全文获取类型
| 收费全文 | 233348篇 |
| 免费 | 14430篇 |
| 国内免费 | 896篇 |
专业分类
| 林业 | 23259篇 |
| 农学 | 14061篇 |
| 基础科学 | 3107篇 |
| 41688篇 | |
| 综合类 | 18349篇 |
| 农作物 | 17148篇 |
| 水产渔业 | 16319篇 |
| 畜牧兽医 | 85312篇 |
| 园艺 | 6343篇 |
| 植物保护 | 23088篇 |
出版年
| 2021年 | 2553篇 |
| 2020年 | 2938篇 |
| 2019年 | 3763篇 |
| 2018年 | 3922篇 |
| 2017年 | 4346篇 |
| 2016年 | 4730篇 |
| 2015年 | 4346篇 |
| 2014年 | 5678篇 |
| 2013年 | 16254篇 |
| 2012年 | 5691篇 |
| 2011年 | 7479篇 |
| 2010年 | 7233篇 |
| 2009年 | 7824篇 |
| 2008年 | 6838篇 |
| 2007年 | 5845篇 |
| 2006年 | 6505篇 |
| 2005年 | 5733篇 |
| 2004年 | 5627篇 |
| 2003年 | 5368篇 |
| 2002年 | 4685篇 |
| 2001年 | 5445篇 |
| 2000年 | 5209篇 |
| 1999年 | 4966篇 |
| 1998年 | 4080篇 |
| 1997年 | 4132篇 |
| 1996年 | 3875篇 |
| 1995年 | 4413篇 |
| 1994年 | 3792篇 |
| 1993年 | 3482篇 |
| 1992年 | 3909篇 |
| 1991年 | 4100篇 |
| 1990年 | 3772篇 |
| 1989年 | 3665篇 |
| 1988年 | 3275篇 |
| 1987年 | 3367篇 |
| 1986年 | 3182篇 |
| 1985年 | 3551篇 |
| 1984年 | 3380篇 |
| 1983年 | 3214篇 |
| 1982年 | 2702篇 |
| 1981年 | 2639篇 |
| 1980年 | 2621篇 |
| 1979年 | 2801篇 |
| 1978年 | 2589篇 |
| 1977年 | 2432篇 |
| 1976年 | 2282篇 |
| 1975年 | 2077篇 |
| 1974年 | 2159篇 |
| 1973年 | 2106篇 |
| 1972年 | 1843篇 |
排序方式： 共有10000条查询结果，搜索用时 640 毫秒
91.
Traditional forest economics deals with regularly-ordered activities.For many reasons, however, choices must often be made amongconflicting operational priorities. In these circumstances,maximizing net discounted revenue per hectare does not maximizeglobal profit. Priorities for action should be chosen in orderof urgency index ratio, defined as the cost of delaying an operationdivided by the units of limited resource needed to undertakethe operation. Forest managers tend to use informal and sometimesconflicting rules to assign priorities among uses of limitedresources. These priorities often differ from those indicatedby urgency index ratio. Urgency index ratio can be determinedby simple calculations based on readily-available data. Theconcept can be extended to include multiple constraints. 相似文献
92.
Mid-storage hydration-dehydration treatments with medium-vigour lettuce seed very effectively reduced physiological deterioration in storage and ultimately showed better field emergence and final yield. Soaking-drying treatment of high-vigour lettuce seed was not effective. Pre-sowing treatment of medium-vigour lettuce seed, though less effective than mid-storage treatment, gave better field performance, but high-vigour seed did not benefit from the treatment. For carrot, both mid-storage and pre-sowing seed treatments proved beneficial, with the former showing better performance than the latter. Unlike lettuce, well-preserved carrot seed responded positively to the pre-sowing treatment. 相似文献
93.
Praveen C. Verma Debasis Chakrabarty Satya Narayan Jena Devesh K. Mishra Pradhyumna K. Singh Samir V. Sawant Rakesh Tuli 《Industrial Crops and Products》2009,29(2-3):581-589
Vanilla is a large genus of about 110 species in the orchid family (Orchidaceae), including the species Vanilla planifolia from which commercial vanilla flavoring is derived. Since most species of vanilla are considered rare and endangered there is an urgent need to conserve them through genetic analysis and propagation/conservation studies on this crop.The present study investigated the genetic diversity among nine leafy- and leaf-less Vanilla species employing 30 decamer RAPD primers and 10 ISSR primers. The species under study were diverse and displayed a range of variability (0–66% and 0–81% for RAPD and ISSR, respectively). A total of 154 RAPD polymorphic markers (83.24%, h = 0.378) and 93 ISSR polymorphic markers (86.11%, h = 0.363) were used to generate a genetic similarity matrix followed by the cluster analysis. Specific groupings were revealed by each cluster analysis with slight variation between two different markers. Among the nine species studied, V. planifolia, Vanilla aphylla and Vanilla tahitensis revealed very low level of variation within their collections, thus indicating a narrow genetic base. The large genetic distance of Vanilla andamanica from other species suggests its different origin. A close genetic affinity was observed between the pairs V. planifolia, V. tahitensis and Vanilla albida, V. aphylla. These are the first comparative results for RAPD and ISSR reporting inter-relationship among nine cultivated, wild and hybrid Vanilla species. 相似文献
94.
95.
H. 《Journal of pest science》1940,16(6):69-71
Ohne Zusammenfassung 相似文献
96.
97.
98.
Fr. 《Journal of pest science》1942,18(11):131
Ohne Zusammenfassung 相似文献
99.
R. 《European Journal of Forest Research》1865,9(1):384-387
Ohne Zusammenfassung 相似文献
100.