全文获取类型
收费全文 | 9253篇 |
免费 | 444篇 |
国内免费 | 14篇 |
专业分类
林业 | 588篇 |
农学 | 229篇 |
基础科学 | 84篇 |
1586篇 | |
综合类 | 1610篇 |
农作物 | 365篇 |
水产渔业 | 829篇 |
畜牧兽医 | 3373篇 |
园艺 | 278篇 |
植物保护 | 769篇 |
出版年
2024年 | 19篇 |
2023年 | 59篇 |
2022年 | 90篇 |
2021年 | 155篇 |
2020年 | 211篇 |
2019年 | 208篇 |
2018年 | 206篇 |
2017年 | 219篇 |
2016年 | 211篇 |
2015年 | 185篇 |
2014年 | 253篇 |
2013年 | 450篇 |
2012年 | 542篇 |
2011年 | 708篇 |
2010年 | 368篇 |
2009年 | 352篇 |
2008年 | 635篇 |
2007年 | 623篇 |
2006年 | 592篇 |
2005年 | 574篇 |
2004年 | 608篇 |
2003年 | 571篇 |
2002年 | 504篇 |
2001年 | 98篇 |
2000年 | 90篇 |
1999年 | 95篇 |
1998年 | 81篇 |
1997年 | 70篇 |
1996年 | 67篇 |
1995年 | 62篇 |
1994年 | 61篇 |
1993年 | 50篇 |
1992年 | 57篇 |
1991年 | 49篇 |
1990年 | 58篇 |
1989年 | 49篇 |
1988年 | 42篇 |
1987年 | 44篇 |
1986年 | 33篇 |
1985年 | 32篇 |
1984年 | 34篇 |
1983年 | 40篇 |
1982年 | 26篇 |
1981年 | 25篇 |
1980年 | 28篇 |
1979年 | 23篇 |
1978年 | 20篇 |
1976年 | 20篇 |
1975年 | 22篇 |
1974年 | 15篇 |
排序方式: 共有9711条查询结果,搜索用时 15 毫秒
991.
Canine plasma and erythrocyte response to a docosahexaenoic acid-enriched supplement: characterization and potential benefits 总被引:1,自引:0,他引:1
Filburn CR Griffin D 《Veterinary therapeutics : research in applied veterinary medicine》2005,6(1):29-42
Results of this study confirm that dietary supplementation in dogs with a natural source of omega-3 fatty acids (salmon oil), with a docosahexaenoic acid:eicosapentaenoic acid (DHA:EPA) ratio of 1.5:1, increases plasma and red blood cell levels of these fatty acids. Supplementation with this DHA-enriched oil improves the long-chain polyunsaturated fatty acid omega-6:omega-3 (n-6:n-3) ratio, which may benefit dogs of all ages. Studies describing some of the neurologic, renal, cardiovascular, immune, and musculoskeletal effects of elevated blood levels of n-3 fatty acids, especially DHA, are reviewed. The importance of providing an enriched source of DHA, instead of its shorter precursors, is emphasized. 相似文献
992.
A raised concentration of serum cardiac troponin I (cTnI) is a sensitive marker of cardiac myocyte injury in the cat and assays developed for its measurement in human patients have been validated in the cat. Raised levels have been associated with a number of cardiac insults including hypertrophic cardiomyopathy and trauma. Hyperthyroidism is a common disease of older cats and excess thyroid hormone is known to produce significant cardiovascular effects in this species. This study evaluated the effect of treatment for hyperthyroidism with radioactive iodine on cTnI concentration, assessed the association between thyroxin levels and glomerular filtration rate (GFR) and cTnI concentration in cats treated for hyperthyroidism and described changes in echocardiographic parameters following treatment. Prior to the treatment serum cTnI was measured and echocardiography performed, thyroxin, cTnI, and echocardiography were then repeated at various time points following radioisotope therapy. The results show that higher thyroxin levels were significantly (P=0.002) associated with a higher likelihood of the cat presenting with detectable levels of cTnI. No significant association was found between GFR and presence of detectable levels of cTnI. Furthermore the results indicate that the effects of hyperthyroidism on echocardiographic parameters appear considerably less in this study than in previous studies and that the main outcome of treatment on these parameters is a significant reduction in fractional shortening (P=0.006). These results suggest that chronic exposure to excess thyroid hormone may induce myocyte damage of sufficient severity to raise serum cTnI concentration in a proportion of cats that resolves following establishment of a euthyroid state. 相似文献
993.
994.
Florent?MouillotEmail author Jean-Pierre?Ratte Richard?Joffre David?Mouillot and ?Serge Rambal 《Landscape Ecology》2005,20(1):101-112
Two hundred years of landscape changes were studied on a 3,760 ha area of central Corsica (France) representing a typical Mediterranean environment. Different historical sources, including an accurate land-cover map from 1774 and statistics on land cover from 1848 and 1913, were used. Three additional maps (1960, 1975 and 1990) were drawn, and a complete fire history from 1957 to 1997 was created. Forests expanded slowly by a border effect. Forest expansion was more rapid in unburnt sites (0.59% per year) than in burnt sites (0.23% per year), mostly because the initial amount of forests was greater. Because of the border effect, the combination of past landscape pattern and short distance colonization abilities of forest species may have allowed the shrublands to persist in some places after land abandonment. This persistence may explain the pattern of fire in the landscape, since shrubland burn more readily than forests. 相似文献
995.
Loma salmonae is a common gill parasite of salmonids, and essentially all species in the genus Oncorhynchus are susceptible. Infections occur in both fresh and salt water. Loma salmonae is directly transmissible by ingestion of spores or infected tissue. The parasite infects the wall of blood vessels of various organs, but the gill is the primary site of infection. Initial infection occurs in the intestine, and xenomas are easily detected in the gills by standard histology at 4-6 wk post-exposure. A few presporogonic stages of the parasite are found in the heart endothelium prior to xenoma formation in the gills. Ultrastructure studies of early infections demonstrated that wandering blood cells transport the meronts to the gills, and that merogony occurs in pillar cells and other cells underlying the gill endothelium. Xenomas develop in these cells, resulting in hypertrophied host cells filled with spores. Xenomas ultimately rupture, and are associated with severe inflammation in which free spores are found in macrophages. The parasites are most pathogenic during this phase of the infection, resulting in severe vasculitis and clinical disease. Both rainbow trout (Oncorhynchus mykiss) and Chinook salmon (Oncorhynchus ishawytscha) recover from infections, but free spores persist in kidney and spleen phagocytes for many months after xenomas are absent in Chinook salmon. Fish that have recovered from the infection show strong immunity against the parasite, lasting up to 1 year. Fish are susceptible to infection by other routes of exposure by spores; co-habitation, anal gavage, and intramuscular, intraperitoneal and intravascular injection. Autoinfection probably occurs following release of spores in blood vessels after xenomas rupture. The optimal temperature for L. salmonae infections is 15-17 degrees C, with a permissive range of 11-20 degrees C. 相似文献
996.
Background
Eukaryotic organisms are defined by the presence of a nucleus, which encloses the chromosomal DNA, and is characterized by its DNA content (C-value). Complex eukaryotic organisms contain organs and tissues that comprise interspersions of different cell types, within which polysomaty, endoreduplication, and cell cycle arrest is frequently observed. Little is known about the distribution of C-values across different cell types within these organs and tissues. 相似文献997.
998.
Dennison AC Van Metre DC Morley PS Callan RJ Plampin EC Ellis RP 《Journal of the American Veterinary Medical Association》2005,227(1):132-138
OBJECTIVE: To compare the frequency of isolation, genotypes, and in vivo production of major lethal toxins of Clostridium perfringens in adult dairy cows affected with hemorrhagic bowel syndrome (HBS) versus left-displaced abomasum (LDA). DESIGN: Case-control study. ANIMALS: 10 adult dairy cattle with HBS (cases) and 10 adult dairy cattle with LDA matched with cases by herd of origin (controls). PROCEDURE: Samples of gastrointestinal contents were obtained from multiple sites during surgery or necropsy examination. Each sample underwent testing for anaerobic bacteria by use of 3 culture methods. The genotype of isolates of C. perfringens was determined via multiplex polymerase chain reaction assay. Major lethal toxins were detected by use of an ELISA. Data were analyzed with multivariable logistic regression and chi2 analysis. RESULTS: C. perfringens type A and type A with the beta2 gene (A + beta2) were the only genotypes isolated. Isolation of C. perfringens type A and type A + beta2 was 6.56 and 3.3 times as likely, respectively, to occur in samples from cattle with HBS than in cattle with LDA. Alpha toxin was detected in 7 of 36 samples from cases and in 0 of 32 samples from controls. Beta2 toxin was detected in 9 of 36 samples from cases and 0 of 36 samples from controls. CONCLUSIONS AND CLINICAL RELEVANCE: C. perfringens type A and type A + beta2 can be isolated from the gastrointestinal tract with significantly greater odds in cattle with HBS than in herdmates with LDA. Alpha and beta2 toxins were detected in samples from cows with HBS but not from cows with LDA. 相似文献
999.
Torres SM Diaz SF Nogueira SA Jessen C Polzin DJ Gilbert SM Horne KL 《Journal of the American Veterinary Medical Association》2005,227(2):239-243
OBJECTIVE: To determine frequency of urinary tract infection (UTI) among dogs with pruritic disorders that were or were not receiving long-term glucocorticoid treatment. DESIGN: Observational study. ANIMALS: 127 dogs receiving glucocorticoids for > 6 months and 94 dogs not receiving glucocorticoids. PROCEDURE: Bacterial culture of urine samples was performed in dogs receiving long-term glucocorticoid treatment, and information was collected on drug administered, dosage, frequency of administration, duration of glucocorticoid treatment, and clinical signs of UTI. For dogs not receiving glucocorticoids, a single urine sample was submitted for bacterial culture. RESULTS: Multiple (2 to 6) urine samples were submitted for 70 of the 127 (55%) dogs receiving glucocorticoids; thus, 240 urine samples were analyzed. For 23 of the 127 (18.1%) dogs, results of bacterial culture were positive at least once, but none of the dogs had clinical signs of UTI. Pyuria and bacteriuria (present vs absent) were found to correctly predict results of bacterial culture for 89.9% and 95.8% of the samples, respectively. Type of glycocorticoid, dosage, frequency of administration, and duration of treatment were not associated with frequency of UTI. None of the urine samples from dogs not receiving glucocorticoids yielded bacterial growth. The frequency of UTI was significantly higher for dogs treated with glucocorticoids than for dogs that had not received glucocorticoids. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that dogs receiving long-term glucocorticoid treatment have an increased risk of developing a UTI. On this basis, we recommend that urine samples be submitted for bacterial culture at least yearly for such dogs. 相似文献
1000.
Garcia-Seco E Wilson DA Kramer J Keegan KG Branson KR Johnson PJ Tyler JW 《Journal of the American Veterinary Medical Association》2005,226(9):1529-1537
OBJECTIVE: To determine the prevalence of pedunculated lipomas and identify risk factors affecting postoperative complications and survival in horses at a veterinary teaching hospital undergoing surgery for colic caused by pedunculated lipomas. DESIGN: Retrospective study. ANIMALS: 102 horses with a diagnosis of pedunculated lipoma. PROCEDURE: Age, breed, weight, and sex of horses with pedunculated lipomas were compared with the total equine hospital population and the population of horses admitted for abdominal surgery during the same period. Follow-up information was obtained by reevaluation or contact with owners via telephone or written request. RESULTS: Prevalence of pedunculated lipomas as a reason for abdominal surgery in horses, compared with the population of horses with and without lipomas admitted for abdominal surgery, was 10%. Castrated male Saddlebred and Arabian horses > 14 years old were identified as being at risk for developing pedunculated lipomas. Postoperative complications were detected in 72% of horses with pedunculated lipomas. Variables associated with low survival rates included surgery before 1992, heart rate > 80 beats/min, abnormal color of abdominal fluid, pale mucous membranes, surgery requiring intestinal resection, and inability to attain a mean arterial pressure > or = 100 mm Hg. Horses undergoing surgery from 1992 to 1996, weighing < 409 kg (900 lb), or requiring jejunojejunal anastomosis had a high survival rate. CONCLUSIONS AND CLINICAL RELEVANCE: Although many of the variables reflected the health of the horse at the time of surgery, results may help veterinarians recognize risk factors associated with development of pedunculated lipomas and better predict the outcome of horses undergoing surgery for colic caused by pedunculated lipomas. 相似文献