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   1951篇
  免费   124篇
  国内免费   15篇
耳鼻咽喉   5篇
儿科学   29篇
妇产科学   17篇
基础医学   241篇
口腔科学   21篇
临床医学   238篇
内科学   569篇
皮肤病学   30篇
神经病学   139篇
特种医学   62篇
外科学   257篇
综合类   18篇
预防医学   196篇
眼科学   31篇
药学   125篇
肿瘤学   112篇
  2023年   14篇
  2022年   22篇
  2021年   57篇
  2020年   38篇
  2019年   42篇
  2018年   45篇
  2017年   35篇
  2016年   45篇
  2015年   53篇
  2014年   64篇
  2013年   109篇
  2012年   146篇
  2011年   139篇
  2010年   76篇
  2009年   79篇
  2008年   130篇
  2007年   134篇
  2006年   125篇
  2005年   120篇
  2004年   117篇
  2003年   79篇
  2002年   78篇
  2001年   31篇
  2000年   32篇
  1999年   41篇
  1998年   21篇
  1997年   6篇
  1996年   7篇
  1995年   15篇
  1994年   11篇
  1993年   12篇
  1992年   23篇
  1991年   18篇
  1990年   23篇
  1989年   18篇
  1988年   8篇
  1987年   8篇
  1986年   4篇
  1985年   8篇
  1984年   7篇
  1983年   4篇
  1982年   8篇
  1981年   6篇
  1980年   2篇
  1978年   4篇
  1974年   4篇
  1973年   2篇
  1972年   2篇
  1969年   3篇
  1946年   2篇
排序方式: 共有2090条查询结果,搜索用时 62 毫秒
81.
The horizontal, shore-perpendicular change in shoreline position along the Outer Banks of North Carolina is found to be a self-affine signal. We measure shoreline change by determining the horizontal change in position of the 0.8-m contour sampled from shore-perpendicular profiles spaced at 20-m intervals along the coast. The profiles are obtained from two light detection and ranging surveys performed in September 1997 and September 1998. For six selected sections of coast, wavelet analysis of the shoreline change signal indicates the signal is self-affine with a scaling exponent that varies from 1.2 to 2.1. This self-affine behavior indicates that the shoreline change signal is nonstationary with long-range persistence. A stochastic diffusion model of sediment transport replicates the observed self-affine behavior observed south of Cape Hatteras (scaling exponent between 1.2 and 1.6) whereas a random walk model replicates the signal observed north of Cape Hatteras (scaling exponent approximately 2.0). Because of the finite nature of the data set, there are limits in space and time to the power law behavior of the system. Characteristics of such systems can be described by upper-truncated power laws, which yield the upper limits of power law behavior. Applying an upper-truncated power law to the data for one section of coast, we find an upper limit of 7 km for the maximum continuous alongshore distance eroding or accreting. For the same section of coast, we find upper limits of 25 m for the maximum shore-perpendicular erosion and 11 m for the maximum shore-perpendicular accretion during the study period.  相似文献   
82.
Delay in hematologic recovery after bone marrow transplantation (BMT) can extend and amplify the risks of infection and hemorrhage, compromise patients' survival, and increase the duration and cost of hospitalization. Because current studies suggest that granulocyte- macrophage (GM) colony-stimulating factor (CSF) may potentiate the sensitivity of hematopoietic progenitor cells to G-CSF, we performed a prospective, randomized trial comparing GM-CSF (250 micrograms/m2/d x 14 days) versus sequential GM-CSF x 7 days followed by G-CSF (5 micrograms/kg/d x 7 days) as treatment for primary or secondary graft failure after BMT. Eligibility criteria included failure to achieve a white blood cell (WBC) count > or = 100/microL by day +21 or > or = 300/microL by day +28, no absolute neutrophil count (ANC) > or = 200/microL by day +28, or secondary sustained neutropenia after initial engraftment. Forty-seven patients were enrolled: 23 received GM-CSF (10 unrelated, 8 related allogeneic, and 5 autologous), and 24 received GM- CSF followed by G-CSF (12 unrelated, 7 related allogeneic, and 5 autologous). For patients receiving GM-CSF alone, neutrophil recovery (ANC > or = 500/microL) occurred between 2 and 61 days (median, 8 days) after therapy, while those receiving GM-CSF+G-CSF recovered at a similar rate of 1 to 36 days (median, 6 days; P = .39). Recovery to red blood cell (RBC) transfusion independence was slow, occurring 6 to 250 days (median, 35 days) after enrollment with no significant difference between the two treatment groups (GM-CSF: median, 30 days; GM-CSF+G- CSF; median, 42 days; P = .24). Similarly, platelet transfusion independence was delayed until 4 to 249 days (median, 32 days) after enrollment, with no difference between the two treatment groups (GM- CSF: median, 28 days; GM-CSF+G-CSF: median, 42 days; P = .38). Recovery times were not different between patients with unrelated donors and those with related donors or autologous transplant recipients. Survival at 100 days after enrollment was superior after treatment with GM-CSF alone. Only 1 of 23 patients treated with GM-CSF died versus 7 of 24 treated with GM-CSF+G-CSF who died 16 to 84 days (median, 38 days) after enrollment, yielding Kaplan-Meier 100-day survival estimates of 96% +/- 8% for GM-CSF versus 71% +/- 18% for GM-CSF+G-CSF (P = .026). These data suggest that sequential growth factor therapy with GM-CSF followed by G-CSF offers no advantage over GM-CSF alone in accelerating trilineage hematopoiesis or preventing lethal complications in patients with poor graft function after BMT.(ABSTRACT TRUNCATED AT 400 WORDS)  相似文献   
83.
Schweyen  Ramona  Arnold  C.  Setz  J. M.  Hey  J. 《Clinical oral investigations》2019,23(3):1425-1434
Objectives

Stud attachments are often too adhesive and too susceptible to damage for use in geriatric patients, especially when implants are angulated. This study aimed to evaluate alternative anchoring systems comprising individual and prefabricated polyvinylsiloxane (PVS) attachments.

Materials and methods

A total of 182 specimens with individual PVS (IPVS) attachments (Shore hardness [SH] 25, SH50, SH65], prefabricated PVS (PPVS) attachments (SM green, yellow, and red), and Locator attachments (LR blue) were fabricated (n = 7 per group). Retention force was measured using the following parameters: insertion/removal (100, 200, 500, 1000, and 5000 cycles), thermal undulation (10,000 cycles at 5–55 °C; one implant per specimen), implant angulation (0°, 5°, and 10° convergence and divergence; two implants per specimen), and artificial saliva.

Results

Insertion/removal and thermal undulation caused no changes in retention force in SM green and IPVS subgroups; conversely, LR blue, SM red, and SM yellow attachments exhibited significant decreases in retention force of up to 66% (all P ≤ 0.001). Implant angulation produced relevant changes in retention force only in LR blue attachments. Artificial saliva caused a general decrease in retention force.

Conclusions

Retention force of low-retentive PVS attachments proved to be comparatively immune to dislocation and thermal undulation, as well as to implant angulation up to 10°.

Clinical relevance

Low-retentive PVS attachments could be a treatment option if reduced denture retention is required and/or if angulated implants are in place. Clinical studies are necessary to evaluate the materials’ durability under oral conditions.

  相似文献   
84.
85.
Coronavirus disease 2019 (COVID-19) continues to impact older adults disproportionately with respect to serious consequences ranging from severe illness and hospitalization to increased mortality risk. Concurrently, concerns about potential shortages of healthcare professionals and health supplies to address these issues have focused attention on how these resources are ultimately allocated and used. Some strategies, for example, misguidedly use age as an arbitrary criterion that disfavors older adults in resource allocation decisions. This is a companion article to the American Geriatrics Society (AGS) position statement, “Resource Allocation Strategies and Age-Related Considerations in the COVID-19 Era and Beyond.” It is intended to inform stakeholders including hospitals, health systems, and policymakers about ethical considerations that should be considered when developing strategies for allocation of scarce resources during an emergency involving older adults. This review presents the legal and ethical background for the position statement and discusses these issues that informed the development of the AGS positions: (1) age as a determining factor, (2) age as a tiebreaker, (3) criteria with a differential impact on older adults, (4) individual choices and advance directives, (5) racial/ethnic disparities and resource allocation, and (6) scoring systems and their impact on older adults. It also considers the role of advance directives as expressions of individual preferences in pandemics. J Am Geriatr Soc 68:1143–1149, 2020.  相似文献   
86.
We estimated interim influenza A vaccine effectiveness (VE) following a late sharp rise in cases during an influenza A(H3N2)-dominated 2021/22 season, after lifting COVID-19 restrictions. In children aged 2–6 years offered a live attenuated influenza vaccine, adjusted VE was 62.7% (95% CI: 10.9–84.4) in hospitalised and 64.2% (95% CI: 50.5–74.1) in non-hospitalised children. In non-hospitalised patients aged 7–44 years, VE was 24.8% (95% CI: 12.8–35.2); VE was non-significant in remaining age groups and hospital/non-hospital settings.  相似文献   
87.
Special materials are required in many applications to fulfill specific medical or industrial necessities. Biodegradable metallic materials present many attractive properties, especially mechanical ones correlated with good biocompatibility with vivant bodies. A biodegradable iron-based material was realized through electric arc-melting and induction furnace homogenization. The new chemical composition obtained presented a special property named SME (shape memory effect) based on the martensite transformation. Preliminary results about this special biodegradable material with a new chemical composition were realized for the chemical composition and structural and thermal characterization. Corrosion resistance was evaluated in Ringer’s solution through immersion tests for 1, 3, and 7 days, the solution pH was measured in time for 3 days with values for each minute, and electro-corrosion was measured using a potentiostat and a three electrode cell. The mass loss of the samples during immersion and electro-corrosion was evaluated and the surface condition was studied by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). SME was highlighted with differential scanning calorimetry (DSC). The results confirm the possibility of a memory effect of the materials in the wrought case and a generalized corrosion (Tafel and cyclic potentiometry and EIS) with the formation of iron oxides and a corrosion rate favorable for applications that require a longer implantation period.  相似文献   
88.
Lifetime prevalence rates of eating disorders and affective disorder were determined in biological relatives of probands with anorexia nervosa, affective disorder, and other types of psychiatric disturbance. Anorexia nervosa was found to cluster in families with intergenerational transmission, and was absent among relatives of controls. Significantly higher rates of affective disorder were found among relatives of anorexics with coexisting depression, suggesting that these probands transmit two disorders to relatives. The results indicate there is familial resemblance for anorexia nervosa, and that the liability is different from that operating in the transmission of affective disorders.  相似文献   
89.
90.
The present study aimed to determine whether an i.c.v. administration of allopregnanolone (ALLO) rapidly modifies the hypothalamic and ovarian 3β‐hydroxysteroid dehydrogenase (3β‐HSD) enzymatic activity and gene expression in in vivo and ex vivo systems in pro‐oestrus (PE) and dioestrus I (DI) rats. Animals were injected with vehicle, ALLO, bicuculline or bicuculline plus ALLO and were then killed. In the in vivo experiment, the hypothalamus, ovaries and serum were extracted and analysed. In the ex vivo experiment, the superior mesenteric ganglion ‐ ovarian nerve plexus ‐ ovary system was extracted and incubated during 120 minutes at 37 ºC. The serum and ovarian compartment fluids were used to determine progesterone by radioimmunoanalysis. In the in vivo experiments, ALLO caused a decrease in hypothalamic and ovarian 3β‐HSD enzymatic activity during PE. During DI, ALLO increased hypothalamic and ovarian 3β‐HSD activity and gene expression. The ovarian 3β‐HSD activity increased in both stages in the ex vivo system; gene expression increased only during DI. ALLO induced an increase in serum progesterone only in D1 and in the ovarian incubation liquids in both stages. All findings were reversed by an injection of bicuculline before ALLO. Ovarian steroidogenic changes could be attributed to signals coming from ganglion neurones, which are affected by the acute central neurosteroid stimulation. The i.c.v. administration of ALLO via the GABAergic system altered 3β‐HSD activity and gene expression, modulating the neuroendocrine axis. The present study reveals the action that ALLO exerts on the GABAA receptor in both the central and peripheral nervous system and its relationship with hormonal variations. ALLO is involved in the “fine tuning” of neurosecretory functions as a potent modulator of reproductive processes in female rats.  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