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   2317篇
  免费   108篇
  国内免费   4篇
  2429篇
  2023年   21篇
  2022年   35篇
  2021年   71篇
  2020年   46篇
  2019年   51篇
  2018年   86篇
  2017年   58篇
  2016年   69篇
  2015年   101篇
  2014年   128篇
  2013年   178篇
  2012年   176篇
  2011年   158篇
  2010年   104篇
  2009年   101篇
  2008年   99篇
  2007年   87篇
  2006年   87篇
  2005年   70篇
  2004年   62篇
  2003年   57篇
  2002年   62篇
  2001年   49篇
  2000年   43篇
  1999年   36篇
  1998年   12篇
  1997年   7篇
  1996年   16篇
  1995年   9篇
  1994年   12篇
  1993年   6篇
  1992年   21篇
  1991年   22篇
  1990年   16篇
  1989年   27篇
  1988年   24篇
  1987年   23篇
  1986年   17篇
  1985年   18篇
  1984年   21篇
  1983年   8篇
  1982年   15篇
  1981年   8篇
  1980年   10篇
  1979年   19篇
  1978年   12篇
  1977年   13篇
  1976年   9篇
  1975年   7篇
  1970年   5篇
排序方式: 共有2429条查询结果,搜索用时 0 毫秒
51.
52.
High levels of antibodies to mucin 1 (MUC1), a membrane-bound glycoprotein that is overexpressed in adenocarcinomas, are associated with good prognosis in patients with breast cancer. The aim of the present investigation was to determine whether GM and KM allotypes—genetic markers of IgG heavy chains and κ-type light chains, respectively—contribute to the magnitude of natural antibody responsiveness to MUC1 in patients with breast cancer. A total of 153 Caucasian subjects with breast cancer were allotyped for several GM and KM markers. These subjects were also characterized for IgG and IgM antibodies to MUC1. Anti-MUC1 IgG antibody levels in subjects who were carriers of the immunoglobulin γ2 allele GM 23 were significantly higher than in those who were noncarriers (P = 0.003). These results could potentially divide the population into high or low responders to MUC1, which has important implications for MUC1-based immunotherapeutic interventions in breast cancer.  相似文献   
53.
54.
Cervical cancer is the second most common cause of cancer-related death among women worldwide, especially in developing countries. Oxidative stress has been associated with cervical cancer. Many studies demonstrated that the low level of antioxidants induces the production of free radicals that cause lipid peroxidation, DNA, and protein damage leading to mutations that favors malignant transformation. This is a case-control institutional study conducted to evaluate the level of oxidative stress in cervical cancer patients and the age-matched healthy controls. We measured level of TBARS expressed as MDA, activity of SOD and GSH level by the spectrophotometric method, and level of 8-OHdG was estimated using a competitive sandwich ELISA assay. Our results showed a significant increase in the level of lipid peroxidation in group IV when compared to the control, group II and group III (p < 0.001). The activity of SOD was also significantly higher in group IV when compared to the control group (p < 0.001), group II (p < 0.001), and group III (p < 0.001). The level of GSH was also significantly lower in group IV when compared to the control group (p < 0.01), group II (p < 0.01), and group III (p < 0.01). The level of 8-OHdG was significantly higher in group IV than in the other groups (p < 0.01). The results suggest that oxidative stress is involved in the pathogenesis of cervical cancer, which is demonstrated by an increased level of lipid peroxidation and higher levels of 8-OHdG and an altered antioxidant defense system.  相似文献   
55.

Background

Light-emitting diode fluorescence microscopy (LED-FM) has been shown to be more sensitive than conventional bright field microscopy using Ziehl-Neelsen (ZN) stain in detecting sputum smear positive tuberculosis in controlled laboratory conditions. In 2012, Auramine O staining based LED-FM replaced conventional ZN microscopy in 200 designated microscopy centres (DMC) of medical colleges operating in collaboration with India’s Revised National Tuberculosis Control Programme. We aimed to assess the impact of introduction of LED-FM services on sputum smear positive case detection under program conditions.

Methods

This was a before and after comparison study. In 15 randomly selected medical college DMCs, all presumptive TB patients who underwent sputum smear examination in the years 2011 (before LED-FM) and 2012 (after LED-FM) were compared. An additional 15 comparable DMCs that implemented conventional ZN sputum smear microscopy were also selected for comparison between 2011 and 2012.

Results

The proportion of presumptive TB patients (PTP)found sputum smear positive increased by 30%- from 13.6% (3432/25159) in 2011 to 17.8% (4706/26426) in 2012 (P value <0.01) in the sites that implemented LED-FM microscopy, whereas in DMCs where the ZN staining procedure is followed the proportion of sputum smear positive had remained unchanged (13.0%versus 12.6%;P value0.31).

Conclusion

Use of LED-FM significantly increased the proportion of smear positive cases among presumptive TB patients under routine program conditions in high workload laboratories. The study provides operational evidence needed to scale-up the use of LED-FM in similar settings in India and beyond.  相似文献   
56.
Human sexual determination is initiated by a cascade of genes that lead to the development of the fetal gonad. Whereas development of the female external genitalia does not require fetal ovarian hormones, male genital development requires the action of testicular testosterone and its more potent derivative dihydrotestosterone (DHT). The "classic" biosynthetic pathway from cholesterol to testosterone in the testis and the subsequent conversion of testosterone to DHT in genital skin is well established. Recently, an alternative pathway leading to DHT has been described in marsupials, but its potential importance to human development is unclear. AKR1C2 is an enzyme that participates in the alternative but not the classic pathway. Using a candidate gene approach, we identified AKR1C2 mutations with sex-limited recessive inheritance in four 46,XY individuals with disordered sexual development (DSD). Analysis of the inheritance of microsatellite markers excluded other candidate loci. Affected individuals had moderate to severe undervirilization at birth; when recreated by site-directed mutagenesis and expressed in bacteria, the mutant AKR1C2 had diminished but not absent catalytic activities. The 46,XY DSD individuals also carry a mutation causing aberrant splicing in AKR1C4, which encodes an enzyme with similar activity. This suggests a mode of inheritance where the severity of the developmental defect depends on the number of mutations in the two genes. An unrelated 46,XY DSD patient carried AKR1C2 mutations on both alleles, confirming the essential role of AKR1C2 and corroborating the hypothesis that both the classic and alternative pathways of testicular androgen biosynthesis are needed for normal human male sexual differentiation.  相似文献   
57.
Decolorization of two monoazo dyes, acid orange 6 (AO6) and acid orange 7 (AO7), were studied in sequential fixed-film anaerobic batch reactor (SFABR) with varying dye concentrations and 500 mg/L glucose as the co-substrate. More than 90% dye decolorization could be achieved, even at 300 mg/L, with both AO6 and AO7 and dye decolorization rates were 168 mg/L/d and 176 mg/L/d, respectively. COD removals with these two monoazo dyes were significantly different, as 75% and 35% decrease were observed with AO6 and AO7, respectively. UV-visible spectral as well as HPLC analysis of SFABR treated effluent showed the accumulation of 4-aminobenzenesulfonate (4-ABS) from AO6 and AO7. Aminoresorcinol (AR) formed from AO6 decolorization could not be detected at the end of SFABR cycle. This along with high COD removal indicated its further degradation. Formation of pink coloration on exposure to air indicated the presence of 1-amino-2-naphthol (AN) in AO7 fed reactor effluent. Thus both 4-ABS and AN were resistant to further degradation under anaerobic conditions. Presence of nitrate did not decrease the observed decolorization at the end of 24h SFABR cycle, although initial rate was decreased. This indicates the suitability of SFABR configuration for the treatment of azo-dye containing wastewaters in the presence of nitrate.  相似文献   
58.
In the present investigation, metabolites of Streptomyces sp. MTN14 and Trichoderma harzianum ThU significantly enhanced biomass yield (3.58 and 3.48 fold respectively) in comparison to the control plants. The secondary metabolites treatments also showed significant augmentation (0.75–2.25 fold) in withanolide A, a plant secondary metabolite. Lignin deposition, total phenolic and flavonoid content in W. somnifera were maximally induced in treatment having T. harzianum metabolites. Also, Trichoderma and Streptomyces metabolites were found much better in invoking in planta contents and antioxidants compared with their live culture treatments. Therefore, identification of new molecular effectors from metabolites of efficient microbes may be used as biopesticide and biofertilizer for commercial production of W. somnifera globally.  相似文献   
59.
The present study was aimed to investigate whether a decrease of nitric oxide (NO) level is beneficial for sponateous resumptiom of meiosis in diplotene-arrested oocytes cultured in vitro. For this purpose, diplotene-arrested oocytes were collected from ovary of immature female rats after a single subcutaneous injection of 20 IU pregnant mare’s serum gonadotropins (PMSG) for 48 h. In vitro effects of S-nitroso-l-acetyl penicillamine (SNAP; an NO donor) and aminoguanidine (AG; an inducible NOS [iNOS] inhibitor), intracellular NO, cyclic guanosine monophosphate (cGMP), Cdc25B, Thr-14/Tyr-15 and Thr-161 phosphorylated cyclin-dependent kinase-1 (CDK1), and cyclin B1 levels were analyzed. The SNAP inhibited spontaneous meiotic resumption form diplotene arrest in a concentration-dependent manner, while AG-induced meiotic resumption form diplotene in 0.1 mmol/L 3-isobutyl-1-methylxanthine (IBMX)-treated oocytes in a concentration-dependent manner. The intracellular NO as well as cGMP levels were decreased significantly during spontaneous meiotic resumption from diplotene arrest. The reduction of Cdc25B expression level was associated with the accumulation of Thr-14/Tyr-15 phosphorylated CDK1 level. However, Thr-161 phosphorylated CDK1 as well as cyclin B1 levels were reduced significantly during meiotic resumption from diplotene arrest. Taken together, these data suggest that the inhibition of iNOS expression leads to a decrease of NO and cGMP levels thereby decreasing Cdc25B level. The reduced CDC25 B level leads to accumulation of Thr-14/Tyr-15 phosphorylated CDK1 level. As a result, Thr-161 phosphorylated CDK1 as well as cyclin B1 levels are decreased leading to maturation-promoting factor (MPF) inactivation. The inactive MPF finally induced meiotic resumption from diplotene stage in rat oocytes cultured in vitro.  相似文献   
60.
Cultivated peanut (Arachis hypogaea L.) is an important grain legume providing high‐quality cooking oil, rich proteins and other nutrients. Shelling percentage (SP) is the 2nd most important agronomic trait after pod yield and this trait significantly affects the economic value of peanut in the market. Deployment of diagnostic markers through genomics‐assisted breeding (GAB) can accelerate the process of developing improved varieties with enhanced SP. In this context, we deployed the QTL‐seq approach to identify genomic regions and candidate genes controlling SP in a recombinant inbred line population (Yuanza 9102 × Xuzhou 68‐4). Four libraries (two parents and two extreme bulks) were constructed and sequenced, generating 456.89–790.32 million reads and achieving 91.85%–93.18% genome coverage and 14.04–21.37 mean read depth. Comprehensive analysis of two sets of data (Yuanza 9102/two bulks and Xuzhou 68‐4/two bulks) using the QTL‐seq pipeline resulted in discovery of two overlapped genomic regions (2.75 Mb on A09 and 1.1 Mb on B02). Nine candidate genes affected by 10 SNPs with non‐synonymous effects or in UTRs were identified in these regions for SP. Cost‐effective KASP (Kompetitive Allele‐Specific PCR) markers were developed for one SNP from A09 and three SNPs from B02 chromosome. Genotyping of the mapping population with these newly developed KASP markers confirmed the major control and stable expressions of these genomic regions across five environments. The identified candidate genomic regions and genes for SP further provide opportunity for gene cloning and deployment of diagnostic markers in molecular breeding for achieving high SP in improved varieties.  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