全文获取类型
收费全文 | 18373篇 |
免费 | 816篇 |
国内免费 | 15篇 |
专业分类
林业 | 1632篇 |
农学 | 623篇 |
基础科学 | 105篇 |
3217篇 | |
综合类 | 718篇 |
农作物 | 901篇 |
水产渔业 | 1426篇 |
畜牧兽医 | 8682篇 |
园艺 | 352篇 |
植物保护 | 1548篇 |
出版年
2023年 | 83篇 |
2022年 | 122篇 |
2021年 | 239篇 |
2020年 | 226篇 |
2019年 | 153篇 |
2018年 | 578篇 |
2017年 | 680篇 |
2016年 | 643篇 |
2015年 | 586篇 |
2014年 | 632篇 |
2013年 | 768篇 |
2012年 | 1181篇 |
2011年 | 980篇 |
2010年 | 477篇 |
2009年 | 431篇 |
2008年 | 623篇 |
2007年 | 555篇 |
2006年 | 465篇 |
2005年 | 1199篇 |
2004年 | 1012篇 |
2003年 | 798篇 |
2002年 | 408篇 |
2001年 | 379篇 |
2000年 | 279篇 |
1999年 | 358篇 |
1992年 | 243篇 |
1991年 | 252篇 |
1990年 | 269篇 |
1989年 | 264篇 |
1988年 | 277篇 |
1987年 | 228篇 |
1986年 | 250篇 |
1985年 | 214篇 |
1984年 | 168篇 |
1983年 | 150篇 |
1979年 | 226篇 |
1978年 | 183篇 |
1977年 | 171篇 |
1976年 | 128篇 |
1975年 | 183篇 |
1974年 | 220篇 |
1973年 | 180篇 |
1972年 | 221篇 |
1971年 | 201篇 |
1970年 | 112篇 |
1969年 | 131篇 |
1968年 | 138篇 |
1967年 | 153篇 |
1966年 | 129篇 |
1965年 | 81篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
Of 62 strains of Staphylococcus aureus, isolated from milk samples of dairy-cows with staphylococcic mastitis from five agricultural enterprises, 68 p. c. could be typified as bacteriophages. In 42 typified strains, altogether 17 different phage pictures were found, in which case, in the different agricultural enterprises, the number of phage picture fluctuated between 1 and 8. Phage picture 42 D was found and dominated in all the agricultural enterprises. Of the typified strains, 76% could be ranked only into one phage group and 24% in the "M" group (= miscellaneous). Of 32 typified strains, 56.3% belonged to phage group IV, 25% to group III, 12.5% to group I, and 6.2% to group II. 相似文献
82.
Of 62 strains of Staphylococcus aureus, isolated from milk samples of dairy-cows with staphylococcic mastitis from five agricultural enterprises, 68 p. c. could be typified as bacteriophages. In 42 typified strains, altogether 17 different phage pictures were found, in which case, in the different agricultural enterprises, the number of phage picture fluctuated between 1 and 8. Phage picture 42 D was found and dominated in all the agricultural enterprises. Of the typified strains, 76% could be ranked only into one phage group and 24% in the "M" group (= miscellaneous). Of 32 typified strains, 56.3% belonged to phage group IV, 25% to group III, 12.5% to group I, and 6.2% to group II. 相似文献
83.
Z Hubálek 《Folia parasitologica》1975,22(1):73-79
Samples of pigeon droppings were taken from 7 sites in a church tower contaminated with C. neoformans, and the distribution patterns of the fungus were studied. From various sites, 0 to 3 x 10(5) viable C. neoformans particles were recovered per one gram of dry excreta. The factors causing the different density of C. neoformans population in the habitat were: uric acid share of the total nitrogen, creatinine content, sunlight and probably pH. Chemical composition of the substrate is the primary factor in the distribution of C. neoformans in droppings. 相似文献
84.
K J S?rensen 《Nordisk veterinaermedicin》1975,27(4):208-212
In 1956 a disease of nursing pigs previously unreported in Denmark, was observed in several swine herds. The disease syndrome appeared identical with that later described by Roe and Alexander in 1958 and by S. F. Cartwright and M. Lucas in 1968. Since 1956 there have been no reports of such outbreaks in Danish herds. To investigate whether the virus is still present, a survey was carried out to detect neutralizing antibodies in sera from a number of boars using a micro technique. In 144 sera from Jutland 12% had titers ranging from 10 to 32 ND-50, 22% from 32 to 90, 37% from 90 to 256, 14% from 256 to 724 and 3% above 724 ND-50 with a total of 86% positive. Of 174 sera from the rest of the country 16% had titers ranging from 10 to 32 ND-50, 18% from 32 to 90, 28% from 90 to 256, 13% from 256 to 724 and 3% exceeding 724 ND-50 with a total of 79% positive. 相似文献
85.
86.
87.
A general bio-economic model for beef cattle production was used to define breeding objectives for Charolais cattle to be utilized in a variety of linked production systems. Economic weights were calculated for 16 traits (some with both direct and maternal components) in three production systems (pure-breeding and terminal crossing with beef or dairy cows) and two marketing strategies (sale or fattening of weaned surplus calves). Economic weights for the total breeding objective were calculated as weighted averages, where weights were numbers of cows expected to be mated with Charolais bulls in each production system and marketing strategy. Results suggest that the direct component of calving performance and cow longevity were of primary economic importance in all systems. Conception rate of cows and weaning weight reached about 50% of the standardized economic weight of calving performance in purebred systems with sale of weaned calves, whereas in purebred systems with fattening the economic importance of the direct component of cow conception rate, losses at calving, mature weight of cows, weaning weight, and fattening traits were of equal importance (each approximately about 20% that of calving performance). In terminal crossing systems, weaning weight was important when calves were sold at weaning, and fattening traits were important for systems selling fattened animals. The bio-economic model performed well under the conditions of this demonstration and could easily be customized for other applications. 相似文献
88.
A Lillehaug B Bergsj? J Schau T Bruheim T Vik?ren K Handeland 《Acta veterinaria Scandinavica》2005,46(1):23-32
Faecal samples were collected, as part of the National Health Surveillance Program for Cervids (HOP) in Norway, from wild red deer, roe deer, moose and reindeer during ordinary hunting seasons from 2001 to 2003. Samples from a total of 618 animals were examined for verocytotoxic E. coli (VTEC); 611 animals for Salmonella and 324 animals for Campylobacter. A total of 50 samples were cultivated from each cervid species in order to isolate the indicator bacterial species E. coli and Enterococcus faecalis/E. faecium for antibiotic resistance pattern studies. Salmonella and the potentially human pathogenic verocytotoxic E. coli were not isolated, while Campylobacter jejuni jejuni was found in one roe deer sample only. Antibiotic resistance was found in 13 (7.3%) of the 179 E. coli isolates tested, eight of these being resistant against one type of antibiotic only. The proportion of resistant E. coli isolates was higher in wild reindeer (24%) than in the other cervids (2.2%). E. faecalis or E. faecium were isolated from 19 of the samples, none of these being reindeer. All the strains isolated were resistant against one (84%) or more (16%) antibiotics. A total of 14 E. faecalis-strains were resistant to virginiamycin only. The results indicate that the cervid species studied do not constitute an important infectious reservoir for either the human pathogens or the antibiotic resistant microorganisms included in the study. 相似文献
89.
Bhupender Singh Fernando Saravia Renée B?ge Heriberto Rodríguez-Martínez 《Acta veterinaria Scandinavica》2005,46(1):1-12
Hormonal asynchronies during oestrus, related to the presence of suprabasal plasma-progesterone (P4) concentrations and a delayed ovulation, interfere with the fertility of repeat-breeder heifers (RBH). Since tubal dysfunction can occur in connection with hormonal asynchronies and constrained availability of fertile spermatozoa at the time of ovulation, the present study tested the hypothesis that frequent sperm deposition from onset of oestrus to ovulation may improve pregnancy rates in RBH. Five RBH and five virgin heifers (VH; controls) were repeatedly artificially inseminated (AI) at 6 h intervals from onset of oestrus to spontaneous ovulation. Hormone analyses revealed suprabasal P4 concentrations and a delay in the occurrence of the luteinising hormone (LH) surge, but a normal cortisol profile in RBH. Compared with controls, RBH presented longer interval from onset of oestrus to ovulation, and therefore, received more AIs. Pregnancy rates in RBH reached control levels (60%; NS), indicating that the hypothesis might be correct. Pregnancy rates in VH were below the expected range, presumably attributed to a deleterious influence of the frequent handling. The study suggests that pregnancy rates can be improved in RBH by frequent AI in relation to spontaneous ovulation. However, this practice of repeated manipulations, while seeming not to show adverse effects, lacks practicality for routine use. 相似文献
90.
Patrick Rehmann Andrea Gr?ne Bruno Gottstein Jürg V?llm Heinz Sager Martin Janovsky Luca N Bacciarini 《Journal of veterinary diagnostic investigation》2005,17(2):183-186
Five animals in a colony of cynomolgus monkeys (Macaca fascicularis) died or were euthanatized because of alveolar echinococcosis, during a period of 5 years. The remainder of the colony was screened for possible infection with Echinococcus multilocularis, using serology and ultrasonography. A total of 46 animals out of a group of 55 were examined. The presence of anti-Em2 antibodies analyzed with enzyme-linked immunosorbent assay was demonstrated in 3 monkeys. In 2 of these 3 monkeys, multilocular structures compatible with metacestodal cysts in the liver were identified, using ultrasonography. The presence of alveolar echinococcosis was subsequently confirmed at postmortem examination in 1 animal. The other animals are still alive. Two other monkeys were negative in the serological examination but had cystic structures in the liver, which were identified as bile duct cysts at postmortem examination in 1 animal. The other monkey is still alive. These findings suggest that serology for antibodies against the Em2 antigen may represent a useful method in identifying animals that might be infected with E. multilocularis and are therefore at risk of developing fatal alveolar echinococcosis. 相似文献