全文获取类型
收费全文 | 147篇 |
免费 | 0篇 |
专业分类
16篇 | |
综合类 | 87篇 |
农作物 | 1篇 |
水产渔业 | 3篇 |
畜牧兽医 | 37篇 |
植物保护 | 3篇 |
出版年
2020年 | 2篇 |
2019年 | 1篇 |
2014年 | 1篇 |
2013年 | 4篇 |
2012年 | 4篇 |
2011年 | 9篇 |
2010年 | 1篇 |
2008年 | 4篇 |
2007年 | 1篇 |
2006年 | 5篇 |
2005年 | 2篇 |
2004年 | 5篇 |
2003年 | 4篇 |
2001年 | 5篇 |
2000年 | 9篇 |
1999年 | 6篇 |
1997年 | 1篇 |
1995年 | 11篇 |
1993年 | 1篇 |
1991年 | 5篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 3篇 |
1973年 | 2篇 |
1972年 | 3篇 |
1971年 | 3篇 |
1970年 | 4篇 |
1969年 | 3篇 |
1967年 | 5篇 |
1966年 | 3篇 |
1963年 | 2篇 |
1955年 | 2篇 |
1950年 | 1篇 |
1947年 | 1篇 |
1945年 | 1篇 |
1944年 | 2篇 |
1943年 | 1篇 |
排序方式: 共有147条查询结果,搜索用时 15 毫秒
101.
An experimental study of two potential methylation agents of mercury in the atmosphere: CH3I and DMS
Experimental results from a study of the gas and aqueous phase reactions of elemental mercury (Hg0) with methyl iodide (CH3I) and dimethyl sulfide (DMS) are presented. In aqueous phase experiments with CH3I we found no observable increase in methyl mercury (MeHg). A small formation of MeHg, however, was observed in some (but not all) gas phase experiments in sunlight. A loss of Hg0 and a simultaneous formation of oxidized mercury (Hg(II)) was also observed in these experiments. No reaction, neither methylation or oxidation, was found between Hg0 and DMS under any conditions investigated. These experiments suggest that a simple homogeneous gas or aqueous phase methylation of Hg0 by DMS or CH3I in the atmosphere cannot account for the significant levels of MeHg observed in precipitation. 相似文献
102.
During summer stratification, total mercury (Hgτ) reached maximum concentrations in the O2 :depleted, hypolimnion of Little Rock Lake, Wl. Initially, the hypolimnetic increase was attributed solely to redox-controlled
release of Hg from bottom sediments. However, subsequent depth profiles of Hg indicated that hypolimnetic Hg enrichment could
also result from the downward transport and recycling of particulate Hg prior to incorporation in the sediments. Contrasts
between Fe and Hg cycles in this lake reinforce this notion. Increases in hypolimnetic Fe were observed during both summer
and winter O2 decreases. In contrast, hypolimnetic Hg concentrations declined during winter. In the ice-free season, the distribution of
particulate mercury (Hgp) correlated with the distribution of chlorophyllous particulates in this lake, re-emphasizing the importance of biotic processes
in controlling Hg cycling in the hypolimnion. 相似文献
103.
Dissolved and particulate Hg speciation was determined on four occasions in the Spring to Fall interval of 1989, at three depths of the water column of Onondaga Lake, New York; an urban system in which the sediments and fish flesh are contaminated with Hg. Species determined included total Hg (Hgt), reactive (‘ionic’) Hg (Hgi), monomethylmercury (CH3HgX), elemental Hg (Hg°) and dimethylmercury (CH3)2Hg). Onondaga Lake was found to contain very high levels of Hgt (2 to 25 ng L?1 Hg), Hgj (0.5 to 10 ng L?1 Hg), and CH3HgX (0.3 to 7 ng L?1 Hg), which generally increased with depth in the lake. These concentrations represent a significant level of contamination, based upon comparisons with other polluted and pristine sites. Elemental Hg levels were typically about 0.05 ng L?1 and (CH3)2Hg was near the limits of detection (?0.001 ng) L?1 in most samples. The greatest CH3HgX concentrations in the hypolimnion, as well as the largest gradients of both CH3HgX and (Hgt), were observed upon the first onset of stratification, in early summer. These concentrations did not become more pronounced, however, as stratification and H2S levels in the hypolimnion increased throughout the summer. The very low concentrations of (CH3)2Hg in these MeHg and sulfide-rich waters calls into question the belief that CH3HgX and H2S will react to yield volatile dimethyl-mercury, which can then escape to the atmosphere by diffusion. Mercury speciation was highly dynamic, indicating active cycling within the lake, and an apparent sensitivity to changes in attendant Iimnological conditions that track the stratification cycle. 相似文献
104.
Shepard FP Curray JR Newman WA Bloom AL Newell ND Tracey JI Veeh HH 《Science (New York, N.Y.)》1967,157(3788):542-544
Investigation of 33 islands, scattered widely across the Caroline and Marshall Island groups in the Central Pacific revealed no emerged reefs in which corals had unquestionably formed in situ, or other direct evidence of postglacial high stands of sea level. Low unconsolidated rock terraces and ridges of reefflat islands, mostly lying between tide levels, were composed of rubble conglomerates; carbon-14 dating of 11 samples from the conglomerates so far may suggest a former slightly higher sea level (nine samples range between 1890 and 3450 and one approaches 4500 years ago). However, recent hurricanes have produced ridges of comparable height and material, and in the same areas relics from World War II have been found cemented in place. Thus these datings do not in themselves necessarily indicate formerly higher sea levels. Rubble tracts are produced by storms under present conditions without any change in datum, and there seems to be no compelling evidence that they were not so developed during various periods in the past. 相似文献
105.
106.
The benefits and costs of human immunodeficiency virus (HIV) testing in employment settings are examined from two points of view: that of private employers whose profitability may be affected by their testing policies and that of public policy-makers who may affect social welfare through their design of regulations related to HIV testing. The results reveal that HIV testing is clearly not cost-beneficial for most firms, although the benefits of HIV testing may outweigh the costs for some large firms that offer generous fringe-benefit packages and that recruit workers from populations in which the prevalence of HIV infection is high. The analysis also indicates that the testing decisions of unregulated employers are not likely to yield socially optimal economic outcomes and that existing state and federal legislation related to HIV testing in employment settings has been motivated primarily by concerns over social equity. 相似文献
107.
C D Nicholls D L Lee T E Adrian S R Bloom A D Care 《Research in veterinary science》1988,45(1):124-126
Radioimmunoassay of plasma gastrin has shown that a hypergastrinaemia occurs in yearling sheep, after infection with 10(6) infective third stage larvae of Haemonchus contortus. Plasma gastrin concentrations began to rise two to four days after infection, that is, at about the same time as, or slightly before, the abomasal pH was observed to increase. 相似文献
108.
109.
110.
J C Bloom L D Meunier P A Thiem T S Sellers 《Journal of the American Veterinary Medical Association》1989,194(1):76-78
A routine health screen of a 7 1/2-year-old female Beagle participating as a control in a long-term study revealed thrombocytopenia. Immune thrombocytopenia was diagnosed on the basis of regenerative bone marrow findings (high number of megakaryocytes) and evidence of antiplatelet antibodies. Treatment with prednisone at dosages up to 1 mg/kg of body weight every 12 hours resulted in limited improvement, with relapses of severe thrombocytopenia thwarting attempts to taper the corticosteroid, and was further complicated by side effects of the drug. Addition of danazol to the treatment regimen (5 mg/kg, q 12 h) resulted in remission of the thrombocytopenia within 2 weeks and permitted the dosage of prednisone to gradually be reduced and discontinued. Associated with this response was a decrease in platelet-associated IgG to values comparable with control samples. 相似文献