全文获取类型
收费全文 | 15080篇 |
免费 | 1127篇 |
国内免费 | 825篇 |
专业分类
17032篇 |
出版年
2024年 | 32篇 |
2023年 | 194篇 |
2022年 | 495篇 |
2021年 | 768篇 |
2020年 | 461篇 |
2019年 | 591篇 |
2018年 | 568篇 |
2017年 | 408篇 |
2016年 | 570篇 |
2015年 | 854篇 |
2014年 | 960篇 |
2013年 | 1077篇 |
2012年 | 1304篇 |
2011年 | 1193篇 |
2010年 | 747篇 |
2009年 | 659篇 |
2008年 | 741篇 |
2007年 | 693篇 |
2006年 | 591篇 |
2005年 | 520篇 |
2004年 | 458篇 |
2003年 | 370篇 |
2002年 | 329篇 |
2001年 | 308篇 |
2000年 | 255篇 |
1999年 | 230篇 |
1998年 | 148篇 |
1997年 | 147篇 |
1996年 | 150篇 |
1995年 | 110篇 |
1994年 | 111篇 |
1993年 | 81篇 |
1992年 | 134篇 |
1991年 | 102篇 |
1990年 | 78篇 |
1989年 | 78篇 |
1988年 | 63篇 |
1987年 | 71篇 |
1986年 | 64篇 |
1985年 | 50篇 |
1984年 | 48篇 |
1983年 | 41篇 |
1982年 | 24篇 |
1981年 | 13篇 |
1980年 | 16篇 |
1979年 | 19篇 |
1977年 | 14篇 |
1976年 | 11篇 |
1973年 | 10篇 |
1972年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
The advances of next-generation sequencing technology have facilitated metagenomics research that attempts to determine directly the whole collection of genetic material within an environmental sample (i.e. the metagenome). Identification of genes directly from short reads has become an important yet challenging problem in annotating metagenomes, since the assembly of metagenomes is often not available. Gene predictors developed for whole genomes (e.g. Glimmer) and recently developed for metagenomic sequences (e.g. MetaGene) show a significant decrease in performance as the sequencing error rates increase, or as reads get shorter. We have developed a novel gene prediction method FragGeneScan, which combines sequencing error models and codon usages in a hidden Markov model to improve the prediction of protein-coding region in short reads. The performance of FragGeneScan was comparable to Glimmer and MetaGene for complete genomes. But for short reads, FragGeneScan consistently outperformed MetaGene (accuracy improved ∼62% for reads of 400 bases with 1% sequencing errors, and ∼18% for short reads of 100 bases that are error free). When applied to metagenomes, FragGeneScan recovered substantially more genes than MetaGene predicted (>90% of the genes identified by homology search), and many novel genes with no homologs in current protein sequence database. 相似文献
42.
Small ubiquitin-related modifier SUMO-3 is a member of a growing family of ubiquitin-like proteins (Ubls). So far, four isoforms of SUMO have been identified in humans. It is generally known that SUMO modification regulates protein localization and activity. Previous structure and function studies have been mainly focused on SUMO-1. The sequence of SUMO-3 is 46% identical with that of SUMO-1; nevertheless, functional heterogeneity has been found between the two homologues. Here we report the solution structure of SUMO-3 C47S (residues 14-92) featuring the beta-beta-alpha-beta-beta-alpha-beta ubiquitin fold. Structural comparison shows that SUMO-3 C47S resembles ubiquitin more than SUMO-1. On the helix-sheet interface, a strong hydrophobic interaction contributes to formation of the globular and compact fold. A Gly-Gly motif at the C-terminal tail, extending away from the core structure, is accessible to enzymes and substrates. In vivo, SUMO modification proceeds via a multistep pathway, and Ubc9 plays an indispensable role as the SUMO conjugating enzyme (E2) in this process. To develop a better understanding of SUMO-3 conjugation, the Ubc9 binding surface on SUMO-3 C47S has been detected by chemical shift perturbation using NMR spectroscopy. The binding site mainly resides on the hydrophilic side of the beta-sheet. Negatively charged and hydrophobic residues of this region are highly or moderately conserved among SUMO family members. Notably, the negatively charged surface of SUMO-3 C47S is highly complementary in its electrostatic potentials and hydrophobicity to the positively charged surface of Ubc9. This work indicates dissimilarities between SUMO-3 and SUMO-1 in tertiary structure and provides insight into the specific interactions of SUMO-3 with its modifying enzyme. 相似文献
43.
Johannes A Hofberger Beifei Zhou Haibao Tang Jonathan DG Jones M Eric Schranz 《BMC genomics》2014,15(1)
Background
Recent advances in DNA sequencing techniques resulted in more than forty sequenced plant genomes representing a diverse set of taxa of agricultural, energy, medicinal and ecological importance. However, gene family curation is often only inferred from DNA sequence homology and lacks insights into evolutionary processes contributing to gene family dynamics. In a comparative genomics framework, we integrated multiple lines of evidence provided by gene synteny, sequence homology and protein-based Hidden Markov Modelling to extract homologous super-clusters composed of multi-domain resistance (R)-proteins of the NB-LRR type (for NUCLEOTIDE BINDING/LEUCINE-RICH REPEATS), that are involved in plant innate immunity.Results
To assess the diversity of R-proteins within and between species, we screened twelve eudicot plant genomes including six major crops and found a total of 2,363 NB-LRR genes. Our curated R-proteins set shows a 50% average for tandem duplicates and a 22% fraction of gene copies retained from ancient polyploidy events (ohnologs). We provide evidence for strong positive selection and show significant differences in molecular evolution rates (Ka/Ks-ratio) among tandem- (mean = 1.59), ohnolog (mean = 1.36) and singleton (mean = 1.22) R-gene duplicates. To foster the process of gene-edited plant breeding, we report species-specific presence/absence of all 140 NB-LRR genes present in the model plant Arabidopsis and describe four distinct clusters of NB-LRR “gatekeeper” loci sharing syntenic orthologs across all analyzed genomes.Conclusion
By curating a near-complete set of multi-domain R-protein clusters in an eudicot-wide scale, our analysis offers significant insight into evolutionary dynamics underlying diversification of the plant innate immune system. Furthermore, our methods provide a blueprint for future efforts to identify and more rapidly clone functional NB-LRR genes from any plant species.Electronic supplementary material
The online version of this article (doi:10.1186/1471-2164-15-966) contains supplementary material, which is available to authorized users. 相似文献44.
Glycoprotein O (gO) is conserved among betaherpesviruses, but little is known about the maturation process of gO in human herpesvirus 6 (HHV-6). We found that HHV-6 gO maturation was accompanied by cleavage of its carboxyl terminus and required coexpression of gH and gL, which promoted the export of gO out of the endoplasmic reticulum (ER). Finally, we also found that gO was not required for HHV-6A growth in T cells. 相似文献
45.
46.
ABSTRACT Massive expansions of the hexanucleotide in C9orf72 are the primary genetic origins of familial amyotrophic lateral sclerosis (ALS) and frontal temporal dementia (FTD). Current studies have found that this repeat sequence participates in the disease process by producing neurotoxic substances and reducing the level of C9orf72 protein; however, the progress in the functional study of C9orf72 is slow. Recently, a stable complex, consisting of C9orf72, SMCR8, and WDR41, has been implicated in regulating membrane trafficking and macroautophagy. We reported the cryo-electron microscopy (cryo-EM) structure of the C9orf72-SMCR8-WDR41 complex (CSW complex), unveiling that the CSW complex is a dimer of heterotrimers. Intriguingly, in the heterotrimer of the C9orf72-SMCR8-WDR41, C9orf72 interacts with SMCR8 in a manner similar to the FLCN-FNIP2 complex. Nevertheless, WDR41 is connected to the DENN domain of SMCR8 through its N-terminal β-strand and C-terminal helix but does not directly interact with C9orf72. Notably, the C9orf72-SMCR8 complex was demonstrated to act as a GAP for RAB8A and RAB11A in vitro. 相似文献
47.
48.
Super-paramagnetic microbeads are widely used for cell isolation. Evaluation of the binding affinity of microbeads to cells using optical microscopy has been limited by its small scope. Here, magnetic property of microbeads was first investigated by using synchrotron radiation (SR) in-line x-ray phase contrast imaging (PCI). The cell line mouse LLC (Lewis lung carcinoma) was selected for cell adhesion studies. Targeted microbeads were prepared by attaching anti-VEGFR2 (vascular endothelial growth factor receptor-2) antibody to the shell of the microbeads. The bound microbeads were found to better adhere to LLC cells than unbound ones. PCI dynamically and clearly showed the magnetization and demagnetization of microbeads in PE-50 tube. The cells incubated with different types of microbeads were imaged by PCI, which provided clear and real-time visualization of the cell isolation. Therefore, PCI might be considered as a novel and efficient tool for further cell isolation studies. 相似文献
49.
R D Wagner E S Krul J Tang K G Parhofer K Garlock P Talmud G Schonfeld 《Journal of lipid research》1991,32(6):1001-1011
A new, large kindred with hypobetalipoproteinemia and a previously undescribed truncated form of apolipoprotein B (apoB) has been identified. The asymptomatic, Caucasian male proband (CK, aged 37 years) has total plasma cholesterol, triglyceride, low density lipoprotein-(LDL) cholesterol, high density lipoprotein- (HDL) cholesterol, and apoB concentrations of 108, 131, 32, 50, and 16 mg/dl, respectively. Plasma samples of 11 family members spanning three generations, which had less than 5th percentile concentrations of LDL-cholesterol, contained three apoB bands detected on immunoblots: the normal apoB-100 and apoB-48 and an unusual band of apparent molecular mass of 299,356 +/- 9580 daltons (approximately 54% the molecular weight of apoB-100). Additional immunoblotting experiments using several different anti-apoB monoclonal antibodies showed that the carboxyl terminal of apoB-100 had been deleted somewhere between amino acid residues 2148-2488. A segment of genomic DNA from the proband was amplified by polymerase chain reaction (PCR) between nucleotides 7491-7791 of Exon 26 of the apoB gene. The DNA segment was cloned into pGEM3Zf(-) and sequenced. A C----T transition was found at nucleotide 7665, resulting in a premature stop codon at amino acid residue 2486 corresponding to apoB-54.8. These results were confirmed by direct sequencing of PCR products from three apoB-54.8 positive and three apoB-54.8 negative kindred members. Allele-specific oligonucleotides were used to identify other affected family members. Cosegregation of apoB-54.8 with the C----T transition occurred in all cases. Based on haplotypes constructed from restriction fragment length polymorphism, variable number of tandem repeats, and 5' insertion/deletion analyses and from the presence or absence of apoB-54.8, it was possible to assign a single allele of apoB to the mutation throughout the family. In contrast with other shorter truncations such as apoB-31, apoB-40, and apoB-46, which are found with particles in the HDL density range, and apoB-89 that is found primarily with LDL, apoB-54.8 was found primarily in very low density lipoproteins, much less in LDL, and was virtually absent in HDL. This suggests that the length of the truncation may significantly affect the metabolism of the associated lipoprotein particles. 相似文献
50.
Ying Liu Jie Tang Jingjing Li Maurycy Daroch Jay J. Cheng 《Applied microbiology and biotechnology》2014,98(23):9643-9652
Thraustochytrids have recently emerged as a promising source for docosahexaenoic acid (DHA) production due to their high growth rate and oil content. In this study, two thraustochytrid isolates, Aurantiochytrium sp. PKU#SW7 and Thraustochytriidae sp. PKU#Mn16 were used for DHA production. Following growth parameters were optimized to maximize DHA production: temperature, pH, salinity, and glucose concentration. Both isolates achieved the highest DHA yield at the cultivation temperature of 28 °C, pH 6, 100 % seawater, and 2 % glucose. A DHA yield of 1.395 g/l and 1.426 g/l was achieved under the optimized culture conditions. Further investigation revealed that both isolates possess simple fatty acids profiles with palmitic acid and DHA as their dominant constituents, accounting for ~79 % of total fatty acids. To date, very few studies have focused on the DHA distribution in various lipid fractions which is an important factor for identifying strains with a potential for industrial DHA production. In the present study, the lipids profiles of each strain both revealed that the majority of DHA was distributed in neutral lipids (NLs), and the DHA distribution in NLs of PKU#SW7 was exclusively in the form of triacylglycerols (TAGs) which suggest that PKU#SW7 could be utilized as an alternative source of DHA for dietary supplements. The fermentation process established for both strains also indicating that Aurantiochytrium sp. PKU#SW7 was more suitable for cultivation in fermenter. In addition, the high percentage of saturated fatty acids produced by the two thraustochytrids indicates their potential application in biodiesel production. Overall, our findings suggest that two thraustochytrid isolates are suitable candidates for biotechnological applications. 相似文献