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   491篇
  免费   21篇
  国内免费   7篇
管理学   14篇
民族学   2篇
人口学   2篇
丛书文集   28篇
理论方法论   3篇
综合类   371篇
社会学   2篇
统计学   97篇
  2023年   7篇
  2022年   1篇
  2021年   5篇
  2020年   14篇
  2019年   8篇
  2018年   6篇
  2017年   9篇
  2016年   15篇
  2015年   12篇
  2014年   12篇
  2013年   22篇
  2012年   18篇
  2011年   25篇
  2010年   17篇
  2009年   27篇
  2008年   26篇
  2007年   31篇
  2006年   23篇
  2005年   27篇
  2004年   21篇
  2003年   25篇
  2002年   24篇
  2001年   21篇
  2000年   18篇
  1999年   15篇
  1998年   11篇
  1997年   14篇
  1996年   14篇
  1995年   13篇
  1994年   4篇
  1993年   9篇
  1992年   8篇
  1991年   4篇
  1990年   5篇
  1989年   2篇
  1988年   1篇
  1987年   3篇
  1985年   2篇
排序方式: 共有519条查询结果,搜索用时 15 毫秒
491.
现代日本语中男性与女性在用语上存在着极具特色的显著差异,这是日本语有别于很多国家语言体系的一个重要特征。研究表明,日本语言发展史上的男性与女性用语自镰仓室町时代起就开始产生了较为明显的位相差异。其重要依据之一,便是这一时期"女训书"的出现和"女房词"的流行与传播。从以上依据入手,解读中世日本女性的言语实践行为及其位相特征,探索其产生的社会意识与根源,从而为日本女性语的发展研究提供独特的研究维度和理论参考。  相似文献   
492.
新中国成立初期,编制经济计划有着复杂的原因。文章系统考察了这一时期经济计划编制工作的进程和成效,并在此基础上对新中国初期经济计划编制工作进行了评析。   相似文献   
493.
Many phase I drug combination designs have been proposed to find the maximum tolerated combination (MTC). Due to the two‐dimension nature of drug combination trials, these designs typically require complicated statistical modeling and estimation, which limit their use in practice. In this article, we propose an easy‐to‐implement Bayesian phase I combination design, called Bayesian adaptive linearization method (BALM), to simplify the dose finding for drug combination trials. BALM takes the dimension reduction approach. It selects a subset of combinations, through a procedure called linearization, to convert the two‐dimensional dose matrix into a string of combinations that are fully ordered in toxicity. As a result, existing single‐agent dose‐finding methods can be directly used to find the MTC. In case that the selected linear path does not contain the MTC, a dose‐insertion procedure is performed to add new doses whose expected toxicity rate is equal to the target toxicity rate. Our simulation studies show that the proposed BALM design performs better than competing, more complicated combination designs.  相似文献   
494.
Recently, molecularly targeted agents and immunotherapy have been advanced for the treatment of relapse or refractory cancer patients, where disease progression‐free survival or event‐free survival is often a primary endpoint for the trial design. However, methods to evaluate two‐stage single‐arm phase II trials with a time‐to‐event endpoint are currently processed under an exponential distribution, which limits application of real trial designs. In this paper, we developed an optimal two‐stage design, which is applied to the four commonly used parametric survival distributions. The proposed method has advantages compared with existing methods in that the choice of underlying survival model is more flexible and the power of the study is more adequately addressed. Therefore, the proposed two‐stage design can be routinely used for single‐arm phase II trial designs with a time‐to‐event endpoint as a complement to the commonly used Simon's two‐stage design for the binary outcome.  相似文献   
495.
The large number of failures in phase III clinical trials, which occur at a rate of approximately 45%, is studied herein relative to possible countermeasures. First, the phenomenon of failures is numerically described. Second, the main reasons for failures are reported, together with some generic improvements suggested in the related literature. This study shows how statistics explain, but do not justify, the high failure rate observed. The rate of failures due to a lack of efficacy that are not expected, is considered to be at least 10%. Expanding phase II is the simplest and most intuitive way to reduce phase III failures since it can reduce phase III false negative findings and launches of phase III trials when the treatment is positive but suboptimal. Moreover, phase II enlargement is discussed using an economic profile. As resources for research are often limited, enlarging phase II should be evaluated on a case‐by‐case basis. Alternative strategies, such as biomarker‐based enrichments and adaptive designs, may aid in reducing failures. However, these strategies also have very low application rates with little likelihood of rapid growth.  相似文献   
496.
膨胀试验作为单井吞吐工艺试验的重要评价手段之一,在油田注气混相与非混相驱试验中已得到应用。目前对不同种类气体注入对原油相态影响国内外虽作了些分析和研究,但针对同一种流体究竟那种注入气体较好,还研究得不多。首先对CO2注入时原油膨胀试验和未注气时的常规PVT数据进行模拟后,对CO2、N2、CH4和烟道气四种不同的注入气体进行了模拟研究,给出了在不同种类气体注入时原油的膨胀系数和泡点压力的影响,同时对混合气体的注入进行了分析。分析了各种气体在单井吞吐试验对地层流体的适应性,对其优缺点也进行了对比分析。  相似文献   
497.
用香烟过滤嘴制为材料自制了固相萃取柱,结合流动注射,建立了环境水样中Cr(Ⅵ)光度测定方法.对该方法进行优化,在Cr(Ⅵ)浓度0.1~4.0μg/L范围内具有较好的线性关系,1.0μg/L的Cr(Ⅵ)标样经11次测量,相对标准偏差为4.3%,方法检出限为0.02μg/L.对实际水样进行检测,加标回收率在94%~110%之间.  相似文献   
498.
The phase II basket trial in oncology is a novel design that enables the simultaneous assessment of treatment effects of one anti-cancer targeted agent in multiple cancer types. Biomarkers could potentially associate with the clinical outcomes and re-define clinically meaningful treatment effects. It is therefore natural to develop a biomarker-based basket design to allow the prospective enrichment of the trials with the adaptive selection of the biomarker-positive (BM+) subjects who are most sensitive to the experimental treatment. We propose a two-stage phase II adaptive biomarker basket (ABB) design based on a potential predictive biomarker measured on a continuous scale. At Stage 1, the design incorporates a biomarker cutoff estimation procedure via a hierarchical Bayesian model with biomarker as a covariate (HBMbc). At Stage 2, the design enrolls only BM+ subjects, defined as those with the biomarker values exceeding the biomarker cutoff within each cancer type, and subsequently assesses the early efficacy and/or futility stopping through the pre-defined interim analyses. At the end of the trial, the response rate of all BM+ subjects for each cancer type can guide drug development, while the data from all subjects can be used to further model the relationship between the biomarker value and the clinical outcome for potential future research. The extensive simulation studies show that the ABB design could produce a good estimate of the biomarker cutoff to select BM+ subjects with high accuracy and could outperform the existing phase II basket biomarker cutoff design under various scenarios.  相似文献   
499.
本文论述了相位无线电导航系统主、副台台址的选择与作用距离,覆盖区大小及其定位误差的关系,介绍了为实现最佳定位而正确选择台址的经验和计算曲线,并指出实际架台时应注意的若干问题。  相似文献   
500.
针对温度为200 K低温冰箱,研制了一台大冷量自由活塞斯特林制冷机.实验测试了充气压力和制冷温度对压缩机共振频率的影响;研究了膨胀机固有频率和运行频率对位移相位差的影响关系;采用多点热负荷静态复温法测试了制冷机的静态冷损,证明了氦气和丝网导热对静态冷损影响极小.该样机在200 K时最大制冷量可达40 W(250 W输入).  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