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   528篇
  免费   33篇
  国内免费   2篇
林业   33篇
农学   16篇
基础科学   3篇
  162篇
综合类   34篇
农作物   36篇
水产渔业   40篇
畜牧兽医   181篇
园艺   19篇
植物保护   39篇
  2024年   1篇
  2023年   7篇
  2022年   10篇
  2021年   13篇
  2020年   17篇
  2019年   11篇
  2018年   24篇
  2017年   21篇
  2016年   23篇
  2015年   11篇
  2014年   20篇
  2013年   38篇
  2012年   35篇
  2011年   58篇
  2010年   42篇
  2009年   24篇
  2008年   35篇
  2007年   31篇
  2006年   32篇
  2005年   28篇
  2004年   25篇
  2003年   15篇
  2002年   16篇
  2001年   6篇
  2000年   2篇
  1999年   2篇
  1997年   4篇
  1996年   3篇
  1995年   2篇
  1994年   1篇
  1993年   1篇
  1990年   1篇
  1988年   1篇
  1980年   1篇
  1979年   1篇
  1978年   1篇
排序方式: 共有563条查询结果,搜索用时 15 毫秒
201.
Squamous cell carcinomas (SCC) of the skin are commonly described in cats. Reported treatments include surgery, radiation therapy and photodynamic therapy. This preliminary study reports on the management of these lesions combining the local administration of bleomycin (plus hyaluronidase for a more uniform distribution) with permeabilizing biphasic electric pulses. Nine cats with SCC graded T(2)-T(4) were treated over a 5 year period, and each cat received two sessions of electrochemotherapy (ECT) 1 week apart. The side effects of this treatment were minimal and limited to mild erythema of the nose. Seven of the cats (77.7%) had a complete response lasting up to 3 years. ECT seems to be a safe and effective option for the treatment of feline sun-induced squamous cell carcinomas and warrants further investigation.  相似文献   
202.

Context

Forest ecosystem carbon uptake is heavily affected by increasing drought in the Mediterranean region.

Aims

The objectives of this study were to assess the capacity of a modified 3-PG model to capture temporal variation in gross primary productivity (GPP), and ecosystem net carbon uptake (NEE) in two Mediterranean forest types.

Methods

The model was upgraded from a monthly (3-PG) to a daily time step (3-PGday), and a soil water balance routine was included to better represent soil water availability. The model was evaluated against seasonal GPP and NEE dynamics from eddy covariance measurements.

Results

Simulated and measured soil water content values were congruent throughout the study period for both forest types. 3-PGday effectively described the following: GPP and NEE seasonal patterns; the transition of forest ecosystems from carbon sink to carbon source; however, the model overestimated diurnal ecosystem respiration values and failed to predict ecosystem respiration peaks.

Conclusions

The model served as a rather effective tool to represent seasonal variation in gross primary productivity, and ecosystem net carbon uptake under Mediterranean drought-prone conditions. However, its semi-empirical nature and the simplicity inherent in the original model formulation are obstacles preventing the model working well for short-term daily predictions.  相似文献   
203.
204.
Three extracts of different polarities of Glycyrrhiza glabra L. leaves were characterized and evaluated for their antioxidant, anti-genotoxic and anti-inflammatory activity. In total, thirty components have been identified and quantified through the use of liquid chromatography (LC) with ultraviolet-visible diode-array-detector (UV-vis-DAD) and mass spectrometry (MS). The main components belong to the polyphenols family, being flavonoid and dihydrostilbene derivatives. The extracts have been investigated for their antioxidant, anti-genotoxic and anti-inflammatory activities, which are fundamental requirements of efficacious chemo-preventive agents. The ethyl acetate extract proved to be the most valuable, evidently for the conspicuous presence of several polyphenols, namely flavonoids and dihydrostilbenes.  相似文献   
205.
Two new cerebrosides have been isolated from the whole plants of Euphorbia peplis L. The structures were established by FT-IR spectroscopy, FAB MS, EI-MS, ESI-MS, 1D and 2D NMR spectroscopy.  相似文献   
206.
207.
We estimated nitrogen (N) use by trees of three poplar species exposed for 3 years to free air CO(2) enrichment (FACE) and determined whether the CO(2) treatment affected the future N availability of the plantation. Trees were harvested at the end of the first 3-year rotation and N concentration and content of woody tissues determined. Nitrogen uptake of fine roots and litter was measured throughout the first crop rotation. The results were related to previously published variations in soil N content during the same period. We estimated retranslocation from green leaves and processes determining N mobilization and immobilization, such as mineralization and nitrification, and N immobilization in litter and microbial biomass. In all species, elevated CO(2) concentration ([CO(2)]) significantly increased nitrogen-use efficiency (NUE; net primary productivity per unit of annual N uptake), decreased N concentration in most plant tissues, but did not significantly change cumulative N uptake by trees over the rotation. Total soil N was depleted more in elevated [CO(2)] than in ambient [CO(2)], although not significantly for all soil layers. The effect of elevated [CO(2)] was usually similar for all species, although differences among species were sometimes significant. During the first 3-year rotation, productivity of the plantation remained high in the elevated [CO(2)] treatment. However, we observed a potential reduction in N availability in response to elevated [CO(2)].  相似文献   
208.
To increase the knowledge on Echinococcus genotypes infesting cattle and water buffaloes (Bubalus bubalis) born and bred in Italy, the germinal layer of hydatid cysts was collected from the liver and the lungs of 80 animals slaughtered in 2007. Two mitochondrial genes (the cytochrome c oxidase subunit I and the NADH subunit I) were tested by PCR. Four genotypes were identified: G1 (sheep strain), G2 (Tasmanian sheep strain), G3 (buffalo strain), and G5 (cattle strain). Fertile cysts were detected only in the lungs of 4.5% of the total G1 lung cysts, of 9.4% of the total G3 lung cysts, and in the only G5 infected animal. This is the first report of Echinococcus ortleppi (genotype G5) in Italy.  相似文献   
209.
Superficial inguinal lymph nodes from 72 wild boars examined in a previous immunohistochemical (IHC) study on porcine circovirus type 2 (PCV2) were selected for a PCV2 polymerase chain reaction (PCR) analysis. Four of these lymph nodes were PCV2-IHC strongly positive with PMWS histological lesions (outcome 1), 6 weak to mild PCV2-IHC positive without PMWS histological lesions (outcome 2) and 62 PCV2-IHC negative. Considering IHC the gold standard for diagnosis, the aims of the study were to evaluate the suitability of the PCV2-DNA extraction from formalin-fixed and paraffin-embedded (FFPE) tissue and the sensitivity and specificity of PCR under two IHC interpretations criteria: (A) the sample was considered positive if the result was outcome 1; (B) the sample was considered positive if the result was outcome 1 or 2. Under (A) criteria, sensitivity and specificity of PCR were 100% and 89.7%, respectively; the Cohen''s Kappa coefficient was 0.49. Under (B) criteria, sensitivity and specificity of PCR were 80.0% and 95.2%, respectively; the Cohen''s Kappa coefficient was 0.72. The high Cohen''s Kappa coefficient under the (B) interpretative criteria indicates good agreement between the two methods. In conclusion, 1) DNA extracted from FFPE specimens of wild boar is suitable for PCR and further represents a screening test for PCV2/PCVD (PCV2 Diseases) investigations in wild boar as well; 2) routine histological sampling can also be useful for PCV2 virological studies in wild boar.  相似文献   
210.
The aim of this study was to investigate the correlation between the histologic invasiveness (histologic stage) and various cell proliferation activity assays (quantity of argyrophil proteins associated with nucleolar organizer regions [AgNORs], mitotic activity, MIB1 [Ki67] immunohistochemical detection) for predicting the biologic behavior of malignant canine mammary tumors. Sixty specimens from malignant canine mammary tumors with no distant metastases (M0) at surgery were selected, and follow-up data were collected over a 2-year period. The histologic invasiveness was graded by histologic stage (stage 0 = tumors without stromal invasion; stage I = tumors with stromal invasion; stage II = tumors with neoplastic emboli in vessels), and the proliferative indices were expressed as MIB1 index (the percentage of nuclear area immunohistochemically stained by MIB1 antibody), mitotic index (the number of mitoses per 1,000 neoplastic cells), and AgNOR index (the ratio between mean AgNOR area of tumor cells and the mean AgNOR area of fibroblasts/lymphocytes). The measures of proliferative activity were compared among groups with different histologic stages, and the influence of different prognostic variables (histologic stage, AgNOR index, mitotic index, MIB1 index) on survival time was evaluated. A significant difference in the proliferation patterns was recorded between the different histologic stages for the mitotic index (P = 0.0006) and MIB1 index (0.0013). Among the different parameters considered, histologic stage (P < 0.05), AgNOR index (P = 0.0291), and MIB1 index (P = 0.014) revealed a significant association with prognosis in univariate analysis. AgNOR index for 1-year survival and histologic stage for 2-year survival were the most significant parameters influencing survival, as determined by multiple nonlinear logistic regression.  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