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   358篇
  免费   14篇
林业   52篇
农学   10篇
  37篇
综合类   18篇
农作物   14篇
水产渔业   29篇
畜牧兽医   189篇
园艺   1篇
植物保护   22篇
  2023年   3篇
  2022年   7篇
  2021年   12篇
  2020年   4篇
  2019年   4篇
  2018年   4篇
  2017年   10篇
  2016年   14篇
  2015年   10篇
  2014年   15篇
  2013年   19篇
  2012年   33篇
  2011年   30篇
  2010年   9篇
  2009年   10篇
  2008年   16篇
  2007年   14篇
  2006年   23篇
  2005年   30篇
  2004年   16篇
  2003年   20篇
  2002年   4篇
  2001年   12篇
  2000年   11篇
  1999年   8篇
  1998年   6篇
  1997年   1篇
  1996年   2篇
  1992年   3篇
  1991年   2篇
  1990年   1篇
  1989年   3篇
  1987年   2篇
  1985年   2篇
  1983年   3篇
  1982年   2篇
  1980年   1篇
  1978年   2篇
  1977年   3篇
  1972年   1篇
排序方式: 共有372条查询结果,搜索用时 15 毫秒
141.
Mitral valve repair is one of the treatment options for mitral regurgitation. Expanded polytetrafluoroethylene (ePTFE) is a polymer that has been widely used in cardiovascular surgery. In this case series, we report the autopsy and histological findings in 6 dogs that underwent cardiopulmonary bypass for mitral annuloplasty using ePTFE sheets and chordoplasty using ePTFE sutures.From May 2005 to October 2009, 3 female and 3 male dogs with severe mitral regurgitation underwent mitral valve repair. This case series included 3 Cavalier King Charles spaniels, 2 Maltese, and 1 Shih Tzu. The survival period after surgery was 19–72 (35 ± 19) months.In all the cases, autopsy revealed that the ePTFE sheets and sutures were not damaged and well integrated into the surrounding highly differentiated, connective tissues. Low-power microscopy revealed that in all cases, the tissues surrounding the ePTFE sheet in the mitral valve annulus had almost completely been covered by granulation tissue. No inflammatory infiltrate or thrombogenesis was observed around the ePTFE in any of the cases.There was no evidence of reactive changes in the region surrounding the ePTFE. These results suggest that ePTFE has excellent tissue compatibility and durability and can be effectively used for canine mitral valve repair.  相似文献   
142.
The present study evaluated the effects of genetic backgrounds on the developmental competence and thermotolerance of bovine in vitro‐produced (IVP) embryos. First, Holstein (Hol) and Japanese Black (JB) oocytes were fertilized with sperm from Hol, JB and a thermotolerant breed (Brahman), and in vitro development was evaluated when the embryos were exposed to heat shock on Day 2 (Day 0 = day of fertilization). Sperm genetic backgrounds affected the developmental competence in controls (P < 0.05). Second, the effect of sperm pre‐incubation for 4 h on subsequent in vitro fertilization was assessed using different sperm genetic backgrounds. The pre‐incubation of sperm did not decrease the embryonic development regardless of the breed of the sperm. A milder heat shock (40.0°C) effect on parthenotes (Hol and JB) and IVP embryos were evaluated. JB parthenotes showed developmental arrest after Day 4, and the rate of development to the blastocyst stage decreased by heat shock, but not in Hol parthenotes. Heat shock decreased developmental competence after cleavage of IVP embryos regardless of genetic background. The thermotolerance of IVP embryos would be controlled by both maternal and paternal factors but genetic involvement was still unclear. Further evaluation is needed to reveal the genetic contribution to thermotolerance.  相似文献   
143.

Objective

To determine whether an ultrasound (US)-guided femoral nerve block using a ventral suprainguinal approach could be successfully achieved in sedated dogs; to measure the time to execute the nerve block, onset time, duration, and complete block rate in sensory and motor nerves; and to examine any differences between two volumes for injection.

Study design

Blinded crossover experimental study.

Animals

A total of 10 clinically healthy adult Beagle dogs.

Methods

The femoral nerve of the right pelvic limb was infiltrated with 0.5% bupivacaine at 0.4 (treatment 0.4B) or 0.2 mL kg?1 (treatment 0.2B), or saline at 0.4 mL kg?1 (control) in sedated dogs. The sensory and motor nerve functions were scored on a scale of 0 (complete blockade) to 2 (normal). The onset time and duration of the sensory and motor nerve blockade were compared between treatments 0.4B and 0.2B using a Wilcoxon signed rank test. Sensory and motor nerve function scores for each of the three treatments were compared at multiple time points using a nonparametric multiple comparisons test.

Results

The time to execute the nerve block was 2.5 ± 0.9 minutes (n = 30). For both 0.4B and 0.2B treatments, the onset times of both the sensory and motor nerve blockades were 15 minutes. The durations of the sensory nerve blockade for 0.4B and 0.2B were 9.9 ± 1.4 and 10.0 ± 1.2 hours, respectively, and those of the motor nerve blockades were 10.5 ± 1.3 and 10.2 ± 1.3 hours, respectively. No adverse effects were noted. No significant difference was observed between 0.4B and 0.2B.

Conclusions and clinical relevance

A US-guided femoral nerve block using a ventral suprainguinal approach demonstrated a short onset and long duration with 0.5% bupivacaine 0.2 mL kg?1 and can be performed under sedation in dogs.  相似文献   
144.
The management of weeds and diseases that are caused by phytopathogenic fungi is important for preventing the loss of agricultural products. The aim of the present study was to identify phytotoxic and antiphytopathogenic agents from the Thai Alpinia galanga rhizome. Extracts of the dried rhizomes of A. galanga (Zingiberaceae) were separated and tested for phytotoxic activity against lettuce (Lactuca sativa L. cv. Great Lakes) and Italian ryegrass (Lolium multiflorum Lam. cv. Wasefudou) and for antiphytopathogenic activity against Alternaria porri, Colletotrichum gloeosporioides, Fusarium oxysporum and Phytophthora nicotianae. 1′‐Acetoxychavicol acetate ( 1 ) was identified as one of the main components, together with transp‐coumaryl acetate ( 3 ) and transp‐acetoxycinnamyl acetate ( 2 ). 1′‐Acetoxychavicol acetate ( 1 ) was solvolyzed with 2% EtOH to yield transp‐coumaryl ethyl ether ( 6 ), transp‐coumaryl acetate ( 3 ) and transp‐coumaryl alcohol ( 5 ). 1′‐Acetoxychavicol acetate ( 1 ) completely inhibited the root growth of the lettuce seedlings at 50 μg mL–1, but had a weaker inhibitory effect on the growth of Italian ryegrass. 1′‐Acetoxychavicol acetate also inhibited the growth of P. nicotianae and A. porri, with minimum inhibition concentration values of 15.6 and 31.5 μg mL–1, respectively. The plant growth‐inhibitory activity and fungal growth‐inhibitory activity of transp‐coumaryl acetate ( 3 ), transp‐coumaryl ethyl ether, transp‐coumaryl alcohol ( 5 ) and transp‐acetoxycinnamyl acetate ( 2 ) were lower than those of 1′‐acetoxychavicol acetate. A structure–activity relationship suggested that the strong phytotoxic and antiphytopathogenic activity of 1′‐acetoxychavicol acetate relied on the 1′‐acetoxyl group.  相似文献   
145.
Serpentinitic soils contain high concentrations of geogenic Ni. During serpentinitic mineral weathering, the Ni released from soils into ecosystems could be a source of non-anthropogenic metal contamination. In this study, soil samples were collected from two pedons in paddy fields in Taiwan and Japan; these samples were used to explore the profile distribution of total and labile Ni, demonstrating the contribution of Ni-bearing Fe and Mn oxides to the Ni partition in these soils. Serpentine and chlorite were the dominant primary minerals; thus, the soils reflected serpentinitic characteristics and exhibited high background concentrations of Ni. The total Ni content ranged from 240 to 520 mg kg?1. Repeated redox and leaching cycles caused the redistribution of Ni in the paddy soils. The diethylenetriamine pentaacetate (DTPA)-extractable Ni, an availability index of Ni, increased as the soil depth decreased in the two pedons. An additional pool of labile Ni was present in the soils because the Ni concentration determined using a 0.1 N HCl extraction was much higher than was that determined using the DTPA extraction. Fe and Mn oxides were closely related to the labile Ni in these paddy soils. However, Ni was predominantly retained by amorphous and crystalline Fe oxides rather than Mn oxides. Shortening the flooded duration of paddy field is required to reduce the solubility of Ni because that the labile Ni and redox-sensitive Fe oxides can affect both the paddy soils and environment when Ni is released into the soil solution and becomes bioavailable under reducing conditions.  相似文献   
146.
利用振动法检测胶合板的抗弯弹性模量   总被引:6,自引:1,他引:6  
通过弯曲振动试验、纵波传播试验及纵波共振试验对胶合板的抗弯弹性模量进行无损检测,并分析了三种试验方法测定结果之间的关系。结果表明:虽然不同方法测得的胶合板弹性模量值不同,但其间存在一定的内在联系。  相似文献   
147.
To investigate micropores and mesopores in the cell walls of dry wood, CO2 gas and N2 gas adsorption onto dry wood were measured at ice-water temperature (273 K) and liquid nitrogen temperature (77 K). CO2 gas adsorption isotherms obtained were used for determining micropore volumes smaller than 0.6 nm by the HK method (Horvath-Kawazoe method), and N2 gas adsorption isotherms obtained were used for determining the mesopore volume between 2 nm and 50 nm by the Barrett-Joyner-Halenda (BJH) method. Micropores and mesopores existed in cell walls of dry wood, and the cumulative pore volume was much larger for micropores than for mesopores. Micropores in the cell wall of dry wood decreased with elevating heat treatment temperature, and the decreased micropore was reproducible by wetting and drying. Mesopores did not decrease so much with elevating heat treatment temperature. Micropore volumes for the softwood Hinoki and the hardwood Buna were compared. A larger amount of micropores existed in hardwood Buna than in softwood Hinoki, and this relationship was considered to correspond to the difference in thermal softening properties for lignin in water-swollen Hinoki and Buna. This result probably indicates that micropores in the cell walls of dry wood relate to the structure of lignin.  相似文献   
148.

Introduction   

The aims of this study were to identify the climatic conditions controlling the distribution of Sasamorpha borealis and to assess the impact of climate change on the species in Japan.  相似文献   
149.
The incidence of different types of luteal activity postpartum and their effect on reproductive performance were studied in 21 postpartum dairy cows. Progesterone concentrations in defatted milk collected 3 times a week were determined by EIA. Reproductive tract examination was undertaken every other week postpartum. Body weight and body condition score (BCS) were measured before and after calving and the average 100-day milk yield was calculated. Nine (42.9%) cows had normal ovarian activity (first luteal activity < or = 50 days postpartum followed by regular cycles), 5 (23.8%) had prolonged luteal phase (PLP; ovarian cycle with luteal activity > or = 20 days pre-service) and in 7 (33.3%) cows the first luteal activity was shown later than 50 days postpartum (DOV). When compared with normal cows, both PLP and DOV had longer interval to first insemination (63.1 +/- 22.0 days versus 77.6 +/- 21.6 and 93.0 +/- 22.3 days, P<0.05 and P<0.01, respectively), lower first insemination conception rate (88.9% versus 0.0% and 57.1%, P<0.01 and P<0.05, respectively) and greater BCS loss (0.81 +/- 0.2 versus 1.05 +/- 0.21 and 1.04 +/- 0.10, respectively, P<0.01). Cows with PLP showed longer interval to uterine involution than normal and DOV groups (54.0 +/- 8.3 days versus 42.4 +/- 5.5 and 43.3 +/- 8.3 days, respectively, P<0.01) and higher 100-day milk yield (38.8 +/- 2.7 kg versus 33.6 +/- 4.7 and 29.9 +/- 6.1 kg, respectively, P<0.01). In conclusion, more than half of the cows had abnormal luteal activity postpartum, which adversely affected reproductive performance.  相似文献   
150.
Do secondary sexual traits, such as large dorsal hump and hooked snout, decrease the swimming efficiency of male pink salmon during freshwater migration? This is the first study to address the effects of secondary sexual traits in pink salmon on oxygen uptake and swimming capacity. We conducted a laboratory experiment using a swimming respirometer and a field study using electromyogram (EMG) telemetry in the Shibetsu River, Hokkaido, Japan. We compared the relationship between MO2 (mg O2·kg?1·h?1) and swimming velocity U (m·s?1) in male and female fish, and also investigated the effects of morphological traits (secondary sexual characters) on the relationship between MO2 (mg O2·kg?1·h?1) and swimming velocity U (m·s?1). Additionally, we compared energy costs and swimming behaviour during upstream migration between male and female pink salmon. The laboratory experiment revealed that MO2 exponentially increased with increasing U; this increase was described by MO2 = 167.9e1.23U for males and 144.9e1.14U for females. Linear mixed models found that hump height and the upper jaw length in males significantly and positively affected the relationship between MO2 and U; no effect was found in females. The field study found that swimming velocity for both sexes estimated from EMG calibration was lower than optimal swimming velocity (Uopt) calculated from the laboratory experiment. We suggest that pink salmon in the Shibetsu River do not swim at the optimal swimming velocity because of the short migration distance involved (20 km).  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