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   1014篇
  免费   65篇
  国内免费   1篇
林业   46篇
农学   34篇
基础科学   4篇
  114篇
综合类   260篇
农作物   55篇
水产渔业   48篇
畜牧兽医   453篇
园艺   9篇
植物保护   57篇
  2023年   5篇
  2022年   10篇
  2021年   12篇
  2020年   19篇
  2019年   27篇
  2018年   17篇
  2017年   25篇
  2016年   20篇
  2015年   17篇
  2014年   28篇
  2013年   42篇
  2012年   46篇
  2011年   49篇
  2010年   32篇
  2009年   26篇
  2008年   51篇
  2007年   49篇
  2006年   32篇
  2005年   43篇
  2004年   38篇
  2003年   47篇
  2002年   35篇
  2001年   25篇
  2000年   23篇
  1999年   19篇
  1998年   12篇
  1997年   12篇
  1996年   14篇
  1995年   11篇
  1994年   5篇
  1993年   8篇
  1992年   14篇
  1991年   12篇
  1990年   8篇
  1989年   14篇
  1988年   15篇
  1987年   14篇
  1986年   9篇
  1985年   13篇
  1984年   7篇
  1983年   13篇
  1981年   6篇
  1980年   5篇
  1979年   14篇
  1975年   11篇
  1974年   7篇
  1972年   5篇
  1970年   7篇
  1969年   7篇
  1968年   7篇
排序方式: 共有1080条查询结果,搜索用时 15 毫秒
171.
Potato virus Y (PVY) is the most important virus in North American seed potato (Solanum tuberosum L.) production. Planting virus-free minitubers in place of field-grown seed, which usually has a low PVY incidence, reduces initial PVY inoculum in the field. However, plants grown from minitubers are smaller and emerge later than those grown from conventional seed, which could make them more likely to become infected with PVY. We tested the effects of seed type of three potato cultivars (Dark Red Norland, Goldrush, and Red La Soda) on PVY incidence, tuber yield, and flowering time. The incidence of PVY in plants grown from minitubers did not differ from that of plants grown from conventional seed. Minituber-grown plants produced lower tuber yields than plants grown from conventional seed. Plants from minitubers also emerged and flowered later, but this did not increase their incidence of PVY. Cultivar-specific differences were observed in tuber yield and flowering times, suggesting that this variation may influence PVY incidence more than seed type.  相似文献   
172.
Municipal annexation is the most common form of local government boundary change and can have profound impacts on the annexing municipality as well as the area being annexed. While urban scholars have often touted the economic benefits of annexation for municipalities, little research has been conducted on the effect of annexation type on the economic well‐being of a municipality. Do voluntary annexations result in a larger economic windfall for annexing municipalities? Do involuntary annexations cost more? This study examined more than 6,000 annexations conducted by North Carolina municipalities between 1990 and 2000 in order to explore the impact annexation methodology had on municipal fiscal health. The results reveal that during the study period annexation resulted in a decrease in municipal fiscal health for North Carolina municipalities and that involuntary annexation had a particularly detrimental effect. This finding contradicts much of the previous research on the economic benefits of annexation for municipalities.  相似文献   
173.
沙门氏菌的防控已经是养禽业的首要任务,但是了解和防控弯曲杆菌可能会成为一项更加艰巨的任务。  相似文献   
174.
在家禽屠宰场内,加工者一般先将屠体废弃物收集并储存在一辆拖车上,现场不进行任何加工提炼.车装满后,将这些下脚料运往炼油厂.  相似文献   
175.
Patterns of shoot development and the production of different types of shoots were compared with scion leaf area index (LAI) to identify how eight clonal Actinidia rootstocks influence scion development. Rootstocks selected from seven Actinidia species (A. chrysantha Merri., A. deliciosa (A. Chev.) C. F. Liang et A.R. Ferguson, A. eriantha Benth., A. hemsleyana Dunn, A. kolomikta (Maxim. et Rupr.) Maxim., A. kolomikta C.F. Liang and A. polygama (Sieb. et Zucc.) Maxim.) were grafted with the scion Actinidia chinensis Planch. var. chinensis 'Hort16A' (yellow kiwifruit). Based on an earlier architectural analysis of A. chinensis, axillary shoot types produced by the scion were classified as short, medium or long. Short and medium shoots produced a restricted number of preformed leaves before the shoot apex ceased growth and aborted, resulting in a 'terminated' shoot. The apex of long shoots continued growth and produced more nodes throughout the growing seasons. Mid-season LAI of the scion was related to the proportion of shoots that ceased growth early in the season. Scions on low-vigor rootstocks had 50% or less leaf area than scions on the most vigorous rootstocks and had a higher proportion of short and medium shoots. On low-vigor rootstocks, a higher proportion of short shoots was retained during pruning to form the parent structure of the following year. Short parent shoots produced a higher proportion of short daughter shoots than long parent shoots, thus reinforcing the effect of the low-vigor rootstocks. However, overall effects of rootstock on shoot development were consistent regardless of parent shoot type and nodal position within the parent shoot. Slower-growing shoots were more likely to terminate and scions on low-vigor rootstocks produced a higher proportion of slow-growing shoots. Shoot termination also occurred earlier on low-vigor rootstocks. The slower growth of terminating shoots was detectable from about 20 days after bud burst. Removal of a proportion of shoots at the end of bud burst increased the growth rate and decreased the frequency of termination of the remaining shoots on all rootstocks, indicating that the fate of a shoot was linked to competitive interactions among shoots during initial growth immediately after bud burst. Rootstock influenced the process of shoot termination independently of its effect on final leaf size. Scions on low-vigor rootstocks had a higher proportion of short shoots and short shoots on all rootstocks had smaller final leaf sizes at equivalent nodes than medium or long shoots. Only later in the development of long shoots was final leaf size directly related to rootstock, with smaller leaves on low-vigor rootstocks. Thus, the most important effect of these Actinidia rootstocks on scion development occurred during the initial period of shoot growth immediately after bud burst.  相似文献   
176.
BACKGROUND: Seed treatments with the chloronicotinyl insecticide imidacloprid (Gaucho 600 FS) were evaluated to determine whether differences in concentration and exposure regime influence the germination and early growth of rice. RESULTS: Continuous exposure to imidacloprid (4 days at 2000 mg AI L(-1)) significantly (P < 0.001) reduced normal germination by an average of 18% across the 15 cultivars examined. Nine days after sowing, plants showed no adverse effects from continuous imidacloprid treatment during germination, with shoot lengths and root system dry weights equalling, or occasionally exceeding (P < 0.05), those of untreated plants. Short-term imidacloprid exposure (2 h at 2000 mg L(-1)) at initial seed wetting did not affect germination (P > 0.05), and short-term (1 h) exposure of 48 h pregerminated seed to imidacloprid (2000 mg L(-1)) similarly had no significant effect on early subsequent growth. Plants arising from 48 h pregerminated seed exposed to imidacloprid (1 h) at concentrations up to 4000 mg L(-1) immediately before sowing were not significantly different from control plants at either 9 or 25 days post-sowing. CONCLUSION: Results show that imidacloprid will have no adverse effects on plant growth if applied to pregerminated rice shortly before sowing. Continuous exposure of seed during germination had more pronounced effects, and the initial response of different cultivars was highly variable. Cultivars with high levels of sensitivity (such as IR72) require further testing before continuous exposure to imidacloprid during germination can be recommended.  相似文献   
177.
In veterinary oncologic specimens, histopathology is the gold standard for determining adequacy of excision. Despite limitations of this technique, the pathologist's interpretation of margin status significantly impacts patient management, including indications for adjuvant therapy. This article aims to summarize peer‐reviewed literature as it relates to histologic margin evaluation in veterinary cancer patients. The value of histologic tumour‐free margins and technical factors influencing histopathologic margin outcomes are also discussed. We review alternative strategies for determining excisional status, and discuss how an evolving understanding of tumour biology might inform clinical and research perspectives on surgical margins. In doing so, we aim to provide context and a stimulus for future investigations into this important yet incompletely understood topic.  相似文献   
178.

Background

Reticulocyte hemoglobin content provided by the Siemens ADVIA (CHr) is an established marker of iron deficiency. The IDEXX ProCyte Dx hematology analyzer now provides a similar variable, reticulocyte hemoglobin equivalent (RET‐He).

Objectives

The objective was to evaluate RET‐He and its diagnostic utility in dogs, and to calculate a cutoff value for diagnosing iron‐deficient erythropoiesis (IDE). Furthermore, the prevalence of RET‐He values below this cutoff value was established.

Methods

One hundred and seventy‐one CBCs of healthy dogs were used to establish a RI. Stability of RET‐He was evaluated by repeated measurements over 48 hours (n = 10). The 25‐run coefficient of variation (CV) was calculated, and correlation and bias between measurements of RET‐He and CHr were assessed (n = 190). A cutoff value for diagnosing IDE was calculated. The utility of RET‐He in the detection of IDE was evaluated in 123 dogs. The prevalence of low RET‐He values was assessed retrospectively in a multicenter study (2012–2014) under participation of 7 veterinary clinics.

Results

Reticulocyte hemoglobin equivalent with an RI of 22.2 to 28.6 pg was statistically stable over 48 hours (P = .10). The CV was 1.8%. A fair correlation (ρ = 0.74) between RET‐He and CHr with a small bias of ?0.6 pg was found. The cutoff value for diagnosing IDE was 20.9 pg (sensitivity: 85%; specificity: 99%). The prevalence of RET‐He values below 20.9 pg was 10.3% (1084/10,553 dogs).

Conclusions

RET‐He on the ProCyte Dx is a precise screening tool in dogs to detect iron‐deficient erythropoiesis.  相似文献   
179.
180.
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