全文获取类型
收费全文 | 4122篇 |
免费 | 210篇 |
国内免费 | 13篇 |
专业分类
林业 | 267篇 |
农学 | 149篇 |
基础科学 | 33篇 |
793篇 | |
综合类 | 655篇 |
农作物 | 238篇 |
水产渔业 | 387篇 |
畜牧兽医 | 1374篇 |
园艺 | 136篇 |
植物保护 | 313篇 |
出版年
2023年 | 35篇 |
2022年 | 26篇 |
2021年 | 87篇 |
2020年 | 93篇 |
2019年 | 101篇 |
2018年 | 91篇 |
2017年 | 91篇 |
2016年 | 97篇 |
2015年 | 65篇 |
2014年 | 101篇 |
2013年 | 192篇 |
2012年 | 240篇 |
2011年 | 278篇 |
2010年 | 180篇 |
2009年 | 144篇 |
2008年 | 232篇 |
2007年 | 251篇 |
2006年 | 224篇 |
2005年 | 230篇 |
2004年 | 223篇 |
2003年 | 212篇 |
2002年 | 199篇 |
2001年 | 55篇 |
2000年 | 51篇 |
1999年 | 51篇 |
1998年 | 36篇 |
1997年 | 30篇 |
1996年 | 45篇 |
1995年 | 32篇 |
1994年 | 33篇 |
1993年 | 45篇 |
1992年 | 29篇 |
1991年 | 39篇 |
1990年 | 34篇 |
1989年 | 40篇 |
1988年 | 31篇 |
1987年 | 22篇 |
1986年 | 29篇 |
1985年 | 27篇 |
1984年 | 34篇 |
1983年 | 22篇 |
1982年 | 13篇 |
1981年 | 16篇 |
1979年 | 14篇 |
1978年 | 13篇 |
1977年 | 11篇 |
1976年 | 12篇 |
1975年 | 16篇 |
1974年 | 16篇 |
1973年 | 16篇 |
排序方式: 共有4345条查询结果,搜索用时 15 毫秒
31.
The Paleocene-Eocene Thermal Maximum (PETM, approximately 55 million years ago) was an interval of global warming and ocean acidification attributed to rapid release and oxidation of buried carbon. We show that the onset of the PETM coincided with a prominent increase in the origination and extinction of calcareous phytoplankton. Yet major perturbation of the surface-water saturation state across the PETM was not detrimental to the survival of most calcareous nannoplankton taxa and did not impart a calcification or ecological bias to the pattern of evolutionary turnover. Instead, the rate of environmental change appears to have driven turnover, preferentially affecting rare taxa living close to their viable limits. 相似文献
32.
Sachin Vyas Maurizio Bettiga Ulrika Rova Paul Christakopoulos Leonidas Matsakas Alok Patel 《Marine drugs》2022,20(3)
The marine microorganisms thraustochytrids have been explored for their potential in the production of various bioactive compounds, such as DHA, carotenoids, and squalene. Squalene is a secondary metabolite of the triterpenoid class and is known for its importance in various industrial applications. The bioinformatic analysis for squalene synthase (SQS) gene (the first key enzyme in the tri-terpenoid synthesis pathway), that is prevailing among thraustochytrids, is poorly investigated. In-silico studies combining sequence alignments and bioinformatic tools helped in the preliminary characterization of squalene synthases found in Aurantiochytrium limacinum. The sequence contained highly conserved regions for SQS found among different species indicated the enzyme had all the regions for its functionality. The signal peptide sequence and transmembrane regions were absent, indicating an important aspect of the subcellular localization. Secondary and 3-D models generated using appropriate templates demonstrated the similarities with SQS of the other species. The 3-D model also provided important insights into possible active, binding, phosphorylation, and glycosylation sites. 相似文献
33.
Susan P. Crowley Fergal O’Gara Orla O’Sullivan Paul D. Cotter Alan D. W. Dobson 《Marine drugs》2014,12(12):5916-5929
Antibiotic resistance among pathogenic microorganisms is becoming ever more common. Unfortunately, the development of new antibiotics which may combat resistance has decreased. Recently, however the oceans and the marine animals that reside there have received increased attention as a potential source for natural product discovery. Many marine eukaryotes interact and form close associations with microorganisms that inhabit their surfaces, many of which can inhibit the attachment, growth or survival of competitor species. It is the bioactive compounds responsible for the inhibition that is of interest to researchers on the hunt for novel bioactives. The genus Pseudovibrio has been repeatedly identified from the bacterial communities isolated from marine surfaces. In addition, antimicrobial activity assays have demonstrated significant antimicrobial producing capabilities throughout the genus. This review will describe the potency, spectrum and possible novelty of the compounds produced by these bacteria, while highlighting the capacity for this genus to produce natural antimicrobial compounds which could be employed to control undesirable bacteria in the healthcare and food production sectors. 相似文献
34.
Iris J. Joye Tim Beliën Kristof Brijs Paul Proost Wim Soetaert Jan A. Delcour 《Journal of Cereal Science》2010
A formerly unknown nucleotide pyrophosphatase/phosphodiesterase (NPP) of wheat (Triticum aestivum L.) (TaNPP) was recombinantly produced in Pichia pastoris (TaNPPr) following assembly of the sequence out of wheat ESTs using sequences of known NPPs. Simultaneously, a phosphodiesterase was purified to homogeneity from wheat germs, characterised and identified as TaNPP. TaNPP contains the highly conserved catalytic substrate and metal binding residues and displays properties [high pH optimum, glycosylation, high thermostability and inhibition by EDTA and adenosine 5′-monophosphate (AMP)] similar to those of mammalian enzymes characterised earlier. The sequence of TaNPP includes that of a putative transmembrane domain, a characteristic of most NPPs. Both recombinant and native TaNPP partially occur as oligomeric proteins on SDS PAGE. Upon addition of DTT, both migrate as monomeric proteins. Part of the native wheat protein even occurs in its truncated form, thus lacking the transmembrane region. Out of a range of tested natural substrates, TaNPP had the highest affinity towards adenine containing nucleotides. While Michaelis-Menten kinetics were valid in the low substrate concentration range, at higher concentrations, they were no longer applicable. TaNPP shows no similarity to the recently characterised rice and barley enzymes and, is hence, one of the first characterised plant NPPs resembling mammalian NPPs. 相似文献
35.
Jadwiga W. Płodowska Peter H. J. Jongebloed Pieter A. C. M. Van De Sanden Paul C. Struik 《Potato Research》1989,32(3):255-266
Summary Single-stemmed potato plants, cv. Bintje, were grown on a nutrient solution under controlled conditions. They were exposed
to a short drought stress, or remained untreated. Short-term changes in tuber volume and in specific leaf weight were measured
non-destructively.
Tubers from control plants increased rapidly in volume during the night and did not grow, or even shrivelled during the day.
Tubers of stressed plants did not show a uniform response; some tubers markedly declined in volume during the day. The patterns
of volume increase of stressed plants became erratic after the stress, mainly because some plants never fully recovered.
Patterns of diurnal fluctuation in tuber volume were similar to diurnal changes in specific leaf weight; tubers within the
same stressed plant sometimes reacted differently. In these cases the effects on the diurnal fluctuation partly reflected
the long-term effects, reported in an earlier paper. 相似文献
36.
Wadley L Sievers C Bamford M Goldberg P Berna F Miller C 《Science (New York, N.Y.)》2011,334(6061):1388-1391
The Middle Stone Age (MSA) is associated with early behavioral innovations, expansions of modern humans within and out of Africa, and occasional population bottlenecks. Several innovations in the MSA are seen in an archaeological sequence in the rock shelter Sibudu (South Africa). At ~77,000 years ago, people constructed plant bedding from sedges and other monocotyledons topped with aromatic leaves containing insecticidal and larvicidal chemicals. Beginning at ~73,000 years ago, bedding was burned, presumably for site maintenance. By ~58,000 years ago, bedding construction, burning, and other forms of site use and maintenance intensified, suggesting that settlement strategies changed. Behavioral differences between ~77,000 and 58,000 years ago may coincide with population fluctuations in Africa. 相似文献
37.
38.
Ingeborg F. Pedersen Peter Srensen Jim Rasmussen Paul J. A. Withers Gitte Holton Rubk 《植物养料与土壤学杂志》2019,182(4):541-551
We investigated the interacting effects of inorganic nitrogen and the main inorganic phosphorus form in dairy manure (dicalcium phosphate, CaHPO4) on growth, nutrient uptake, and rhizosphere pH of young maize plants. In a pot experiment, three levels of CaHPO4 (0, 167, and 500 mg P pot?1) were combined with nitrogen (637 mg N pot?1) applied at five NH4‐N : NO3‐N ratios (0 : 100, 25 : 75, 50 : 50, 75 : 25, and 100 : 0) and a nitrification inhibitor in a concentrated layer of a typical acid sandy soil from Denmark. 15N‐labeled NH4‐N was applied to differentiate the role of nitrification and to partition nitrogen uptake derived from NH4‐N. Among treatments including nitrogen, shoot biomass, rooting and phosphorus uptake were significantly higher at the five‐leaf stage when CaHPO4 was applied with NH4‐N : NO3‐N ratios of 50 : 50 and 75 : 25. In these treatments, rhizosphere pH dropped significantly in direct proportion with NH4‐N uptake. The fertilizers in the concentrated layer had a root‐inhibiting effect in treatments without phosphorus supply and in treatments with pure NO3‐N or NH4‐N supply. Increased nitrogen uptake as NH4‐N instead of NO3‐N reduced rhizosphere pH and enhanced acquisition of applied CaHPO4 by young maize plants, which may have positive implications for the enhanced utilization of manure phosphorus. 相似文献
39.
Thakur Manisha Luharch Rakshandha Sharma Vishal Sharma Dharam Paul 《Genetic Resources and Crop Evolution》2022,69(2):567-575
Genetic Resources and Crop Evolution - Santa Rosa and Frontier are the major Japanese plum (Prunus salicina Lindl.) cultivars grown throughout the world. The present investigation was performed to... 相似文献
40.
Movement of polyethylene glycol (PEG) 1000 from wood cell lumens into adjacent cell walls was studied for different cell wall
moisture contents (MCs) and PEG solvents; relative amounts of PEG that penetrated into the cell walls were estimated by Raman
microscopy. It was shown that samples treated with PEG from chloroform solution adsorb less PEG than samples treated with
PEG-water solution even in the case of samples with open cell wall structure near fibre saturation point MC. Reconditioning
of PEG-chloroform treated samples at high relative humidities enhanced PEG bulking of cell walls, but not to the maximum amounts
observed with PEG-water treatments. Raman microscopy was a useful tool for estimating relative PEG amounts in the cell walls. 相似文献