全文获取类型
收费全文 | 5390篇 |
免费 | 387篇 |
国内免费 | 1篇 |
出版年
2023年 | 33篇 |
2022年 | 56篇 |
2021年 | 129篇 |
2020年 | 83篇 |
2019年 | 107篇 |
2018年 | 131篇 |
2017年 | 127篇 |
2016年 | 184篇 |
2015年 | 279篇 |
2014年 | 278篇 |
2013年 | 323篇 |
2012年 | 469篇 |
2011年 | 388篇 |
2010年 | 247篇 |
2009年 | 234篇 |
2008年 | 374篇 |
2007年 | 270篇 |
2006年 | 309篇 |
2005年 | 234篇 |
2004年 | 243篇 |
2003年 | 205篇 |
2002年 | 194篇 |
2001年 | 72篇 |
2000年 | 56篇 |
1999年 | 53篇 |
1998年 | 60篇 |
1997年 | 40篇 |
1996年 | 27篇 |
1995年 | 45篇 |
1994年 | 33篇 |
1993年 | 26篇 |
1992年 | 35篇 |
1991年 | 30篇 |
1990年 | 25篇 |
1989年 | 28篇 |
1988年 | 24篇 |
1987年 | 24篇 |
1986年 | 22篇 |
1985年 | 25篇 |
1984年 | 17篇 |
1983年 | 17篇 |
1982年 | 18篇 |
1981年 | 27篇 |
1980年 | 22篇 |
1979年 | 11篇 |
1978年 | 20篇 |
1977年 | 19篇 |
1976年 | 13篇 |
1974年 | 15篇 |
1973年 | 12篇 |
排序方式: 共有5778条查询结果,搜索用时 15 毫秒
921.
Armstrong LE Casa DJ Roti MW Lee EC Craig SA Sutherland JW Fiala KA Maresh CM 《Journal of strength and conditioning research / National Strength & Conditioning Association》2008,22(3):851-860
This investigation evaluated the effects of a nutritional supplement (the organic osmolyte betaine) in rehydration solutions, with and without carbohydrate and electrolytes. Ten male runners ((mean +/- SD) age, 20 +/- 2 years; weight, 70.6 +/- 6.8 kg; maximal aerobic power, 63.5 +/- 4.1 mL O2 x kg(-1) x min(-1)) dehydrated to -2.7% of body weight. They next rehydrated to -1.4% of body weight by consuming 1 L fluid during each of four experiments (double-blind, randomized, cross-over design): flavored, non-caloric water (W); W + 5 g x L(-1) betaine (W+B); 6% carbohydrate-electrolyte fluid (C); or C + 5 g x L(-1) betaine (C+B). Subjects then performed prolonged treadmill running (75 minutes at 65%Vo2max) plus a performance sprint to volitional exhaustion (3.1-3.8 minutes at 84%Vo2max) in an environmental chamber (31.1 degrees C, 88.0 degrees F). Only W versus W+B and C versus C+B statistical comparisons were germane to the research questions. Observations indicated that rehydration with fluids containing betaine resulted in significant differences (p < 0.05) of plasma volume, oxygen consumption, plasma lactate concentration, and thermal sensation. The present experiments did not support the use of betaine to improve sprint duration, but nonsignificant trends occurred when betaine trials were compared with non-betaine trials (mean C+B > C by 32 seconds, +16%; mean W+B > W by 38 seconds, +21%). We interpret the increases of both aerobic and anaerobic metabolism (C+B > C) to mean that further investigation of betaine as a nutritional supplement, using other types of exercise, is warranted. 相似文献
922.
de Gouvêa PF Soriani FM Malavazi I Savoldi M Goldman MH Loss O Bignell E da Silva Ferreira ME Goldman GH 《Fungal genetics and biology : FG & B》2008,45(7):1135-1146
Phosphate is an ion that is essential for fungal growth. The systems for inorganic phosphate (Pi) acquisition in eukaryotic cells (PHO) have been characterized as a low-affinity (that assures a supply of Pi at normal or high external Pi concentrations) and a high-affinity (activated in response to Pi starvation). Here, as an initial step to understand the PHO pathway in Aspergillus fumigatus, we characterized the PHO80 homologue, PhoBPHO80. We show that the ΔphoBPHO80 mutant has a polar growth defect (i.e., a delayed germ tube emergence) and, by phenotypic and phosphate uptake analyses, establish a link between PhoBPHO80, calcineurin and calcium metabolism. Microarray hybridizations carried out with RNA obtained from wild-type and ΔphoBPHO80 mutant cells identify Afu4g03610 (phoDPHO84), Afu7g06350 (phoEPHO89), Afu4g06020 (phoCPHO81), and Afu2g09040 (vacuolar transporter Vtc4) as more expressed both in the ΔphoBPHO80 mutant background and under phosphate-limiting conditions of 0.1 mM Pi. Epifluorescence microscopy revealed accumulation of poly-phosphate in ΔphoBPHO80 vacuoles, which was independent of extracellular phosphate concentration. Surprisingly, a phoDPHO84 deletion mutant is indistinguishable phenotypically from the corresponding wild-type strain. mRNA analyses suggest that protein kinase A absence supports the expression of PHO genes in A. fumigatus. Furthermore, ΔphoBPHO80 and ΔphoDPHO84 mutant are fully virulent in a murine low dose model for invasive aspergillosis. 相似文献
923.
de Magalhães Lima K Machado Barbosa de Castro CM Fonsêca Nogueira Cambuim II Carvalhaes de Oliveira J Delgado M Sette de Melo Rego R 《Revista iberoamericana de micología》2008,25(1):45-49
Patients infected with human immunodeficiency virus (HIV) are a risk group for onychomycosis, fungal infections caused mainly by dermatophytes and yeast. However, non-dermatohytic moulds are becoming common agents for nail infections in this population of patients. We report four cases of onychomycosis caused by non-dermatophytic moulds (Aspergillus niger, Scytalidium hyalinum, Scytalidium dimidiatum and Fusarium solani) in patients infected with HIV from Recife, Pernambuco, Brazil. Onychomicosis by non-dermatophytic species in HIV-positive patients requires special attention in the clinical and the laboratory. A proper diagnosis is necessary to establish the specific and adequate treatment, preventing fungal invasion. 相似文献
924.
Characterisation of inosine monophosphate dehydrogenase expression during retinal development: differences between variants and isoforms 总被引:1,自引:0,他引:1
Gunter JH Thomas EC Lengefeld N Kruger SJ Worton L Gardiner EM Jones A Barnett NL Whitehead JP 《The international journal of biochemistry & cell biology》2008,40(9):1716-1728
In mammals there are two ubiquitous, catalytically indistinguishable isoforms of inosine monophosphate dehydrogenase and mutations in the type I isoform, but not type II, cause retina-specific disorders. We have characterised the spatio-temporal expression of these proteins during development of the rat retina and performed functional investigations of the recently described retinal type I variants. Inosine monophosphate dehydrogenase was present in all immature cells throughout the retina during embryonic and neonatal development. Following eye opening and cell differentiation its distribution was restricted to the photoreceptors and bipolar cells, becoming prominent in Müller cells with aging. Type II was present in early, developing retinae whilst type I was undetectable. An isoform switch occurred around P10, after which the type I variants, type Ialpha and type Igamma, were the major forms. Functional investigations indicate type Igamma has greater catalytic activity compared with other variants and isoforms. Finally, all forms of type I show an increased propensity to form intracellular macrostructures compared to type II and these structures appear to be regulated in response to changing intracellular GTP levels. Collectively these data demonstrate that (i) type I does not play a role in early retinal development, (ii) type Igamma has greater activity and (iii) there are differences between type I and type II isoforms. These observations are consistent with the aetiology of retinitis pigmentosa and raise the possibility that programmed expression of specific inosine monophosphate dehydrogenase proteins may have arisen to meet the requirements of the cellular environment. 相似文献
925.
Characterization of biofilm formation on a humic material 总被引:1,自引:0,他引:1
Rodrigues AL Brito AG Janknecht P Silva J Machado AV Nogueira R 《Journal of industrial microbiology & biotechnology》2008,35(11):1269-1276
Biofilms are major sites of carbon cycling in streams. Therefore, it is crucial to improve knowledge about biofilms’ structure
and microbial composition to understand their contribution in the self-purification of surface water. The present work intends
to study biofilm formation in the presence of humic substances (HSs) as a carbon source. Two biofilm flowcells were operated
in parallel; one with synthetic stream water, displaying a background carbon concentration of 1.26 ± 0.84 mg L−1, the other with added HSs and an overall carbon concentration of 9.68 ± 1.00 mg L−1. From the biofilms’ results of culturable and total countable cells, it can be concluded that the presence of HSs did not
significantly enhance the biofilm cell density. However, the biofilm formed in the presence of HSs presented slightly higher
values of volatile suspended solids (VSS) and protein. One possible explanation for this result is that HSs adsorbed to the
polymeric matrix of the biofilm and were included in the quantification of VSS and protein. The microbial composition of the
biofilm with addition of HSs was characterized by the presence of bacteria belonging to beta-Proteobacteria, Cupriavidus metallidurans and several species of the genus Ralstonia were identified, and gamma-Proteobacteria, represented by Escherichia coli. In the biofilm formed without HSs addition beta-Proteobacteria, represented by the species Variovorax paradoxus, and bacteria belonging to the group Bacteroidetes were detected. In conclusion, the presence of HSs did not significantly
enhance biofilm cell density but influenced the bacterial diversity in the biofilm. 相似文献
926.
927.
928.
929.
Max Bylesjö Mattias Rantalainen Jeremy K Nicholson Elaine Holmes Johan Trygg 《BMC bioinformatics》2008,9(1):106
Background
Kernel-based classification and regression methods have been successfully applied to modelling a wide variety of biological data. The Kernel-based Orthogonal Projections to Latent Structures (K-OPLS) method offers unique properties facilitating separate modelling of predictive variation and structured noise in the feature space. While providing prediction results similar to other kernel-based methods, K-OPLS features enhanced interpretational capabilities; allowing detection of unanticipated systematic variation in the data such as instrumental drift, batch variability or unexpected biological variation. 相似文献930.