全文获取类型
收费全文 | 151716篇 |
免费 | 7996篇 |
国内免费 | 101篇 |
专业分类
林业 | 6145篇 |
农学 | 4874篇 |
基础科学 | 963篇 |
19587篇 | |
综合类 | 23954篇 |
农作物 | 6170篇 |
水产渔业 | 7446篇 |
畜牧兽医 | 78483篇 |
园艺 | 2052篇 |
植物保护 | 10139篇 |
出版年
2019年 | 1539篇 |
2018年 | 2312篇 |
2017年 | 2646篇 |
2016年 | 2395篇 |
2015年 | 1947篇 |
2014年 | 2537篇 |
2013年 | 6353篇 |
2012年 | 4586篇 |
2011年 | 5730篇 |
2010年 | 3676篇 |
2009年 | 3811篇 |
2008年 | 5565篇 |
2007年 | 5251篇 |
2006年 | 4872篇 |
2005年 | 4514篇 |
2004年 | 4277篇 |
2003年 | 4385篇 |
2002年 | 3904篇 |
2001年 | 4607篇 |
2000年 | 4671篇 |
1999年 | 3712篇 |
1998年 | 1625篇 |
1997年 | 1536篇 |
1996年 | 1426篇 |
1995年 | 1717篇 |
1994年 | 1506篇 |
1993年 | 1382篇 |
1992年 | 2857篇 |
1991年 | 2990篇 |
1990年 | 2894篇 |
1989年 | 2912篇 |
1988年 | 2619篇 |
1987年 | 2596篇 |
1986年 | 2686篇 |
1985年 | 2586篇 |
1984年 | 2115篇 |
1983年 | 1890篇 |
1979年 | 2071篇 |
1978年 | 1639篇 |
1977年 | 1394篇 |
1976年 | 1501篇 |
1975年 | 1569篇 |
1974年 | 1852篇 |
1973年 | 1826篇 |
1972年 | 1714篇 |
1971年 | 1554篇 |
1970年 | 1520篇 |
1969年 | 1577篇 |
1968年 | 1349篇 |
1967年 | 1437篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
D. J. STEWART B. L. CLARK J. E. PETERSON D. L. EMERY E. F. SMITH† D. A. GRIFFITHS† I. J. O'DONNELL‡ 《Australian veterinary journal》1985,62(5):153-159
A highly purified pilus vaccine prepared from cells of Bacteroides nodosus strain 198 provided a high level of protection against homologous challenge and small, not statistically significant, levels of protection against challenge with 4 other strains each from different serogroups. In a second experiment, a partially purified pilus vaccine from strain 198 induced significant immunity to 1 of 4 heterologous strains which were different from those used in the first experiment. In a third experiment a strain 198 whole cell vaccine produced significant immunity against 3 of 6 heterologous strains used in the first 2 experiments. There was no obvious relationship between the colony type, degree of piliation and level of cross-protection obtained against a particular strain. The results provide further evidence that immunogens associated with, but distinct from, the pilus are involved in cross-protection and that cross-protective antigens are common to some, but not all, strains. 相似文献
992.
Ten cats with a total of 15 cancerous or precancerous lesions were examined for clinical response to and histopathologic changes after treatment with 13-cis-retinoic acid. Before treatment was started, the lesions were graded according to clinical severity and biopsied for histopathologic examination. Serum samples were prepared for determining vitamin A concentrations. For comparison, serum vitamin A concentrations in 10 clinically healthy cats were determined. 13-cis-Retinoic acid (approx 3.0 mg/kg) was given to affected cats once a day for an average of 68 days. At the completion of the therapeutic trial, additional biopsy tissues were obtained for histopathologic examination, and serum was assayed for 13-cis-retinoic acid. Of the 15 lesions examined, only 1 showed partial clinical and microscopic improvement during the therapy period. The mean serum vitamin A concentration of the affected cats was not statistically different from that of the 10 healthy cats. The results of this trial indicated that 13-cis-retinoic acid used at this dosage, daily frequency, and duration did not have therapeutic efficacy for squamous cell carcinomas or preneoplastic lesions in the cat and that the mean serum vitamin A concentration did not differ between the affected cats and clinically healthy cats. 相似文献
993.
A total of 39 Holstein cattle were grazed in tracts of wild grassland on account of shortage in pasture grass. Twenty-nine cattle were affected and 26 of them died during a 21-day period. The main signs were depression, anorexia, ascites, and oliguria. There was elevated serum urea nitrogen and sugar and protein in the urine. Pathological examination revealed turbid swelling of the kidney, an increase in the amount of fluid in the body cavity, edema in the perirenal adipose tissue and hemorrhage in various visceral organs and tissues. Histologically, acute tubular necrosis in the kidney, hypoplasia of the erythroblast series in the bone marrow, atrophy and degeneration of the lymphatic tissue and focal necrosis of the liver were observed in many of the cattle. Among cows experimentally fed Narthecium asiaticum Maxim., Polygonum sachalinense Fr. Schum., and Vitis coignetiae Pulliat which were presumed to have been ingested in large amounts by grazing cattle in the field, the cows fed N. asiaticum revealed the clinical, biochemical and pathological changes similar to those noticed in naturally affected cattle. Cows fed P. sachalinense and V. coignetiae showed no distinct systemic symptoms except transient anorexia and hypothermia. 相似文献
994.
Increasing dietary metabolisable energy (ME) at particular amino acid: ME ratios significantly improved growth and food utilisation of broilers kept at moderate (18 to 26 degrees C) and high (25 to 35 degrees C) ambient temperatures during the finishing period from 22 d of age. The optimum amino acid: ME ratio varied with dietary ME concentration in the hot, but not in the moderate environment. Relatively greater increases in food intake and growth rate occurred in the hot environment when dietary ME was increased and the amino acid: ME ratio was reduced. The minimum rate of food intake did not coincide with the period of maximum temperature. Increasing the dietary protein at particular ME concentrations had little or no effect on the food intake and growth rate of birds kept at high temperatures. Supplementation with dietary fat had no beneficial effect on performance at high temperatures. The rectal temperatures of birds in the hot environment increased with age and, towards the end of the finishing period, when higher energy diets were fed. 相似文献
995.
996.
L M Krista E E Pierson G R McDaniel E C Mora J A McGuire S L Bolden L E Miller 《British poultry science》1985,26(3):349-356
Twenty-one male Broad Breasted White turkeys which had been selected for high or low blood pressure were put on an exercise regimen to determine its effect on semen quality. Eleven were from the hypertensive line and 10 from the hypotensive line. Eleven (6 hypertensive and 5 hypotensive) turkeys were placed on an exercise regime of walking (herding) about 1 mile daily for 6 weeks before the experiment began, and then for a further 6 weeks during semen collection. Semen was collected from 11 turkeys on the exercise regime and 10 nonexercised control birds which were kept in their experimental pens during the trial. Both hypertensive and exercised groups showed an improved semen colour score at the first collection period (P less than or equal to 0.09). Only the exercised group showed a significantly (P less than or equal to 0.05) better score than the control group during periods 2 and 3. The hypertensive line showed significantly higher spermatozoa count than the hypotensive line during the first collection period. There was no effect of either exercise or selection for high or low blood pressure on semen volume. 相似文献
997.
998.
J P Hoover R J Bahr M A Nieves R T Doyle M A Zimmer S E Lauzon 《Journal of the American Veterinary Medical Association》1985,187(11):1154-1161
In the first year (1984) of a reintroduction study, 10 American river otters (Lutra canadensis) from Louisiana were transported to Oklahoma, held for 5 days for clinical evaluation, surgical implantation with intra-abdominal radiotelemetry devices, and then released in Oklahoma. Four of 10 otters released died within 32 days. Clinical evaluation indicated that respiratory tract disease, bacterial and parasitic infections, and inanition may have contributed to the death of these otters. In the second year (1985) of the study, an exotic feline diet was fed, and the holding period for 10 otters was increased to provide time for evaluation and treatment before surgery, postsurgical acclimation to Oklahoma, and reevaluation before release. Although the initial clinical findings on otters in the second year were similar to those found in the first year, otter body weights increased, and the prevalence and severity of clinical abnormalities decreased with treatment during the second-year holding period. Three of 10 second-year otters died during the holding period, and contributing causes of death were determined to be: trauma (hepatic hematoma), inanition, renal disease, pneumonia, salmonellosis (Salmonella anatum), and a retropharyngeal abscess (Klebsiella pneumoniae). Seven healthy otters were reintroduced into Oklahoma in 1985, and postrelease deaths were not experienced. 相似文献
999.
1000.
Wobeser G Gajadhar AA Hunt HM 《The Canadian veterinary journal. La revue veterinaire canadienne》1985,26(8):241-244
Infection with Fascioloides magna, the large American liver fluke, was diagnosed in two moose (Alces alces) and six wapiti (Cervus elaphus) from central Saskatchewan. This is believed to be the first record of the parasite in the province. Fecal samples collected from wild wapiti at five sites in the commercial forest zone in Saskatchewan contained eggs believed to be those of F. magna. Trematode eggs were not found in feces from five captive herds of wapiti in the province, nor in samples from wild wapiti in Moose Mountain Provincial Park. Operculate eggs were found in feces of wild wapiti from Cypress Hills, but these were believed to be from trematodes other than F. magna. The distribution and significance of F. magna in Canada, based partially on responses to a mail questionnaire, are reviewed. 相似文献