全文获取类型
收费全文 | 1562篇 |
免费 | 131篇 |
专业分类
1693篇 |
出版年
2021年 | 23篇 |
2019年 | 11篇 |
2018年 | 9篇 |
2016年 | 23篇 |
2015年 | 35篇 |
2014年 | 46篇 |
2013年 | 62篇 |
2012年 | 87篇 |
2011年 | 94篇 |
2010年 | 45篇 |
2009年 | 58篇 |
2008年 | 61篇 |
2007年 | 65篇 |
2006年 | 80篇 |
2005年 | 57篇 |
2004年 | 53篇 |
2003年 | 38篇 |
2002年 | 48篇 |
2001年 | 51篇 |
2000年 | 44篇 |
1999年 | 54篇 |
1998年 | 26篇 |
1997年 | 23篇 |
1996年 | 17篇 |
1995年 | 23篇 |
1994年 | 26篇 |
1993年 | 12篇 |
1992年 | 40篇 |
1991年 | 37篇 |
1990年 | 26篇 |
1989年 | 30篇 |
1988年 | 20篇 |
1987年 | 22篇 |
1986年 | 29篇 |
1985年 | 29篇 |
1984年 | 25篇 |
1983年 | 18篇 |
1982年 | 11篇 |
1981年 | 15篇 |
1980年 | 13篇 |
1979年 | 22篇 |
1978年 | 16篇 |
1977年 | 13篇 |
1976年 | 18篇 |
1975年 | 8篇 |
1974年 | 18篇 |
1973年 | 9篇 |
1972年 | 11篇 |
1971年 | 9篇 |
1969年 | 10篇 |
排序方式: 共有1693条查询结果,搜索用时 0 毫秒
991.
Katsuhiro Shiono Miho Ando Shunsaku Nishiuchi Hirokazu Takahashi Kohtaro Watanabe Motoaki Nakamura Yuichi Matsuo Naoko Yasuno Utako Yamanouchi Masaru Fujimoto Hideki Takanashi Kosala Ranathunge Rochus B. Franke Nobukazu Shitan Naoko K. Nishizawa Itsuro Takamure Masahiro Yano Nobuhiro Tsutsumi Lukas Schreiber Kazufumi Yazaki Mikio Nakazono Kiyoaki Kato 《The Plant journal : for cell and molecular biology》2014,80(1):40-51
Suberin is a complex polymer composed of aliphatic and phenolic compounds. It is a constituent of apoplastic plant interfaces. In many plant species, including rice (Oryza sativa), the hypodermis in the outer part of roots forms a suberized cell wall (the Casparian strip and/or suberin lamellae), which inhibits the flow of water and ions and protects against pathogens. To date, there is no genetic evidence that suberin forms an apoplastic transport barrier in the hypodermis. We discovered that a rice reduced culm number1 (rcn1) mutant could not develop roots longer than 100 mm in waterlogged soil. The mutated gene encoded an ATP‐binding cassette (ABC) transporter named RCN1/OsABCG5. RCN1/OsABCG5 gene expression in the wild type was increased in most hypodermal and some endodermal roots cells under stagnant deoxygenated conditions. A GFP‐RCN1/OsABCG5 fusion protein localized at the plasma membrane of the wild type. Under stagnant deoxygenated conditions, well suberized hypodermis developed in wild types but not in rcn1 mutants. Under stagnant deoxygenated conditions, apoplastic tracers (periodic acid and berberine) were blocked at the hypodermis in the wild type but not in rcn1, indicating that the apoplastic barrier in the mutant was impaired. The amount of the major aliphatic suberin monomers originating from C28 and C30 fatty acids or ω‐OH fatty acids was much lower in rcn1 than in the wild type. These findings suggest that RCN1/OsABCG5 has a role in the suberization of the hypodermis of rice roots, which contributes to formation of the apoplastic barrier. 相似文献
992.
Modern coexistence theory (MCT) is one of the leading methods to understand species coexistence. It uses invasion growth rates—the average, per-capita growth rate of a rare species—to identify when and why species coexist. Despite significant advances in dissecting coexistence mechanisms when coexistence occurs, MCT relies on a ‘mutual invasibility’ condition designed for two-species communities but poorly defined for species-rich communities. Here, we review well-known issues with this component of MCT and propose a solution based on recent mathematical advances. We propose a clear framework for expanding MCT to species-rich communities and for understanding invasion resistance as well as coexistence, especially for communities that could not be analysed with MCT so far. Using two data-driven community models from the literature, we illustrate the utility of our framework and highlight the opportunities for bridging the fields of community assembly and species coexistence. 相似文献
993.
994.
Vanessa Kloke Rebecca S. Schreiber Carina Bodden Julian M?llers Hanna Ruhmann Sylvia Kaiser Klaus-Peter Lesch Norbert Sachser Lars Lewejohann 《PloS one》2014,9(8)
Cognitive bias, the altered information processing resulting from the background emotional state of an individual, has been suggested as a promising new indicator of animal emotion. Comparable to anxious or depressed humans, animals in a putatively negative emotional state are more likely to judge an ambiguous stimulus as if it predicts a negative event, than those in positive states. The present study aimed to establish a cognitive bias test for mice based on a spatial judgment task and to apply it in a pilot study to serotonin transporter (5-HTT) knockout mice, a well-established mouse model for the study of anxiety- and depression-related behavior. In a first step, we validated that our setup can assess different expectations about the outcome of an ambiguous stimulus: mice having learned to expect something positive within a maze differed significantly in their behavior towards an unfamiliar location than animals having learned to expect something negative. In a second step, the use of spatial location as a discriminatory stimulus was confirmed by showing that mice interpret an ambiguous stimulus depending on its spatial location, with a position exactly midway between a positive and a negative reference point provoking the highest level of ambiguity. Finally, the anxiety- and depression-like phenotype of the 5-HTT knockout mouse model manifested - comparable to human conditions - in a trend for a negatively distorted interpretation of ambiguous information, albeit this effect was not statistically significant. The results suggest that the present cognitive bias test provides a useful basis to study the emotional state in mice, which may not only increase the translational value of animal models in the study of human affective disorders, but which is also a central objective of animal welfare research. 相似文献
995.
The amyloid precursor protein (APP) is a large, ubiquitous integral membrane protein with a small amyloid-β (Aβ) domain. In the human brain, endosomal processing of APP produces neurotoxic Aβ-peptides, which are involved in Alzheimer's disease. Here, we show that the Aβ sequence exerts a physiological function when still present in the unprocessed APP molecule. From the extracellular site, Aβ concentrates APP molecules into plasmalemmal membrane protein clusters. Moreover, Aβ stabilization of clusters is a prerequisite for their targeting to endocytic clathrin structures. Therefore, we conclude that the Aβ domain directly mediates a central step in APP trafficking, driving its own conversion into neurotoxic peptides. 相似文献
996.
Matheus S Gasparini Leandro M dos Santos Ahmad MA Hamade Luísa G Gross Arthur P Favarato Jos PC de Vasconcellos Mnica B de Melo Pierina L Parise Camila L Simeoni Natlia B Silva Marcelo A da Silva Mori Andr S Vieira Alessandro dos Santos Farias Fabiana Granja Angelica Z Schreiber Maria L Moretti Jos L Proena-Modena Mnica Alves 《Experimental biology and medicine (Maywood, N.J.)》2021,246(23):2495
997.
Henning Hormann Christian Neubauer Kozi Asada Ulrich Schreiber 《Photosynthesis research》1993,37(1):69-80
The pH-dependence of light-driven O2-reduction in intact spinach chloroplasts is studied by means of chlorophyll fluorescence quenching analysis and polarographic O2-uptake measurements. Most experiments are carried out in presence of KCN, which blocks activities of Calvin cycle, ascorbate peroxidase and superoxide dismutase. pH is varied by equilibration with external buffers in presence of nigericin. Vastly different pH-optima for O2-dependent electron flow are observed in the presence and absence of the redox catalyst methyl viologen. Both fluorescence quenching analysis and O2-uptake reveal a distinct pH 5 optimum of O2-reduction in the absence of methyl viologen. In the presence of this catalyst, O2-reduction is favoured in the alkaline region, with an optimum around pH 8, similar to other types of Hill reaction. It is suggested that in the absence of methyl viologen the extent of irreversibility of O2-reduction is determined by the rate of superoxide protonation. This implies that O2-reduction takes place within the aprotic phase of the thylakoid membrane and that superoxide-reoxidation via oxidized PS I donors competes with protonation. Superoxide protonation is proposed to occur at the internal surface of the thylakoid membrane. There is no competition between superoxide reoxidation and protonation when in the presence of methyl viologen the site of O2-reduction is shifted into the protic stroma phase. In confirmation of this interpretation, fluorescence measurements in the absence of KCN reveal, that non-catalysed O2-dependent electron flow is unique in beingstimulated by the transthylakoidal pH-gradient. On the basis of these findings a major regulatory role of O2-dependent electron flow under excess light conditions is postulated. 相似文献
998.
Amplified fragment length polymorphism (AFLP) is a recently developed, PCR-based high resolution fingerprinting method that is able to generate complex banding patterns which can be used to delineate intraspecific genetic relationships among bacteria. In the present study, AFLP was evaluated for its usefulness in the molecular typing of Salmonella typhi in comparison to ribotyping and pulsed-field gel electrophoresis (PFGE). Six S. typhi isolates from diverse geographic areas (Malaysia, Indonesia, India, Chile, Papua New Guinea and Switzerland) gave unique, heterogeneous profiles when typed by AFLP, a result which was consistent with ribotyping and PFGE analysis. In a further study of selected S. typhi isolates from Papua New Guinea which caused fatal and non-fatal disease previously shown to be clonally related by PFGE, AFLP discriminated between these isolates but did not indicate a linkage between genotype with virulence. We conclude that AFLP (discriminatory index=0.88) has a higher discriminatory power for strain differentiation among S. typhi than ribotyping (DI=0.63) and PFGE (DI=0.74). 相似文献
999.
1000.
Genetic evidence for interaction of the 5q31 cytokine locus and the CARD15 gene in Crohn disease 总被引:7,自引:0,他引:7 下载免费PDF全文
Mirza MM Fisher SA King K Cuthbert AP Hampe J Sanderson J Mansfield J Donaldson P Macpherson AJ Forbes A Schreiber S Lewis CM Mathew CG 《American journal of human genetics》2003,72(4):1018-1022
A common haplotype spanning 250 kb in the cytokine gene cluster on chromosome 5q31 has recently been reported to be strongly associated with Crohn disease (CD) in Canadian families. We have replicated this finding by both the transmission-disequilibrium test (TDT) (P=.016) and in a case-control association study (P=.008) in a large European cohort of patients with CD, although the increase in disease risk was small (odds ratio 1.49 for homozygotes, 95% CI 1.11-2.0). No association was detected in families or individuals with ulcerative colitis (UC). Stratification of offspring with CD in the TDT sample by mutation status in the CD susceptibility gene CARD15 showed that the association with the 5q31 risk haplotype was present only in offspring with at least one of the known CARD15 disease susceptibility alleles (P=.044). The 5q31 risk haplotype frequency was 53.1% in unrelated individuals with CD who had one or two CARD15 mutations versus 43.7% in control subjects (P=.0001) but was not significantly elevated in individuals with CD who had no CARD15 mutations (45.4%, P=.41). Kaplan-Meier survival analysis of age at disease onset showed a significantly earlier onset in homozygotes for the 5q31 risk haplotype (P=.0019). These findings suggest that genetic variants at the 5q31 (IBD5) locus may hasten the onset of Crohn disease and cooperate with CARD15 in disease causation. 相似文献