全文获取类型
收费全文 | 7894篇 |
免费 | 544篇 |
国内免费 | 2篇 |
专业分类
8440篇 |
出版年
2023年 | 44篇 |
2022年 | 95篇 |
2021年 | 166篇 |
2020年 | 93篇 |
2019年 | 131篇 |
2018年 | 160篇 |
2017年 | 142篇 |
2016年 | 250篇 |
2015年 | 377篇 |
2014年 | 418篇 |
2013年 | 542篇 |
2012年 | 612篇 |
2011年 | 598篇 |
2010年 | 421篇 |
2009年 | 324篇 |
2008年 | 460篇 |
2007年 | 460篇 |
2006年 | 478篇 |
2005年 | 409篇 |
2004年 | 413篇 |
2003年 | 360篇 |
2002年 | 342篇 |
2001年 | 78篇 |
2000年 | 55篇 |
1999年 | 75篇 |
1998年 | 77篇 |
1997年 | 86篇 |
1996年 | 63篇 |
1995年 | 42篇 |
1994年 | 50篇 |
1993年 | 44篇 |
1992年 | 36篇 |
1991年 | 43篇 |
1990年 | 30篇 |
1989年 | 36篇 |
1988年 | 30篇 |
1987年 | 22篇 |
1986年 | 27篇 |
1985年 | 32篇 |
1984年 | 30篇 |
1983年 | 24篇 |
1982年 | 36篇 |
1981年 | 32篇 |
1980年 | 25篇 |
1979年 | 18篇 |
1978年 | 14篇 |
1977年 | 17篇 |
1976年 | 14篇 |
1975年 | 13篇 |
1973年 | 21篇 |
排序方式: 共有8440条查询结果,搜索用时 0 毫秒
101.
Puneetpal?SinghEmail author Monica?Singh Harinder?Singh?Nagpal Taranpal?Kaur Shallu?Khullar Gurpreet?Kaur Harjot?Dhillon Mario?Di?Napoli Sarabjit?MastanaEmail author 《Molecular biology reports》2014,41(9):5851-5862
According to several epidemiological and clinical studies, the concentration of C-reactive protein (CRP) in blood is associated with the risk of coronary heart disease (CHD). However, these studies are limited in high incidence and prevalence area of North-West India. The present case control study investigated the contribution of three relevant CRP single nucleotide polymorphisms: ?717A>G located in the promoter region (rs2794521), +1059G>C on exon2 (rs1800947) and +1444C>T in the 3′ UTR (rs1130864) in 180 angiographically verified CHD cases and 175 control subjects. Minor allele frequencies (G, C and T) of rs2794521, rs1800947 and rs1130864 are observed to be 21.1, 11.7, 29.4 and 11.4, 10.0, 19.7 % in CHD cases and controls respectively. AA genotype of ?717A>G and TT genotype of +1444C>T were significantly associated (P = 0.02 & 0.03 respectively) with the risk of CHD whereas, +1059G and +1444T were found to be strongly related (P = 0.023 & P = 0.008 respectively) with multivariable adjusted CRP levels. AGT Haplotype was significantly associated with the adjusted CRP levels (P < 0.05). Disease association analysis revealed that haplotype AGT influences CHD risk (OR 2.4, 95 % CI 1.23–4.84, P = 0.006) which exacerbates after correcting the confounding effects of risk variables (OR 2.5, 95 % CI 1.27–4.99, P = 0.004). With the global index of Akaike information criterion, it has been observed that the carrying each single unit of this susceptibility haplotype increases CHD risk by a value of 2.41 ± 0.439 (β ± SE) in the recessive mode. 相似文献
102.
103.
104.
Anna Zanfardino Odile F Restaino Eugenio Notomista Donatella Cimini Chiara Schiraldi Mario De Rosa Maurilio De Felice Mario Varcamonti 《Microbial cell factories》2010,9(1):34
Background
Chondroitin sulphate is a complex polysaccharide having important structural and protective functions in animal tissues. Extracted from animals, this compound is used as a human anti-inflammatory drug. Among bacteria, Escherichia coli K4 produces a capsule containing a non-sulphate chondroitin and its development may provide an efficient and cheap fermentative production of the polysaccharide. 相似文献105.
The aim of this paper was to examine finger and bow string movements during archery by investigating a top Austrian athlete (FITA score = 1233) under laboratory conditions. Maximum lateral bow string deflection and angular displacements for index, third, and ring fingers between the full draw position and the end of the release were quantified using a motion tracking system. Stepwise multiple regression analyses were used to determine whether bow string deflection and finger movements are predictive for scoring. Joint ranges of motion during the shot itself were large in the proximal and distal interphalangeal joints, and much smaller in the metacarpophalangeal joints. Contrary to our expectations, greater deflection leads to higher scores (R2 = .18, p < .001) and the distal interphalangeal joint of the third finger weakly predicts the deflection (R2 = .11, p < .014). More variability in the joint angles of the third finger was found in bad shots than in good shots. Findings in this study let presume that maximum lateral bow string deflection does not adversely affect the archer's performance. 相似文献
106.
The crystal structure of the major component of the Vipera ammodytes ammodytes venomic, a flavotoxin, member of the l-amino acid oxidase (LAAO) family, has been determined and refined at 2.6 ? resolution. The asymmetric unit consists of four molecules, each bound to oxidized FAD, representing a dimer of dimers. The binding of four Zn(2+) ions stabilizes the enzymatically active quaternary structure and is considered important for the biological activity of LAAO and other flavoproteins. Each monomer consists of three domains with a cofactor bound between the FAD and substrate binding domains, and a solvent exposed glycosylation site which is considered crucial for the toxicity. Comparison of LAAO structures in the absence and presence of a substrate indicates conformational changes in the dynamic active site. The active site H-bond network involving the triad Lys326-Water-N5 of FAD is formed only upon substrate binding, and results in the increased mobility of the isoalloxazine system. Details of the catalytic transformation of amino acid substrates are discussed. 相似文献
107.
This article presents an immune inspired algorithm to tackle the Multiple Sequence Alignment (MSA) problem. MSA is one of the most important tasks in biological sequence analysis. Although this paper focuses on protein alignments, most of the discussion and methodology may also be applied to DNA alignments. The problem of finding the multiple alignment was investigated in the study by Bonizzoni and Vedova and Wang and Jiang, and proved to be a NP-hard (non-deterministic polynomial-time hard) problem. The presented algorithm, called Immunological Multiple Sequence Alignment Algorithm (IMSA), incorporates two new strategies to create the initial population and specific ad hoc mutation operators. It is based on the 'weighted sum of pairs' as objective function, to evaluate a given candidate alignment. IMSA was tested using both classical benchmarks of BAliBASE (versions 1.0, 2.0 and 3.0), and experimental results indicate that it is comparable with state-of-the-art multiple alignment algorithms, in terms of quality of alignments, weighted Sums-of-Pairs (SP) and Column Score (CS) values. The main novelty of IMSA is its ability to generate more than a single suboptimal alignment, for every MSA instance; this behaviour is due to the stochastic nature of the algorithm and of the populations evolved during the convergence process. This feature will help the decision maker to assess and select a biologically relevant multiple sequence alignment. Finally, the designed algorithm can be used as a local search procedure to properly explore promising alignments of the search space. 相似文献
108.
Evaluation of the inhibitory effects of human serum components on bactericidal activity of human beta defensin 3 总被引:2,自引:1,他引:2
Maisetta G Di Luca M Esin S Florio W Brancatisano FL Bottai D Campa M Batoni G 《Peptides》2008,29(1):1-6
Naturally occurring cationic antimicrobial peptides (CAPs) are an essential component of the innate immune system of multicellular organisms. At concentrations generally higher than those found in vivo, most CAPs exhibit strong antibacterial properties in vitro, but their activity may be inhibited by body fluids, a fact that could limit their future use as antimicrobial and/or immunomodulatory agents. In the present study, we evaluated the effects of human serum components on bactericidal activity of the human beta-defensin 3 (hBD-3), a CAP considered particularly promising for future therapeutic employment. Human serum diluted to 20% strongly inhibited the bactericidal activity of the peptide against both the Gram-positive species Staphylococcus aureus and the Gram-negative species Acinetobacter baumannii. Such activity was not restored in serum devoid of salts (dialyzed), pre-treated with protease inhibitors, or subjected to both of these treatments. The addition of physiological concentrations of NaCl, CaCl2, and human albumin in the bactericidal assay abolished bactericidal activity of hBD-3 against S. aureus, while it only partially inhibited the activity of the peptide against A. baumannii. Although a proteolytic activity of serum on hBD-3 was demonstrated at the protein level by Western blot, addition of physiological concentrations of trypsin to the bactericidal assay only partially affected the antibacterial properties of the peptide. Altogether, these results demonstrate a major role of mono-divalent cations and serum proteins on inhibition of hBD-3 antibacterial properties and indicate a relative lack in sensitivity of the bactericidal activity of this peptide to trypsin and trypsin-like proteases. 相似文献
109.
ATP25, a new nuclear gene of Saccharomyces cerevisiae required for expression and assembly of the Atp9p subunit of mitochondrial ATPase 总被引:1,自引:0,他引:1 下载免费PDF全文
We report a new nuclear gene, designated ATP25 (reading frame YMR098C on chromosome XIII), required for expression of Atp9p (subunit 9) of the Saccharomyces cerevisiae mitochondrial proton translocating ATPase. Mutations in ATP25 elicit a deficit of ATP9 mRNA and of its translation product, thereby preventing assembly of functional F(0). Unlike Atp9p, the other mitochondrial gene products, including ATPase subunits Atp6p and Atp8p, are synthesized normally in atp25 mutants. Northern analysis of mitochondrial RNAs in an atp25 temperature-sensitive mutant confirmed that Atp25p is required for stability of the ATP9 mRNA. Atp25p is a mitochondrial inner membrane protein with a predicted mass of 70 kDa. The primary translation product of ATP25 is cleaved in vivo after residue 292 to yield a 35-kDa C-terminal polypeptide. The C-terminal half of Atp25p is sufficient to stabilize the ATP9 mRNA and restore synthesis of Atp9p. Growth on respiratory substrates, however, depends on both halves of Atp25p, indicating that the N-terminal half has another function, which we propose to be oligomerization of Atp9p into a proper size ring structure. 相似文献
110.
Improvement of drought tolerance and grain yield in common bean by overexpressing trehalose-6-phosphate synthase in rhizobia 总被引:2,自引:0,他引:2
Suárez R Wong A Ramírez M Barraza A Orozco Mdel C Cevallos MA Lara M Hernández G Iturriaga G 《Molecular plant-microbe interactions : MPMI》2008,21(7):958-966
Improving stress tolerance and yield in crops are major goals for agriculture. Here, we show a new strategy to increase drought tolerance and yield in legumes by overexpressing trehalose-6-phosphate synthase in the symbiotic bacterium Rhizobium etli. Phaseolus vulgaris (common beans) plants inoculated with R. etli overexpressing trehalose-6-phosphate synthase gene had more nodules with increased nitrogenase activity and higher biomass compared with plants inoculated with wild-type R. etli. In contrast, plants inoculated with an R. etli mutant in trehalose-6-phosphate synthase gene had fewer nodules and less nitrogenase activity and biomass. Three-week-old plants subjected to drought stress fully recovered whereas plants inoculated with a wild-type or mutant strain wilted and died. The yield of bean plants inoculated with R. etli overexpressing trehalose-6-phosphate synthase gene and grown with constant irrigation increased more than 50%. Macroarray analysis of 7,200 expressed sequence tags from nodules of plants inoculated with the strain overexpressing trehalose-6-phosphate synthase gene revealed upregulation of genes involved in stress tolerance and carbon and nitrogen metabolism, suggesting a signaling mechanism for trehalose. Thus, trehalose metabolism in rhizobia is key for signaling plant growth, yield, and adaptation to abiotic stress, and its manipulation has a major agronomical impact on leguminous plants. 相似文献