首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   4727篇
  免费   277篇
  国内免费   11篇
林业   219篇
农学   247篇
基础科学   64篇
  789篇
综合类   368篇
农作物   211篇
水产渔业   205篇
畜牧兽医   2353篇
园艺   113篇
植物保护   446篇
  2021年   41篇
  2020年   83篇
  2019年   67篇
  2018年   87篇
  2017年   97篇
  2016年   84篇
  2015年   65篇
  2014年   89篇
  2013年   205篇
  2012年   181篇
  2011年   249篇
  2010年   189篇
  2009年   182篇
  2008年   224篇
  2007年   195篇
  2006年   199篇
  2005年   176篇
  2004年   161篇
  2003年   157篇
  2002年   174篇
  2001年   134篇
  2000年   119篇
  1999年   108篇
  1998年   53篇
  1997年   36篇
  1996年   42篇
  1995年   37篇
  1994年   49篇
  1993年   57篇
  1992年   83篇
  1991年   75篇
  1990年   81篇
  1989年   76篇
  1988年   43篇
  1987年   61篇
  1986年   49篇
  1985年   59篇
  1984年   63篇
  1983年   52篇
  1982年   55篇
  1980年   36篇
  1979年   41篇
  1978年   46篇
  1977年   44篇
  1976年   45篇
  1975年   35篇
  1974年   43篇
  1972年   35篇
  1971年   39篇
  1969年   43篇
排序方式: 共有5015条查询结果,搜索用时 15 毫秒
11.
Summary Hereditary changes of certain Mendelian traits in red pepper after grafting are described. It is suggested that these changes are induced by a mechanism similar to that of transformation in higher organisms.The abstracts of this paper and the parts to follow have been presented at the XIII International Congress of Genetics held in August 1973 at Berkeley, California, USA as both a contributed paper and an exhibit including real herbarial specimen and color pictures of the variants genetically analyzed.  相似文献   
12.
K. Peremans  DVM  F. De  Winter  MD  L. Janssens  DVM  PhD  F. Dumont  PhD  H. Van  Bree  DVM  PhD  R. Dierckx  MD  PhD 《Veterinary radiology & ultrasound》2002,43(2):178-182
This case report describes the use of the 99mTc-labeled radiopharmaceutical ciprofloxacin (Infecton) in a case of hip prosthesis loosening in a dog. Serial planar radiographs were not conclusive, and culture of the synovial fluid was negative. Antibiotic treatment did not result in improvement of the lameness. Scintigraphy was performed with 99-Tc-Infecton, a tracer claimed to be specific for infection. Antibiotic treatment was interrupted 6 weeks prior to the examination. Planar and tomographic images at 3 h and at 24 h postinjection showed increased activity along the acetabulum and the proximal femoral bone surrounding the femoral prosthesis, indicating focal infection. Bacteriology performed after removal of the implant revealed Pseudomonas aeruginosa.  相似文献   
13.
A large Schistosoma mettheei ovum containing two miracidia was recovered from a squash preparation of the liver of an experimentally infected hamster. When observed, the miracidia were motile and facing in opposite directions.  相似文献   
14.
The Cornell Net Carbohydrate and Protein System (CNCPS), a mechanistic model that predicts nutrient requirements and biological values of feeds for cattle, was modified for use with sheep. Published equations were added for predicting the energy and protein requirements of sheep, with a special emphasis on dairy sheep, whose specific needs are not considered by most sheep-feeding systems. The CNCPS for cattle equations that are used to predict the supply of nutrients from each feed were modified to include new solid and liquid ruminal passage rates for sheep, and revised equations were inserted to predict metabolic fecal N. Equations were added to predict fluxes in body energy and protein reserves from BW and condition score. When evaluated with data from seven published studies (19 treatments), for which the CNCPS for sheep predicted positive ruminal N balance, the CNCPS for sheep predicted OM digestibility, which is used to predict feed ME values, with no mean bias (1.1 g/100 g of OM; P > 0.10) and a low root mean squared prediction error (RMSPE; 3.6 g/100 g of OM). Crude protein digestibility, which is used to predict N excretion, was evaluated with eight published studies (23 treatments). The model predicted CP digestibility with no mean bias (-1.9 g/100 g of CP; P > 0.10) but with a large RMSPE (7.2 g/100 g of CP). Evaluation with a data set of published studies in which the CNCPS for sheep predicted negative ruminal N balance indicated that the model tended to underpredict OM digestibility (mean bias of -3.3 g/100 g of OM, P > 0.10; RMSPE = 6.5 g/100 g of OM; n = 12) and to overpredict CP digestibility (mean bias of 2.7 g/100 g of CP, P > 0.10; RMSPE = 12.8 g/100 g of CP; n = 7). The ability of the CNCPS for sheep to predict gains and losses in shrunk BW was evaluated using data from six studies with adult sheep (13 treatments with lactating ewes and 16 with dry ewes). It accurately predicted variations in shrunk BW when diets had positive N balance (mean bias of 5.8 g/d; P > 0.10; RMSPE of 30.0 g/d; n = 15), whereas it markedly overpredicted the variations in shrunk BW when ruminal balance was negative (mean bias of 53.4 g/d, P < 0.05; RMSPE = 84.1 g/d; n = 14). These evaluations indicated that the Cornell Net Carbohydrate and Protein System for Sheep can be used to predict energy and protein requirements, feed biological values, and BW gains and losses in adult sheep.  相似文献   
15.
Home monitoring of blood glucose (HMBG) concentrations has been recommended in the monitoring of human diabetics for 3 decades. During the last number of years, it also gained popularity in long-term follow-up of diabetic cats and dogs. The aim of this retrospective study was to evaluate the practical feasibility of and identify the major problems encountered with HMBG in diabetic pets. A standard questionnaire was filled in by owners of 9 diabetic pets monitored with HMBG. The need for more than 1 puncture to obtain a blood drop, the creation of a sufficient blood drop, the need for assistance in restraining the pet, and the resistance of the pet were the most frequently encountered problems during HMBG. The major obstacles for the owners to start with HMBG were also identified. In conclusion, HMBG is a practical and simple technique for most owners and, overall, owners were satisfied.  相似文献   
16.
The significance of food allergy as a primary cause for gastrointestinal disturbances in domestic animals, especially calves and piglets, is discussed. The immunological backgrounds and pathogenesis are described in some detail. The clinical and pathological manifestations in animals are related to those in man. Diagnostic possibilities, therapy and prevention, as far as known in animals, are mentioned and, based on human experiences, further extensions are proposed.  相似文献   
17.
18.

Between July and August 2018, two outbreaks of infectious laryngotracheitis caused the death of over 116,000 commercial poultry (layers and broilers) near the city of Windhoek, Namibia. A third outbreak occurred in September 2018 in the north of the country approximately 800 km from the original outbreaks. Sample collection and molecular epidemiological analyses revealed that the outbreaks were most likely caused by poor vaccination practices leading to the reversion to virulence of an ILT vaccine strain. The analyses also indicate that inaccurate declarations were made by one of the farms involved and that illegal movement of animals most likely occurred.

  相似文献   
19.
One-day-old leghorn chickens were used in a laboratory assay to determine the toxicity of crude extracts of the tick Argas (Persicargas) walkerae and of fractions obtained during the isolation procedure. Extracts of unfed and engorged larvae, nymphae and females were tested using this in vivo test system. Only extracts of replete A. (P.) walkerae larvae produced paralysis. A toxic fraction was isolated from replete larval extracts by gel-permeation and ion-exchange chromatography. This fraction with a pI of 4,5, showed 2 major bands corresponding to a Mr of 32 kDa and 60 kDa after SDS-polyacrylamide gel electrophoresis.  相似文献   
20.
Genetic variation is being used extensively for individual identification and linkage analysis, and may be useful for interpopulation studies. Previously, blood groups and biochemical variants in blood cell and serum proteins have been used to study (evolutionary) relationships in mammals. But genetic divergence and gene flow among closely related populations are difficult to measure with these classical markers because their mutation rate is so low that new mutations have not had sufficient time to appear and become fixed. So they have a small number of alleles and a relatively low level of heterozygosity. These markers are now replaced by DNA markers, mostly microsatellites. These microsatellite loci are useful genetic markers at which alleles differ in length due to differences in the number of short sequence motifs arranged adjacent to one another. They are abundantly distributed throughout the mammalian genome. They have a large number of alleles, a high level of heterozygosity and are inherited in true Mendelian fashion. These characteristics make them valuable for parentage control, linkage analysis, genome mapping and phylogenetic studies. In terrestrial vertebrates with limited mobility, genetic differentiation often increases with the distance between populations or corresponds to the extent of geographic and habitat barriers (R oy et al. 1994). Investigations of short tandem repeats yield a considerable volume of genetic data regarding the similarities and divergence times of different cattle populations. Microsatellite markers are suitable for the estimation of these parameters as they are not generally subject to direct selection and environmental influences. Computation of genetic distances based on data from several loci can be used to evaluate the taxonomic relationship between populations. The aim of this study was to estimate the relative genetic variability between Belgian cattle breeds and to reconstruct the evolutionary relationship among them, also using two small genetically isolated cattle-like populations.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号