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   60318篇
  免费   3417篇
  国内免费   36篇
林业   2426篇
农学   1851篇
基础科学   301篇
  6616篇
综合类   10228篇
农作物   2087篇
水产渔业   2798篇
畜牧兽医   33010篇
园艺   706篇
植物保护   3748篇
  2018年   895篇
  2017年   912篇
  2016年   808篇
  2015年   773篇
  2014年   839篇
  2013年   2575篇
  2012年   1670篇
  2011年   2020篇
  2010年   1269篇
  2009年   1250篇
  2008年   1879篇
  2007年   1846篇
  2006年   1727篇
  2005年   1581篇
  2004年   1501篇
  2003年   1545篇
  2002年   1470篇
  2001年   1809篇
  2000年   1783篇
  1999年   1462篇
  1998年   620篇
  1997年   606篇
  1996年   546篇
  1995年   641篇
  1994年   600篇
  1993年   571篇
  1992年   1221篇
  1991年   1369篇
  1990年   1258篇
  1989年   1265篇
  1988年   1163篇
  1987年   1136篇
  1986年   1194篇
  1985年   1194篇
  1984年   961篇
  1983年   900篇
  1982年   582篇
  1979年   891篇
  1978年   701篇
  1977年   694篇
  1976年   712篇
  1975年   715篇
  1974年   866篇
  1973年   843篇
  1972年   812篇
  1971年   728篇
  1970年   769篇
  1969年   734篇
  1968年   650篇
  1967年   656篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
Cerebral phaeohyphomycosis in a dog   总被引:2,自引:0,他引:2  
Cerebral phaeohyphomycosis was diagnosed in a 9-year-old spayed dog that had a series of epileptic convulsions a day before death. About 6 weeks before her death, she had been treated for severe demodectic mange. During this period, persistent leukopenia, lymphocytopenia, and thrombocytopenia were found by blood analyses. At necropsy, multiple large pyogranulomatous lesions were found in the cerebrum and meninges. Dematiaceous fungi with brown, branching, septate hyphae and budding yeasts were found within tissue cells and in the necrotic areas.  相似文献   
192.
193.
194.
Three experiments were conducted to test the hypothesis that methionine, isoleucine, valine or nitrogen either singly or in combination are limiting in an 11% crude protein, lysine-tryptophan-threonine-supplemented, corn-soybean meal diet for growing pigs. A 16% crude protein diet was used as a positive control in each experiment and all amino acid additions were made, at a minimum, to equal requirements. Average initial weights were 21.3 kg, 23.0 kg and 19.1 kg in Exp. 1, 2 and 3, respectively. The experiments averaged 4 wk in duration. In Exp. 1 and 2, neither the addition of glutamic acid as a source of nitrogen, nor methionine to the 11% diet resulted in any improvement (P greater than .20) in rate or efficiency of growth. Addition of the combination of isoleucine and valine to the 11% diet resulted in an increase (P less than .05) in both growth rate and feed efficiency to a level not different (P greater than .20) from that of the pigs consuming the positive control diet. The addition of valine to the 11% crude protein diet with supplemental lysine, tryptophan and threonine (Exp. 3) caused an improvement in daily gain (P less than .05) but not feed efficiency (P greater than .10). Isoleucine addition tended to reduce pig performance. The results of these experiments suggest that an 11% crude protein, corn-soybean meal diet fortified with lysine, tryptophan and threonine is not limiting in sulfur amino acids or nitrogen. Valine may be the only limiting amino acid.  相似文献   
195.
Positron emission tomography (PET) is often used to stage and monitor human cancer and has recently been used in a similar fashion in veterinary medicine. The most commonly used radiopharmaceutical is 2‐Deoxy‐2‐[18F]‐Fluoro‐d ‐glucose (18F‐FDG), which is concentrated and trapped within cells that use glucose as their energy substrate. We characterized the normal distribution of 18F‐FDG in 10 healthy Hispaniolan Amazon parrots (Amazona ventralis) by performing whole body PET scans at steady state, 60 min after injection. Significant variability was found in the intestinal activity. Avian species are known to reflux fluid and electrolytes from their cloaca into their colon. To evaluate reflux as the cause of variability in intestinal distribution of 18F‐FDG, dynamic PET scans were performed on the coelomic cavity of six Hispaniolan Amazon parrots from time 0 to 60 min postinjection of radiotracer. Reflux of radioactive material from the cloaca into the colon occurred in all birds to varying degrees and occurred before 60 min. To evaluate the intestinal tract of clinical avian patients, dynamic scans must be performed starting immediately after injection so that increased radioactivity due to metabolism or hypermetabolic lesions such as cancer can be differentiated from increased radioactivity due to reflux of fluid from the cloaca.  相似文献   
196.
Pilus proteins from Escherichia coli serotypes O1, O2, and O78 pathogenic to poultry were compared with regard to their antigenic relatedness and partial amino acid sequences. Agglutination, immunodiffusion, and immunoblot assays with polyclonal antibodies to these pili showed that these pili not only share some common antigens but also contain antigens unique to each pilus. The partial amino-terminal amino acid sequences support our earlier findings that the pili are different but contain some structural homologies.  相似文献   
197.
Growth and reproductive data were obtained on 779 beef heifers at the San Juan Basin Research Center, Hesperus, Co. Genetic parameters were estimated for age of puberty (AOP), age of first calving (AOC), julian day of first calving (DOC), julian day of second calving (DOSC), birth weight, weaning weight, yearling weight, and average daily gain from weaning to yearling and to cycling weights. The least squares model included birth year, age of dam and breed as fixed effects, sire/breed as a random variable, and day of birth and percent inbreeding as covariates. Day of birth was not included in the analyses of AOC, DOC or DOSC. Paternal half-sib estimates of heritability were: AOP, .10 +/- .17; AOC, .01 +/- .12; DOC, .09 +/- .13 and DOSC, .36 +/- .18. Genetic and phenotypic correlations were generally favorable, but genetic correlations were variable with large standard errors. Inbreeding had a detrimental effect on reproductive traits, and a seasonal effect was present for AOP.  相似文献   
198.
This study aimed to investigate the distribution of Malassezia species yeasts on the skin of healthy horses. Acetate tape samples were obtained from the lip, axilla, interbulbar region, groin and anus of 12 healthy horses. The samples were stained and examined microscopically and sites harbouring yeast-like organisms were identified. Contact plates were applied to the skin at these sites and cultured at 26 degrees C and 32 degrees C. No growth was obtained on horse blood, Sabouraud's dextrose or modified Dixon's agar. A pure growth of a Malassezia-type organism was obtained on Sabouraud's dextrose agar enriched with oleic acid when it was incubated at 30 degrees C. It was identified by 26S ribosomal DNA D1/D2 sequence analysis as a member of the genus Malassezia, and most closely related to Malassezia sympodialis. However, the level of sequence divergence indicated that it was a novel species.  相似文献   
199.
The Nc-Spain 7 isolate of Neospora caninum, which was newly obtained from an asymptomatic congenitally infected calf, demonstrated a similar virulence as Nc-1 strain in mouse models. The aim of this study was to characterize the pathogenesis of Nc-Spain 7 isolate in cattle after experimental infection at 65 days of gestation. For this purpose, thirteen pregnant heifers were divided into three groups as follows: group A: 7 heifers inoculated with 1×10(8) tachyzoites of Nc-Spain 7 isolate; group B: 4 heifers inoculated with 1×10(8) tachyzoites of Nc 1 strain; and group C: 2 heifers received PBS. Serum samples were collected weekly and heparinized blood samples were collected three times (0, 28 and 42 days after inoculation) by jugular venipuncture. Placenta and fetal tissue samples were collected at time of necropsy. Specific antibody response in the dams was tested by IFAT, indirect ELISA, and rNcGRA7 and rNcSAG4 based-ELISA. Specific antibody response in fetal fluids was tested by IFAT. IFN-γ production was measured after in vitro culture of PBMC and the supernatant was assessed using a commercial kit (BOVIGAM). A significant increase in N. caninum antibody responses was detected in groups A and B by IFAT and by i-ELISA from day 14 after inoculation onwards. Besides, antibody response against rNCGra7 protein was also detected in all inoculated heifers by rNcGra7-based ELISA. Four fetuses from group A and one from group B were aborted between 3 and 5 weeks after infection. In the recovered fetuses, only 3 out of 4 fetal fluids from fetuses of group A and 1 out of 3 of group B were seropositive by IFAT, but all of them were positive by PCR. Transplacental transmission could be determined in all fetuses from groups A and B by PCR and/or IHC. Heifers of group C and their fetuses remained negative by all techniques. The results of this study demonstrate that the NC-Spain 7 isolate could be transmitted transplacentally, and produced fetal death and abortion in cattle.  相似文献   
200.
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