全文获取类型
收费全文 | 561篇 |
免费 | 35篇 |
专业分类
596篇 |
出版年
2021年 | 4篇 |
2020年 | 4篇 |
2019年 | 7篇 |
2018年 | 4篇 |
2017年 | 7篇 |
2016年 | 12篇 |
2015年 | 23篇 |
2014年 | 30篇 |
2013年 | 26篇 |
2012年 | 39篇 |
2011年 | 30篇 |
2010年 | 10篇 |
2009年 | 8篇 |
2008年 | 25篇 |
2007年 | 31篇 |
2006年 | 26篇 |
2005年 | 34篇 |
2004年 | 19篇 |
2003年 | 20篇 |
2002年 | 24篇 |
2001年 | 11篇 |
2000年 | 8篇 |
1999年 | 7篇 |
1998年 | 8篇 |
1997年 | 6篇 |
1996年 | 3篇 |
1995年 | 11篇 |
1994年 | 7篇 |
1993年 | 10篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 10篇 |
1989年 | 11篇 |
1988年 | 10篇 |
1987年 | 9篇 |
1986年 | 6篇 |
1985年 | 6篇 |
1984年 | 12篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 8篇 |
1976年 | 5篇 |
1975年 | 5篇 |
1973年 | 4篇 |
1968年 | 2篇 |
1966年 | 3篇 |
排序方式: 共有596条查询结果,搜索用时 0 毫秒
81.
82.
Novel Members of Glycoside Hydrolase Family 13 Derived from Environmental DNA 总被引:1,自引:0,他引:1 下载免费PDF全文
Antje Labes Eva Nordberg Karlsson Olafur H. Fridjonsson Pernilla Turner Gudmundur O. Hreggvidson Jakob K. Kristjansson Olle Holst Peter Schnheit 《Applied microbiology》2008,74(6):1914-1921
Starch and pullulan-modifying enzymes of the α-amylase family (glycoside hydrolase family 13) have several industrial applications. To date, most of these enzymes have been derived from isolated organisms. To increase the number of members of this enzyme family, in particular of the thermophilic representatives, we have applied a consensus primer-based approach using DNA from enrichments from geothermal habitats. With this approach, we succeeded in isolating three new enzymes: a neopullulanase and two cyclodextrinases. Both cyclodextrinases displayed significant maltogenic amylase side activity, while one showed significant neopullulanase side activity. Specific motifs and domains that correlated with enzymatic activities were identified; e.g., the presence of the N domain was correlated with cyclodextrinase activity. The enzymes exhibited stability under thermophilic conditions and showed features appropriate for biotechnological applications. 相似文献
83.
The natural preindustrial ANC and pH decline associated with 22 melt events from 11 streams during spring flood of 1997 and 1998 in Northern Sweden have been assessed using the Boreal Dilution Model (BDM). The results show that the spring flood pH decline of 0.5 to 2.5 pH units in the streams was largely caused by natural processes. The most important driving factors influencing pH were TOC increase in combination with ANC dilution. The study also demonstrates that pH in some streams can decline to pH values close to 4.5 as a result of natural processes alone. In general the anthropogenic component of the pH decline was between 0.1 and 0.3 pH units superimposed on the natural pH decline. Furthermore, the anthropogenic contribution to ANC and pH decline generally followed the gradient of anthropogenic S deposition in the region. The sites with the greatest inferred anthropogenic influence are also those for which the assumptions used in the BDM were most sensitive. Nevertheless, the results from this study suggest that the regional impact of anthropogenic acid deposition on the ANC and pH in northern Sweden is currently limited. 相似文献
84.
85.
Sigrid C Roberts Jerry Scott Judith E Gasteier Yuqui Jiang Benjamin Brooks Armando Jardim Nicola S Carter Olle Heby Buddy Ullman 《The Journal of biological chemistry》2002,277(8):5902-5909
The polyamine biosynthetic enzyme, S-adenosylmethionine decarboxylase (ADOMETDC) has been advanced as a potential target for antiparasitic chemotherapy. To investigate the importance of this protein in a model parasite, the gene encoding ADOMETDC has been cloned and sequenced from Leishmania donovani. The Delta adometdc null mutants were created in the insect vector form of the parasite by double targeted gene replacement. The Delta adometdc strains were incapable of growth in medium without polyamines; however, auxotrophy could be rescued by spermidine but not by putrescine, spermine, or methylthioadenosine. Incubation of Delta adometdc parasites in medium lacking polyamines resulted in a drastic increase of putrescine and glutathione levels with a concomitant decrease in the amounts of spermidine and the spermidine-containing thiol trypanothione. Parasites transfected with an episomal ADOMETDC construct were created in both wild type and Delta adometdc parasites. ADOMETDC overexpression abrogated polyamine auxotrophy in the Delta adometdc L. donovani. In addition, ADOMETDC overproduction in wild type parasites alleviated the toxic effects of 5'-(((Z)-4-amino-2-butenyl)methylamino)-5'-deoxyadenosine (MDL 73811), but not pentamidine, berenil, or methylglyoxyl bis(guanylhydrazone), all inhibitors of ADOMETDC activities in vitro. The molecular, biochemical, and genetic characterization of ADOMETDC establishes that it is essential in L. donovani promastigotes and a potential target for therapeutic validation. 相似文献
86.
Olle Anderbrant Jan Lfqvist Hans-Erik Hgberg Erik Hedenstrm 《Entomologia Experimentalis et Applicata》1995,74(1):83-90
Mating disruption of the pine sawflyNeodiprion sertifer (Geoffroy) (Hymenoptera: Diprionidae) was strongly indicated by reduced male trap catches in pine plantations permeated with
the sex phermone, (2S, 3S, 7S)-diprionly acetate. The trap catch reduction was 95 to near 100% when dispensers every 10 m were used, giving a total release
of about 3 mg per hectare and day. Two mg of pheromone per cotton roll dispenser maintained low catches for the whole season
(about 2 months) without any renewal of disruption dispensers. Anerythro-mixture was as effective as the pure pheromone isomer. The effects of the experiments on population density and sex ratio
were not possible to investigate, due to a general collapse of the population, also outside experimental plots, the year after
the experiments. 相似文献
87.
Photoreceptor adaptation ensures appropriate visual responses during changing light conditions and contributes to colour constancy. We used behavioural tests to compare UV-sensitivity of budgerigars after adaptation to UV-rich and UV-poor backgrounds. In the latter case, we found lower UV-sensitivity than expected, which could be the result of photon-shot noise corrupting cone signal robustness or nonlinear background adaptation. We suggest that nonlinear adaptation may be necessary for allowing cones to discriminate UV-rich signals, such as bird plumage colours, against UV-poor natural backgrounds. 相似文献
88.
89.
Extracellular-regulated protein kinase cascades are activated in response to injury in human skeletal muscle 总被引:6,自引:0,他引:6
90.
Olle Lindvall Anders Björklund Tomas Hökfelt Åke Ljungdahl 《Histochemistry and cell biology》1973,35(1):31-38
Summary The glyoxylic acid fluorescence histochemical method for the visualization of neuronal monoamines has been applied to fresh or glyoxylic acid-perfused brain tissue, sectioned with the Vibratome intrument. This technique demonstrates the central noradrenaline and dopamine neuron systems with a sensitivity and richness in details that is superior to the standard Falck-Hillarp formaldehyde method, as observed in the following three ways: First, the entire axon, including the non-terminal portions, became fluorescent; second, more extensive terminal systems were detected in certain brain regions ; third, due to the absence of diffusion, the delicate dopamine-containing fibres in e. g. the caudate nucleus and the median eminence had a distinct fluorescence. It is concluded that the glyoxylic acid method applied to Vibratome sections should be ideal for precise and detailed neuroanatomical studies on central catecholamine neuron systems. 相似文献