首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   193302篇
  免费   10571篇
  国内免费   114篇
林业   7754篇
农学   5962篇
基础科学   1319篇
  22822篇
综合类   33952篇
农作物   7237篇
水产渔业   9493篇
畜牧兽医   99523篇
园艺   2384篇
植物保护   13541篇
  2018年   2386篇
  2017年   2656篇
  2016年   2507篇
  2015年   2184篇
  2014年   2665篇
  2013年   7219篇
  2012年   4990篇
  2011年   6169篇
  2010年   3962篇
  2009年   3997篇
  2008年   6133篇
  2007年   5821篇
  2006年   5603篇
  2005年   5282篇
  2004年   5083篇
  2003年   5168篇
  2002年   4910篇
  2001年   5938篇
  2000年   5768篇
  1999年   4672篇
  1998年   1926篇
  1997年   1969篇
  1995年   2284篇
  1994年   2031篇
  1993年   1946篇
  1992年   3982篇
  1991年   4214篇
  1990年   4309篇
  1989年   4243篇
  1988年   3952篇
  1987年   4035篇
  1986年   4106篇
  1985年   3968篇
  1984年   3419篇
  1983年   3006篇
  1982年   2077篇
  1981年   1892篇
  1980年   1844篇
  1979年   3074篇
  1978年   2498篇
  1977年   2215篇
  1976年   2018篇
  1975年   2144篇
  1974年   2792篇
  1973年   2839篇
  1972年   2726篇
  1971年   2486篇
  1970年   2346篇
  1969年   2218篇
  1967年   1981篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Between 1977 and 1992, 15 adult dogs were presented to the Universities of Bristol, Glasgow, Liverpool and London with fractures of the radial carpal bone which had occurred without a known episode of violent trauma. Eleven of the dogs were boxers and the other breeds affected were a Pharaoh hound, rottweiler, springer spaniel and a greyhound. The condition was bilateral in three cases. Eleven dogs were treated surgically by cast immobilisation (four cases), fragment removal (one case), lag screw fixation (three cases), pan-carpal arthrodesis (one case) and lag screw reduction followed by pan-carpal arthrodesis (two cases). The remaining four dogs were treated conservatively with rest and tactical use of non-steroidal anti-inflammatory drugs. Follow-up periods ranged from two months to 11 years. Varying degrees of lameness, which tended to be exacerbated by exercise, persisted in all cases. The radial carpal bone appears to have at least three separate centres of ossification which eventually fuse; their planes of fusion correspond approximately to the two main fracture lines. These areas of fusion could be weak points within the radial carpal bone.  相似文献   
992.
The life and work is told of John Pottie (1832-1908), a Scotsman who graduated from Edinburgh Veterinary College in 1858. A year later, he contracted to provide veterinary care to a consignment of horses bound for Australia. Once there, he founded a firm that has survived to the present day, still marketing products that originated in his own veterinary remedies. John Pottie brought with him a European tradition of livestock care and treatment that was epitomised in Clater's title and book, Every man his own farrier. His career is of interest for several reasons. Firstly it is because he used this tradition to launch a business enterprise in a new and different market in Australia. Secondly, although his training lay in what may be termed the pre-scientific era of the profession's history, he was able to adapt old traditions successfully to the changes that came in the age of Pasteur and Koch. Finally, the manner in which he did this, besides demonstrating his business acumen, also shows how the professional veterinary qualification gained in value in a new age of science.  相似文献   
993.
A 9-year-old pregnant mare was referred for evaluation of a nonhealing wound of 8 weeks' duration on the lateral aspect of the left forelimb. A soft tissue mass encircled the proximal two thirds of the metacarpus; radiography revealed a moderate periosteal reaction affecting metacarpal bone i.v. Histologic and immunohistochemical examinations revealed eosinophilic granulomatous inflammation and Pythium sp in the soft tissues. The mare was treated for 12 days with antimicrobials, medicated wound dressings, debridement, and i.v. administration of sodium iodide; radiography revealed progression of the bone lesions. The mare was treated by regional arterial perfusion with miconazole and excision of affected soft tissues and the distal two thirds of metacarpal bone i.v. The mare recovered without complications and gave birth to a healthy foal. Regional perfusion of antifungal agents provides high concentrations in soft and osseous tissues and permits use of low dosages of agents administered by other routes, which reduces cost, adverse effects, and teratogenic effects.  相似文献   
994.
OBJECTIVE: To determine prevalence of enteric zoonotic organisms in cats in north-central Colorado. DESIGN: Prospective study. SAMPLE POPULATION: Serum and fecal samples from 87 cats with diarrhea, 106 cats without diarrhea, and 12 cats for which fecal consistency was unknown. PROCEDURES: Samples were obtained from client-owned cats and cats at a humane society shelter. Serum was assayed for feline leukemia virus antigen and antibodies against feline immunodeficiency virus, IgM antibodies against Toxoplasma gondii, and IgG antibodies against T gondii and Cryptosporidium parvum. Microscopic examination of unstained feces was performed after centrifugation in a zinc sulfate solution, thin fecal smears were stained with acid fast stain and examined for C parvum, and bacteriologic culture of feces was used to detect aerobic and anaerobic bacteria. RESULTS: Enteric zoonotic organisms were detected in feces from 27 of 206 (13.1%) cats and included C parvum (5.4%), Giardia spp (2.4%). Toxocara cati (3.9%), Salmonella enterica serotype Typhimurium (1.0%), and Campylobacter jejuni (1.0%); each organism was detected in samples from cats with and without diarrhea. Although differences between groups were not significant, a higher proportion of shelter cats (18.2%) had enteric zoonotic organisms than client-owned cats (10.1%). CONCLUSIONS AND CLINICAL RELEVANCE: Enteric zoonotic organisms were detected in feces of 13.1% of cats, suggesting that cats, particularly those in homes of immunocompromised humans, should be evaluated for enteric zoonotic organisms.  相似文献   
995.
The insecticidal effects of the phenylpyrazole, fipronil, and a pyrethroid, beta-cyfluthrin, on larvae of the blowfly Lucilia sericata were determined in laboratory assays. When first stage larvae of L. sericata were reared on homogenized pig liver which had been treated with known amounts of test compounds, both fipronil and beta-cyfluthrin induced significant levels of mortality compared to acetone and water controls. However, fipronil was approximately 10 times more toxic than beta-cyfluthrin to L. sericata larvae following ingestion. Beta-cyfluthrin had little effect on mortality until concentrations of approximately 0.5 ppm were reached. In contrast, fipronil effected L. sericata mortality at a concentration of 0.05 ppm and 100% mortality was reached by 0.5 ppm. The lethal concentration (LC50) value for beta-cyfluthrin was 1.56 ppm as compared to 0.14 ppm for fipronil. Following contact of first and third stage larvae with cloth impregnated with known amounts of test compound, the mortality profiles of fipronil and beta-cyfluthrin were similar. At short contact times, the LC50 values for fipronil were lower than those for beta-cyfluthrin. However, at the highest contact time evaluated for the first stage larvae, 300 s, there was a reversal in this trend. The results suggest that the phenylpyrazole fipronil may represent a new potential insecticide for development against blowfly strike of sheep.  相似文献   
996.
Transfer of antibiotic resistances via the food chain is possible through the ingestion of resistant parts of the original food microflora. Lactic acid bacteria (especially glycopeptide resistant enterococci) are considered as important vectors because of their ability to transfer resistances by genetic mechanisms. Therefore a literature review and own investigations concerning the incidence and the resistance profile of enterococci from fresh meat were performed. The isolates harboured in part resistances relevant for human medicine. However, they could be isolated only sporadically and could not be demonstrated quantitatively in most cases. The resistance profile differed from those of human clinical origin. These results were confirmed by other authors. Additionally other investigators could prove molecular differences compared to clinical strains. Therefore food can only be considered as a vector if resistance transfer from food isolates to pathogenic microorganisms is possible. Such a transfer could be shown only in very low frequencies. In conclusion so far lactic acid bacteria cannot be considered as the main source for the incidence of antibiotic resistances in man.  相似文献   
997.
998.
999.
1000.
Genetic parameters of traits related to hepatic lipid metabolism, carcass composition, and product quality of overfed mule ducks were estimated on both parental lines of this hybrid: the common duck line for the maternal side and the Muscovy line for the paternal side. The originality of the statistical model was to include simultaneously the additive genetic effect of the common ducks and that of the Muscovy ducks, revealing a greater genetic determinism in common than in Muscovy. Plasma metabolic indicators (glucose, triglyceride, and cholesterol contents) were heritable, in particular at the end of the overfeeding period, and heritabilities increased with the overfeeding stage. Carcass composition traits were highly heritable in the common line, with values ranging from 0.15 for liver weight, 0.21 for carcass weight, and 0.25 for abdominal fat weight to 0.32 for breast muscle weight. Heritabilities of technological outputs were greater for the fatty liver (0.19 and 0.08, respectively, on common and Muscovy sides for liver melting rate) than for the pectoralis major muscle (between 0.02 and 0.05 on both parental sides for cooking losses). Fortunately, the processing industry is mainly facing problems in liver quality, such as too high of a melting rate, than in meat quality. The meat quality appraisal criteria (such as texture and cooking losses), usually dependent on pH and the rate of decline of pH, were also very lowly heritable. This study demonstrated that genetic determinism of meat quality and ability of overfeeding is not similar in the common population and in the Muscovy population; traits related to fattening, muscle development, and BW have heritability values from 2 to 4 times greater on the common line than on the Muscovy line, which is relevant for considering different selection strategies.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号