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   2866247篇
  免费   223036篇
  国内免费   5238篇
耳鼻咽喉   41062篇
儿科学   89640篇
妇产科学   74981篇
基础医学   413250篇
口腔科学   81982篇
临床医学   261605篇
内科学   554815篇
皮肤病学   59418篇
神经病学   232980篇
特种医学   113021篇
外国民族医学   946篇
外科学   431971篇
综合类   66945篇
现状与发展   3篇
一般理论   1096篇
预防医学   227895篇
眼科学   67540篇
药学   216116篇
  7篇
中国医学   6180篇
肿瘤学   153068篇
  2018年   29418篇
  2017年   22714篇
  2016年   25119篇
  2015年   28315篇
  2014年   40328篇
  2013年   61324篇
  2012年   82469篇
  2011年   87134篇
  2010年   51331篇
  2009年   48917篇
  2008年   82351篇
  2007年   88031篇
  2006年   89012篇
  2005年   86077篇
  2004年   83167篇
  2003年   80008篇
  2002年   78915篇
  2001年   134737篇
  2000年   139037篇
  1999年   117109篇
  1998年   33203篇
  1997年   29902篇
  1996年   29866篇
  1995年   28740篇
  1994年   26941篇
  1993年   25097篇
  1992年   94263篇
  1991年   91592篇
  1990年   88774篇
  1989年   85835篇
  1988年   79574篇
  1987年   78187篇
  1986年   74131篇
  1985年   70484篇
  1984年   53132篇
  1983年   45176篇
  1982年   26993篇
  1981年   24075篇
  1979年   49686篇
  1978年   34972篇
  1977年   29434篇
  1976年   27859篇
  1975年   29578篇
  1974年   36183篇
  1973年   34314篇
  1972年   32232篇
  1971年   29734篇
  1970年   28120篇
  1969年   26128篇
  1968年   23796篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.

Objective

To systematically review literature on uptake and timeliness of diphtheria-tetanus-pertussis, measles-mumps-rubella, and/or polio-containing vaccines in infants who were born preterm, with a low birth weight, and/or with chronic health conditions that were diagnosed within the first 6?months of life.

Methods

Using a standardized search strategy developed by a medical librarian, records were extracted from MEDLINE, Embase, Database of Abstracts of Reviews of Effects, and CINAHL up to May 8, 2018.

Results

Out of the 1997 records that were screened, we identified 21 studies that met inclusion criteria. Eleven studies assessed vaccine coverage and/or timeliness in preterm infants, 6 in low birth weight infants, and 7 in children with chronic health conditions. Estimates of coverage in these populations were highly variable, ranging from 40% to 100% across the vaccines and population groups.

Conclusions

There is a lack of studies reporting coverage and timeliness of routine immunizations in special populations of children.

Policy implications

Our review suggests a need for improved surveillance of immunization status in special populations of infants, as well as a need for standardization of reporting practices.  相似文献   
102.
Few studies have examined the effects of parental incarceration (PI) on outcomes above and beyond other risk and adverse childhood experiences (ACEs). The objectives of this study were to (1) the associations between PI and mental health problems (attention, externalizing, internalizing, and total behavioral problems) and (2) the mediating role of current socioeconomic status and cumulative ACEs. An observational and cross-sectional design was employed. Analyses included hierarchical multivariable linear regression modeling. The analytic sample included 613 adolescents (11–17?years). On average, youth exposed to PI experienced three times as many ACEs compared with youth unexposed. Youth exposed to PI were more likely to have behavioral problems than their unexposed peers. The main effect for all models was attenuated by current economic hardship as well as exposure to increasing numbers of ACEs. Exposure to PI can be viewed as a marker of accumulative risk for intervention since youth impacted by PI are more likely to experience behavioral difficulties and associated adverse childhood experiences. Due to the associated adversity that impact youth exposed to PI, mental health providers need to be able to identify and screen for symptoms associated with trauma.  相似文献   
103.
Dynamic contrast-enhanced ultrasound (DCE-US) has been proposed as a powerful tool for cancer diagnosis by estimation of perfusion and dispersion parameters reflecting angiogenic vascular changes. This work was aimed at identifying which vascular features are reflected by the estimated perfusion and dispersion parameters through comparison with acoustic angiography (AA). AA is a high-resolution technique that allows quantification of vascular morphology. Three-dimensional AA and 2-D DCE-US bolus acquisitions were used to monitor the growth of fibrosarcoma tumors in nine rats. AA-derived vascular properties were analyzed along with DCE-US perfusion and dispersion to investigate the differences between tumor and control and their evolution in time. AA-derived microvascular density and DCE-US perfusion exhibited good agreement, confirmed by their spatial distributions. No vascular feature was correlated with dispersion. Yet, dispersion provided better cancer classification than perfusion. We therefore hypothesize that dispersion characterizes vessels that are smaller than those visible with AA.  相似文献   
104.
105.
Background: Egyptian street youth use substances including tobacco, illicit drugs, and pharmaceutical drugs. To understand the circumstances, including adverse childhood experiences, that place adolescents at risk for engaging in substance use, we conducted in-depth interviews among a sample of Egyptian street children. Methods: From youth residing at or attending Caritas, a non-profit organization, which provides shelter and education to street youth, seven girls and twelve boys, aged 12–18 years, participated in open-ended, in-depth interviews. Results: Eight out of the 19 participants reported family history (early exposure) to substance use; and seven of them were initiated by either a family member (sibling), friend or coworker. Most of the participants reported a history of conflict with or abuse (verbal or physical) by their parents or siblings, or stressful situations at home; they used substance(s) to alleviate their stress. Few attended school, and some were forced to work and help their family. Conclusions: Among Egyptian youth, adverse childhood experiences, such as poverty, child abuse, and family substance use, challenge somewhat susceptible youths and lead them to the path of substance use and addiction. Prevention intervention should be multifaceted, culturally adaptable, and primarily targeting the social environment during childhood.  相似文献   
106.
107.
108.
Affinity peptide and protein‐ (APP) based radiotracers are an increasingly popular class of radiotracer in positron emission tomography (PET), which was once dominated by the use of small molecule radiotracers. Radiolabelled monoclonal antibodies (mAbs) are important examples of APPs, yet a preference for smaller APPs, which exhibit fast pharmacokinetics and permit rapid PET aided diagnosis, has become apparent. 18F exhibits favourable physical characteristics for APP radiolabelling and has been described as an ideal PET radionuclide. Notwithstanding, 18F radiolabelling of APP is challenging, and this is echoed in the literature where a number of diverse approaches have been adopted. This review seeks to assess and compare the approaches taken to 18F APP radiolabelling with the intention of highlighting trends within this expanding field. Generic themes have emerged in the literature, namely the use of mild radiolabelling conditions, a preference of site‐specific methodologies with an impetus for short, automated procedures which produce high‐yielding [18F]APPs.  相似文献   
109.
110.
Rheological behaviour of pharmaceutical semisolid preparations significantly affects manufacturing process, administration, stability, homogeneity of incorporated drug, accuracy of dosing, adhesion in the place of application, drug release, and resulting therapeutic effect of the product. We performed test of consistency by penetrometry, rotational, oscillation and creep tests, and squeeze and tack tests of model samples to introduce methods suitable for characterization and comparison of semisolids in practice. Penetrometry is a simple method allowing sorting the semisolids to low and high stress-resistant materials but deficient for rheological characterization of semisolids. Value of yield stress, generally considered to be appropriate feature of semisolids, is significantly influenced by the method of testing and the way of evaluation. The hysteresis loops of model semisolids revealed incomplete thixotropy, therefore, three-step thixotropy test was employed. Semisolids showed nonlinear response in the creep phase of tests and partial recovery of structure by storing energy in the recovery phase. Squeeze and tack tests seem to be convenient ways for comparison of semisolids. Our study can contribute to a better understanding of different flow behaviour of semisolids given by different physicochemical properties of excipients and can bring useful approaches to evaluation and comparison of semisolids in practice.  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