全文获取类型
收费全文 | 716篇 |
免费 | 47篇 |
国内免费 | 84篇 |
出版年
2024年 | 3篇 |
2023年 | 9篇 |
2022年 | 27篇 |
2021年 | 15篇 |
2020年 | 30篇 |
2019年 | 37篇 |
2018年 | 28篇 |
2017年 | 19篇 |
2016年 | 28篇 |
2015年 | 23篇 |
2014年 | 28篇 |
2013年 | 73篇 |
2012年 | 23篇 |
2011年 | 29篇 |
2010年 | 23篇 |
2009年 | 32篇 |
2008年 | 18篇 |
2007年 | 35篇 |
2006年 | 29篇 |
2005年 | 40篇 |
2004年 | 32篇 |
2003年 | 20篇 |
2002年 | 21篇 |
2001年 | 27篇 |
2000年 | 16篇 |
1999年 | 13篇 |
1998年 | 14篇 |
1997年 | 13篇 |
1996年 | 10篇 |
1995年 | 16篇 |
1994年 | 7篇 |
1993年 | 17篇 |
1992年 | 13篇 |
1991年 | 5篇 |
1990年 | 6篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 10篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1974年 | 6篇 |
1972年 | 1篇 |
排序方式: 共有847条查询结果,搜索用时 15 毫秒
61.
Monte Carlo simulations of molecular recognition at the consensus binding site of the constant fragment (Fc) of human immunoglobulin G (Ig) protein have been performed to analyze structural and thermodynamic aspects of binding for the 13-residue cyclic peptide DCAWHLGELVWCT. The energy landscape analysis of a hot spot at the intermolecular interface using alanine scanning and equilibrium-simulated tempering dynamics with the simplified, knowledge-based energy function has enabled the role of the protein hot spot residues in providing the thermodynamic stability of the native structure to be determined. We have found that hydrophobic interactions between the peptide and the Met-252, Ile-253, His-433, and His-435 protein residues are critical to guarantee the thermodynamic stability of the crystallographic binding mode of the complex. Binding free energy calculations, using a molecular mechanics force field and a solvation energy model, combined with alanine scanning have been conducted to determine the energetic contribution of the protein hot spot residues in binding affinity. The conserved Asn-434, Ser-254, and Tyr-436 protein residues contribute significantly to the binding affinity of the peptide-protein complex, serving as an energetic hot spot at the intermolecular interface. The results suggest that evolutionary conserved hot spot protein residues at the intermolecular interface may be partitioned in fulfilling thermodynamic stability of the native binding mode and contributing to the binding affinity of the complex. 相似文献
62.
O. Macias‐Macias J. Chuc P. Ancona‐Xiu O. Cauich J. J. G. Quezada‐Euán 《Journal of Applied Entomology》2009,133(6):456-465
In the tropics the contribution of bees as pollinators of important economic indigenous crops remains largely undocumented. We studied the diversity of bee species visiting indigenous tomato (Solanum lycopersicon) and habanero pepper (Capsicum chinense) in subtropical Yucatán, México. The contribution of two native bees, Exomalopsis (E) and Augochloropsis (AG) was compared with that of the introduced Africanized Apis mellífera (HB) for pollinating unvisited flowers in both crops. Apis mellífera and stingless bees were dominant in habanero pepper but solitary bee species were important visitors of tomato. In spite of both crops being autogamic, there was a significant contribution of native bees for pollination of both tomato and habanero pepper. The comparison of fruit weight, number of seeds, and a pollination index based on the latter showed that E and AG were more effective pollinators compared to HB in both crops (ca. Spear’s index of ca. 0.7 vs. 0.35 respectively). In tomato, a further evaluation of the contribution to pollination provided by the three bee species was made using the rate of visits to flowers. Although E and AG were the most efficient pollinators at single flower visits in tomato, none of the three species (including HB) were able to provide single visits to all flowers per unit time to the crop. Our results underline the importance of maintaining diverse assemblages and abundant populations of bee species that can synergically contribute to the productivity of tomato and hot pepper in the Neotropics. 相似文献
63.
64.
The relative importance of the processes that generate and maintain biodiversity is a
major and controversial topic in evolutionary biology with large implications for
conservation management. The Atlantic Forest of Brazil, one of the world''s richest
biodiversity hot spots, is severely damaged by human activities. To formulate an efficient
conservation policy, a good understanding of spatial and temporal biodiversity patterns
and their underlying evolutionary mechanisms is required. With this aim, we performed a
comprehensive phylogeographic study using a low-dispersal organism, the land planarian
species Cephaloflexa bergi (Platyhelminthes, Tricladida). Analysing multi-locus
DNA sequence variation under the Approximate Bayesian Computation framework, we evaluated
two scenarios proposed to explain the diversity of Southern Atlantic Forest (SAF) region.
We found that most sampled localities harbour high levels of genetic diversity, with
lineages sharing common ancestors that predate the Pleistocene. Remarkably, we detected
the molecular hallmark of the isolation-by-distance effect and little evidence of a recent
colonization of SAF localities; nevertheless, some populations might result from very
recent secondary contacts. We conclude that extant SAF biodiversity originated and has
been shaped by complex interactions between ancient geological events and more recent
evolutionary processes, whereas Pleistocene climate changes had a minor influence in
generating present-day diversity. We also demonstrate that land planarians are an
advantageous biological model for making phylogeographic and, particularly, fine-scale
evolutionary inferences, and propose appropriate conservation policies. 相似文献
65.
66.
以提取物中蒽醌类物质含量综合评价,利用正交实验比较了浸提、超声提取和索氏提取优选库拉索(Aloe vera L.)中蒽醌类物质的最佳提取工艺条件,为芦荟蒽醌类物质的开发提供科学依据和实验基础。从而得出最佳提取方法为超声提取,最佳醇沉工艺条件为:幼叶叶皮60目,乙醇40℃超声45min。 相似文献
67.
68.
Test methods and response surface models for hot,humid air decontamination of materials contaminated with dirty spores of Bacillus anthracis ∆Sterne and Bacillus thuringiensis Al Hakam
下载免费PDF全文
![点击此处可从《Journal of applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
69.
Pallapolu VR Lee YY Garlock RJ Balan V Dale BE Kim Y Mosier NS Ladisch MR Falls M Holtzapple MT Sierra-Ramirez R Shi J Ebrik MA Redmond T Yang B Wyman CE Donohoe BS Vinzant TB Elander RT Hames B Thomas S Warner RE 《Bioresource technology》2011,102(24):11115-11120
The objective of this work is to investigate the effects of cellulase loading and β-glucosidase supplementation on enzymatic hydrolysis of pretreated Dacotah switchgrass. To assess the difference among various pretreatment methods, the profiles of sugars and intermediates were determined for differently treated substrates. For all pretreatments, 72 h glucan/xylan digestibilities increased sharply with enzyme loading up to 25 mg protein/g-glucan, after which the response varied depending on the pretreatment method. For a fixed level of enzyme loading, dilute sulfuric acid (DA), SO2, and Lime pretreatments exhibited higher digestibility than the soaking in aqueous ammonia (SAA) and ammonia fiber expansion (AFEX). Supplementation of Novozyme-188 to Spezyme-CP improved the 72 h glucan digestibility only for the SAA treated samples. The effect of β-glucosidase supplementation was discernible only at the early phase of hydrolysis where accumulation of cellobiose and oligomers is significant. Addition of β-glucosidase increased the xylan digestibility of alkaline treated samples due to the β-xylosidase activity present in Novozyme-188. 相似文献
70.