全文获取类型
收费全文 | 6166篇 |
免费 | 615篇 |
国内免费 | 9篇 |
专业分类
6790篇 |
出版年
2023年 | 25篇 |
2022年 | 56篇 |
2021年 | 91篇 |
2020年 | 79篇 |
2019年 | 70篇 |
2018年 | 94篇 |
2017年 | 78篇 |
2016年 | 114篇 |
2015年 | 209篇 |
2014年 | 240篇 |
2013年 | 290篇 |
2012年 | 362篇 |
2011年 | 407篇 |
2010年 | 262篇 |
2009年 | 210篇 |
2008年 | 318篇 |
2007年 | 355篇 |
2006年 | 339篇 |
2005年 | 339篇 |
2004年 | 291篇 |
2003年 | 269篇 |
2002年 | 295篇 |
2001年 | 75篇 |
2000年 | 81篇 |
1999年 | 96篇 |
1998年 | 86篇 |
1997年 | 57篇 |
1996年 | 48篇 |
1995年 | 59篇 |
1994年 | 49篇 |
1993年 | 45篇 |
1992年 | 53篇 |
1991年 | 59篇 |
1990年 | 58篇 |
1989年 | 52篇 |
1988年 | 46篇 |
1987年 | 36篇 |
1986年 | 34篇 |
1985年 | 46篇 |
1984年 | 34篇 |
1983年 | 43篇 |
1982年 | 46篇 |
1981年 | 52篇 |
1980年 | 51篇 |
1979年 | 40篇 |
1978年 | 32篇 |
1976年 | 41篇 |
1975年 | 37篇 |
1974年 | 25篇 |
1973年 | 27篇 |
排序方式: 共有6790条查询结果,搜索用时 15 毫秒
71.
Kathleen D. Murray Eleanor Groden Francis A. Drummond A. Randall Alford Richard H. Storch Michael D. Bentley 《Entomologia Experimentalis et Applicata》1996,80(3):503-510
The effects of citrus limonoids, applied topically to potato (Solanum tuberosum L. var. Katahdin) foliage, on Colorado potato beetle (Leptinotarsa decemlineata) (Say) (Chrysomelidae) larval development, growth, and survival were quantified in laboratory assays and a small-plot field test. In laboratory assays, survival, development rate, and body weight decreased with increasing limonoid concentration, however these measures of larval response did not significantly differ among varying periods of limonoid exposure (three, six, or nine days). Significant limonoid application concentration and frequency effects on survival, development rate, and defoliation were observed in the field test. These results indicate the potential utility of lethal and non-lethal effects of citrus limonoids for management of the Colorado potato beetle. 相似文献
72.
The prevalence of gentamicin 2'-N-acetyltransferase in the Proteeae and its role in the O-acetylation of peptidoglycan 总被引:1,自引:0,他引:1
Abstract The prevalence of aac(2')-Ia , a gene coding for gentamicin 2'-JV-acetyltransferase in Providenda stuartii , among species of the Proteeae was investigated to determine if it is a common resistance factor and whether the correlation observed in P. stuartii between its expression and the levels of peptidoglycan O -acetylation represents a general feature of bacteria producing this form of modified peptidoglycan. An evaluation of the MICs of gentamicin for each of the species of the Proteeae did not reveal any apparent relationship between resistance and the degree of O-acetylation of peptidoglycan. The entire aac(2')-Ia gene was used as a probe in Southern hybridization experiments against genomic DNA from each species of the Proteeae. A sequence with strong homology to aac(2')-Ia was present only in Proteus penneri while weak hybridization was also observed to the restriction digested DNA from Providenda rettgeri . Other bacteria that O -acetylate peptidoglycan were also screened with this probe and a homologous DNA sequence was only found in Neisseria subflava . These data suggest that AAC(2')-Ia may contribute to the rO -acetylation of peptidoglycan in P. stuartii , but a more specific enzyme must also be produced for this function. 相似文献
73.
74.
75.
76.
A. M. Theodosiou K. E. Morrison A. M. Nesbit R. J. Daniels L. Campbell M. J. Francis Z. Christodoulou K. E. Davies 《American journal of human genetics》1994,55(6):1209-1217
Childhood-onset proximal spinal muscular atrophy (SMA) is a heritable neurological disorder, which has been mapped by genetic linkage analysis to chromosome 5q13, in the interval between markers D5S435 and D5S557. Here, we present gene sequences that have been isolated from this interval, several of which show sequence homologies to exons of beta-glucuronidase. These gene sequences are repeated several times across the candidate region and are also present on chromosome 5p. The arrangement of these repetitive gene motifs is polymorphic between individuals. The high degree of variability observed may have some influence on the expression of the genes in the region. Since SMA is not inherited as a classical autosomal recessive disease, novel genomic rearrangements arising from aberrant recombination events between the complex repeats may be associated with the phenotype observed. 相似文献
77.
Murielle Rinaldi-Carmona Francis Barth Michel Haulme David Shire Bernard Calandra Christian Congy Serge Martinez Jeanne Maruani Gervais Nliat Daniel Caput Pascual Ferrara Philippe Soubri Jean Claude Brelire Grard Le Fur 《FEBS letters》1994,350(2-3):240-244
SR141716A is the first selective and orally active antagonist of the brain cannabinoid receptor. This compound displays nanomolar affinity for the central cannabinoid receptor but is not active on the peripheral cannabinoid receptor. In vitro, SR141716A antagonises the inhibitory effects of cannabinoid receptor agonists on both mouse vas deferens contractions and adenylyl cyclase activity in rat brain membranes. After intraperitoneal or oral administration SR141716A antagonises classical pharmacological and behavioural effects of cannabinoid receptor agonists. This compound should prove to be a powerful tool for investigating the in vivo functions of the anandamide/cannabinoid system. 相似文献
78.
79.
J A Jacobson B E White M P Battin L P Francis D J Green E S Kasworm 《The Western journal of medicine》1994,161(3):232-236
The Patient Self-Determination Act was implemented in December 1991. Before and after its implementation, we used a structured interview of 302 randomly selected patients to determine their awareness, understanding, and use of advance directives. Implementation of the Act did not have a major effect on these. Although more than 90% of patients were aware of the living will, only about a third selected the correct definition or the correct circumstances in which it applied, and less than 20% of patients had completed one. About a third of patients were aware of a Durable Power of Attorney for Health Care and chose the correct definition, and about half identified the correct circumstances in which it applies; less than 10% had completed such a document. Surprisingly, patients who said they had completed advance directives did not demonstrate better understanding of these documents. Our results indicate that many patients, including some who have completed advance directives, do not fully understand them. It may be unwise to regard these documents as carefully considered, compelling statements of patients'' preferences. Appropriate responses to our findings include increased public education, revising state statutes to bring them into congruence with public perception, and expanding the dialogue between physicians and patients. 相似文献
80.
The techniques of 27Al- and 31P-nuclear magnetic resonance (NMR) spectroscopy were used to investigate the interactions of aluminium with intracellular ligands within the mycelium of the ectomycorrhizal basidiomycete Laccaria bicolor (Maire) Orton (S238). The vegetative mycelium was grown on medium containing 0.5 mM AlCl3 for 0.5 to 3 d. The 27Al-NMR spectra showed that aluminium was rapidly taken up and accumulated into polyphosphate complexes in the vacuole. Comparison with Al-polyphosphate complexes obtained in vitro on model systems indicated that Al forms at least three mixed-solvation complexes with Pi and polyphosphates, that there is more than one complex present under any set of conditions, and that the equilibrium between these complexes shifts dramatically with Al concentration in the medium. The high phosphate concentrations in the growth medium favoured the accumulation of the Al-polyphosphate complexes. When mycelium containing Al-polyphosphate complexes was transferred to Al-free nutrient solution for 9 d, the Alpolyphosphate complexes were not remobilized. The sequestration of Al in the polyphosphate complexes could therefore make a significant contribution to the protection of mycorrhizal plants against aluminium toxicity.Abbreviations NMR
nuclear magnetic resonance
- PolyP
polyphosphate(s)
- PP1
terminal phosphate of PolyP
- PP3
middle phosphate of PolyP
We thank Prof. Daniel Canet (Laboratoire de Méthodologie RMN, University of Nancy I, Vandceuvre-lès-Nancy, France) for his constant encouragement and Christine Delaruelle for skilled technical assistance in growing the fungal cultures. This work was supported by a research grant from the Commission of the European Communities (STEP-CT90-0059, Role of Ectomycorrhiza in Stress Tolerance of Forest Trees) to F.M. and a travel grant from the Institut National de la Recherche Agronomique to I.K.; R.C. is a recipient of a Postdoctoral Fellowship from the Natural Sciences and Engineering Research Council of Canada. 相似文献