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   73344篇
  免费   4132篇
  国内免费   32篇
林业   3173篇
农学   2399篇
基础科学   466篇
  8672篇
综合类   12026篇
农作物   2819篇
水产渔业   3525篇
畜牧兽医   38614篇
园艺   835篇
植物保护   4979篇
  2018年   966篇
  2017年   1073篇
  2016年   1000篇
  2015年   846篇
  2014年   1046篇
  2013年   2745篇
  2012年   1946篇
  2011年   2268篇
  2010年   1533篇
  2009年   1559篇
  2008年   2322篇
  2007年   2220篇
  2006年   2034篇
  2005年   1969篇
  2004年   1846篇
  2003年   1989篇
  2002年   1806篇
  2001年   2239篇
  2000年   2190篇
  1999年   1748篇
  1998年   714篇
  1997年   776篇
  1996年   685篇
  1995年   866篇
  1994年   735篇
  1993年   734篇
  1992年   1494篇
  1991年   1637篇
  1990年   1606篇
  1989年   1607篇
  1988年   1496篇
  1987年   1459篇
  1986年   1538篇
  1985年   1450篇
  1984年   1271篇
  1983年   1065篇
  1982年   748篇
  1979年   1171篇
  1978年   888篇
  1977年   840篇
  1976年   800篇
  1975年   829篇
  1974年   1030篇
  1973年   1070篇
  1972年   1019篇
  1971年   951篇
  1970年   928篇
  1969年   900篇
  1968年   755篇
  1967年   844篇
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
991.
Zoonotic diseases are endemic in the country of Georgia. Using the non‐linear canonical correlation (NCC) method, the aim of this study was to examine the relationship between thirteen epidemiological risk factors and seropositivity to five zoonotic infections (anthrax, Q fever, tularemia, leptospirosis, and Crimean‐Congo hemorrhagic fever [CCHF]) among Georgian military recruits during 2014–2016. According to this multivariate statistical technique, which is suitable for the analysis of two or more sets of qualitative variables simultaneously, two canonical variables were identified. These variables accounted for 68% of the variation between the two sets of categorical variables (“risk factors” and “zoonotic infections”). For the first canonical variable, there was a relationship among CCHF (canonical loading, which is interpreted in the same way as the Pearson's correlation coefficient, [cl] = 0.715), tick bites (cl = 0.418) and slaughter of animals (cl = 0.351). As for the second canonical variable, Q fever (cl = ?0.604) and leptospirosis (cl = ?0.486) were related to rodents inside and outside home (cl = ?0.346) and sweeping in or around home (cl = ?0.317). The NCC method allows researchers to obtain additional insights into the complex relationship between epidemiological risk factors and multiple zoonotic infections.  相似文献   
992.
An adult great‐horned owl (Bubo virginianus; GHOW) presented with a history of recurrent corneal ulceration of the right eye (OD). Findings included ulcerative superficial keratitis, proliferative conjunctivitis, and iris pigmentary changes. The ulcer was initially nonresponsive to medical therapy, but showed rapid and appropriate healing following diamond burr debridement. Proliferative conjunctivitis markedly improved following topical antiviral therapy with cidofovir 1%, interferon alpha 2B ophthalmic solutions, and oral l ‐lysine. Histopathologic evaluation of a conjunctival biopsy revealed epithelial features suspicious for viral cytopathic changes and intranuclear structures suspicious for viral inclusions, suggestive of a possible viral‐induced papillomatous conjunctivitis. A novel alphaherpesvirus, referred to as Strigid Herpesvirus 1 (StrHV1), was identified using PCR and gene sequencing. This case represents a new clinical manifestation of a previously unreported herpesvirus in the GHOW. Identification of the herpes virus was critical to administration of appropriate therapy and resolution of the conjunctivitis, and corneal epithelial debridement promoted resolution of the chronic corneal epithelial defect.  相似文献   
993.
994.
The aim of this study was to determine the effects of indigenous chicken Lactobacillus species isolates from different parts of the gastrointestinal tract on Eimeria tenella invasion in vitro and to characterise the nature of inhibition, if any. The effects of competitive exclusion, steric interference and bacterial extracellular factors on E. tenella invasion were examined in an MDBK cell model. Several Lactobacillus species were initially isolated from chickens and identified by biochemical characteristics and 16S-rRNA. All Lactobacillus species isolates tested, significantly inhibited E. tenella invasion. Steric interference did not affect parasite invasion. Extracellular metabolic factors secreted by Lactobacillus species isolates into the surrounding media were shown to inhibit parasite invasion and these factors appeared to be heat stable. These results show that the natural microflora of poultry can provide a source of E. tenella-inhibiting Lactobacillus species in vitro, and thus may contribute to the control of Eimeria infection.  相似文献   
995.
OBJECTIVE: To document, using pressure platform gait analysis, the effect of perioperative oral carprofen on limb function and pain after cranial cruciate ligament surgery in dogs. STUDY DESIGN: Blinded, prospective clinical investigation. ANIMALS: Twenty dogs with naturally occurring unilateral cranial cruciate disease. PROCEDURE: Physiologic indices, subjective pain scoring, and pressure platform gait analyses were performed before and 24, 48, and 72 hours after surgery. Correlations were assessed between methods of evaluation and the data was compared across treatment groups. RESULTS: No strong correlations were noted between physiologic data, subjective scoring systems, or gait analysis data at a walk or stance. Although average measures of limb function were nearly twice as large in dogs treated with carprofen, no significant differences between groups over time were identified. No significant differences were noted in any other measure of pain or limb function. Power analysis of peak vertical force at a walk indicated that significant difference would have been detected had the number of dogs in each group been increased to 35. CONCLUSION: When limb function was assessed with pressure platform gait analysis no statistical difference was noted between groups with respect to PVF and VI at a walk or stance, although average ground reaction forces for dogs in the carprofen group were greater than the traditional pain management group at all time points. CLINICAL RELEVANCE: Oral carprofen appears to provide some benefit for the treatment of postoperative orthopedic pain.  相似文献   
996.
Diversity of the ovine DQA2 gene   总被引:6,自引:0,他引:6  
Variation in the ovine DQA2 gene was investigated in approximately 2,000 sheep from six breeds. Fragments of DNA containing the ovine DQA2 exon 2 were amplified using PCR. Single-strand conformational polymorphism analysis and DNA sequence analysis were employed to detect genetic variation. Twenty-three nucleic acid sequences, encoding 22 DQA2 amino acid sequences, were identified. This increases the number of alleles identified from 10 to 23. In some cases, three or four unique sequences were isolated from individual sheep, suggesting that these DQA2 sequences may represent two loci. Phylogenetic tree analysis revealed that 5 of these 23 sequences were more closely related to cattle DQA3 or DQA4 sequences than to other sheep DQA2 sequences. These sequences clustered together and were called DQA2-like to differentiate them from other DQA2 sequences. There was no evidence of DQA5-like sequences in sheep. Information theory-based analysis indicated that some of the DQA2-like sequences had low information content at splice sites, suggesting that these alleles may have low functional activity. Allelic lineages were observed not only at the DQA2 locus, but also at the DQA2-like locus, supporting the trans-species mode of evolution of MHC genes. Comparison of the allelic sequences suggests that polymorphism seems to have arisen largely by point mutation and gene conversion, and a recent gene conversion event seems to have occurred between the DQA2 and DQA2-like loci. The high level of sequence polymorphism detected and varied number of loci demonstrate the extensive diversity of the ovine DQA2 gene.  相似文献   
997.
Traceability of meat has become a very important aspect of quality assurance of food. DNA analyses could be used for identification and verification of farm animals and animal derived products. A prerequisite is the collection of qualified samples from entire populations of production animals or from regionally or specially characterised animal populations. The expenditure for conventional carrying out collection, preservation, cataloguing, and storage would be enormous. Therefore we have developed a simple, reliable, and inexpensive method for the collection using the ear tagging process and for preservation of samples at room temperature. A similar collection technology can also be used for sampling of carcasses, meat and meat products. Isolation of DNA from these tissue samples can be preformed using a new single step technology. For identifying individuals microsatellites and single nucleotide polymorphisms are analysed. Comparison of DNA fingerprints or SNP signatures allows to traceback samples collected from products to the animals they are coming from. If the system will be established on a nationwide basis the total costs would be less than 0.05 EUR per kilogram meat sold.  相似文献   
998.
999.
1000.
(1) Two hundred and twenty-seven adult turkeys of both sexes, of two varieties (104 Black and 123 White) were used to evaluate their immunocompetence status and body weights. (2) Response to sheep red blood cells (SRBC) (humoral immunity) was measured by Haemagglutination (HA) test 5 days post immunisation (dpi) and expressed as log2 values. Mercaptoethanol resistant (MER) antibodies representing IgG were determined by Mercaptoethanol HA test and Mercaptoethanol sensitive (MES) antibodies, representing IgM as the difference in total HA titre and IgG. Serum lysozyme concentrations were estimated by 'Lysoplate assay' and expressed in log2 values. (3) Least squares analysis of variance revealed that the White variety had higher adult body weight (4.788 +/- 0.040 kg) than the Black (3.774 +/- 0.044 kg). Sexual dimorphism was apparent and meals were heavier than females in both varieties. The interaction effect of variety and sex on body weight was also significant. (4) Least squares means for immunological traits, namely, total anti-SRBC antibodies, MER, MES titres and serum lysozyme were 7.161 +/- 0.189, 0.801 +/- 0.071, 6.362 +/- 0.160 and 1.766 +/- 0.043 microg/ml, respectively. The Black variety had a higher MES antibody titre than the White. (5) Sex had an effect on all the immunological traits except on MER titres. Females generally had higher anti-SRBC, MER and MES titres and serum lysozyme. The variety x sex interaction effect was significant for MES titres and serum lysozyme. White males had the lowest MES titres.  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