全文获取类型
收费全文 | 1148篇 |
免费 | 79篇 |
专业分类
林业 | 109篇 |
农学 | 36篇 |
基础科学 | 8篇 |
286篇 | |
综合类 | 76篇 |
农作物 | 87篇 |
水产渔业 | 82篇 |
畜牧兽医 | 438篇 |
园艺 | 23篇 |
植物保护 | 82篇 |
出版年
2024年 | 4篇 |
2023年 | 13篇 |
2022年 | 16篇 |
2021年 | 32篇 |
2020年 | 33篇 |
2019年 | 58篇 |
2018年 | 45篇 |
2017年 | 44篇 |
2016年 | 45篇 |
2015年 | 31篇 |
2014年 | 52篇 |
2013年 | 65篇 |
2012年 | 83篇 |
2011年 | 103篇 |
2010年 | 67篇 |
2009年 | 43篇 |
2008年 | 57篇 |
2007年 | 72篇 |
2006年 | 51篇 |
2005年 | 37篇 |
2004年 | 48篇 |
2003年 | 43篇 |
2002年 | 37篇 |
2001年 | 15篇 |
2000年 | 10篇 |
1999年 | 12篇 |
1998年 | 4篇 |
1997年 | 7篇 |
1996年 | 6篇 |
1995年 | 8篇 |
1994年 | 7篇 |
1993年 | 9篇 |
1992年 | 13篇 |
1991年 | 7篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1982年 | 2篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1974年 | 2篇 |
1972年 | 5篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有1227条查询结果,搜索用时 828 毫秒
71.
Of the oxidants and nitrogenous compounds found in ambient air, O3 and NO2 are among those most thoroughy investigated. Large health data bases have been compiled in air quality criteria documents, which serve as the basis for review of primary (health) national ambient air quality standards (NAAQS) for each pollutant. When comparisons can be made, O3 is generally more toxic than other photochemical oxidant species at or near ambient levels, although NO2 does not appear to be of more concern with respect to carcinogenesis. Public health effects of concern for O3 range from acute symptoms (e.g. cough) and decreased lung function to persistent functional changes and permanent scarring of lung tissue, a possible precursor to chronic lung disease. Impairment of immune defenses and increased susceptibility to lung infection have also been associated with O3 exposure. Populations at greatest risk include exercising healthy persons, children, and those with preexisting lung disease. Nitrogen dioxide exhibits similar health effects but at higher concentrations. These effects include acute symptoms and lung function impairment, increased susceptibility to acute respiratory infection, and possibly conditions leading to chronic lung disease. Populations potentially at risk include children, asthmatics, and individuals who exercise in the presence of NO2. Health effects data for O3 and NO2 are under consideration in the current review of both primary NAAQS. 相似文献
72.
Effect of different treatments on the evolution of polyamines during refrigerated storage of eggplants 总被引:3,自引:0,他引:3
Rodriguez Sdel C López B Chaves AR 《Journal of agricultural and food chemistry》2001,49(10):4700-4705
The applicability of a thermal treatment was compared with modified-atmosphere (MA) storage in relation to chilling injury (CI) and polyamines evolution in eggplants. Fruits underwent physiological disorders at 3 degrees C, evidenced by the appearance of surface injuries at the third day of storage, and, after moving the fruits to 20 degrees C, by increased respiratory activity and more intense ethylene production. Storage of fruits in sealed low-density polyethylene bags and a previous treatment with heated air (1 h at 35 degrees C) were both effective in retarding chilling injury, though the former was better. Two free polyamines were found in cv. Black Nite: putrescine, in greater proportion, and spermidine. Putrescine increased in control (untreated) fruits stored at 3 degrees C in parallel with the external appearance of chilling injury, whereas this increase was either not exhibited or retarded in treated or MA stored fruits. Spermidine did not change in control fruits at 3 degrees C, remaining almost constant over the whole storage period, whereas in heat- and MAP-treated fruits spermidine levels exhibited a decrease. 相似文献
73.
The filamentous fungal ascomycete Colletotrichum magna causes anthracnose in cucurbit plants. Isolation of a nonpathogenic mutant of this species (path-1) resulted in maintained wild-type levels of in vitro sporulation, spore adhesion, appressorial formation, and infection. Path-1 grew throughout host tissues as an endophyte and retained the wild-type host range, which indicates that the genetics involved in pathogenicity and host specificity are distinct. Prior infection with path-1 protected plants from disease caused by Colletotrichum and Fusarium.Genetic analysis of a cross between path-1 and wild-type strains indicated mutation of a single locus. 相似文献
74.
A mutualistic association between a fungal endophyte and a tropical panic grass allows both organisms to grow at high soil temperatures. We characterized a virus from this fungus that is involved in the mutualistic interaction. Fungal isolates cured of the virus are unable to confer heat tolerance, but heat tolerance is restored after the virus is reintroduced. The virus-infected fungus confers heat tolerance not only to its native monocot host but also to a eudicot host, which suggests that the underlying mechanism involves pathways conserved between these two groups of plants. 相似文献
75.
Prevention of vaginal SHIV transmission in rhesus macaques through inhibition of CCR5 总被引:1,自引:0,他引:1
Lederman MM Veazey RS Offord R Mosier DE Dufour J Mefford M Piatak M Lifson JD Salkowitz JR Rodriguez B Blauvelt A Hartley O 《Science (New York, N.Y.)》2004,306(5695):485-487
Topical agents, such as microbicides, that can protect against human immunodeficiency virus (HIV) transmission are urgently needed. Using a chimeric simian/human immunodeficiency virus (SHIV SF162), which is tropic for the chemokine receptor CCR5, we report that topical application of high doses of PSC-RANTES, an amino terminus-modified analog of the chemokine RANTES, provided potent protection against vaginal challenge in rhesus macaques. These experimental findings have potentially important implications for understanding vaginal transmission of HIV and the design of strategies for its prevention. 相似文献
76.
Reoviruslike agent in stools: association with infantile diarrhea and development of serologic tests 总被引:39,自引:0,他引:39
A Z Kapikian H W Kim R G Wyatt W J Rodriguez S Ross W L Cline R H Parrott R M Chanock 《Science (New York, N.Y.)》1974,185(156):1049-1053
Reoviruslike particles were visualized by electron microscopy in stool filtrates prepared from stools of infants and young children with severe acute gastroenteritis. Patients who had such particles in their stools and whose paired acute and convalescent serums were tested developed an antibody response to the reoviruslike agent, which was measured by immune electron microscopy and by complement fixation. The reoviruslike agent was antigenically related to the epizootic diarrhea of infant mice virus and the Nebraska calf diarrhea virus. 相似文献
77.
Montañez IP Tabor NJ Niemeier D Dimichele WA Frank TD Fielding CR Isbell JL Birgenheier LP Rygel MC 《Science (New York, N.Y.)》2007,315(5808):87-91
The late Paleozoic deglaciation is the vegetated Earth's only recorded icehouse-to-greenhouse transition, yet the climate dynamics remain enigmatic. By using the stable isotopic compositions of soil-formed minerals, fossil-plant matter, and shallow-water brachiopods, we estimated atmospheric partial pressure of carbon dioxide (pCO2) and tropical marine surface temperatures during this climate transition. Comparison to southern Gondwanan glacial records documents covariance between inferred shifts in pCO2, temperature, and ice volume consistent with greenhouse gas forcing of climate. Major restructuring of paleotropical flora in western Euramerica occurred in step with climate and pCO2 shifts, illustrating the biotic impact associated with past CO2-forced turnover to a permanent ice-free world. 相似文献
78.
Mueller CA Broz P Müller SA Ringler P Erne-Brand F Sorg I Kuhn M Engel A Cornelis GR 《Science (New York, N.Y.)》2005,310(5748):674-676
Many pathogenic bacteria use injectisomes to deliver effector proteins into host cells through type III secretion. Injectisomes consist of a basal body embedded in the bacterial membranes and a needle. In Yersinia, translocation of effectors requires the YopB and YopD proteins, which form a pore in the target cell membrane, and the LcrV protein, which assists the assembly of the pore. Here we report that LcrV forms a distinct structure at the tip of the needle, the tip complex. This unique localization of LcrV may explain its crucial role in the translocation process and its efficacy as the main protective antigen against plague. 相似文献
79.
80.
Muñoz J Felicísimo AM Cabezas F Burgaz AR Martínez I 《Science (New York, N.Y.)》2004,304(5674):1144-1147
Anisotropic (direction-dependent) long-distance dispersal (LDD) by wind has been invoked to explain the strong floristic affinities shared among landmasses in the Southern Hemisphere. Its contribution has not yet been systematically tested because of the previous lack of global data on winds. We used global winds coverage from the National Aeronautics and Space Administration SeaWinds scatterometer to test whether floristic similarities of Southern Hemisphere moss, liverwort, lichen, and pteridophyte floras conform better with (i) the anisotropic LDD hypothesis, which predicts that connection by "wind highways" increases floristic similarities, or (ii) a direction-independent LDD hypothesis, which predicts that floristic similarities among sites increase with geographic proximity. We found a stronger correlation of floristic similarities with wind connectivity than with geographic proximities, which supports the idea that wind is a dispersal vehicle for many organisms in the Southern Hemisphere. 相似文献