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   9298篇
  免费   833篇
  国内免费   27篇
  10158篇
  2023年   44篇
  2022年   119篇
  2021年   167篇
  2020年   122篇
  2019年   149篇
  2018年   201篇
  2017年   189篇
  2016年   269篇
  2015年   482篇
  2014年   492篇
  2013年   602篇
  2012年   734篇
  2011年   663篇
  2010年   435篇
  2009年   414篇
  2008年   575篇
  2007年   517篇
  2006年   457篇
  2005年   420篇
  2004年   391篇
  2003年   351篇
  2002年   325篇
  2001年   185篇
  2000年   168篇
  1999年   136篇
  1998年   81篇
  1997年   69篇
  1996年   53篇
  1995年   76篇
  1994年   46篇
  1993年   52篇
  1992年   87篇
  1991年   74篇
  1990年   79篇
  1989年   83篇
  1988年   80篇
  1987年   76篇
  1986年   64篇
  1985年   73篇
  1984年   52篇
  1983年   44篇
  1982年   34篇
  1980年   29篇
  1979年   47篇
  1978年   43篇
  1977年   29篇
  1976年   41篇
  1975年   32篇
  1974年   32篇
  1973年   26篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
63.

Background

We conducted a study using a case-crossover design to clarify the risk of acute effects of zolpidem and benzodiazepine on all-sites of fractures in the elderly.

Design of study

Case-crossover design.

Methods and Materials

Elderly enrollees (n = 6010) in Taiwan’s National Health Insurance Research Database with zolpidem or benzodiazepine use were analyzed for the risk of developing fractures.

Results

After adjusting for medications such as antipsychotics, antidepressants, and diuretics, or comorbidities such as hypertension, osteoarthritis, osteoporosis, rheumatoid arthritis and depression, neither zolpidem nor benzodiazepine was found to be associated with increased risk in all-sites fractures. Subjects without depression were found to have an increased risk of fractures. Diazepam is the only benzodiazepine with increased risk of fractures after adjusting for medications and comorbidities. Hip and spine were particular sites for increased fracture risk, but following adjustment for comorbidities, the associations were found to be insignificant.

Conclusion

Neither zolpidem nor benzodiazepine was associated with increased risk of all-site fractures in this case cross-over study after adjusting for medications or comorbidities in elderly individuals with insomnia. Clinicians should balance the benefits and risks for prescribing zolpidem or benzodiazepine in the elderly accordingly.  相似文献   
64.
Targeting pathogenic T cells with Ag-specific tolerizing DNA vaccines encoding autoantigens is a powerful and feasible therapeutic strategy for Th1-mediated autoimmune diseases. However, plasmid DNA contains abundant unmethylated CpG motifs, which induce a strong Th1 immune response. We describe here a novel approach to counteract this undesired side effect of plasmid DNA used for vaccination in Th1-mediated autoimmune diseases. In chronic relapsing experimental autoimmune encephalomyelitis (EAE), combining a myelin cocktail plus IL-4-tolerizing DNA vaccine with a suppressive GpG oligodeoxynucleotide (GpG-ODN) induced a shift of the autoreactive T cell response toward a protective Th2 cytokine pattern. Myelin microarrays demonstrate that tolerizing DNA vaccination plus GpG-ODN further decreased anti-myelin autoantibody epitope spreading and shifted the autoreactive B cell response to a protective IgG1 isotype. Moreover, the addition of GpG-ODN to tolerizing DNA vaccination therapy effectively reduced overall mean disease severity in both the chronic relapsing EAE and chronic progressive EAE mouse models. In conclusion, suppressive GpG-ODN effectively counteracted the undesired CpG-induced inflammatory effect of a tolerizing DNA vaccine in a Th1-mediated autoimmune disease by skewing both the autoaggressive T cell and B cell responses toward a protective Th2 phenotype. These results demonstrate that suppressive GpG-ODN is a simple and highly effective novel therapeutic adjuvant that will boost the efficacy of Ag-specific tolerizing DNA vaccines used for treating Th1-mediated autoimmune diseases.  相似文献   
65.
The artificial gene coding for anticoagulant hirudin was placed under the control of theGAL10 promoter and expressed in the galactokinase-deficient strain (Δgal1) ofSaccharomyces cereivisiae, which uses galactose only as a gratuitous inducer in order to avoid its consumption. For efficient production of recombinant hirudin, a carbon source other than galactose should be provided in the medium to support growth of the Δgal1 strain. Here we demonstrate the successful use of glucose in the fed-batch fermentation of the Δgal1 strain to achieve efficient production of recombinant hirudin, with a yield of up to 400 mg hirudin/L.  相似文献   
66.
Acquired enamel pellicle (AEP) is a protein film that forms on the enamel surface of teeth by selective adsorption of proteins and peptides present in the mouth. This protein film forms the interface between enamel and the damage oral biofilm, which modulates the attachment of bacteria found in oral biofilm. The overall goal of this study was to gain insight into the biological formation of the human in vivo AEP. This study hypothesized that AEP is created by the formation of successive protein layers, which consist of initial binding to enamel and subsequent protein-protein interactions. This hypothesis was examined by observing quantitative and qualitative changes in pellicle composition during the first two hours of AEP formation in the oral cavity. Quantitative mass spectrometry approaches were used to generate an AEP protein profile for each time-point studied. Relative proteomic quantification was carried out for the 50 proteins observed in all four time-points. Notably, the abundance of important salivary proteins, such as histatin 1, decrease with increasing of the AEP formation, while other essential proteins such as statherin showed constant relative abundance in all time-points. In summary, this is the first study that investigates the dynamic process to the AEP formation by using proteomic approaches. Our data demonstrated that there are significant qualitative and quantitative proteome changes during the AEP formation, which in turn will likely impact the development of oral biofilms.  相似文献   
67.

Purpose

Standard treatment for glioblastoma (GBM) is surgery followed by radiation (RT) and temozolomide (TMZ). While there is variability in survival based on several established prognostic factors, the prognostic utility of other factors such as tumor size and location are not well established.

Experimental Design

The charts of ninety two patients with GBM treated with RT at the National Cancer Institute (NCI) between 1998 and 2012 were retrospectively reviewed. Most patients received RT with concurrent and adjuvant TMZ. Topographic locations were classified using preoperative imaging. Gross tumor volumes were contoured using treatment planning systems utilizing both pre-operative and post-operative MR imaging.

Results

At a median follow-up of 18.7 months, the median overall survival (OS) and progression-free survival (PFS) for all patients was 17.9 and 7.6 months. Patients with the smallest tumors had a median OS of 52.3 months compared to 16.3 months among patients with the largest tumors, P = 0.006. The patients who received bevacizumab after recurrence had a median OS of 23.3 months, compared to 16.3 months in patients who did not receive it, P = 0.0284. The median PFS and OS in patients with periventricular tumors was 5.7 and 17.5 months, versus 8.9 and 23.3 months in patients with non-periventricular tumors, P = 0.005.

Conclusions

Survival in our cohort was comparable to the outcome of the defining EORTC-NCIC trial establishing the use of RT+TMZ. This study also identifies several potential prognostic factors that may be useful in stratifying patients.  相似文献   
68.
Previous studies have shown that glucose-6-phosphate dehydrogenase (G6PD)-deficient cells are under increased oxidative stress and undergo premature cellular senescence. The present study demonstrates that G6PD-deficient cells cultured under 3% oxygen concentration had an extended replicative lifespan, as compared with those cultured under atmospheric oxygen level. This was accompanied by a reduction in the number of senescence-associated β-galactosidase (SA-β-Gal) positive and morphologically senile cells at comparable population doubling levels (PDL). Concomitant with the extension of lifespan was decreased production of reactive oxygen species. Additionally, lifespan extension was paralleled by the greatly abated formation of such oxidative damage markers as 8-hydroxy-deoxyguanosine (8-OHdG) as well as the oxidized and cross-linked proteins. Moreover, the mitochondrial mass increased, but the mitochondrial membrane potential ΔΨm decreased in cells upon serial propagation. These changes were inhibited by lowering the oxygen tension. Our findings provide additional support to the notion that oxidative damage contributes to replicative senescence of G6PD-deficient cells and reduction of oxidative damage by lowering oxygen tension can delay the onset of cellular senescence.  相似文献   
69.
Park C  Lee I  Jang JH  Kang WK 《FEBS letters》2007,581(20):3800-3804
Recently, negative effects of phosphatase in tumorigenesis and metastasis have been suggested in various tumor types. In this study, we showed that RhoA activation modulated phosphatase during senescence-like arrest in human prostate cancer cells. Under senescence-inducing condition, decreased Erk phosphorylation was detected in caRhoA-transfected cells and inactivation of Erk, but not p38, prevented doxorubicin-induced cell senescence. Cells were induced to senescence by inhibition of phosphatase activity (VHR, MKP3, or PP2A) without additional cellular stress. Of interest, caRhoA prevented doxorubicin-induced decrease of phosphatase. Thus, we postulate that RhoA signaling may protect cells against cellular senescence by maintaining phosphatase activity and Erk dephosphorylation.  相似文献   
70.
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