全文获取类型
收费全文 | 477篇 |
免费 | 26篇 |
专业分类
林业 | 60篇 |
农学 | 14篇 |
基础科学 | 4篇 |
72篇 | |
综合类 | 55篇 |
农作物 | 29篇 |
水产渔业 | 62篇 |
畜牧兽医 | 139篇 |
园艺 | 32篇 |
植物保护 | 36篇 |
出版年
2022年 | 7篇 |
2021年 | 11篇 |
2020年 | 8篇 |
2019年 | 20篇 |
2018年 | 11篇 |
2017年 | 10篇 |
2016年 | 12篇 |
2015年 | 16篇 |
2014年 | 14篇 |
2013年 | 23篇 |
2012年 | 24篇 |
2011年 | 26篇 |
2010年 | 18篇 |
2009年 | 17篇 |
2008年 | 28篇 |
2007年 | 27篇 |
2006年 | 29篇 |
2005年 | 22篇 |
2004年 | 25篇 |
2003年 | 16篇 |
2002年 | 11篇 |
2000年 | 9篇 |
1999年 | 5篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 6篇 |
1995年 | 9篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 9篇 |
1988年 | 2篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1978年 | 5篇 |
1977年 | 2篇 |
1974年 | 3篇 |
1973年 | 2篇 |
1969年 | 2篇 |
1962年 | 2篇 |
1960年 | 3篇 |
1959年 | 2篇 |
1958年 | 2篇 |
排序方式: 共有503条查询结果,搜索用时 0 毫秒
61.
A comparison was made of the effectiveness of permethrin and deet against Ornithodoros parkeri (Acari: Argasidae), Leptotrombidium fletcheri (Acari: Trombiculidae), Rhodnius prolixus (Heteroptera: Reduviidae), Phlebotomus papatasi and Lutzomyia longipalpis (Diptera: Psychodidae), Anopheles Stephensi, Anopheles albimanus, Aedes taeniorhynchus, Aedes aegypti and Culex pipiens (Diptera: Culicidae), Glossina morsitans (Diptera: Glossinidae) and Xenopsylla cheopis (Siphonaptera: Pulicidae), using dose-response methods. At the ED95 (95% effective dose) level, deet was more potent (P<0.05) than permethrin against all species except O. parkeri and R. prolixus. In addition, the slope of the dose-response line for deet was greater than that for permethrin against all species except O. parkeri and R. prolixus. Permethrin exhibited repellent and/or toxic effects, depending on the dose used and the individual tolerances of members of the insect test population. 相似文献
62.
63.
64.
Borenstein N Behr L Chetboul V Tessier D Nicole A Jacquet J Carlos C Retortillo J Fayolle P Pouchelon JL Daniel P Laborde F 《Veterinary surgery : VS》2004,33(4):309-313
OBJECTIVE: To report a technique for minimally invasive occlusion of patent ductus arteriosus (PDA) and outcome in 5 dogs. STUDY DESIGN: Clinical cases. Animals: Five, 4-6-month-old, dogs with PDA. MATERIALS AND METHODS: Titanium ligating clips were used for PDA closure in all dogs. Three dogs had video-enhanced mini-thoracotomy PDA occlusion. Two other dogs had thoracoscopic PDA occlusion using a custom-designed thoracoscopy clip applicator. RESULTS: Thoracoscopic PDA occlusion was successful in both dogs in which it was attempted. Complete PDA closure was achieved in 4 dogs. Three months after surgery, the largest dog had residual ductal flow that hemodynamically was insignificant. CONCLUSIONS: Although technically demanding, minimally invasive PDA occlusion is a safe and reliable technique in dogs. Preoperative measurement of the diameter of the PDA is crucial to determine if complete closure with metal clips can be achieved. CLINICAL RELEVANCE: Minimally invasive PDA occlusion should be considered as an alternative to occlusion via conventional thoracotomy. 相似文献
65.
66.
67.
68.
Sfeir MY Beetz T Wang F Huang L Huang XM Huang M Hone J O'Brien S Misewich JA Heinz TF Wu L Zhu Y Brus LE 《Science (New York, N.Y.)》2006,312(5773):554-556
We simultaneously determined the physical structure and optical transition energies of individual single-walled carbon nanotubes by combining electron diffraction with Rayleigh scattering spectroscopy. These results test fundamental features of the excited electronic states of carbon nanotubes. We directly verified the systematic changes in transition energies of semiconducting nanotubes as a function of their chirality and observed predicted energy splittings of optical transitions in metallic nanotubes. 相似文献
69.
ML Reaves S Sinha JD Rabinowitz L Kruglyak RJ Redfield 《Science (New York, N.Y.)》2012,337(6093):470-473
A strain of Halomonas bacteria, GFAJ-1, has been claimed to be able to use arsenate as a nutrient when phosphate is limiting and to specifically incorporate arsenic into its DNA in place of phosphorus. However, we have found that arsenate does not contribute to growth of GFAJ-1 when phosphate is limiting and that DNA purified from cells grown with limiting phosphate and abundant arsenate does not exhibit the spontaneous hydrolysis expected of arsenate ester bonds. Furthermore, mass spectrometry showed that this DNA contains only trace amounts of free arsenate and no detectable covalently bound arsenate. 相似文献
70.
Zdobnov EM von Mering C Letunic I Torrents D Suyama M Copley RR Christophides GK Thomasova D Holt RA Subramanian GM Mueller HM Dimopoulos G Law JH Wells MA Birney E Charlab R Halpern AL Kokoza E Kraft CL Lai Z Lewis S Louis C Barillas-Mury C Nusskern D Rubin GM Salzberg SL Sutton GG Topalis P Wides R Wincker P Yandell M Collins FH Ribeiro J Gelbart WM Kafatos FC Bork P 《Science (New York, N.Y.)》2002,298(5591):149-159
Comparison of the genomes and proteomes of the two diptera Anopheles gambiae and Drosophila melanogaster, which diverged about 250 million years ago, reveals considerable similarities. However, numerous differences are also observed; some of these must reflect the selection and subsequent adaptation associated with different ecologies and life strategies. Almost half of the genes in both genomes are interpreted as orthologs and show an average sequence identity of about 56%, which is slightly lower than that observed between the orthologs of the pufferfish and human (diverged about 450 million years ago). This indicates that these two insects diverged considerably faster than vertebrates. Aligned sequences reveal that orthologous genes have retained only half of their intron/exon structure, indicating that intron gains or losses have occurred at a rate of about one per gene per 125 million years. Chromosomal arms exhibit significant remnants of homology between the two species, although only 34% of the genes colocalize in small "microsyntenic" clusters, and major interarm transfers as well as intra-arm shuffling of gene order are detected. 相似文献