全文获取类型
收费全文 | 4035篇 |
免费 | 373篇 |
国内免费 | 3篇 |
出版年
2023年 | 30篇 |
2022年 | 60篇 |
2021年 | 131篇 |
2020年 | 79篇 |
2019年 | 92篇 |
2018年 | 115篇 |
2017年 | 106篇 |
2016年 | 170篇 |
2015年 | 309篇 |
2014年 | 275篇 |
2013年 | 270篇 |
2012年 | 444篇 |
2011年 | 359篇 |
2010年 | 230篇 |
2009年 | 186篇 |
2008年 | 267篇 |
2007年 | 240篇 |
2006年 | 196篇 |
2005年 | 189篇 |
2004年 | 132篇 |
2003年 | 129篇 |
2002年 | 107篇 |
2001年 | 17篇 |
2000年 | 17篇 |
1999年 | 12篇 |
1998年 | 27篇 |
1997年 | 9篇 |
1996年 | 8篇 |
1995年 | 12篇 |
1994年 | 10篇 |
1993年 | 12篇 |
1992年 | 16篇 |
1991年 | 13篇 |
1990年 | 9篇 |
1988年 | 12篇 |
1987年 | 5篇 |
1985年 | 5篇 |
1984年 | 13篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1981年 | 9篇 |
1980年 | 4篇 |
1979年 | 8篇 |
1978年 | 4篇 |
1976年 | 4篇 |
1975年 | 8篇 |
1974年 | 4篇 |
1972年 | 4篇 |
1969年 | 4篇 |
1968年 | 4篇 |
排序方式: 共有4411条查询结果,搜索用时 46 毫秒
991.
992.
Marcia O. Fenley Wilma K. Olson Irwin Tobias Gerald S. Manning 《Biophysical chemistry》1994,50(3):255-271
We present Monte Carlo simulations of the equilibrium configurations of short closed circular DNA that obeys a combined elastic, hard-sphere, and electrostatic energy potential. We employ a B-spline representation to model chain configuration and simulate the effects of salt on chain folding by varying the Debye screening parameter. We obtain global equilibrium configurations of closed circular DNA, with several imposed linking number differences, at two salt concentrations (specifically at the extremes of no added salt and the high salt regime), and for different chain lengths. Minimization of the composite elastic/long-range potential energy under the constraints of ring closure and fixed chain length is found to produce structures that are consistent with the configurations of short supercoiled DNA observed experimentally. The structures generated under the constraints of an electrostatic potential are less compact than those subjected only to an elastic term and a hard-sphere constraint. For a fixed linking number difference greater than a critical value, the interwound structures obtained under the condition of high salt are more compact than those obtained under the condition of no added salt. In the case of no added salt, the electrostatic energy plays a dominant role over the elastic energy in dictating the shape of the closed circular DNA. The DNA supercoil opens up with increasing chain length at low salt concentration. A branched three-leaf rose structure with a fixed linking number difference is higher in energy than the interwound form at both salt concentrations employed here. 相似文献
993.
994.
Adriana Sanchez Roseli Soncini Tobias Wang Pia Koldkjaer Edwin W. Taylor Mogens L.Glass 《Comparative biochemistry and physiology. Part A, Molecular & integrative physiology》2001,130(4):86-687
Lungfishes (Dipnoi) occupy an evolutionary transition between water and air breathing and possess well-developed lungs and reduced gills. The South American species, Lepidosiren paradoxa, is an obligate air-breather and has the lowest aquatic respiration of the three extant genera. To study the relative importance, location and modality of reflexogenic sites sensitive to oxygen in the generation of cardio-respiratory responses, we measured ventilatory responses to changes in ambient oxygen and to reductions in blood oxygen content. Animals were exposed to aquatic and aerial hypoxia, both separately and in combination. While aerial hypoxia elicited brisk ventilatory responses, aquatic hypoxia had no effect, indicating a primary role for internal rather than branchial receptors. Reducing haematocrit and blood oxygen content by approximately 50% did not affect ventilation during normoxia, showing that the specific modality of the internal oxygen sensitive chemoreceptors is blood PO(2) per se and not oxygen concentration. In light of previous studies, it appears that the heart rate responses and the changes in pulmonary ventilation during oxygen shortage are similar in lungfish and tetrapods. Furthermore, the modality of the oxygen receptors controlling these responses is similar to tetrapods. Because the cardio-respiratory responses and the modality of the oxygen receptors differ from typical water-breathing teleosts, it appears that many of the changes in the mechanisms exerting reflex control over cardio-respiratory functions occurred at an early stage in vertebrate evolution. 相似文献
995.
Matteo Ramazzotti Irene Stefanini Monica Di Paola Carlotta De Filippo Lisa Rizzetto Luisa Berná Leonardo Dapporto Damariz Rivero Noemi Tocci Tobias Weil Marcello S. Lenucci Paolo Lionetti Duccio Cavalieri 《Environmental microbiology》2019,21(1):50-71
The quest to discover the variety of ecological niches inhabited by Saccharomyces cerevisiae has led to research in areas as diverse as wineries, oak trees and insect guts. The discovery of fungal communities in the human gastrointestinal tract suggested the host's gut as a potential reservoir for yeast adaptation. Here, we report the existence of yeast populations associated with the human gut (HG) that differ from those isolated from other human body sites. Phylogenetic analysis on 12 microsatellite loci and 1715 combined CDSs from whole-genome sequencing revealed three subclusters of HG strains with further evidence of clonal colonization within the host's gut. The presence of such subclusters was supported by other genomic features, such as copy number variation, absence/introgressions of CDSs and relative polymorphism frequency. Functional analysis of CDSs specific of the different subclusters suggested possible alterations in cell wall composition and sporulation features. The phenotypic analysis combined with immunological profiling of these strains further showed that sporulation was related with strain-specific genomic characteristics in the immune recognition pattern. We conclude that both genetic and environmental factors involved in cell wall remodelling and sporulation are the main drivers of adaptation in S. cerevisiae populations in the human gut. 相似文献
996.
Lukas Hebing Tobias Neymann Sebastian Engell 《Biotechnology and bioengineering》2020,117(7):2058-2073
In macroscopic dynamic models of fermentation processes, elementary modes (EM) derived from metabolic networks are often used to describe the reaction stoichiometry in a simplified manner and to build predictive models by parameterizing kinetic rate equations for the EM. In this procedure, the selection of a set of EM is a key step which is followed by an estimation of their reaction rates and of the associated confidence bounds. In this paper, we present a method for the computation of reaction rates of cellular reactions and EM as well as an algorithm for the selection of EM for process modeling. The method is based on the dynamic metabolic flux analysis (DMFA) proposed by Leighty and Antoniewicz (2011, Metab Eng, 13(6), 745–755) with additional constraints, regularization and analysis of uncertainty. Instead of using estimated uptake or secretion rates, concentration measurements are used directly to avoid an amplification of measurement errors by numerical differentiation. It is shown that the regularized DMFA for EM method is significantly more robust against measurement noise than methods using estimated rates. The confidence intervals for the estimated reaction rates are obtained by bootstrapping. For the selection of a set of EM for a given st oichiometric model, the DMFA for EM method is combined with a multiobjective genetic algorithm. The method is applied to real data from a CHO fed-batch process. From measurements of six fed-batch experiments, 10 EM were identified as the smallest subset of EM based upon which the data can be described sufficiently accurately by a dynamic model. The estimated EM reaction rates and their confidence intervals at different process conditions provide useful information for the kinetic modeling and subsequent process optimization. 相似文献
997.
998.
Anna I. Weaver Valeria Jimnez‐Ruiz Srikar R. Tallavajhala Brett P. Ransegnola Kimberly Q. Wong Tobias Drr 《Molecular microbiology》2019,112(4):1100-1115
The cell wall is a crucial structural feature in the vast majority of bacteria and comprises a covalently closed network of peptidoglycan (PG) strands. While PG synthesis is important for survival under many conditions, the cell wall is also a dynamic structure, undergoing degradation and remodeling by ‘autolysins’, enzymes that break down PG. Cell division, for example, requires extensive PG remodeling, especially during separation of daughter cells, which depends heavily upon the activity of amidases. However, in Vibrio cholerae, we demonstrate that amidase activity alone is insufficient for daughter cell separation and that lytic transglycosylases RlpA and MltC both contribute to this process. MltC and RlpA both localize to the septum and are functionally redundant under normal laboratory conditions; however, only RlpA can support normal cell separation in low‐salt media. The division‐specific activity of lytic transglycosylases has implications for the local structure of septal PG, suggesting that there may be glycan bridges between daughter cells that cannot be resolved by amidases. We propose that lytic transglycosylases at the septum cleave PG strands that are crosslinked beyond the reach of the highly regulated activity of the amidase and clear PG debris that may block the completion of outer membrane invagination. 相似文献
999.
1000.
Christoph J. von Borell Tobias L. Kordsmeyer Tanja M. Gerlach Lars Penke 《Evolution and human behavior》2019,40(2):235-248
The theory of facultative calibration, which explains personality differences as responses to variation in other phenotypic traits of individuals, received mixed results throughout the last years. Whereas there is strong evidence that individual differences in human behavior are correlated with the self-perception of other traits, it still needs to be questioned whether they are also adjusted to objective differences in body condition (i.e. formidability). In two independent studies (N1?=?119 men and 124 women, N2?=?165 men) we tested hypotheses of facultative personality calibration in an integrative way, assessing various outcomes of previous studies in the same samples (including Anger Proneness, Extraversion, Neuroticism, Narcissism, Shyness, Vengefulness, and Sociosexual Orientation). Formidability was derived from assessments of physical strength and various anthropometric measures from full-body 3D scans and paired with measures of self-perceived and other-rated physical attractiveness (based on rotating morphometric 3D body models and facial photographs). We could replicate positive correlations with self-perceived attractiveness across outcomes, though these were not corroborated by more objective assessments of attractiveness: an effect of other-rated attractiveness was clearly not supported in our results for either sex, regardless of the personality outcome. Anthropometric measures and physical strength were also largely unrelated to personality, with the exception of Extraversion, Utility of Personal Aggression, and Sociosexual Orientation. While the two samples differed in their results for domain-level Extraversion, at least the Extraversion facets Activity and Assertiveness were related to strength and masculinity in men. For Sociosexual Orientation the results of our two samples varied more substantially, a positive association was only present in Study 2. Future studies need to clarify whether formidability, potentially an indicator of genetic quality for males, enhances their orientation and success in short-term mating. Furthermore we propose longitudinal twin-difference studies as means to evaluate the theory of personality recalibration in a more controlled manner. 相似文献