全文获取类型
收费全文 | 48997篇 |
免费 | 2702篇 |
国内免费 | 33篇 |
专业分类
林业 | 1714篇 |
农学 | 1662篇 |
基础科学 | 251篇 |
5837篇 | |
综合类 | 8198篇 |
农作物 | 1548篇 |
水产渔业 | 2717篇 |
畜牧兽医 | 26345篇 |
园艺 | 574篇 |
植物保护 | 2886篇 |
出版年
2019年 | 416篇 |
2018年 | 777篇 |
2017年 | 823篇 |
2016年 | 743篇 |
2015年 | 607篇 |
2014年 | 750篇 |
2013年 | 1736篇 |
2012年 | 1348篇 |
2011年 | 1691篇 |
2010年 | 1154篇 |
2009年 | 1096篇 |
2008年 | 1684篇 |
2007年 | 1595篇 |
2006年 | 1498篇 |
2005年 | 1382篇 |
2004年 | 1394篇 |
2003年 | 1371篇 |
2002年 | 1185篇 |
2001年 | 1913篇 |
2000年 | 1985篇 |
1999年 | 1498篇 |
1998年 | 569篇 |
1997年 | 500篇 |
1996年 | 450篇 |
1995年 | 613篇 |
1994年 | 525篇 |
1993年 | 462篇 |
1992年 | 1153篇 |
1991年 | 1211篇 |
1990年 | 1178篇 |
1989年 | 1097篇 |
1988年 | 1057篇 |
1987年 | 1081篇 |
1986年 | 1034篇 |
1985年 | 967篇 |
1984年 | 803篇 |
1983年 | 683篇 |
1982年 | 421篇 |
1981年 | 383篇 |
1979年 | 635篇 |
1978年 | 500篇 |
1977年 | 441篇 |
1976年 | 408篇 |
1975年 | 451篇 |
1974年 | 523篇 |
1973年 | 507篇 |
1972年 | 531篇 |
1971年 | 449篇 |
1970年 | 424篇 |
1969年 | 464篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
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
112.
113.
A. S. J. P. A. M. VAN MIEKT C. T. M. VAN DUIN Th. WENSING† 《Journal of veterinary pharmacology and therapeutics》1992,15(4):332-342
Tumour necrosis factor (TNF), a polypeptide produced by mononuclear phagocytes, has been implicated as an important mediator of inflammatory processes and of clinical manifestations in acute infectious diseases. To study further the potential role of TNF in infectious diseases, recombinant Escherichia coli (E. coli) derived human (r.HuTNF-alpha) and bovine TNF (r.BoTNF-alpha) were intravenously (i.v.) administered in dwarf goats. Rectal temperature, heart rate, rumen motility, plasma zinc and iron concentrations, and certain other blood biochemical and haematological values were studied and compared with the changes seen after E. coli endotoxin (LPS) was administered (dose: 0.1 microgram/kg i.v.). Following a single injection of 4 micrograms/kg of r.BoTNF-alpha, shivering and biphasic febrile response were observed, accompanied by tachycardia, inhibition of rumen contractions, drop in plasma zinc and iron concentrations, lymphopenia, and neutropenia followed by neutrophilia. The i.v. administration of a single injection of 4 micrograms/kg r.HuTNF-alpha induced shivering and biphasic febrile responses, accompanied by anorexia and a similar drop in plasma trace metal concentrations when compared with r.BoTNF-alpha-treated goats. The TNF-alpha-induced symptoms were essentially the same as those that occurred after LPS administration. However, the time of onset of these changes after the injection of TNF-alpha was significantly shorter than after LPS. Moreover, the r.BoTNF-alpha induced a longer lasting neutrophilic leucopenia, less neutrophilia, and a more persistent lymphopenia than after LPS injection. Neither r.BoTNF-alpha nor LPS caused severe haemo-concentration. Furthermore, no cross-tolerance between r.BoTNF-alpha and LPS could be demonstrated. We conclude that both r.BoTNF-alpha and r.HuTNF-alpha induce many of the physiologic, haematologic and metabolic changes that characterize the acute phase response to LPS. The overlapping biological activities of r.BoTNF-alpha, r.HuTNF-alpha and LPS in dwarf goats may indicate that both recombinant tumour necrosis factors have some homology with caprine TNF-alpha. 相似文献
114.
A. T. Szabó 《Genetic Resources and Crop Evolution》2005,52(3):347
115.
Sugar beet mash silage (BMS) was offered in amounts up to 35% of DM to dairy cows as a component of a total-mixed-ration (TMR). Barley and molasses in the control ration were replaced by BMS half in ration BMS 1/2 and in total in ration BMS 1/1 on the basis of the calculated contents of net energy for lactation. Two trials were carried out. In trial I each ration was tested on parameters of rumen fermentation and digestibility of crude nutrients using 4 Holstein cows with rumen fistula. Chewing activity was tested on 2 Holstein cows for each ration. With the BMS rations the ruminal NH3 concentration was lower and the drop in pH was less than in the control ration. The pattern of volatile fatty acids in the rumen fluid from the BMS groups tended towards more propionic and butyric acid. The feeding of BMS showed no negative impact on chewing and rumination. Energy digestibility raised significantly from 59.8% in the control ration to 72.6% in the BMS 1/1 ration. In trial II the same rations were fed in a change-overdesign to a herd of 24 Holstein cows to test feed intake and animal performance. The results showed no significant effects of BMS rations on DM intake and milk production. The results of both trials indicate that even high amounts of cereals can be replaced by BMS without negative effects on rumen fermentation, milk yield and milk composition with slight drop in fat content. For a better handling of BMS, it is of advantage to include it in a TMR. 相似文献
116.
T Kokkonen A Tsehai Tesfa M Tuori S Yrj?nen L Syrj?l?-Qvist 《Archives of Animal Nutrition》2002,56(3):213-227
Twenty-one multiparous dairy cows were fed concentrates containing three levels (119, 154 and 191 g/kg DM) of crude protein (CP) during the first ten weeks of lactation. Part of the grain and molassed sugar beat pulp was substituted with 0% (RSM0), 15% (RSM15) or 30% (RSM30) repeseed meal. Wilted grass silage was fed ad libitum after calving. The average response between RSM0 and RSM15 was +1.66 kg milk/d per percentage unit change in concentrate CP content. No further response occurred between RSM15 and RSM30. The positive effect of RSM inclusion was seen throughout the experimental period and was associated with increased plasma non esterified fatty acids (NEFA) and decreased plasma insulin concentration one week after calving, and higher efficiency of metabolisable energy utilisation for milk production. Digestibility of the diet remained unaffected. Milk and plasma urea tended to increase with RSM30 indicating excessive supply of rumen degradable protein. Because of the limited potential of cows to compensate for a deficit in feed protein supply by mobilising tissue protein, a substantial milk yield response can be achieved with a moderate level of protein supplementation during early lactation. 相似文献
117.
Morphological characterization of the interaction between Diplocarpon rosae and various rose species
Blackspot, caused by Diplocarpon rosae , is the most severe and ubiquitous disease of garden roses, but information is lacking about genotype-specific forms of resistance and susceptibility of the host. Macro- and microscopic analyses of 34 rose genotypes with a defined monoconidial culture black spot inoculum identified susceptible and resistant rose genotypes and further genotype-specific subdivisions, indicating the presence of partial forms of resistance and different resistance mechanisms. In total, eight interaction types were characterized, five representing compatible (types 1–5) and three representing incompatible interactions (types 6–8). The incompatible interactions were characterized by the lack of any visible fungal structures beneath the cuticle (type 8), single-cell necroses (type 7) or necroses of larger cell clusters (type 6), the latter two types with penetration hyphae and haustoria in epidermal cells. 相似文献
118.
D. M. Zhao S. Tateyama N. Miyoshi K. Uchida R. Yamaguchi T. Yamagami T. Hayashi 《Research in veterinary science》1995,59(3)
Cloning of the canine yes oncogene was attempted from a c
library derived from a healthy canine spleen using a human c-yes-1 probe. The nucleotide and amino acid sequences revealed that the canine yes gene contained an open reading frame consisting of 539 amino acids. Its product had a molecular mass of 60,368 Daltons and showed 95·9 per cent and 90·4 per cent homology with human and chick p61c-yes, respectively. Moreover, the product had a myristylation signal, src homology region (SH) 3, SH2, and tyrosine kinase domains showing 98·8 per cent and 96·0 per cent homology with those of human beings and chickens, respectively. These findings indicate that the products of the canine yes gene may have non-receptor-type tyrosine kinase activity on the cell membrane, as is the case in human and chick p61c-yes 相似文献
119.
Yunita T. Winarto 《Agriculture and Human Values》1995,12(4):47-57
The 1989 National Integrated Pest Management Program in Indonesia is a case of a breakthrough in national policy to enhance the ecological balance by conserving natural enemies and diminishing the indiscriminate use of pesticides in the protection of food crops. The Program provided training to agricultural officials and farmers to shift their perspectives in pesticide use through “knowledge transmission” rather than the transferal of “technological packages.” This paper examines how farmers, with the novel understanding they had, responded to the persisting top-down policy of the “complete credit packages” from the government rice intensification agencies and the recurrent outbreak of pests in 1990–1992. IPM knowledge and training provided initial understanding of, and the stimulus to discover, unknown phenomena on the basis of which farmers improved their knowledge and learning capacity. Constraints largely came from the inflexibility of the subsidized scheme of inputs and the inadequate explanation and extension services provided to farmers 相似文献
120.
Mazuzan GT 《Science (New York, N.Y.)》1987,236(4804):979-980