全文获取类型
收费全文 | 389篇 |
免费 | 48篇 |
专业分类
437篇 |
出版年
2022年 | 2篇 |
2021年 | 4篇 |
2020年 | 3篇 |
2019年 | 7篇 |
2018年 | 7篇 |
2017年 | 4篇 |
2016年 | 7篇 |
2015年 | 10篇 |
2014年 | 13篇 |
2013年 | 12篇 |
2012年 | 21篇 |
2011年 | 19篇 |
2010年 | 4篇 |
2009年 | 11篇 |
2008年 | 16篇 |
2007年 | 15篇 |
2006年 | 16篇 |
2005年 | 21篇 |
2004年 | 14篇 |
2003年 | 14篇 |
2002年 | 16篇 |
2001年 | 15篇 |
2000年 | 21篇 |
1999年 | 20篇 |
1998年 | 5篇 |
1997年 | 9篇 |
1996年 | 3篇 |
1995年 | 6篇 |
1994年 | 6篇 |
1993年 | 5篇 |
1992年 | 10篇 |
1991年 | 9篇 |
1990年 | 11篇 |
1989年 | 10篇 |
1988年 | 11篇 |
1987年 | 10篇 |
1986年 | 7篇 |
1985年 | 2篇 |
1984年 | 6篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1975年 | 3篇 |
1971年 | 3篇 |
1970年 | 2篇 |
1969年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有437条查询结果,搜索用时 10 毫秒
81.
The theory of parent-offspring conflict (POC) provides a plausible evolutionary foundation for the dissonant behavioral interactions commonly observed between adults and their progeny. It has been modelled extensively, but its predictions for phenotypes are murky and have been subjected to scant empirical testing. The least ambiguous cases are likely to involve taxa where offspring exert real power. Recent experimental work indicates that worker bees manipulate brood sex ratios differently from the queen. By contrast, most studies of avian brood reduction and mammalian ‘weaning conflict’ remain open to multiple interpretations. In general, POC may owe its current hegemony to the paucity of alternative explanations for parent-offspring squabbles. Reassessments of basic assumptions about what both parties ‘really want’ need to be linked to experimentation, field-oriented modelling and pluralism for this provocative theory to become broadly useful. 相似文献
82.
Baker C. Jacyn Mock Norton M. Deahl Kenneth Domek John 《Plant Cell, Tissue and Organ Culture》1997,51(2):111-117
A method is described that allows the rate of oxygen consumption to be monitored in plant cell suspensions. The method utilized
oxygen electrodes placed in beakers of plant cells subjected to various treatments. The voltage readings from calibrated electrodes
were converted to % oxygen (100% equals air equilibration) and the rate of oxygen consumption was estimated by calibration
graphs made with no cells present. This system simultaneously monitors one to sixteen or more samples, allowing comparison
of treatments on identically treated cells. We have used this method to study the respiratory burst of plant cells produced
in response to viable or heat-killed bacteria. Because the system was computer-monitored and open to the atmosphere, data
could be collected over several hours. Various factors that affected the measurement of dissolved oxygen concentration with
this technique were explored and considered.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
83.
Plasmid pLAX3, carrying the colicin E3 gene, was used to direct the in vitro synthesis of a colicin E3* molecule totally devoid of its immunity protein. We established that this molecule is able to kill sensitive Escherichia coli cells in the total absence of immunity protein. Therefore, all of the information required for colicin E3 action is located on the colicin polypeptide itself. Furthermore, our studies indicated that immunity protein protects the C-terminal enzymatic part of native colicin E3 protein against proteolytic degradation before or during its translocation across the cell envelope. These results are discussed in relation to the mode of entry of colicin E3 into bacterial cells. 相似文献
84.
Nuclear magnetic resonance studies of hemoglobins 总被引:3,自引:0,他引:3
85.
A pH-induced increase in hydrophobicity as a possible step in the penetration of colicin E3 through bacterial membranes 总被引:3,自引:0,他引:3
V Escuyer P Boquet D Perrin C Montecucco M Mock 《The Journal of biological chemistry》1986,261(23):10891-10898
Exposure to low pH triggers an increase in the hydrophobicity of the colicin E3 molecule. Using a [3H] Triton X-100 binding assay we have shown that the amount of detergent (at supramicellar concentrations) associated with colicin E3 increased dramatically at pH 3.8 and below. Interaction of colicin E3 with asolectin vesicles was monitored by following its cross-linking with two different photoactivatable radioactive phospholipid analogues. At neutral pH colicin E3 was cross-linked with the phospholipid probing the membrane surface whereas at pH 4.5 and below, the bacteriocin reacted with the phospholipid probing the hydrophobic core of the bilayer. With the use of phase partitioning of proteins in Triton X-114 it was shown that at acidic pH whole colicin E3 and its immunity protein segregated in the detergent phase. After trypsin digestion of the colicin-immunity complex, the N-terminal portion of E3 (T1) and the immunity partitioned in the detergent phase at low pH. In contrast, the enzymic domain of the colicin (T2) remained in the aqueous phase and was recovered in a highly active form as a consequence of its dissociation from the immunity protein. These results are discussed in relation to the mechanism of entry of colicin E3 into bacterial cells. 相似文献
86.
William L. Mock Jin-Tann Chen Joseph W. Tsang 《Biochemical and biophysical research communications》1981,102(1):389-396
Substitution of the active site zinc ion of carboxypeptidase A by cadmium yields an enzyme inactive towards ordinary peptide substrates. However, a substrate analog (BzGlyNHCH2CSPheOH) containing a thioamide linkage at the scissile position is cleaved to the thioacid. The kinetic parameters and their pH dependencies are , decreasing with either acid or base (PKE1 = 5.64, pKE2 = 9.55), and kcat = 1.02 × 102 min?1, decreasing with acid (pKES = 6.61). The thiopeptide is less efficiently cleaved by native (zinc) carboxypeptidase A. This cadmium-sulfur synergism supports a mechanism wherein the substrate amide is activated by metal ion coordination to its (thio) carbonyl. 相似文献
87.
Maddalena Bayer‐Giraldi Christiane Uhlig Uwe John Thomas Mock Klaus Valentin 《Environmental microbiology》2010,12(4):1041-1052
Fragilariopsis is a dominating psychrophilic diatom genus in polar sea ice. The two species Fragilariopsis cylindrus and Fragilariopsis curta are able to grow and divide below freezing temperature of sea water and above average sea water salinity. Here we show that antifreeze proteins (AFPs), involved in cold adaptation in several psychrophilic organisms, are widespread in the two polar species. The presence of AFP genes (afps) as a multigene family indicated the importance of this group of genes for the genus Fragilariopsis, possibly contributing to its success in sea ice. Protein phylogeny showed the potential mobility of afps, which appear to have crossed kingdom and domain borders, occurring in Bacteria, diatoms, crustaceans and fungi. Our results revealed a broad distribution of AFPs not only in polar organisms but also in taxa apparently not related to cold environments, suggesting that these proteins may be multifunctional. The relevance of AFPs to Fragilariopsis was also shown by gene expression analysis. Under stress conditions typical for sea ice, with subzero temperatures and high salinities, F. cylindrus and F. curta strongly expressed selected afps. An E/G point mutation in the Fragilariopsis AFPs may play a role in gene expression activity and protein function. 相似文献
88.
The dynamics of plant invasions from initial colonization through patch expansion are driven in part by mode of reproduction, i.e., sexual (seed) and asexual (clonal fragments and expansion) means. Expansion of existing patches—both rate and mode of spread into a matrix of varying conditions—is important for predicting potential invader impacts. In this study, we used fine-scale genetic assessments and remote sensing to describe both the rate and mode of expansion for 20 Phragmites australis patches in flooded and unflooded wetland units on the Great Salt Lake, UT. We found that the majority of Phragmites patch expansion occurred via clonal spread but we also documented instances of (potentially episodic) seedling recruitment. The mode of patch expansion, inferred from patch edge genet richness, was unrelated to flooding in the wetland unit in the preceding growing season. The rate of Phragmites patch expansion varied from 0.09 to 0.35 year?1 and was unrelated to the mode of spread. In six patches monitored across two years, monoclonal patches stayed monoclonal, whereas patches with higher genet richness had a marked increase in diversity in the second year. The findings of the present study suggest how this partially clonal species can exploit the benefits of both sexual (i.e., genetic recombination, widespread dispersal, colonization of new areas) and asexual reproduction (i.e., stability of established clones suited to local environmental conditions) to become one of the most successful wetland plant invaders. To control this species, both forms of reproduction need to be fully addressed through targeted management actions. 相似文献
89.
90.