全文获取类型
收费全文 | 504篇 |
免费 | 31篇 |
专业分类
林业 | 23篇 |
农学 | 13篇 |
基础科学 | 5篇 |
81篇 | |
综合类 | 69篇 |
农作物 | 16篇 |
水产渔业 | 28篇 |
畜牧兽医 | 262篇 |
园艺 | 19篇 |
植物保护 | 19篇 |
出版年
2023年 | 7篇 |
2022年 | 4篇 |
2021年 | 4篇 |
2020年 | 14篇 |
2019年 | 21篇 |
2018年 | 13篇 |
2017年 | 11篇 |
2016年 | 9篇 |
2015年 | 11篇 |
2014年 | 11篇 |
2013年 | 36篇 |
2012年 | 25篇 |
2011年 | 36篇 |
2010年 | 19篇 |
2009年 | 8篇 |
2008年 | 26篇 |
2007年 | 28篇 |
2006年 | 27篇 |
2005年 | 35篇 |
2004年 | 23篇 |
2003年 | 33篇 |
2002年 | 20篇 |
2001年 | 11篇 |
2000年 | 4篇 |
1999年 | 6篇 |
1998年 | 5篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1994年 | 2篇 |
1992年 | 4篇 |
1991年 | 6篇 |
1990年 | 6篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1986年 | 5篇 |
1985年 | 6篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1969年 | 2篇 |
1967年 | 4篇 |
1934年 | 1篇 |
1917年 | 1篇 |
1916年 | 1篇 |
1915年 | 1篇 |
1912年 | 1篇 |
排序方式: 共有535条查询结果,搜索用时 187 毫秒
41.
Colbourne JK Pfrender ME Gilbert D Thomas WK Tucker A Oakley TH Tokishita S Aerts A Arnold GJ Basu MK Bauer DJ Cáceres CE Carmel L Casola C Choi JH Detter JC Dong Q Dusheyko S Eads BD Fröhlich T Geiler-Samerotte KA Gerlach D Hatcher P Jogdeo S Krijgsveld J Kriventseva EV Kültz D Laforsch C Lindquist E Lopez J Manak JR Muller J Pangilinan J Patwardhan RP Pitluck S Pritham EJ Rechtsteiner A Rho M Rogozin IB Sakarya O Salamov A Schaack S Shapiro H Shiga Y Skalitzky C Smith Z Souvorov A Sung W 《Science (New York, N.Y.)》2011,331(6017):555-561
We describe the draft genome of the microcrustacean Daphnia pulex, which is only 200 megabases and contains at least 30,907 genes. The high gene count is a consequence of an elevated rate of gene duplication resulting in tandem gene clusters. More than a third of Daphnia's genes have no detectable homologs in any other available proteome, and the most amplified gene families are specific to the Daphnia lineage. The coexpansion of gene families interacting within metabolic pathways suggests that the maintenance of duplicated genes is not random, and the analysis of gene expression under different environmental conditions reveals that numerous paralogs acquire divergent expression patterns soon after duplication. Daphnia-specific genes, including many additional loci within sequenced regions that are otherwise devoid of annotations, are the most responsive genes to ecological challenges. 相似文献
42.
Adriani O Barbarino GC Bazilevskaya GA Bellotti R Boezio M Bogomolov EA Bonechi L Bongi M Bonvicini V Borisov S Bottai S Bruno A Cafagna F Campana D Carbone R Carlson P Casolino M Castellini G Consiglio L De Pascale MP De Santis C De Simone N Di Felice V Galper AM Gillard W Grishantseva L Jerse G Karelin AV Koldashov SV Krutkov SY Kvashnin AN Leonov A Malakhov V Malvezzi V Marcelli L Mayorov AG Menn W Mikhailov VV Mocchiutti E Monaco A Mori N Nikonov N Osteria G Palma F Papini P Pearce M 《Science (New York, N.Y.)》2011,332(6025):69-72
Protons and helium nuclei are the most abundant components of the cosmic radiation. Precise measurements of their fluxes are needed to understand the acceleration and subsequent propagation of cosmic rays in our Galaxy. We report precision measurements of the proton and helium spectra in the rigidity range 1 gigavolt to 1.2 teravolts performed by the satellite-borne experiment PAMELA (payload for antimatter matter exploration and light-nuclei astrophysics). We find that the spectral shapes of these two species are different and cannot be described well by a single power law. These data challenge the current paradigm of cosmic-ray acceleration in supernova remnants followed by diffusive propagation in the Galaxy. More complex processes of acceleration and propagation of cosmic rays are required to explain the spectral structures observed in our data. 相似文献
43.
Gunn-Moore DA McFarland SE Schock A Brewer JI Crawshaw TR Clifton-Hadley RS Shaw DJ 《Journal of Feline Medicine and Surgery》2011,13(12):945-952
This study investigated 339 cases of feline mycobacterial infection, with histopathology findings from 225 cases, and treatment and outcome information from 184 cases. Tissue samples from cats with cutaneous lesions or suspicious masses at exploratory laparotomy were submitted to the Veterinary Laboratories Agency for mycobacterial culture over a 4-year period to December 2008. The study reviewed the files for information about histopathology, treatment and outcome, and blindly reviewed histopathological changes (including staining for acid-fast bacteria [AFB]) in a sub-set of 45 cases. When a cat is suspected of having a mycobacterial infection, accurate identification of the species involved helps to determine possible treatment options and prognosis. The study confirmed that histopathology and the presence of AFB are useful tools in the recognition of mycobacterial infection. Unfortunately, they did little to help determine the species of mycobacteria involved. The study identified a group of cats that were negative for AFB at the primary laboratory, but from which mycobacteria could be cultured; commonly Mycobacterium bovis or Mycobacterium microti. The study also identified a group of cats which where culture negative, despite typical signs of mycobacterial infection and positive AFB staining. Many cases responded favourably to treatment (56% of the cases where information was available), and many cats gained complete remission (42%). However, relapses were common (64%) and often followed by pulmonary and/or systemic spread that may have resulted from treatment with short courses of single drugs. This study shows that the diagnosis and treatment of feline mycobacteriosis is complex and challenging. 相似文献
44.
Lyons MM Yu C Toma RB Cho SY Reiboldt W Lee J van Breemen RB 《Journal of agricultural and food chemistry》2003,51(20):5867-5870
Resveratrol in the fruits of bilberry (Vaccinium myrtillus L.), the lowbush "wild" blueberry (Vaccinium angustifolium Aiton), the rabbiteye blueberry (Vaccinium ashei Reade), and the highbush blueberry (Vaccinium corymbosum L.) were measured using a new assay based on high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS). The LC-MS/MS assay provided lower limits of detection than previous methods for resveratrol measurement, 90 fmol of trans-resveratrol injected on-column, and a linear standard curve spanning >3 orders of magnitude. The recoveries of resveratrol from blueberries spiked with 1.8, 3.6, or 36 ng/g were 91.5 +/- 4.5, 95.6 +/- 6.5, and 88.0 +/- 3.6%, respectively. trans-Resveratrol but not cis-resveratrol was detected in both blueberry and bilberry samples. The highest levels of trans-resvertatrol in these specimens were 140.0 +/- 29.9 pmol/g in highbush blueberries from Michigan and 71.0 +/- 15.0 pmol/g in bilberries from Poland. However, considerable regional variation was observed; highbush blueberries from British Columbia contained no detectable resveratrol. Because blueberries and bilberries are often consumed after cooking, the effect of baking on resveratrol content was investigated. After 18 min of heating at 190 degrees C, between 17 and 46% of the resveratrol had degraded in the various Vaccinium species. Therefore, the resveratrol content of baked or heat-processed blueberries or bilberries should be expected to be lower than in the raw fruit. Although blueberries and bilberries were found to contain resveratrol, the level of this chemoprotective compound in these fruits was <10% that reported for grapes. Furthermore, cooking or heat processing of these berries will contribute to the degradation of resveratrol. 相似文献
45.
Jacqueline W.M. Postma Pål Axel Olsson Ursula Falkengren-Grerup 《Soil biology & biochemistry》2007,39(2):400-408
Colonisation by root endophytes can be beneficial to plants growing on acid, nutrient-poor soils. Arbuscular mycorrhizal (AM) fungi can supply herbs with nutrients and may give protection against aluminium toxicity. Two other root colonising fungi, fine endophytes (FE) and dark septate fungi (DSE), are less well known but are potentially of benefit to their host plant. AM fungi are the most prevalent symbionts in herbs at neutral to acidic soil pH. At extremely low pH, fungal growth can be limited and AM colonisation is usually rare. Fine and dark septate endophytes, on the other hand, have been observed more often under these conditions. In order to relate endophyte colonisation to a gradient in soil pH, we investigated root colonisation by AM, FE and DSE in Maianthemum bifolium, Galium odoratum, Mercurialis perennis and Stellaria nemorum, from a range of acidic beech forests. With decreasing pH, colonisation by AM decreased, whereas the other two endophytes increased. AM and FE colonisation were inversely correlated in Maianthemum bifolium. We compared changes in root colonisation with those in chemical composition of soil and leaf samples and found a positive correlation between leaf magnesium concentrations and the presence of DSE in Galium odoratum. Aluminium concentration in Maianthemum bifolium tended to be lower when FE colonisation was high, suggesting a possible role for the fungi in plant protection against Al. We suggest that FE and DSE may replace AM fungi in herbaceous vegetation at extremely low pH, counteracting some of the negative effects of high soil acidity on plants. 相似文献
46.
A new Fourier transform infrared (FTIR) spectroscopic method based on single-bounce attenuated total reflectance (SB-ATR) spectroscopy was developed for the analysis of distilled liquors and wines. For distilled liquors, a partial least-squares (PLS) calibration was developed for alcohol determination based on the SB-ATR/FTIR spectra of mixtures of ethanol and distilled water. An independent set of 12 different distilled liquor samples was predicted from the PLS calibration, and a standard deviation of the differences for accuracy (SDD(a)) between actual and predicted values of 0.142% (v/v) was obtained. The potential utility of SB-ATR/FTIR spectroscopy for the analysis of wines was initially evaluated based on a comparison with Fourier transform near-infrared (FT-NIR) spectroscopy and FTIR spectroscopy using a flow-through transmission cell. PLS calibrations for alcohol, total reducing sugars, total acidity and pH were developed using pre-analyzed wine samples (n = 28), and for SB-ATR/FTIR spectroscopy, the SDD(a) for the leave-one-out cross-validation statistics were of the order of 0.100% (v/v), 0.707 g L(-1), 0.189 g L(-1) (H2SO4), and 0.230, respectively. Overall, the SB-ATR/FTIR results were better than those obtained using FT-NIR spectroscopy and comparable to those obtained with transmission FTIR spectroscopy. A PLS calibration based on preanalyzed wine samples (n = 72) for the prediction of 11 different components and parameters in wines by SB-ATR/FTIR spectroscopy was subsequently developed and validated using an independent sample set (n = 77). Good coefficients of correlation between the reference and predicted values for the validation set were obtained for most of the components and parameters except citric acid, volatile acids, and total SO2. The results of this study demonstrate the suitability of SB-ATR/FTIR spectroscopy for the routine analysis of distilled liquors and wines. 相似文献
47.
Vieira HS Takahashi JA Boaventura MA 《Journal of agricultural and food chemistry》2002,50(13):3704-3707
In the search for new routes in the synthesis of hydroxylated kaurane diterpenoids, Verticillium lecanii, grown in a mineral liquid medium for 48 h, was fed with ent-17,19-dihydroxy-16betaH-kaurane, obtained by hydroboration/oxidation of kaurenoic acid, a natural product easily isolated from plants of the genera Xylopia (Annonaceae) and Wedelia (Asteraceae). After 14 days, the culture medium was extracted with ethyl acetate, and the metabolites were purified by column chromatography on silica gel. The results show that V. lecanii biotransformed the starting material into three novel compounds: ent-11alpha,17,19-trihydroxy-16betaH-kaurane; ent-7alpha,17,19-trihydroxy-16betaH-kaurane; and ent-7beta,17,19-trihydroxy-16betaH-kaurane, the structures of which were fully elucidated by using classical and modern two-dimensional NMR techniques. 相似文献
48.
A four-year-old entire male cocker spaniel was presented with a history of dyspnoea due to tracheal stenosis. As part of the clinical approach, a coagulation screening profile revealed moderately reduced levels of Factor VIII procoagulant activity (VIII: C), but elevated factor VHI-related antigen levels (VIIIR: Ag). A diagnosis of haemophilia A (classic haemophilia) was made and the tracheal stenosis attributed to a mediastinal haematoma. The dyspnoea was alleviated by the surgical insertion of a tracheostomy tube and the dog was treated with citrated whole blood and fresh-frozen canine plasma. Response to treatment was excellent and follow-up radiography three months later revealed resolution of the tracheal stenosis. 相似文献
49.
Scimitar horned oryx (Oryx dammah), kept under confined and unconfined conditions were immobilised with etorphine in combination with acepromazine or xylazine or both, and with xylazine alone. Both groups of animals were successfully sedated with etorphine and xylzine, with or without acepromazine, although hypothermia and mild hypoxaemia and a fall in packed cell volume were frequently noted. Xylazine alone produced a dose dependent degree of sedation in semitame subadult animals kept in confinement, but only slight depression in their wild, unconfined counterparts. If xylazine was not included in the immobilising mixture induction was traumatic and full sedation not achieved. Heart rates and arterial pressures (systemic and pulmonary) were also monitored but no remarkable changes were noted. The only abnormalities in blood biochemistry were raised aspartate transminase and creatine kinase. Ruminal regurgitation could be a major problem if endotracheal intubation was not achieved early in the procedure. 相似文献
50.