全文获取类型
收费全文 | 132239篇 |
免费 | 7635篇 |
国内免费 | 80篇 |
专业分类
林业 | 6203篇 |
农学 | 4871篇 |
基础科学 | 873篇 |
16828篇 | |
综合类 | 18599篇 |
农作物 | 4849篇 |
水产渔业 | 7176篇 |
畜牧兽医 | 70915篇 |
园艺 | 1717篇 |
植物保护 | 7923篇 |
出版年
2019年 | 1289篇 |
2018年 | 2186篇 |
2017年 | 2471篇 |
2016年 | 2310篇 |
2015年 | 1957篇 |
2014年 | 2377篇 |
2013年 | 5374篇 |
2012年 | 4122篇 |
2011年 | 5006篇 |
2010年 | 3288篇 |
2009年 | 3240篇 |
2008年 | 4777篇 |
2007年 | 4550篇 |
2006年 | 4436篇 |
2005年 | 3904篇 |
2004年 | 3726篇 |
2003年 | 3765篇 |
2002年 | 3456篇 |
2001年 | 4899篇 |
2000年 | 4683篇 |
1999年 | 3715篇 |
1998年 | 1469篇 |
1997年 | 1499篇 |
1996年 | 1320篇 |
1995年 | 1512篇 |
1994年 | 1336篇 |
1993年 | 1315篇 |
1992年 | 2773篇 |
1991年 | 2932篇 |
1990年 | 2922篇 |
1989年 | 2796篇 |
1988年 | 2548篇 |
1987年 | 2563篇 |
1986年 | 2518篇 |
1985年 | 2372篇 |
1984年 | 1946篇 |
1983年 | 1609篇 |
1982年 | 1132篇 |
1979年 | 1703篇 |
1978年 | 1316篇 |
1976年 | 1119篇 |
1975年 | 1206篇 |
1974年 | 1408篇 |
1973年 | 1376篇 |
1972年 | 1345篇 |
1971年 | 1288篇 |
1970年 | 1279篇 |
1969年 | 1214篇 |
1968年 | 1090篇 |
1967年 | 1146篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
A stripspawning methodology was evaluated for tilapia (oreochromid) species. This technique achieved an average hatching success of 68.6 ± 3.6% (N= 31). Female fecundity and spawning frequency were dependant on both genetical and husbandry factors. Egg yields for Oreochromis niloticus, O. mossambicus, and O. niloticus±O. mossambicus hybrids averaged 4.54, 10.86 and 10.36 eggs/g female/spawn, respectively. Female broodstock that were adapted to an intensive spawning regime exhibited a significant increase in fecundity. Additionally, egg survival was not affected by hydration for up to 15 minutes prior to fertilization. Results suggest that the strip spawning of tilapia species may be an efficient method of providing viable gametes for hatchery purposes. 相似文献
82.
83.
84.
A combined ultracentrifugationl/precipitation method for the measurement of lipoprotein cholesterol concentrations was developed and validated for use with canine plasma. Very low density lipoproteins (VLDL) were isolated by flotation ultracentrifugation and low density lipoproteins (LDL) separated from high density lipoproteins (HDL) by precipitation with heparin-manganese chloride. Effective separation of these classes was confirmed by agarose gel electrophoresis of native lipoproteins and by sodium dodecyl sulphate polyacrylamide gel electrophoresis of their apolipoprotein distributions. There was trace contamination of the LDL precipitate with HDL, but this represented less than 4 and 9 per cent of the total plasma HDL in normo- and hypercholesterolaemic dogs, respectively. The intra-assay and interassay coefficients of variation for LDL- and HDL-cholesterol concentrations were between 3·3 and 6·9 per cent, and 7·2 and 9·0 per cent, respectively, for plasma cholesterol concentrations between 2·67 and 8·14 mmoll/litre. The intra-assay coefficient of variation for VLDL-cholesterol was 53·8 and 18·4 per cent at plasma cholesterol concentrations of 2·67 and 8·14 mmol/litre, respectively. The interassay coefficient of variation for VLDL was 22·5 per cent. Storage of plasma at -20°C for between two and eight weeks did not affect VLDL-cholesterol concentrations, but led to an increase in LDL-cholesterol and a decrease in HDL-cholesterol concentrations of approximately 10 per cent. The method described is appropriate for the measurement of lipoprotein concentrations in plasma from normo- and hypercholesterolaemic dogs, but samples should not be subjected to prolonged storage before analysis. 相似文献
85.
J L Becht R D Park S L Kraft P F Steyn R H Wrigley 《Veterinary Clinics of North America: Equine Practice》2001,17(1):1-18
Effective radiographic interpretation requires a veterinarian who is knowledgeable of equine limb anatomy and the various principles that affect the resulting image. The normal and its variations must be recognized and understood before the abnormal can be confidently identified as pathologic. Proper patient positioning and sound radiographic technique are mandatory if reliable diagnostic radiographs are to be produced. This review emphasizes equine foot radiographic variations of normal and pseudolesions that occur with commonly used radiographic views performed in equine practice. 相似文献
86.
Sandy‐textured Mediterranean soils are invariably depleted in organic matter and supply only small amounts of N to crops. To compensate for these deficiencies, we tested the N supply from six organic wastes applied to a Cambic Arenosol in pots growing ryegrass. The results showed that the behaviour of the wastes in supplying N to a ryegrass crop grown in this soil can be predicted by observing their performance in laboratory aerobic incubations. The N made available during these incubations fitted well to a one‐pool kinetic model. 相似文献
87.
The transformation of recent igneous rock occurs with participation of microorganisms associated with the deposition of iron and aluminum on their cell surface. An identity of morphological structures was found in the microorganisms in both cases, and this fact counts in favor of their similarity and wide distribution in the rock being transformed. The polymorphous acid-resisting organism identified by our studies was tentatively classified with the Metallogenium-Siderococcus group. 相似文献
88.
A ten-year-old female poodle was presented for left hindlimb lameness. Radiographically, irregular intramedullary densities of long bones (bone infarcts) and a lytic lesion in the left distal femur were detected. Two years after the first examination, the lesions in the distal femur were definitely identified as osteosarcoma and the dog was euthanized. Pathological and histological changes of the bone infarcts as well as of the osteosarcoma are described. Regarding bibliographical data, occurrence and aetiopathogenesis of osteosarcoma associated with multifocal bone infarction in man and dog are discussed. 相似文献
89.
Laurence O. Whiteley DVM PhD Samuel K. Maheswaran BVSc PhD Douglas J. Weiss DVM PhD Trevor R. Ames DVM MS Mathur S. Kannan BVSc PhD 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》1992,6(1):11-22
The severe fibrinonecrotic pneumonia associated with pneumonic pasteurellosis usually results from colonization of the lower respiratory tract by Pasteurella haemolytica biotype A, serotype 1(A1). Despite recent research efforts, the authors lack a detailed understanding of the interactions and host response to P. haemolytica in the respiratory tract. The authors hypothesize that management and environmental stress factors or viral infection alters the upper respiratory tract (URT) epithelium allowing P. haemolytica to colonize the epithelium. Once the URT is colonized, large numbers of organisms enter the lung where they interact with alveolar macrophages. Endotoxin, released from the bacteria, crosses the alveolar wall where it activates pulmonary intravascular macrophages, endothelium, neutrophils, lymphocytes, platelets, complement, and Hageman factor leading to complex interactions of cells and mediators. It is the progression of this inflammatory response with neutrophil influx that is ultimately responsible for the pulmonary injury. Leukotoxin is a major virulence factor of P. haemolytica that allows it to survive by destroying phagocytic cells. At subcytolytic concentrations it may also enhance the inflammatory response by activating cells to produce mediators and release reactive oxygen metabolites and proteases. 相似文献
90.
S Makimura M Sawaki 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》1992,54(1):63-67
Zymosan-induced and luminol-aided chemiluminescence (CL) of whole blood from beagle dogs was estimated for the function of polymorphonuclear leucocytes (PMNs). Whole blood (0.1 ml) was examined directly and results were obtained within 20 min. A phagocytic function of PMNs can be estimated from the peak CL counts and the number of PMNs in a specimen, and the opsonic activity can also be estimated by the peak time showing peak CL after the addition of non-opsonized zymosan. The optimal temperatures to keep diluted whole blood for the CL measurement was around 13 degrees C. Thus, this method offers information concerning the functions of phagocytic cells in whole blood. 相似文献