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   1623篇
  免费   76篇
  国内免费   1篇
林业   150篇
农学   238篇
基础科学   23篇
  327篇
综合类   49篇
农作物   103篇
水产渔业   66篇
畜牧兽医   529篇
园艺   68篇
植物保护   147篇
  2023年   11篇
  2022年   31篇
  2021年   40篇
  2020年   39篇
  2019年   29篇
  2018年   72篇
  2017年   61篇
  2016年   74篇
  2015年   41篇
  2014年   45篇
  2013年   132篇
  2012年   62篇
  2011年   81篇
  2010年   63篇
  2009年   49篇
  2008年   68篇
  2007年   58篇
  2006年   52篇
  2005年   40篇
  2004年   36篇
  2003年   47篇
  2002年   45篇
  2001年   32篇
  2000年   27篇
  1999年   29篇
  1998年   14篇
  1997年   10篇
  1996年   15篇
  1995年   12篇
  1994年   10篇
  1993年   12篇
  1992年   18篇
  1991年   20篇
  1990年   31篇
  1989年   21篇
  1988年   14篇
  1987年   20篇
  1986年   17篇
  1985年   17篇
  1984年   11篇
  1983年   12篇
  1982年   15篇
  1981年   17篇
  1980年   14篇
  1979年   21篇
  1978年   15篇
  1977年   12篇
  1970年   8篇
  1969年   14篇
  1968年   12篇
排序方式: 共有1700条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
5.

Background

Diabetes mellitus (DM) is a common endocrinopathy in cats. No known diagnostic test or patient characteristic at the time of diagnosis can predict likely disease course, unlike in people in whom computed tomographic angiography (CTA) is used. No published data exist regarding the CTA appearance of the pancreas in cats with DM, and thus, it is unknown what if any CTA variables should be further assessed for associations with pancreatic endocrine function.

Hypothesis/Objectives

A significant difference in pancreatic attenuation, volume, and size will be identified between normal cats and those with chronic DM on CTA.

Animals

Ten healthy control cats and 15 cats with naturally occurring DM present for >12 months.

Methods

Prospective cross‐sectional study comparing pancreatic attenuation, enhancement pattern, size, volume, pancreatic volume‐to‐body weight ratio (V:BW), pancreatic arterial: portal phase ratio (A:P), time‐to‐arterial enhancement, and time‐to‐peak portal enhancement on CTA between sedated healthy control cats and those with chronic DM.

Results

The pancreas in cats with chronic DM was significantly larger, had higher volume, higher V:BW, and shorter time‐to‐peak portal enhancement on CTA when compared to normal cats.

Conclusions and Clinical Importance

Peak portal enhancement time, pancreatic size, pancreatic volume, and V:BW can be used to differentiate normal sedated cats from those with chronic DM by CTA. These variables warrant further investigation to identify possible associations with endocrine function.  相似文献   
6.
Eight maize complexes and varieties representing high and low yield levels were tested for their suitability as top cross testers by comparing the performance of the crosses in relation to the combining ability of the parents estimated by diallel analysis. The discriminating ability of the testers was compared by Schumann and Bradley test. In both cases the results clearly showed that the low performing testers were better and more reliable than the high performing complexes. The utility of per se performance as an indication of general combining ability of the complexes has been discussed.  相似文献   
7.
RNA-silencing suppressors of geminiviruses   总被引:2,自引:0,他引:2  
  相似文献   
8.
Waste milk samples from 103 farms in England and Wales were examined for the presence of β-lactam antibiotics and ESBL-producing Enterobacteriaceae. Approximately 10 months after the initial sampling, further waste milk, environmental and faecal samples from farms shown to be positive for CTX-M Escherichia coli were investigated further. Isolates with an ESBL phenotype were tested by PCR for the presence of blaCTX-M, blaOXA, blaSHV and blaTEM genes. Isolates positive for blaCTX-M were sequenced to determine CTX-M type. Representative isolates were further examined by PFGE, plasmid replicon typing and serotyping. Of particular interest, 21.4% of waste milk samples contained residues of the cephalosporin cefquinome, which was significantly associated with CTX-M bacteria. Such bacteria occurred in 5.8% of the waste milk samples (including 3.9% CTX-M E. coli). CTX-M types identified were 1, 14, 14b and 15, but none of the E. coli were serotype O25, the serotype of the human pandemic strain.  相似文献   
9.
10.
This study analysed the alleviating effect of elevated CO2 on stress‐induced decreases in photosynthesis and changes in carbohydrate metabolism in two wheat cultivars (Triticum aestivum L.) of different origin. The plants were grown in ambient (400 μl l?1) and elevated (800 μl l?1) CO2 with a day/night temperature of 15/10 °C. At the growth stages of tillering, booting and anthesis, the plants were subjected to heat stress of 40 °C for three continuous days. Photosynthetic parameters, maximum quantum efficiency of photosystem II (PSII) photochemistry (Fv/Fm) and contents of pigments and carbohydrates in leaves were analysed before and during the stress treatments as well as after 1 day of recovery. Heat stress reduced PN and Fv/Fm in both wheat cultivars, but plants grown in elevated CO2 maintained higher PN and Fv/Fm in comparison with plants grown in ambient CO2. Heat stress reduced leaf chlorophyll contents and increased leaf sucrose contents in both cultivars grown at ambient and elevated CO2. The content of hexoses in the leaves increased mainly in the tolerant cultivar in response to the combination of elevated CO2 and heat stress. The results show that heat stress tolerance in wheat is related to cultivar origin, the phenological stage of the plants and can be alleviated by elevated CO2. This confirms the complex interrelation between environmental factors and genotypic traits that influence crop performance under various climatic stresses.  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