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   234篇
  免费   21篇
  国内免费   45篇
测绘学   1篇
大气科学   2篇
地球物理   60篇
地质学   28篇
海洋学   163篇
综合类   44篇
自然地理   2篇
  2023年   3篇
  2022年   4篇
  2021年   2篇
  2020年   6篇
  2019年   13篇
  2018年   4篇
  2017年   10篇
  2016年   10篇
  2015年   9篇
  2014年   13篇
  2013年   16篇
  2012年   5篇
  2011年   10篇
  2010年   7篇
  2009年   14篇
  2008年   17篇
  2007年   19篇
  2006年   6篇
  2005年   15篇
  2004年   9篇
  2003年   11篇
  2002年   16篇
  2001年   4篇
  2000年   6篇
  1999年   14篇
  1998年   13篇
  1997年   11篇
  1996年   5篇
  1995年   4篇
  1994年   2篇
  1993年   4篇
  1992年   6篇
  1991年   2篇
  1990年   5篇
  1989年   2篇
  1985年   1篇
  1982年   2篇
排序方式: 共有300条查询结果,搜索用时 15 毫秒
151.
交配前雄性大鼠分别按每 kg 体质量1.25、2.50、5.00 g 的剂量灌服半叶马尾藻多糖,连续灌胃60 d,雌性大鼠分别以相同剂量连续灌胃14 d,以雄雌1∶1的比例合笼5 d,每天做阴道分泌物涂片检查,见精子者记为妊娠第1天,交配后雄鼠处死,测定血清睾酮(T)水平,取雄鼠附睾进行精子成活率、精子计数和精子畸形率测定,计算睾丸、附睾脏器比,并进行病理组织学检查;雌鼠继续灌胃至妊娠7 d,于妊娠14 d 处死,计算受孕率、着床数、黄体数、死胎、活胎和吸收胎,测定血清促卵泡生成素(FSH)、黄体生成素(LH)和雌二醇(E2)水平,计算脏器比并进行病理组织学检查.结果显示,给药组大鼠的精子成活率、精子计数、精子畸形率、受孕率、着床数、黄体数、死胎、活胎、吸收胎、睾丸、附睾和卵巢脏器比以及血清 T、FSH、LH 和 E2水平与对照组相比差异无统计学意义(P >0.05),生殖器官病理组织学检查未见明显异常.在本实验条件下,半叶马尾藻多糖对大鼠无明显生殖毒性  相似文献   
152.
Trace metals play crucial roles in the carbon and nitrogen metabolism of cyanobacteria. Physiological responses to metal limitation and toxicity in culture have shown that iron is important for photosynthesis and energy distribution in the cell while both iron and molybdenum are biochemically involved in nitrate reduction and nitrogen fixation. Nitrogen fixation is also relatively sensitive to copper toxicity. Consequently, factors that affect the supply rate, chemical speciation, or the recycling of trace metals can alter patterns of primary productivity and nitrogen metabolism. Overall, three trace metal dependent processes may contribute towards dominance: efficient use of limiting light, nitrogen fixation, and production of extracellular iron binding compounds.  相似文献   
153.
重庆老龙洞地下河间隙水重金属污染及毒性评估   总被引:3,自引:2,他引:1  
为查明重庆岩溶地区老龙洞地下河重金属污染情况,于2013年9月采集了地下河上覆水体和表层沉积物间隙水共7组水样,用ICP-OES测定地下河上覆水体和表层沉积物间隙水中的Mn含量,ICP-MS测定Cu、Cd、Cr、As和Pb含量,分析了老龙洞地下河表层沉积物间隙水中各重金属元素的空间分布,对不同介质中的重金属元素进行相关性分析,并参考美国EPA推荐的“国家推荐水质标准”对间隙水中重金属可能产生的生物毒性进行评估。结果表明:老龙洞地下河上覆水体中Mn和Pb的浓度超过了GB 5749-2006规定的生活饮用水限值(Mn≤100 ug/L,Pb≤10 ug/L),不可作为饮用水源;间隙水中各重金属元素的浓度都比上覆水体高,有向上覆水体扩散的潜在可能性。除Pb、Mn外,间隙水中重金属的含量大小依次为上游>中游>下游。上覆水中除Mn与As、Cd与Cr外,其他金属元素之间的相关性不大;间隙水中Cr、Cu、As和Cd的相关系数分别为0.895~0.997,呈高度正相关。间隙水中金属元素除As不会对水生生态系统产生急性毒性外,Cr、Cu、Cd和Pb都会对水生生态系统产生急性毒性,尤以Cr、Cu、Cd最为严重。   相似文献   
154.
The effects of BDE-47 on the growth and antioxidative responses of the seedlings of Kandelia obovata (Ko) and Avicennia marina (Am) were compared in an 8-week hydroponic culture spiked with different levels of BDE-47, 0.1, 1, 5 and 10 mg l−1. The two highest BDE-47 levels significantly suppressed the growth and increased the activities of three antioxidative enzymes, superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), of Ko in week 1. However, SOD and POD activities at high levels of BDE-47 became lower than the control in week 8. On the contrary, growth of Am was not affected at all contamination levels, and the activities of three enzymes were enhanced by BDE-47 in weeks 1 and 4, but such stimulatory effect became insignificant in week 8. Avicennia was more tolerant to BDE-47 toxicity than Kandelia, as its antioxidative enzymes could better counter-balance the oxidative stress caused by BDE-47.  相似文献   
155.
通过分析2,2',3,4,4',5'-六氯联苯(PCB_(138))对牟氏角毛藻(Chaetoceros muelleri)和亚心形扁藻(Platymonas subcordiformis)生长的影响,以及PCB_(138)对两种微藻超氧化物歧化酶(Superoxide dismutase,SOD)活性的影响,研究多氯联苯对海洋微藻的毒性效应,并采用气相色谱法研究了两种微藻对PCB_(138)的生物富集效应。结果表明,PCB_(138)对牟氏角毛藻和亚心形扁藻均有明显的毒性效应作用,对2种藻类的96 h半抑制质量浓度(96hEC_(50))分别为0.057 mg/和0.354 mg/L,与亚心形扁藻相比,牟氏角毛藻对PCB_(138)更敏感,耐受性更差;低浓度的PCB_(138)对两种微藻SOD酶活性有诱导作用,但当PCB_(138)浓度过高时,SOD酶活性下降;两种微藻对PCB_(138)均有明显的富集作用,随着培养时间的延长,牟氏角毛藻中富集的PCB_(138)含量呈上升趋势,而亚心形扁藻中PCB_(138)含量呈现先上升后下降趋势。  相似文献   
156.
Abstract

The influence of temperature on the acute toxicity of a technical formulation (86%) and pure formulation (99%) of pentachlorophenol (PCP) to less than 24‐h‐old Simocephalus vetulus neonates was determined with 48‐h static toxicity tests. The technical grade PCP was significantly more toxic to S. vetulus than the pure PCP (P < 0.05). Sensitivity of S. vetulus to technical PCP also significantly increased with temperature (P < 0.05), but a significant temperature effect was not found with the pure PCP. The mean 48‐h LC50 values for neonates exposed to technical PCP were 140 and 199 μg l?1 at 22°C and 16°C, respectively, and for those exposed to pure PCP were 262 and 304 μg l?1, respectively.  相似文献   
157.
The effect of hexavalent chromium on the carp,Cyprinus carpio was assessed using static bioassay. The 96h LC50 was found to be 93.6mg · l–1. In carp exposed to sublethal concentrations of chromium (15 and 25 mg · l–1), significant depletion of liver and muscle glycogen and decreasing leucocyte counts were recorded during prolonged exposure and with increasing concentration of chromium. The other blood parameters examined (haemoglobin, erythrocyte count, hematocrit, serum protein, serum glucose) increased similarly during exposure to two chromium concentrations.  相似文献   
158.
甲醛溶液对发头裸腹溞及其体表聚缩虫影响的试验   总被引:1,自引:0,他引:1  
不同浓度的甲醛溶液对枝角类发头裸腹溞Moinairrasa的致毒效应以及对其体表附着的聚缩虫Zoothamniumsp.的杀灭效果的试验结果表明,12h、24h两个作用时段中,甲醛浓度与发头探腹溞相对存活率之间以及甲醇浓度与发头裸腹溞表聚缩虫营养体脱落率之间存在一定的函数关系.在确立上述函数基础上,可得出控制聚缩虫感染的两种有效方法:①在保证溞存活率不低于66%的情况下,选用最低有效浓度(19.mg/kg)的甲醛溶液作用24h可杀灭100%聚缩虫;②在保持溞存活率较高(70%-90%)的情况下,选用相应浓度的甲醛液作用24h杀灭87%-29%聚缩虫,并辅以更换新水等措施,也可将聚缩虫感染的危害控制在一定的范围内.  相似文献   
159.
Several attempts to stock fish in acidified alpine lakes have so far proven unsuccessful. In an effort to investigate the problems associated with the stocking of fish, the Swiss alpine Lake Laiozza was chosen for experimentation. An analysis of Lake Laiozza water revealed low ion concentrations (0.5 mg Ca/L, 0.13 mg Na/L, 0.02 mg Cl/L), moderate aluminium concentrations (121 ± 28 µg Al/L), and a moderately low pH (5.41 ± 0.21). As in common practice, one and two year old brown trout were exposed in a closed keep-net in Lake Laiozza. The water of Lake Laiozza proved to be acutely toxic to the fish. Mucous clogging of the gills, gill epithelial damage, plasma electrolyte losses, and high hematocrits were the predominant symptoms observed. All symptoms observed are typical for an acute intoxication with aluminium. This stands in contrast to the generally accepted view that aluminium concentrations lower than 200 µg Al/L should not be toxic to brown trout at a pH 5.4. The low Na and Cl and low Ca concentrations in the Lake Laiozza water seem to have rendered the fish much more susceptible to aluminium intoxication.  相似文献   
160.
通过噻唑蓝(MTT)比色法、微核试验、单细胞凝胶电泳实验(SCGE),检测了3种硅酸盐矿物粉体(绢云母、石英、钠长石)对V79和A549细胞存活率、微核及DNA损伤的影响,比较和探讨了3种硅酸盐矿物粉体细胞遗传毒性的差异。研究结果表明,3种硅酸盐矿物粉体均不同程度抑制细胞增殖,诱发细胞染色体和DNA损伤,作用大小顺序均为绢云母石英钠长石,且对V79细胞的增殖抑制率和DNA损伤率均明显强于A549细胞,推测一定浓度范围内的硅酸盐矿物粉体对细胞遗传物质的稳定性可能存在影响,对人体可能具有遗传毒性。  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