全文获取类型
收费全文 | 96922篇 |
免费 | 5996篇 |
国内免费 | 7834篇 |
专业分类
林业 | 7842篇 |
农学 | 5409篇 |
基础科学 | 4067篇 |
9177篇 | |
综合类 | 44392篇 |
农作物 | 7401篇 |
水产渔业 | 4708篇 |
畜牧兽医 | 16655篇 |
园艺 | 6870篇 |
植物保护 | 4231篇 |
出版年
2024年 | 454篇 |
2023年 | 1680篇 |
2022年 | 3811篇 |
2021年 | 3942篇 |
2020年 | 3606篇 |
2019年 | 3375篇 |
2018年 | 2652篇 |
2017年 | 4418篇 |
2016年 | 2894篇 |
2015年 | 4466篇 |
2014年 | 4744篇 |
2013年 | 5652篇 |
2012年 | 8146篇 |
2011年 | 8047篇 |
2010年 | 7365篇 |
2009年 | 6515篇 |
2008年 | 6727篇 |
2007年 | 6296篇 |
2006年 | 5152篇 |
2005年 | 4996篇 |
2004年 | 3196篇 |
2003年 | 2109篇 |
2002年 | 2038篇 |
2001年 | 1798篇 |
2000年 | 1558篇 |
1999年 | 774篇 |
1998年 | 182篇 |
1997年 | 135篇 |
1996年 | 119篇 |
1995年 | 116篇 |
1994年 | 99篇 |
1993年 | 106篇 |
1992年 | 224篇 |
1991年 | 228篇 |
1990年 | 236篇 |
1989年 | 196篇 |
1988年 | 206篇 |
1987年 | 153篇 |
1986年 | 170篇 |
1985年 | 123篇 |
1979年 | 134篇 |
1975年 | 137篇 |
1974年 | 129篇 |
1973年 | 116篇 |
1972年 | 139篇 |
1971年 | 118篇 |
1969年 | 102篇 |
1968年 | 113篇 |
1967年 | 125篇 |
1966年 | 104篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
R K?stlin 《Tier?rztliche Praxis》1988,16(4):351, 436-351, 437
92.
Eradication of lice in cattle. 总被引:8,自引:0,他引:8
The purpose of this field study was to develop and evaluate eradication as a strategy to control lice in cattle. Thirty-three herds of cattle were selected and observed during a period of two and a half years. Before eradication, biting lice (Damalinia bovis) were present in 94% of the herds and 27% of the animals. Sucking lice (Linognathus vituli) were present in 42% of the herds and 5% of the animals. These levels were very similar to those reported from other countries in Northern Europe. The eradication strategy was successful in 28 of 33 herds, but lice were still present in 5 herds 3 to 6 months after treatment. Biting lice were present in all these 5 herds, sucking lice were present in 3 herds. During the next 12 months, nine of the 28 herds were reinfected with lice. Six herds were reinfected with just biting lice, 2 herds with just sucking lice and one herd was reinfected with both. There was no significant difference between the 2 louse species regarding the risk of unsuccessful eradication or reinfection. The only significant risk factor for reinfection was either purchase of livestock or use of common pasture, combined with failure in pre-treatment of newly introduced animals. 相似文献
93.
94.
M D Pérez Alenza E Tabanera L Pe?a 《Journal of the American Veterinary Medical Association》2001,219(8):1110-1114
OBJECTIVE: To determine epidemiologic, clinical, and pathologic characteristics of inflammatory mammary carcinoma (IC) in dogs. DESIGN: Retrospective study. ANIMALS: 33 dogs with IC and 153 dogs with malignant mammary tumors other than IC. PROCEDURES: Medical records were reviewed, and signalment, history, physical examination findings, and results of thoracic radiography and necropsy were obtained. RESULTS: 33 of 436 (7.6%) dogs examined at a veterinary teaching hospital because of dysplasia or tumors of the mammary glands and 33 of 186 (17.7%) dogs with at least 1 malignant tumor had IC. Thirty-two of the 33 dogs were sexually intact. Dogs with IC were significantly older than were dogs with other malignant mammary tumors, and in dogs with IC, the tumor was initially noticed a mean of 52 days after the beginning of the last observed estrus, whereas in dogs with other mammary tumors, the tumor was initially noticed a mean of 137 days after the beginning of the last observed estrus. Dogs with IC were more likely to be anorectic and to have generalized weakness, weight loss, and thoracic metastases. Dogs with IC survived a mean of 25 days with palliative treatment. Histologically, involvement of dermal lymphatic vessels was identified in 14 of 19 (74%) dogs with IC. Two clinical forms of IC (primary and secondary) were identified. Dogs with primary IC had a worse clinical condition. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that IC is an uncommon but distinct entity in dogs. A histologic finding of dermal lymphatic involvement should be considered a hallmark for the pathologic diagnosis of IC in dogs. 相似文献
95.
不同方法构建磺胺二甲氧嘧啶免疫抗原的比较研究 总被引:3,自引:0,他引:3
为探讨合成磺胺二甲氧嘧啶(SDM)免疫抗原的有效途径,采用重氮偶合法和戊二醛法分别合成SDM免疫抗原,并对其结构特征、光谱特征和SDM结合比进行比较.结果表明,在合成SDM-BSA中采用重氮偶合法比戊二醛法好. 相似文献
96.
AIM: To evaluate the genotype , muscle histopathology and ultrastructure in dko mice. METHODS: Dystrophin/Utrophin-deficient double knockouts (dko) mice were obtained from university of Oxford, UK. Genotype of filial generation of heterozygote was evaluated by PCR-SSP. HE staining and fluorescent immunohistochemistry by SABC-Cy3 were used to detect striated muscle of dko mouse, and the muscle ultrastructure was observed by transmission electron microscope(TEM). RESULTS: In 112 filial generation mice, there were 28 mdx (25.0%), 26 dko (23.2%) and 58 heterozygote (51.8%), which coincided with the law of Mendelian inheritance. HE staining showed that the myocytes were not very uniform, there were phenomenon of round outline, centrally nucleated fibers, widening interspace, inflammatory cell infiltration and connective tissue proliferation in dko mice. There were no any immunofluorescent expression of dystrophin and utrophin in sarcolemma in dko mice. TEM showed sarcolemma breakage, separation and edema, and loose myofibril texture, inflammatory cell infiltration and connective tissue proliferation in dko mice. CONCLUSION: PCR-SSP is a very quick and accurate way for genotype evaluation of filial generation. The pathophysiology of dko mouse was very similar to Duchenne muscular dystrophy (DMD), and dko mouse is an ideal animal model for study of DMD clinical therapy. 相似文献
97.
通过随机抽样,计算我国57家上市公司1998年-2002年的平均盈利指标和风险指标,根据各公司多元化熵值的大小对样本总体进行分组,分析多元化程度对企业绩效的影响.研究发现1.多元化程度越高,公司的平均净资产收益率越高;2.多元化经营降低了公司收益率的波动水平;3.资产规模越小的公司越倾向于选择多元化经营. 相似文献
98.
99.
100.
对匍匐翦股颖粤选1号种茎采收前24 h和采收后分别进行不同浓度的6-BA(1.0、2.5、5.0、7.5 mg/L)和尿素(0.5%、1.5 %、2.5%)处理,清水对照(CK),探讨其对粤选1号匍匐翦股颖种茎扦插成活率和生长的影响.通过观测种茎的外观变化,种茎成活率、根长、生根数、根重、分蘖数、根系活力和叶绿素含量的的变化,初步确定种茎采前处理用2.5 mg/L 6-BA和2.5%尿素处理、采后用1.5%尿素处理均优于各自对照,但采前、采后处理中除根系活力与各自对照有显著差异(P<0.05)外,其它指标均未达各自对照的显著水平;种茎采前与采后处理对比,采前处理效果总体好于采后处理.综上所述,种茎采收前选用2.5%尿素处理能明显提高种茎成活率和生根质量. 相似文献