全文获取类型
收费全文 | 1605篇 |
免费 | 88篇 |
专业分类
林业 | 36篇 |
农学 | 34篇 |
基础科学 | 16篇 |
157篇 | |
综合类 | 292篇 |
农作物 | 76篇 |
水产渔业 | 101篇 |
畜牧兽医 | 885篇 |
园艺 | 36篇 |
植物保护 | 60篇 |
出版年
2021年 | 15篇 |
2019年 | 27篇 |
2018年 | 15篇 |
2017年 | 26篇 |
2016年 | 28篇 |
2015年 | 25篇 |
2014年 | 18篇 |
2013年 | 123篇 |
2012年 | 49篇 |
2011年 | 78篇 |
2010年 | 41篇 |
2009年 | 31篇 |
2008年 | 63篇 |
2007年 | 49篇 |
2006年 | 55篇 |
2005年 | 46篇 |
2004年 | 58篇 |
2003年 | 48篇 |
2002年 | 52篇 |
2001年 | 51篇 |
2000年 | 45篇 |
1999年 | 24篇 |
1998年 | 12篇 |
1997年 | 17篇 |
1996年 | 15篇 |
1995年 | 21篇 |
1994年 | 14篇 |
1992年 | 34篇 |
1991年 | 27篇 |
1990年 | 23篇 |
1989年 | 28篇 |
1988年 | 28篇 |
1987年 | 25篇 |
1986年 | 30篇 |
1985年 | 22篇 |
1984年 | 25篇 |
1983年 | 17篇 |
1981年 | 18篇 |
1980年 | 22篇 |
1979年 | 21篇 |
1978年 | 23篇 |
1976年 | 16篇 |
1974年 | 20篇 |
1973年 | 20篇 |
1972年 | 16篇 |
1971年 | 16篇 |
1970年 | 15篇 |
1969年 | 20篇 |
1967年 | 11篇 |
1966年 | 11篇 |
排序方式: 共有1693条查询结果,搜索用时 15 毫秒
91.
92.
93.
Gerald J. Seiler Thomas Gulya Gary Kong Susan Thompson Jeffrey Mitchell 《Genetic Resources and Crop Evolution》2018,65(8):2215-2229
Although wild annual sunflower (Helianthus annuus L.) is indigenous to North America, it has been both inadvertently and intentionally introduced into other countries, such as Australia, where it has become naturalized. Prior to this research, there were no collections of naturalized H. annuus from Australia in the USDA National Plant Germplasm System gene bank. The possibility exists that naturalized Australian populations may contain distinct traits, such as oil content and fatty-acid composition, differing from their North American progenitors due to the different environments, diseases, and insect-pest complexes. The objective of this study was to collect naturalized H. annuus populations from the five states of Australia and to analyze them for oil content and fatty-acid composition. Fifty-six populations were collected throughout the broad distributional range of this species and then analyzed for oil content and fatty-acid composition. The mean oil content of the H. annuus populations was 28%, ranging from a low of 19% to a high of 31%, similar to populations of this species in its native North American habitats. Fatty-acid profiles were also similar for North American wild populations, Australian naturalized populations, and improved cultivars. Oil concentration of hybrids can be rapidly increased to acceptable levels by backcrossing with cultivated sunflower. Based on this fact, there should be little concern about the relatively low oil content of these naturalized populations when they are used as a source of other unique traits for cultivated sunflower improvement. 相似文献
94.
Disorientation, muscle fasciculations and weakness seen in a 12-year-old neutered female domestic shorthaired cat were attributed to hypoglycaemia associated with a large hepatoma. Glucagon tolerance tests on this cat and a healthy cat showed that their plasma glucose concentrations increased and decreased at about the same rate. Plasma insulin concentrations in the healthy cat increased and decreased in parallel with the plasma glucose concentration. In the affected cat, plasma insulin concentrations increased initially but decreased more rapidly. Reflecting these observations, the amended insulin to glucose ratios in the affected cat were much lower than those of the healthy cat, until the 4-hour sample. Serum somatostatin, somatomedin and gastrin concentrations were measured but no conclusions as to pathogenesis of the hypoglycaemia could be made. The alterations in insulin secretion in the affected cat suggested that altered hormonal control of glucose homeostasis may have occurred with this tumour. 相似文献
95.
T Guimarães C Miranda M Pinto E Silva L Damásio AL Costa MJ Correia JC Duarte C Cosinha G Lopes G Thompson A Rocha 《Reproduction in domestic animals》2014,49(6):926-933
A possible role of breeding activities in the composition of the microbial population in stallions' external genitalia (EG) and the relationship between micro‐organisms colonizing the skin of the abdomen and the ones colonizing the EG have not been studied. In experiment 1, EG microbiological samples were collected from 41 stallions used for both natural cover and semen collection (BST) and from 18 non‐breeding stallions (NBST). A higher (p < 0.05) frequency of isolation of potentially pathogenic species was found for BST. Age did not influence number of micro‐organism species isolated both in BST and NBST. In experiment 2, the microbial content of the EG and semen was compared in 23 BST. Most micro‐organisms isolated from the EG were present in semen, albeit with a numerically lower prevalence. In 7 stallions, six microbial species isolated from semen were absent from the EG cultures, suggesting contamination by the operator. In experiment 3, a numerically higher number of micro‐organism species was isolated from the EG of 31 stallions, than from their skin of the ventral abdomen in contact with the penis or from the skin of the thorax. With the sole exception of Escherichia coli, potentially pathogenic bacteria were only isolated from the EG but not from the skin. Results suggest that breeding activity increased the number of species colonizing the EG; most species isolated from the EG were also found in semen even if with a lower frequency, and additional semen contamination seemed to occur during its manipulation. Many micro‐organism species of the skin were also isolated from the penis, but independently of being or not in contact with the penis, skin did not seem to provide an adequate environment for the growth of potentially pathogenic bacteria that were isolated from EG, with the sole exception for E. coli. 相似文献
96.
Pelger-Hu?t anomaly was diagnosed in a young male cat on the basis of persistent nuclear hyposegmentation of blood granulocytes, absence of clinical disease or feline leukemia virus infection, and demonstration of genetic transmission of the anomaly. Neutrophils, eosinophils, basophils, and monocytes had significantly less nuclear segmentation when compared to similar leukocyte types from a control cat. On smears of bone marrow, megakaryocytes also appeared hyposegmented. A test mating with an unaffected queen produced a litter of five kittens (three males, two females). One male and one female kitten had the Pelger-Hu?t trait on examination of blood smears. Autosomal dominant transmission of this anomaly is suspected based on these findings. 相似文献
97.
R. P. Kibblewhite Norman S. Thompson Dale G. Williams 《Wood Science and Technology》1971,5(2):101-120
Summary Although the bonds between the cellular components of pine epithelia (isolated from holocellulose) can be strengthened by the addition of multivalent ions such as those of calcium, iron, uranium, etc., it was observed that these bonds are only weakened and not destroyed by the removal of the ions from the tissues. Reagents, such as KOH and K2SO4, which do not yield soluble calcium salts, do not cause a discernible weakening of the bonds between the cellulose components of epithelia pretreated with Ca ion. Washing the weakened epithelia with water causes them to swell. The separation of epithelial cells occurs only after the application of mechanical forces to the tissues. Electron microscopic examination of the swollen and unswollen tissues shows that fibrils and lamellae extend between the individual cells which must be destroyed by mechanical action before cell separation can occur. The swelling of the tissues by washing after removal of multivalent ions was attributed to the expansion of electrical double layers and to the increasing osmotic pressure from the increasing Donnan potential, while the difference in swelling as a result of HCl treatment vs. KCl and K4Fe(CN)6 was attributed to differences in charge development and to hydrogen bonding between acidic components. The restrengthening of the tissue as a result of the readdition of multivalent ion was attributed to the collapse of the electrical double layers and the reduction of the Donnan potential, with the re-forming of bonds between the components of the epithelia. Evidence suggesting that multivalent ions actually participate in bonding was obtained and although the nature of the bonding cannot be determined, both salt formation and complex formation between the ions and the components of the tissues is suggested. 相似文献
98.
99.
100.
Claudia Böhm Manuela Schnyder Stig Milan Thamsborg Caryn M. Thompson Candace Trout Sonja Wolken Beate Schnitzler 《Veterinary parasitology》2014,199(3-4):272-277
Angiostrongylus vasorum is an increasingly reported parasite in Europe that develops in dogs after ingestion of infective third stage larvae (L3) that reside in gastropod molluscs which are needed to complete the parasite's life-cycle. Infection can produce a diversity of clinical signs, determined by involvement of the respiratory, neurological, and/or coagulation system, with a likely fatal outcome in the absence of treatment. Few drugs have been shown to reliably prevent infection, and data on treatment of infections is limited. A controlled, randomized, partially blinded laboratory study was therefore executed to evaluate the efficacy and safety of a combination tablet of spinosad/milbemycin oxime in dogs inoculated with approximately 250 A. vasorum L3. Sixteen healthy nematode free adult dogs were randomly allocated to two study groups of 8 dogs each. Thirty days post inoculation (dpi) all dogs in the fed state were treated: dogs in group B were treated with spinosad and milbemycin oxime at the dose rates of 45–60 mg/kg and 0.75–1.0 mg/kg bodyweight, respectively, approximately the lower half portion of the expected full unit dose range; dogs in group A were treated with placebo tablets. All dogs were euthanized and necropsied 56–58 dpi. The heart and lungs were examined to determine the presence of A. vasorum. All placebo group dogs were infected at necropsy with counts ranging from 22 to 98 adult worms and a geometric mean worm count of 55.2. In contrast, the geometric mean worm count in the spinosad/milbemycin oxime group was 0.7 with worm numbers ranging from 0 to 8. The results of this study demonstrate that a single treatment with the tablet combination of spinosad and milbemycin oxime administered 30 dpi provided 98.8% preventive efficacy against development of adult A. vasorum infections. Monthly treatments with spinosad and milbemycin oxime have the potential to prevent the establishment of infections with A. vasorum in dogs. 相似文献