全文获取类型
收费全文 | 13481篇 |
免费 | 1166篇 |
国内免费 | 10篇 |
专业分类
14657篇 |
出版年
2023年 | 48篇 |
2022年 | 127篇 |
2021年 | 231篇 |
2020年 | 141篇 |
2019年 | 185篇 |
2018年 | 207篇 |
2017年 | 171篇 |
2016年 | 329篇 |
2015年 | 568篇 |
2014年 | 587篇 |
2013年 | 798篇 |
2012年 | 953篇 |
2011年 | 976篇 |
2010年 | 630篇 |
2009年 | 559篇 |
2008年 | 831篇 |
2007年 | 870篇 |
2006年 | 775篇 |
2005年 | 747篇 |
2004年 | 767篇 |
2003年 | 715篇 |
2002年 | 655篇 |
2001年 | 144篇 |
2000年 | 90篇 |
1999年 | 144篇 |
1998年 | 166篇 |
1997年 | 122篇 |
1996年 | 114篇 |
1995年 | 104篇 |
1994年 | 93篇 |
1993年 | 107篇 |
1992年 | 100篇 |
1991年 | 67篇 |
1990年 | 80篇 |
1989年 | 60篇 |
1988年 | 76篇 |
1987年 | 75篇 |
1986年 | 56篇 |
1985年 | 83篇 |
1984年 | 81篇 |
1983年 | 79篇 |
1982年 | 104篇 |
1981年 | 96篇 |
1980年 | 90篇 |
1979年 | 54篇 |
1978年 | 55篇 |
1977年 | 53篇 |
1976年 | 53篇 |
1974年 | 49篇 |
1973年 | 57篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Modulation of DNA repair and recombination by the bacteriophage lambda Orf function in Escherichia coli K-12 下载免费PDF全文
Poteete AR 《Journal of bacteriology》2004,186(9):2699-2707
The orf gene of bacteriophage lambda, fused to a promoter, was placed in the galK locus of Escherichia coli K-12. Orf was found to suppress the recombination deficiency and sensitivity to UV radiation of mutants, in a Delta(recC ptr recB recD)::P(tac) gam bet exo pae cI DeltarecG background, lacking recF, recO, recR, ruvAB, and ruvC functions. It also suppressed defects of these mutants in establishing replication of a pSC101-related plasmid. Compared to orf, the recA803 allele had only small effects on recF, recO, and recR mutant phenotypes and no effect on a ruvAB mutant. In a fully wild-type background with respect to known recombination and repair functions, orf partially suppressed the UV sensitivity of ruvAB and ruvC mutants. 相似文献
992.
Marie Paul Audrey Mayi David Forfuet Foncha Cyril Kowo Timoleon Tchuinkam Katherine Brisco Damian Nota Anong Sehgal Ravinder Anthony John Cornel 《Journal of vector ecology》2019,44(2):271-281
Deforestation is a major threat to biodiversity but little data exist on how deforestation in real‐time affects the overall mosquito species community despite its known role in the transmission of diseases. We compared the abundance and diversity of Culex mosquitoes before and after deforestation along a gradient of three different anthropogenic disturbance levels in a tropical rainforest in southwestern Cameroon. The collections were conducted in unlogged forest (January, 2016), selectively logged forest (January, 2017), and within a young palm plantation (October, 2017) using net traps, sweep nets, resting traps, and dipping for immature stages in water bodies. Mosquitoes were morphologically identified to subspecies, groups, and species. A total of 2,556 mosquitoes was collected of which 1,663 (65.06%) belong to the genus Culex, (n=427 (25.68%) in the unlogged forest; n=900 (54.12%) in the selectively logged forest; and n=336 (20.2%) in the young palm plantation) with a significant difference among the habitats. Diversity and richness of mosquitoes varied significantly among habitats with the highest values found in the selectively logged forest (H=2.4; DS=0.87; S=33) and the lowest value in the unlogged forest (H=1.37; DS=0.68; S=13). The results of this study showed that deforestation affects the abundance and diversity of Culex mosquitoes and favors the invasion of anthropophilic mosquitoes. Higher mosquito abundance and diversity in the selectively logged forest than in the pristine forest is notable and some explanations for these differences are discussed. 相似文献
993.
994.
995.
Protein kinase-mediated phosphorylation is among the most important post-translational modifications. However, few phosphorylation sites have been experimentally identified for most species, making it difficult to determine the degree to which phosphorylation sites are conserved. The goal of this study was to use computational methods to characterize the conservation of human phosphorylation sites in a wide variety of eukaryotes. Using experimentally-determined human sites as input, homologous phosphorylation sites were predicted in all 432 eukaryotes for which complete proteomes were available. For each pair of species, we calculated phosphorylation site conservation as the number of phosphorylation sites found in both species divided by the number found in at least one of the two species. A clustering of the species based on this conservation measure was concordant with phylogenies based on traditional genomic measures. For a subset of the 432 species, phosphorylation site conservation was compared to conservation of both protein kinases and proteins in general. Protein kinases exhibited the highest degree of conservation, while general proteins were less conserved and phosphorylation sites were least conserved. Although preliminary, these data tentatively suggest that variation in phosphorylation sites may play a larger role in explaining phenotypic differences among organisms than differences in the complements of protein kinases or general proteins. 相似文献
996.
Susan Rees Derrick Silove Teresa Verdial Natalino Tam Elisa Savio Zulmira Fonseca Rosamund Thorpe Belinda Liddell Anthony Zwi Kuowei Tay Robert Brooks Zachary Steel 《PloS one》2013,8(8)
Introduction
Women in conflict-affected countries are at risk of mental disorders such as posttraumatic stress disorder and depression. No studies have investigated the association between experiences of abuse and injustice and explosive anger amongst women in these settings, and the impact of anger on women''s health, family relationships and ability to participate in development.Methods
A mixed methods study including an epidemiological survey (n = 1513, 92.6% response) and qualitative interviews (n = 77) was conducted in Timor-Leste. The indices measured included Intermittent Explosive Disorder, posttraumatic stress disorder; severe distress; days out of role (the number of days that the person was unable to undertake normal activities); gender-specific trauma; conflict/violence; poverty; and preoccupations with injustice.Results
Women with Intermittent Explosive Disorder (n = 184, 12.2%) were more disabled than those without the disorder (for >5 days out of role, 40.8% versus 31.5%, X2 (2) = 12.93 p = 0.0016). Multivariable associations with Intermittent Explosive Disorder, controlling for the presence of PTSD, psychological distress and other predictors in the model, included the sense of being sick (OR 1.73; 95% CI 1.08–2.77); victimization as a result of helping the resistance movement (OR 2.33, 95% CI 1.48–3.68); war-related trauma specific to being a woman (OR 1.95, 95%, CI 1.09–3.50); ongoing family violence and community conflict (OR 1.88, 95% CI 1.27–2.77); extreme poverty (OR 1.23, 95%, CI 1.08–1.39); and distressing preoccupations with injustice (relating to 2/3 historical periods, OR 2.10, 95% CI 1.35–3.28). In the qualitative study, women elaborated on the determinants of anger and its impact on their health, family and community functioning, child-rearing, and capacity to engage in development. Women reflected on the strategies that might help them overcome their anger.Conclusions
Intermittent Explosive Disorder is prevalent and disabling amongst women in conflict-affected Timor-Leste, impacting on their health, child-rearing and ability to participate fully in socio-economic development. 相似文献997.
McCaughan B Rouanet C Fowley C Nomikou N McHale AP McCarron PA Callan JF 《Bioorganic & medicinal chemistry letters》2011,21(19):5750-5752
A combination of light and ultrasound activation of two conventional photosensitising drugs, methylene blue and rose bengal, was shown to generate higher levels of reactive oxygen species (ROS) and lower LD50 values than either light or ultrasound activation alone. 相似文献
998.
Anthony B. Pinkerton Eduard Sergienko Yalda Bravo Russell Dahl Chen-Ting Ma Qing Sun Michael R. Jackson Nicholas D.P. Cosford José Luis Millán 《Bioorganic & medicinal chemistry letters》2018,28(1):31-34
Tissue-nonspecific alkaline phosphatase (TNAP) is an ectoenzyme crucial for bone matrix mineralization via its ability to hydrolyze extracellular inorganic pyrophosphate (ePPi), a potent mineralization inhibitor, to phosphate (Pi). By the controlled hydrolysis of ePPi, TNAP maintains the correct ratio of Pi to ePPi and therefore enables normal skeletal and dental calcification. In other areas of the body low ePPi levels lead to the development of pathological soft-tissue calcification, which can progress to a number of disorders. TNAP inhibitors have been shown to prevent these processes via an increase of ePPi. Herein we describe the use of a whole blood assay to optimize a previously described series of TNAP inhibitors resulting in 5-((5-chloro-2-methoxyphenyl)sulfonamido)nicotinamide (SBI-425), a potent, selective and oral bioavailable compound that robustly inhibits TNAP in vivo. 相似文献
999.
Ribonucleotide reduction is the only known biological means for de novo production of deoxyribonucleotides, the building blocks of DNA. These are produced from ribonucleotides, the building blocks
of RNA, and the direction of this reaction has been taken to support the idea that, in evolution, RNA preceded DNA as genetic
material. However, an understanding of the evolutionary relationships among the three modern-day classes of ribonucleotide
reductase and how the first reductase arose early in evolution is still far off. We propose that the diversification of this
class of enzymes is inherently tied to microbial colonization of aerobic and anaerobic niches. The work is of broader interest,
as it also sheds light on the process of adaptation to oxygenic environments consequent to the evolution of atmospheric oxygen. 相似文献
1000.
Continuous plankton records stand the test of time: evaluation of flow rates, clogging and the continuity of the CPR time-series 总被引:1,自引:0,他引:1
John Eurgain H.; Batten Sonia D.; Stevens Darren; Walne Anthony W.; Jonas Tanya Jonas; Hays Graeme C. 《Journal of plankton research》2002,24(9):941-946
The Continuous Plankton Recorder (CPR) survey is one of themost extensive biological time-series in existence and has beenin operation over major regions of the North Atlantic since1932. However, there is little information about the volumeof water filtered through each sample, but rather a generalassumption has persisted that each sample represents 3 m3. Datafrom electromagnetic flowmeters, deployed on CPRs between 1995and 1998, was examined. The mean volume filtered through sampleswas 3.11 m3 and the effect of clogging on filtration efficiencieswas not great. Consequently, even when the likely variationsin flow due to clogging are taken into account, previously identifiedlinks between zooplankton abundance and climatic signals remainstrong. 相似文献