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   346篇
  免费   9篇
  国内免费   1篇
林业   41篇
农学   6篇
基础科学   1篇
  67篇
综合类   16篇
农作物   15篇
水产渔业   46篇
畜牧兽医   92篇
园艺   8篇
植物保护   64篇
  2023年   3篇
  2021年   8篇
  2020年   5篇
  2019年   3篇
  2018年   6篇
  2017年   6篇
  2016年   8篇
  2015年   10篇
  2014年   9篇
  2013年   33篇
  2012年   14篇
  2011年   25篇
  2010年   12篇
  2009年   20篇
  2008年   21篇
  2007年   19篇
  2006年   22篇
  2005年   31篇
  2004年   21篇
  2003年   20篇
  2002年   10篇
  2001年   11篇
  2000年   9篇
  1999年   7篇
  1998年   4篇
  1997年   3篇
  1995年   1篇
  1994年   1篇
  1990年   1篇
  1985年   1篇
  1984年   1篇
  1983年   3篇
  1982年   1篇
  1981年   1篇
  1977年   1篇
  1975年   1篇
  1967年   1篇
  1966年   2篇
  1963年   1篇
排序方式: 共有356条查询结果,搜索用时 15 毫秒
331.
The objective of this study was to evaluate the effects of a progesterone-releasing intravaginal device (PRID) containing an estradiol benzoate capsule on ovarian dysfunction, including ovarian quiescence, follicular cyst (FC) and luteal cyst or cystic corpus luteum (LC/CCL), in postpartum dairy cows. These ovarian dysfunctions were examined by palpation per rectum relative to plasma progesterone status. The results of clinical examination and hormone assay determined ovarian quiescence in 13 cows, FC in 15 cows and LC/CCL in 7 cows. These cows were treated with PRID for 12 d and then clinical examination was performed. After PRID removal, the proportion of cows exhibiting estrous signs within 7 d and confirmed formation of CL within 7-14 d (markedly effective) were 69.2 % (n=9) for ovarian quiescence, 46.7 % (n=7) for FC, and 28.6 % (2 cows) for LC/CCL. Two cows (15.4 %) in ovarian quiescence, 5 cows (33.3%) with FC and 4 cows (57.1 %) with LC/CCL did not exhibit estrous signs but were recognized as having formed CL within 12-16 d after removal of PRID (effective). These results suggest that treatments of PRID with estradiol benzoate for 12 d have therapeutic efficacy on ovarian dysfunction including ovarian quiescence, FC and LC/CCL in postpartum dairy cows.  相似文献   
332.
333.
The oral vaccination against Fowlpox was investigated via drinking water containing the F132-c strain of Fowlpox virus to be effective even though the vaccine virus-titer was 10(4) TCID (50)/dose each time. When the virus-titer of the F132-c strain was 10(4-5 )TCID(50)/dose per single drinking water vaccination, 90% or more of chickens were not protected, however, they were protected when vaccinated twice via drinking water. A weak immune response occurred by a slight infection after the first vaccination, and due to memory cells, a booster could work well after the second vaccination. These results suggest the possibility of reducing both the amount of virus required for a vaccine via drinking water and the labor cost in the field.  相似文献   
334.
The distribution and morphology of immunoreactive estrogen receptor alpha (ERalpha)- containing cells were examined in the cattle brain. The brains were collected from two cows and a male calf. One of the cows was sacrificed one week after parturition. ERalpha expressions in the preoptic area of the rostral forebrain and the medial basal hypothalamic area were evaluated immunohistochemically using a mouse monoclonal antibody. In all animals, the signals that indicate ERalpha were detected in the medial preoptic area, the level of the organum vasculosum of the lamina terminalis and the bed nucleus of the stria terminalis. In the caudal hypothalamic region, they were detected in the arcuate nucleus, the periventricular and ventromedial hypothalamic nuclei. ERalpha-containing cells were characterized by a dense nuclear reaction product. In all the subjects examined, ERalpha signals were clearly detected in the cytoplasm as well. The density of ERalpha expression was different among the three cattle; the number of ERalpha containing cells in the postpartum cow was much lower than that in the other cow and the male calf. The present findings suggest that ERalpha expression in the forebrain is influenced by the reproductive status in the cattle.  相似文献   
335.
336.
337.
1) CO2 compensation points of the plants tested correlate well with the leaf anatomy. Low CO2 compensation plants had well-developed VBS containing large and specialized chloroplasts but no plant with a high CO2 compensation point possessed chloroplasts in the VBS.

2) CO2 Compensation Points Closely Correlated With The Major Carboxylation Pathway In Photosynthesis. Low Compensation Plants Fixed CO2 Via The C-4 Pathway (C-4 Plants) While High Compensation Plants Carried Out CO2 Fixation By The Calvin Cycle (C-3 Plants).

3) Close correlations could be established for the CO2 compensation point, the major carboxylation pathway, and glycolate oxidase activity. Glycolate oxidase activity was much higher in C-3 plants than in C-4 plants. On the other hand, dark respiration in C-4 plants was higher than that in C-3 plants.

4) TCA cycle activity in detached leaves was not inhibited to any large extent by illumination.

In C-3 plants, the release of 14CO2 from alanine-1-14C increased with an increase in the ambient O2 concentration; whereas, radioactivity in the sugar fraction was quite small at all O2 concentrations. In C-4 plants the release of 14CO2 was little affected by the ambient O2 concentration while sugar formation was stimulated at high O2 concentrations. This indicates that in C-3 plants CO2 fixation is blocked at a high O2 concentration, therefore, internal 14CO2 is released from the leaf without being refixed, but in C-4 plants internal 14CO2 can be efficiently refixed and metabolized to sugar by a combination of active PEP carboxylase and the ‘Kranz type’ of leaf anatomy.  相似文献   
338.
It was observed previously that, when a fully developed leaf of the rice plant (Oryza sativa) was detached and kept in the light, more rapid loss of chlorophyll took place than in the dark during their incubation. Since this had been considered to be associated with photosynthesis, the effects of CMU (p-chlorophenyl dimethyl urea) and other compounds on the degradation of chlorophyll were studied. CMU had a significant effect in retarding the degradation of chlorophyll in the light irrespective of the presence of sucrose, whereas monoiodo acetic acid was far less effective. The degradation of chlorophyll was greatly promoted, especially in the light, when a detached leaf was kept in oxygen gas, but was delayed in nitrogen gas.

Electron microscopic observation showed that grana fret-work system and chlorophyll membrane were maintained in a healthy condition for the first few days during treatment with CMU. But they were completely degraded without CMU, and the disorganization of chloroplasts was accompanied by a rapid degradation of chlorophyll. It was assumed that oxygen evolved in photosynthetic reaction causes light-induced degradation of chlorophyll, and CMU represses degradation by inhibiting oxygen evolution in the light reaction of photosynthesis. A suggestion was made as to the scheme of light-induced degradation of chlorophyll relative to photosynthetic reaction and the mode of action of CMU.  相似文献   
339.
The process of solid-state fermentation was used to produce a cocktail enzyme of Trichoderma reesei ATCC 66587 and Aspergillus tubingensis KRCF 700-33. Wheat bran, corncob, and sugi pulp were supplemented with ammonium sulfate as an enzyme-producing medium using T. reesei and A. tubingensis. The corncob blend ratio, duration of incubation, and ammonium sulfate concentration were optimized for enhancing cellulase production from T. reesei using a Box-Behnken design. Filter paper degrading activity more than tripled when T. reesei was grown in the optimized medium, as compared with the initial medium. The highest activity of 4.03 FPU/ml (about 29 FPU/g of dry material) was obtained with a cocktail enzyme having a 25 % content of A. tubingensis and 75 % of T. reesei. The sugi pulp was then fermented to ethanol with the cocktail enzyme and thermotolerant yeast (Saccharomyces cerevisiae BA-11) under simultaneous saccharification and fermentation (SSF) at 40 °C. An ethanol concentration of 4.48 % (w/v) was achieved using the cocktail enzyme (4 FPU/g-pulp) that was produced on-site with a substrate loading level of 12.5 wt %, which achieved an ethanol yield of 76 % after 72 h.  相似文献   
340.
Static bending tests and compressive test parallel to the grain of sugi (Japanese cedar, Cryptomeria japonica) green round timber were conducted to confirm whether its strength would satisfy the referenced strength determined by the Construction Ministry. The strength of green round timber and air-dried round timber were compared for bending and compression parallel to the grain. The strength change ratio in response to a 1 % change in the moisture content of round timber was compared with that of small clear specimens and timber. The results revealed that a 5 % parametric tolerance limit of bending and compressive strength parallel to the grain satisfied the referenced strength, even when using green round timber. The average strength of air-dried round timber was higher than that of green round timber, in both bending and compression parallel to the grain, with significant differences indicated at a 5 % significance level. The relation between the cross-section area that includes round timber, timber and the small clear specimens, and the strength change ratio in response to a 1 % change in moisture content change was fitted to a logarithm curve. Thus, the size of the specimen was considered to affect the strength change ratio.  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