全文获取类型
收费全文 | 1205篇 |
免费 | 143篇 |
专业分类
1348篇 |
出版年
2021年 | 11篇 |
2020年 | 12篇 |
2018年 | 11篇 |
2016年 | 23篇 |
2015年 | 31篇 |
2014年 | 34篇 |
2013年 | 50篇 |
2012年 | 64篇 |
2011年 | 45篇 |
2010年 | 39篇 |
2009年 | 26篇 |
2008年 | 44篇 |
2007年 | 36篇 |
2006年 | 37篇 |
2005年 | 46篇 |
2004年 | 27篇 |
2003年 | 34篇 |
2002年 | 36篇 |
2001年 | 34篇 |
2000年 | 33篇 |
1999年 | 28篇 |
1998年 | 14篇 |
1997年 | 15篇 |
1996年 | 19篇 |
1995年 | 13篇 |
1994年 | 12篇 |
1993年 | 12篇 |
1992年 | 24篇 |
1991年 | 15篇 |
1990年 | 23篇 |
1989年 | 26篇 |
1988年 | 19篇 |
1987年 | 16篇 |
1986年 | 17篇 |
1985年 | 25篇 |
1984年 | 18篇 |
1983年 | 25篇 |
1982年 | 16篇 |
1981年 | 11篇 |
1980年 | 18篇 |
1978年 | 19篇 |
1974年 | 15篇 |
1973年 | 21篇 |
1972年 | 21篇 |
1971年 | 10篇 |
1970年 | 11篇 |
1969年 | 12篇 |
1968年 | 15篇 |
1966年 | 13篇 |
1963年 | 10篇 |
排序方式: 共有1348条查询结果,搜索用时 13 毫秒
41.
Macroscopic biofilms in fracture-dominated sediment that anaerobically oxidize methane 总被引:1,自引:0,他引:1
Briggs BR Pohlman JW Torres M Riedel M Brodie EL Colwell FS 《Applied and environmental microbiology》2011,77(19):6780-6787
Methane release from seafloor sediments is moderated, in part, by the anaerobic oxidation of methane (AOM) performed by consortia of archaea and bacteria. These consortia occur as isolated cells and aggregates within the sulfate-methane transition (SMT) of diffusion and seep-dominant environments. Here we report on a new SMT setting where the AOM consortium occurs as macroscopic pink to orange biofilms within subseafloor fractures. Biofilm samples recovered from the Indian and northeast Pacific Oceans had a cellular abundance of 10(7) to 10(8) cells cm(-3). This cell density is 2 to 3 orders of magnitude greater than that in the surrounding sediments. Sequencing of bacterial 16S rRNA genes indicated that the bacterial component is dominated by Deltaproteobacteria, candidate division WS3, and Chloroflexi, representing 46%, 15%, and 10% of clones, respectively. In addition, major archaeal taxa found in the biofilm were related to the ANME-1 clade, Thermoplasmatales, and Desulfurococcales, representing 73%, 11%, and 10% of archaeal clones, respectively. The sequences of all major taxa were similar to sequences previously reported from cold seep environments. PhyloChip microarray analysis detected all bacterial phyla identified by the clone library plus an additional 44 phyla. However, sequencing detected more archaea than the PhyloChip within the phyla of Methanosarcinales and Desulfurococcales. The stable carbon isotope composition of the biofilm from the SMT (-35 to -43‰) suggests that the production of the biofilm is associated with AOM. These biofilms are a novel, but apparently widespread, aggregation of cells represented by the ANME-1 clade that occur in methane-rich marine sediments. 相似文献
42.
43.
Ken W. Smith Linda Smith Elisabeth Charman Kevin Briggs Malcolm Burgess Chris Dennis 《Bird Study》2013,60(4):506-511
Capsule Frass fall was later and of longer duration in woods to the north and west of Britain compared with those in the southeast. Aims Defoliating caterpillars are a major food resource for woodland breeding birds and our aims were to quantify large-scale patterns in the timing and duration of the spring peak in abundance of these caterpillars in oak woodlands in Britain. Methods We deployed traps to collect caterpillar frass at regular intervals through spring in 19 oak woods distributed through England, Wales and Scotland. Models of the temporal patterns of the rate of frass fall were used to explore relationships with geographic variables and average local temperature. Results The date of peak frass fall in 2010 ranged from 20 May to 18 June and was significantly related to altitude, latitude and local April–May temperature. The duration of the peak ranged from 20 to 53 days and was correlated with the date of the peak and April–May temperature. Limited data from 2008 and 2009 indicated considerable between-year variation in the date of the peak, which was consistent with the relationship with local temperature found in 2010. Conclusions The date of peak frass fall was later and the duration of the peak longer in the north and west of Britain compared with the southeast which will have considerable implications for nesting woodland birds such as Pied Flycatchers. The date of the peak was well modelled by local April–May temperature offering the prospect of good predictive models. However, the duration of the peak was less well modelled by local temperature and may be determined by other factors. 相似文献
44.
The mitochondrial phosphate transport protein (PTP) has six (A--F) transmembrane (TM) helices per subunit of functional homodimer with all mutations referring to the subunit of the homodimer. In earlier studies, conservative replacements of several residues located either at the matrix end (Asp39/helix A, Glu137/helix C, Asp236/helix E) or at the membrane center (His32/helix A, Glu136/helix C) of TM helices yielded inactive single mutation PTPs. Some of these residues were suggested to act as phosphate ligands or as part of the proton cotransport path. We now show that the mutation Ser158Thr, not part of a TM helix but located near the center of the matrix loop (Ile141--Ser171) between TM helices C and D, inactivates PTP and is thus also functionally relevant. On the other side of the membrane, the single mutation Glu192Asp at the intermembrane space end of TM helix D yields a PTP with 33% wild-type activity. We constructed double mutants by adding this mutation to the six transport-inactivating mutations. Transport was detected only in those with Asp39Asn, Glu137Gln, or Ser158Thr. We conclude that TM helix D can interact with TM helices A and C and matrix loop Ile141--Ser171 and that Asp39, Glu137, and Ser158 are not essential for phosphate transport. Since our results are consistent with residues present in all 12 functionally identified members of the mitochondrial transport protein (MTP) family, they lead to a general rule that specifies MTP residue types at 7 separate locations. The conformations of all the double mutation PTPs (except that with the matrix loop Ser158Thr) are significantly different from those of the single mutation PTPs, as indicated by their very low liposome incorporation efficiency and their requirement for less detergent (Triton X-100) to stay in solution. These dramatic conformational differences also suggest an interaction between TM helices D and E. The results are discussed in terms of TM helix movements and changes in the PTP monomer/dimer ratio. 相似文献
45.
A. Briggs 《Journal of applied microbiology》1966,29(3):490-504
S ummary . The resistance of the spores of 6 species of Bacillus to 5% (w/v) of phenol at 37°, heat and gamma radiation has been determined. Two, and with heat treatment three, different shapes of log survivor time curves were observed with each lethal agent. In relation to the conditions employed in accepted sterilization procedures, all of the strains were highly resistant to phenol. Bacillus stearothermophilus, B. licheniformis and B. subtilis were resistant to gamma radiation, all three having a D value of 0.22 Mrad. Only B. stearothermophilus was heat resistant having a D value of 22.6 min at 115°. When the relative order of resistance to each agent was considered, with the exception of B. stearothermophilus , the spores showed little evidence of any relationship between their resistances to phenol, heat and gamma radiation. 相似文献
46.
47.
48.
49.
50.