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   9847篇
  免费   482篇
  国内免费   96篇
耳鼻咽喉   95篇
儿科学   187篇
妇产科学   171篇
基础医学   1138篇
口腔科学   237篇
临床医学   853篇
内科学   2802篇
皮肤病学   165篇
神经病学   1063篇
特种医学   317篇
外科学   1202篇
综合类   28篇
预防医学   456篇
眼科学   114篇
药学   629篇
中国医学   43篇
肿瘤学   925篇
  2023年   72篇
  2022年   168篇
  2021年   289篇
  2020年   169篇
  2019年   208篇
  2018年   275篇
  2017年   188篇
  2016年   245篇
  2015年   303篇
  2014年   342篇
  2013年   525篇
  2012年   804篇
  2011年   707篇
  2010年   438篇
  2009年   421篇
  2008年   637篇
  2007年   679篇
  2006年   596篇
  2005年   662篇
  2004年   565篇
  2003年   476篇
  2002年   456篇
  2001年   94篇
  2000年   85篇
  1999年   73篇
  1998年   94篇
  1997年   78篇
  1996年   45篇
  1995年   53篇
  1994年   47篇
  1993年   36篇
  1992年   44篇
  1991年   50篇
  1990年   40篇
  1989年   38篇
  1988年   37篇
  1987年   40篇
  1986年   32篇
  1985年   38篇
  1984年   26篇
  1983年   22篇
  1982年   21篇
  1981年   25篇
  1980年   37篇
  1979年   15篇
  1978年   11篇
  1977年   12篇
  1976年   12篇
  1975年   13篇
  1974年   7篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
The determinants of the susceptibility to severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) infection and severe coronavirus disease 2019 (COVID-19) manifestations are yet not fully understood. Amino-bisphosphonates (N-BPs) have anti-inflammatory properties and have been shown to reduce the incidence of lower respiratory infections, cardiovascular events, and cancer. We conducted a population-based retrospective observational cohort study with the primary objective of determining if oral N-BPs treatment can play a role in the susceptibility to development of severe COVID-19. Administrative International Classification of Diseases, Ninth Revision, Clinical ModificationI (ICD-9-CM) and anatomical-therapeutic chemical (ATC) code data, representative of Italian population (9% sample of the overall population), were analyzed. Oral N-BPs (mainly alendronate and risedronate) were included in the analysis, zoledronic acid was excluded because of the low number of patients at risk. Incidence of COVID-19 hospitalization was 12.32 (95% confidence interval [CI], 9.61–15.04) and 11.55 (95% CI, 8.91–14.20), of intensive care unit (ICU) utilization because of COVID-19 was 1.25 (95% CI, 0.38–2.11) and 1.42 (95% CI, 0.49–2.36), and of all-cause death was 4.06 (95% CI, 2.50–5.61) and 3.96 (95% CI, 2.41–5.51) for oral N-BPs users and nonusers, respectively. Sensitivity analyses that excluded patients with prevalent vertebral or hip fragility fractures and without concomitant glucocorticoid treatment yielded similar results. In conclusion, we found that the incidence of COVID-19 hospitalization, intensive care unit (ICU) utilization, and COVID-19 potentially related mortality were similar in N-BPs–treated and nontreated subjects. Similar results were found in N-BPs versus other anti-osteoporotic drugs. We provide real-life data on the safety of oral N-BPs in terms of severe COVID-19 risk on a population-based cohort. Our results do not support the hypothesis that oral N-BPs can prevent COVID-19 infection and/or severe COVID-19; however, they do not seem to increase the risk. © 2021 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).  相似文献   
82.
BackgroundWe aim to evaluate the impact of multiparametric magnetic resonance imaging and fusion-target biopsy for early reclassification of patients with low-risk Prostate Cancer in a randomized trial.Materials and methodsBetween 2015 and 2018, patients diagnosed with Prostate Cancer after random biopsy fulfilling PRIAS criteria were enrolled and centrally randomized (1:1 ratio) to study group or control group. Patients randomized to study group underwent multiparametric magnetic resonance imaging at 3 months from enrollment: patients with positive findings (PIRADS-v2>2) underwent fusion-target biopsy; patients with negative multiparametric magnetic resonance imaging or confirmed ISUP - Grade Group 1 at fusion-target biopsy were managed according to PRIAS schedule and 12-core random biopsy was performed at 12 months. Patients in control group underwent PRIAS protocol, including a confirmatory 12-core random biopsy at 12 months. Primary endpoint was a reduction of reclassification rate at 12-month random biopsy in study group at least 20% less than controls. Reclassification was defined as biopsy ISUP Grade Group 1 in >2 biopsy cores or disease upgrading.ResultsA total of 124 patients were randomized to study group (n = 62) or control group (n = 62). Around 21 of 62 patients (34%) in study group had a positive multiparametric magnetic resonance imaging, and underwent fusion-target biopsy, with 11 (17.7%) reclassifications. Considering the intention-to-treat population, reclassification rate at 12-month random biopsy was 6.5% for study group and 29% for control group, respectively (P < 0.001).ConclusionsThe early employment of multiparametric magnetic resonance imaging for active surveillance patients enrolled after random biopsy consents to significantly reduce reclassifications at 12-month random biopsy.  相似文献   
83.

Since the emergence of the COVID-19 pandemic, there has been an increasing body of research focused on the effects that measures like stay-at-home orders and social distancing are having on other aspects of health, including mental health and sexual health. Currently, there are limited extant data on the effects of the pandemic on sexual and gender minorities. Between April 15, 2020, and May 15, 2020, we invited participants in an ongoing U.S. national cohort study (Together 5000) to complete a cross-sectional online survey about the pandemic, and its effects on mental and sexual health and well-being (n?=?3991). Nearly all (97.7%) were living in an area where they were told they should only leave their homes for essentials. Most (70.1%) reported reducing their number of sex partners as a result of the pandemic. Among the 789 participants prescribed HIV pre-exposure prophylaxis (PrEP), 29.9% said they stopped taking their PrEP entirely, and 14.2% started selectively skipping doses. For those who had been taking PrEP, discontinuing PrEP was associated with having no new sex partners (β?=?0.90, 95% CI 0.40–1.40). Among the 152 HIV-positive participants, 30.9% said they were unable to maintain an HIV-related medical appointment because of the pandemic and 13.8% said they had been unable to retrieve HIV medications. Additionally, 35.3% of participants were experiencing moderate to severe anxiety because of the pandemic and 36.7% reported symptoms of depression. In a multivariable logistic regression, reporting a new sex partner in the prior 30 days was significantly associated with being aged 30 or older (vs. not, AOR?=?1.21), being Black (AOR?=?1.79) or Latinx (AOR?=?1.40, vs. white), and being unsure if they had been in close contact with someone diagnosed with COVID-19 (AOR?=?1.32, vs. no contact). It was unassociated with COVID-19-induced anxiety, depression, or knowing someone hospitalized with COVID-19. The pandemic has caused disruptions in sexual behavior (partner reduction) as well as difficulties navigating PrEP and HIV care continua. Findings will guide more comprehensive public health responses to optimize HIV prevention and treatment in the era of COVID-19.

  相似文献   
84.
Dendritic cells (DC) are key components of innate and adaptive immune responses. Plasmacytoid DC (PDC) are a specialized DC subset that produce high amounts of type I interferons in response to microbes. High mobility group box 1 protein (HMGB1) is an abundant nuclear protein, which acts as a potent pro-inflammatory factor when released extracellularly. We show that HMGB1 leaves the nucleus of maturing PDC following TLR9 activation, and that PDC express on the plasma membrane the best-characterized receptor for HMGB1, RAGE. Maturation and type I IFN secretion of PDC is hindered when the HMGB1/RAGE pathway is disrupted. These results reveal HMGB1 and RAGE as the first known autocrine loop modulating the maturation of PDC, and suggest that antagonists of HMGB1/RAGE might have therapeutic potential for the treatment of systemic human diseases.  相似文献   
85.
The spin-echo procedure is the basic technique in a magnetic resonance (MR) study (the magnetization vector is flipped by 90° onto the ortogonal plane to the main magnetic field). Very soon after the MR procedure was developed, it was pointed out how important it is to achieve the needed contrast with shorter repetition times (TRs) to reduce the imaging time. Recently, fast imaging techniques have been introduced (partial flip angles, short TRs, and the lack of 180° radiofrequency pulses to refocus the spins are their main characteristics; the spins are refocused by the application of a gradient reversal technique). These techniques are particularly needed in pediatric neuroradiology, where the examination time must be as short as possible. At present, partial flip-angle techniques are almost completely replacing the conventional spin-echo procedure, but the variations in flip angle could result in a change in contrast. For these reasons, conventional spin-echo techniques may still be useful in a routine MR study.Presented at the 11th Meeting of the European Society for Paediatric Neurosurgery, Naples 1988  相似文献   
86.
In the human neuroblastoma cell line SK-N-BE(2), arachidonic acid (AA), supplied in the medium at micromolar concentrations, markedly ehnanced [14C]stearic acid (SA) (but not [14C]palmitic acid or [14C]oleic acid) incorporation into phosphatidylinositol (PtdIns). AA failed to stimulate [14C]SA incorporation into PtdIns precursors, namely phosphatidic acid and cytidinediphosphodiacylglycerol; furthermore, enhanced [14C]SA incorporation, brought about by exogenously administered AA, was not restricted to PtdIns tetraenoic species. When cells were pulsed for 1 h with [14C]SA (either in the presence or absence of AA) and then reincubated in AA- and [14C]SA-free medium, a marked loss of radioactivity from PtdIns was observed, that however was restricted to molecular species other than tetraenoic. These results are discussed in the light of possible mechanisms through which PtdIns achieves the 1-stearoyl-2-arachidonoyl configuration.  相似文献   
87.
Stimulation of SK-N-BE(2) cells with 1 mM carbachol (Cch) elicited phosphoinositide (PPI) hydrolysis and a rapid elevation of cytosolic Ca2+ concentration ([Ca2+]i) from 115 nM to about 500 nM, followed by a plateau around 200 nM. In myo [3H]inositol-labelled cells, Cch-evoked accumulation of [3H]inositol phosphates (IPs) was not affected when [Ca2+]i was clamped at resting by cell loading with 10 M BAPTA/AM; under these conditions, maximal 1,4,5-inositol trisphosphate accumulation was not reduced either. When [Ca2+]i was clamped around 700 nM by cell treatment with 600 nM ionomycin, Cch-evoked [3H]IPs accumulation was enhanced by less than 20%, but it was impaired by a 30% and a 55% after [Ca2+]i reduction to about 70 nM and 35—50 nM, by cell loading with 20 M or 40 M BAPTA/AM, respectively. These results show that, in SK-N-BE(2) cells, Cch-activated PPI-specific phospholipase C is sensitive to [Ca2+]i but it already operates under suboptimal conditions at resting [Ca2+]i.  相似文献   
88.
A focus group comprised of persons who use power wheelchairs and professionals working in the field were asked to participate in a brainstorming session to determine priorities for the development and application of power mobility input devices and control concepts. The group consensus was that durability and reliability are the most important criteria. Essentially, the expectation is that a power wheelchair must work everyday in the way a person needs it and wants it. At the same time, there is a desire to enhance and advance the features of input devices and control systems. Many would say these changes constitute designing "smarter" power wheelchairs, such as systems that can independently detect obstacles and can provide users with more feedback. This paper presents the rationale behind forming this focus group and details of the results of a brainstorming session where ideas were generated and prioritized. The five most important issues as determined by the group are discussed in depth.  相似文献   
89.
Potentials were measured with nonpolarizable salt electrodes (agar KCl-AgCl) during the estral cycle and pregnancy of the rat. The vaginal fundus is positive in regard to the external end of the vagina and does not present changes associated with the estral cycle. Vaginal-tongue potentials present biphasic cyclic changes associated with the estral cycle, the vagina being (-) during estro and (+) during diestro. Vaginal-abdominal skin potentials present monophasic modifications associated with the estral cycle. Vaginal-tongue potentials registered during pregnancy were (-) on the first day of pregnancy, (+) throughout pregnancy, and (-) on the first day postpartum.  相似文献   
90.
A renal tumor developing in a patient receiving cyclophosphamide (Cytoxan) therapy for Wegener granulomatosis is reported. The tumor was similar histologically to the "immunoblastic" sarcoma that develops in renal allograft recipients as a complication of immunosuppressive therapy. This case report strengthens the cause and effect relationship between immunosuppressive drug usage and the subsequent development of neoplasia.  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