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   466篇
  免费   73篇
  国内免费   2篇
林业   13篇
农学   5篇
基础科学   1篇
  25篇
综合类   71篇
农作物   12篇
水产渔业   34篇
畜牧兽医   364篇
园艺   2篇
植物保护   14篇
  2022年   4篇
  2020年   12篇
  2019年   7篇
  2018年   7篇
  2017年   14篇
  2016年   8篇
  2015年   6篇
  2014年   19篇
  2013年   19篇
  2012年   38篇
  2011年   22篇
  2010年   9篇
  2009年   19篇
  2008年   23篇
  2007年   21篇
  2006年   17篇
  2005年   12篇
  2004年   13篇
  2003年   19篇
  2002年   18篇
  2001年   5篇
  2000年   15篇
  1999年   11篇
  1998年   6篇
  1996年   4篇
  1995年   5篇
  1994年   6篇
  1993年   6篇
  1992年   5篇
  1991年   15篇
  1990年   7篇
  1989年   10篇
  1988年   8篇
  1987年   6篇
  1986年   4篇
  1985年   11篇
  1984年   9篇
  1983年   9篇
  1982年   5篇
  1981年   3篇
  1980年   5篇
  1979年   3篇
  1978年   5篇
  1977年   10篇
  1975年   5篇
  1974年   5篇
  1973年   7篇
  1972年   6篇
  1967年   6篇
  1966年   4篇
排序方式: 共有541条查询结果,搜索用时 0 毫秒
161.
Radar images at a 12.5-centimeter wavelength made with the Goldstone radar interferometer in 1980 and 1986, together with lunar radar images and recent Venera 15 and 16 data, indicate that material on the surface and subsurface of Venus has a Fresnel reflectivity in excess of 50 percent. Such high reflectivities have been reported on the surface in mountainous regions. Material of high reflectivity may also underlie lower reflectivity surficial materials of the plains regions, where it has been excavated by impact cratering in some areas.  相似文献   
162.
Are honeybees deficient in phosphomannose isomerase?   总被引:1,自引:0,他引:1  
  相似文献   
163.
164.
Human taste papillae are sensitive to two or more chemical stimuli. Individual papillae produce stable response patterns (quality and intensity) over a month's time. Hence, the response pattern does not appear to be affected by turnover of receptor cells.  相似文献   
165.
Congenital heart disease is an important subset of all cardiovascular disease in dogs and cats that is present at birth and most often detected in young animals but can be diagnosed in adulthood. The range of abnormalities that can occur during development of the heart is vast incorporating simple and complex defects, varying degrees of severity and clinical presentations that include heart failure and cyanosis. While some defects do not result in morbidity in an individual animal, others cause severe clinical signs and death at a young age. Advances in imaging and expanding treatment options offer increasingly more possibilities in the diagnosis and management of congenital heart disease which is the focus of this review. The objective is to provide a broad overview of current practice and highlight key aspects to guide practitioners in their approach to congenital heart disease diagnosis and knowledge of available treatment options.  相似文献   
166.
Nineteen of the major strawberry (Fragaria × ananassa Duch.) cultivars grown in the UnitedStates and Canada were examined for AFLP markerpolymorphisms. For the AFLP reactions, the EcoRI-ACC primer was used in combination with fourMseI primers (MseI-CAC, MseI-CAG,MseI-CAT, or MseI-CTT). Each set ofprimers produced 46–66 scorable fragments ranging insize between 50 and 500 bp. The polymorphic fragmentsproduced from each set of primers were more thansufficient to distinguish among all the cultivars,demonstrating the usefulness of AFLP markers forcultivar identification. Similarity coefficients werecalculated based on data from 228 AFLP markers anddata from 15 previously characterized RAPD markers. The RAPD markers had been specifically selected forfingerprinting purposes because they succesfullydistinguish 41 strawberry cultivars, including the 19cultivars analyzed in this study. Separatedendrograms were constructed based on analysis of theAFLP and RAPD marker data using a neighbor-joiningalgorithm. The dendrograms were compared and found tobe very different. Correlations between similaritycoefficients calculated from AFLP marker data,similarity coefficients calculated from RAPD markerdata, and coefficients of coancestry calculated frompedigree information were evaluated. Interestingly,a better correlation with the coefficients ofcoancestry was observed with the RAPD marker data thanwith the AFLP marker data.  相似文献   
167.
Osteosarcoma is the most common paediatric primary bone malignancy. The major cause of death in osteosarcoma is drug‐resistant pulmonary metastasis. Previous studies have shown that thioredoxin reductase 2 is a driver of metastasis in osteosarcoma and can be inhibited by auranofin (AF). Moreover, studies have shown that AF significantly reduces pulmonary metastases in xenotransplant models. Here, we describe a phase I/II study of AF in canine osteosarcoma, a well‐recognized spontaneous model of human osteosarcoma. We performed a single‐arm multicentre pilot study of AF in combination with standard of care (SOC) (amputation + carboplatin). We recruited 40 dogs to the trial and used a historical SOC‐only control group (n = 26). Dogs >15 kg received 9 mg AF q3d PO and dogs <15 kg received 6 mg q3d. Follow‐up occurred over at least a 3‐year period. Auranofin plus SOC improved overall survival (OS) (P = .036) in all dogs treated. The improved outcome was attributable entirely to improved OS in male dogs (P = .009). At the time of writing, 10 dogs (25%) survive without measurable disease in the treatment group with survival times ranging between 806 and 1525 days. Our study shows that AF improves OS in male dogs when combined with SOC. Our findings have translational relevance for the management of canine and human osteosarcoma. Our data justify a larger multicentre phase 2 trial in dogs and a phase I/II trial in human patients with refractory disease at the time of initial surgery.  相似文献   
168.
  • 1. The large size, patchiness and fragility of serpulid reefs present difficulties for the measurement of reef coverage for mapping and monitoring studies. Video transect measures of cover are assessed in terms of accuracy and sensitivity of the method for the identification of spatial or temporal changes.
  • 2. By comparison with direct in situ measurement of reef cover, it was found that still photography was capable of providing an accurate means for the measurement of the seabed coverage by individual reefs.
  • 3. By comparison of video and still photographic measurement of reef cover, it was found that video transects were capable of providing cover estimates of sufficient accuracy for conservation purposes, differing from still photographic estimates by 0.3% cover.
  • 4. Power analysis was employed on replicate video estimates of reef cover in order to determine the degree of replication required to identify different levels of spatial or temporal change in cover using video transects of different lengths. The modest level of replication required to identify changes in coverage as small as 25% of the initial value suggests that the use of video transects offers great potential in monitoring and mapping studies.
Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   
169.
170.
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