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   2327篇
  免费   37篇
  国内免费   46篇
教育   1611篇
科学研究   332篇
各国文化   9篇
体育   220篇
综合类   192篇
文化理论   3篇
信息传播   43篇
  2024年   1篇
  2023年   10篇
  2022年   32篇
  2021年   61篇
  2020年   57篇
  2019年   39篇
  2018年   21篇
  2017年   16篇
  2016年   28篇
  2015年   57篇
  2014年   125篇
  2013年   130篇
  2012年   172篇
  2011年   204篇
  2010年   166篇
  2009年   144篇
  2008年   172篇
  2007年   153篇
  2006年   148篇
  2005年   140篇
  2004年   106篇
  2003年   104篇
  2002年   97篇
  2001年   54篇
  2000年   38篇
  1999年   24篇
  1998年   19篇
  1997年   16篇
  1996年   15篇
  1995年   8篇
  1994年   10篇
  1993年   9篇
  1992年   6篇
  1991年   4篇
  1990年   3篇
  1989年   5篇
  1985年   3篇
  1984年   2篇
  1982年   5篇
  1981年   3篇
  1979年   1篇
  1978年   1篇
  1977年   1篇
排序方式: 共有2410条查询结果,搜索用时 0 毫秒
61.
In this paper,we investigate the effect and the possible mechanism of high glucose levels on the calcification of human aortic smooth muscle cells (HASMCs).HASMCs were divided into four groups: normal glucose group (NG),osmolality control group (OC),high glucose group (HG,HASMCs culture medium containing 30 mmol/L glucose),and high glucose plus recombinant human Noggin protein (bone morphogenetic protein-2 (BMP-2) antagonist) group (HN).The mRNA levels and the protein expressions of BMP-2 and core binding factor alpha-1 (Cbfα-1) were measured by real-time quantitative polymerase chain reaction (PCR) and Western blot.After induced by 10 mmol/L β-glycerol phosphoric acid,cells were harvested for assessments of alkaline phosphatase (ALP) activities at Days 1,2,and 3,and intracellular calcium contents at Days 7 and 14,respectively.High glucose levels increased the mRNA levels and the protein expressions of BMP-2 and Cbfα-1 (P0.05).The expression of Cbfα-1 was partially blocked by Noggin protein (P0.05),while BMP-2 was not (P0.05).After being induced by β-glycerol phosphoric acid,high glucose levels increased the ALP activity [(48.63±1.03) vs.(41.42±2.28) U/mg protein,Day 3;P0.05] and the intracellular calcium content [(2.76±0.09) vs.(1.75±0.07) μmol/mg protein,Day 14;P0.05] in a time-dependent manner when compared with the NG group,while the ALP activity could not be blocked by Noggin protein [(48.63±1.03) vs.(47.37±0.97) U/mg protein,Day 3;P0.05].These results show that high glucose levels can evoke the calcification of HASMCs by inducing osteoblastic trans-differentiation and intracellular calcium deposition via the BMP-2/Cbfα-1 pathway,which can be partially blocked by Noggin protein.  相似文献   
62.
维普数据库Z39.50服务端系统设计方案   总被引:1,自引:0,他引:1  
介绍了维普数据库Z39.50服务端系统的设计方案,该方案有两条解决途径:基于TCP/IP的Z39.50服务端系统和基于HTTP的SRU服务端系统,笔者将这两种思路做了比较。本系统突破了传统Z39.50协议只运用于对书目数据的提供,而是提供电子期刊数据,这是本方案的特色所在。  相似文献   
63.
运用文献资料和逻辑分析法,研究街头篮球起源及发展的文化背景,分析中国街头篮球的发展历程、现状及发展方向,探讨其对中国职业篮球发展的影响。  相似文献   
64.
借鉴求线性矩阵方程组同类约束解的MCG算法(修正共轭梯度法),建立了求多个未知矩阵的线性矩阵方程组的一种异类约束解的MCG1-3-5算法,证明了该算法的收敛性。该算法不仅可以判断矩阵方程组的异类约束解是否存在,而且在有异类约束解,且不考虑舍入误差时,可在有限步计算后求得矩阵方程组的一组异类约束解;选取特殊初始矩阵时,求得矩阵方程组的极小范数异类约束解。同时还能求取指定矩阵在该矩阵方程组异类约束解集合中的最佳逼近。算例表明,该算法有效。  相似文献   
65.
ABSTRACT

Background and Context: Current introductory instruction fails to identify, structure, and sequence the many skills involved in programming.

Objective: We proposed a theory which identifies four distinct skills that novices learn incrementally. These skills are tracing, writing syntax, comprehending templates (reusable abstractions of programming knowledge), and writing code with templates. We theorized that explicit instruction of these skills decreases cognitive demand.

Method: We conducted an exploratory mixed-methods study and compared students’ exercise completion rates, error rates, ability to explain code, and engagement when learning to program. We compared material that reflects this theory to more traditional material that does not distinguish between skills.

Findings: Teaching skills incrementally resulted in improved completion rate on practice exercises, and decreased error rate and improved understanding of the post-test.

Implications: By structuring programming skills such that they can be taught explicitly and incrementally, we can inform instructional design and improve future research on understanding how novice programmers develop understanding.  相似文献   
66.
运用李对称方法得到了(3+1)维Kadomtsev Petviashvili Boussinesq(KPB)方程的对称和约化方程。进而,利用齐次平衡原理和椭圆函数方法得到了方程的精确解。最后,给出了该方程的守恒律。  相似文献   
67.
68.
69.
张维朋 《科技通报》2011,27(4):479-483
研究女性胆固醇随年龄变化的趋势.采集大最女性胆固醇数据,以10岁为年龄段,计算每个年龄段健康女性胆固醇平均值,并以女性70岁以下6个年龄段的胆固醇为原始数列,建立了女性胆固醇随年龄变化的灰色系统(GM(1,1))模型预测.后验差检验合格,预测70~79岁、80以上年龄段的女性胆固醇.预测分析结果表明,灰色系统GM(1,...  相似文献   
70.
BackgroundCecropin P1, acting as an antimicrobial, has a broad-spectrum antibacterial activity with some antiviral and antifungal properties. It is a promising natural alternative to antibiotics which is originally isolated from the pig intestinal parasitic nematode Ascaris suum. Many studies have shown that Cecropin P1 is helpful for the prevention or treatment of clinical diseases. Therefore, it is very necessary to establish a safe, nontoxic, and efficient expression method of Cecropin P1.ResultsThe results indicated that the recombinant protein was about 5.5 kDa showed by Tricine–SDS–PAGE and Western blot. And Cecropin P1 was efficiently secreted and expressed after 12 h of induction, with an increasing yield over the course of the induction. Its maximum concentration was 7.83 mg/L after concentration and purification. In addition, in vitro experiments demonstrated that Cecropin P1 not only exerted a strong inhibitory effect on Escherichia coli, Salmonella sp., Shigella sp., and Pasteurella sp., but also displayed an antiviral activity against PRRSV NADC30-Like strain.ConclusionsCollectively, the strategy of expressing Cecropin P1 in Saccharomyces cerevisiae is harmless, efficient, and safe for cells. In addition, the expressed Cecropin P1 has antiviral and antibacterial properties concurrently.How to cite: Jiang R, Zhang P, Wu X, et al., Expression of antimicrobial peptide Cecropin P1 in Saccharomyces cerevisiae and its antibacterial and antiviral activity in vitro. Electron J Biotechnol 2021;50. https://doi.org/10.1016/j.ejbt.2020.12.006  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