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   7458篇
  免费   488篇
  国内免费   6篇
  7952篇
  2024年   10篇
  2023年   23篇
  2022年   86篇
  2021年   126篇
  2020年   78篇
  2019年   114篇
  2018年   151篇
  2017年   137篇
  2016年   251篇
  2015年   426篇
  2014年   470篇
  2013年   518篇
  2012年   713篇
  2011年   636篇
  2010年   416篇
  2009年   386篇
  2008年   507篇
  2007年   423篇
  2006年   395篇
  2005年   360篇
  2004年   339篇
  2003年   292篇
  2002年   244篇
  2001年   154篇
  2000年   143篇
  1999年   130篇
  1998年   63篇
  1997年   51篇
  1996年   36篇
  1995年   28篇
  1994年   27篇
  1993年   21篇
  1992年   32篇
  1991年   26篇
  1990年   17篇
  1989年   13篇
  1988年   11篇
  1987年   6篇
  1986年   10篇
  1984年   7篇
  1982年   5篇
  1981年   4篇
  1980年   5篇
  1978年   5篇
  1977年   7篇
  1976年   4篇
  1974年   7篇
  1969年   4篇
  1967年   5篇
  1966年   6篇
排序方式: 共有7952条查询结果,搜索用时 15 毫秒
101.
Background and Aims: Lafutidine is a novel H2‐receptor antagonist with gastroprotective activity that includes enhancement of gastric mucosal blood flow. The aim of the present study was to test the efficacy of 7‐ or 14‐day lafutidine–clarithromycin–amoxicillin therapy versus a lansoprazole‐based regimen for Helicobacter pylori eradication. Methods: Four hundred and sixty‐three patients with H. pylori‐infected peptic ulcer disease were randomized to one of four regimens: (1) lafutidine (20 mg b.i.d.), clarithromycin (500 mg b.i.d.) and amoxicillin (1000 mg b.i.d.) for 7 days (the 7LFT group) or (2) for 14 days (the 14LFT group); (3) lansoprazole (30 mg b.i.d.), clarithromycin (500 mg b.i.d.), and amoxicillin (1000 mg b.i.d.) for 7 days (the 7LPZ group); or (4) for 14 days (the 14LPZ group). The eradication rates, drug compliance, and adverse effects among the four regimens were compared. Results: The eradication rates by the intention‐to‐treat and per‐protocol analyses in the 7LFT and 7LPZ groups were 76.5% and 81.6%, and 76.9% and 82.0% (p = .94 and .95), respectively. The eradication rates by intention‐to‐treat and per‐protocol analyses in the 14LFT and 14LPZ groups were 78.2% and 82.2%, and 80.4% and 85.9% (p = .70 and .49), respectively. The treatment duration for 7 days or 14 days did not affect the eradication rates. In addition, the adverse effect rates and discontinuation rates were similar among the four groups. Furthermore, the ulcer cure rate and symptom response rate were similar in the lafutidine and lansoprazole groups. Conclusion: The results of this study showed that lafutidine–clarithromycin–amoxicillin therapy was a safe and effective as lansoprazole‐based triple therapy for the eradication rate of H. pylori, and could be considered as an additional treatment option.  相似文献   
102.
Palsson BO  Oh DJ  Koller MR 《Cytotechnology》1995,18(1-2):125-131
The capability to expand human bone marrow mononuclear cells (BM MNC) in high density perfusion culture chambers (bioreactors) has recently been developed. In these bioreactors, total cell colony-forming unit-granulocyte/macrophage (CFU-GM), and long-term culture-initiating cell (LTC-IC) numbers increase significantly over a 14-day period. However, cell growth ceases after the 14-day period, possibly due to cell density limitations. Because of the remaining presence of early cells, it should be feasible to replate the cells and obtain continued expansion. In this study, we demonstrate that bioreactors generate cells, which upon replating into secondary bioreactors, lead to continued cell, CFU-GM, and LTC-IC8 (measured after 8 weeks of secondary culture) expansion. A two-stage protocol, involving the replating of cells on days 9 to 12 of culture into new bioreators at the original seeding density, yielded greater than 50-fold cell expansion from BM MNC in 25 days. CFU-GM were expanded inhibitory factor (LIF) had no significant effect on total cells, CFU-GM, or LTC-IC5 in this system. We conclude that two-stage bioreactor cultures are capable of supporting extended growth of human BM MNC, CFU-GM, and LTC-IC8. The continued expansion of these primitive cells in the second stage of culture suggests that primitive cells with significant proliferative potential were generated in this system, and previous data on LTC-IC5 expansion has now been extended to LTC-IC8 expansion. Further optimization of culture conditions is likely to improve on the results obtained here, thus making perfusion bioreactor culture correspondingly more attractive for expanding BM MNC for BM transplantation.  相似文献   
103.
The 15,389-bp long complete mitogenome of the endangered red-spotted apollo butterfly, Parnassius bremeri (Lepidoptera: Papilionidae) was determined in this study. The start codon for the COI gene in insects has been extensively discussed, and has long remained a matter of some controversy. Herein, we propose that the CGA (arginine) sequence functions as the start codon for the COI gene in lepidopteran insects, on the basis of complete mitogenome sequences of lepidopteran insects, including P. bremeri, as well as additional sequences of the COI start region from a diverse taxonomic range of lepidopteran species (a total of 53 species from 15 families). In our extensive search for a tRNA-like structure in the A+T-rich region, one tRNATrp-like sequence and one tRNALeu (UUR)-like sequence were detected in the P. bremeri A+T-rich region, and one or more tRNA-like structures were detected in the A+T-rich region of the majority of other sequenced lepidopteran insects, thereby indicating that such features occur frequently in the lepidopteran mitogenomes. Phylogenetic analysis using the concatenated 13 amino acid sequences and nucleotide sequences of PCGs of the four macrolepidopteran superfamilies together with the Tortricoidea and Pyraloidea resulted in the successful recovery of a monophyly of Papilionoidea and a monophyly of Bombycoidea. However, the Geometroidea were unexpectedly identified as a sister group of the Bombycoidea, rather than the Papilionoidea.  相似文献   
104.

Background

Cigarette smoking and obesity are leading public health concerns. Both increase the risk for cardiovascular disease, cancer, and metabolic abnormalities. This study was conducted to assess the association between cigarette smoking and different types of obesity.

Methodology/Principal Findings

Two hundred eighty-three visitors to university hospitals located in four main provinces of South Korea were participated. All participants were classified as either current/past or never smokers and were divided into quartiles according to the total pack-years. Body mass index, waist circumference, total body fat percentage, and area of visceral and abdominal subcutaneous fat were measured. These results of each groups were compared. Waist circumference, and visceral fat area showed a J- or U-shaped association with total smoking amount during a lifetime. After restricting the analyses to past/current smokers, we found significant dose-dependent associations of smoking pack-years with abdominal and visceral obesity. Overall obesity measured by body mass index and total body fat percentage did not show such associations. Although current smokers clearly showed significant associations, we could not demonstrate these in past smokers, possibly because of the limited sample size.

Conclusions/Significance

Although smokers did not show significant difference in mean body mass index than those who never smoked, they showed more metabolically adverse fat distributions with increasing smoking amounts. This finding suggests that smoking is not beneficial for weight control. Therefore, smoking cessation and avoidance of smoking commencement should be addressed as important public health issues in preventing obesity and related complications.  相似文献   
105.
106.
Previously, we developed a non-replicating recombinant baculovirus coated with human endogenous retrovirus envelope protein (AcHERV) for enhanced cellular delivery of human papillomavirus (HPV) 16L1 DNA. Here, we report the immunogenicity of an AcHERV-based multivalent HPV nanovaccine in which the L1 segments of HPV 16, 18, and 58 genes were inserted into a single baculovirus genome of AcHERV. To test whether gene expression levels were affected by the order of HPV L1 gene insertion, we compared the efficacy of bivalent AcHERV vaccines with the HPV 16L1 gene inserted ahead of the 18L1 gene (AcHERV-HP16/18L1) with that of AcHERV with the HPV 18L1 gene inserted ahead of the 16L1 gene (AcHERV-HP18/16L1). Regardless of the order, the bivalent AcHERV DNA vaccines retained the immunogenicity of monovalent AcHERV-HP16L1 and AcHERV-HP18L1 DNA vaccines. Moreover, the immunogenicity of bivalent AcHERV-HP16/18L1 was not significantly different from that of AcHERV-HP18/16L1. In challenge tests, both bivalent vaccines provided complete protection against HPV 16 and 18 pseudotype viruses. Extending these results, we found that a trivalent AcHERV nanovaccine encoding HPV 16L1, 18L1, and 58L1 genes (AcHERV-HP16/18/58L1) provided high levels of humoral and cellular immunogenicity against all three subtypes. Moreover, mice immunized with the trivalent AcHERV-based nanovaccine were protected from challenge with HPV 16, 18, and 58 pseudotype viruses. These results suggest that trivalent AcHERV-HPV16/18/58L1 could serve as a potential prophylactic baculoviral nanovaccine against concurrent infection with HPV 16, 18, and 58.  相似文献   
107.
Porolithon is one of the most ecologically important genera of tropical and subtropical crustose (non-geniculate) coralline algae growing abundantly along the shallow margins of coral reefs and functioning to cement reef frameworks. Thalli of branched, fruticose Porolithon specimens from the Indo-Pacific Ocean traditionally have been called P. gardineri, while massive, columnar forms have been called P. craspedium. Sequence comparisons of the rbcL gene both from type specimens of P. gardineri and P. craspedium and from field-collected specimens demonstrate that neither species is present in east Australia and instead resolve into four unique genetic lineages. Porolithon howensis sp. nov. forms columnar protuberances and loosely attached margins and occurs predominantly at Lord Howe Island; P. lobulatum sp. nov. has fruticose to clavate forms and free margins that are lobed and occurs in the Coral Sea and on the Great Barrier Reef (GBR); P. parvulum sp. nov. has short (<2 cm), unbranched protuberances and attached margins and is restricted to the central and southern GBR; and P. pinnaculum sp. nov. has a mountain-like, columnar morphology and occurs on oceanic Coral Sea reefs. A rbcL gene sequence of the isotype of P. castellum demonstrates it is a different species from other columnar species. In addition to the diagnostic rbcL and psbA marker sequences, the four new species may be distinguished by a combination of features including thallus growth form, margin shape (attached or unattached), and medullary system (coaxial or plumose). Porolithon species, because of their ecological importance and sensitivity to ocean acidification, need urgent documentation of their taxonomic diversity.  相似文献   
108.
A metagenomic fosmid library was constructed using genomic DNA isolated from abalone intestine. Screening of a library of 3,840 clones revealed a 36 kb insert of a cellulase positive clone (pAMHElO). A shotgun clone library was constructed using the positive clone (pAMHElO) and further screening of 3,840 shotgun clones with an approximately 5 kb insert size using a Congo red overlay revealed only one cellulase positive clone (pAMHL9). The pAMHL9 consisted of a 5,293-bp DNA sequence and three open reading frames (ORFs). Among the three ORFs, cellulase activity was only shown in the recombinant protein (CelAMll) coded by ORF3, which showed 100% identity with outer membrane protein A from Vibrio alginolyticus 12G01, but no significant sequence homology to known cellulases. The expressed protein (CelAMll) has a molecular weight of approximately 37 kDa and the highest CMC hydrolysis activity was observed at pH 7.0 and 37°C. The carboxymethyl cellulase activity was determined by zymogram active staining and different degraded product profiles for CelAMll were obtained when cellotetraose and cellopentaose were used as the substrates, while no substrate hydrolysis was observed on oligosaccharides such as cellobiose and cellotriose.  相似文献   
109.
Although D-glucosamine has been reported as an inhibitor of tumor growth both in vivo and in vitro, the mechanism for the anticancer effect of D-glucosamine is still unclear. Since there are several reports suggesting D-glucosamine inhibits protein synthesis, we examined whether D-glucosamine affects p70S6K activity, an important signaling molecule involved in protein translation. In the present study, we found D-glucosamine inhibited the activity of p70S6K and the proliferation of DU145 prostate cancer cells and MDA-MB-231 breast cancer cells. D-glucosamine decreased phosphorylation of p70S6K, and its downstream substrates RPS6, and eIF-4B, but not mTOR and 4EBP1 in DU145 cells, suggesting that D-glucosamine induced inhibition of p70S6K is not through the inhibition of mTOR. In addition, D-glucosamine enhanced the growth inhibitory effects of rapamycin, a specific inhibitor of mTOR. These findings suggest that D-glucosamine can inhibit growth of cancer cells through dephosphorylation of p70S6K.  相似文献   
110.
Factors indicating culture status of two Spirulina platensis strains were monitored in a batch mode cultivation for 36 days. Changing mode in all factors showed a common turning point, indicating shift of cell or culture status. Mean biomass productivity was highly sustained until day 22, chlorophyll a concentration peaked on day 22, pH value was >12 on day 22, coil number was abruptly shortened on day 22, and floating activity was sustained at greater than 79% after day 22, indicating that day 22 is a criterion reflecting phase-transfer in cell physiology in a batch culture system. Many of these changes may have been caused by increased pH, suggesting that pH control is essential for mass production of S. platensis. Fluctuations in floating activity were likely induced by the number of cellular gas vacuoles. Consequently, coil number per trichome and floating activity of S. platensis could readily act as simple indicators for determination of culture status or harvesting time of cells.  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