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   210篇
  免费   17篇
林业   14篇
农学   13篇
  34篇
综合类   20篇
农作物   7篇
水产渔业   27篇
畜牧兽医   94篇
园艺   1篇
植物保护   17篇
  2023年   1篇
  2022年   4篇
  2021年   3篇
  2020年   4篇
  2019年   8篇
  2018年   5篇
  2017年   8篇
  2016年   12篇
  2015年   4篇
  2014年   6篇
  2013年   12篇
  2012年   10篇
  2011年   19篇
  2010年   7篇
  2009年   17篇
  2008年   11篇
  2007年   11篇
  2006年   10篇
  2005年   10篇
  2004年   4篇
  2003年   8篇
  2002年   6篇
  2001年   3篇
  2000年   4篇
  1999年   4篇
  1998年   4篇
  1997年   3篇
  1996年   5篇
  1995年   2篇
  1993年   3篇
  1992年   4篇
  1990年   2篇
  1988年   2篇
  1987年   1篇
  1985年   1篇
  1981年   1篇
  1979年   1篇
  1978年   2篇
  1976年   1篇
  1974年   3篇
  1973年   1篇
排序方式: 共有227条查询结果,搜索用时 15 毫秒
41.
42.
The IgG antibody response to Calicophoron daubneyi (Digenea: Paramphistomidae) excretory/secretory antigens was evaluated in naturally infected cattle from Lugo (Galicia, NW Spain) by using an ELISA procedure. Two studies were conducted, first a survey in 524 cattle separated into three groups according to age, G-1 (0–2 years old), G-2 (3–5 years old) and G-3 (>6 years old). In the second study, three groups of cattle were employed: G-I, naturally infected; G-T, naturally infected and treated with oxyclozanide plus levamisole (Nilzan Plus®); G-C, cattle maintained in a farm where C. daubneyi has never diagnosed. Variations on egg-output and haematic parameters (erythrocytes, haematocrite, leukocytes and lymphocytes) were also analyzed.

The ELISA procedure showed that 61.2% of the cattle in the first study had been exposed to the trematode, but only 10.1% passed eggs in the feces. Age-association with egg-output was shown but not with the IgG values. In the second experiment, the administration of the anthelmintic reduced significantly the IgG kinetic levels and the C. daubneyi-egg-output was suppressed during 12 weeks in the G-T group. The values of red cells, haematocrite, leukocytes and lymphocytes increased significantly in the treated cattle 5 weeks after chemotherapy; however, new reduction after week 5 was recorded, as results of the challenge of these cattle.

This is the first investigation in which evaluation of the IgG humoral response against C. daubneyi in cattle has been carried out. We proved that a notable IgG response in naturally infected cattle is induced, and can be detected by using an ELISA procedure. The IgG antibodies did not increase after challenge infection. Our results proved an important percentage of cattle were exposed to this trematode in the area of study and suitable measures for preventing this relationship must be considered.  相似文献   

43.
Advocates, practitioners and policy-makers continue to use and advocate for marine protected areas (MPAs) to meet global ocean protection targets. Yet many of the worlds MPAs, and especially no-take MPAs, are plagued by poaching and ineffective governance. Using a global dataset on coral reefs as an example, we quantify the potential ecological gains of governing MPAs to increase compliance, which we call the ‘compliance gap’. Using ecological simulations based on model posteriors of joint Bayesian hierarchical models, we demonstrate how increased compliance in no-take MPAs could nearly double target fish biomass (91% increases in median fish biomass), and result in a 292% higher likelihood of encountering top predators. Achieving these gains and closing the compliance gap necessitates a substantial shift in approach and practice to go beyond optimizing enforcement, and towards governing for compliance. This will require engaging and integrating a broad suite of actors, principles, and practices across three key domains: (i)) harnessing social influence, (ii) integrating equity principles, and (iii) aligning incentives through market-based instruments. Empowering and shaping communication between actor groups (e.g., between fishers, practitioners, and policy-makers) using theoretically underpinned approaches from the behavioural sciences is one of the most essential, but often underserved aspects of governing MPAs. We therefore close by highlighting how this cross-cutting tool could be further integrated in governance to bolster high levels of compliance in MPAs.  相似文献   
44.
Oxidative stress indicators, malondialdehyde (MDA) accumulation and chlorophyll retention, were tested as tools for salt‐tolerance screening in Chloris gayana (Kunth), a forage grass exhibiting inter‐ and intra‐cultivar variability in the response to salt stress. Three types of experimental system were compared, salt shock, gradual salt treatment and leaf segments floated on control and saline solutions. Results followed the same trend in the three systems, but leaf segments or gradually salinized plants are the most convenient. Lower mean MDA and higher mean chlorophyll content were found under salinity in cv. ‘Katambora’, which is considered, from previous field trials, to be more salt tolerant than cv. ‘Boma’. Nevertheless, chlorophyll content did not give consistent results in other tests and it is not recommended for selection purposes. Within cv. ‘Boma’, clones rating higher in a salt tolerance evaluation under greenhouse conditions had lower MDA content under salinity and lower mean MDA ratios between salt‐treated and control samples. The survival of 80‘Boma’ plants under increasing NaCl concentration was assessed and MDA was measured in the leaves of very plant before the final NaCl level was reached, to assess whether it was predictive of survival capability. MDA values were significantly lower in the group surviving longer, thus, a selection based on low MDA values would have enriched the original population with more tolerant individuals.  相似文献   
45.
46.
The awn and the fur hair of Pudu were investigated. Values of the length are between 14 and 56 mm for the awn hair, and 9 to 36 mm for the fur hair. Hair thickness--especially at the thickest point--ranges from 140 to 236 microns for the awn hair and from 19 to 106 microns for the fur hair. The values of the cuticle scales are between 12 and 18 microns for the length and between 41 and 66 microns for the width. The shape of the scales is rectangular in the basal three quarters (R) and becomes crenated (R/Z) in the apical quarter. The medulla is continuous with large hollow vesicles. The similarity to the hair of european red deer is surprising.  相似文献   
47.
Conventional in vitro fertilization has not yet been implemented in the equine species. One of the main reasons has been the inability to develop a culture medium and incubation conditions supporting high levels of stallion sperm capacitation and hyperactivation in vitro. Although different culture media have been used for this purpose, human tubal fluid (HTF) medium, widely used in the manipulation of human and mice gametes, has not been reported so far in stallion sperm culture. The first part of this study aimed to compare HTF and Whitten's media on different stallion sperm quality and capacitation variables. Additionally, the effect of procaine, aminopyridine and caffeine in both media was evaluated on sperm motility parameters at different incubation times. Integrity and destabilization of the plasma membrane were evaluated by merocyanine 540/SYTOX Green (MC540), mitochondrial membrane potential (?Ψm) using tetramethylrhodamine methyl ester perchlorate (TMRM), acrosome membrane integrity by PNA/FITC and tyrosine phosphorylation by P‐tyrosine mouse mAb conjugated to Alexa Fluor® by flow cytometry. Motility parameters were evaluated using the integrated semen analysis system (ISAS®). We found no differences between Whitten's and HTF media and incubation time in terms of sperm viability, uninduced acrosome membrane damage or mitochondrial membrane potential at 30‐ and 120‐min incubation. Membrane fluidity (MC540) increased in both media at 30‐ and 120‐min incubation compared to noncapacitating conditions. Similarly, tyrosine phosphorylation increased in both media in capacitating conditions at 2‐ and 4‐hr incubation compared to noncapacitating conditions. Although procaine showed the best result in terms of sperm hyperactivated motility in both media, aminopyridine also showed parameters consistent with the hyperactivation including an increase in curvilinear velocity and decrease in straightness. In conclusion, HTF medium and aminopyridine equally support capacitation‐related parameters in stallion sperm.  相似文献   
48.
49.
Oliet  J.  Planelles  R.  López Arias  M.  Artero  F. 《New Forests》2002,23(1):31-44
The capacity of Aleppo pine (Pinus halpensis Mill.) seedlings to overcome the planting shock in dry conditions was assessed by firstly studying the survival and water status during the first year after planting in relation to soil water content. In spite of receiving only 177 mm rainfall during the year studied, survival of planted Aleppo pine was very high (88.5%). Soil water during summer months (after receiving 67 mm rainfall in winter and spring) was only available at 30–60 cm depth, with tension values of –1.1 and –1.3 MPa in July and August respectively; in these conditions, July predawn xylem water potential measured was –2.5 MPa, and midday potential was –3.6 MPa. According to different authors, these values don't jeopardize the survival of Aleppo pine. In addition, acclimation of outplanted seedlings to environmental conditions was followed by comparing their water relations with those of naturally regenerated seedlings on the site. Predawn and midday xylem water potential showed differences in favour of outplanted seedlings since June, indicating an adjustment to this dry site. Compared to naturally regenerated trees, nursery grown stock of the same age before field planting had much more biomass and higher N and P concentrations and contents; although shoot:root balance and Dickson quality index were not significantly different. Finally, planted seedlings acclimation level during first year was also evaluated by Transplant Stress Index, which value (–0.1278) indicated a slight planting impact.  相似文献   
50.
Gonadotropin-releasing hormone (GnRH) antagonists are particularly useful when a rapid inhibitory effect on the gonadal axis is required. The aim of this study was to test the efficacy and clinical safety of a low and high dose of the third generation GnRH antagonist, acyline, on pregnancy termination in female dogs. The effect of the antagonist on the progesterone (P4) serum concentration was also described. Twenty-one mid-pregnant bitches were randomly assigned to a single subcutaneous (SC) dose of a placebo (PLACE; n = 7), a low (ACY-L; 110 μg/kg; n = 6) or high (ACY-H; 330 μg/kg; n = 8) dose of acyline. The animals were followed up for 15 days. All ACY treated but no placebo-treated animals terminated their pregnancy by abortion (p < 0.01). The ACY-L and ACY-H groups interrupted their pregnancy 7 ± 1.9 and 6.4 ± 1.3   days after treatment, respectively (p = 0.7). A significant interaction between treatment and day was found (p < 0.01) for P4 serum concentrations when PLACE was compared with both ACY groups. No difference was found for this hormone between both ACY groups (p > 0.05) where P4 diminished throughout the study. The decreasing rate varied among animals and was closely related to the time of abortion when P4 reached basal concentrations. In PLACE animals, gestation progressed normally and P4 did not change throughout the study (p > 0.05). None of the bitches presented side effects. It was concluded that acyline safely terminated mid-pregnancy by permanently decreasing P4 serum concentrations.  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