全文获取类型
收费全文 | 7787篇 |
免费 | 738篇 |
国内免费 | 2篇 |
出版年
2023年 | 33篇 |
2022年 | 22篇 |
2021年 | 165篇 |
2020年 | 117篇 |
2019年 | 136篇 |
2018年 | 170篇 |
2017年 | 177篇 |
2016年 | 220篇 |
2015年 | 417篇 |
2014年 | 466篇 |
2013年 | 591篇 |
2012年 | 727篇 |
2011年 | 697篇 |
2010年 | 439篇 |
2009年 | 408篇 |
2008年 | 563篇 |
2007年 | 504篇 |
2006年 | 494篇 |
2005年 | 436篇 |
2004年 | 459篇 |
2003年 | 327篇 |
2002年 | 371篇 |
2001年 | 77篇 |
2000年 | 43篇 |
1999年 | 65篇 |
1998年 | 82篇 |
1997年 | 52篇 |
1996年 | 30篇 |
1995年 | 26篇 |
1994年 | 25篇 |
1993年 | 31篇 |
1992年 | 14篇 |
1991年 | 14篇 |
1990年 | 20篇 |
1989年 | 14篇 |
1988年 | 7篇 |
1987年 | 10篇 |
1986年 | 6篇 |
1985年 | 5篇 |
1984年 | 12篇 |
1983年 | 7篇 |
1982年 | 8篇 |
1981年 | 7篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1973年 | 3篇 |
1967年 | 2篇 |
1960年 | 3篇 |
排序方式: 共有8527条查询结果,搜索用时 31 毫秒
61.
Neighboring plant influences on arbuscular mycorrhizal fungal community composition as assessed by T-RFLP analysis 总被引:2,自引:1,他引:1
Controls on root colonization by arbuscular mycorrhizal fungi (AMF) include host nutrient status, identity of symbionts and soil physico-chemical properties. Here we show, in the field, that the subset of the AMF community colonizing the roots of a common grass species, Dactylis glomerata, was strongly controlled by neighboring roots of a different plant species, Centaurea maculosa, an invasive forb, thus adding a biological spatial component to controls on root colonization. Using an AMF-specific, 18s rDNA-based terminal restriction fragment length polymorphism (T-RFLP) analysis method, significant differences were found between AMF community fingerprints of samples derived from roots of grasses with (GCm) and without (G0) neighboring C. maculosa. There were also significant differences between samples derived from C. maculosa roots (Cmac) and both GCm and G0 roots. Sample ordination indicated three generally distinct groups consisting of Cmac, GCm and G0, with GCm samples being of intermediate distance between G0and Cmac. Our results indicate that, with the presence of C. maculosa, AMF communities of D. glomerata shift to reflect community composition associated with C. maculosa roots. These results highlight the importance of complex spatial distributions of AMF communities at the scale of a root system. An additional dimension to our study is that C. maculosa is an aggressively invasive plant in the intermountain West. Viewed in this light, these results suggest that pervasive influences of this plant on AMF communities, specifically in roots of its competitors, may represent a mechanism contributing to its invasive success. However, further work is clearly required to determine the extent to which AMF genotypic alteration by neighboring plants influences competitive relationships. 相似文献
62.
High-Pressure-Mediated Survival of Clostridium botulinum and Bacillus amyloliquefaciens Endospores at High Temperature 下载免费PDF全文
Dirk Margosch Matthias A. Ehrmann Roman Buckow Volker Heinz Rudi F. Vogel Michael G. Gnzle 《Applied microbiology》2006,72(5):3476-3481
Endospores of proteolytic type B Clostridium botulinum TMW 2.357 and Bacillus amyloliquefaciens TMW 2.479 are currently described as the most high-pressure-resistant bacterial spores relevant to food intoxication and spoilage in combined pressure-temperature applications. The effects of combined pressure (0.1 to 1,400 MPa) and temperature (70 to 120°C) treatments were determined for these spores. A process employing isothermal holding times was established to distinguish pressure from temperature effects. An increase in pressure (600 to 1,400 MPa) and an increase in temperature (90 to 110°C) accelerated the inactivation of C. botulinum spores. However, incubation at 100°C, 110°C, or 120°C with ambient pressure resulted in faster spore reduction than treatment with 600 or 800 MPa at the same temperature. This pressure-mediated spore protection was also observed at 120°C and 800, 1,000, or 1,200 MPa with the more heat-tolerant B. amyloliquefaciens TMW 2.479 spores. Inactivation curves for both strains showed a pronounced pressure-dependent tailing, which indicates that a small fraction of the spore populations survives conditions of up to 120°C and 1.4 GPa in isothermal treatments. Because of this tailing and the fact that pressure-temperature combinations stabilizing bacterial endospores vary from strain to strain, food safety must be ensured in case-by-case studies demonstrating inactivation or nongrowth of C. botulinum with realistic contamination rates in the respective pressurized food and equipment. 相似文献
63.
Metschnikowia Strains Isolated from Botrytized Grapes Antagonize Fungal and Bacterial Growth by Iron Depletion 下载免费PDF全文
Matthias Sipiczki 《Applied microbiology》2006,72(10):6716-6724
Noble-rotted grapes are colonized by complex microbial populations. I isolated pigment-producing Metschnikowia strains from noble-rotted grapes that had antagonistic activity against filamentous fungi, yeasts, and bacteria. A red-maroon pigment was formed from a diffusible colorless precursor released by the cells into the medium. The conversion of the precursor required iron and could occur both in the cells (red colonies) and in the medium (red halos around colonies). The intensity of pigmentation was correlated with the intensity of the antimicrobial activity. Mutants that did not form pigment also lacked antifungal activity. Within the pigmented halos, conidia of the sensitive fungi did not germinate, and their hyphae did not grow and frequently lysed at the tips. Supplementation of the medium with iron reduced the size of the halos and the inhibition zones, while it increased the pigment accumulation by the colonies. The iron-binding agent tropolone had a similar effect, so I hypothesize that pigmented Metschnikowia isolates inhibit the growth of the sensitive microorganisms by pigment formation, which depletes the free iron in the medium. As the pigment is a large nondiffusible complex produced in the presence of both low and high concentrations of ferric ions, the proposed mechanism is different from the mechanisms operating in microbes that release siderophores into the environment for iron acquisition. 相似文献
64.
Limonium failachicum, a new diploid (2n=18) species ofPlumbaginaceae, is described from Arabia. The species is taxonomically related toL. iranicum andL. carnosum. The new taxon is so far the only known endemic species for the State of Kuwait. Ecology and distribution of the new species is briefly discussed. 相似文献
65.
66.
67.
Mircea Winter Mirjam A Moser Dominique Meunier Katharina Mattes Christina Murko Christina Humer Tina Meischel Gerald Brosch Patrick Matthias Maria Sibilia Christian Seiser 《The EMBO journal》2013,32(24):3176-3191
The histone deacetylases HDAC1 and HDAC2 remove acetyl moieties from lysine residues of histones and other proteins and are important regulators of gene expression. By deleting different combinations of Hdac1 and Hdac2 alleles in the epidermis, we reveal a dosage‐dependent effect of HDAC1/HDAC2 activity on epidermal proliferation and differentiation. Conditional ablation of either HDAC1 or HDAC2 in the epidermis leads to no obvious phenotype due to compensation by the upregulated paralogue. Strikingly, deletion of a single Hdac2 allele in HDAC1 knockout mice results in severe epidermal defects, including alopecia, hyperkeratosis, hyperproliferation and spontaneous tumour formation. These mice display impaired Sin3A co‐repressor complex function, increased levels of c‐Myc protein, p53 expression and apoptosis in hair follicles (HFs) and misregulation of HF bulge stem cells. Surprisingly, ablation of HDAC1 but not HDAC2 in a skin tumour model leads to accelerated tumour development. Our data reveal a crucial function of HDAC1/HDAC2 in the control of lineage specificity and a novel role of HDAC1 as a tumour suppressor in the epidermis. 相似文献
68.
69.
The decoupled sites representation (DSR) is a theoretical instrument which allows to regard complex pH titration curves of biomolecules with several interacting proton binding sites as composition of isolated, non-interacting sites, each with a standard Henderson–Hasselbalch titration curve. In this work, we present the mathematical framework in which the DSR is embedded and give mathematical proofs for several statements in the periphery of the DSR. These proofs also identify exceptions. To apply the DSR to any molecule, it is necessary to extend the set of binding energies from ${\mathbb{R}}$ to a stripe within ${\mathbb{C}}$ . An important observation in this context is that even positive interaction energies (repulsion) between the binding sites will not guarantee real binding energies in the decoupled system, at least if the molecule has more than four proton binding sites. Moreover, we show that for a given overall titration curve it is not only possible to find a corresponding system with an interaction energy of zero but with any arbitrary fix interaction energy. This result also effects practical work as it shows that for any given titration curve, there is an infinite number of corresponding hypothetical molecules. Furthermore, this implies that—using a common definition of cooperative binding on the level of interaction energies—a meaningful measure of cooperativity between the binding sites cannot be defined solely on the basis of the overall titration. Consequently, all measures of cooperativity based on the overall binding curve do not measure the type of cooperativity commonly defined on the basis of interaction energies. Understanding the DSR mathematically provides the basis of transferring the DSR to biomolecules with different types of interacting ligands, such as protons and electrons, which play an important role within electron transport chains like in photosynthesis. 相似文献
70.
Atanas G. Atanasov Jian N. Wang Shi P. Gu Jing Bu Matthias P. Kramer Lisa Baumgartner Nanang Fakhrudin Angela Ladurner Clemens Malainer Anna Vuorinen Stefan M. Noha Stefan Schwaiger Judith M. Rollinger Daniela Schuster Hermann Stuppner Verena M. Dirsch Elke H. Heiss 《Biochimica et Biophysica Acta (BBA)/General Subjects》2013