全文获取类型
收费全文 | 575篇 |
免费 | 75篇 |
专业分类
650篇 |
出版年
2022年 | 5篇 |
2021年 | 11篇 |
2019年 | 8篇 |
2018年 | 12篇 |
2017年 | 9篇 |
2016年 | 18篇 |
2015年 | 16篇 |
2014年 | 20篇 |
2013年 | 23篇 |
2012年 | 15篇 |
2011年 | 16篇 |
2010年 | 15篇 |
2009年 | 16篇 |
2008年 | 30篇 |
2007年 | 19篇 |
2006年 | 24篇 |
2005年 | 13篇 |
2004年 | 17篇 |
2003年 | 20篇 |
2002年 | 29篇 |
2001年 | 17篇 |
2000年 | 23篇 |
1999年 | 18篇 |
1998年 | 11篇 |
1997年 | 9篇 |
1996年 | 11篇 |
1995年 | 9篇 |
1994年 | 11篇 |
1993年 | 9篇 |
1992年 | 10篇 |
1991年 | 15篇 |
1990年 | 8篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 11篇 |
1986年 | 10篇 |
1985年 | 14篇 |
1984年 | 5篇 |
1983年 | 12篇 |
1982年 | 5篇 |
1980年 | 5篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1976年 | 6篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1972年 | 4篇 |
1970年 | 4篇 |
1967年 | 4篇 |
1942年 | 3篇 |
排序方式: 共有650条查询结果,搜索用时 0 毫秒
41.
42.
43.
Analysis of the fecal microflora of human subjects consuming a probiotic product containing Lactobacillus rhamnosus DR20 总被引:13,自引:0,他引:13
Tannock GW Munro K Harmsen HJ Welling GW Smart J Gopal PK 《Applied and environmental microbiology》2000,66(6):2578-2588
The composition of the fecal microflora of 10 healthy subjects was monitored before (6-month control period), during (6-month test period), and after (3-month posttest period) the administration of a milk product containing Lactobacillus rhamnosus DR20 (daily dose, 1.6 x 10(9) lactobacilli). Monthly fecal samples were examined by a variety of methods, including bacteriological culture analysis, fluorescent in situ hybridization with group-specific DNA probes, denaturing gradient gel electrophoresis of the V2-V3 region of 16S rRNA genes amplified by PCR, gas-liquid chromatography, and bacterial enzyme activity analysis. The composition of the Lactobacillus population of each subject was analyzed by pulsed-field gel electrophoresis of bacterial DNA digests in order to differentiate between DR20 and other strains present in the samples. Representative isolates of lactobacilli were identified to the species level by sequencing the V2-V3 region of their 16S rRNA genes and comparing the sequences obtained (BLAST search) to sequences in the GenBank database. DR20 was detected in the feces of all of the subjects during the test period, but at different frequencies. The presence of DR20 among the numerically predominant strains was related to the presence or absence of a stable indigenous population of lactobacilli during the control period. Strain DR20 did not persist at levels of >10(2) cells per g in the feces of most of the subjects after consumption of the product ceased; the only exception was one subject in which this strain was detected for 2 months during the posttest period. We concluded that consumption of the DR20-containing milk product transiently altered the Lactobacillus and enterococcal contents of the feces of the majority of consumers without markedly affecting biochemical or other bacteriological factors. 相似文献
44.
Effects of sulfate on cadmium uptake by Swiss chard: II. Effects due to sulfate addition to soil 总被引:3,自引:0,他引:3
Sulfate complexation of Cd in nutrient solution has been shown to have little impact on Cd uptake by plants. This study examined the effect of sulfate added to soil on Cd concentrations in soil solution and Cd uptake by Swiss chard (Beta vulgaris L. cv. Fordhook Giant). Swiss chard was grown in soil which was wetted with complete nutrient solution containing equivalent salt concentrations of NaNO3 or Na2SO4. Plant growth was reduced by increasing both NO3 and SO4 concentrations in soil solution, with growth reductions similar for both salts. The Cd concentration in soil solution increased P< 0.05) more consistently with increasing concentrations of SO4 compared to NO3 in soil solution. Solution speciation, calculated with GEOCHEM-PC, showed significant increases of Cd2+ activities with increasing salt rates. Shoot Cd content in 19-day-old Swiss chard plants was marginally but significantly P <0.05) increased with increasing SO4 concentration but no effect was observed with increasing NO3 concentration. These results are compared with earlier work on the marked effect of Cl- salinity on Cd availability in Swiss chard. Possible mechanisms explaining the smaller effect of SO4 compared to Cl on Cd availability are proposed. 相似文献
45.
46.
Structure of turnip crinkle virus. III. Identification of a unique coat protein dimer 总被引:1,自引:0,他引:1
P G Stockley A L Kirsh E P Chow J E Smart S C Harrison 《Journal of molecular biology》1986,191(4):721-725
The minor structural protein (p80), found in about one copy per virion in turnip crinkle virus (TCV), is shown by amino acid analysis and peptide mapping to be a covalent dimer of the major coat protein (p40). The covalent linkage occurs near the N termini of the crosslinked chains. These data suggest that TGV and related viruses contain 178 copies of p40 (89 non-covalent dimers) and one copy of p80 (covalent dimer of two additional p40 chains). The presence of p80 in the salt-stable RNA-protein complex formed when TCV dissociates, as described in an accompanying paper, indicates that the covalent modification affects binding to RNA. We suggest that p80 might be the final dimer to be incorporated into the shell and that it might also be the site for initiation of uncoating. 相似文献
47.
J. I. Smith N. J. Smart M. Misawa W. G. W. Kurz S. G. Tallevi F. DiCosmo 《Plant cell reports》1987,6(2):142-145
Vanadyl sulphate (10–500 mg/l), when added to cell suspension cultures of Catharanthus roseus stimulated increased intracellular accumulation of catharanthine and ajmalicine. This response was demonstrated in both flask and fermenter (30 litre) systems. The response varied, and depended upon cell line, concentration of vanadyl sulphate and the stage of the growth phase at which the cells were treated. This process has the potential to increase the yield and reduce the production time for commercially useful secondary plant metabolites.Abbreviations Ajm
ajmalicine
- Cath
catharanthine
- CAS
ceric ammonium sulphate
- VOSO4
vanadyl sulphate
- FW
fresh weight
- n.d.
not detected 相似文献
48.
49.
Smart AD Course MM Rawson J Selleck S Van Vactor D Johnson KG 《Developmental neurobiology》2011,71(7):608-618
Axon guidance is influenced by the presence of heparan sulfate (HS) proteoglycans (HSPGs) on the surface of axons and growth cones (Hu, [2001]: Nat Neurosci 4:695-701; Irie et al. [2002]: Development 129:61-70; Inatani et al. [2003]: Science 302:1044-1046; Johnson et al. [2004]: Curr Biol 14:499-504; Steigemann et al. [2004]: Curr Biol 14:225-230). Multiple HSPGs, including Syndecans, Glypicans and Perlecans, carry the same carbohydrate polymer backbones, raising the question of how these molecules display functional specificity during nervous system development. Here we use the Drosophila central nervous system (CNS) as a model to compare the impact of eliminating Syndecan (Sdc) and/or the Glypican Dally-like (Dlp). We show that Dlp and Sdc share a role in promoting accurate patterns of axon fasciculation in the lateral longitudinal neuropil; however, unlike mutations in sdc, which disrupt the ability of the secreted repellent Slit to prevent inappropriate passage of axons across the midline, mutations in dlp show neither midline defects nor genetic interactions with Slit and its Roundabout (Robo) receptors at the midline. Dlp mutants do show genetic interactions with Slit and Robo in lateral fascicle formation. In addition, simultaneous loss of Dlp and Sdc demonstrates an important role for Dlp in midline repulsion, reminiscent of the functional overlap between Robo receptors. A comparison of HSPG distribution reveals a pattern that leaves midline proximal axons with relatively little Dlp. Finally, the loss of Dlp alters Slit distribution distal but not proximal to the midline, suggesting that distinct yet overlapping pattern of HSPG expression provides a spatial system that regulates axon guidance decisions. 相似文献
50.