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   15080篇
  免费   1127篇
  国内免费   825篇
  17032篇
  2024年   32篇
  2023年   194篇
  2022年   495篇
  2021年   768篇
  2020年   461篇
  2019年   591篇
  2018年   568篇
  2017年   408篇
  2016年   570篇
  2015年   854篇
  2014年   960篇
  2013年   1077篇
  2012年   1304篇
  2011年   1193篇
  2010年   747篇
  2009年   659篇
  2008年   741篇
  2007年   693篇
  2006年   591篇
  2005年   520篇
  2004年   458篇
  2003年   370篇
  2002年   329篇
  2001年   308篇
  2000年   255篇
  1999年   230篇
  1998年   148篇
  1997年   147篇
  1996年   150篇
  1995年   110篇
  1994年   111篇
  1993年   81篇
  1992年   134篇
  1991年   102篇
  1990年   78篇
  1989年   78篇
  1988年   63篇
  1987年   71篇
  1986年   64篇
  1985年   50篇
  1984年   48篇
  1983年   41篇
  1982年   24篇
  1981年   13篇
  1980年   16篇
  1979年   19篇
  1977年   14篇
  1976年   11篇
  1973年   10篇
  1972年   10篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
BackgroundPolycystic ovary syndrome (PCOS) is a common reproductive endocrinological disease with heterogeneous phenotype. Obesity contributes to the increased prevalence and severity of PCOS. Whether the intakes of major nutrients are higher in Chinese PCOS patients is still unknown.ObjectivesTo study the intakes of total energy, protein, fat and carbohydrate in Southwest Chinese PCOS patients.Methods1854 women were included in the cross-sectional study. A population-based case-control study was conducted. The dietary habits and nutrients intake status of 169 PCOS patients and 338 age-matched controls were investigated by the method of semi-quantitative food frequency questionnaire.ResultsThe actual intake of total energy (P = 0.01) and fat (P = 0.01) were higher, but carbohydrate was lower (P = 0.01) in PCOS patients as compared with the controls. The energy percentage supplied by protein (12.33%±2.27% vs. 19.26%±5.91%, P<0.001) and carbohydrate (48.72%±6.41% vs. 68.31%±8.37%, P<0.001) were lower in Southwest Chinese PCOS patients than those of control, however, the energy percentage supplied by fat was higher (38.95%±5.71% vs. 12.42%±5.13%, P<0.001) in PCOS.ConclusionsLimit the intake of total energy and fat shall be recommended to the Southwest Chinese PCOS patients. Women with PCOS in Southwest China shall consult with the nutritionist for improving the dietary structure.  相似文献   
962.
Hodgkin’s lymphoma (HL) is a lymphoid neoplasm characterized by Hodgkin’s and Reed-Sternberg (H/RS) cells, which is regulated by CD99. We previously reported that CD99 downregulation led to the transformation of murine B lymphoma cells (A20) into cells with an H/RS phenotype, while CD99 upregulation induced differentiation of classical Hodgkin’s lymphoma (cHL) cells (L428) into terminal B-cells. However, the molecular mechanism remains unclear. In this study, using fluorescence two-dimensional differential in-gel electrophoresis and matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS), we have analyzed the alteration of protein expression following CD99 upregulation in L428 cells as well as downregulation of mouse CD99 antigen-like 2 (mCD99L2) in A20 cells. Bioinformatics analysis showed that SEPTIN2 and STATHMIN, which are cytoskeleton proteins, were significantly differentially expressed, and chosen for further validation and functional analysis. Differential expression of SEPTIN2 was found in both models and was inversely correlated with CD99 expression. STATHMIN was identified in the A20 cell line model and its expression was positively correlated with that of CD99. Importantly, silencing of SEPTIN2 with siRNA substantially altered the cellular cytoskeleton in L428 cells. The downregulation of STATHMIN by siRNA promoted the differentiation of H/RS cells toward terminal B-cells. These results suggest that SEPTIN2-mediated cytoskeletal rearrangement and STATHMIN-mediated differentiation may contribute to changes in cell morphology and differentiation of H/RS cells with CD99 upregulation in HL.  相似文献   
963.
The high mortality rate in colorectal cancer is mostly ascribed to metastasis, but the only clinical biomarker available for disease monitoring and prognosis is the carcinoembryonic antigen (CEA). However, the prognostic utility of CEA remains controversial. In an effort to identify novel biomarkers that could be potentially translated for clinical use, we collected the secretomes from the colon adenocarcinoma cell line HCT‐116 and its metastatic derivative, E1, using the hollow fiber culture system, and utilized the multilectin affinity chromatography approach to enrich for the secreted glycoproteins (glyco‐secretome). The HCT‐116 and E1 glyco‐secretomes were compared using the label‐free quantitative SWATH‐MS technology, and a total of 149 glycoproteins were differentially secreted in E1 cells. Among these glycoproteins, laminin β‐1 (LAMB1), a glycoprotein not previously known to be secreted in colorectal cancer cells, was observed to be oversecreted in E1 cells. In addition, we showed that LAMB1 levels were significantly higher in colorectal cancer patient serum samples as compared to healthy controls when measured using ELISA. ROC analyses indicated that LAMB1 performed better than CEA at discriminating between colorectal cancer patients from controls. Moreover, the diagnostic performance was further improved when LAMB1 was used in combination with CEA.  相似文献   
964.
965.
Sip1/tuftelin‐interacting protein (STIP), a multidomain nuclear protein, is a novel factor associated with the spliceosome, yet its role and molecular function in cancer remain unknown. In this study, we show, for the first time, that STIP is overexpressed in non‐small cell lung cancer (NSCLC) tissues compared to adjacent normal lung tissues. The depletion of endogenous STIP inhibited NSCLC cell proliferation in vitro and in vivo, caused cell cycle arrest and induced apoptosis. Cell cycle arrest at the G2/M phase was associated with the expression and activity of the cyclin B1‐CDK1 (cyclin‐dependent kinase 1) complex. We also provide evidence that STIP knockdown induced apoptosis by activating both caspase‐9 and caspase‐3 and by altering the Bcl‐2/Bax expression ratio. RNA sequencing data indicated that the MAPK mitogen‐activated protein kinases, Wnt, PI3K/AKT, and NF‐κB (nuclear factor kappa‐light‐chain‐enhancer of activated B cells) signalling pathways might be involved in STIP‐mediated tumour regulation. Collectively, these results suggest that STIP may be a novel potential diagnostic and therapeutic target for NSCLC.  相似文献   
966.
Leaf senescence is an important physiological process during the plant life cycle. However, systemic studies on the impact of microRNAs (miRNAs) on the expression of senescence‐associated genes (SAGs) are lacking. Besides, whether other Argonaute 1 (AGO1)‐enriched small RNAs (sRNAs) play regulatory roles in leaf senescence remains unclear. In this study, a total of 5,123 and 1,399 AGO1‐enriched sRNAs, excluding miRNAs, were identified in Arabidopsis thaliana and rice (Oryza sativa), respectively. After retrieving SAGs from the Leaf Senescence Database, all of the AGO1‐enriched sRNAs and the miRBase‐registered miRNAs of these two plants were included for target identification. Supported by degradome signatures, 200 regulatory pairs involving 120 AGO1‐enriched sRNAs and 40 SAGs, and 266 regulatory pairs involving 64 miRNAs and 42 SAGs were discovered in Arabidopsis. Moreover, 13 genes predicted to interact with some of the above‐identified target genes at protein level were validated as regulated by 17 AGO1‐enriched sRNAs and ten miRNAs in Arabidopsis. In rice, only one SAG was targeted by three AGO1‐enriched sRNAs, and one SAG was targeted by miR395. However, five AGO1‐enriched sRNAs were conserved between Arabidopsis and rice. Target genes conserved between the two plants were identified for three of the above five sRNAs, pointing to the conserved roles of these regulatory pairs in leaf senescence or other developmental procedures. Novel targets were discovered for three of the five AGO1‐enriched sRNAs in rice, indicating species‐specific functions of these sRNA–target pairs. These results could advance our understanding of the sRNA‐involved molecular processes modulating leaf senescence.  相似文献   
967.
968.
Our previous studies have indicated that a novel curcumin derivate nicotinate-curcumin (NC) has beneficial effects on the prevention of atherosclerosis, but the precise mechanisms are not fully understood. Given that autophagy regulates lipid metabolism, the present study was designed to investigate whether NC decreases foam cell formation through restoring autophagy flux in oxidized low-density lipoprotein (ox-LDL)-treated THP-1 cells. Our results showed that ox-LDL (100 μg/ml) was accumulated in THP-1 cells and impaired autophagy flux. Ox-LDL-induced impairment of autophagy was enhanced by treatment with the autophagy inhibitor chloroquine (CQ) and rescued by the autophagy inducer rapamycin. The aggregation of ox-LDL was increased by CQ, but decreased by rapamycin. In addition, colocalization of lipid droplets with LC3-II was remarkably reduced in ox-LDL group. In contrast, NC (10 μM) rescued the impaired autophagy flux by significantly increasing level of LC3-II, the number of autophagolysosomes, and the degradation of p62 in ox-LDL-treated THP-1 cells. Inhibition of the PI3K-Akt-mTOR signaling was required for NC-rescued autophagy flux. Notably, our results showed that NC remarkably promoted the colocalization of lipid droplets with autophagolysosomes, increased efflux of cholesterol, and reduced ox-LDL accumulation in THP-1 cells. However, treatment with 3-methyladenine (3-MA) or CQ reduced the protective effects of NC on lipid accumulation. Collectively, the findings suggest that NC decreases lipid accumulation in THP-1 cells through restoring autophagy flux, and further implicate that NC may be a potential therapeutic reagent to reverse atherosclerosis.  相似文献   
969.
A new flow-through electrochemical immunosensor was designed for sensitive detection of alpha-fetoprotein (AFP) in human serum by using nanogold-functionalized magnetic graphene nanosheets as immunosensing probes. Initially, amino functionalized magnetic beads were covalently immobilized on the surface of graphene oxide nanosheets (MGPs), then nanogold particles were adsorbed on the amino groups of the MGPs to construct GoldMag nanocomposites functionalized graphene nanosheets (GMGPs), and then horseradish peroxidase-anti-AFP conjugates (HRP-anti-AFP) were assembled onto the surface of nanogold particles (bio-GMGP). With the aid of an external magnet, the formed bio-GMGPs were attached onto the base electrode in the flow system. With a non-competitive immunoassay format, the injected sample containing AFP antigens was produced transparent immunoaffinity reaction with the immobilized HRP-anti-AFP on the bio-GMGPs. The formed immunocomplex inhibited partly the active center of HRP, and decreased the labeled HRP toward the reduction of H(2)O(2). The performance and factors influencing the performance of the immunosensor were investigated in detail. Under optimal conditions, the electrochemical immunosensor displayed a wide working range of 0.01-200 ng mL(-1) with a low detection limit (LOD) of 1.0 pg mL(-1) AFP (at 3s(B)). Intra- and inter-assay coefficients of variation (CV) were below 10%. In addition, the methodology was validated with real serum samples, receiving a good correlation with the results obtained from commercially available electrochemiluminescence automated analyzer.  相似文献   
970.
A series of new HIV-1 protease inhibitors with the hydroxyethylamine core and different hydroxyprolinamide P2 ligands were designed and synthesized. Variation of substitutions at the P2 significantly affected the enzyme inhibitory potency of the inhibitors. Compounds 2a and 2d showed excellent enzyme inhibitory activity with IC50 values in the nanomolar range. An active site binding model for inhibitors 2a and 2d was suggested based upon the computational-docking results of the ligand with HIV-1 protease. This model offers molecular insights regarding ligand-binding site interactions of the hydroxyprolinamide-derived novel P2-ligand.  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