全文获取类型
收费全文 | 11405篇 |
免费 | 805篇 |
专业分类
林业 | 1162篇 |
农学 | 423篇 |
基础科学 | 42篇 |
2614篇 | |
综合类 | 726篇 |
农作物 | 484篇 |
水产渔业 | 772篇 |
畜牧兽医 | 4616篇 |
园艺 | 285篇 |
植物保护 | 1086篇 |
出版年
2023年 | 101篇 |
2022年 | 130篇 |
2021年 | 234篇 |
2020年 | 224篇 |
2019年 | 158篇 |
2018年 | 549篇 |
2017年 | 525篇 |
2016年 | 469篇 |
2015年 | 374篇 |
2014年 | 424篇 |
2013年 | 651篇 |
2012年 | 902篇 |
2011年 | 819篇 |
2010年 | 447篇 |
2009年 | 351篇 |
2008年 | 709篇 |
2007年 | 662篇 |
2006年 | 534篇 |
2005年 | 564篇 |
2004年 | 511篇 |
2003年 | 470篇 |
2002年 | 385篇 |
2001年 | 277篇 |
2000年 | 240篇 |
1999年 | 216篇 |
1998年 | 68篇 |
1997年 | 56篇 |
1996年 | 42篇 |
1995年 | 62篇 |
1994年 | 37篇 |
1993年 | 33篇 |
1992年 | 79篇 |
1991年 | 68篇 |
1990年 | 60篇 |
1989年 | 56篇 |
1988年 | 52篇 |
1987年 | 48篇 |
1986年 | 52篇 |
1985年 | 48篇 |
1984年 | 44篇 |
1983年 | 34篇 |
1979年 | 37篇 |
1978年 | 21篇 |
1974年 | 26篇 |
1973年 | 23篇 |
1972年 | 22篇 |
1971年 | 25篇 |
1970年 | 27篇 |
1969年 | 27篇 |
1968年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
991.
Variability in conspecific predation among longnose lancetfish Alepisaurus ferox in the western Indian Ocean 总被引:1,自引:0,他引:1
Evgeny V Romanov Frédéric Ménard Veniamin V Zamorov Michel Potier 《Fisheries Science》2008,74(1):62-68
ABSTRACT: Conspecific predation among longnose lancetfish Alepisaurus ferox was investigated in four spatio-temporal strata of the western Indian Ocean. The cannibalism level varied from 0 to 45.5% by frequency of occurrence and was negatively related with abundance of non-evasive prey (such as crustaceans Charybdis smithii and Natosquilla investigatoris ) and foraging success. Predation by lancetfish is often described as a non-selective process, constrained by local prey availability and by its feeding speed during an attack of prey. Our results show that lancetfish may adapt its opportunistic foraging behavior, feeding on non-conspecific abundant prey such as crustaceans when available, and switching to a high level of conspecific predation in poor waters. 相似文献
992.
N Barré E Camus G Borel R Aprelon 《Revue d'élevage et de médecine vétérinaire des pays tropicaux》1991,44(4):453-458
The examination of 458 domestic and wild hosts of the tick A. variegatum allowed to collect 8,581 larvae, 646 nymphs, 685 adults in 9 different animal species and to determine their preferential attachment sites. In another survey on 15 goats and 5 cattle, 12,345 larvae, 2,111 nymphs and 4,625 adults were counted on the anatomic sites. Immature ticks feed preferentially on the head, neck and limbs of birds, the limbs of mongoose and the limbs and ears of dogs, goats and cattle. Adults feed only on hosts of medium to large size and attach on ventral parts of the body, especially the groin, perineum, axillae and the dewlap of cattle. This tick species should be searched for on these sites when estimating its propagation in a threatened area or the evolution of its population during an eradication campaign. Moreover, the acaricide concentration on these sites must be optimal during systematic treatments. 相似文献
993.
G Mathé I Blazsek C Canon M Gil-Delgado J L Misset 《Comparative immunology, microbiology and infectious diseases》1986,9(2-3):241-252
Severe impairment of the lymphopoietic cell renewal system is an important etiological factor of cancer development and it may be the consequence of massive radio and/or chemotherapeutic regimens. In a comparative study, we analysed the potential, systemic immunorestoratory capacity of bestatin, a microbial leucil-aminopeptidase inhibitor and of the ubiquitous trace element zinc. In vivo administration of bestatin in mice stimulated both Interleukin 1 and Interleukin 2 production, and enhanced T cell, B cell as well as macrophage mediated immunoreactions. In a phase II clinical trial on 41 patients with non-Hodgkin lymphoma, Hodgkin disease and solid tumors, bestatin treatment corrected the pathological frequency of both OKT4 and OKT8 lymphocyte subpopulations. Zinc-saturated transferrin had a significative stimulatory effect on the ongoing DNA synthesis of antigen activated human lymphocytes in culture. Oral administration of zinc-gluconate to patients who manifested a severe T cell subpopulation defect corrected preferentially the OKT8 suppressor/cytotoxic T cell unbalances. The clinical results obtained by both bestatin and zinc were observed only on a short-term, so further studies are needed to elaborate long lasting regiments and to establish whether these treatments have determinant influence on the underlying disease. 相似文献
994.
J. Hervás J. C. Gómez-Villamandos A. Méndez L. Carrasco M. A. Sierra 《Veterinary research communications》1996,20(3):285-299
African swine fever is a viral haemorrhagic disease of pigs which has been used as a model for the study of viral haemorrhagic diseases in man. The acute course of the disease is characterized by acute proliferative glomerulonephritis, with viral replication in mesangial cells and occasional focal necrosis of the renal tubular system; hyperplasia of the collecting ducts is associated with evident virus replication. Haemorrhages have been attributed to endothelial dysfunction, aggravated by virus replication in endothelial cells in the final stages of the disease. The renal interstitium displays intense oedema and an infiltrate largely composed of macrophages. Virus replication has also been observed in fibroblasts and in the smooth0muscle cells of arterioles and venules.In subacute-chronic forms of the disease, various types of glomerulonephritis are observed, ranging from mesangial proliferative glomerulonephritis to focal and segmental hyalinosis associated with immune-mediated phenomena. No striking changes are reported in the renal tubular system. Interstitial haemorrhages are associated with diapedesis due to immunologically mediated events. The interstitium has also been found to contain a lymphohistiocytic infiltrate with abundant plasma cells. No evidence has been reported of viral replication in any cell population.Abbreviations ASF
African swine fever
- ASFV
African swine fever virus
- C
complement component
- DNA
deoxyribonucleic acid
- HAD50
50% haemoadsorbing doses
- Ig
immunoglobulin
- MPS
mononuclear phagocytic system
- PAS
periodic acid-Schiff reagent 相似文献
995.
Adherence of Actinobacillus pleuropneumoniae to porcine tracheal epithelial cells and frozen lung sections 总被引:3,自引:0,他引:3
The ability of 23 different Actinobacillus pleuropneumoniae isolates to adhere in vitro to porcine tracheal epithelial cells and to porcine frozen lung sections was examined. It was found that A. pleuropneumoniae adhered poorly to isolated tracheal epithelial cells. On the other hand, A. pleuropneumoniae adhered to frozen lung sections and marked variations were observed between and within serotypes. Adherence to lung sections did not seem related to the hemagglutinating activity of the isolate. Two noncapsulated variants adhered to lung sections in greater numbers than their capsulated parent strains. Adherence to lung sections was not inhibited by the extracellular matrix components tested namely, laminin, fibronectin, and collagen, but was inhibited by homologous serotype-specific antiserum. The data indicated that the A. pleuropneumoniae isolates tested possess the ability to adhere to porcine lung tissue, a property which did not seem to be related to the serotype and did not seem to involve the capsular material or the hemagglutinins of the isolates. 相似文献
996.
Infection and pyogranulomas induced by Corynebacterium pseudotuberculosis were experimentally reproduced in lambs. In two separate experiments, bacterial multiplication and dissemination were studied in 30 male lambs inoculated subcutaneously into the right ear with 1.1 or 1.5 X 10(8) viable C. pseudotuberculosis strain 19R. Infected lambs were necropsied at various times until the 28th day following inoculation. After a transient hyperthermia and a strong local inflammatory reaction, an abscess developed in the right ear from postinoculation day (PID) 6; it enlarged until PID 14 and stabilized thereafter and was associated with adenopathy of lymph nodes draining the head. Three acute phase indicators of inflammation were followed in 14 out of 30 lambs; plasma levels of copper and haptoglobin increased rapidly following inoculation whereas zinc levels decreased. The peaks were reached from PID 1 to 5, and thereafter the values came back slowly to the baseline. Antibodies against C. pseudotuberculosis exotoxin increased from PID 5 and reached a plateau on PID 21. Bacterial dissemination, assessed by the number of infected organs per lamb, was maximal on PID 16 and then stabilized until the end of the experiment. Lungs were infected in seven out of 18 lambs necropsied on PID 28. These results demonstrate a significant relationship between the clinical score of superficial lymph nodes or inoculation site and the infection level of these organs, and an early localization of pyogranulomatous lesions in regional lymph nodes. The subsequent development of the disease was related to the enlargement of these lesions and, in some animals, to a bacterial dissemination from primary sites of infection in the right prescapular lymph node and in the lung. 相似文献
997.
M Tr?vén S Alenius C Fossum B Larsson 《Zentralblatt für Veterin?rmedizin. Reihe B. Journal of veterinary medicine. Series B》1991,38(6):453-462
Six calves, aged 24 to 58 days and not previously exposed to bovine viral diarrhoea virus (BVDV), were infected with this agent by nose-to-nose contact with a persistently BVDV viraemic calf. The study was conducted in two trials, using 3 calves in each. All 6 calves showed a peak interferon level in serum at 4 days post infection (dpi), and they seroconverted to BVDV at 16-21 dpi. The calves in trial 1 had diarrhoea for 2 or 3 days between 2 and 6 dpi and one calf again from 9 to 11 dpi. During the periods of fever, the calves were slightly depressed. Those in trial 2 were more depressed and their oral and nasal mucous membranes were reddened but they never had diarrhoea. In both trials, fever (up to 41.3 degrees C) was a prominent symptom at 8 to 9 dpi and 2 calves showed a diphasic fever course. Respiratory affection was mild and no medical treatment was required. Haematological assessment demonstrated a transient but significant leukopenia and lymphopenia at 4 dpi (P less than 0.01 and P less than 0.05 respectively) and 11 dpi (P less than 0.05 and P less than 0.01 respectively). A significant decrease in thrombocyte count was seen at 4 dpi (P less than 0.05, n = 3). This study has demonstrated that nose-to-nose contact is an effective way of transmitting BVDV from persistently infected to susceptible cattle. 相似文献
998.
999.
1000.