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   26872篇
  免费   826篇
林业   4510篇
农学   1632篇
基础科学   168篇
  5156篇
综合类   1420篇
农作物   2492篇
水产渔业   2479篇
畜牧兽医   5696篇
园艺   1303篇
植物保护   2842篇
  2023年   107篇
  2022年   130篇
  2021年   239篇
  2020年   236篇
  2019年   161篇
  2018年   3055篇
  2017年   3008篇
  2016年   1576篇
  2015年   443篇
  2014年   455篇
  2013年   673篇
  2012年   1633篇
  2011年   2820篇
  2010年   2426篇
  2009年   1551篇
  2008年   1971篇
  2007年   2170篇
  2006年   571篇
  2005年   672篇
  2004年   625篇
  2003年   628篇
  2002年   449篇
  2001年   285篇
  2000年   282篇
  1999年   217篇
  1998年   68篇
  1997年   57篇
  1996年   42篇
  1995年   63篇
  1994年   39篇
  1993年   45篇
  1992年   86篇
  1991年   67篇
  1990年   62篇
  1989年   60篇
  1988年   64篇
  1987年   47篇
  1986年   47篇
  1985年   46篇
  1984年   42篇
  1983年   35篇
  1979年   36篇
  1974年   26篇
  1973年   21篇
  1972年   23篇
  1971年   23篇
  1970年   27篇
  1969年   27篇
  1968年   29篇
  1967年   21篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
This paper presents empirical evidence on the impact of socio-economic factors on the adoption of agroforestry practices in Cameroon. The analysis uses primary farm-level data collected from June to December 1996. Three major provinces of the country were covered, namely Centre, Southwest and Northwest Several agroforestry technologies have been promoted among farmers in the zone, including alley farming, improved fallow, live fencing, cut-and-carry fodder and apiculture. The status of adoption of each agroforestry practice is described and factors that affect adoption identified. These are gender of farmer, household family size, level of education, farmer’s experience, membership within farmers’ associations, contact with research and extension, security of land tenure, agroecological zone, distance of the village from nearest town, village accessibility and income from livestock. Research findings indicate that since factors affecting farmers’ adoption of agroforestry practices differ across techniques, generalisation is to be avoided.  相似文献   
12.
SMEDWI-2 is a PIWI-like protein that regulates planarian stem cells   总被引:1,自引:0,他引:1  
We have identified two genes, smedwi-1 and smedwi-2, expressed in the dividing adult stem cells (neoblasts) of the planarian Schmidtea mediterranea. Both genes encode proteins that belong to the Argonaute/PIWI protein family and that share highest homology with those proteins defined by Drosophila PIWI. RNA interference (RNAi) of smedwi-2 blocks regeneration, even though neoblasts are present, irradiation-sensitive, and capable of proliferating in response to wounding; smedwi-2(RNAi) neoblast progeny migrate to sites of cell turnover but, unlike normal cells, fail at replacing aged tissue. We suggest that SMEDWI-2 functions within dividing neoblasts to support the generation of cells that promote regeneration and homeostasis.  相似文献   
13.
Feline haemoplasma infection can cause haemolytic anaemia. The natural method of transmission of haemoplasmas between cats is currently unknown but the nature of some of the risk factors for infection suggests that saliva may act as a mode of transmission. The aim of this study was to determine if Mycoplasma haemofelis (Mhf) and 'Candidatus Mycoplasma haemominutum' (CMhm) DNAs could be amplified from saliva and salivary gland samples collected from haemoplasma-infected cats.  相似文献   
14.
Liveweight gain was evaluated in tropical Dorper X Pelibuey lambs under intensive continuous grazing of native grasslands dominated by Paspalum notatum (PN) or Axonopus compressus (AC) in the subtropics of Central Mexico. Two trials were undertaken. Trial 1 lasted 12 weeks with 10 lambs (initial weight 18 +/- 2.57 kg, 3 months old) per treatment in 2002, and Trial 2 for 13 weeks with 8 lambs (initial weight 24.0 +/- 2.0 kg, 4 months old) per treatment. Lambs were weighed once per week, and liveweight change was estimated by linear regression over day of the experiment, using individual regression coefficients as unbiased estimates of daily liveweight change; analysed in a random block design. Lambs on Trial 1 gained 0.061 kg/lamb/day on PN and 0.047 kg/lamb/day on AC (P > 0.05) at an overall mean stocking rate of 25 lambs/ha. In Trial 2, liveweight gain was significantly larger in PN (0.060 kg/lamb/day) than on AC (0.043 kg/lamb/day) (P < 0.05), at a mean stocking rate of 21.5 lambs/ha. It is concluded that intensive continuous grazing of native grasslands in the subtropics of the highlands of Central Mexico enables moderate liveweight gains for weaned lambs during the rainy season; with better results in grasslands dominated by Paspalum notatum.  相似文献   
15.
16.
The morphology of Onchocerca lupi, responsible for canine ocular onchocercosis, is unique within the genus. Earlier analyses of the 5S ribosomal RNA gene spacer region sequence of the parasite and the 16S ribosomal RNA gene sequence of its Wolbachia endosymbiotic bacteria (Rickettsiales) supported the morphological and biological arguments that O. lupi is a distinct species. However, the exact phylogenetic position of O. lupi and its endosymbiont could not be unambiguously determined. Herein we report analyses based on the mitochondrial cytochrome oxidase I (COI) gene of the filarial species and the Wolbachia surface protein (wsp) and the bacterial cell-cycle ftsZ genes of their wolbachiae. Our results indicate that O. lupi separated from other Onchocerca spp. early in evolution. This is in line with the previous morphological analysis demonstrating that O. lupi is an atypical Onchocerca species showing both primitive and evolved characters. The phylogenetic trees generated for the COI sequences of filariae and the wsp and ftsZ sequences of their wolbachiae were congruent with each other, which supports the hypothesis that nematodes and their Wolbachia endobacteria share a long co-evolutionary history.  相似文献   
17.
This study compared vitamin A, vitamin E, selenium (Se), and L-lactate in blood and synovial fluid in 2 groups of 6 dogs; a control group (without OA) and an osteoarthritic group with spontaneous cranial cruciate ligament rupture and OA. Concentrations of vitamin E were significantly higher in serum than in synovial fluid in both OA (P = 0.006) and control (P = 0.0008) groups. Vitamin E concentration in synovial fluid was significantly higher in the OA group than in the control group (P = 0.009). Concentrations of Se were significantly higher in serum than in synovial fluid in both OA (P = 0.003) and control (P = 0.0006) groups. There were no significant differences in levels of Se, vitamin A, and L-lactate between the 2 groups. This is the first study to show an increased concentration of vitamin E in the synovial fluid of dogs with OA compared with dogs that did not have OA.  相似文献   
18.
19.
The therapeutic value of antibiotics depends on the susceptibility of the infecting microorganism and the pharmacological profile of the drugs. To assess the value of an antibiotic combination of polymyxin B and miconazole this study examined the in vitro synergistic potential of the two drugs on Gram-negative and Gram-positive bacteria and yeast. Antifungal and antibacterial activity was tested by minimum inhibitory concentration (MIC) of broth macrodilution and urea broth microdilution, by fluorescence microscopy and flow cytometry. Synergism was calculated using the fractional inhibitory concentration index (FICi). With Staphylococcus intermedius as target we found up to an eightfold reduction of the individual MICs when both drugs were combined. However, the FICi was 0.63 suggesting no real interaction between the two drugs. With Escherichia coli, Pseudomonas aeruginosa, and Malassezia pachydermatis as targets the antimicrobial drug combination reduced the MICs of polymyxin B and miconazole from fourfold to hundredfold resulting in FICi between 0.06 and 0.5 which defines a synergistic action. Thus, if polymyxin B and miconazole are combined their effect is greater than the sum of the effects observed with polymyxin B and miconazole independently, revealing bactericidal and fungicidal synergism. Our results indicate a strong therapeutic value for the combination of these antimicrobial agents against Gram-negative bacteria and yeast and a weaker value against Gram positive bacteria for clinical situations where these pathogens are involved.  相似文献   
20.
Olivier M.  Lepage  DMV  MSc  Renée  Léveillé  DMV  Luc  Breton  DMV  MSc  Marcel  Marcoux  DMV  MSc 《Veterinary radiology & ultrasound》1995,36(5):384-386
An 11-month-old Thoroughbred colt was presented with a hard swelling at the proximal third of the right 4th metatarsal bone. A medial dislocation of the deep digital flexor tendon ( flexor digitorum profundus ) was also observed on the same leg. On the plantaroproximal-plantarodistal projection of the calcaneus, there was flattening and shortening of the sustentaculum tali. The smooth bony proliferation at the proximal third of the right 4th metatarus was compatible with a chronic splint bone fracture. This report describes a medial deep digital flexor dislocation associated with hypoplasia of the sustentaculum tali .  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