全文获取类型
收费全文 | 116603篇 |
免费 | 5744篇 |
国内免费 | 1409篇 |
专业分类
林业 | 5079篇 |
农学 | 4395篇 |
基础科学 | 1635篇 |
12899篇 | |
综合类 | 26606篇 |
农作物 | 4532篇 |
水产渔业 | 5459篇 |
畜牧兽医 | 54692篇 |
园艺 | 1884篇 |
植物保护 | 6575篇 |
出版年
2021年 | 1076篇 |
2020年 | 1138篇 |
2019年 | 1299篇 |
2018年 | 1628篇 |
2017年 | 1958篇 |
2016年 | 1718篇 |
2015年 | 1704篇 |
2014年 | 1865篇 |
2013年 | 4229篇 |
2012年 | 3378篇 |
2011年 | 4007篇 |
2010年 | 2968篇 |
2009年 | 2834篇 |
2008年 | 3729篇 |
2007年 | 3532篇 |
2006年 | 3208篇 |
2005年 | 3006篇 |
2004年 | 2749篇 |
2003年 | 2700篇 |
2002年 | 2487篇 |
2001年 | 3322篇 |
2000年 | 3298篇 |
1999年 | 2583篇 |
1998年 | 1094篇 |
1997年 | 1056篇 |
1995年 | 1190篇 |
1994年 | 1055篇 |
1992年 | 2287篇 |
1991年 | 2399篇 |
1990年 | 2428篇 |
1989年 | 2400篇 |
1988年 | 2259篇 |
1987年 | 2254篇 |
1986年 | 2226篇 |
1985年 | 2164篇 |
1984年 | 1788篇 |
1983年 | 1557篇 |
1982年 | 1051篇 |
1979年 | 1627篇 |
1978年 | 1332篇 |
1977年 | 1176篇 |
1976年 | 1099篇 |
1975年 | 1234篇 |
1974年 | 1543篇 |
1973年 | 1470篇 |
1972年 | 1556篇 |
1971年 | 1422篇 |
1970年 | 1355篇 |
1969年 | 1241篇 |
1967年 | 1145篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Cellular alterations in level of expression of mRNA encoding for prostaglandin endoperoxide synthase were quantified within ovarian tissues of sheep obtained before, during and after induction of the preovulatory surge of LH and ovulation with LHRH. This was accomplished by isotopic in situ hybridization using a selective cRNA probe to ovine prostaglandin endoperoxide synthase mRNA. A significant elevation in mRNA was detected within the theca interna of the preovulatory follicle at 8, 16 and 24 hr following administration of LHRH. Very close to the time of ovulation (ie., at 24 hr post-LHRH) a marked rise in mRNA was observed in association with epithelial cells covering the apical surface of the follicle. Ovarian cyclooxygenase metabolites of arachidonic acid produced during the ovulatory process in the ewe originate within the thecal layer and germinal epithelium of the follicle destined to ovulate. 相似文献
72.
73.
74.
75.
山羊脑灰质软化症 (POLIOEN CEPHALOMALACIA)和李氏杆菌病 (LIS TERIOSIS)是症状相似治疗方法截然不同的两种疾病。山羊饲养者和兽医工作者必须从两种疾病的细微差别中进行鉴别 ,以便正确治疗和处理病羊。多数情况下 ,这两种疾病出现在饲养条件比较好、但饲养方法不当的地方。特别是在快速育肥时。精饲料喂量过多 ,而含粗纤维的饲料喂量过少是诱发两种疾病的重要因素。突然更换饲料常常导致此病突然发作。脑灰质软化症 (通常又称为大脑皮层坏死症 )是缺乏硫胺 (即维生素B1)而造成的一种代谢性疾病。瘤胃环… 相似文献
76.
77.
W Petchpoo P Tan-ariya V Boonsaeng C R Brockelman P Wilairat S Panyim 《Veterinary parasitology》1992,42(3-4):189-198
A genomic library of Babesia bovis DNA from the Mexican strain M was constructed in plasmid pUN121 and cloned in Escherichia coli. Several recombinants which hybridized strongly to radioactively labeled B. bovis genomic DNA in an in situ screening were selected and further analyzed for those which specifically hybridized to B. bovis DNA. It was found that pMU-B1 had the highest sensitivity, detecting 25 pg of purified B. bovis DNA, and 300 parasites in 10 microliters of whole infected blood, or 0.00025% parasitemia. pMU-B1 contained a 6.0 kb B. bovis DNA insert which did not cross-hybridize to Babesia bigemina, Trypanosoma evansi, Plasmodium falciparum, Anaplasma marginale, Boophilus microplus and cow DNA. In the Southern blot analysis of genomic DNA, pMU-B1 could differentiate between two B. bovis geographic isolates, Mexican strain M and Thai isolate TS4. Thus, the pMU-B1 probe will be useful in the diagnosis of Babesia infection in cattle and ticks, and in the differentiation of B. bovis strains. 相似文献
78.
Colitis cystica profunda in dogs has been diagnosed in one case only. The two own cases were characterized by repeated, partly bloody diarrhea, vomitus, and painful defecation. The disease was diagnosed by clinical examination and colonoscopy with the ensuing histological examination of biopsy specimens. The disease could be managed by administration of a diet, sulfasalazine and corticosteroids. 相似文献
79.
Ariana M.P. Nap Yvonne W.E.A. Pollak Walter E. van den Brom Ad Rijnberk DVM PhD 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》1994,8(4):302-303
Thyroidal 99m TcO4 (pertechnetate) uptake percentages were determined in unanesthetized euthyroid (n = 13) and hyperthyroid (n = 18) cats. Maximal uptakes were observed 60 minutes after IV injection of the radionuclide and ranged from 0.3 to 3.9% of the dose in euthyroid cats (median 2.23%) and from 5.2% to 23.9% of the dose in hyperthyroid cats (median 14.8%) ( P < .05). There were no overlaps in pertechnetate uptake percentages during any of the intervals evaluated. It is concluded that the optimal time for visualization of the thyroid by 99m TcO4 -scanning is 60 minutes after IV injection of the radionuclide. Calculation of the percentage uptake is of additional diagnostic value. 相似文献
80.
Russell T. Greene Gregory C. Troy 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》1995,9(2):86-91
Coccidioidomycosis was diagnosed in 48 cats. Forty-one cases were identified within a period of 3 years. Coccidioides immitis was revealed by cytological or histopathological examinations, or culture in 70% of cats. The remaining 30% of cases were diagnosed by appropriate clinical signs, radiographic lesions, and serological test results. The average age of affected cats was 6.2 years with a median age of 5.0 years. Fifty-four percent (n = 26) were female and 46% (n = 22) were male. Domestic shorthaired and longhaired breeds comprised 89% (n = 41) of affected cats. Sixty-seven percent of cases were diagnosed during the 6-month period of December through May. Cats infected with C immitis were presented for evaluation of dermatologic (56%), respiratory (25%), musculoskeletal (19%), and neurological or ophthalmologic signs (19%). Fever, inappetence, and weight loss were present in 44% of the cats. Duration of clinical signs before diagnosis was less than 4 weeks in 85% (n = 42) of cats, with an average of 3.8 weeks and a median of 2 weeks. Agar gel immunodiffusion tests were positive in all 39 cats tested at sometime during the course of their disease. Hyperproteinemia (greater than 7.9 g/dL) was present in 52% (10/23) of cases. The majority of cats (n = 39) were negative for feline leukemia virus. Antibodies to feline immunodeficiency virus were absent in the 19 cats tested. Ketoconazole was the most common antifungal agent used to treat cats with Coccidioidomycosis. Duration of treatment ranged from less than 1 week to 43 months. Thirty-two cats are currently asymptomatic, with or without treatment. Eleven cats died or were euthanized. Five cats were lost to follow-up. Ketoconazole likely is more suppressive than curative because relapses were common after discontinuing therapy. 相似文献