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   4448篇
  免费   274篇
  国内免费   10篇
林业   217篇
农学   238篇
基础科学   48篇
  746篇
综合类   335篇
农作物   188篇
水产渔业   208篇
畜牧兽医   2208篇
园艺   111篇
植物保护   433篇
  2021年   43篇
  2020年   79篇
  2019年   61篇
  2018年   88篇
  2017年   101篇
  2016年   79篇
  2015年   64篇
  2014年   85篇
  2013年   196篇
  2012年   170篇
  2011年   226篇
  2010年   178篇
  2009年   165篇
  2008年   211篇
  2007年   175篇
  2006年   174篇
  2005年   163篇
  2004年   146篇
  2003年   145篇
  2002年   168篇
  2001年   129篇
  2000年   116篇
  1999年   108篇
  1998年   52篇
  1997年   34篇
  1996年   40篇
  1995年   36篇
  1994年   46篇
  1993年   54篇
  1992年   83篇
  1991年   74篇
  1990年   79篇
  1989年   72篇
  1988年   42篇
  1987年   58篇
  1986年   47篇
  1985年   56篇
  1984年   61篇
  1983年   51篇
  1982年   53篇
  1980年   33篇
  1979年   39篇
  1978年   45篇
  1977年   45篇
  1976年   43篇
  1975年   34篇
  1974年   41篇
  1972年   34篇
  1971年   34篇
  1969年   42篇
排序方式: 共有4732条查询结果,搜索用时 15 毫秒
981.
The relationship between antibody titres in the microtitration serum agglutination test and the complement fixation test in bovine brucellosis is described. For low and high MSAT values there is good agreement between the 2 tests. This is not the case for MSAT values between 54 and 338 IU/ml. For practical reasons, results falling into this category cannot all be repeated. Repetitions are so structured that less than 4% of the tests need to be repeated. If the level of repetitions should show an increase above 4%, it is assumed that technical or human error has occurred.  相似文献   
982.
Septic arthritis was induced in one antebrachiocarpal joint of seven horses by the intra-articular injection of 1 mL Staphylococcus aureus suspension containing a mean of 10(5) colony-forming units. Twenty-four hours after inoculation, four horses were treated by regional perfusion with 1 g of gentamicin sulfate, and three horses received 2.2 mg/kg gentamicin sulfate intravenously (IV) every 6 hours. Synovial fluid was collected for culture and cytology at regular intervals, and the synovial membranes were collected for culture and histologic examination at euthanasia 24 hours after the first treatment. Gentamicin concentration in the septic synovial fluid after three successful perfusions was 221.2 +/- 71.4 (SD) micrograms/mL; after gentamicin IV, it was 7.6 +/- 1.6 (SD) micrograms/mL. The mean leukocyte count in the inoculated joints decreased significantly by hour 24 in the successfully perfused joints. Terminal bacterial cultures of synovial fluid and synovial membranes were negative in two horses with successfully perfused joints. S. aureus was isolated from the infected joints in all three horses treated with gentamicin IV.  相似文献   
983.
Fire is an important factor in the Imperata grassland ecosystem. It prevents or slows down the natural succession to shrubs and/or secondary forest vegetation and is a major threat to (agro)forestry options for Imperata grassland rehabilitation. Forest fires can also be a primary cause of the extension of Imperata grasslands. In this review an attempt is made to integrate biophysical and socioeconomic aspects of the causation of fires in a conceptual model. Fire effects on vegetation are examined. The management options at the level of a farmer, a village community and a national government are analyzed.  相似文献   
984.
The bioavailability and pharmacokinetics of ibuprofen, a nonsteroidal antiinflammatory drug, was studied in healthy Shetland ponies. Ibuprofen was administered IV, as a suspension, and as a solid solution oral paste to ponies from which food was withheld. The suspension paste was also administered to ponies that received hay and water ad libitum. Both formulations had an absolute bioavailability of about 80%. Bioavailability was not influenced by feeding.  相似文献   
985.
The growth of flower buds in a gynoecious cucumber cultivar was studied at 15, 21 and 27°C. Competition between buds in the same node was measured as the ratio of the growth rates of individual buds. This competition was stronger at 21 and 27 than at 15°C. At 15°C, at least 3 buds were about equally strong; at 21°C, 2 buds developed fast and suppressed the other buds; at 27°C, the first bud which developed suppressed all other buds. When plants were transferred from one temperature to another, the growth-rate ratio between buds in older nodes was maintained. In nodes formed in the new temperature regime, the growth-rate ratio was determined by the new temperature.  相似文献   
986.
Serologic diagnosis of ovine contagious agalactia (Mycoplasma agalactiae) with the enzyme-linked immunosorbent assay (ELISA) developed by Agence Fran?aise de Sécurité Sanitaire des Aliments (AFSSA) may produce a few false-positive (FP) and false-negative (FN) results. When the prevalence of disease is low, these erroneous results may generate problems for eradication schemes. To prevent this, 2 commercial ELISAs were compared with the AFSSA ELISA. Flocks of known status were selected and classified into 4 categories: true positive (TP), FP, true negative (TN), and FN; 20 sheep per flock were submitted for blood sampling. A flock was considered positive when at least 1 out of 20 sera was positive or 2 sera were doubtful. In the flock, the diagnostic sensitivity of the 3 kits was very good (100%), and the diagnostic specificity showed an improvement from 46% (AFSSA test) to 88% and 92% (commercial tests). Considering individual animals, very few positive ewes were detected within TN or FP flocks; the proportion of positive ewes varied greatly from one kit to another (48% to 82%) within TP flocks. The kinetics of antibody response in sheep experimentally infected with various field strains of M. agalactiae were quite similar with all 3 ELISAs. The agreement between the 3 tests, assessed using the kappa value, varied from moderate to good (respective values of 0.56, 0.61, and 0.86). The 2 commercial ELISAs showed better performances, probably because of a superior analytical sensitivity, and are a good alternative for the serodiagnosis of contagious agalactia in sheep.  相似文献   
987.
Small dogs and cats, naturally infected with nematodes and cestodes, were used in a critical test under laboratory conditions to determine the palatability and efficacy of flubendazole as a past formulation. Subsequently, a control test in dogs was conducted under field conditions. A 4.4% past formulation was given at a dosage of 22 mg/kg of body weight once a day for 2 or 3 consecutive days. In a critical test in dogs, the efficacy against Toxocara canis was 97.4% after a 2-day administration and 100% after 3 days. Toxascaris leonina seemed to be the most susceptible worm species, since either 2 or 3 treatments were 100% active. The efficacy against Uncinaria stenocephala was 97.5% after 2 treatments; the same dose level for 3 days improved the efficacy to 100%. The efficacy was 100% for the removal of Trichuris vulpis after a daily dosage for 2 days and 96.7% after 3 days. One of 2 dogs infected with Taenia pisiformis was cleared of the infection after a 2-day treatment, and 3 of 4 dogs were cleared after a 3-day regimen. All cats were cleared of Toxocara cati after 2 or 3 days of treatment. One of 2 cats infected with Hydatigera taeniaeformis was cleared of the infection after a 2-day treatment; a 3-day treatment in 7 cats was 100% effective. The results in the laboratory test in dogs were confirmed under field conditions by a control test, based on the reduction of eggs per gram of feces count after treatment. The paste formulation was well accepted by all dogs and cats without any side effects.  相似文献   
988.
The Herd Health and Production Service program for use in veterinary dairy practice is comprised of a basic and a flexible system. The basic system is a uniform system of data recording, standard veterinary activities and problem detection. In problem detection 4 index lists play a key role. The 4 comprise of the parameters or index figures that are relevant in monitoring the efficiency of milk production, calf rearing and cow replacement. Data on milk production, health status and reproduction of both individual animals and the herd are collected by the farmer and the veterinarian and transformed into index figures.This paper introduces index list “3”, with index figures for the monitoring of calf rearing and cow culling as parts of a herd health program. The development, implementation and significance of the index figures are presented. The index figures serve to detect unsatisfactory farm situations or problems in calf rearing and in cow culling. They trigger further investigation and aid the solution to and prevention of problems. Relationships with farm parameters mentioned in other index lists are also considered. Objectives and reference values where applicable are provided.  相似文献   
989.
The Cornell Net Carbohydrate and Protein System (CNCPS) has equations for predicting nutrient requirements, feed intake, and feed utilization over wide variations in cattle (frame size, body condition, and stage of growth), feed carbohydrate and protein fractions and their digestion and passage rates, and environmental conditions. Independent data were used to validate the ability of the CNCPS to predict responses compared to National Research Council (NRC) systems. With DMI in steers, the CNCPS had a 12% lower standard error of the Y estimate (Sy.x) and three percentage units less bias than the NRC system. For DMI in heifers, both systems had a similar Sy.x but the NRC had four percentage units less bias. With lactating dairy cows' DMI, the CNCPS had a 12% lower Sy.x. Observed NEm requirement averaged 5% under NRC and 6% under CNCPS predicted values at temperatures above 9 degrees C but were 18% over NRC and 9% under CNCPS at temperatures under 9 degrees C. Energy retained was predicted with an R2 of .80 and .95 and a bias of 8 and 4% for the NRC and CNCPS, respectively. Protein retained was predicted with an R2 of .75 and .85 with a bias of 0 and -1% for NRC and CNCPS, respectively. Biases due to frame size, implant, or NEg were small. Body condition scores predicted body fat percentage in dairy cows with an R2 of .93 and a Sy.x of 2.35% body fat. The CNCPS predicted metabolizable protein allowable ADG with a bias of 1.6% with a Sy.x of .07 kg compared to values of -30% and .10 kg, respectively for the NRC system.  相似文献   
990.
The Cornell Net Carbohydrate and Protein System (CNCPS) has a kinetic submodel that predicts ruminal fermentation. The ruminal microbial population is divided into bacteria that ferment structural carbohydrate (SC) and those that ferment nonstructural carbohydrate (NSC). Protozoa are accommodated by a decrease in the theoretical maximum growth yield (.50 vs .40 g of cells per gram of carbohydrate fermented), and the yields are adjusted for maintenance requirements (.05 vs .150 g of cell dry weight per gram of carbohydrate fermented per hour for SC and NSC bacteria, respectively). Bacterial yield is decreased when forage NDF is < 20% (2.5% for every 1% decrease in NDF). The SC bacteria utilize only ammonia as a N source, but the NSC bacteria can utilize either ammonia or peptides. The yield of NSC bacteria is enhanced by as much as 18.7% when proteins or peptides are available. The NSC bacteria produce less ammonia when the carbohydrate fermentation (growth) rate is rapid, but 34% of the ammonia production is insensitive to the rate of carbohydrate fermentation. Ammonia production rates are moderated by the rate of peptide and amino acid uptake (.07 g of peptide per gram of cells per hour), and peptides and amino acids can pass out of the rumen if the rate of proteolysis is faster than the rate of peptide utilization. The protein-sparing effect of ionophores is accommodated by decreasing the rate of peptide uptake by 34%. Validation with published data of microbial flow from the rumen gave a regression with a slope of .94 and an r2 of .88.  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