全文获取类型
收费全文 | 1035篇 |
免费 | 39篇 |
专业分类
林业 | 218篇 |
农学 | 19篇 |
394篇 | |
综合类 | 79篇 |
农作物 | 34篇 |
水产渔业 | 34篇 |
畜牧兽医 | 262篇 |
园艺 | 7篇 |
植物保护 | 27篇 |
出版年
2021年 | 9篇 |
2020年 | 17篇 |
2019年 | 16篇 |
2018年 | 28篇 |
2017年 | 12篇 |
2016年 | 14篇 |
2015年 | 19篇 |
2014年 | 27篇 |
2013年 | 35篇 |
2012年 | 42篇 |
2011年 | 40篇 |
2010年 | 24篇 |
2009年 | 23篇 |
2008年 | 44篇 |
2007年 | 60篇 |
2006年 | 55篇 |
2005年 | 41篇 |
2004年 | 31篇 |
2003年 | 39篇 |
2002年 | 29篇 |
2001年 | 13篇 |
2000年 | 15篇 |
1998年 | 7篇 |
1996年 | 7篇 |
1994年 | 9篇 |
1992年 | 17篇 |
1991年 | 12篇 |
1990年 | 12篇 |
1989年 | 15篇 |
1988年 | 12篇 |
1987年 | 9篇 |
1986年 | 8篇 |
1985年 | 19篇 |
1984年 | 18篇 |
1979年 | 7篇 |
1978年 | 7篇 |
1977年 | 8篇 |
1976年 | 8篇 |
1971年 | 9篇 |
1968年 | 8篇 |
1943年 | 6篇 |
1936年 | 6篇 |
1935年 | 8篇 |
1933年 | 9篇 |
1928年 | 11篇 |
1926年 | 13篇 |
1919年 | 10篇 |
1911年 | 6篇 |
1896年 | 6篇 |
1895年 | 6篇 |
排序方式: 共有1074条查询结果,搜索用时 15 毫秒
91.
Amplified Fragment Length Polymorphisms (AFLPs) were employed within the taxonomically difficult Solanum nigrum L. complex in order to characterize the genetic diversity present in a collection of the Gatersleben Genebank, to classify taxonomically unknown material, and to correlate the clustering of the examined accessions with their geographic origin. The results from AFLP analyses using two primer combinations on 44 entries from five species led to the detection of four major clusters, simultaneously uncovering significant differences in the levels of genetic diversity within or between species. S. americanumexhibited the highest infraspecific variation despite close geographic origins, simultaneously being placed in a clearly separated cluster in comparison to the other examined species of the complex. In addition, these other species showed even less interspecific variation than was found at the infraspecific level in S. americanum. In terms of taxonomy, the application of AFLPs helped in the classification of 13 black nightshade accessions formerly only listed as Solanum sp. This also was confirmed by morphological determination. Furthermore, one accession formerly classified as S. physalifolium var. nitidibaccatum i) clustered with AFLPs and ii) was identified morphologically as S. villosum. Contradictory classifications remain for two further entries from the same species, found within the S. nigrum cluster after AFLP analyses, while belonging to S. physalifolium var. nitidibaccatum according to herbarium specimen. Finally, as indicated by the information on provenance in geographically separated subclusters in S. americanum and partially in S. villosum, clues on the currently unknown origin of accessions from the genebank seem feasible by AFLP data. 相似文献
92.
Temporal and Spatial Monitoring of the pH and Heavy Metals in a Soil Polluted by Mine Spill. Post Cleaning Effects 总被引:1,自引:0,他引:1
Rafaela Ordóñez Fernandez Juan Vicente Giráldez Cervera Karl Vanderlinden Rosa Carbonell Bojollo Pedro González Fernández 《Water, air, and soil pollution》2007,178(1-4):229-243
The bursting of the mining dam of Aznalcollar (Seville, Spain) triggered an increase in the concentration of heavy metals in the soils of the river Guadiamar valley as a result of the leaching of the pyritic sludge deposited on them. After the cleaning operations which included, as well as mechanical clearing, the addition of different amendments, some areas with residual sludge remained, from which some heavy metals are being mobilized by the cyclical recharge and discharge processes of water in the profiles. This paper analyzes the effect of the soil recovery operations and the climatology on the concentration of metals and their distribution in the soil profile in an area affected by the toxic spill. Fourteen points have been selected in a plot in which acidity persists, there is no vegetation, and residual sludge stains can be seen at a glance. The temporal and spatial evolution of the extractable metals: Fe, Cu, Mn and Zn, the pH and the oxidable fraction has been measured in-depth. The results obtained up to now indicate a leaching of the pollutant towards deeper horizons, finding, at a depth of 757 cm, pH values of 3.5 and very high Fe and Mn concentrations available, especially in the profiles with large sized pores, with a big fraction of sand. On the surface, seasonally, there are low pH values of around 2.5 and extractable Fe contents of over 4000 ppm, which might have an influence on the quality of surface runoff or underground water. 相似文献
93.
Application of a Balanced Scorecard System for Supporting Decision-Making in Contaminated Sites Remediation 总被引:1,自引:0,他引:1
Alberto Bezama Nóra Szarka Jürgen Wolfbauer Karl E. Lorber 《Water, air, and soil pollution》2007,181(1-4):3-16
This work introduces the development and application of a multi-goal evaluation procedure for assessing sets of remedial options that have previously been found technically suitable for managing a certain contaminated site. The construction of this decision support tool, in the form of a balanced scorecard, has followed a multi-attribute conception of the contaminated sites problem, identifying the most critical aspects considered by all stakeholders involved in contaminated sites management decisions. The developed tool has been checked in its formulation and application against an export benchmark of an Austrian remediation project. The performed evaluation allowed to identify and suggest a remedial option that best fitted the expectations of all stakeholders involved in the project. Furthermore, through the accomplishment of a sensitivity analysis it has been demonstrated that the system is stable and robust in terms of the chosen elicitation schemes, and that the preferences of the different stakeholders are influencing factors on the final result. The results and conclusions of this work present the benefits of implementing the developed balanced scorecard as a tool for supporting decision making in contaminated sites remediation projects. 相似文献
94.
Karl A.Dawson 《中国家禽》2001,23(9):32-35
1 简介霉菌毒素是霉菌代谢的次级产物,这种物质很可能在饲料的制造与贮存过程中污染到饲料。目前已知至少有300种以上霉菌代谢产物会使动物及人类中毒,全世界谷物中有25%受到霉菌毒素的污染,而且达到可量测的浓度。在这些毒素中,已知有很多种物质明显影响动物的健康,对动物生产造成重大影响。2 霉菌毒素的产生在自然状态下霉菌毒素的产生是一个全球性问题,但是世界上某些特定地区霉菌毒素产生的情形比其他地区频繁。在较冷或气候较温和的地区,例如加拿大、美国的北部及多数欧洲国家,黄曲霉毒素并不是主要问题,除了进口的饲料原料… 相似文献
95.
96.
97.
98.
A method was developed to follow a lactic acid bacterial strain, Enterococcus faecium Cernelle 68, with respect to adhesion, multiplication, colonization, and persistence in the digestive tract of mink. Also the spread of the strain in the cage was examined. When adding 5 x 10(9) c.f.u. of a rifampicin resistant mutant per kg feed, high viable counts were registered throughout the digestive tract, apart from the oesophagus. Counts were increasing in the aboral direction, suggesting some multiplication in the intestine. It was possible to detect the strain in the intestinal tract 4 days after discontinuation of administration. Neither culture nor scanning electron microscopy gave evidence to suggest that E. faecium Cernelle 68 adhered to the mucosa. The spread of the E. faecium strain was observed in the environment. Counts of E. coli, lactobacilli, staphylococci, and clostridia were low, and none of these bacteria were constant findings. 相似文献
99.
100.
Ivar V gsholm Hans Olav Djupvik Finn Victor Willumsen Anne Marie Tveit Karl Tangen 《Preventive veterinary medicine》1994,19(3-4):277-290
A case-control study is reported of 57 holdings (holdings in which salmon are raised in sea-water) with infectious salmon anaemia (ISA) and 61 holdings without ISA, together with a follow-up study of the control holdings, during 1988–1990. Generally the identified risk factors implied poor biosecurity since passive transmission (proximity to other ISA holdings) and active transmission (management practices which increased exposure to foreign biological material) were found to be major risk factors. The findings indicated that ISA was spread by infected live salmon or infected biological material i.e. animal waste or discharge from normal operations and slaughter. The findings also indicated that decreased host resistance could be important, but these results could be also be explained by a misclassification bias. Moreover, the findings indicate that a prompt eradication policy and improved biosecurity would be important means of controlling ISA. 相似文献