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   431篇
  免费   20篇
  国内免费   1篇
林业   34篇
农学   22篇
  68篇
综合类   17篇
农作物   8篇
水产渔业   64篇
畜牧兽医   178篇
园艺   2篇
植物保护   59篇
  2023年   3篇
  2022年   7篇
  2021年   10篇
  2020年   5篇
  2019年   2篇
  2018年   12篇
  2017年   13篇
  2016年   14篇
  2015年   17篇
  2014年   22篇
  2013年   42篇
  2012年   28篇
  2011年   23篇
  2010年   15篇
  2009年   9篇
  2008年   25篇
  2007年   23篇
  2006年   27篇
  2005年   18篇
  2004年   14篇
  2003年   14篇
  2002年   10篇
  2001年   7篇
  2000年   8篇
  1999年   7篇
  1998年   5篇
  1997年   3篇
  1996年   2篇
  1992年   4篇
  1991年   2篇
  1990年   3篇
  1989年   3篇
  1988年   7篇
  1987年   3篇
  1986年   3篇
  1985年   4篇
  1984年   4篇
  1983年   2篇
  1982年   4篇
  1981年   2篇
  1980年   2篇
  1979年   5篇
  1977年   3篇
  1976年   3篇
  1975年   3篇
  1974年   4篇
  1973年   1篇
  1969年   2篇
  1965年   1篇
  1964年   1篇
排序方式: 共有452条查询结果,搜索用时 15 毫秒
91.
Portal vein aneurysm (PVA) is a rare abnormal dilatation of the portal vein, which has not been reported in dogs. We describe the findings of ultrasound and computed tomography in a case of PVA in a young male toy poodle, with the final diagnosis established by explorative surgical observation. The dog had an aneurysmal fusiform dilatation in the extrahepatic portal vein with portal hypertension and multiple portsystemic shunts. This is the first report of canine PVA.  相似文献   
92.
Genetically modified corn has been approved as an animal feed in several countries, but information about the fate of genetically modified DNA and protein in vivo is insufficient. Genetically modified corn Bt11 is developed by inserting a recombinant DNA sequence encoding insecticidal Cry1Ab protein from Bacillus thuringiensis subsp. kurstaki. We examined the presence of corn intrinsic and recombinant cry1Ab gene by PCR, and the Cry1Ab protein by immunological tests in the gastrointestinal contents of five genetically modified corn Bt11-fed and five nongenetically modified corn-fed pigs. Fragments of corn zein (242 bp), invertase (226 bp) and of ribulose-1,5-bisphosphate carboxylase/ oxygenase genes (1,028 bp) were detected in the gastrointestinal contents of both Bt11 and nongenetically modified corn-fed pigs. Fragments of recombinant cry1Ab gene (110 bp and 437 bp) were detected in the gastrointestinal contents of the Bt11-fed pigs but not in the control pigs. Neither corn intrinsic nor cry1Ab gene fragments were detected in the peripheral blood by PCR. The gastrointestinal contents were positive for Cry1Ab protein by ELISA, immunochromatography, and immunoblot; however, these methods did not work for blood and precluded conclusions about any potential absorption of the protein. These results suggest that ingested corn DNA and Cry1Ab protein were not totally degraded in the gastrointestinal tract, as shown by their presence in a form detectable by PCR or immunological tests.  相似文献   
93.
Inflammatory cytokine mRNA expression in the lymphatic organs of neonatal, 1-month-old and adult pigs was compared. The mRNA expression of interleukin (IL)-1β, IL-6, IL-18 and tumor necrosis factor (TNF)- in the spleen, thymus, tonsil and popliteal and mesenteric lymph nodes was investigated by semi-quantitative RT-PCR. Stronger IL-1β mRNA expression was observed in the 1-day-old and 1-month-old piglets than in the adult pigs. In thymus, tonsil and mesenteric lymph node, IL-1β mRNA expression in 1-day-old piglets was stronger than in 1-month-old pigs. The expression of IL-6 mRNA in the 1-day-old and 1-month-old tonsil tended to be stronger than in the adult pigs. IL-18 and TNF- mRNA expression was constant in all the samples examined. The expression of IL-1β and IL-6 mRNA may reflect an inflammatory reaction against the exo- and endogenous foreign bodies occurring in the lymphatic organs, especially in the tonsil, of neonatal piglets.  相似文献   
94.
The kinetic constants of a variety of substituted phenyl N-methyl- and N,N-dimethylcarbamates, which inhibit bovine erythrocyte acetylcholinesterase, were determined by various experimental procedures. A procedure in the presence of a chromogenic substrate was developed, based on the suggestion of Hart and O'Brien, and was compared with the conventional Main method. The dissociation equilibrium constant, Kd, and the carbamylation rate constant, k2, were shown to apparently depend on the inhibitor concentration range used for the determination in both procedures. Assuming that the binding of further inhibitor molecules to the reversible complex and the carbamylated enzyme is significant under conditions with high inhibitor concentrations, the concentration dependence of the kinetic constants was nicely delineated. It is indicated that reliable constants are obtainable with a rather low inhibitor concentration range, whose product by ki is of the order of 0.2–1.0 min?1.  相似文献   
95.
In lindane-treated house flies, a cis-dehydrogenated metabolite, (3645)-hexachlorocyclohexene, was identified by gas-liquid chromatography and mass spectrometry. The in vitro metabolism study showed that in the presence of NADPH the microsomal fraction of house flies converted lindane to three hexane-soluble metabolites. This conversion was inhibited by piperonyl butoxide, SKF-525A, and carbon monoxide. These metabolites were identified as (3645)-hexachlorocyclohexene, (3645)- and (3465)-pentachlorocyclohexene (PCCHE) by gas-liquid chromatography. They, as well as lindane, were excellent substrates for the reaction with the postmicrosomal fraction in the presence of glutathione. While the reaction with lindane-d6 showed a significant deuterium isotope effect (6.82), that of (3645)-PCCHE-d5 did not (1.18). Enzymatic conjugation with glutathione probably occurs at the stage of PCCHE.  相似文献   
96.
 Rice reflectance was measured to determine the spectral regions most sensitive to leaf blast infection with a multispectral radiometer. As disease severity increased, reflectance also increased in the 400–500 nm (blue), 570–700 nm (red), and 900–2000 nm regions but decreased in the 500–570 nm and 700–900 nm regions. The increased reflectance in the blue and red regions may be attributed to decreased chlorophyll and carotenoid contents in response to the blast infection. The maximum and minimum reflectance differences occurred at 680 nm and 760 nm for the nondiseased and diseased rice, respectively. The spectral location of maximum sensitivity was 675 nm regardless of disease severity. Rice reflectance ratios were evaluated as indicators of leaf blast severity. Two ratios, R550/R675 (reflectance at 550 nm divided by reflectance at 675 nm), and R570/R675 quantified the significant disease severity. These wavelengths were selected based on the sensitivity minima and maxima. The ratios of nondiseased rice plants varied depending on growth stage. The variation in ratios must be considered when they are used to estimate leaf blast severity. Received: April 2, 2002 / Accepted: August 12, 2002  相似文献   
97.
ABSTRACT:   Horse mackerel and tilapia surimi were subjected to six different heat and pressure treatments in order to compare gelation characteristics of easy- and difficult-setting gels, that is, temperature dependence, by observing rheological properties and microscopic molecular mobility. The stress–relaxation and proton spin–spin relaxation time (1H T 2) of water were measured for all treated gels. Horse mackerel gel demonstrated higher elasticity, large distribution of the stress–relaxation process, and smaller water 1H T 2 than tilapia in both heat and pressure treatments. The water 1H T 2 was steeply increased in the pressure treatment at around 294 MPa for both fishes. In contrast, the 1H T 2 rarely changed in the heat treatment in spite of the considerable change in rheological properties. From the experimental results, it is considered that the gelation of horse mackerel (easy setting) surimi is induced by highly unfolding and re-aggregation of protein, which contributes to the formation of a strong network structure compared with tilapia in both heat and pressure treatments, and that pressure treatments hardly improve the gel strength of tilapia (difficult setting) surimi. The water 1H T 2 measurement was used effectively in order to study gelation characteristics of easy- and difficult-setting fish through observing its molecular dynamics.  相似文献   
98.
ABSTRACT:   Immature Pacific bluefin tuna Thunnus orientalis , tagged with archival tags, were released near Tsushima Island in the East China Sea (ECS) during the winters of 1995, 1996 and 1997. Geolocations were estimated using the archival tags from recovered fish. These data, together with sea surface temperature (SST) data from satellite remote sensing, are used to describe the habitat used by these bluefin in the ECS from January to June for 3 years (1996, 1997, 1998), and to asses the effect of water temperature on fish distribution and movement. The results indicate that their geolocations ranged from the area north-east of Tsushima Island to the offshore area in the south-west. However, the area of highest density differed among years, being furthest south in 1996 and furthest north in 1998. The differences were probably caused by changes in SST associated with La Niña (1996) and El Niño (1998) events. Another densely populated area was identified in offshore waters of latitude 28–30 °N in 1996 (only), on the cold side of the Kuroshio front. These fish may have been prevented from moving northwards by an intrusion of Kuroshio water of approximately 25°C into the region immediately to the north-east.  相似文献   
99.
100.
An enzyme-linked immunosorbent assay was developed for the determination of canine beta2-microglobulin (beta2-m) in plasma and urine. The detectable sensitivity for pure canine beta2-m was 0.05 microg/l and the analytical range was 0.1 to 50 microg/l. The mean analytical recovery when pure canine beta2-m was added to normal plasma was 101.9%. The mean analytical recovery in the urine was 102.1%. The intra-day variation coefficient was 3.1% in plasma, 4.3% in serum and 1.9% in urine. No difference was found between the concentration of beta2-m in plasma and serum (n=17). The concentration of beta2-m in the plasma of normal dogs was 1.82 +/- 0.57 mg/l (n=31). The mean excretion in 24 hr urine collected from normal dogs was 17.6 +/- 9.2 microg/l, 0.22 +/- 0.12 microg/kg of body weight or 14.2 +/- 9.4 microg/g of urine creatinine. The beta2-m creatinine index of random urine samples was 23.5 +/- 16.6 microg/g (n=26). There was a close correlation between the beta2-m creatinine index of 24 hr urine samples and that of random urine samples (r=0.872).  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