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   2432篇
  免费   233篇
林业   185篇
农学   104篇
基础科学   11篇
  408篇
综合类   86篇
农作物   157篇
水产渔业   353篇
畜牧兽医   1059篇
园艺   58篇
植物保护   244篇
  2024年   4篇
  2023年   24篇
  2022年   81篇
  2021年   132篇
  2020年   161篇
  2019年   170篇
  2018年   164篇
  2017年   158篇
  2016年   129篇
  2015年   90篇
  2014年   115篇
  2013年   159篇
  2012年   190篇
  2011年   184篇
  2010年   91篇
  2009年   99篇
  2008年   115篇
  2007年   104篇
  2006年   77篇
  2005年   50篇
  2004年   51篇
  2003年   50篇
  2002年   42篇
  2001年   37篇
  2000年   34篇
  1999年   22篇
  1998年   16篇
  1997年   9篇
  1996年   14篇
  1995年   7篇
  1994年   4篇
  1992年   7篇
  1991年   5篇
  1990年   5篇
  1989年   7篇
  1988年   5篇
  1985年   3篇
  1984年   5篇
  1983年   5篇
  1982年   2篇
  1981年   4篇
  1980年   5篇
  1979年   2篇
  1977年   2篇
  1976年   3篇
  1975年   2篇
  1973年   3篇
  1970年   2篇
  1969年   3篇
  1948年   2篇
排序方式: 共有2665条查询结果,搜索用时 15 毫秒
131.
Phytoparasitica - The current agricultural scenario faces a range of challenges, with phytosanitary ones being paramount. In most cases, plant diseases are treated with chemicals; however, they...  相似文献   
132.
Two experiments were conducted to evaluate reduced supplementation frequencies for grazing beef cattle in rainy season. In experiment 1, evaluating the nutritional parameters, four rumen-cannulated Nellore bulls (BW = 410 kg) were used. In experiment 2, evaluating animal performance, 48 Nellore bulls (BW = 358 kg) were used. The treatments were as follows: mineral supplement (MS) alone and MS plus protein-energy supplement provided 3×, 5× and 7×/week. Supplementation frequency did not affect (P > 0.05) intake and digestibility. Average daily gain was greater (P < 0.001) to supplementation compared with MS. The supplementation 5×/week resulted in greater weight gain per hectare (9.24) and higher economic returns during the study period (1.64%) compared to other supplementations. Supplementation 5×/week increased animal performance and positively influenced economic returns.  相似文献   
133.
The saffron finch (Sicalis flaveola brasiliensis) is a Passeriforme of the Brazilian wildlife. There are scarcely any morphological studies on it, although it is frequently trafficked for its birdsong abilities. Its peculiarities, such as territorialism and developed syrinx that provides outstanding song, draw attention towards its domestication. Thus, this study aimed to morphologically describe the tongue and digestive tube organs of this species to furnish subsidies for nutritional, clinical and conservation studies. Forty‐one birds from the Wild Animal Screening Center (CETAS)/Brazilian Institute of Environment (IBAMA)/city of Cabedelo, state of Paraíba (PB) were used. Samples were collected, identified and sent to standard light microscopy; samples of proventriculus and gizzard were sent to Scanning Electron Microscopy (SEM). The samples showed stratification similar to that of other domestic and wild birds, confirmed in the scanning electron microscopy; however, they differed in the absence of dermal papillae in the tongue, lack of ingluvial glands and lack of muscular mucosa and sub‐mucosa in the large intestine.  相似文献   
134.
Magnetic fields (MFs) have been applied for the first time in orchid micropropagation. Protocorm-like bodies (PLBs) – approximately 3 mm in diameter – first derived from leaf segment culture of Phalaenopsis Gallant Beau ‘George Vazquez’, were subcultured every 2 months, and served as initial explants. The proliferation of Phalaenopsis PLBs in liquid medium in the Miracle Pack® culture system was affected by the action of different intensities and polarities of MFs: 0.1, 0.15 and 0.2 Tesla (T) at North (N) and South (S) poles. The MF of 0.1 T – S resulted in the greatest fresh weight of regenerated PLBs. The average number of neo-PLBs formed per clusters in the PLB treated by MF: 0.1–0.2 T was decreased compared to the control exposed to natural MF (5 × 10−6 T). The proliferation of PLBs under 0.15 T – MF at both N and S poles for 2 and 7 weeks demonstrated that a longer duration of exposure to an MF of 0.15 T, regardless of the polarity, resulted in greater biomass of newly formed PLBs and smaller average number of newly formed PLBs. The S pole of MF had stronger effects on Phalaenopsis PLBs proliferation than the N pole did in all treatments.  相似文献   
135.
Granulosa cell tumour, an ovarian neoplasm of stromal origin, is an important tumour related to oestrogenic dominance syndrome and cystic endometrial hyperplasia–pyometra complex. In order to analyse ovarian tumour´s malignant potential, immunohistochemical markers can be used, such as anti-HER2 and anti-Ki-67. The aim of this study was to evaluate the expression of immunohistochemical markers HER-2 and Ki-67 in granulosa cell tumour from bitches´ ovaries. In HER-2 immunomarker analysis using the HercepTest® method, most tumours were classified as 2+ (moderate labelling). Concerning Ki-67 immunomarker, only one case was described as having a high proliferative index. An association was found between immunostained cell percentage by anti-HER-2 antibodies and high pleomorphism, represented by the pattern of follicular/trabecular tumour arrangement. There was no correlation between anti-Ki-67 and anti-HER-2 antibody immunostaining intensities, probably due to only one case with a high Ki-67 index. With an effective protocol for HER-2 and Ki-67 immunohistochemical identification in granulosa cell tumours in bitches, it was possible to characterize this neoplasm proliferation profile.  相似文献   
136.
Seriolella violacea, a new species to be potentially farmed in Chile and Peru, has shown cranial malformations during farming that could adversely affect its commercial development. This study seeks to generate early knowledge of the osteological development and type of cranial abnormalities that this species presents under culture conditions. Larvae from wild caught broodstock were reared from 1 to 60 days post hatching (DPH) (4.8 ± 0.1 mm TL and 11.8 ± 1.0 mm TL respectively). Larvae samples were collected throughout the experimental trial for recording cranial osteological development and abnormalities in cartilage and bone. At 5.7 ± 0.1 mm TL, coraco‐scapular, sclerotic, ethmoid plate and quadrate cartilages were present. At 8.0 ± 0.6 mm TL, early ossification was observed in the jaw, premaxilla and maxilla. At 11.8 ± 1.0 mm TL, the branchiostegal rays, jaw, maxilla and opercular complex were ossified. The first cartilaginous structures observed were the Meckel's cartilage, the branchial arches and the suspensory ligament. The first cranial malformations were detected at 5.7 ± 0.1 mm TL, coinciding with mouth opening. The most frequent malformations were a curvature of the lower jaw (23.1%), abnormal separation between branchial arches and the Meckel's cartilage (19.4%) and bulging jaws (15.7%).  相似文献   
137.
Lippia alba (Mill.) N.E. Brown, the ginger grass, is a medicinal and aromatic plant widely used in Latin America. In this work the effect of the geographical origin and different drying methodologies on L. alba leaves production, essential oil content and composition were evaluated. Field experiments were conducted in three different municipalities (Amargosa, Cruz das Almas and Santo Antônio de Jesus) from Bahia region (Brazil) and two drying methodologies (traditional and artificial with controlled conditions) were assessed. Fresh and dried leaves essential oils were extracted by hydro-distillation and their volatiles were determined by gas chromatography.The geographical origin affected the mass production, essential oil content and both qualitative and quantitative fractions of their composition. Leaves from Cruz das Almas had higher yield in essential oil content. Overall, 26 oil constituents were identified. Carvone, germacrene D and limonene were the main oil constituents. The drying methodologies combined with the geographic origin influenced essential oil composition showing that L. alba constituents were influenced by post-harvest treatments. Some constituents were sensitive to both methods applied, while some enhanced their content like germacrene D.  相似文献   
138.
Copper biosorption onto chemically modified biomass of marine alga Sargassum filipendula was investigated in a batch reactor and a fixed bed column. Experiments were carried out in the batch reactor to obtain kinetic and equilibrium data and to assess the copper desorption efficiency of different eluent solutions. The pseudo-first-order, pseudo-second-order, and Langmuir kinetic models were used to correlate kinetic data. The experimental data fitted well to the pseudo first order and Langmuir kinetic models. Langmuir and Freundlich models were applied to describe the equilibrium data obtained at a fixed temperature of 30°C and at pH values of 3.0, 4.0, 5.0, and 6.0. The maximum capacities of copper biosorption onto the algal biomass were 1.43, 1.59, 2.40, and 2.36 mequiv./g at pH 3.0, 4.0, 5.0, and 6.0, respectively. The efficiencies of two eluent solutions (calcium chloride and hydrochloric acid) for copper removal from the biomass were evaluated at different concentrations (0.1, 0.2, 0.5, and 1.0 mol/L). The efficiencies of the calcium chloride solutions varied from 1% to 14%, while efficiencies varying from 95% to 99% were obtained when hydrochloric acid solutions were applied. Three adsorption/desorption cycles were carried out in a fixed bed column using 0.1 mol/L hydrochloric acid as eluent solution. The results showed that an increase in the number of cycles led to a reduction in the adsorption capacity of the alga. The desorbed copper fraction presented no significant variation, remaining around 63% in the three adsorption/desorption cycles.  相似文献   
139.
Consistent data demonstrate the positive response of sap-sucking insects to water-stressed plants, but there is a lack of information about the performance of chewing species, including whether their responses vary according to their feeding specializations. We tested the hypothesis that herbivores with distinct feeding strategies and host specialization will respond differently to two plant conditions, i.e. water deficit and kaolin treatment, where the latter is used to reduce abiotic and biotic plant stressors. We determined the development and reproduction of four major cotton pest species with different feeding strategies (chewing and sap sucking) and with specializations ranging from monophagous to polyphagous using well-watered or water-stressed cotton plants, which were treated or not treated with kaolin. Three chewing (lepidopteran) species, Alabama argillacea (Hüb.), Heliothis virescens (Fabr.) and Chrysodeixis includens (Walk), as well as one sap-sucking species, Bemisia tabaci (Gen.), were used as models. The neonate larvae of all three chewing species exhibited lower survival when fed the leaves of water-stressed plants. In addition, the neonate larvae fed leaves from water-stressed and kaolin-treated plants did not complete their development or they exhibited low survival. Older larvae also exhibited significantly lower survival on kaolin-treated plants. The effects on life history traits were more obvious in monophagous chewing species compared with polyphagous species when fed leaves from water-stressed plants. The performance of B. tabaci was superior on water-stressed and untreated kaolin plants. Thus, water-stressed and kaolin-treated plants negatively affected all chewing species, whereas water-stressed plants only positively affected the sap-sucking species.  相似文献   
140.
Seven species of Solanum were screened for their molluscicidal properties against Biomphalaria glabrata, the intermediated host of Schistosoma mansoni, Solanum agrarium, S. jabrense, S. melissarum, S. megalonyx, S. paludosum, S. paraibanum and S. stipulaceum. Four extracts showed molluscicidal activity with LC(50) from 22 to 56 microg/ml.  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