全文获取类型
收费全文 | 163547篇 |
免费 | 8267篇 |
国内免费 | 99篇 |
专业分类
林业 | 8954篇 |
农学 | 5641篇 |
基础科学 | 1167篇 |
19909篇 | |
综合类 | 26479篇 |
农作物 | 7579篇 |
水产渔业 | 9296篇 |
畜牧兽医 | 77901篇 |
园艺 | 2752篇 |
植物保护 | 12235篇 |
出版年
2018年 | 4355篇 |
2017年 | 4514篇 |
2016年 | 3022篇 |
2015年 | 1732篇 |
2014年 | 2082篇 |
2013年 | 5555篇 |
2012年 | 4672篇 |
2011年 | 6919篇 |
2010年 | 5011篇 |
2009年 | 4232篇 |
2008年 | 6068篇 |
2007年 | 6096篇 |
2006年 | 4541篇 |
2005年 | 4305篇 |
2004年 | 4200篇 |
2003年 | 4239篇 |
2002年 | 4068篇 |
2001年 | 4737篇 |
2000年 | 4616篇 |
1999年 | 3728篇 |
1998年 | 1486篇 |
1997年 | 1508篇 |
1996年 | 1426篇 |
1995年 | 1769篇 |
1994年 | 1602篇 |
1993年 | 1546篇 |
1992年 | 3172篇 |
1991年 | 3303篇 |
1990年 | 3344篇 |
1989年 | 3348篇 |
1988年 | 3078篇 |
1987年 | 3149篇 |
1986年 | 3241篇 |
1985年 | 3109篇 |
1984年 | 2631篇 |
1983年 | 2324篇 |
1982年 | 1583篇 |
1981年 | 1484篇 |
1980年 | 1435篇 |
1979年 | 2325篇 |
1978年 | 1919篇 |
1977年 | 1634篇 |
1976年 | 1452篇 |
1975年 | 1550篇 |
1974年 | 2088篇 |
1973年 | 2097篇 |
1972年 | 2059篇 |
1971年 | 1821篇 |
1970年 | 1716篇 |
1969年 | 1573篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
Serum antibody (virus neutralisation, complement fixation, IgM and IgG) responses to equine herpesvirus-1 (EHV-1) infection were measured in six foals which were initially free from EHV-1 and EHV-4 infection and maternally-derived antibodies. Following primary infection, high titres of virus neutralisation and complement fixation antibodies were detectable against EHV-1, however, corresponding antibody levels against EHV-4 were low or inapparent, although the two viruses share a number of cross-reactive epitopes. In addition, following the primary infection with EHV-1, IgM levels increased before those of IgG, virus neutralisation and complement fixation antibodies, peaked sooner and thereafter declined. Stimulation of IgM levels was observed on secondary infection with EHV-1 given 61 days later. In contrast, IgG, virus neutralisation and complement fixation antibodies following primary infection were more sustained and no increase in their levels was observed on secondary infection. No consistent changes in IgM or IgG levels were seen after administration of dexamethasone to reactivate latent virus. 相似文献
122.
J B Herrick 《Veterinary Clinics of North America: Food Animal Practice》1989,5(3):457-469
Marketing to veterinarians is the process of synchronizing the business aspects of his or her goods and services so that they are understood and desired by animal owners. The basic components of a successful marketing program are in four categories: the individual, the situation, the needs, and the implementation. Each category is important and all are interrelated; however, the implementation of a program should not begin until a self-analysis has been done and the situation and its needs are thoroughly researched. Programs that have been used by successful practitioners can be copied. No program can be effective unless the economic status of the client's enterprise is known and understood. 相似文献
123.
Three different milk sampling techniques were evaluated during milk sampling: a direct aseptic collection from the udder through a sterile cannula was used as the reference technique, compared with either a manual or a mechanical sampling method. In this study 30 high-yielding Holstein-Friesian dairy cows at different stages of lactation and free of udder infection were used. For each milk sample, the influence of milk sampling techniques was determined for the following parameters: somatic cell count, milk composition, bacterial contamination, viability, in vitro phagocytosis and overall killing of Staphylococcus aureus Newbould 305, and cellular chemiluminescence. Because milk sampling occurred throughout lactation, the differences between early, mid- and late lactation were estimated. It was concluded that bacterial contamination was not significantly different in manual milking samples and the reference technique; bacterial contamination was, however, significantly (P < 0.001) higher in machine milking samples than in the reference technique. Among the different sampling techniques, no significant effects on SCC, milk composition, viability and functions of the cells isolated from milk were observed. It was found that viability, intracellular killing and cellular chemiluminescence of milk PMN were significantly lower (P < 0.05) in early lactation compared to mid-lactation. Phagocytosis was significantly (P < 0.05) higher in early lactation compared to mid- and late lactation, and no significant differences were observed between mid- and late lactation. From this study, it can be concluded that despite a higher bacterial contamination obtained with the mechanical sampling method, the 3 milk sampling techniques described in this study can be used for the evaluation of milk cell functions. 相似文献
124.
Taenia saginata cyst fluid was examined for host proteins; IgG1 and IgG2 as well as haemolytic complement activity were detected. Polyacrylamide gel electrophoresis revealed differences in proteinograms among the samples taken from 1-, 4-, and 10-month old cysts. Fluid from older cysts had fewer protein components and showed a weaker antigenic reaction with sera of bovines infected with T. saginata than that of younger cysts. The roles of antibody and complement in initiating degeneration of the parasite are discussed. 相似文献
125.
Reduced levels of total iron binding capacity and unsaturated iron binding capacity were observed in the blood of trichinous and iron-injected trichinous pigs. No change was observed in their serum iron and saturation concentration levels. Also, reduced iron concentration levels were observed in the livers of trichinous pigs, while increased iron concentration levels were observed in the spleens of trichinous pigs and the livers and spleens of iron-injected pigs. No difference was found with regard to weight gains, number of larvae per gram of tissues, or histologic characteristics of 'nurse cells'. 相似文献
126.
P. Laffaille A. Acou J. Guillouët B. Mounaix A. Legault 《Ecology of Freshwater Fish》2006,15(4):583-588
Abstract – Changes in the numbers and size-class structure of European silver eels, Anguilla anguilla , in the River Frémur (France) were examined over a 9-year period after installation of downstream eel passes. The number of silver eels migrating downstream peaked in 1999, then decreased strongly and steadily after 2000, reaching relatively low levels. At the same time, a gradual shift in the silver eel sex ratio from a dominance of males (size from 270 to 442 mm, age from 3 to 6 years) to females (size from 366 to 1112 mm, age from 4 to 9 years) was recorded. Possible explanations for the escapement patterns observed are environmental sex determination and the installation of eel passes on the main hydraulic engineering structures in 1992 and 1996. 相似文献
127.
Experiments conducted m a phytotron on three rice varieties of different salinity tolerance revealed an increase in the content of endogenous abscisic acid (ABA) with increasing NaCl salinity in IR20 (semi salt-tolerant), but in Pokkali (salt-tolerant) and IR28 (salt-sensitive) the increase in ABA content was marginal. Under sahnity stress, in general, 5 weekly sprayings of ABA (10-4 mol L-1 ) decreased Na and K concentrations in the shoot to the extent of 29.5 % and 3.3 %, respectively. However, ABA application significantly improved the K/Na ratio as well as the chlorophyll fluorescence decrease ratio (Rfd, indicator for potential photosynthetic activity), the number of green leaves per plant and the shoot dry weight. The response of IR20 and IR28 to ABA application was significantly better than that of Pokkali. Increasing salinity caused marked nutrient imbalances, decreased Rfd values and shoot dry weight. The results are discussed in relation to possible mechanism of salinity tolerance. 相似文献
128.
Palca J 《Science (New York, N.Y.)》1991,251(4990):153-154
129.
130.