全文获取类型
收费全文 | 62737篇 |
免费 | 2834篇 |
国内免费 | 42篇 |
专业分类
林业 | 2521篇 |
农学 | 1646篇 |
基础科学 | 429篇 |
6171篇 | |
综合类 | 14765篇 |
农作物 | 2484篇 |
水产渔业 | 2388篇 |
畜牧兽医 | 31124篇 |
园艺 | 643篇 |
植物保护 | 3442篇 |
出版年
2017年 | 553篇 |
2016年 | 536篇 |
2014年 | 540篇 |
2013年 | 1864篇 |
2012年 | 1203篇 |
2011年 | 1437篇 |
2010年 | 917篇 |
2009年 | 879篇 |
2008年 | 1429篇 |
2007年 | 1390篇 |
2006年 | 1374篇 |
2005年 | 1389篇 |
2004年 | 1318篇 |
2003年 | 1391篇 |
2002年 | 1355篇 |
2001年 | 1493篇 |
2000年 | 1473篇 |
1999年 | 1206篇 |
1998年 | 535篇 |
1997年 | 543篇 |
1995年 | 601篇 |
1994年 | 581篇 |
1993年 | 570篇 |
1992年 | 1319篇 |
1991年 | 1410篇 |
1990年 | 1458篇 |
1989年 | 1498篇 |
1988年 | 1411篇 |
1987年 | 1362篇 |
1986年 | 1405篇 |
1985年 | 1387篇 |
1984年 | 1157篇 |
1983年 | 1012篇 |
1982年 | 721篇 |
1981年 | 691篇 |
1980年 | 646篇 |
1979年 | 1129篇 |
1978年 | 920篇 |
1977年 | 823篇 |
1976年 | 770篇 |
1975年 | 862篇 |
1974年 | 1129篇 |
1973年 | 1065篇 |
1972年 | 1128篇 |
1971年 | 1081篇 |
1970年 | 1022篇 |
1969年 | 875篇 |
1968年 | 712篇 |
1967年 | 847篇 |
1966年 | 693篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Gómez Alvarez CB Wennerstrand J Bobbert MF Lamers L Johnston C Back W van Weeren PR 《Equine veterinary journal》2007,39(3):197-201
REASONS FOR PERFORMING STUDY: Lameness has often been suggested to result in altered movement of the back, but there are no detailed studies describing such a relationship in quantitative terms. OBJECTIVES: To quantify the effect of induced subtle forelimb lameness on thoracolumbar kinematics in the horse. METHODS: Kinematics of 6 riding horses was measured at walk and at trot on a treadmill before and after the induction of reversible forelimb lameness grade 2 (AAEP scale 1-5). Ground reaction forces (GRF) for individual limbs were calculated from kinematics. RESULTS: The horses significantly unloaded the painful limb by 11.5% at trot, while unloading at walk was not significant. The overall flexion-extension range of back motion decreased on average by 0.2 degrees at walk and increased by 3.3 degrees at trot (P<0.05). Changes in angular motion patterns of vertebral joints were noted only at trot, with an increase in flexion of 0.9 degrees at T10 (i.e. angle between T6, T10 and T13) during the stance phase of the sound diagonal and an increase in extension of the thoracolumbar area during stance of the lame diagonal (0.7degrees at T13, 0.8 degres at T17, 0.5 degres at L1, 0.4 degrees at L3 and 0.3 degrees at L5) (P<0.05). Lameness further caused a lateral bending of the cranial thoracic vertebral column towards the lame side (1.3 degrees at T10 and 0.9 degrees at T13) (P<0.05) during stance of the lame diagonal. CONCLUSIONS: Both range of motion and vertebral angular motion patterns are affected by subtle forelimb lameness. At walk, the effect is minimal, at trot the horses increased the vertebral range of motion and changed the pattern of thoracolumbar motion in the sagittal and horizontal planes, presumably in an attempt to move the centre of gravity away from the lame side and reduce the force on the affected limb. POTENTIAL RELEVANCE: Subtle forelimb lameness affects thoracolumbar kinematics. Future studies should aim at elucidating whether the altered movement patterns lead to back and/or neck dysfunction in the case of chronic lameness. 相似文献
992.
Ingestion of foreign bodies is uncommon in horses when compared with indiscriminate grazers such as cattle. This case report describes the diagnosis and treatment of a cervical abscess in a Thoroughbred racehorse thought to be associated with ingestion of wire. Radiographic and ultrasonographic examination provided a diagnosis, and conservative treatment of the lesion with antimicrobials initially allowed the lesion to localise closer to the skin for safer surgical exploration. Intra-operative ultrasonographic imaging facilitated surgical access, removal of the foreign body, and drainage. While surgical treatment is usually necessary to resolve an abscess, initially conservative therapy may help to improve the prognosis by simplifying surgical access and reducing the risk of surgical complications. 相似文献
993.
Casey L. Donnelly MS Christophe Staub PhD Dickson Varner PhD DVM Terry Blanchard PhD DVM Larry Johnson PhD David W. Forrest PhD 《Journal of Equine Veterinary Science》2007,27(5):212-216
Apoptosis is necessary for both initiation and control of spermatogenesis; however, an increase in apoptosis can lead to subfertility/infertility in stallions, causing substantial financial loss in the equine industry. The ability of stem cell factor (SCF), leukemia-inhibiting factor (LIF), granulocyte–macrophage colony-stimulating factor (GM-CSF), and estradiol (E2), alone or in combination, to prevent apoptosis of germ cells in short-term equine testicular cultures was examined. Testicular tissue was sectioned into approximately 2-mm cubes and placed in media-filled culture chambers. Concentrations of SCF (100 ng/mL), LIF (10 ng/mL), GM-CSF (5 ng/mL), and E2 (10−9 mol/l) were added alone or in combination to each well. After 6 hours in culture, the tissue was fixed and immunohistochemically (terminal deoxynucleotidyl transferase-mediated nick-end labeling; TUNEL) stained for apoptosis detection. Apoptotic cells per 100 Sertoli cell nuclei within seminiferous tubules were counted until the 500th Sertoli cell nuclei was reached. This counting procedure was used for each slide. An analysis of variance (ANOVA) with a Tukey's test was used to compare apoptotic rates. In comparison with the control, GM-CSF alone lowered apoptosis by 34.77%. GM-CSF–treated tissue combined with SCF and LIF as well as GM-CSF combined with SCF, LIF, and E2 reduced apoptosis when compared with the control (37.45% and 44.40%, respectively) or other treatment combinations. GM-CSF alone reduced apoptosis; results suggest possible synergy for the combinations of SCF and LIF with GM-CSF and for E2 with SCF, LIF, and GM-CSF. 相似文献
994.
Studies have indicated the importance of business education in improving the income level attained by veterinarians and the quality of service they provide. The Veterinary Business Management Association (VBMA), a national organization of veterinary students, has the potential to augment veterinary curricula by providing additional education to help ensure professional success. Local chapters at 27 of the 28 veterinary colleges in the United States (as of 2007) supplement the curriculum by focusing on business topics. A national governing board oversees the chapters, helping to ensure that high-quality educational programs are conducted and providing a conduit for communication. 相似文献
995.
Ottinger CA Brown JJ Densmore CL Starliper CE Blazer VS Weyers HS Beauchamp KA Rhodes MW Kator H Gauthier DT Vogelbein WK 《Journal of aquatic animal health》2007,19(2):99-108
Eighty striped bass Morone saxatilis were obtained from Delaware Bay using commercial gill nets set adjacent to Woodland Beach (n = 70) and Bowers Beach (n = 10) in December 2003. Fish were examined for gross lesions. Total lengths (TLs) and eviscerated weights were determined to calculate condition factors (K). Portions of spleens were aseptically harvested for bacterial culture, and portions of spleens, kidneys (anterior and posterior), livers, and gonads were obtained for histological examination. The size distribution of the striped bass was relatively homogeneous; the mean TL was about 600 mm for all samples. Mean K exceeded 0.95 in all samples and was not significantly different (P > 0.05) among samples. Significant differences in mycobacterial infection prevalence (P < or = 0.05) were observed among samples; samples obtained at Woodland Beach (WB) on December 10 (53.8%, n = 13) and December 17 (7.1%, n = 42) exhibited the most striking differences in prevalence. Mycobacterial infection intensity ranged from 1 X 10(2) to 1 X 10(7) colony-forming units per gram of spleen. Acanthocephalan infection prevalence and intensity, non-acid-fast bacterial infection prevalence, and fish sex ratio were also significantly different among the samples (P < or = 0.05). Similar to the mycobacterial infections, differences in sex ratio, acanthocephalan infection, and non-acid-fast bacterial infection were observed between the WB samples taken on December 10 and 17. However, no significant associations (P > 0.05) were observed between sex ratio or these infections and mycobacterial infection. The differences in bacterial and parasite infection prevalence and intensity and fish sex ratio in some samples indicate that these fish had a different history and that the epizootiology of mycobacterial infection in striped bass from Delaware Bay may be relatively complex. 相似文献
996.
Seasonal and photoperiodic regulation of secretion of hormones associated with reproduction in Magang goose ganders 总被引:1,自引:0,他引:1
Shi ZD Huang YM Liu Z Liu Y Li XW Proudman JA Yu RC 《Domestic animal endocrinology》2007,32(3):190-200
This study examined the reproductive endocrine profile under natural and artificial photoperiods in Magang goose ganders. Group 1 ganders (n=8) served as non-treated controls and were exposed to natural photoperiod throughout the experiment from 13th January to 17th December 2004. Group 2 ganders (n=8) were exposed to 18 h long daily photoperiod for 60 days from 13 January till 15 March 2004 and again to 16 h photoperiod for 75 days till 10th October 2004, and the 11h short photoperiod in the remainder periods of the experiment. In control ganders, plasma LH concentrations were high in normal breeding seasons (August-March) and decreased to low levels in non-breeding season from April to July. Testosterone concentrations changed similarly to that of LH throughout the seasons. Seasonal pattern of PRL concentrations was opposite to those of LH and testosterone, with low values in breeding season and high values in non-breeding season. In artificial photoperiod treated ganders, increasing photoperiod increased PRL and decreased LH and testosterone concentrations, while decreasing photoperiod reversed these changes. There were no seasonal or photoperiod caused changes in plasma T3 concentrations in both control ganders and artificial photoperiod treated ganders. These results demonstrated that in Magang goose ganders that long photoperiod stimulates PRL secretion and decreases LH secretion, which terminates reproductive season in spring and early summer, and short photoperiod stimulates LH secretion and inhibits PRL secretion rendering ganders enter into reproductive season. 相似文献
997.
Hernandez JA Garbarino EJ Shearer JK Risco CA Thatcher WW 《Journal of the American Veterinary Medical Association》2007,230(1):89-93
OBJECTIVE: To assess the efficacy of prophylactic hoof health examination and trimming during midlactation at reducing the incidence of lameness during late lactation in dairy cows. DESIGN: Randomized field trial. ANIMALS: 333 Holstein cows. PROCEDURES: Cows without apparent lameness were randomly allocated into 1 of 2 groups approximately 204 days after calving. Cows allocated to the treatment group (n = 161) were examined on a tilt table for diagnosis and underwent hoof-trimming procedures, if needed, for treatment of hoof disorders or lesions. Cows in the control group (n = 172) were not examined. Cows were assigned a locomotion score weekly for 28 weeks after allocation to a group. The number of cows classified as lame during late lactation (approx 205 to 400 days after calving) was compared between groups to assess the efficacy of prophylactic examination and trimming. RESULTS: Incidence of lameness during late lactation was 24% in cows in the control group and 18% in cows in the treatment group. CONCLUSIONS AND CLINICAL RELEVANCE: The 25% decrease in number of new cases of lameness in cows undergoing prophylactic hoof health examination and trimming during midlactation may be relevant for the well-being of dairy cows and should not represent a major economic burden to producers. 相似文献
998.
In vitro antimycoplasmal activity of six Jordanian medicinal plants against three Mycoplasma species
Al-Momani W Abu-Basha E Janakat S Nicholas RA Ayling RD 《Tropical animal health and production》2007,39(7):515-519
The in vitro effect of six Jordanian traditional medicine plant methanolic extracts were tested against 32 isolates of Mycoplasma species; Mycoplasma mycoides subsp. mycoides LC (6), Mycoplasma capricolum subsp. capricolum (8) and M. putrefaciens (18), all isolated from either nasal swabs or milk, from sheep and goats in different regions in Jordan. All Mycoplasma species showed susceptibility to Artemisia herba-alba and Artemisia arborescens with MIC ranges from 3.125–12.5 mg/ml. Allium sativum and Punica grantum showed limited activity against some Mycoplasma isolates. Olea europea and Citrullus colocynthis showed no in vitro activity against any of the Mycoplasma species tested. Artemisia herba-alba and Artemisia arborescens may therefore be useful for the treatment of mycoplasma infections.
The authors are British Civil Servants and as such their work is subject to British Crown Copyright. This means the exclusive
copyright for the article cannot be transferred. 相似文献
999.
Genetic and phenotypic parameters and annual trends for milk production and fertility traits of the Sahiwal cattle in semi arid Kenya 总被引:1,自引:0,他引:1
Data comprising 7211 lactation records of 2894 cows were used to estimate genetic and phenotypic parameters for milk production
(lactation milk yield, LMY and lactation length, LL) and fertility (calving interval, CI; number of services per conception,
NSC and age at first calving, AFC) traits. Genetic, environmental and phenotypic trends were also estimated. Variance components
were estimated using univariate, bivariate and trivariate animal models on based restricted maximum likelihood procedures.
Univariate models were used for each trait, while bivariate models were used to estimate genetic and phenotypic correlations
between milk production and fertility traits and between LMY, LL, CI and NSC within each lactation. Trivariate models were
used in the analysis of LMY, LL, CI and NSC in the first three lactations. Heritability estimates from the univariate model
were 0.16, 0.07, 0.03, 0.04 and 0.01 for LMY, LL, CI, AFC and NSC, respectively. The heritability estimates from trivariate
analysis were higher for milk production traits than those from univariate analyses. Genetic correlations were high and undesirable
between milk production and fertility traits, while phenotypic correlations were correspondingly low. Genetic trends were
close to zero for all traits, while environmental and phenotypic trends fluctuated over the study period. 相似文献
1000.
Barbour E.K. Bouljihad M. Hamdar B. Sakr W. Eid A. Safieh-Garabedian B. 《Veterinary research communications》1999,23(3):191-200
The dynamics of the serum concentration of protein 27 (P27) of avian leukosis virus and transforming growth factor 2 (TGF-2) were compared during the period between 29 and 59 weeks of age in two flocks of broiler chicken breeding stock undergoing outbreaks of severe lymphoid leukosis (LL) associated with persistent high mortality (susceptible) and in another two flocks of breeding stock with the presence of avian leukosis virus in association with low mortality due to LL (resistant). The average mean concentration of serum P27 in the LL-susceptible flocks was significantly higher (<0.05) than that in the LL-resistant flocks in six out of seven samplings performed at 5-week intervals, between 29 and 59 weeks of age. The peak in the average rise of serum P27 in the LL-resistant flocks (309 pg/ml) was associated with the highest level of TGF-2 (1282 pg/ml) among all flocks and at all sampling times. The significance of TGF-2 in inhibition of lymphoid tumour development is discussed. 相似文献