全文获取类型
收费全文 | 21922篇 |
免费 | 1498篇 |
国内免费 | 9篇 |
出版年
2024年 | 19篇 |
2023年 | 126篇 |
2022年 | 311篇 |
2021年 | 580篇 |
2020年 | 351篇 |
2019年 | 470篇 |
2018年 | 593篇 |
2017年 | 478篇 |
2016年 | 809篇 |
2015年 | 1215篇 |
2014年 | 1343篇 |
2013年 | 1659篇 |
2012年 | 1948篇 |
2011年 | 1893篇 |
2010年 | 1174篇 |
2009年 | 1016篇 |
2008年 | 1376篇 |
2007年 | 1287篇 |
2006年 | 1179篇 |
2005年 | 1081篇 |
2004年 | 981篇 |
2003年 | 927篇 |
2002年 | 751篇 |
2001年 | 117篇 |
2000年 | 106篇 |
1999年 | 135篇 |
1998年 | 125篇 |
1997年 | 115篇 |
1996年 | 89篇 |
1995年 | 86篇 |
1994年 | 90篇 |
1993年 | 88篇 |
1992年 | 53篇 |
1991年 | 56篇 |
1990年 | 63篇 |
1989年 | 45篇 |
1988年 | 50篇 |
1987年 | 38篇 |
1986年 | 42篇 |
1985年 | 51篇 |
1984年 | 39篇 |
1983年 | 44篇 |
1982年 | 32篇 |
1981年 | 42篇 |
1980年 | 26篇 |
1979年 | 34篇 |
1978年 | 33篇 |
1977年 | 29篇 |
1976年 | 25篇 |
1975年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
881.
882.
883.
Paula E Adams Anna B Crist Ellen M Young John H Willis Patrick C Phillips Janna L Fierst 《Molecular biology and evolution》2022,39(1)
The deleterious effects of inbreeding have been of extreme importance to evolutionary biology, but it has been difficult to characterize the complex interactions between genetic constraints and selection that lead to fitness loss and recovery after inbreeding. Haploid organisms and selfing organisms like the nematode Caenorhabditis elegans are capable of rapid recovery from the fixation of novel deleterious mutation; however, the potential for recovery and genomic consequences of inbreeding in diploid, outcrossing organisms are not well understood. We sought to answer two questions: 1) Can a diploid, outcrossing population recover from inbreeding via standing genetic variation and new mutation? and 2) How does allelic diversity change during recovery? We inbred C. remanei, an outcrossing relative of C. elegans, through brother-sister mating for 30 generations followed by recovery at large population size. Inbreeding reduced fitness but, surprisingly, recovery from inbreeding at large populations sizes generated only very moderate fitness recovery after 300 generations. We found that 65% of ancestral single nucleotide polymorphisms (SNPs) were fixed in the inbred population, far fewer than the theoretical expectation of ∼99%. Under recovery, 36 SNPs across 30 genes involved in alimentary, muscular, nervous, and reproductive systems changed reproducibly across replicates, indicating that strong selection for fitness recovery does exist. Our results indicate that recovery from inbreeding depression via standing genetic variation and mutation is likely to be constrained by the large number of segregating deleterious variants present in natural populations, limiting the capacity for recovery of small populations. 相似文献
884.
885.
Danielle K. Walkup Anna Michelle Lawing Toby J. Hibbitts Wade A. Ryberg 《Ecology and evolution》2022,12(2)
The western massasauga (Sistrurus tergeminus) is a small pit viper with an extensive geographic range, yet observations of this species are relatively rare. They persist in patchy and isolated populations, threatened by habitat destruction and fragmentation, mortality from vehicle collisions, and deliberate extermination. Changing climates may pose an additional stressor on the survival of isolated populations. Here, we evaluate historic, modern, and future geographic projections of suitable climate for S. tergeminus to outline shifts in their potential geographic distribution and inform current and future management. We used maximum entropy modeling to build multiple models of the potential geographic distribution of S. tergeminus. We evaluated the influence of five key decisions made during the modeling process on the resulting geographic projections of the potential distribution, allowing us to identify areas of model robustness and uncertainty. We evaluated models with the area under the receiver operating curve and true skill statistic. We retained 16 models to project both in the past and future multiple general circulation models. At the last glacial maximum, the potential geographic distribution associated with S. tergeminus occurrences had a stronghold in the southern part of its current range and extended further south into Mexico, but by the mid‐Holocene, its modeled potential distribution was similar to its present‐day potential distribution. Under future model projections, the potential distribution of S. tergeminus moves north, with the strongest northward trends predicted under a climate scenario increase of 8.5 W/m2. Some southern populations of S. tergeminus have likely already been extirpated and will continue to be threatened by shifting availability of suitable climate, as they are already under threat from desertification of grasslands. Land use and habitat loss at the northern edge of the species range are likely to make it challenging for this species to track suitable climates northward over time. 相似文献
886.
Amer I. Tawfik Anna Mat'hov Frantiek Sehnal Sayed H. Ismail 《Archives of insect biochemistry and physiology》1996,31(4):427-438
In the penultimate and last instar larvae of Schistocerca gregaria, 20-hydroxyecdysone (20E) makes up 74–84% of detected ecdysteroids in the females, and 63–74% in the males. Remaining ecdysteroids include ecdysone, a compound with HPLC and TLC retention times of makisterone A, and highly polar metabolites. Except for the last instar females, the contents of ecdysone and the unknown compound are higher in the solitary phase, while that of polar metabolites is higher in the gregarious phase. The phases also differ in that the molt-inducing ecdysteroid peaks last longer in the gregarious than in the solitary larvae. Peak concentrations reach 3.0–4.0 μg 20E equiv./ml in penultimate female instar, 2.5–3.0 μg/ml in penultimate male instar, and 1.5–2.0 μg/ml in the last larval instar of both sexes. © 1996 Wiley-Liss, Inc. 相似文献
887.
Uzay Gormus Alka Chaubey Suresh Shenoy Yong Wee Wong Lee Yin Chan Bao Ping Choo Liza Oraha Anna Gousseva Fredrik Persson Lawrence Prensky Ephrem Chin Madhuri Hegde 《Current issues in molecular biology》2021,43(2):958
Background: Rolling-circle replication (RCR) is a novel technology that has not been applied to cell-free DNA (cfDNA) testing until recently. Given the cost and simplicity advantages of this technology compared to other platforms currently used in cfDNA analysis, an assessment of RCR in clinical laboratories was performed. Here, we present the first validation study from clinical laboratories utilizing RCR technology. Methods: 831 samples from spontaneously pregnant women carrying a singleton fetus, and 25 synthetic samples, were analyzed for the fetal risk of trisomy 21 (T21), trisomy 18 (T18) and trisomy 13 (T13), by three laboratories on three continents. All the screen-positive pregnancies were provided post-test genetic counseling and confirmatory diagnostic invasive testing (e.g., amniocentesis). The screen-negative pregnancies were routinely evaluated at birth for fetal aneuploidies, using newborn examinations, and any suspected aneuploidies would have been offered diagnostic testing or confirmed with karyotyping. Results: The study found rolling-circle replication to be a highly viable technology for the clinical assessment of fetal aneuploidies, with 100% sensitivity for T21 (95% CI: 82.35–100.00%); 100.00% sensitivity for T18 (71.51–100.00%); and 100.00% sensitivity for T13 analyses (66.37–100.00%). The specificities were >99% for each trisomy (99.7% (99.01–99.97%) for T21; 99.5% (98.62–99.85%) for T18; 99.7% (99.03–99.97%) for T13), along with a first-pass no-call rate of 0.93%. Conclusions: The study showed that using a rolling-circle replication-based cfDNA system for the evaluation of the common aneuploidies would provide greater accuracy and clinical utility compared to conventional biochemical screening, and it would provide comparable results to other reported cfDNA methodologies. 相似文献
888.
Teresa Fazia Daria Marzanati Anna Laura Carotenuto Ashley Beecham Athena Hadjixenofontos Jacob L. McCauley Valeria Saddi Marialuisa Piras Luisa Bernardinelli Davide Gentilini 《Current issues in molecular biology》2021,43(3):1778
Multiple Sclerosis (MS) is a complex multifactorial autoimmune disease, whose sex- and age-adjusted prevalence in Sardinia (Italy) is among the highest worldwide. To date, 233 loci were associated with MS and almost 20% of risk heritability is attributable to common genetic variants, but many low-frequency and rare variants remain to be discovered. Here, we aimed to contribute to the understanding of the genetic basis of MS by investigating potentially functional rare variants. To this end, we analyzed thirteen multiplex Sardinian families with Immunochip genotyping data. For five families, Whole Exome Sequencing (WES) data were also available. Firstly, we performed a non-parametric Homozygosity Haplotype analysis for identifying the Region from Common Ancestor (RCA). Then, on these potential disease-linked RCA, we searched for the presence of rare variants shared by the affected individuals by analyzing WES data. We found: (i) a variant (43181034 T > G) in the splicing region on exon 27 of CUL9; (ii) a variant (50245517 A > C) in the splicing region on exon 16 of ATP9A; (iii) a non-synonymous variant (43223539 A > C), on exon 9 of TTBK1; (iv) a non-synonymous variant (42976917 A > C) on exon 9 of PPP2R5D; and v) a variant (109859349-109859354) in 3′UTR of MYO16. 相似文献
889.
890.
Anna Romanowska Ewa Katzenellenbogen Magorzata Kuakowska rzej Gamian Danuta Witkowska Marian Mulczyk Elbieta Romanowska 《FEMS microbiology letters》1988,47(3):151-155
Abstract Lipopolysaccharides (LPS) of 33 strains of Hafnia alvei were isolated and purified. LPS content of the dry bacterial mass ranged from 1.2 to 4.5%. All examined lipopolysaccharides contained glucose, glucosamine, heptose, 3-deoxy-octulosonic acid and often galactose. Rhamnose, mannose, galactosamine, mannosamine and unidentified amino sugars were found in some H. alvei strains. Sialic acid was present in LPS of one strain. d -3-Hydroxybutyryl groups also were identified in lipopolysaccharides of 5 strains of this genus.
SDS-PAGE of the lipopolysaccharides was presented in the paper. According to these results two core types exist in H. alvei . 相似文献
SDS-PAGE of the lipopolysaccharides was presented in the paper. According to these results two core types exist in H. alvei . 相似文献