全文获取类型
收费全文 | 2907篇 |
免费 | 186篇 |
国内免费 | 6篇 |
专业分类
林业 | 151篇 |
农学 | 56篇 |
基础科学 | 21篇 |
416篇 | |
综合类 | 530篇 |
农作物 | 58篇 |
水产渔业 | 280篇 |
畜牧兽医 | 1326篇 |
园艺 | 83篇 |
植物保护 | 178篇 |
出版年
2023年 | 21篇 |
2022年 | 24篇 |
2021年 | 56篇 |
2020年 | 65篇 |
2019年 | 86篇 |
2018年 | 79篇 |
2017年 | 95篇 |
2016年 | 74篇 |
2015年 | 61篇 |
2014年 | 73篇 |
2013年 | 133篇 |
2012年 | 173篇 |
2011年 | 235篇 |
2010年 | 136篇 |
2009年 | 72篇 |
2008年 | 175篇 |
2007年 | 204篇 |
2006年 | 150篇 |
2005年 | 162篇 |
2004年 | 166篇 |
2003年 | 150篇 |
2002年 | 118篇 |
2001年 | 50篇 |
2000年 | 42篇 |
1999年 | 27篇 |
1998年 | 10篇 |
1997年 | 17篇 |
1996年 | 18篇 |
1995年 | 25篇 |
1994年 | 16篇 |
1992年 | 25篇 |
1991年 | 22篇 |
1990年 | 30篇 |
1989年 | 35篇 |
1988年 | 26篇 |
1987年 | 20篇 |
1986年 | 27篇 |
1985年 | 19篇 |
1984年 | 18篇 |
1981年 | 7篇 |
1979年 | 8篇 |
1978年 | 12篇 |
1977年 | 7篇 |
1975年 | 9篇 |
1973年 | 12篇 |
1971年 | 10篇 |
1970年 | 11篇 |
1968年 | 6篇 |
1967年 | 8篇 |
1966年 | 7篇 |
排序方式: 共有3099条查询结果,搜索用时 16 毫秒
21.
Different procedures for preparing and purifying F4ac fimbriae of the enterotoxigenic Escherichia coli strain GIS 26 (O149:K91:F4ac LT+Sta+STb+) were performed and the purity and yield of F4ac were compared. Fimbriae were prepared by either mechanical shearing or heatshock treatment of concentrated bacterial suspensions (10(11) bacteria/ml). The mechanical shearing procedure resulted in approximately 1.7 mg fimbriae (i.e. 74.4% of the isolated protein) and 0.6 mg (25.6%) contaminating proteins per 10(12) bacteria, whereas the yield of fimbriae following heatshock treatment was lower (0.3 mg per 10(12) bacteria, i.e. 26.2%) and the relative contamination higher (1.0 mg per 10(12) bacteria, i.e. 73.8%). A further purification consisted of either anion exchange chromatography (AEC) or electro-elution from SDS-polyacrylamide gels. The electroelution procedure was performed under reducing and denaturing conditions, so that purified FaeG subunits, the major subunit of F4, were finally obtained. The binding activity of fimbriae, nonpurified as well as purified, and FaeG to F4-specific receptors on isolated intestinal villi was assessed in an inhibition adhesion assay. Native fimbriae as well as major subunits were able to bind to the receptors, and the specificity of the binding was demonstrated by blockage with F4ac-specific MAb. 相似文献
22.
A 22-yr-old multiparous beluga, Delphinapterus leucas, with consistently elevated serum progesterone concentrations post-artificial insemination was diagnosed with viable twins at 149 days postconception. Twins were of similar size at least until day 264, the last point when ultrasound measurements of both twins were made. However, ultrasound was used to determine the viability of both fetuses on days 365, 393, and 400. After 90% of normal gestation, or 434 days, steroids were administered to encourage fetal lung maturation. Seven days later a 40.9-kg live female calf was delivered headfirst. A second 22.7-kg stillborn calf was delivered in fluke-first presentation 8 hr later. Immediately after birth, the live calf was administered surfactant intratracheally. The next day, it was given beluga immunoglobulin intramuscularly, and started on oral antibiotics and provided nutritional support via an oral gastric tube. The calf started nursing voluntarily on day 3. Antibiotic and nutritional support was discontinued on day 10. Bimonthly weight and length measurements demonstrated that after an initial increased growth rate, the calf has grown within normal parameters after birth. This calf represents the first known successful surviving twin of any cetacean species and sets an important precedent for treatment modalities that may be available to assist the premature cetacean neonate. 相似文献
23.
Christopher R. Lamb MA VetMB Kenneth W. Simpson BVM&S PhD 《Veterinary radiology & ultrasound》1995,36(2):139-145
Pancreatitis can be induced in dogs by intravenous infusion of supraphysiologic doses of synthetic cholecystokinin octapeptide (CCK-8). Eight anesthetized female beagles were given either CCK-8 or saline in a randomized, blinded fashion and had abdominal ultrasonography to study the development of pancreatic lesions. Pancreatic lesions were apparent 2 hours after the start of CCK-8 infusion and included swelling, interlobular and subcapsular fluid accumulation and patchy hypoechogenicity of the gland parenchyma. CCK-8 had a variable effect on gallbladder emptying. No signs of biliary obstruction or duodenal lesions were identified. Dogs given CCK-8 had severe edematous pancreatitis at necropsy six hours after the start of the infusion. Compared to the oleic acid model of pancreatitis, CCK-8 infusion induces a rapid onset of pancreatitis and an ultrasonographic appearance that reflects diffuse edema of the gland. The short time-scale of the experiment may account for the relative absence of secondary lesions affecting the biliary tract or duodenum compared to the naturally-occurring disease. 相似文献
24.
Nine groups of rats (n = 5 per group) received an intramuscular (IM) injection of one of the following drugs or drug combinations: saline, atropine (0.05 mg/kg), glycopyrrolate (0.5 mg/kg), ketamine:xylazine (85:15 mg/kg), ketamine:detomidine (60:10 mg/kg), atropine:ketamine:xylazine (0.05: 85:15 mg/kg), glycopyrrolate: ketamine:xylazine (0.5:85:15 mg/kg), atropine:ketamine:detomidine (0.05: 60:10 mg/kg) or glycopyrrolate: ketamine:detomidine (0.5:60:10). Similarly six groups of rabbits (n = 5) received an IM injection of either saline, atropine (0.2 mg/kg), atropine (2 mg/kg), glycopyrrolate (0.1 mg/kg), ketamine:xylazine (35:10 mg/kg) or glycopyrrolate:ketamine:xylazine (0.1:35:10 mg/kg). In rats, atropine sulfate (0.05 mg/kg) and glycopyrrolate (0.5 mg/kg) produced an increase in heart rate for 30 and 240 min, respectively. In rabbits atropine sulfate at either 0.2 or 2.0 mg/kg did not induce a significant increase in heart rate, but glycopyrrolate (0.1 mg/kg) elevated the heart rate above saline treated animals for over 50 min. Both atropine and glycopyrrolate provided protection against a decrease in heart rate in rats anesthetized with ketamine: xylazine (85:15 mg/kg) or ketamine: detomidine (60:10 mg/kg); however, glycopyrrolate was significantly more effective in maintaining the heart rate within the normal range. Glycopprrolate also prevented a decrease in heart rate in rabbits anesthetized with ketamine:xylazine (35:5 mg/kg). Neither glycopyrrolate nor atropine influenced respiration rate, core body temperature or systolic blood pressure when used alone or when combined with the injectable anesthetic. Glycopyrrolate is an effective anticholinergic agent in rabbits and rodents and more useful as a preanesthetic agent than atropine sulfate in these animals. 相似文献
25.
OBJECTIVE: To determine quantitative values for components of body composition in clinically normal dogs of various breeds by use of dual energy x-ray absorptiometry (DEXA) and validate the precision and accuracy of DEXA technology in dogs. ANIMALS: 103 clinically normal sexually intact adult dogs. PROCEDURE: In a cross-sectional study, Beagles, Pembroke Welsh Corgis, Golden Retrievers, Great Danes, Pointers, Rottweilers, and nonpurebred dogs received total body DEXA scans. For the validation portion of the study, the results of DEXA scans of 6 dogs were compared with values obtained by chemical analyses of tissues from euthanatized dogs to determine the accuracy of this modality in dogs. RESULTS: Results (coefficient of variation) of the precision tests ranged from 0.10% for lean tissue to 5.19% for fat tissue, whereas accuracy tests revealed a difference between percentage bone mineral content and ash values. Body composition differed by sex, such as higher lean tissue and bone mineral content in males within some breeds, and among breeds. Regardless of body size or weight, the percentage of body weight that was bone mineral ranged from 3 to 4.0% [corrected]. CONCLUSIONS AND CLINICAL RELEVANCE: Results of this cross-sectional study provide valuable body composition data for clinically normal adult dogs, which may have research and clinical applications. 相似文献
26.
Christopher A. Ellison Quentin D. Skinner Larry S. Hicks 《Strength and Conditioning Journal》2009,62(4):371-386
Quantifying the effects of watershed improvement efforts is critical to agencies responsible for protecting water resources of the semiarid western United States. A complex water quality data set collected from 1994 to 2004 of upper Muddy Creek Basin was subjected to cluster analysis, discriminant analysis, and canonical correlation analysis to improve understanding of basin fluvial processes and to investigate whether livestock grazing best-management practices (BMPs) improved the water quality of the watershed. Hierarchical agglomerative cluster analysis grouped nine sampling sites into two clusters based on similarity of biological indices, separating the clusters into aquatic communities more and less tolerant of degraded stream conditions. Discriminant analysis yielded strong spatial and temporal distinctions, providing important data reduction by rendering seven key parameters (total dissolved solids [TDS], temperature, elevation, slope, 10-dominant taxa, percent collector-gatherers, and percent Plecoptera) for the spatial variation and four parameters (TDS, dissolved oxygen, total taxa, and community tolerance quotient) for the temporal variation. Canonical correlation analysis identified strong negative relationships among Plecoptera taxa and total taxa with TDS and turbidity in addition to strong positive associations with elevation, slope, and channel substrate weighted embeddedness value. Despite the onset of severe drought midway through the study period, overall reductions of 13% for TDS and a 30% increase in macroinvertebrate total taxa occurred across years, strongly suggesting that improvements in water quality were correlated to BMPs that stabilized stream channels and improved the condition of riparian areas. 相似文献
27.
The predominant immunoglobulin isotype on most mucosal surfaces is secretory immunoglobulin A (SIgA), a polypeptide complex comprising two IgA monomers, the connecting J chain, and the secretory component. The molecular stability and strong anti-inflammatory properties make SIgA particularly well suited to provide protective immunity to the vulnerable mucosal surfaces by preventing invasion of inhaled and ingested pathogens. In contrast to SIgA, IgA in serum functions as an inflammatory antibody through interaction with FcalphaR on immune effector cells. Although IgA appears to share common features and protective functions in different species, significant variations exist within the IgA systems of different species. This review will give an overview of the basic concepts underlying mucosal IgA defence which will focus on the variations present among species in structure, antibody repertoire development, pIgR-mediated transport, colostral IgA content, hepatobiliary transport, and function with particular emphasis on the IgA system of the pig and dog. These interspecies variations emphasise the importance of elucidating and analysing the IgA system within the immune system of the species of interest rather than inferring roles from conclusions made in human and mouse studies. 相似文献
28.
Monorchidism in the horse 总被引:1,自引:0,他引:1
Six horses with monorchidism, identified at surgery for cryptorchidectomy, are reported. All six presented with a single scrotal testis. Following surgical removal of one testis, they were either hormonally, anatomically or behaviourally determined to be geldings. Three other horses reported in the literature are reviewed. Of these nine cases of monorchidism, eight were thought to be caused by testicular degeneration and one by testicular agenesis. The vaginal process was present in all of the former and absent in the latter. The left side was involved in five of these eight horses. In seven, the epididymis was absent and, in the remaining two, only the epididymal tail was present. The condition was thought to be congenital in the six horses in this series. A surgical approach to identify accurately monorchid horses is described. 相似文献
29.
Molly D. Gleeson Bret A. Moore Sydney G. Edwards Sarah Stevens April L. Childress James F.X. Wellehan Jessica Robertson Christopher J. Murphy Michelle G. Hawkins Joanne Paul‐Murphy 《Veterinary ophthalmology》2019,22(1):67-75
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
30.
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