全文获取类型
收费全文 | 111445篇 |
免费 | 6504篇 |
国内免费 | 50篇 |
专业分类
林业 | 4548篇 |
农学 | 4026篇 |
基础科学 | 754篇 |
14530篇 | |
综合类 | 16389篇 |
农作物 | 4168篇 |
水产渔业 | 5772篇 |
畜牧兽医 | 59461篇 |
园艺 | 1411篇 |
植物保护 | 6940篇 |
出版年
2019年 | 1158篇 |
2018年 | 1964篇 |
2017年 | 2256篇 |
2016年 | 2038篇 |
2015年 | 1647篇 |
2014年 | 2089篇 |
2013年 | 4819篇 |
2012年 | 3513篇 |
2011年 | 4347篇 |
2010年 | 2882篇 |
2009年 | 2855篇 |
2008年 | 4202篇 |
2007年 | 3922篇 |
2006年 | 3765篇 |
2005年 | 3183篇 |
2004年 | 3076篇 |
2003年 | 3076篇 |
2002年 | 2787篇 |
2001年 | 3878篇 |
2000年 | 3805篇 |
1999年 | 2934篇 |
1998年 | 1163篇 |
1997年 | 1215篇 |
1996年 | 1009篇 |
1995年 | 1212篇 |
1994年 | 1056篇 |
1993年 | 1048篇 |
1992年 | 2142篇 |
1991年 | 2230篇 |
1990年 | 2175篇 |
1989年 | 2176篇 |
1988年 | 1877篇 |
1987年 | 1870篇 |
1986年 | 1895篇 |
1985年 | 1786篇 |
1984年 | 1486篇 |
1983年 | 1275篇 |
1979年 | 1429篇 |
1978年 | 1060篇 |
1976年 | 1055篇 |
1975年 | 1180篇 |
1974年 | 1311篇 |
1973年 | 1247篇 |
1972年 | 1156篇 |
1971年 | 1070篇 |
1970年 | 1093篇 |
1969年 | 1136篇 |
1968年 | 1056篇 |
1967年 | 1104篇 |
1966年 | 1001篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
van Miert AS 《The Veterinary quarterly》1985,7(3):200-216
Summary Acute febrile diseases are characterized by specific and non-specific symptoms. The non-specific responses are presented under the headings: fever, inflammation and pain, experimental models for investigating febrile reactions, haematologic changes, blood biochemical changes, cardiovascular effects, changes in gastric function, and the effects of fever upon pharmacokinetics of drugs. It was the purpose of this review to describe present concepts of thermoregulation and fever, the associated reactions produced by bacterial pyrogens and the mechanisms of these reactions. The available data illustrate, that many questions have not yet been clearly answered. However, the entire field of research involving endogenous substances, such as interleukin-1, is now moving ahead with great speed. Furthermore, there is some evidence which suggests that fever and the associated lower plasma zinc and iron levels act together as a co-ordinated non-specific host defence mechanism. Since experimental fever has a distinct effect upon the pharmacokinetics of drugs, more attention should be given to this aspect. 相似文献
62.
Dogs vaccinated with a Leptospira interrogans vaccine containing serogroups Canicola and Icterohaemorrhagiae and prepared from cultures grown in a protein-free medium resisted challenge with heterologous representatives of these serogroups. In contrast, control dogs were pyrexic and leptospires were isolated from the blood for nine days following Canicola challenge and six days after Icterohaemorrhagiae challenge. Leptospires were isolated from the urine of controls throughout the post challenge period and from kidneys at post mortem examination of six out of six and four out of six Canicola and Icterohaemorrhagiae challenged controls, respectively. There have been no reports of hypersensitivity reactions to this vaccine since its introduction in 1980. 相似文献
63.
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
64.
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
65.
Roland W. S. Weber 《Erwerbs-Obstbau》2009,51(3):115-120
Whereas the rise in temperature during the past 30–40 years has already had clear impacts on the phenology of fruit trees and pathogenic insects, there is a lack of such correlations for fungal pathogens. An examination of fruit rots indicates that pathogenic fungi react differentially to climate change due to their complex infection biology. The appearance of the black rot fungus Diplodia seriata in Northwestern Europe is best explained by rising temperatures during the vegetation period. An increase in fruit rot caused by Nectria galligena is anticipated when milder and more humid winter months favour canker formation on twigs and branches, thereby increasing inoculum for fruit infections. An increasing importance of Neofabraea alba and Glomerella cingulata and/or G.??acutata as storage rots of apples in Northern Germany cannot be safely correlated with the climate change at present. Research on fungi is currently being expanded at the OVB Jork in order to ensure a faster identification of new pathogens and a more thorough investigation of relevant features of their infection biology. 相似文献
66.
Softening process and total antioxidant activity were evaluated in kiwifruit differently exposed to light intensity and harvested at two different times (October 10 and November 14). Fruit was stored for 2 months at 0 °C (S1) and then maintained for a week at ambient temperature (S2). The results showed that fruit harvested later presented a faster softening rate during storage than fruit harvested earlier, even if antioxidant activity did not change. Light-exposed fruit showed higher flesh firmness than that of shaded ones. Polygalacturonase activity was higher in kiwifruit maintained for a week at ambient temperature after cool storage and, in particular the highest value was recorded in fruit harvested later. The behaviour of β-galactosidase was different: it did not show changes in fruit harvested later and significantly decreased in light- and shade-exposed fruit harvested earlier. 相似文献
67.
68.
69.
70.
Woodworth RS 《Science (New York, N.Y.)》1941,94(2438):265-270