全文获取类型
收费全文 | 12182篇 |
免费 | 696篇 |
国内免费 | 36篇 |
专业分类
12914篇 |
出版年
2024年 | 34篇 |
2023年 | 129篇 |
2022年 | 408篇 |
2021年 | 612篇 |
2020年 | 369篇 |
2019年 | 462篇 |
2018年 | 514篇 |
2017年 | 383篇 |
2016年 | 534篇 |
2015年 | 640篇 |
2014年 | 741篇 |
2013年 | 924篇 |
2012年 | 995篇 |
2011年 | 900篇 |
2010年 | 534篇 |
2009年 | 421篇 |
2008年 | 542篇 |
2007年 | 520篇 |
2006年 | 460篇 |
2005年 | 455篇 |
2004年 | 351篇 |
2003年 | 298篇 |
2002年 | 255篇 |
2001年 | 125篇 |
2000年 | 125篇 |
1999年 | 99篇 |
1998年 | 70篇 |
1997年 | 40篇 |
1996年 | 43篇 |
1995年 | 51篇 |
1994年 | 34篇 |
1993年 | 37篇 |
1992年 | 57篇 |
1991年 | 54篇 |
1990年 | 58篇 |
1989年 | 53篇 |
1988年 | 51篇 |
1987年 | 40篇 |
1986年 | 40篇 |
1985年 | 45篇 |
1984年 | 37篇 |
1983年 | 34篇 |
1982年 | 28篇 |
1981年 | 30篇 |
1979年 | 22篇 |
1978年 | 24篇 |
1977年 | 27篇 |
1976年 | 23篇 |
1975年 | 29篇 |
1972年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
691.
Kurtoğlu S Sen B Melikoğlu G Becker H Zapp J Kiemer AK Meriçli F Meriçli AH 《Zeitschrift für Naturforschung. C, Journal of biosciences》2012,67(3-4):103-107
From the roots of Aconitum vulparia Rchb., collected in Prüm (Germany), a new norditerpenoid alkaloid, named alexhumboldtine, has been isolated along with the known norditerpenoid alkaloids lappaconitine, anthranoyllycoctonine, lycoctonine, puberaconitine, ajacine, and septentriodine. The structure of alexhumboldtine was established on the basis of 1H, 13C, DEPT, homonuclear 1H COSY, NOESY, HSQC, and HMBC NMR studies. From the aerial parts of the plant another norditerpenoid alkaloid, aconorine, has been isolated. 相似文献
692.
The genus Sathrophyllia Stål, 1874 from Pakistan is reviewed with four species recorded. The diagnostic characters are given and two new species Sathrophyllia
saeedi
sp. n. and Sathrophyllia
irshadi
sp. n. are described. In addition to that Sathrophyllia
nr.
rugosa (Linnaeus, 1758) and Sathrophyllia
femorata (Fabricius, 1787) are re-described. Further information on the distribution and ecology of the species is given and a key to studied species of Sathrophyllia is presented. Sathrophyllia
femorata (Fabricius, 1787) and Sathrophyllia
rugosa (Linnaeus, 1758) are recorded from Rawalakot (KPK) and Tharparker (Sindh), Pakistan for first the time. 相似文献
693.
Motahare-Sadat Hosseini Ali Asghar Katbab 《Reports of Biochemistry & Molecular Biology》2014,3(1):20-28
Background:
One area of nanoscience deals with nanoscopic interactions between nanostructured materials and biological systems. To elucidate the effects of the substrate surface morphology and viscoelasticity on cell proliferation, fractal analysis was performed on endothelial cells cultured on nanocomposite samples based on silicone rubber (SR) and various concentrations of organomodified nanoclay (OC).Methods:
The nanoclay/SR ratio was tailored to enhance cell behavior via changes in sample substrate surface roughness and viscoelasticity.Results:
Surface roughness of the cured SR filled with negatively-charged nanosilicate layers had a greater effect than elasticity on cell growth. The surface roughness of SR nanocomposite samples increased with increasing the OC content, leading to enhanced cell growth and extracellular matrix (ECM) remodeling. This was consistent with the decrease in SR segmental motions and damping factor as the primary viscoelastic parameters by the nanosilicate layers with increasing clay concentrations.Conclusions:
The inclusion of clay nanolayers affected the growth and behavior of endothelial cells on microtextured SR.Key Words: Silicone rubber, Nanoclay, Elastic Modulus, Roughness, Cell proliferation 相似文献694.
695.
Poojah Jawallapersand Samson Sitheni Mashele Lidija Kova?i? Jure Stojan Radovan Komel Suresh Babu Pakala Nada Kra?evec Khajamohiddin Syed 《PloS one》2014,9(9)
Cytochrome P450 monooxygenases (CYPs/P450s) are heme-thiolate proteins whose role as a drug target against pathogenic microbes has been explored because of their stereo- and regio-specific oxidation activity. We aimed to assess the CYP53 family''s role as a common alternative drug target against animal (including human) and plant pathogenic fungi and its role in fungal-mediated wood degradation. Genome-wide analysis of fungal species revealed the presence of CYP53 members in ascomycetes and basidiomycetes. Basidiomycetes had a higher number of CYP53 members in their genomes than ascomycetes. Only two CYP53 subfamilies were found in ascomycetes and six subfamilies in basidiomycetes, suggesting that during the divergence of phyla ascomycetes lost CYP53 P450s. According to phylogenetic and gene-structure analysis, enrichment of CYP53 P450s in basidiomycetes occurred due to the extensive duplication of CYP53 P450s in their genomes. Numerous amino acids (103) were found to be conserved in the ascomycetes CYP53 P450s, against only seven in basidiomycetes CYP53 P450s. 3D-modelling and active-site cavity mapping data revealed that the ascomycetes CYP53 P450s have a highly conserved protein structure whereby 78% amino acids in the active-site cavity were found to be conserved. Because of this rigid nature of ascomycetes CYP53 P450s'' active site cavity, any inhibitor directed against this P450 family can serve as a common anti-fungal drug target, particularly toward pathogenic ascomycetes. The dynamic nature of basidiomycetes CYP53 P450s at a gene and protein level indicates that these P450s are destined to acquire novel functions. Functional analysis of CYP53 P450s strongly supported our hypothesis that the ascomycetes CYP53 P450s ability is limited for detoxification of toxic molecules, whereas basidiomycetes CYP53 P450s play an additional role, i.e. involvement in degradation of wood and its derived components. This study is the first report on genome-wide comparative structural (gene and protein structure-level) and evolutionary analysis of a fungal P450 family. 相似文献
696.
Ali Akbar Velayati Parissa Farnia Mohadese Mozafari Donya Malekshahian Shima Seif Snaz Rahideh Mehdi Mirsaeidi 《PloS one》2014,9(12)
Introduction
While NTM infection is mainly acquired from environmental exposure, monitoring of environmental niches for NTM is not a routine practice. This study aimed to find the prevalence of environmental NTM in soil and water in four highly populated suburbs of Tehran, Iran.Material and Methods
A total of 4014 samples from soil and water resources were collected and studied. Sediments of each treated sample were cultured in Lowenstein-Jensen medium and observed twice per week for growth rate, colony morphology, and pigmentation. Colonies were studied with phenotypic tests. Molecular analysis was performed on single colonies derived from subculture of original isolates. Environmental samples were compared with 34 NTM isolates from patients who were residents of the study locations.Results
Out of 4014 samples, mycobacteria were isolated from 862 (21.4%) specimens; 536 (62.1%) belonged to slow growing mycobacteria (SGM) and 326 (37.8%) were rapid growing mycobacteria (RGM). The five most frequent NTM were M. farcinogens (105/862; 12.1%), M. fortuitum (72/862; 8.3%), M. senegalense (58/862; 6.7%), M. kansasii (54/862; 6.2%), and M. simiae (46/862; 5.3%). In total, 62.5% (539/862) of mycobacterial positive samples were isolated from water and only 37.4% (323/862) of them were isolated from soil samples (P<0.05). Out of 5314 positive clinical samples for mycobacteria, 175 (3.2%) isolates were NTM. The trend of NTM isolates increased from 1.2% (13 out of 1078) in 2004 to 3.8% (39 out of 1005) in 2014 (P = 0.0001). The major clinical isolates were M. simiae (51; 29.1%), M. kansasii (26; 14.8%), M. chelonae (28; 16%), and M. fortuitum (13; 7.4%).Conclusions
Comparing the distribution pattern of environmental NTM isolates with clinical isolates suggests a possible transmission link, but this does not apply to all environmental NTM species. Our study confirms an increasing trend of NTM isolation from clinical samples that needs further investigation. 相似文献697.
Shadab Anwar Manas Ranjan Dikhit Krishn Pratap Singh Rajiv Kumar Kar Amir Zaidi Ganesh Chandra Sahoo Awadh Kishore Roy Tomoyoshi Nozaki Pradeep Das Vahab Ali 《PloS one》2014,9(10)
Iron-Sulfur (Fe-S) proteins are involved in many biological functions such as electron transport, photosynthesis, regulation of gene expression and enzymatic activities. Biosynthesis and transfer of Fe-S clusters depend on Fe-S clusters assembly processes such as ISC, SUF, NIF, and CIA systems. Unlike other eukaryotes which possess ISC and CIA systems, amitochondriate Entamoeba histolytica has retained NIF & CIA systems for Fe-S cluster assembly in the cytosol. In the present study, we have elucidated interaction between two proteins of E. histolytica CIA system, Cytosolic Fe-S cluster deficient 1 (Cfd1) protein and Nucleotide binding protein 35 (Nbp35). In-silico analysis showed that structural regions ranging from amino acid residues (P33-K35, G131-V135 and I147-E151) of Nbp35 and (G5-V6, M34-D39 and G46-A52) of Cfd1 are involved in the formation of protein-protein complex. Furthermore, Molecular dynamic (MD) simulations study suggested that hydrophobic forces surpass over hydrophilic forces between Nbp35 and Cfd1 and Van-der-Waal interaction plays crucial role in the formation of stable complex. Both proteins were separately cloned, expressed as recombinant fusion proteins in E. coli and purified to homogeneity by affinity column chromatography. Physical interaction between Nbp35 and Cfd1 proteins was confirmed in vitro by co-purification of recombinant Nbp35 with thrombin digested Cfd1 and in vivo by pull down assay and immunoprecipitation. The insilico, in vitro as well as in vivo results prove a stable interaction between these two proteins, supporting the possibility of its involvement in Fe-S cluster transfer to target apo-proteins through CIA machinery in E. histolytica. Our study indicates that initial synthesis of a Fe-S precursor in mitochondria is not necessary for the formation of Cfd1-Nbp35 complex. Thus, Cfd1 and Nbp35 with the help of cytosolic NifS and NifU proteins can participate in the maturation of non-mitosomal Fe-S proteins without any apparent assistance of mitosomes. 相似文献
698.
Moiez Ali Tatiana A. Chernova Gary P. Newnam Luming Yin John Shanks Tatiana S. Karpova Andrew Lee Oskar Laur Sindhu Subramanian Dami Kim James G. McNally Nicholas T. Seyfried Yury O. Chernoff Keith D. Wilkinson 《The Journal of biological chemistry》2014,289(40):27625-27639
Yeast prions are self-propagating amyloid-like aggregates of Q/N-rich protein that confer heritable traits and provide a model of mammalian amyloidoses. [PSI+] is a prion isoform of the translation termination factor Sup35. Propagation of [PSI+] during cell division under normal conditions and during the recovery from damaging environmental stress depends on cellular chaperones and is influenced by ubiquitin proteolysis and the actin cytoskeleton. The paralogous yeast proteins Lsb1 and Lsb2 bind the actin assembly protein Las17 (a yeast homolog of human Wiskott-Aldrich syndrome protein) and participate in the endocytic pathway. Lsb2 was shown to modulate maintenance of [PSI+] during and after heat shock. Here, we demonstrate that Lsb1 also regulates maintenance of the Sup35 prion during and after heat shock. These data point to the involvement of Lsb proteins in the partitioning of protein aggregates in stressed cells. Lsb1 abundance and cycling between actin patches, endoplasmic reticulum, and cytosol is regulated by the Guided Entry of Tail-anchored proteins pathway and Rsp5-dependent ubiquitination. Heat shock-induced proteolytic processing of Lsb1 is crucial for prion maintenance during stress. Our findings identify Lsb1 as another component of a tightly regulated pathway controlling protein aggregation in changing environments. 相似文献
699.
Faris Q. Alenzi Badi Q. Alenazi Fatma H. AL-anazy Abdulla M. Mubaraki Mohamed L. Salem Ali A. Al-Jabri Mahmoud Lotfy Mohammad S. Bamaga Mohammed W. AlRabia Richard K.H. Wyse 《Saudi Journal of Biological Sciences》2010,17(1):29-36
Caspases are key intracellular molecules in the control of apoptosis, but little is known concerning their relative contribution to the cascade of events leading to eosinophil apoptosis. We examined caspase-3, -8, and -9 activities in receptor ligation dependent apoptosis induction in the cultured eosinophils (CE). CE cultured alone for 48 hours exhibited constitutive apoptosis (12% ± 1.2). Significant (P < 0.05) enhancement of eosinophil apoptosis was observed following monoclonal antibody (Mab) treatment with CD45 (40% ± 0.7), CD95 (36% ± 1.6), or CD69 (34% ± 0.2). Caspase activity was analysed using the novel CaspaTagTM technique and flow cytometry. CE ligated with CD45 (Bra55), CD95 (Fas) and CD69 Mab resulted in caspase-3 and -9 activation after 16 hours post-ligation. This trend in caspase-3 and -9 activation continued to increase significantly through to the 20 and 24 hours time points when compared to isotype control. Activated up-stream caspase-8 was detected 16 and 20 hours after treatment with CD45, CD95 and CD69 Mab followed by a trend toward basal levels at 24 hours. Ligation of CD95 was followed by mitochondrial permeabilization, as demonstrated by marked increase in mitochondrial transmembrane potential (ΔΨm) at all time points. However, ligation with CD45 and CD69 failed to induce a change in ΔΨm at 16 hours post-treatment compared to isotype control even though there was an alteration in mitochondrial downstream-caspase activity following ligation with these Mab(s) at this time point. At 20 and 24 hours post-ligation, CD45 or CD69 induce significantly altered levels of ΔΨm. Thus, the intrinsic and extrinsic caspase pathways are involved in controlling receptor ligation-mediated apoptosis induction in human eosinophils, findings that may aid the development of a more targeted, anti inflammatory therapy for asthma. 相似文献
700.
Yeong C Kim Yong-Chul Jung Jun Chen Ali H Alhasan Parawee Kaewsaard Yanming Zhang Shuo Ma Steve Rosen San Ming Wang 《BMC research notes》2010,3(1):341