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   12361篇
  免费   990篇
  国内免费   386篇
  13737篇
  2023年   108篇
  2022年   197篇
  2021年   300篇
  2020年   244篇
  2019年   283篇
  2018年   329篇
  2017年   284篇
  2016年   374篇
  2015年   584篇
  2014年   639篇
  2013年   798篇
  2012年   891篇
  2011年   815篇
  2010年   516篇
  2009年   396篇
  2008年   599篇
  2007年   587篇
  2006年   534篇
  2005年   498篇
  2004年   459篇
  2003年   455篇
  2002年   381篇
  2001年   335篇
  2000年   338篇
  1999年   285篇
  1998年   120篇
  1997年   92篇
  1996年   77篇
  1995年   62篇
  1994年   92篇
  1993年   63篇
  1992年   172篇
  1991年   154篇
  1990年   142篇
  1989年   162篇
  1988年   124篇
  1987年   113篇
  1986年   110篇
  1985年   102篇
  1984年   71篇
  1983年   75篇
  1982年   49篇
  1979年   53篇
  1977年   79篇
  1976年   50篇
  1975年   46篇
  1974年   57篇
  1973年   42篇
  1971年   45篇
  1969年   44篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.

Background

To systematically evaluate the visual performance of aspheric AcrySof IQ and spherical AcrySof Natural intraocular lens (IOL) after cataract surgery.

Methodology/Principal Findings

Potential randomized controlled trials (RCTs) that involved implanting AcrySof IQ and AcrySof Natural were searched from PubMed, Web of science, EMBASE, Chinese Science and Technology Periodicals Databases and Cochrane Central Register of Controlled Trials. The methodological quality of the studies was assessed by the Jadad method. Standardized mean differences (SMDs) with 95% confidence intervals (CIs) of best-corrected visual acuity (BCVA), contrast sensitivity and spherical aberration were pooled using a random-effects model. Seven studies were identified and analyzed to compare AcrySof IQ (236 eyes) with AcrySof Natural (232 eyes) after phacoemulsification. There was no significant difference in postoperative BCVA between AcrySof IQ and AcrySof Natural (p =0.137) after a follow up of 3 months. For contrast sensitivity, these differences reached statistical significance under photopic conditions at two spatial frequencies (3 cycles per degree (cpd), 6 cpd, 12 cpd, and 18 cpd; p =0.022, p =0.017, p = 0.065, and p=0.191, respectively) and under mesopic conditions at three spatial frequencies (3 cpd, 6 cpd, 12 cpd, and 18 cpd; p =0.007, p =0.033, p =0.030, and p =0.080, respectively). Eyes with AcrySof IQ also had statistically significant less spherical aberration than eyes with AcrySof Natural (p<0.001). Sensitivity analysis showed that the results were relatively stable and reliable.

Conclusions/Significance

The overall findings indicate that AcrySof IQ with a modified aspheric surface induced significantly less spherical aberration than AcrySof Natural. Contrast sensitivity in eyes with AcrySof IQ is better than that in eyes with AcrySof Natural, especially under mesopic conditions.  相似文献   
993.
OBJECTIVE: To determine the expression of HECA-452 epitope in mycosis fungoides (MF), assess whether its expression increases in relapsed MF compared with nonrelapsed MF and determine the potential prognostic relevance of HECA-452 expression. STUDY DESIGN: HECA-452 expression was evaluated by immunohistochemistry in a consecutive series of 20 MF. In all patients we evaluated the disease-free survival rate according to HECA-452 expression in a univariate analysis. RESULTS: We found a low expression in 5 MF (25%), a moderate expression in 8 MF (40%) and a high expression in 7 MF (35%) in the intraepidermal area. All patients were disease-free after appropriate therapy. Four of 20 patients (20%) relapsed within 2 years. HECA-452 expression significantly correlated with disease relapse in these patients. In fact, among the 7 patients whose lesions had a high expression, 4 had a disease recurrence (57%), whereas 0 of 13 (0%) with a low or moderate expression relapsed (p < 0.05). CONCLUSION: HECA-452 expression correlates with disease relapse in MF. Correlation with disease progression suggests that HECA-452 could be of prognostic relevance in the early stage of mycosis fungoides.  相似文献   
994.
杨秀芹  刘慧  郭丽娟  关庆芝  许尧  刘娣 《遗传》2008,30(6):741-746
以野猪、民猪和大白猪为研究对象, 根据网上公布的序列设计了7对引物, 采用测序、PCR-SSCP和PCR-RFLP方法对CAPN1基因的部分外显子和3′UTR区进行了单核苷酸多态性检测和基因型分析, 探讨CAPN1基因多态性与瘦肉率和嫩度的关系。研究发现11个SNPs, 其中5个位于外显子, 4个位于内含子, 2个位于3′UTR区, 外显子中的突变有一处是错义突变, 导致了蛋白质多肽链第260位氨基酸发生了M/V的替代。群体遗传学分析表明, 在所检测的各多态位点上, 野猪、民猪、大白猪3个品种间不同基因型的分布都存在着极显著的差异(P<0.01), 而野猪和民猪之间各基因型的分布差异不显著(P>0.05), 民猪和大白猪之间各基因型的分布存在着极显著的差异(P<0.01)。结合品种特性分析表明, P4、P6引物和3′ UTR区HinfⅠ位点所检测的不同基因型和瘦肉率具有一定的相关性。  相似文献   
995.
Phospholipase D2 (PLD2), one of the two mammalian members of the PLD family, has been implicated in cell proliferation, transformation, tumor progression and survival. However, as precise mechanistic details are still unknown, we investigated here if the PLD2 isoform would signal through the PI3K/AKT pathway. Transient expression of PLD2 in COS7 cells with either the WT or with a Y179F mutant, resulted in an increased basal phosphorylation of AKT in residues T308 and S473, in a PI3K-dependent manner. Transfection of PLD2-Y179F (but not the wild type) caused an increased (>2-fold) DNA synthesis even in the absence of extracellular stimuli. Other signaling mechanisms downstream such PLD/PI3K dependence (that might lead to DNA synthesis regulation) were further studied. PLD2-Y179F caused an increase in phosphorylation of p42/p44 ERK and in the expression of G0/G1 phase transition markers (p21 CIP, PCNA), and these effects, too, were dependent on PI3K. Interestingly, Akt, once activated induced the phosphorylation of PLD2 on residue T175, an effect that was inhibited by LY296004. Lastly, if PLD2-Y179F is further mutated in residue K758 (PLD2 Y179F-K758R), which renders inactive a catalytic site, DNA synthesis is then abrogated, indicating that the activity of the enzyme (i.e. synthesis of PA) is necessary for the observed effects. In conclusion, the unavailability of residue Y179 on PLD2 to become phosphorylated leads to an augmentation of DNA synthesis concomitantly with MEK and AKT phosphorylation, in a process that is dependent on PI3K and independent of any extracellular stimuli. This might be critical for the maintenance of the PLD2-regulated proliferative status.  相似文献   
996.
An amidic derivative of a carboxymethylcellulose-based hydrogel was obtained and characterized in terms of amidation degree. NMR studies and FT-IR imaging spectroscopy demonstrated that the reaction allowed a polymer to be obtained that was characterized by a regular distribution of amidic groups along the polysaccharide chains. Through this regularity, a homogenous three-dimensional scaffold was obtained, which maintained the thixotropic property of the linear polysaccharide.  相似文献   
997.
998.
999.
Neuritogenesis, the first step of neuronal differentiation, takes place as nascent neurites bud from the immediate postmitotic neuronal soma. Little is known about the mechanisms underlying the dramatic morphological changes that characterize this event. Here, we show that RhoA activity plays a decisive role during neuritogenesis of cultured hippocampal neurons by recruiting and activating its specific kinase ROCK, which, in turn, complexes with profilin IIa. We establish that this previously uncharacterized brain-specific actin-binding protein controls neurite sprouting by modifying actin stability, a function regulated by ROCK-mediated phosphorylation. Furthermore, we determine that this novel cascade is switched on or off by physiological stimuli. We propose that RhoA/ROCK/PIIa-mediated regulation of actin stability, shown to be essential for neuritogenesis, may constitute a central mechanism throughout neuronal differentiation.  相似文献   
1000.
A diverse natural product-like (NPL) synthetic abietane diterpenoid library containing 86 compounds were obtained and the SARs were studied based on their antibacterial potential. Further in vitro cytotoxic and in silico drug-like properties evaluation showed that the potent antibacterial compound 84 had good drug-like properties and displayed low cytotoxicity toward noncancerous mammalian cells, indicating the study of AA and DHAA might be a good starting point for the search of novel antimicrobial molecules. Future work should be focused on the optimization of their potency and selectivity.  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