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   60864篇
  免费   18572篇
  国内免费   2634篇
  2024年   95篇
  2023年   449篇
  2022年   516篇
  2021年   1102篇
  2020年   3473篇
  2019年   5054篇
  2018年   5216篇
  2017年   5289篇
  2016年   4938篇
  2015年   4820篇
  2014年   4915篇
  2013年   5756篇
  2012年   4514篇
  2011年   4903篇
  2010年   4239篇
  2009年   3340篇
  2008年   3592篇
  2007年   2942篇
  2006年   2824篇
  2005年   2346篇
  2004年   1948篇
  2003年   1973篇
  2002年   1671篇
  2001年   1337篇
  2000年   887篇
  1999年   691篇
  1998年   343篇
  1997年   310篇
  1996年   272篇
  1995年   256篇
  1994年   244篇
  1993年   219篇
  1992年   209篇
  1991年   184篇
  1990年   147篇
  1989年   130篇
  1988年   105篇
  1987年   103篇
  1986年   111篇
  1985年   72篇
  1984年   86篇
  1983年   67篇
  1982年   98篇
  1981年   53篇
  1980年   68篇
  1979年   38篇
  1978年   36篇
  1977年   19篇
  1976年   14篇
  1972年   19篇
排序方式: 共有10000条查询结果,搜索用时 593 毫秒
81.
82.
83.
Simple demographic and infectious disease models of buffaloes and other domestic hosts for animal trypanosomosis (surra) caused by Trypanosoma evansi were developed. The animal models contained deterministic and stochastic elements and were linked to simulate the benefit of control regimes for surra in village domestic animal populations in Mindanao, Philippines. The impact of the disease on host fertility and mortality were key factors in determining the economic losses and net-benefit from the control regimes. If using a high (99%) efficacy drug in surra-moderate to high risk areas, then treating all animals twice each year yielded low prevalence in 2 years; targeted treatment of clinically sick animals, constantly monitored (monthly), required 75% fewer treatments but took longer to reach a low prevalence than treating all animals twice each year. At high drug efficacy both of these treatment strategies increased the benefit over untreated animals by 81%. If drug efficacy declined then the benefit obtained from twice yearly treatment of all animals declined rapidly compared with regular monitoring and targeting treatment to clinically sick animals. The current control regimen applied in the Philippines of annual sero-testing for surra and only treating sero-positive animals provided the lowest net-benefit of all the control options simulated and would not be regarded as effective control. The total net-benefit from effective surra control for a typical village in a moderate/high risk area was 7.9 million pesos per annum (US $158,000). The value added to buffaloes, cattle, horses, goats/sheep and pigs as a result of this control was US $88, $84, $151, $7, $114 per animal/year, respectively.  相似文献   
84.
Moment-based criteria for determining bioequivalence   总被引:1,自引:0,他引:1  
  相似文献   
85.
This research presents the results of constructing and parameterizing an individual-based model of spatiotemporal dynamics of mixed forest stands. The model facilitates computerized experiments with forest stands having different combinations of species and age structures. These forest stands grow on temperate areas where light is the main system-forming factor that shapes and develops forest ecosystems. The model TEMFORM (TEMperate FORests Model) is developed with few equations and parameters, most of which can be estimated using standard forest inventory data. Parameterization of the model used the growth tables of a set of basic forest-forming species in Far East Russia. Simulation results of the development of the natural single- and mixed-species stands and the effects of different types of disturbances on the stand dynamics and compositions are presented.  相似文献   
86.
Bile micelles play an important role in oral absorption of low‐solubility compounds. Bile micelles can affect solubility, dissolution rate, and permeability. For the pH–solubility profile in bile micelles, the HendersonHasselbalch equation should be modified to take bile‐micelle partition into account. For the dissolution rate, in the NernstBrunner equation, the effective diffusion coefficient in bile‐micelle media should be used instead of the monomer diffusion coefficient. The diffusion coefficient of bile micelles is 8‐ to 18‐fold smaller than that of monomer molecules. For permeability, the effective diffusion coefficient in the unstirred water layer adjacent to the epithelial membrane, and the free fraction at the epithelial membrane surface should be taken into account. The importance of these aspects is demonstrated here using several in vivo and clinical oral‐absorption data of low‐solubility model compounds. Using the theoretical equations, the food effect on oral absorption is further discussed.  相似文献   
87.
88.
Thanks to the numerous studies that have been carried out recently in the field of cytosolic DNA sensing, STING (Stimulator of Interferon Genes) is now recognized as a key mediator of innate immune signaling. A substantial body of evidence derived from in vivo mouse models demonstrates that STING-regulated pathways underlie the pathogenesis of many diseases including infectious diseases and cancers. It has also become evident from these studies that STING is a promising therapeutic target for the treatment of cancer. However, mouse strains commonly used for modelling innate immune response against infections or tumors do not allow investigators to accurately reproduce certain specific characteristics of immune response observed in human cells. In this review, we will discuss recent data demonstrating that the use of wild-derived genetically distinct inbred mice as a model for investigation into the innate immunity signaling networks may provide valuable insight into the STING-regulated pathways specific for human cells. The maximum complexity of STING-mediated mechanisms can probably be seen in case of DNA virus-induced carcinogenesis in which STING may perform unexpected biological activities. Therefore, in another part of this review we will summarize emerging data on the role of STING in human DNA virus-related oncopathologies, with particular attention to HPV-associated cervical cancer, aiming to demonstrate that STING indeed “starts a new chapter” in research on this issue and that wild-derived mouse models of STING-mediated response to infections will probably be helpful in finding out molecular basis for clinical observations.  相似文献   
89.
90.
Ying Yuan  Guosheng Yin 《Biometrics》2010,66(1):105-114
Summary .  We study quantile regression (QR) for longitudinal measurements with nonignorable intermittent missing data and dropout. Compared to conventional mean regression, quantile regression can characterize the entire conditional distribution of the outcome variable, and is more robust to outliers and misspecification of the error distribution. We account for the within-subject correlation by introducing a   ℓ2   penalty in the usual QR check function to shrink the subject-specific intercepts and slopes toward the common population values. The informative missing data are assumed to be related to the longitudinal outcome process through the shared latent random effects. We assess the performance of the proposed method using simulation studies, and illustrate it with data from a pediatric AIDS clinical trial.  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