全文获取类型
收费全文 | 8765篇 |
免费 | 433篇 |
国内免费 | 9篇 |
专业分类
林业 | 592篇 |
农学 | 276篇 |
基础科学 | 62篇 |
1430篇 | |
综合类 | 1539篇 |
农作物 | 547篇 |
水产渔业 | 655篇 |
畜牧兽医 | 3231篇 |
园艺 | 217篇 |
植物保护 | 658篇 |
出版年
2023年 | 48篇 |
2022年 | 78篇 |
2021年 | 140篇 |
2020年 | 155篇 |
2019年 | 176篇 |
2018年 | 157篇 |
2017年 | 152篇 |
2016年 | 178篇 |
2015年 | 132篇 |
2014年 | 184篇 |
2013年 | 350篇 |
2012年 | 419篇 |
2011年 | 572篇 |
2010年 | 321篇 |
2009年 | 310篇 |
2008年 | 563篇 |
2007年 | 517篇 |
2006年 | 527篇 |
2005年 | 552篇 |
2004年 | 457篇 |
2003年 | 496篇 |
2002年 | 433篇 |
2001年 | 105篇 |
2000年 | 96篇 |
1999年 | 109篇 |
1998年 | 92篇 |
1997年 | 79篇 |
1996年 | 69篇 |
1995年 | 92篇 |
1994年 | 86篇 |
1993年 | 74篇 |
1992年 | 59篇 |
1991年 | 65篇 |
1990年 | 78篇 |
1989年 | 109篇 |
1988年 | 83篇 |
1987年 | 89篇 |
1986年 | 96篇 |
1985年 | 99篇 |
1984年 | 52篇 |
1983年 | 52篇 |
1982年 | 36篇 |
1981年 | 29篇 |
1980年 | 35篇 |
1979年 | 31篇 |
1978年 | 42篇 |
1977年 | 43篇 |
1976年 | 36篇 |
1975年 | 39篇 |
1974年 | 34篇 |
排序方式: 共有9207条查询结果,搜索用时 0 毫秒
171.
172.
173.
Larry J. Gut Keywan Lee John A. Juvik Carole C. Rebeiz Carl E. Bouton Constantin A. Rebeiz 《Pest management science》1993,39(1):19-30
The porphyric-insecticide-modulating activities of 1,10-phenanthroline and eight of its analogs were investigated. The insecticidal efficacy of these compounds was closely associated with their ability to enhance the conversion of exogenous δ-aminolevulinic acid (ALA) to protoporphyrin IX (Proto). As observed for photodynamic herbicidal effects in plants, the presence of nitrogen atoms at positions 1 and 10 of the macrocycle was essential for porphyric insecticidal activity. This was evidenced by the very limited activity of phenanthrene, in which positions 1 and 10 are occupied by carbon instead of nitrogen atoms. On the other hand, enhancement of Proto formation and porphyric insecticidal activity were maintained following methyl, chloro and nitro group substitution at the periphery of 1,10-phenanthroline. In contrast, Proto levels and photodynamic toxicity were reduced by hydroxy and phenyl substitution at the same positions. Benzyl substitution at the 2–3 and 8–9 positions was also inhibitory. Quantitative structure-activity calculations suggested a relationship between peripheral group substitution and physicochemical properties of the substituted compounds. Electron density changes in 1,10-phenanthroline and its analogs that appeared to be related to reduced efficacy included (a) appearance of positive charge-binding volumes at positions 4 and 7 of the 1,10-phenanthroline macrocycle, which flanks positive charge-repelling volumes, (b) a dramatic increase in superdelocalisability (i.e. electron density) over some unoccupied molecular orbitals, and (c) electronic charge at positions 1 and 10 of the macrocycle. Large increases in van der Waals volumes also exerted negative effects on insecticidal efficacy. 相似文献
174.
175.
Outbreak of acute colitis on a horse farm associated with tetracycline-contaminated sweet feed 下载免费PDF全文
Keir AA Stämpfli HR Crawford J 《The Canadian veterinary journal. La revue veterinaire canadienne》1999,40(10):718-720
Exposure of a group of horses to tetracycline-contaminated feed resulted in acute colitis and subsequent death in one horse and milder diarrhea in 3 others. The most severely affected animal demonstrated clinical and pathological findings typical of colitis X. The other herdmates responded well to administration of zinc bacitracin. 相似文献
176.
H Li T C McGuire U U Müller-Doblies T B Crawford 《Journal of veterinary diagnostic investigation》2001,13(4):361-364
An earlier competitive inhibition enzyme-linked immunosorbent assay (CI-ELISA) was developed for detection of specific antibody against malignant catarrhal fever (MCF) viruses (MCFV) in ruminants. In this study, the indirect CI-ELISA was improved by conjugating the monoclonal antibody 15-A directly with horseradish peroxidase and by developing a method of producing precoated, dried antigen plates. This new test is referred to as a direct CI-ELISA. The reformatted test yielded a significantly improved sensitivity, and the time required was reduced to about one-sixth of the previous time. Of 37 MCF cases in cattle that were confirmed by histopathology and polymerase chain reaction (PCR) assay, 37 (100%) were positive by the new test, whereas the indirect CI-ELISA detected only 23 (62%). The direct CI-ELISA detected antibody to MCFV in 100% of 48 sheep that had been defined as infected with ovine herpesvirus 2 (OvHV-2) by PCR, whereas the indirect CI-ELISA detected only 41 (85%). Comparison of antibody titers measured by the 2 assays for sera collected from OvHV-2-infected sheep and from cattle, bison, and deer with clinical sheep-associated MCF revealed that the direct CI-ELISA offered a 4-fold increase in analytical sensitivity over the indirect format. The number of seropositive animals detected by the direct CI-ELISA among apparently normal cattle and bison was 2-3 times greater than the number detected by the indirect CI-ELISA, indicating that a significant percentage of normal cattle and bison are subclincally infected with MCFV. 相似文献
177.
Thomas E. Schwedler Joe R. Tomasso John A. Collier 《Journal of the World Aquaculture Society》1989,20(3):158-161
Production characteristics of channel catfish (Ictalurus punctatus) reared in cages and open ponds were compared. Fish reared in open ponds had significantly better growth and food conversion ratios than fish reared in cages. Cages and open ponds stocked with fish which were closely graded in size produced fish with less size variability at harvest compared to ponds and cages stocked with nongraded and coarsely graded fish. The decrease in size variability at harvest was reflected in a greater proportion of marketable fish. 相似文献
178.
Mary M. Christopher John D. Broussard Mark E. Peterson 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》1995,9(1):24-31
Oxidative damage plays an important role in the pathophysiology of diabetes and diabetic complications. Feline hemoglobin is uniquely susceptible to oxidative denaturation; therefore, Heinz body formation is a highly sensitive indicator of in vivo oxidative stress in this species. Heinz bodies also contribute to anemia. We investigated hematological and clinical biochemical changes in 30 cats with spontaneous diabetes mellitus (as compared to 15 healthy control cats) and evaluated the relationship of these changes to erythrocyte oxidative damage. Cats were categorized as ketoacidotic or nonketoacidotic based on their clinical presentation and the presence of urine ketones. Ketoacidotic cats had significantly ( P = .0009) more Heinz bodies (28.3% ± 9.1 %) than nonketotic diabetic cats (6.5% ± 1.60%) and healthy control cats (0.6% ± 0.2%). Percent Heinz bodies in diabetic cats directly correlated with plasma β-hydroxy-butyrate concentration ( r = .622; P = .0002), as well as with serum chloride concentration ( r = -0.576; P = 0.0009) and the number of monocytes ( r = .536; P = .0023). Percent Heinz bodies were negatively correlated with erythrocyte glutathione concentrations. Erythrocyte membrane lipid peroxidation was slightly but not significantly increased in diabetic cats. There were no significant associations between percent Heinz bodies and degree of anemia, hyperglycemia, or glycohemoglobin. These data indicate that ketones are associated with oxidative hemoglobin damage in cats, and suggest that ketone metabolism, ie by cytochrome P450 2E1, may be a potential source of in vivo oxygen radical generation in animals with ketosis. 相似文献
179.
180.