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   1460篇
  免费   139篇
  国内免费   3篇
林业   96篇
农学   35篇
基础科学   7篇
  179篇
综合类   312篇
农作物   51篇
水产渔业   192篇
畜牧兽医   588篇
园艺   59篇
植物保护   83篇
  2024年   3篇
  2023年   26篇
  2022年   25篇
  2021年   45篇
  2020年   62篇
  2019年   72篇
  2018年   65篇
  2017年   57篇
  2016年   62篇
  2015年   40篇
  2014年   56篇
  2013年   76篇
  2012年   102篇
  2011年   157篇
  2010年   81篇
  2009年   49篇
  2008年   99篇
  2007年   84篇
  2006年   70篇
  2005年   63篇
  2004年   72篇
  2003年   62篇
  2002年   51篇
  2001年   11篇
  2000年   8篇
  1999年   6篇
  1998年   5篇
  1997年   6篇
  1996年   9篇
  1995年   8篇
  1994年   7篇
  1993年   6篇
  1992年   7篇
  1991年   5篇
  1990年   2篇
  1988年   2篇
  1987年   2篇
  1984年   2篇
  1959年   3篇
  1956年   3篇
  1955年   2篇
  1921年   2篇
  1917年   2篇
  1916年   2篇
  1914年   1篇
  1913年   2篇
  1909年   1篇
  1906年   1篇
  1903年   1篇
  1902年   1篇
排序方式: 共有1602条查询结果,搜索用时 15 毫秒
971.
972.
973.
Uterine and cervical size of Holstein dairy cows is reported among reasons for a decline in dairy cow fertility. Therefore, the objectives of this study were to (a) determine whether size of the cervix and uterus at 4 weeks postpartum impacted subsequent fertility at first service in Jersey cattle, (b) determine whether progesterone level at 4 weeks postpartum impacted cyclicity and (c) the association of the presence of corpus luteum and uterus and cervix size. Body condition scores at calving, presence of postpartum diseases, parity number and milk weights were taken from lactating Jersey dairy cows (N = 147) for 28 days postpartum. During the fourth week postpartum, a blood sample was obtained for progesterone concentration, and transrectal ultrasonography was performed by a high-resolution ultrasound machine to determine cervical and uterine horn diameter, as well as ovarian structures measurements. Correcting for parity number, BCS at calving, presence of diseases and milk yield, cows with a cervix >2.54 ± 0.63 cm and uterine horn >2.25 ± 0.59 cm were less likely to become pregnant at first service (p = .04 and p = .003, respectively). The cows with larger cervix had a trend to be less likely to have a corpus luteum present at the 4th week of lactation (p = .067). Cows with larger uterine horn size were less likely to have a corpus luteum present at the 4th week of lactation (p = .015). It is concluded that a larger cervix and/or uterus during the postpartum was associated negatively with fertility and cyclicity in Jersey cows.  相似文献   
974.
Freshwater turtle species are suffering from anthropocentric‐caused population declines, making preservation of professionally managed populations increasingly important. Turtles under professional care have an increased risk to develop hepatic lipidosis, potentially resulting in early death. Computed tomography can provide an antemortem screening for increased fatty liver composition. A goal of this prospective analytical cross‐sectional study was to assess the hepatic attenuation measured as Hounsfield units (HU) in a wild population of a freshwater turtle species, and then compare hepatic HU to freshwater turtles under professional care. Ninety‐five wild Blanding's turtles (BT; Emydoidea blandingii) as well as 10 Vietnamese Pond turtles (VPT; Mauremys annamensis) and six Northern Snake‐Necked turtles (NSNT; Chelodina oblonga) under professional care underwent CT with quantification of hepatic HU. Hepatic HU were correlated to serum chemistry findings and the presence of follicles was recorded in BT. The mean (±SD) hepatic attenuation for 95 wild BT was 97.5 HU ±9.6. There were significant differences in hepatic attenuation among VPT, NSNT, and BT, with median HU values (range) of 5.39 HU (–6.45 to 61.50), 71.74 HU (59.44‐94.49), and 95.43 HU (74.41‐124.56), respectively. Aspartate aminotransferase (AST) values had a weak negative correlation to HU with a coefficient of –0.85 (P < .001). The hepatic attenuation was significantly higher for individuals undergoing folliculogenesis (P = .007). The decreased HU values were significantly negatively correlated with AST values. Findings supported the use of CT as an aid for guiding future management practices in freshwater turtles.  相似文献   
975.
This retrospective study aimed to describe and classify cats with intraocular lymphoma, determine the proportion of cases with presumed solitary ocular lymphoma (PSOL) compared with ocular manifestations of multicentric disease and assess the clinical outcomes of these patients. One hundred seventy‐two cases identified through biopsy submissions were reviewed histologically; 163 of these cases were subtyped according to the WHO classification system. Cases were categorized as having PSOL or ocular lymphoma with suspected systemic involvement (SSI) based on submission forms and follow‐up data. The majority of cases exhibited concurrent uveitis (75%) and secondary glaucoma (58%). Diffuse large B‐cell lymphoma was the most common subtype (n = 86; 53%), followed by peripheral T‐cell lymphoma (n = 44; 27%). Other subtypes included anaplastic large T‐ (n = 8; 5%) and B‐cell (n = 4; 2.5%) lymphomas, and 15 cases (9%) were negative for all immunohistochemical markers. In sixty‐nine cases (40%), adequate clinical data and sufficient survival data were obtained to distinguish PSOL from SSI. PSOL comprised the majority of cases (64%), while 36% had SSI. When covarying for age at diagnosis, the median survival time was significantly higher (P = 0.003) for cases of PSOL (154 days) versus those with SSI (69 days); hazards ratio of 0.47 for PSOL (95% CI: 0.241‐0.937). The subtype of lymphoma did not affect survival time. Cats with PSOL represent a greater proportion of the disease population, and this subset of cats with intraocular lymphoma has a better clinical outcome.  相似文献   
976.
977.
978.
Many infectious diseases lack robust estimates of incidence from endemic areas, and extrapolating incidence when there are few locations with data remains a major challenge in burden of disease estimation. We sought to combine sentinel surveillance with community behavioural surveillance to estimate leptospirosis incidence. We administered a questionnaire gathering responses on established locally relevant leptospirosis risk factors and recent fever to livestock‐owning community members across six districts in northern Tanzania and applied a logistic regression model predicting leptospirosis risk on the basis of behavioural factors that had been previously developed among patients with fever in Moshi Municipal and Moshi Rural Districts. We aggregated probability of leptospirosis by district and estimated incidence in each district by standardizing probabilities to those previously estimated for Moshi Districts. We recruited 286 community participants: Hai District (n = 11), Longido District (59), Monduli District (56), Moshi Municipal District (103), Moshi Rural District (44) and Rombo District (13). The mean predicted probability of leptospirosis by district was Hai 0.029 (0.005, 0.095), Longido 0.071 (0.009, 0.235), Monduli 0.055 (0.009, 0.206), Moshi Rural 0.014 (0.002, 0.049), Moshi Municipal 0.015 (0.004, 0.048) and Rombo 0.031 (0.006, 0.121). We estimated the annual incidence (upper and lower bounds of estimate) per 100,000 people of human leptospirosis among livestock owners by district as Hai 35 (6, 114), Longido 85 (11, 282), Monduli 66 (11, 247), Moshi Rural 17 (2, 59), Moshi Municipal 18 (5, 58) and Rombo 47 (7, 145). Use of community behavioural surveillance may be a useful tool for extrapolating disease incidence beyond sentinel surveillance sites.  相似文献   
979.

Background

The use of secondary data is widespread in a range of surveillance and monitoring applications because of the low cost and high availability associated with this form of data. However, as they are often collected for quite unrelated purposes, they are not necessarily fit for the new purpose that is required of them. Routine meat inspection data were originally collected with the purpose of safeguarding food, but have been re-tasked to also include animal welfare assessment. The objective of the present study was to compare the recording of pericarditis, pleuritis and lungs with lesions at routine meat inspection (RMI) with those performed at systematic health monitoring (SHM) in Danish pigs at slaughter, in order to assess the usefulness of RMI for monitoring the prevalence of these diseases. Data originating from 165 Danish pig herds were collected in the period September 2011 to November 2013. From each herd, a batch consisting of all pigs slaughtered on a specific day from a specific farm were included as the RMI data, while lungs and hearts sampled from the batches were used for the SHM. The RMI data and SHM data included recordings related to a) chronic pericarditis, b) chronic pleuritis and c) lung lesions. The proportion of carcases with a specific disease recording was estimated for each batch of pigs, and linear regression was used to relate the RMI-proportion to the SHM-proportion for the conditions mentioned above.

Results

The coefficients of determination (R2) were estimated as R2,pericarditis = 0.16; R2,pleuritis = 0.67; R2,lungs with lesions = 0.40. R2,pericarditis changed to 0.42 when the regression analysis included inspection type at the abattoir (with purely visual inspection of the hearts versus traditional inspection including an incision into the heart).

Conclusions

Overall, the results suggest that the correlation between findings at RMI and SHM was moderate for pleuritis and lungs with lesions, but poor for pericarditis. The latter could partly be explained by the type of meat inspection conducted at the abattoir. We conclude that caution should be used whenever RMI data are used for purposes other than those for which they were originally intended.  相似文献   
980.
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