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   14605篇
  免费   1084篇
  国内免费   73篇
林业   708篇
农学   848篇
基础科学   125篇
  2164篇
综合类   1704篇
农作物   526篇
水产渔业   1091篇
畜牧兽医   7152篇
园艺   232篇
植物保护   1212篇
  2023年   92篇
  2022年   77篇
  2021年   95篇
  2020年   129篇
  2019年   209篇
  2018年   383篇
  2017年   351篇
  2016年   348篇
  2015年   318篇
  2014年   338篇
  2013年   657篇
  2012年   504篇
  2011年   611篇
  2010年   478篇
  2009年   447篇
  2008年   585篇
  2007年   605篇
  2006年   503篇
  2005年   554篇
  2004年   434篇
  2003年   464篇
  2002年   375篇
  2001年   775篇
  2000年   732篇
  1999年   602篇
  1998年   181篇
  1997年   168篇
  1996年   126篇
  1995年   151篇
  1994年   157篇
  1993年   122篇
  1992年   322篇
  1991年   347篇
  1990年   294篇
  1989年   267篇
  1988年   272篇
  1987年   321篇
  1986年   247篇
  1985年   197篇
  1984年   171篇
  1983年   147篇
  1982年   95篇
  1981年   83篇
  1980年   79篇
  1979年   142篇
  1978年   94篇
  1977年   73篇
  1975年   79篇
  1974年   81篇
  1969年   71篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
In 2008, two deer hunters in Virginia and Connecticut were infected with a unique strain of pseudocowpox virus, a parapoxvirus. To estimate the prevalence of this virus, and in an attempt to define the reservoir, Parapoxvirus surveillance was undertaken between November 2009 and January 2010. 125 samples from four ruminant species (cows, goat, sheep and white‐tailed deer) were collected in Virginia, and nine samples from white‐tailed deer were collected in Connecticut. We found no evidence that the parapoxvirus species that infected the deer hunters is circulating among domesticated ruminants or white‐tailed deer. However, parapoxvirus DNA of a different parapoxvirus species, bovine papular stomatitis virus (BPSV), was detected in 31 samples obtained from asymptomatic cattle in Virginia. Parapoxvirus DNA–positive cattle originated from the same counties indicating probable transmission among animals. Molecular analysis identified BPSV as the parapoxvirus affecting animals. Asymptomatic parapoxvirus infections in livestock, particularly young animals, may be common, and further investigation will inform our knowledge of virus transmission.  相似文献   
92.
Yang, F., Sun, N., Sun, Y. X., Shan, Q., Zhao, H. Y., Zeng, D. P., Zeng, Z. L. A physiologically based pharmacokinetics model for florfenicol in crucian carp and oral‐to‐intramuscular extrapolation. J. vet. Pharmacol. Therap.  36 , 192–200. In this study, an oral physiologically based pharmacokinetics (PBPK) model was developed for florfenicol in crucian carp (Carassius auratus). Subsequently, oral‐to‐intramuscular extrapolation was performed and the two models were used to predict florfenicol concentrations in the edible tissues of crucian carp. The oral model gave good predictions in most tissues, except for kidney and liver in which the florfenicol concentrations were underestimated at the later time points. In contrast, using the intramuscular model, the concentrations in the kidney were overestimated at the later time points. Both models had the best predictive ability in the main edible tissue, the muscle. The oral model also accurately predicted the florfenicol concentrations in the muscle after multiple doses. The present study demonstrated the feasibility of predicting florfenicol concentrations in the edible tissues of crucian carp using a route‐to‐route extrapolation method.  相似文献   
93.
Efficient oral endotracheal intubation of laboratory animals is a challenging technique in veterinary research. This study introduces a miniaturized lighted stylet for rabbit intubation. An experiment with repeated measures on two factors was used to assess the feasibility and efficacy of this method. The first factor compared stylet intubation vs. laryngoscopic intubation. The second compared three practitioners, one with prior experience and two without. Success rates on the initial attempt were not statistically different (χ2 = 2.46, P = 0.12). The time difference between methods was significant (F = 41.007, P < 0.001), although the effect of practitioners was not (F = 1.038, P = 0.365). The mean ± SD of the intubation time, combining results from the three practitioners, was 20.34 ± 17.15 s for the stylet method and 57.58 ± 64.21 s for the laryngoscopic method. The results of this study demonstrate that lighted stylet intubation is efficient, robust, and independent of practitioner experience.  相似文献   
94.
95.
1. This study aimed to evaluate the effects of juniper oil on growth performance and meat quality in quails to determine its use as a safe and natural method to reduce overdependence on the use of antibiotic.

2. A total of 1000 1-d-old Pharaoh (Coturnix coturnix Pharaoh) quails, including both males and females, were divided into 4 groups containing 250 quails and treated as follows: (1) a control group with 0 mg volatile oil/kg diet; (2) 100 mg/kg juniper oil; (3) 150 mg/kg juniper oil and (4) 200 mg/kg juniper oil. The diets were prepared fresh for each treatment. The experiment was carried out for 42 d.

3. The results of the study showed that supplementation with juniper oil (100 and 150 mg/kg) caused a significant increase in live weight, live weight gain and carcass yields during the growing and finishing periods. Feed intake and feed conversion ratio were not significantly influenced by treatments.

4. The quails given rations containing juniper oil had reduced thiobarbituric acid levels in raw thigh meat samples at different storage times. Juniper oil was found to have significant antioxidant activity and prevented lipid oxidation in stored meat.

5. In conclusion, natural antioxidants such as a juniper oil can be used instead of synthetic antioxidants to retard lipid oxidation in animal diets to improve meat product quality and animal performance.  相似文献   

96.
The Lanyu pig is an indigenous breed from the Lanyu Islet, which is southeast of Taiwan. Two herds of Lanyu pigs were introduced from the Lanyu Islet into Taiwan in 1975 and 1980. The current population of conserved Lanyu pigs consists of only 44 animals with unknown genetic lineage. The Lanyu pig possesses a distinct maternal genetic lineage remote from Asian and European pigs. The present study aimed to understand the phylogenetic relationship among conserved Lanyu, Asian, and European type pigs based on the cytochrome b coding gene, to ascertain the maternal lineage and genetic diversity within the conserved Lanyu pigs, and to address whether genetic introgression from exotic or Formosan wild pigs had occurred in the conserved Lanyu pigs. Entire mitochondrial genomes of both types of Lanyu pig comprised 2 ribosomal RNA, 22 transfer RNA, and 13 protein-coding genes. Only 2 haplotypes of the mitochondrial DNA (mtDNA) control region and cytochrome b were identified in the conserved Lanyu pig herds. When maximum likelihood trees were constructed, the Type I Lanyu mitochondrial genes formed a unique clade with a large pairwise distance of both cytochrome b and the control region from Asian and European type breeds, Formosan wild pigs, and exotic breeds. Significant loss of genetic diversity of mtDNA within the conserved Lanyu pigs was demonstrated by low haplotype and nucleotide diversities, supported by Fu and Li's D* neutrality test (1.44055; P < 0.05). The mtDNA control region sequences of extant pigs in the Lanyu Islet, however, showed high haplotype and nucleotide diversity, and clustered with exotic pigs. These results indicate no maternal lineage mtD-NA gene introgression from Formosan wild pigs and introduced exotic pigs to conserved Type I Lanyu pigs, and a severe loss of heterozygosity of mtDNA in conserved Lanyu pigs. The remaining extant pigs on the Lanyu Islet have been introgressed with exotic breeds. Strategies for future conservation of native Lanyu pigs are now even more urgent and important.  相似文献   
97.
We assessed the interaction of GH gene polymorphisms (AA, AB and BB genotypes) with body weight and measures of endocrine function in Japanese black calves at 10 months of age. The average body weight for the BB genotype (281+/-5 kg) was significantly lower (P=0.0017, ANOVA) than those for the AA (324+/-9 kg) and AB (317+/-7 kg) genotypes. Plasma concentrations of insulin and IGF-I were greater for the AA genotype than for the AB genotype, and AB and BB genotypes, respectively. There were significant differences in the triglyceride and cholesterol concentrations among the GH genotypes. The area under the basal GH concentration was significantly greater (P=0.0314) for the AA genotype than for the two other genotypes. The incremental area over the basal GH concentrations in response to intravenous GHRH injection (0.4 microg/kg BW) was significantly smaller (P=0.0005) for the BB genotype than for the two other genotypes. In addition, linear regression analysis between GH incremental area induced by GHRH and body weight demonstrated that there was a positive linear correlation (r=0.6496, P<0.002) for incremental areas less than 600 ng min/ml, but a negative correlation (r=0.6473, P<0.05) for incremental areas over 600 ng min/ml. These findings indicate that the GH genotypes of the animals could be associated with difference in the GH response in Japanese black cattle at 10 months of age. We also observed a relationship between genotype and animal performances, but other studies on more animals in different conditions must be realized to make a definite conclusion.  相似文献   
98.
The present study examined, at identical daily nutrient intakes, the impact of separating protein and lactose intakes across two daily meals on the metabolic and endocrine status in heavy veal calves. Calves were assigned to one of six degrees of separating protein and lactose over the two meals (termed nutrient synchrony, SYN 1-6; 6 calves/treatment). They were fed the protein-rich (P-)meal and the lactose-rich (L-)meal at 06:00 and 18:00h, respectively, or vice versa. At SYN 1, calves were fed with 50% of the daily protein and 50% of the daily lactose intake in each meal. Protein and lactose were iso-energetically exchanged between the two daily meals from SYN 1 to 6. At SYN 6, 85% of the daily protein and 20% of the daily lactose was fed in the P-meal and the remainder in the L-meal. Blood samples were collected hourly during 24h. Mean 24h glucose concentrations increased and insulin concentrations decreased from SYN 1 to 6. Postprandial 5h areas under concentration curves (AUC(0-5h)) of glucose increased with increasing meal lactose content. AUC(0-5h) of non-esterified fatty acids increased after P- and L-meals from SYN 1 to 6. Urea concentrations increased after L-meals from SYN 1 to 6, but decreased after P-meals from SYN 1 to 6. Insulin AUC(0-5h) decreased after L-meals and after P-meals from SYN 1 to 6. Nutrient asynchrony did not affect insulin-like growth factor-1, glucagon, growth hormone, leptin, 3,5,3'-triiodothyronine and thyroxine. In conclusion, separation of protein and lactose intake over meals inhibited insulin responses to a lactose-rich meal in heavy veal calves despite high plasma glucose concentrations.  相似文献   
99.
100.
The role of endothelium-derived relaxing factors was studied in the regulation of vascular responses in the Krebs perfused equine isolated digit. Perfusion pressure was recorded in response to bolus doses of 5-hydroxytryptamine (6 nmol) alone or co-administered with carbachol (CCh; 0.2 micromol), bradykinin (BK; 0.2 nmol), substance P (SP; 0.2 nmol) or sodium nitroprusside (SNP; 0.2 micromol). N(omega)-Nitro-L-Arginine methyl ester hydrochloride (L-NAME; 300 microm) caused partial but significant inhibition of CCh-induced vasodilatory response, whereas BK and SP-induced responses were resistant to L-NAME. High potassium (K(+), 30 mm) and the cytochrome P-450 (CYP) epoxygenase inhibitor, clotrimazole (10 microm) plus L-NAME (100 microm), completely abolished the CCh, BK and SP-induced vasodilatory responses, whereas the response to SNP was unaffected. In contrast, the L-NAME-resistant proportion of CCh, BK and SP-induced vasodilatory response was not inhibited by the highly selective CYP2C9 inhibitor, sulphaphenazole (10 microm). The cyclo-oxygenase inhibitor, ibuprofen (10 microm) did not affect the CCh, BK and SP-induced responses. These data demonstrate that CCh, BK and SP-induced relaxation in the equine digit involve a combination of the NO and endothelium-derived hyperpolarizing factor (EDHF) pathways. These results do not support the evidence for the involvement of CYP-derived epoxyeicosatrienoic acids and the exact nature of EDHF in the equine digit remains to be established.  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