全文获取类型
收费全文 | 38219篇 |
免费 | 2240篇 |
国内免费 | 285篇 |
专业分类
林业 | 1584篇 |
农学 | 1414篇 |
基础科学 | 324篇 |
5484篇 | |
综合类 | 5659篇 |
农作物 | 1487篇 |
水产渔业 | 1801篇 |
畜牧兽医 | 19859篇 |
园艺 | 456篇 |
植物保护 | 2676篇 |
出版年
2021年 | 363篇 |
2020年 | 423篇 |
2019年 | 468篇 |
2018年 | 787篇 |
2017年 | 830篇 |
2016年 | 747篇 |
2015年 | 626篇 |
2014年 | 782篇 |
2013年 | 1831篇 |
2012年 | 1310篇 |
2011年 | 1528篇 |
2010年 | 1057篇 |
2009年 | 1090篇 |
2008年 | 1481篇 |
2007年 | 1332篇 |
2006年 | 1257篇 |
2005年 | 1077篇 |
2004年 | 1037篇 |
2003年 | 1029篇 |
2002年 | 910篇 |
2001年 | 1244篇 |
2000年 | 1231篇 |
1999年 | 928篇 |
1998年 | 387篇 |
1997年 | 418篇 |
1996年 | 341篇 |
1995年 | 392篇 |
1994年 | 341篇 |
1992年 | 656篇 |
1991年 | 780篇 |
1990年 | 687篇 |
1989年 | 720篇 |
1988年 | 662篇 |
1987年 | 624篇 |
1986年 | 666篇 |
1985年 | 591篇 |
1984年 | 463篇 |
1983年 | 412篇 |
1979年 | 553篇 |
1978年 | 431篇 |
1977年 | 358篇 |
1976年 | 365篇 |
1975年 | 396篇 |
1974年 | 459篇 |
1973年 | 474篇 |
1972年 | 447篇 |
1970年 | 366篇 |
1969年 | 400篇 |
1968年 | 357篇 |
1967年 | 359篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
Wade N 《Science (New York, N.Y.)》1978,199(4324):30-1, 33
142.
N H Nabbut 《American journal of veterinary research》1978,39(5):893-895
Animal feed-additive samples (n = 300) were examined for the presence of salmonellae, using the selenite-F broth-enrichment method followed by subculturing on Salmonella-Shigella and brilliant green agar with sulfadiazine selective agar plates. Samples consisted of a variety of feed additives: 119 bone meal samples, 77 meat meal samples, 40 fish meal samples, and 64 miscellaneous meal samples. Results of examination found 49 (41.2%) of the bone meal samples, 6 (7.8%) of the meat meal samples and 2 (5%) of the fish meal samples contained salmonellae. Of 57 isolates representing 24 serotypes, 4 most frequently isolated serotypes were Salmonella meleagridis (35.1%), Salmonella tennessee (7%), Salmonella chester (5.2%), and Salmonella senftenberg (5.2%). This study shows a high Salmonella-contamination rate of bone meal compared with meat meal and fish meal samples. Of 12 known positive bone meal samples that were examined, 100% of 25-g samples, compared with 70% to 100% of 2.5-g samples and 30% to 90% of 0.25-g samples and 30% to 90% of 0.25-g samples, were positive for salmonellae. 相似文献
143.
P J Ihrke R M Schwartzman K McGinley L N Horwitz R R Marples 《American journal of veterinary research》1978,39(9):1487-1489
Quantitative and qualitative bacterial assays were performed on the skin of 15 normal and 32 seborrheic dogs. Nonionic detergent scrubs were made on areas demarcated by glass sidearm cylinders. Quantitative analysis was accomplished by the serial dilution technique, and the bacteria were identified by individual and colonial morphology and by enzyme production. Areas measured on control dogs had a markedly lower total bacterial count than similar areas measured on seborrheic animals. Control dogs had a flora consisting primarily of coagulase-negative cocci, whereas seborrheic dogs usually had a cutaneous flora composed primarily of Stahylococcus aureus, coagulase-positive. 相似文献
144.
145.
146.
N.G. SANTACROCE 《EPPO Bulletin》1978,8(1):67-72
One of the programs utilized by PPQ-APHIS-USDA2) to prevent the introduction of hazardous pests and pathogens is known as preclearance. Preclearance relies more on inspection at origin than it does on inspection upon arrival or entry into the United States. Two such programs have been developed by PPQ for plant materials. One, established in 1951, is for bulbs, while the other, established in 1975, is for a few ornamental crops. The USDA, in co-operation with the Plant Protection Services of the Netherlands, Belgium, France, Italy, Fed. Rep. of Germany, Israel and South Africa, has been performing preclearance for bulbous plant propagative materials. Flower bulbs are being precleared in all of the above countries at the request of the exporter's groups of the respective countries. The objective of this clearance is to facilitate the entry of this material, reduce the chances of introducing plant pests and diseases into the United States, and save APHIS manpower at US ports of entry. This is achieved by having USDA personnel working cooperatively with foreign plant protection services in the inspection of material in the field and packing houses in the country of origin. Detection and elimination of plant pests and diseases is a co-operative effort for mutual benefit of both parties. 相似文献
147.
I W Lesslie C N Herbert K J Burn B N MacClancy W J Donnelly 《The Veterinary record》1975,96(15):332-334
A tuberculin testing trial in cattle was carried out in the Republic of Ireland to compare the specificity for bovine tuberculosis of a human purified protein derivative (PPD) tuberculin (Weybridge) with that of a bovine PPD (Rotterdam), and to determine whether discrimination between specific and non-specific reactions to mammalian tuberculin is better with doses of tuberculins smaller than those traditonally used for testing cattle. Tests were carried out in 510 cattle, 395 of which were shown by post mortem examination to be tuberculous and 115 non-tuberculous. Three dilutions at five-fold intervals of both mammalian tuberculins were used together with two dose levels of avian tuberculin PPD (Weybridge), and all reactions were measured both by increase in skin fold thickness and by diameter of induration. In the environment of this trial, the bovine PPD was shown to be more specific for bovine tuberculosis than the human PPD, and particularly in differentiating from "skin tuberculosis". There was no indication of greater specificity at lower doses of tuberculin. Measurement of induration diameter proved a satisfactory alternative method of reading tuberculin reactions in cattle under field conditions. 相似文献
148.
149.
N Kolstrup 《Acta veterinaria Scandinavica》1975,16(1):1-13
- Onchocerca gutturosa is reported in Danish cattle for the first time. Microfilariae were found in 38 (9.4%) of 406 cows that were 2 years or older.
- Microfilariae were not randomly distributed throughout the skin but were concentrated in the umbilical area.
- No difference in prevalence was observed between breeds of cattle.
- Most of the infected cows had grazed on fields close to streams that contained Simulium ornatum, the vector of O. gutturosa.
- Differences in preferred biting sites of S. ornatum from cow to cow were correlated with the arrangement of hair.
150.
Assessing the potential impacts of alternative landscape designs on amphibian population dynamics 总被引:2,自引:1,他引:2
An individual-based, spatially explicit population model was used to predict the consequences of future land-use alternatives for populations of four amphibian species in two central Iowa (midwest USA) agricultural watersheds. The model included both breeding and upland habitat and incorporated effects of climatic variation and demographic stochasticity. Data requirements of the model include life history characteristics, dispersal behavior, habitat affinities, as well as land use and landcover in geographic information systems databases. Future scenarios were ranked according to change in breeder abundance, saturation, and distribution, compared to baseline conditions. Sensitivity of simulation results to changes in model parameters was also examined. Simulated results suggest that while all four species modeled are likely to persist under present and future scenario conditions, two may be more at risk from future landscape change. Although the study species are all widespread generalists regarded as having a low conservation priority, they depend on wetlands and ponds, increasingly endangered habitats in agricultural landscapes. Broader conservation strategies in the region would ensure that these currently common organisms do not become the endangered species of the future.This revised version was published online in May 2005 with corrections to the Cover Date. 相似文献