全文获取类型
收费全文 | 807篇 |
免费 | 41篇 |
专业分类
林业 | 140篇 |
农学 | 64篇 |
基础科学 | 4篇 |
78篇 | |
综合类 | 106篇 |
农作物 | 16篇 |
水产渔业 | 32篇 |
畜牧兽医 | 369篇 |
园艺 | 14篇 |
植物保护 | 25篇 |
出版年
2021年 | 9篇 |
2020年 | 6篇 |
2019年 | 10篇 |
2018年 | 14篇 |
2017年 | 19篇 |
2016年 | 12篇 |
2015年 | 17篇 |
2014年 | 17篇 |
2013年 | 26篇 |
2012年 | 35篇 |
2011年 | 30篇 |
2010年 | 12篇 |
2009年 | 22篇 |
2008年 | 34篇 |
2007年 | 27篇 |
2006年 | 25篇 |
2005年 | 24篇 |
2004年 | 18篇 |
2003年 | 30篇 |
2002年 | 22篇 |
2001年 | 27篇 |
2000年 | 27篇 |
1999年 | 11篇 |
1998年 | 8篇 |
1997年 | 8篇 |
1996年 | 8篇 |
1994年 | 9篇 |
1992年 | 12篇 |
1991年 | 14篇 |
1990年 | 10篇 |
1989年 | 20篇 |
1988年 | 18篇 |
1987年 | 11篇 |
1985年 | 10篇 |
1984年 | 9篇 |
1983年 | 11篇 |
1980年 | 5篇 |
1979年 | 8篇 |
1978年 | 10篇 |
1977年 | 14篇 |
1975年 | 8篇 |
1974年 | 10篇 |
1973年 | 6篇 |
1972年 | 9篇 |
1971年 | 8篇 |
1969年 | 8篇 |
1967年 | 8篇 |
1966年 | 14篇 |
1924年 | 5篇 |
1921年 | 9篇 |
排序方式: 共有848条查询结果,搜索用时 15 毫秒
61.
A 4‐month‐old male British Blue cat with catarrhal to haemorrhagic enteritis showed massive colonization of the stomach, small intestine and caecum with spiral‐shaped bacilli. In the stomach, organisms were located in foveolae and gland lumina and within unaltered and degenerate epithelial cells. Inflammatory infiltration was moderate and T cell dominated. In the intestine, bacilli were found in the gut lumen, between villi, in crypt lumina and within epithelial cells. Degeneration of crypt epithelial cells as well as crypt dilation and moderate to massive macrophage‐dominated infiltration of the mucosa and submucosa were observed. Immunohistochemically, bacilli were positive with an antibody against Helicobacter. Ultrastructurally, the organisms strongly resembled ‘Flexispira rappini’, a spiral‐shaped Helicobacter species known as a normal intestinal colonizer in dogs and mice. 相似文献
62.
D T Campbell J Maas D W Weber O R Hedstrom B B Norman 《American journal of veterinary research》1990,51(5):813-817
One hundred fifty Se-deficient, pregnant, crossbred beef cows were assigned to 1 of 4 treatment groups: group A, Se-deficient control; group B, 1 Se bolus at 0 and 119 days; group C, 1 Se bolus at 0 days; and group D, 2 Se pellets at 0 days. The Se bolus is an osmotic pump designed to release 3 mg of Se/d into the reticulorumen. The Se pellets weight approximately 30 g and contain 10% elemental Se, which is liberated in the reticulorumen. The Se bolus is designed to provide Se supplementation for 120 days and the Se pellets provide supplementation for up to 18 months. Cattle were maintained on Se-deficient pasture or forages prepared from these pastures for the duration of the experiment. Blood samples were collected from cows prior to treatment (time 0) and at 28, 52, 119, and 220 days thereafter and analyzed for blood Se (BSe) concentration. Body weights were recorded at each sampling time. Blood Se concentration of cows from all supplemented groups were significantly (P less than 0.01) higher than control values at all sample dates after treatments began. By the end of the 220-day study, treatment group-B cattle had significantly (P less than 0.01) higher BSe concentrations than any other group. Body weights of treatment groups fluctuated throughout the study, but did not differ (P greater than 0.05) between groups. One cow and 6 calves born to cows during the experimental period died. Necropsy of 5 calves provided no evidence linking these deaths to treatments.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
63.
Two Asian small-clawed otters (Amblonyx cinereus) died acutely in their exhibit within a 4-day period. Neither animal had significant gross lesions at necropsy. Histologic findings were consistent with acute vascular shock and disseminated intravascular coagulation, and a toxic etiology was suspected. The animals' exhibit contained opened, uneaten loquat (Eriobotrya japonica) fruit with the seeds removed and large quantities of undigested loquat seed material in the feces of the remaining animals. Cyanide was detected in the stomach contents collected at necropsy and in fresh loquat seeds from the exhibit. Loquat is related to other cyanide-containing fruit trees, including cherries, peaches, and almonds. 相似文献
64.
Prunus mandshurica [(Maxim.) Koehne] from Central Asia is a species related to apricot and grown in China and Mongolia. This species has been used in apricot breeding as a source of frost resistance. In addition, P. mandshurica has been suggested as the possible origin of some North American apricot cultivars resistant to sharka (Plum pox virus, PPV). The aim of this work was to transmit the resistance to PPV from P. mandshurica to the Spanish apricot cultivar ‘Currot’ by traditional crossing. The resistance to a Dideron PPV isolate of the descendants of P. mandshuricaבCurrot’ and their progenitors was evaluated under controlled conditions in a greenhouse. The results showed the susceptibility of both, the progenitors and the offspring to PPV, as being much higher than in other apricot seedlings. The results showed that the P. mandshurica accession studied is not a good progenitor in breeding apricot for PPV resistance, but just the opposite. The possible role of P. mandshurica as a source of resistance in apricot resistant cultivars is questioned. 相似文献
65.
W. E. Weber 《Euphytica》1982,31(2):493-502
Summary The response to selection is determined by the genetic and nongenetic variance, the selection intensity, and the size of the experiments. If, in pure line breeding, selection starts in segregating generations, the gain depends on the relation of additive to epistatic variance. The gain can be increased if an index is constructed using the information from relatives. From animal breeding this kind of selection is known as combined selection. In this paper the optimal number of families and subfamilies is determined that will maximise the selection response by combined selection for a fixed total size of experiments. The composition of the genetic variance has a imited influence on the optimal size of the progenies. If epistatic variance is important, then the number of F2 families has to be reduced and the number of F3 families and F4 families must be increased. The same is true if the nongenetic variance is increased. 相似文献
66.
67.
68.
P. Monneveux M. P. Reynolds J. González Aguilar R. P. Singh W. E. Weber 《Plant Breeding》2003,122(5):379-384
The 7DL.7Ag translocation from Lophopyrum elongatum that carries Lr19, a leaf rust resistance gene, was found to be associated with a significant increase in grain yield under irrigated, disease‐free conditions, but a generally lower yield under moisture stress conditions. These studies, however, involved a limited number of genetic recipients and environments, and the effect of the translocation on physiological traits was not considered. We examined the translocation effect in six different recipient genotypes and under five environmental conditions, including drought and heat stress. The increase in grain yield under irrigated conditions was associated with a higher rate of biomass production in the 7DL.7Ag lines and may be attributed to higher sink strength. Effect of the translocation on physiological traits was noted only under heat stress and was not associated with difference in yield. Under moisture stress conditions, 7DL.7Ag lines yielded less than their corresponding recipients, possibly because of a longer growing cycle. It is concluded that the effect of the 7DL. 7Ag translocation may very much depend on the phenological adaptation of the recipient genotype and the translocation may be useful for enhancing yield, mainly under favourable conditions. 相似文献
69.
Sex-linked SSR markers in hemp 总被引:3,自引:0,他引:3
Hemp is a dioecious plant with sex chromosomes X and Y, the male sex being heterogametic. The quality of the fibre depends on the sex type. The sex chromosomes can be characterized by molecular markers. In this report, sex‐linked simple sequence repeat (SSR) markers are described. One SSR marker was polymorphic in both the populations derived from single crosses, two other markers in but one of the two populations. Three alleles were detected for two SSR markers indicating polymorphism not only between X and Y, but also between different X chromosomes. In addition, several sex‐linked RAPD markers were detected in one population. Recombination within the sex chromosomes was observed for nearly all markers. 相似文献
70.
A rapid and efficient microspore culture protocol was applied to produce homozygous progeny of crosses between low erucic canola and high erucic resynthesized rapeseed (Brassica napus L.). Microspores of Canadian cultivars ‘Excel’ and ‘Profit’ as well as three F1 hybrids with the resynthetic line ‘RS239’ were treated with colchicine immediately after isolation. Flow cytometry was applied for early identification of doubled haploid (DH) regenerants. The diploidization rate was subsequently verified by scoring flower morphology. In vitro colchicine treatment had a positive effect on induced diploidization, and was associated with the frequency of preliminary spontaneous diploidization which was, however, determined by the genotype. In addition, the effects of colchicine treatment on embryoid formation and regeneration have been evaluated. The method presented is feasible for commercial large‐scale production of DHs in rapeseed as the genotype‐specific diploidization can be efficiently balanced by in vitro colchicine treatment. In addition, the use of flow cytometry immediately after in vitro culture allows efficient selection for DHs, thus saving labour and cost and in the laboratory and subsequent greenhouse phase. 相似文献