全文获取类型
| 收费全文 | 1840篇 |
| 免费 | 272篇 |
| 国内免费 | 8篇 |
专业分类
| 林业 | 217篇 |
| 农学 | 201篇 |
| 基础科学 | 74篇 |
| 340篇 | |
| 综合类 | 368篇 |
| 农作物 | 93篇 |
| 水产渔业 | 95篇 |
| 畜牧兽医 | 475篇 |
| 园艺 | 44篇 |
| 植物保护 | 213篇 |
出版年
| 2025年 | 5篇 |
| 2024年 | 20篇 |
| 2023年 | 18篇 |
| 2022年 | 20篇 |
| 2021年 | 53篇 |
| 2020年 | 35篇 |
| 2019年 | 53篇 |
| 2018年 | 51篇 |
| 2017年 | 36篇 |
| 2016年 | 42篇 |
| 2015年 | 60篇 |
| 2014年 | 57篇 |
| 2013年 | 91篇 |
| 2012年 | 121篇 |
| 2011年 | 113篇 |
| 2010年 | 87篇 |
| 2009年 | 88篇 |
| 2008年 | 130篇 |
| 2007年 | 114篇 |
| 2006年 | 121篇 |
| 2005年 | 126篇 |
| 2004年 | 82篇 |
| 2003年 | 81篇 |
| 2002年 | 63篇 |
| 2001年 | 36篇 |
| 2000年 | 31篇 |
| 1999年 | 31篇 |
| 1998年 | 34篇 |
| 1997年 | 36篇 |
| 1996年 | 20篇 |
| 1995年 | 26篇 |
| 1994年 | 26篇 |
| 1993年 | 20篇 |
| 1992年 | 9篇 |
| 1991年 | 18篇 |
| 1990年 | 14篇 |
| 1989年 | 13篇 |
| 1988年 | 12篇 |
| 1987年 | 8篇 |
| 1986年 | 14篇 |
| 1985年 | 12篇 |
| 1984年 | 12篇 |
| 1983年 | 12篇 |
| 1982年 | 7篇 |
| 1981年 | 10篇 |
| 1980年 | 10篇 |
| 1979年 | 6篇 |
| 1978年 | 9篇 |
| 1977年 | 9篇 |
| 1975年 | 4篇 |
排序方式： 共有2120条查询结果，搜索用时 20 毫秒
1.
2.
Extract Madam:– Thank you for the opportunity to reply to the letter from Dr. Wiessing. 相似文献
3.
Tsegaye Habtemariam Roger Ruppanner Hans P. Riemann Jerold H. Theis 《Preventive veterinary medicine》1983,1(2):147-156
The effect of various disease-vector control alternatives on the prevalence of trypanosomiasis in southwest Ethiopia was examined with the aid of an epidemiologic model. The alternatives considered included vegetation clearing by manual labor, game elimination, insecticidal spraying from airplanes coupled with settlement, use of sterile male Glossina, avoidance of tsetse infested areas, increasing the resistance of the cattle population, therapy, and combinations of the above methods. First, the currently estimated endemic prevalence of trypanosomiasis (27.3%) in the simulated area of Ethiopia was established and maintained over a 10 year period. Then, various control alternatives were introduced and the simulation was run for an additional 10 years to observe the effect of these control alternatives on the prevalence. The combined use of vegetation clearing, insecticides, therapy, and settlement (or resettlement) was the most effective and feasible method of trypanosomiasis control for the simulated situation. 相似文献
4.
The brain keenly depends on glucose for energy, and mammalians have redundant systems to control glucose production. An increase in circulating glucose inhibits glucose production in the liver, but this negative feedback is impaired in type 2 diabetes. Here we report that a primary increase in hypothalamic glucose levels lowers blood glucose through inhibition of glucose production in rats. The effect of glucose requires its conversion to lactate followed by stimulation of pyruvate metabolism, which leads to activation of adenosine triphosphate (ATP)-sensitive potassium channels. Thus, interventions designed to enhance the hypothalamic sensing of glucose may improve glucose homeostasis in diabetes. 相似文献
5.
Foster AP Naylor RD Howie NM Nicholas RA Ayling RD 《Veterinary journal (London, England : 1997)》2009,179(3):455-457
Signs of severe otitis media in 20% of dairy calves on one farm were associated with Mycoplasma bovis infection, based on isolation from the external ear canal and nares. Affected calves seroconverted to M. bovis and no other significant bacteria were isolated. Infection was considered likely to have originated from cows in the milking herd based on evidence of seroconversion and detection of infection in a milk sample. M. bovis infection should be considered when investigating otitis problems in calves. 相似文献
6.
7.
Objective— To compare standard interlocking nails (ILN) with a newly designed ILN featuring an angle-stable locking mechanism (ILNn).
Study design— Six experimental groups.
Sample population— Bone models (n=48) treated with 6 and 8 mm nails locked with screws or bolts (ILN6s, ILN8s, ILN6b, ILN8b, respectively), ILNn, and a 3.5 mm broad-DCP (br-DCP); n=4/testing mode.
Methods— Specimens were tested in torsion or 4-point bending. Construct compliance, deformation, and slack were statistically compared ( P <.05).
Results— Regardless of testing mode, construct compliance was greater with smaller ILN. Screwed constructs were more compliant than bolted ones, with a significant difference between ILN6s and ILN6b in torsion. Plated constructs were significantly more compliant than the ILNn. Angular deformation was consistently greater with smaller ILN. Screwed ILN constructs sustained ∼2 × the torsional deformation of the bolted ones (∼36° [ILN6s] versus ∼18° [ILN6b]). Comparatively, ILNn constructs had significantly less torsional (∼8°) and bending (∼4°) deformation than other constructs. Whereas standard ILN constructs had slack in both modes, ILNn and br-DCP construct deformations consistently occurred without slack.
Conclusions— Use of bolts rather than screws improved ILN mechanical behavior, but neither locking mechanism completely counteracted torsion and bending forces. Conversely, the ILNn angle-stable locking system eliminated torsional and bending slack, resulting in comparable mechanical performances between ILNn and plated constructs.
Clinical Relevance— The angle-stable locking mechanism of the new ILN eliminates all slack in the system; thus, interfragmentary motion will likely be reduced compared with standard ILN, which may improve the local environment for fracture healing. 相似文献
Study design— Six experimental groups.
Sample population— Bone models (n=48) treated with 6 and 8 mm nails locked with screws or bolts (ILN6s, ILN8s, ILN6b, ILN8b, respectively), ILNn, and a 3.5 mm broad-DCP (br-DCP); n=4/testing mode.
Methods— Specimens were tested in torsion or 4-point bending. Construct compliance, deformation, and slack were statistically compared ( P <.05).
Results— Regardless of testing mode, construct compliance was greater with smaller ILN. Screwed constructs were more compliant than bolted ones, with a significant difference between ILN6s and ILN6b in torsion. Plated constructs were significantly more compliant than the ILNn. Angular deformation was consistently greater with smaller ILN. Screwed ILN constructs sustained ∼2 × the torsional deformation of the bolted ones (∼36° [ILN6s] versus ∼18° [ILN6b]). Comparatively, ILNn constructs had significantly less torsional (∼8°) and bending (∼4°) deformation than other constructs. Whereas standard ILN constructs had slack in both modes, ILNn and br-DCP construct deformations consistently occurred without slack.
Conclusions— Use of bolts rather than screws improved ILN mechanical behavior, but neither locking mechanism completely counteracted torsion and bending forces. Conversely, the ILNn angle-stable locking system eliminated torsional and bending slack, resulting in comparable mechanical performances between ILNn and plated constructs.
Clinical Relevance— The angle-stable locking mechanism of the new ILN eliminates all slack in the system; thus, interfragmentary motion will likely be reduced compared with standard ILN, which may improve the local environment for fracture healing. 相似文献
8.
9.
10.
Mammalian parental investment (i.e. care of descendant offspring) is largely biased towards maternal contributions due to the specific feeding needs of mammalian offspring; however, varying degrees of paternal investment have been reported in about 10% of all mammalian species. Within the order Carnivora, paternal contribution to rearing offspring is particularly high: an estimated 32% of all studied carnivore species exhibit direct paternal care. Despite the prominence of paternal investment in carnivores, the endocrine basis of this behaviour is not well understood. This review examines the current – highly constrained – state of knowledge about the endocrine basis of carnivore paternal investment. We attempt to link changes in androgen and glucocorticoid levels with variation in direct and indirect paternal care behaviour making specific predictions regarding the way forward. Well-studied species, such as bat-eared foxes (Otocyon megalotis), dwarf mongoose (Helogale parvula) and meerkats (Suricata suricatta), where social dynamics are relatively well understood, can act as ideal model systems through which we may further investigate the endocrine basis of paternal investment in carnivores. 相似文献