全文获取类型
收费全文 | 892篇 |
免费 | 12篇 |
专业分类
林业 | 141篇 |
农学 | 67篇 |
基础科学 | 9篇 |
82篇 | |
综合类 | 117篇 |
农作物 | 16篇 |
水产渔业 | 35篇 |
畜牧兽医 | 396篇 |
园艺 | 15篇 |
植物保护 | 26篇 |
出版年
2021年 | 10篇 |
2020年 | 6篇 |
2019年 | 11篇 |
2018年 | 14篇 |
2017年 | 20篇 |
2016年 | 14篇 |
2015年 | 18篇 |
2014年 | 18篇 |
2013年 | 42篇 |
2012年 | 35篇 |
2011年 | 30篇 |
2010年 | 15篇 |
2009年 | 27篇 |
2008年 | 39篇 |
2007年 | 30篇 |
2006年 | 25篇 |
2005年 | 26篇 |
2004年 | 19篇 |
2003年 | 30篇 |
2002年 | 22篇 |
2001年 | 27篇 |
2000年 | 27篇 |
1999年 | 11篇 |
1998年 | 10篇 |
1997年 | 9篇 |
1996年 | 12篇 |
1994年 | 9篇 |
1993年 | 6篇 |
1992年 | 12篇 |
1991年 | 15篇 |
1990年 | 10篇 |
1989年 | 20篇 |
1988年 | 19篇 |
1987年 | 11篇 |
1985年 | 10篇 |
1984年 | 9篇 |
1983年 | 11篇 |
1979年 | 8篇 |
1978年 | 10篇 |
1977年 | 14篇 |
1975年 | 8篇 |
1974年 | 10篇 |
1973年 | 6篇 |
1972年 | 9篇 |
1971年 | 8篇 |
1969年 | 8篇 |
1967年 | 8篇 |
1966年 | 14篇 |
1924年 | 5篇 |
1921年 | 9篇 |
排序方式: 共有904条查询结果,搜索用时 0 毫秒
61.
62.
W. E. Weber 《Euphytica》1982,31(2):493-502
Summary The response to selection is determined by the genetic and nongenetic variance, the selection intensity, and the size of the experiments. If, in pure line breeding, selection starts in segregating generations, the gain depends on the relation of additive to epistatic variance. The gain can be increased if an index is constructed using the information from relatives. From animal breeding this kind of selection is known as combined selection. In this paper the optimal number of families and subfamilies is determined that will maximise the selection response by combined selection for a fixed total size of experiments. The composition of the genetic variance has a imited influence on the optimal size of the progenies. If epistatic variance is important, then the number of F2 families has to be reduced and the number of F3 families and F4 families must be increased. The same is true if the nongenetic variance is increased. 相似文献
63.
A lean phenotype has been detected in vitamin D receptor (VDR) knockout mice; however, the gender differences in fat metabolism between male and female mice both with age and in response to a high‐fat diet have not been studied before. The objective of our study was to assess changes in body and fat tissue weight, food intake and serum cholesterol and triglyceride in VDR knockout mice from weaning to adulthood and after a challenge of adult animals with a high‐fat diet. Although VDR knockout mice of both sexes consumed more food than wild‐type and heterozygous littermates, their body weight and the weight of fat depots was lower after 6 months on a diet with 5% crude fat content. When adult animals were challenged with a high‐fat diet containing 21% crude fat content for 8 weeks, VDR knockout mice of both sexes had a significantly higher food intake but gained less weight than their wild‐type littermates. Cholesterol levels were higher after 2 days on the high‐fat diet in both sexes, but in the VDR knockout mice, less cholesterol was detected in the serum after 8 weeks. Wild‐type male mice showed signs of fatty liver disease at the end of the experiment, which was not detected in the other groups. In conclusion, lack of the VDR receptor results in reduced fat accumulation with age and when adult mice are fed a high‐fat diet, despite a higher food intake of VDR knockout mice relative to their wild‐type littermates. These effects can be detected in both sexes. Wild‐type male mice react with the highest weight gain and cholesterol levels of all groups and develop fatty liver disease after 8 weeks on a high‐fat diet, while male VDR knockout mice appear to be protected. 相似文献
64.
100 faeces samples of cattle were investigated in comparison to a recent commercially available Salmonella Rapid Test (OXOID) and a cultural standard method (non-selective enrichment in buffered peptone water, selective enrichment in RAPPAPORT-VASSILIADIS-medium) for presence of Salmonella. The Salmonella Rapid Test showed in positive results an accuracy ("sensitivity") of 94.7% and in negative results an assurance ("specificity") of 97.5% and is therefore suitable for rapid detection (within 2 days) of faeces sample of cattle with Salmonella. 相似文献
65.
Amorphus globosus is a rare entity, more common in the cow but also reported in mares, buffaloes and goats. In respect of both development and clinical presentation, this abnormity can be evolved very variably. Previously, it has been discussed whether it is a form of twin pregnancy or placental teratoma. This case report deals with morphology and genetic observations in an unusual bovine amorphus globosus exhibiting a rudimentary clitoris and vulva, gut‐like structures and rudimentary bones. The amorphus globosus was shown to be dizygotic to the normal male twin using the BovineSNP50 v2 BeadChip and had a genetical female sex. Aspects of aetiology and pathogenesis as well as the possible impact of amorphus globosus in the emergence of freemartinism are discussed. 相似文献
66.
Schmoekel HG Weber FE Hurter K Schense JC Seiler G Ryrz U Spreng D Schawalder P Hubbell J 《The Journal of small animal practice》2005,46(1):17-21
OBJECTIVES: To test a non-glycosylated recombinant human bone morphogenetic protein-2 (ngly-rhBMP-2)/fibrin composite, which has been shown experimentally to enhance healing of bone defects in rodents, in a clinical case series of dogs and cats undergoing treatment for fracture non-unions and arthrodesis. METHODS: A ngly-rhBMP-2/fibrin composite was applied in 41 sites in 38 dogs and cats for which a cancellous bone autograft was indicated, replacing the graft. RESULTS: Bridging of the bone defect with functional bone healing was achieved in 90 per cent of the arthrodesis and fracture nonunions treated in this manner. CLINICAL SIGNIFICANCE: This prospective clinical study demonstrates the beneficial effects of ngly-rhBMP-2 in a specially designed fibrin matrix on the treatment of bone defects, and validates the use of this composite as an alternative to bone autografts in dogs and cats. 相似文献
67.
Successful selection of interspecific hybrid progenies with superior ability to regenerate shoots from apical meristems was performed in sunflower which now allows for the development of lines for improved biotechnological applications. Early generations of interspecific hybrids originating from crosses between the two H. annuus CMS lines ‘HA89’ and ‘Baso’, and 9 wild species were screened for their ability to regenerate in vitro. Evaluation of 36 progenies allowed to identify seven progenies from crosses involving H. mollis, H. giganteus, H. strumosus, and H. decapetalus which showed a significantly higher regeneration potential than the commercial hybrid ‘Albena’ regarding the number of shoots per explant. Among these progenies, 47.2 to 62.4% of explants produced shoots with an average of 2.3 to 3.5 shoots per cultured explant. Regeneration in vitro was significantly determined by the genotype. More than half of the investigated interspecific hybrids performed better than the inbred ‘HA89’ demonstrating that the high regeneration potential available in the wild species can be efficiently transferred to cultivated sunflower. The seven progenies with high regeneration potential in vitro were characterised by agronomic performance in the field. Two of the interspecific hybrids derived from H. strumosus and H. decapetalus not only showed a superior regeneration potential but also proved to be competitive to commercial hybrids with regard to important agronomic traits, e.g. fat content and TGW. This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
68.
Hidden allergens are a common problem in food safety that has been known for many years. This is why the European Parliament adopted Directive 2003/89/EC amending 2000/13/EC. In addition to specific ingredients, Directive 2003/89/EC also requests the declaration of specific products that were used in the production and could be a risk for allergic individuals. This also includes the declaration of fining agents and lysozyme used in wines. In fact, it could be assumed that fining agents would be almost completely removed during the manufacturing process; however, until now there has been no necessity to analyze wine for these fining agents. By applying enzyme-linked immunosorbent assay (ELISA), residuals of fining agent proteins and the stabilizer lysozyme were investigated in various German wines. The results showed no detectable amounts of fining agents in wines, except for dried egg white and lysozyme, both derived from hen's egg white. For those products, adverse reactions against treated wines could not be excluded. 相似文献
69.
Weber HA Zart MK Hodges AE Molloy HM O'Brien BM Moody LA Clark AP Harris RK Overstreet JD Smith CS 《Journal of agricultural and food chemistry》2003,51(25):7352-7358
The characterization of herbal materials is a significant challenge to analytical chemists. Goldenseal (Hydrastis canadensis L.), which has been chosen for toxicity evaluation by NIEHS, is among the top 15 herbal supplements currently on the market and contains a complex mixture of indigenous components ranging from carbohydrates and amino acids to isoquinoline alkaloids. One key component of herbal supplement production is botanical authentication, which is also recommended prior to initiation of efficacy or toxicological studies. To evaluate material available to consumers, goldenseal root powder was obtained from three commercial suppliers and a strategy was developed for characterization and comparison that included Soxhlet extraction, HPLC, GC-MS, and LC-MS analyses. HPLC was used to determine the weight percentages of the goldenseal alkaloids berberine, hydrastine, and canadine in the various extract residues. Palmatine, an isoquinoline alkaloid native to Coptis spp. and other common goldenseal adulterants, was also quantitated using HPLC. GC-MS was used to identify non-alkaloid constituents in goldenseal root powder, whereas LC-MS was used to identify alkaloid components. After review of the characterization data, it was determined that alkaloid content was the best biomarker for goldenseal. A 20-min ambient extraction method for the determination of alkaloid content was also developed and used to analyze the commercial material. All three lots of purchased material contained goldenseal alkaloids hydrastinine, berberastine, tetrahydroberberastine, canadaline, berberine, hydrastine, and canadine. Material from a single supplier also contained palmatine, coptisine, and jatrorrhizine, thus indicating that the material was not pure goldenseal. Comparative data for three commercial sources of goldenseal root powder are presented. 相似文献
70.
Diego Prestes Gomes Brunele Weber Chaves Alexssandro Geferson Becker Bernardo Baldisserotto 《Aquaculture Research》2011,42(6):878-886
The present study investigated the effects of water pH (5.0, 7.0 and 9.0), hardness (0, 20 and 120 mg CaCO3 L?1) and temperature (15, 23 and 30 °C) on the induction of sedation and anaesthesia, and subsequent recovery, of silver catfish exposed to eugenol. Moreover, the blood gas tensions (PvO2 and PvCO2) and blood pH in silver catfish acclimated to these temperatures were investigated after exposure to eugenol. Water pH, hardness, temperature and fish size affect the efficacy of eugenol in silver catfish, particularly at the lower concentrations tested (20 and 30 mg L?1). Sedation of this species can be induced at concentrations as low as 20 mg L?1, but for anaesthesia, a concentration of at least 40 mg L?1 of eugenol must be used to compensate for the influence of fish size and water quality. Blood gas tension and pH were affected by eugenol anaesthesia, but only in fish acclimated to 30 °C. 相似文献