankton also differed greatly from inshore to the open sea. In the coastal and shelf region, diatoms were important components in the whole water column. Cyanobacteria also had a high abundance at the Subsurface Chlorophyll a Maxima (SCM) in the shelf region. In the slope and open sea, Prochlorococcus and cyanobacteria were important groups above the SCM, while pelagophytes dominated below the SCM. 相似文献
87.
Ultrasound-assisted solvent extraction was confirmed as a novel,effective method for separating lipid from mackerel pro-tein,resulting in a degreasing rate (DR) of 95% and a nitrogen recovery (NR) of 88.6%.To obtain protein hydrolysates with high ni-trogen recovery and low bitter taste,enzymatic hydrolysis was performed using eight commercially available proteases.It turned out that the optimum enzyme was the ‘Mixed enzymes for animal proteolysis’.An enzyme dosage of 4%,a temperature of 50℃,and a hydrolysis time of 300 min were found to be the optimum conditions to obtain high NR (84.28%) and degree of hydrolysis (DH,16.18%) by orthogonal experiments.Glutamic acid was the most abundant amino acid of MDP (defatted mackerel protein) and MDPH (defatted mackerel protein hydrolysates).Compared with the FAO/WHO reference protein,the essential amino acid chemical scores (CS) were greater than 1.0 (1.0 1.7) in MDPH,which is reflective of high nutritional value.This,coupled with the light color and slight fishy odor,indicates that MDPH would potentially have a wide range of applications such as nutritional additives,functional ingredients,and so on. 相似文献
88.
The influence of freeze-thaw cycles on the granulometric composition of Moscow morainic clay 总被引:2,自引:0,他引:2
The freeze-thaw cycling process considerably changes the composition,structure,and properties of soils.Since the grain size is the most important factor in determining soil characteristics,our current research primarily aims to investigate dynamic changes of the soil fraction when exposed to freeze-thaw conditions.We observed two series of Moscow morainic clayey specimens(g QmII):(I) the original series,and(II) the remolded series.We subjected each series of soil specimens to different frequencies of freeze-thaw cycles(3,6,20,and 40 cycles),and we used granulometric tests to analyze both series before and after exposure to freeze-thaw conditions.As a result of our experiments,the granulometric compositions tended to be distributed evenly after 40 freeze-thaw processes(i.e.,content of fraction for 0.1–0.05 mm was increased after 40 freeze-thaw cycles) because the division of coarse grains and the aggregation of fine grains were synchronized during the freeze-thaw process.The soil grains in both series changed bi-directionally.In the original series,changes of the sand grains were conjugated with the clay grains,and in the remolded series,changes of the sand grains were conjugated with the silt grains,because potential energy difference caused the division and aggregation processes to relate to the counteraction process.The even distribution of soil grain size indicated the state of equilibrium or balance.The granulometric compositions were altered the most during the sixth freeze-thaw cycle,because the coefficient of the intensity variation of the grain fineness(Kvar) had its maximum value at that time. 相似文献
89.
以室内实验测定了方斑东风螺(Babylonia areolata)在饥饿120d过程中形态、组织生化成分及RNA/DNA比值的连续变化.结果显示,饥饿前期幼螺体重变幅较小,肝体比与体壳比下降迅速,三者分别于饥饿80、40、20d时显著地低于对照组,至饥饿120d时其降幅分别为22.33%、44.02%、30.39%.方斑东风螺在饥饿过程中,螺足肌与肝胰脏的水分含量分别从80.19%、48.44%上升至89.68%、63.97%;灰分含量分别从11.35%、8.92%增加至22.80%、16.52%;肝胰脏蛋白质含量从53.18%上升至56.65%.饥饿40d时,其足肌、肝胰脏脂肪含量均显著低于对照组,糖原含量在其饥饿20、40d时也显著地下降.饥饿120d时,其足肌的脂肪和糖原含量相应降幅分别为32.22%、44.64%,而肝胰脏的脂肪和糖原含量相应降幅则分别为26.87%、47.17%.足肌蛋白质含量在其饥饿80d前较稳定,后期迅速下降,实验结束时降幅为8.61%.这2种组织的RNA/DNA比值也呈逐渐下降趋势.上述结果表明,在饥饿状态下幼螺主要消耗这2种组织中脂肪与糖原的供能,当禁食长达80d后则加大对足肌蛋白质的动用,而相对保留肝胰脏蛋白质.组织含水量、RNA/DNA比值均可作为方斑东风螺饥饿状态下的营养预测指标. 相似文献
90.
地理信息服务应用中,单一的功能服务往往无法独立完成复杂的地理信息应用,需要不同粒度的服务组合及协调机制。本文重点研究地理信息服务的组合建模方法,提出基于Petri网的地理信息服务组合建模理论。首先,给出基于Petri网的地理信息服务的定义和图形化描述,然后结合三维地理信息的应用,给出了三维空间分析服务组合的实例分析,最后通过烟草行业的地理信息服务应用验证基于Petri网的服务组合模型的可行性。 相似文献