全文获取类型
收费全文 | 88908篇 |
免费 | 4132篇 |
国内免费 | 32篇 |
专业分类
林业 | 6638篇 |
农学 | 3619篇 |
基础科学 | 595篇 |
11279篇 | |
综合类 | 12702篇 |
农作物 | 4836篇 |
水产渔业 | 5256篇 |
畜牧兽医 | 39556篇 |
园艺 | 1852篇 |
植物保护 | 6739篇 |
出版年
2018年 | 3580篇 |
2017年 | 3629篇 |
2016年 | 2132篇 |
2015年 | 906篇 |
2014年 | 1060篇 |
2013年 | 2750篇 |
2012年 | 2692篇 |
2011年 | 4315篇 |
2010年 | 3548篇 |
2009年 | 2744篇 |
2008年 | 3575篇 |
2007年 | 3717篇 |
2006年 | 2061篇 |
2005年 | 2058篇 |
2004年 | 1941篇 |
2003年 | 2139篇 |
2002年 | 1863篇 |
2001年 | 2242篇 |
2000年 | 2229篇 |
1999年 | 1748篇 |
1998年 | 714篇 |
1997年 | 776篇 |
1996年 | 685篇 |
1995年 | 866篇 |
1994年 | 734篇 |
1993年 | 744篇 |
1992年 | 1498篇 |
1991年 | 1634篇 |
1990年 | 1602篇 |
1989年 | 1609篇 |
1988年 | 1503篇 |
1987年 | 1456篇 |
1986年 | 1536篇 |
1985年 | 1449篇 |
1984年 | 1270篇 |
1983年 | 1063篇 |
1982年 | 748篇 |
1979年 | 1171篇 |
1978年 | 887篇 |
1977年 | 843篇 |
1976年 | 799篇 |
1975年 | 829篇 |
1974年 | 1030篇 |
1973年 | 1070篇 |
1972年 | 1018篇 |
1971年 | 951篇 |
1970年 | 927篇 |
1969年 | 899篇 |
1968年 | 758篇 |
1967年 | 844篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
Toxoplasmosis in two cats with inflammatory intestinal disease 总被引:1,自引:0,他引:1
J L Peterson M D Willard G E Lees M R Lappin T Dieringer E Floyd 《Journal of the American Veterinary Medical Association》1991,199(4):473-476
Lymphocytic-plasmacytic enteritis, a chronic inflammatory intestinal disease, was diagnosed in 2 cats. In 1 cat, recurrence of clinical signs after initiating treatment was attributed to relapse of the inflammatory intestinal disease, but was found to be attributable to relapsing toxoplasmosis secondary to immunosuppressive drug therapy. Treatment with clindamycin resolved the recurrent toxoplasmosis. In the second cat, clinical signs of toxoplasmosis did not develop, but serologic testing yielded evidence of active toxoplasmosis. Treatment with clindamycin caused the titers to decrease. Relapsing toxoplasmosis may be responsible for apparent resistance to treatment in cats for inflammatory intestinal disease being treated with immunosuppressive drugs. 相似文献
132.
A. Sisto M. G. Cipriani S. Tegli M. Cerboneschi G. Stea E. Santilli 《Plant pathology》2007,56(3):366-372
The genetic diversity of 71 Pseudomonas savastanoi pv. savastanoi strains isolated from different host species and from diverse geographical regions was determined by fluorescent amplified fragment length polymorphism (f-AFLP) analysis. The study was carried out using three different selective primer combinations. Strains of P. syringae pv. syringae , P. syringae pv. phaseolicola , P. syringae pv. glycinea , P. syringae pv. tagetis and P. amygdali were also included as outgroups. Based on cluster analysis of f-AFLP data, all P. savastanoi pv. savastanoi strains showed a high degree of similarity, grouping in a cluster and forming a taxon clearly separate from outgroup strains. AFLP analyses failed to support placing strains of P. savastanoi pv. savastanoi , P. syringae pv. phaseolicola and P. syringae pv. glycinea in the same species. Strains of P. savastanoi pv. savastanoi formed subclusters that correlated with the host species. Strains identified within these subclusters were related to the geographical region where the strains were isolated. Strains of P. savastanoi pv. savastanoi from olive were divided into two subclusters. Strains from oleander were differentiated from those from ash and were divided into two additional subclusters, distinct from olive strains. Three strains isolated from jasmine showed a high level of similarity among them but, at a lower Dice similarity coefficient, were linked to a subcluster including olive strains. Finally, two strains isolated from privet were similar to strains from olive and were included in the same subcluster. 相似文献
133.
J. Bordes G. Charmet R. Dumas de Vaulx A. Lapierre M. Pollacsek M. Beckert A. Gallais 《Euphytica》2007,154(1-2):41-51
Progress made in the in situ gynogenesis technique since 1990 now allows production of a high number of maize (Zea mays L.) doubled-haploid (DH) lines. The aim of the study was to compare DH lines versus selfing lines for testcross performance.
DH and single-seed descent (SSD) lines were produced from random S1 progenies of a broad-base population. For grain yield, kernel moisture, plant height, ear height and leaf length, the three
population means were similar. Except for kernel moisture, the genetic variance of DH lines was nearly twice as high as the
genetic variance of S1 families, as expected. On the other hand, genetic variance among SSD lines was only 1.5 times higher than the genetic variance
of S1 families. This lower variance could be due to a selection bias in the method of production of SSD lines. However, for all
traits, heritability of SSD or DH lines was higher than heritability of S1 families. Epistasis effects in DH progenies were not significant. The consequence was a high correlation between S1 testcross progenies and DH or SSD testcross progenies, meaning that the S1 testcross value can be used to select the best families from which DH lines will be extracted. As a whole, the observed variation
in DH lines appeared to be more in accordance with the observed variation among S1 families than with the observed variation among SSD lines. 相似文献
134.
Tuta absoluta (Meyrick) is an invasive pest of tomato native to South America, where it is responsible for extensive damage. It rapidly spread into several European countries, becoming a key pest. Knowledge of its main biological traits can be used to develop effective plant protection management strategies. It is a multivoltine species with a homodynamous behaviour, and the length of its life cycle depends on environmental conditions, particularly temperature. The larvae feed and develop inside tomato leaves, stems and fruits throughout the entire growing cycle. The adults have crepuscular habits, and in Mediterranean conditions they can be easily detected throughout the year. Damage is directly related to the reduction of plants' photosynthetic capacity and of production levels in both protected and open‐field tomato crops; indirect damage can be also caused by secondary infections, with pathogens developing on the infested plant and fruit tissues. 相似文献
135.
Renal concentrating mechanism: possible role for sodium-potassium activated adenosine triphosphatase 总被引:2,自引:0,他引:2
M Martinez-Maldonado J C Allen G Eknoyan W Suki A Schwartz 《Science (New York, N.Y.)》1969,165(895):807-808
Sodium-potassium activated adenosine triphosphatase activity was found to be almost twice as high in renal medulla as in cortex. Infusion of digoxin, a specific inhibitor of the enzyme, into one renal artery of the dog resulted in unilateral natriuresis, impaired concentrating capacity, and reduction of the enzyme activity in both cortex and medulla. It is suggested that the sodium-potassium adenosine triphosphatase plays an important role in urine concentration mechanisms. 相似文献
136.
137.
J. Martínez-Calvo M. Naval E. Zuriaga G. Llácer M. L. Badenes 《Genetic Resources and Crop Evolution》2013,60(1):233-241
Diospyros kaki Thunb. originated in Eastern Asia, as evidenced of its culture in China as early as several centuries B.C. In the seventh century, persimmon was introduced to Japan and later, in the fourteenth century to Korea. There is no information about persimmon culture in Europe until the seventeenth century, with the spread over the world occurring in the eighteenth century. The genus Diospyros contains more than 400 species, with levels of ploidy ranging from diploid (2n = 2x = 30) up to nonaploid (2n = 9x = 135). The primary economic crop species is Diospyros kaki Thunb., which is mainly hexaploid (2n = 6x = 90) and includes hundreds of cultivars. Although a relatively recent introduction in Europe, the species has adapted well, and the genetic diversity have been expanded with culture and selection for the past 200 years in the Mediterranean basin. These locally adapted cultivars were evaluated with cultivars from Asian origin in a germplasm collection established at IVIA in Valencia, Spain. In this paper 27 cultivars from the IVIA collection were studied by multivariate analysis, and 37 variables were analyzed using a Principal Components Analysis and cluster analysis following the method UPGMA. Studies on correlations and significance among variables identified the most relevant ones, and thus provided information for a future core collection. 相似文献
138.
139.
T. SVÅSAND O. T. SKILBREI G. I. VAN DER MEEREN M. HOLM 《Fisheries Management and Ecology》1998,5(6):473-490
Abstract The main question which must be raised when planning to enhance natural populations through sea ranching is whether reared organisms are fit for a life in the wild, or more specifically, whether there are differences between reared and naturally resident individuals. The causes and effects of these differences are reviewed, and results from the Norwegian enhancement programme, which compared reared and wild individuals of Atlantic salmon, Salmo salar L., Atlantic cod, Gadus morhua L., and European lobster, Homarus gammarus L., are discussed with emphasis on morphological and behavioural differences. It was concluded that exposure to an artificial rearing environment during ontogeny can affect both the phenotype and the behaviour of the reared individuals, and thereby, their potential for survival after release into the wild as well. Suggestions are made as to how to diminish observed differences, and thereby, improve the survival potential. 相似文献
140.
Garosi LS Rossmeisl JH de Lahunta A Shelton GD Lennox G 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》2005,19(4):606-609
Two Great Danes were presented for an investigation of 6-month histories of incessant tremor of all 4 limbs and trunk occurring only when the dogs were standing at rest. Dog 1 was a 2-year-old intact female harlequin Great Dane living in the UK, and dog 2 was a 2-year-old castrated male fawn Great Dane living in the United States. The owners described both dogs as having constant quivering of the limbs while standing, suggestive of an involuntary dance, since the age of 18 months. The intensity of the tremors was reported in both dogs to have steadily increased since onset. In dog 1, tremors were noticed to be more pronounced in the fore limbs when she was eating and more pronounced in the hind limbs when she was trying to sit. The owner of dog 1 also reported that the dog could no longer assume a position of recumbency without manual assistance because of the severity of the tremors. Intermittently, tremors were reported to involve the facial musculature of dog 2. Vaccinations were current, and the owners of both dogs did not report any previous medical history, exposure to natural or manufactured toxins, or concurrent treatment. No familial relationship was identified between these 2 dogs. 相似文献