全文获取类型
收费全文 | 109716篇 |
免费 | 1809篇 |
国内免费 | 824篇 |
出版年
2023年 | 73篇 |
2022年 | 173篇 |
2021年 | 407篇 |
2020年 | 209篇 |
2019年 | 273篇 |
2018年 | 12107篇 |
2017年 | 10875篇 |
2016年 | 7866篇 |
2015年 | 1266篇 |
2014年 | 1054篇 |
2013年 | 1259篇 |
2012年 | 5476篇 |
2011年 | 14028篇 |
2010年 | 12721篇 |
2009年 | 8912篇 |
2008年 | 10748篇 |
2007年 | 12307篇 |
2006年 | 1236篇 |
2005年 | 1377篇 |
2004年 | 1813篇 |
2003年 | 1833篇 |
2002年 | 1495篇 |
2001年 | 509篇 |
2000年 | 372篇 |
1999年 | 297篇 |
1998年 | 223篇 |
1997年 | 180篇 |
1996年 | 174篇 |
1995年 | 114篇 |
1994年 | 126篇 |
1993年 | 146篇 |
1992年 | 147篇 |
1991年 | 188篇 |
1990年 | 125篇 |
1989年 | 136篇 |
1988年 | 133篇 |
1987年 | 117篇 |
1986年 | 86篇 |
1985年 | 120篇 |
1984年 | 109篇 |
1983年 | 96篇 |
1982年 | 55篇 |
1981年 | 58篇 |
1980年 | 47篇 |
1979年 | 55篇 |
1975年 | 46篇 |
1974年 | 57篇 |
1973年 | 48篇 |
1972年 | 286篇 |
1971年 | 298篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Amino acid sequence surrounding the lipoic acid cofactor of bovine kidney 2-oxoglutarate dehydrogenase complex 总被引:4,自引:0,他引:4
The 2-oxoglutarate dehydrogenase complex was succinylated using 2-oxo[5-14C]glutarate in the presence of N-ethylmaleimide to label the lipoic acid cofactor of the transuccinylase (E2) component. Following peptic digestion, 14C-lipoate-containing peptides were purified and subjected to automated Edman degradation and amino acid analysis. The amino acid sequence surrounding the lipoyllysine residue is reported. 相似文献
102.
103.
Kevin J. Beiler Suzanne W. Simard Valerie LeMay Daniel M. Durall 《Molecular ecology》2012,21(24):6163-6174
Understanding ectomycorrhizal fungal (EMF) community structure is limited by a lack of taxonomic resolution and autecological information. Rhizopogon vesiculosus and Rhizopogon vinicolor (Basidiomycota) are morphologically and genetically related species. They are dominant members of interior Douglas‐fir (Pseudotsuga menziesii var. glauca) EMF communities, but mechanisms leading to their coexistence are unknown. We investigated the microsite associations and foraging strategy of individual R. vesiculosus and R. vinicolor genets. Mycelia spatial patterns, pervasiveness and root colonization patterns of fungal genets were compared between Rhizopogon species and between xeric and mesic soil moisture regimes. Rhizopogon spp. mycelia were systematically excavated from the soil and identified using microsatellite DNA markers. Rhizopogon vesiculosus mycelia occurred at greater depth, were more spatially pervasive, and colonized more tree roots than R. vinicolor mycelia. Both species were frequently encountered in organic layers and between the interface of organic and mineral horizons. They were particularly abundant within microsites associated with soil moisture retention. The occurrence of R. vesiculosus shifted in the presence of R. vinicolor towards mineral soil horizons, where R. vinicolor was mostly absent. This suggests that competition and foraging strategy may contribute towards the vertical partitioning observed between these species. Rhizopogon vesiculosus and R. vinicolor mycelia systems occurred at greater mean depths and were more pervasive in mesic plots compared with xeric plots. The spatial continuity and number of trees colonized by genets of each species did not significantly differ between soil moisture regimes. 相似文献
104.
105.
Mingyue Wang Pranab K Mukherjee Jyotsna Chandra Ali Abdul Lattif Thomas S McCormick Mahmoud A Ghannoum 《BMC microbiology》2008,8(1):31
Background
We have previously shown that supernatant from Candida albicans (CA) culture contains a Secretory Interleukin (IL)-12 Inhibitory Factor (CA-SIIF), which inhibits IL-12 production by human monocytes. However, the effect of CA-SIIF on secretion of other cytokines by monocytes is unknown, and detailed characterization of this factor has not been performed. 相似文献106.
Dana M. Bergstrom George R. Stewart Patricia M. Selkirk Susanne Schmidt 《Oecologia》2002,130(2):309-314
'15N signatures of fossil peat were used to interpret past ecosystem processes on tectonically active subantarctic Macquarie Island. By comparing past vegetation reconstructed from the fossil record with present-day vegetation analogues, our evidence strongly suggests that changes in the '15N signatures of fossil peat at this location reflect mainly past changes in the proportion of plant nitrogen derived from animal sources. Associated with uplift above sea level over the past 8,500 years, fossil records in two peat deposits on the island chronicle a change from coastal vegetation with fur and elephant seal disturbance to the existing inland herbfield. Coupled with this change are synchronous changes in the '15N signatures of peat layers. At two sites 15N-enriched peat '15N signatures of up to +17 were associated with a high abundance of pollen of the nitrophile Callitriche antarctica (Callitrichaceae). At one site fossil seal hair was also associated with enriched peat '15N. Less 15N enriched '15N signatures (e.g. -1.9 to +3.9) were measured in peat layers which lacked animal associated C. antarctica and Acaena spp. Interpretation of a third peat profile indicates continual occupation of a ridge site by burrowing petrels for most of the Holocene. We suggest that 15N signatures of fossil peat remained relatively stable with time once deposited, providing a significant new tool for interpreting the palaeoecology. 相似文献
107.
108.
109.
Background
With increasing computer power, simulating the dynamics of complex systems in chemistry and biology is becoming increasingly routine. The modelling of individual reactions in (bio)chemical systems involves a large number of random events that can be simulated by the stochastic simulation algorithm (SSA). The key quantity is the step size, or waiting time, τ, whose value inversely depends on the size of the propensities of the different channel reactions and which needs to be re-evaluated after every firing event. Such a discrete event simulation may be extremely expensive, in particular for stiff systems where τ can be very short due to the fast kinetics of some of the channel reactions. Several alternative methods have been put forward to increase the integration step size. The so-called τ-leap approach takes a larger step size by allowing all the reactions to fire, from a Poisson or Binomial distribution, within that step. Although the expected value for the different species in the reactive system is maintained with respect to more precise methods, the variance at steady state can suffer from large errors as τ grows. 相似文献110.
Victoria Levterova Stefan Panaiotov Nadia Brankova Kristin Tankova 《Molecular biotechnology》2010,45(1):34-38
Identification of genetic markers involved in stress response to physical factors or chemical substances in organisms is a
challenging task. Typing of upregulated gene expression due to selective antibacterial pressure is a promising approach in
the search of molecular mechanisms responsible for development of resistance. cDNA-Fluorescent Amplified Fragment Length Polymorphism
(cDNA-FAFLP) strategy was developed and applied in the search of antimycotic drug resistance marker(s) in medically important
fungi as an alternative method to microarray analysis. We compared differential gene expression of two sensitive Candida albicans reference strains (ATCC 10231 and ATCC 60133) and two of their paired resistant to fluconazole and itraconazole mutants.
Resistant mutants Candida albicans
FLC-R, resistant to fluconazole (MIC > 128 μg/ml) and Candida albicans ICZ-R, resistant to itraconazole (MIC > 4 μg/ml) were obtained in subcultures with gradual increase of the antifungal in the culture
medium. cDNA-AFLP profile in both itraconazole resistant mutants showed specific spectrophotometric peaks with 5–6-fold RNA
overexpression product of 500 bp length compared to the sensitive strains. Fluconazole mutants do not reveal RNA level changes
under tested by us typing conditions. These results indicate that the cDNA-FAFLP strategy is a relatively rapid, simple, and
reliable method for simultaneous typing of both constitutive and induced differences in expression of host genes providing
insight into the biological processes involved in response to drugs in bacteria and fungi. Moreover, this methodology could
be tested for typing of the genome response of any organism to physical or chemical stress factors. 相似文献