全文获取类型
收费全文 | 1753篇 |
免费 | 68篇 |
国内免费 | 2篇 |
专业分类
林业 | 53篇 |
农学 | 28篇 |
基础科学 | 5篇 |
260篇 | |
综合类 | 186篇 |
农作物 | 54篇 |
水产渔业 | 68篇 |
畜牧兽医 | 1074篇 |
园艺 | 39篇 |
植物保护 | 56篇 |
出版年
2023年 | 9篇 |
2022年 | 10篇 |
2021年 | 21篇 |
2020年 | 24篇 |
2019年 | 35篇 |
2018年 | 29篇 |
2017年 | 27篇 |
2016年 | 28篇 |
2015年 | 25篇 |
2014年 | 37篇 |
2013年 | 57篇 |
2012年 | 94篇 |
2011年 | 146篇 |
2010年 | 80篇 |
2009年 | 54篇 |
2008年 | 109篇 |
2007年 | 132篇 |
2006年 | 140篇 |
2005年 | 132篇 |
2004年 | 127篇 |
2003年 | 118篇 |
2002年 | 108篇 |
2001年 | 16篇 |
2000年 | 19篇 |
1999年 | 27篇 |
1998年 | 20篇 |
1997年 | 17篇 |
1996年 | 10篇 |
1995年 | 16篇 |
1994年 | 14篇 |
1993年 | 12篇 |
1992年 | 9篇 |
1991年 | 21篇 |
1990年 | 13篇 |
1989年 | 11篇 |
1988年 | 4篇 |
1987年 | 9篇 |
1986年 | 2篇 |
1985年 | 13篇 |
1984年 | 3篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1974年 | 3篇 |
1965年 | 2篇 |
排序方式: 共有1823条查询结果,搜索用时 546 毫秒
111.
Margaret A Miller José A Ramos-Vara Mary F Dickerson Gayle C Johnson Lanny W Pace John M Kreeger Susan E Turnquist James R Turk 《Journal of veterinary diagnostic investigation》2003,15(6):515-522
Thirteen uterine tumors were diagnosed in 13 cats and accounted for 0.29% of all feline neoplasms received during a 9.6-year period. Age at diagnosis ranged from 3 to 16 years; median 9 years. Six were Domestic Shorthair cats, and 7 were purebred cats of 5 different breeds. Eight adenocarcinomas and 1 mixed Müllerian tumor (adenosarcoma) comprised the endometrial tumors. Myometrial tumors included 3 leiomyomas and 1 leiomyosarcoma. One of the adenocarcinomas developed in the uterine stump of an ovariohysterectomized cat; the other cats were sexually intact. Concurrent mammary adenocarcinoma was diagnosed in 1 cat with uterine adenocarcinoma and in another with uterine leiomyoma. Tumors were discovered during elective ovariohysterectomy in 2 cats, but at least 3 others had experienced reproductive problems (infertility or pyometra). Five cats presented for abdominal or pelvic masses. Endometrial adenocarcinomas were positive immunohistochemically for cytokeratins and negative for smooth muscle actin (SMA): 1 of 6 cats was positive for vimentin and 4 of 8 were positive for estrogen receptor-alpha (ER alpha). Adenosarcoma stromal cells were positive for vimentin and ER alpha but negative for cytokeratins and SMA. Smooth muscle tumors were positive for vimentin and SMA and negative for cytokeratins. Leiomyomas, but not the leiomyosarcomas, were positive for ER alpha. Adenocarcinomas in 4 cats had metastasized by the time of ovariohysterectomy. Two other cats were euthanized 5 months after ovariohysterectomy; at least one of these cats had developed an abdominal mass that was not examined histologically. Only 2 cats with endometrial adenocarcinoma had disease-free intervals longer than 5 months after surgery. Metastasis was not detected in any mesenchymal tumor; however, these cats were either euthanized on discovery of the tumor or the tumor was first detected at necropsy. 相似文献
112.
Larry D. Galuppo DVM Diplomate ACVS Susan M. Stover DVM PhD Diplomate ACVS David G. Jensen BS Neil H. Willits PhD 《Veterinary surgery : VS》2001,30(4):332-340
OBJECTIVE: To compare drilling, tapping, and screw-insertion torque, force, and time for the 4.5-mm AO and 6.5-mm Acutrak Plus (AP) bone screws, and to compare the mechanical shear strength and stiffness of a simulated complete lateral condylar fracture of the equine third metacarpal bone (MC3) stabilized with either an AO or AP screw. STUDY DESIGN: In vitro biomechanical assessment of screw-insertion variables, and shear failure tests of a bone-screw-stabilized simulated lateral condylar fracture. SAMPLE POPULATION: Eight pairs of cadaveric equine MC3s METHODS: Metacarpi were placed in a fixture and centered on a biaxial load cell in a materials-testing system to measure torque, compressive force, and time for drilling, tapping, and screw insertion. Standardized simulated lateral condylar fractures were stabilized by either an AO or AP screw and tested in shear until failure. A paired t test was used to assess differences between screws, with significance set at P < .05. RESULTS: Insertion and mechanical shear testing variables were comparable for AO and AP insertion equipment and screws. CONCLUSION: The 6.5-mm tapered AP screw can be inserted in equine third metacarpal condyles and is mechanically comparable with the 4.5-mm AO screw for fixation of a simulated lateral condylar fracture. CLINICAL RELEVANCE: Considering the comparable mechanical behavior, the potential for less-persistent soft-tissue irritation with the headless design, and the ability to achieve interfragmentary compression by inserting the screw in one hole drilled perpendicular to the fracture plane, the 6.5-mm tapered AP screw may be an attractive alternative for repair of incomplete lateral condylar fractures in horses. 相似文献
113.
John M Kreeger Alison Templer Susan E Tumquist Keith L Bailey Philip J Johnson David A Wilson 《Journal of veterinary diagnostic investigation》2002,14(4):322-325
Paranasal meningioma was diagnosed in a 5-year-old Appaloosa gelding. The mass occupied the right maxillary, frontal, and sphenopalatine sinuses but did not invade the calvarium. The diagnosis was based on histologic evaluation, positive immunohistochemical staining for vimentin and cytokeratin, and ultrastructural features including the presence of interdigitating spindle cells with numerous desmosomes. 相似文献
114.
115.
116.
117.
David A. Bass Neville D. Crossman Susan L. Lawrie Mark R. Lethbridge 《Euphytica》2006,148(1-2):97-109
Summary This paper examines the roles of plant demography, seed dispersal ecology and habitat suitability in influencing invasiveness
of horticulturally important species. Section one investigates the relative invasiveness of two woody species, Crataegus monogyna and Prunus mahaleb, and concentrates on differences in demographic and dispersal traits. The second section delineates the invasion of two Asparagus spp. and concentrates on differences in seed dispersal ecology. Section three reports the use of a geographical information system
analysis to determine whether habitat suitability, seed dispersal or land management is more important in determining threat
of invasion by adventive Olea europaea. C. monogyma, P. mahaleb are closely related with similar habits and overlapping home ranges in Europe. Crataegus monogyna is very invasive in northern New South Wales, having spread rapidly and conspicuously throughout the region and elsewhere
in southern Australia at rates of 80–120 m yr−1. Prunus mahaleb is far less invasive, being restricted to a small population, which is expanding at 20 m yr−1. Demographic analysis showed that potential growth rates of P. mahaleb (1.713–1.490) are greater than those for C. monogyna (1.138–1.103). Assessment of the seed dispersal ecology of both species revealed that C. monogyna had seeds dispersed by one bird and three mammals over many kilometers. P. mahaleb had seeds dispersed by six birds and four mammals over distances generally < 100 m. The role of humans in introducing both
species and the characteristics of seed dispersal are more influential than demography in determining invasiveness. The more
invasive Asparagus asparagoides has smaller fruit with a bicoloured display up to 1.5 m above ground. Less invasive A. declinatus has larger, translucent white fruit displayed at heights < 0.5 m above ground. The role of humans has also been important
in shaping the course of invasion. Sensitivity analysis confirms that land management practices, which affect Olea europaea seedling establishment and survival, are most important at a landscape scale in determining invasiveness. The main factors
determining the difference in invasiveness relate directly to the changing nature of human management of each species and
the ecological interactions between the plants and the invaded environment. This research has implications for the prediction
and management of biological invasions; emphasizing the importance of seed dispersal and human activities in determining the
course of invasions: both of which cannot be readily predicted. 相似文献
118.
Summary Achenes of wild forms of Anemone coronaria growing in Israel differ in their germination requirements from achenes of the cultivated de Caen type. The optimum temperature for dark germination was between 10–15°C in the former and between 15–20°C in the latter. Maximum daily rates of germination were higher, reaching 16% per day, and the minimum lag period between sowing and seedling emergence was shorter in achenes of the cultivated than in those of the wild anemone when the two types were incubated under identical conditions. Wild achenes showed a marked post-harvest maturation requirement, and attained full germination, a minimum pre-emergence lag period after sowing, and a maximum daily germination rate only when dry-stored for several months subsequent to harvesting. In the cultivated plant this requirement was far less pronounced or absent. Most embryos in freshly harvested achenes of both the wild and the cultivated anemone were torpedo-shaped but in the cultivated form embryos were larger. In both types embryos remained unchanged in shape and size during dry storage. 相似文献
119.
120.
Previous studies have shown that organic acids have an impact on both Fe(II) and Fe(III) uptake in Caco-2 cell. However, to what extent this effect is correlated with the anion of organic acids per se, or with the resulting decrease in pH, has not yet been clarified. Therefore, we studied the effect of five organic acids (tartaric, succinic, citric, oxalic, and propionic acid) on the absorption of Fe(II) and Fe(III) in Caco-2 cells and compared this with sample solutions without organic acids but set to equivalent pH by HCl. The results showed that the mechanisms behind the enhancing effect of organic acids differed for the two forms of iron. For ferric iron the organic acids promoted uptake both by chelation and by lowering the pH, whereas for ferrous iron the promoting effect was caused only by the lowered pH. 相似文献