首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1082篇
  免费   60篇
  国内免费   4篇
  1146篇
  2023年   7篇
  2022年   23篇
  2021年   30篇
  2020年   13篇
  2019年   20篇
  2018年   34篇
  2017年   35篇
  2016年   57篇
  2015年   60篇
  2014年   75篇
  2013年   105篇
  2012年   109篇
  2011年   94篇
  2010年   56篇
  2009年   42篇
  2008年   71篇
  2007年   67篇
  2006年   38篇
  2005年   45篇
  2004年   44篇
  2003年   37篇
  2002年   26篇
  2001年   5篇
  2000年   8篇
  1999年   6篇
  1998年   6篇
  1997年   3篇
  1996年   4篇
  1995年   5篇
  1994年   1篇
  1993年   1篇
  1992年   3篇
  1991年   2篇
  1990年   1篇
  1989年   2篇
  1988年   1篇
  1987年   1篇
  1986年   1篇
  1984年   3篇
  1983年   1篇
  1981年   1篇
  1980年   1篇
  1978年   1篇
  1976年   1篇
排序方式: 共有1146条查询结果,搜索用时 0 毫秒
1.
Identification of different protein functions facilitates a mechanistic understanding of Japanese encephalitis virus (JEV) infection and opens novel means for drug development. Support vector machines (SVM), useful for predicting the functional class of distantly related proteins, is employed to ascribe a possible functional class to Japanese encephalitis virus protein. Our study from SVMProt and available JE virus sequences suggests that structural and nonstructural proteins of JEV genome possibly belong to diverse protein functions, are expected to occur in the life cycle of JE virus. Protein functions common to both structural and non-structural proteins are iron-binding, metal-binding, lipid-binding, copper-binding, transmembrane, outer membrane, channels/Pores - Pore-forming toxins (proteins and peptides) group of proteins. Non-structural proteins perform functions like actin binding, zinc-binding, calcium-binding, hydrolases, Carbon-Oxygen Lyases, P-type ATPase, proteins belonging to major facilitator family (MFS), secreting main terminal branch (MTB) family, phosphotransfer-driven group translocators and ATP-binding cassette (ABC) family group of proteins. Whereas structural proteins besides belonging to same structural group of proteins (capsid, structural, envelope), they also perform functions like nuclear receptor, antibiotic resistance, RNA-binding, DNA-binding, magnesium-binding, isomerase (intra-molecular), oxidoreductase and participate in type II (general) secretory pathway (IISP).  相似文献   
2.
Superoxide dismutase, which has been shown to be present in a number of tissues, exhibits cyclic changes during the reproductive cycle of rats. An inverse correlation is seen between the levels of superoxide dismutase and superoxide radical. In immature, pseudopregnant rats, primed with human Chorionic Gonadotropin, lutropin seemed to induce ovarian superoxide dismutase, which could be blocked significantly by the introduction of anti-LH serum. These results point out the specific induction of superoxide dismutase by lutropin. It is reasonable to postulate that during luteal functioning, luteinizing hormone induces superoxide dismutase which in turn seems to play a central role generating hydrogen peroxide from superoxide anion radicals. Hydrogen peroxide, thus formed, drives the peroxidase-ascorbate system, responsible for production of progesterone.  相似文献   
3.
Using the overlapping deficiencies Df(3R)GC14 and Df(3R)e Gp 4 of the 93D region of Drosophila melanogaster, the benzamide (BM)-inducible site in polytene chromsomes was localised to the 93D6-7 region, which had earlier been identified as heat inducible. The normal developmental and BM-induced 93D6-7 puff was found to be dosage compensated since in larvae heterozygotus for a deficiency, with one dose of 93D6-7, the rate of 3H-uridine incorporation in this puff was the same as in the wild type with two doses. Curiously, however, heat shock (37° C) caused regression of the 93D6-7 puff on the normal chromosome in heterozygotes. In agreement with earlier results from our laboratory, the non-inducibility of the single-dose 93D locus by heat shock in the heterozygotes, caused the 87C puff to be nearly half as active as the 87A puff at 37° C. However, in e Gp 4/GC14 larvae, lacking the 93D6-7 locus on both homologues, the 87C puff was less active than 87A in some heat-shocked larvae but in other larvae 87A and 87C were equally active. Possible reasons for this inter-larval variability are discussed.  相似文献   
4.
In recent years, drug manufacturers and researchers have begun to consider the nanobiotechnology approach to improve the drug delivery system for tumour and cancer diseases. In this article, we review current strategies to improve tumour and cancer drug delivery, which mainly focuses on sustaining biocompatibility, biodistribution, and active targeting. The conventional therapy using cornerstone drugs such as fludarabine, cisplatin etoposide, and paclitaxel has its own challenges especially not being able to discriminate between tumour versus normal cells which eventually led to toxicity and side effects in the patients. In contrast to the conventional approach, nanoparticle-based drug delivery provides target-specific delivery and controlled release of the drug, which provides a better therapeutic window for treatment options by focusing on the eradication of diseased cells via active targeting and sparing normal cells via passive targeting. Additionally, treatment of tumours associated with the brain is hampered by the impermeability of the blood–brain barriers to the drugs, which eventually led to poor survival in the patients. Nanoparticle-based therapy offers superior delivery of drugs to the target by breaching the blood–brain barriers. Herein, we provide an overview of the properties of nanoparticles that are crucial for nanotechnology applications. We address the potential future applications of nanobiotechnology targeting specific or desired areas. In particular, the use of nanomaterials, biostructures, and drug delivery methods for the targeted treatment of tumours and cancer are explored.  相似文献   
5.
6.
The infertility associated with oligospermia had been suspected to be a direct consequence of the impairment in fertilizing ability of the spermatozoa rather than the presence of low sperm number per se. This study defines some of these impairments, which include an over expression of superoxide dismutase, poor superoxide anion radical generation capacity and a lack of sperm-surface thiols in oligospermia. The abnormal biochemical make-up of spermatozoa could explain their low fertilizing ability in case of oligospermia.  相似文献   
7.
Summary The effect of selenium and phosphorus application on Berseem (Trifolium alexandrium) was studied in the green house. Each dose of selenium from O to 16 ppm decreased the dry matter yield of Berseem significantly at all the levels of applied phosphorus. Phosphorus stimulated the dry matter yield at all levels of selenium. Yields in the second cutting were of a higher order than in the first cut. Selenium application increased selenium and phosphorus content in Berseem, but at 8 and 16 ppm of selenium the phosphorus content decreased significantly. Sulphur concentration decreased with selenium application but application of phosphorus increased sulphur concentration showing synergetic effect.Studies on residual effect of selenium revealed that the application of 50 ppm of phosphorus increased the yield while that of 100 ppm decreased it. Selenium concentration which increased with increasing phosphorus was many fold higher in the first cutting than in the second cutting and similar was the trend with phosphorus and sulphur.  相似文献   
8.
BackgroundThe prevalence of Strongyloides stercoralis infection is estimated to be 30–100 million worldwide, although this an underestimate. Most cases remain undiagnosed due to the asymptomatic nature of the infection. We wanted to estimate the seroprevalence of S. stercoralis infection in a South Indian adult population.MethodsTo this end, we performed community-based screening of 2351 individuals (aged 18–65) in Kanchipuram District of Tamil Nadu between 2013 and 2020. Serological testing for S. stercoralis was performed using the NIE ELISA.ResultsOur data shows a seroprevalence of 33% (768/2351) for S. stercoralis infection which had a higher prevalence among males 36% (386/1069) than among females 29.8% (382/1282). Adults aged ≥55 (aOR = 1.65, 95% CI: 1.25–2.18) showed higher adjusted odds of association compared with other age groups. Eosinophil levels (39%) (aOR = 1.43, 95% CI: 1.19–1.74) and hemoglobin levels (24%) (aOR = 1.25, 95% CI: 1.11–1.53) were significantly associated with S. stercoralis infection. In contrast, low BMI (aOR = 1.15, 95% CI: 0.82–1.61) or the presence of diabetes mellitus (OR = 1.18, 95% CI: 0.83–1.69) was not associated with S. stercoralis seropositivity.ConclusionsOur study provides evidence for a very high baseline prevalence of S. stercoralis infection in South Indian communities and this information could provide realistic and concrete planning of control measures.  相似文献   
9.
The polypeptides of etioplast and chloroplast fractions, purified on Percoll discontinuous gradient, were phosphorylated in vitro using (γ-32P)ATP, resolved by SDS-PAGE and autoradiographed. In general, about 15-18 phosphopolypeptides in the range of 14-150 kD were distinctly visible in autoradiograms of both organelle fractions with varying degree of radiolabel incorporation. Although short-term irradiation with red or far-red light did not have any significant effect on phosphorylation status of etioplast polypeptides, in vivo irradiation with 1 h white light, followed by in vitro phosphorylation, decreased phosphorylation of a 116 kD polypeptide and increased the phosphorylation of polypeptides of 38 kD and a doublet around 20 kD. Strikingly, the phosphorylation status of 116 kD etioplast polypeptide was adversely affected by Ca2+ as well, and this phosphopolypeptlde was not distinctly visible in the autoradiogram of the chloroplast fraction proteins. However, in vitro phosphorylation of 98, 57 and 50 kD polypeptides of both etioplast and chloroplast fractions was found to be Ca2+ dependent. Unlike Ca2+, 3′,5′-cyclic AMP down-regulated the phosphorylation of several polypeptides of both etioplasts and chloroplasts, including 98 and 50 kD, and up-regulated the phosphorylation of 32 and 57 kD polypeptides. The significance of these observations on changes in phosphoprotein profile of etioplasts and chloroplasts, as influenced by light, Ca2+ and cyclic nucleotides, has been discussed.  相似文献   
10.
Vitamin A deficiency remains one of the world's major public health problems despite food fortification and supplements strategies. Biofortification of staple crops with enhanced levels of pro‐vitamin A (PVA) offers a sustainable alternative strategy to both food fortification and supplementation. As a proof of concept, PVA‐biofortified transgenic Cavendish bananas were generated and field trialed in Australia with the aim of achieving a target level of 20 μg/g of dry weight (dw) β‐carotene equivalent (β‐CE) in the fruit. Expression of a Fe'i banana‐derived phytoene synthase 2a (MtPsy2a) gene resulted in the generation of lines with PVA levels exceeding the target level with one line reaching 55 μg/g dw β‐CE . Expression of the maize phytoene synthase 1 (ZmPsy1) gene, used to develop ‘Golden Rice 2’, also resulted in increased fruit PVA levels although many lines displayed undesirable phenotypes. Constitutive expression of either transgene with the maize polyubiquitin promoter increased PVA accumulation from the earliest stage of fruit development. In contrast, PVA accumulation was restricted to the late stages of fruit development when either the banana 1‐aminocyclopropane‐1‐carboxylate oxidase or the expansin 1 promoters were used to drive the same transgenes. Wild‐type plants with the longest fruit development time had also the highest fruit PVA concentrations. The results from this study suggest that early activation of the rate‐limiting enzyme in the carotenoid biosynthetic pathway and extended fruit maturation time are essential factors to achieve optimal PVA concentrations in banana fruit.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号