首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   6306篇
  免费   935篇
  国内免费   1066篇
测绘学   992篇
大气科学   649篇
地球物理   1208篇
地质学   3145篇
海洋学   921篇
天文学   48篇
综合类   504篇
自然地理   840篇
  2024年   27篇
  2023年   80篇
  2022年   180篇
  2021年   253篇
  2020年   261篇
  2019年   304篇
  2018年   207篇
  2017年   258篇
  2016年   291篇
  2015年   269篇
  2014年   387篇
  2013年   432篇
  2012年   392篇
  2011年   418篇
  2010年   332篇
  2009年   380篇
  2008年   411篇
  2007年   442篇
  2006年   423篇
  2005年   313篇
  2004年   280篇
  2003年   258篇
  2002年   248篇
  2001年   230篇
  2000年   202篇
  1999年   165篇
  1998年   157篇
  1997年   132篇
  1996年   117篇
  1995年   96篇
  1994年   75篇
  1993年   74篇
  1992年   49篇
  1991年   34篇
  1990年   28篇
  1989年   27篇
  1988年   20篇
  1987年   13篇
  1986年   15篇
  1985年   7篇
  1984年   6篇
  1983年   1篇
  1982年   4篇
  1981年   5篇
  1979年   2篇
  1977年   1篇
  1975年   1篇
排序方式: 共有8307条查询结果,搜索用时 46 毫秒
51.
52.
南极中山站大气气溶胶的化学组成及其来源的判别   总被引:1,自引:1,他引:1  
从1998年3月7日至1999年11月23日历时21个月,在南极中山站连续采集89个海洋气溶胶样品,本文提供全部样品的13种化学元素Cu、Pb、Zn、Cd、Fe、Al、Mn、Cr、V、K、Na、Ca、Mg含量的实测值.研究表明中山站气溶胶化学成份的含量具有季节性变化的特征.通过相关分析、因子分析、富集因子等方法判别不同时间段中山站气溶胶化学成份的来源。  相似文献   
53.
54.
A risk assessment of Tributyltin (TBT) in Tokyo Bay was conducted using the Margin of Exposure (MOE) method at the species level using the Japanese short-neck clam, Ruditapes philippinarum. The assessment endpoint was defined to protect R. philippinarum in Tokyo Bay from TBT (growth effects). A No Observed Effect Concentration (NOEC) for this species with respect to growth reduction induced by TBT was estimated from experimental results published in the scientific literature. Sources of TBT in this study were assumed to be commercial vessels in harbors and navigation routes. Concentrations of TBT in Tokyo Bay were estimated using a three-dimensional hydrodynamic model, an ecosystem model and a chemical fate model. MOEs for this species were estimated for the years 1990, 2000, and 2007. Estimated MOEs for R. philippinarum for 1990, 2000, and 2007 were approximately 1–3, 10, and 100, respectively, indicating a declining temporal trend in the probability of adverse growth effects.A simplified software package called RAMTB was developed by incorporating the chemical fate model and the databases of seasonal flow fields and distributions of organic substances (phytoplankton and detritus) in Tokyo Bay, simulated by the hydrodynamic and ecological model, respectively.  相似文献   
55.
ARGO剖面浮标数据质量控制过程剖析   总被引:12,自引:4,他引:12  
ARGO计划的观测目标是能取得精度分别为0.5℃和0.01PSU的海水温度和盐度资料。然而,由于目前海水盐度是采用海水电导率间接导出的,而测量海水电导率的传感器很容易产生偏差。因此,必须对获得的ARGO数据进行质量控制。文章详细介绍了ARGO剖面浮标资料实时质量控制模式和延时质量控制模式及其采用的质量控制方法等。  相似文献   
56.
利用低温显微镜系统对含有不同浓度海藻糖的脂质体悬浮液 ,在不同的降温速率下的结晶现象进行显微研究 ,得出不同条件下的冰晶生长图像 ;并研究脂质体在不同的降温速率下的冻干过程 ,比较了不同降温速率下的冻干脂质体的外观和冻干脂质体复水后的囊泡粒径变化。结果表明 ,对于液体药品快速冻结后得到的冻干品质量优于慢速冻结。  相似文献   
57.
Abstract-Intertidal zone is a significant wetland between land and ocean. It plays an important rolein maintaining local ecological balance. Both Mai Po and Futian intertidal mudflats are located in Shen-zhen Bay and are important "refueling" point along the East Asian/Australian flyway of migratory birds.The environmental quality of Mai Po and Futian mudflats have aroused great concern due to rapid eco-nomic developments in Hong Kong and Shenzhen in recent decades. Microinfauna of Mai Po and Futianmudflats was investigated in December 2000 and the faunal data were used to assess their environmentalquality. Two other mudflats, namely Ma Wan Typhoon Shelter (a more disturbed area) and Luk Kengintertidal mudflat (a place with relatively less human disturbance), were also sampled for macroinfaunaand used as reference mudflats. Shannon-Weaver species diversity index (I_(sd)), biotic coefficient (C_b)and macrofaunal pollution index (I_(mp)) of the macrofauna community on four intertidal mudflats wereused to  相似文献   
58.
An overview of the Oyashio ecosystem   总被引:3,自引:0,他引:3  
The Oyashio shelf region and the seasonally ice-covered areas north of Hokkaido are highly productive, supporting a wide range of species including marine mammals, seabirds and commercially important species in the western subarctic Pacific. The fishes include gadids, such as walleye pollock and Pacific cod, and subarctic migratory pelagic fishes such as chum salmon and pink salmon. It is also an important summer feeding ground for subtropical migrants such as the Japanese sardine, Japanese anchovy, Pacific saury, mackerels, Japanese common squid, whales and seabirds. In recent decades, some components of the Oyashio ecosystem (i.e., phytoplankton, mesozooplankton, gadid fish, and subtropical migrants) have shown changes in species abundance or distribution that are correlated with environmental changes such as the 1976/1977 and 1988/1989 regime shifts. The First Oyashio Intrusion moved northward from the mid-1960s until the late 1970s, when it moved southward until the 1980s, after which it returned to the north again after the mid-1990s. The sea-surface temperature in spring decreased after the late 1970s, increased after the late 1980s, and remained high during the 1990s. The extent of ice cover in the Sea of Okhostk also decreased during the latest warming in the 1980–1990s but has increased again since the late 1990s. This and other variabilities affect the Oyashio ecosystem and the surrounding region.  相似文献   
59.
有机饵料常规饵料对扣蟹品质的比较研究   总被引:2,自引:0,他引:2  
从扣蟹的体重、壳长、壳宽,扣蟹体内粗蛋白、氨基酸及药物残留和重金属含量等几个方面比较了在有机养殖和常规养殖模式下扣蟹的品质。结果显示,在有机养殖模式下,扣蟹的体重增长,壳长、壳宽与常规养殖差异显著(p<0.05);体内粗蛋白含量、必需氨基酸含量中,有机养殖组为55.43%、48.07%,常规养殖组为46.55%、40.64%,常规养殖组扣蟹的氨基酸含量明显低于有机饵料养殖组;在药残和重金属含量方面,除常规养殖组的六六六检出外,其余指标均符合有机蟹卫生质量地方标准(DB32/T609.3-2003),但有机养殖组的重金属含量则远较常规养殖组低。  相似文献   
60.
王波 《海岸工程》2002,21(4):6-12
简要介绍了活性污泥1号模型中14个污水水质参数与5个化学计量系数的估测方法和典型取值。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号