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   17874篇
  免费   1295篇
  国内免费   67篇
耳鼻咽喉   142篇
儿科学   548篇
妇产科学   542篇
基础医学   2483篇
口腔科学   292篇
临床医学   2035篇
内科学   3379篇
皮肤病学   478篇
神经病学   1799篇
特种医学   492篇
外科学   1879篇
综合类   113篇
一般理论   7篇
预防医学   1953篇
眼科学   423篇
药学   1055篇
  1篇
中国医学   19篇
肿瘤学   1596篇
  2024年   25篇
  2023年   234篇
  2022年   355篇
  2021年   687篇
  2020年   465篇
  2019年   584篇
  2018年   759篇
  2017年   512篇
  2016年   606篇
  2015年   670篇
  2014年   828篇
  2013年   1110篇
  2012年   1635篇
  2011年   1603篇
  2010年   815篇
  2009年   762篇
  2008年   1167篇
  2007年   1178篇
  2006年   1027篇
  2005年   948篇
  2004年   829篇
  2003年   752篇
  2002年   716篇
  2001年   87篇
  2000年   50篇
  1999年   76篇
  1998年   106篇
  1997年   101篇
  1996年   62篇
  1995年   52篇
  1994年   49篇
  1993年   56篇
  1992年   40篇
  1991年   25篇
  1990年   21篇
  1989年   19篇
  1987年   8篇
  1986年   18篇
  1985年   16篇
  1984年   18篇
  1983年   16篇
  1982年   23篇
  1981年   12篇
  1980年   10篇
  1979年   8篇
  1978年   11篇
  1977年   9篇
  1971年   9篇
  1969年   7篇
  1967年   8篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
OBJECTIVE: To evaluate the clinical efficacy and tolerability of topical gabapentin in the treatment of women with vulvodynia. METHODS: A retrospective study was designed to ascertain clinical responses to topical gabapentin. Patient demographic and medical characteristics, including present and prior treatment for vulvodynia, were routinely collected. The final outcome was defined by a comparison between pretreatment and posttreatment mean pain scores based on a discrete visual analog scale of 0 to 10. Categorical data were compared by Fisher exact test, continuous variables between groups by the Wilcoxon rank sum test, and mean change in pain score between pretreatment and posttreatment by paired Student t test. RESULTS: Between January 2001 and December 2006, 51 women with vulvodynia (19 or 37% with generalized vulvodynia, 32 or 63% with localized) were treated with 2% to 6% gabapentin. After a minimum of 8 weeks of therapy, the mean pain score among the 35 evaluable women was significantly reduced from 7.26 to 2.49 (mean change -4.77, 95% confidence interval -5.47 to -4.07). Overall, 28 of 35 (80%) demonstrated at least a 50% improvement in pain scores. Among patients with localized vulvodynia, sexual function improved in 17 of 20 with evaluable results (6 of 9 reinstituted vaginal intercourse, whereas all 11 patients experiencing decreased frequency of intercourse reported increased frequency after treatment). Discontinuations occurred in 7 of 50 (14%) treated. CONCLUSION: Topical gabapentin seems to be well-tolerated and associated with significant pain relief in women with vulvodynia. LEVEL OF EVIDENCE: III.  相似文献   
82.
ObjectiveWe evaluated the long-term results of sigmoid vaginoplasty in women with gynecologic malignancies after radical pelvic surgery, with specific focus on safety and effects of the procedure on patients' sexuality and self image.MethodsThis prospective study included women with gynecologic malignancies who underwent partial or complete colpectomy as part of the cancer treatment. In all cases a pedicled sigmoid loop was used for the neovaginal reconstruction. Systematic clinical examination was performed and validated questionnaires about sexuality (Female Sexual Function Index), quality of life (SF-12) and susceptibility to depression (ADSk-15) were answered by all patients at the earliest 6 months after vaginoplasty.ResultsSeven patients with sigmoid vaginoplasty, recruited between 11/2003 and 02/2008, were evaluated in the present analysis. Mean patients age was 48 ± 8.49 years. Mean neovaginal length was 6.4 cm (range: 2–12 cm). The mean Female Sexual Function Index (FSFI)-score of all patients was 16.6 ± 12.6. In the subset of sexually active patients the mean FSFI-score was 22.5 ± 9.4 higher. Regarding early operative morbidity and complications, sigmoid vaginal reconstruction appears to be a safe procedure, though in a long-term assessment 85% of the patients developed a vaginal stenosis with the need for operative bougienage.ConclusionsThe vaginal reconstruction using a sigmoid loop is a safe and well accepted procedure in patients with gynecologic malignancies. However lower sexuality scores seem to be achieved than in non-cancer patients after equivalent vaginoplasty. Cancer-related physical and psychological comorbidity seem to have negative effects on the overall outcome and patient's satisfaction.  相似文献   
83.
84.
Antenatal testing is a common component of care for the high-risk pregnancy. The goals of antenatal testing include the prevention of stillbirth and the detection of the hypoxic fetus to allow intervention before acidosis and long-term damage. Data regarding the efficacy of antenatal testing are limited by a lack of randomized controlled trials. The majority of available data hinge on observational studies with the inherent potential for bias. There is also a paucity of data comparing the various testing modalities and addressing the issue of the optimal timing of initiation of testing. As well, data are limited regarding the various conditions most likely to benefit from testing and the frequency with which testing should be performed. The issue of cost relating to antenatal testing is an important one. Central to the issue of estimating cost is an understanding of the efficacy of the test. Given our current limitations, we have significant difficulty accurately estimating the cost of antenatal testing; however, rough estimates of cost are made.  相似文献   
85.
OBJECTIVE: We studied hypophosphatasia (HP) mutations in 19 cases prenatally detected by ultrasonography without familial history of HP. We correlated the mutations with the reported ultrasound signs, and discussed genetic counseling with regard to the particular dominantly inherited prenatal benign form of HP. METHOD: The coding sequence of the tissue nonspecific alkaline phosphatase (TNSALP) gene was analyzed by DNA sequencing, and 3D modeling was used to locate the mutated amino acids with regard to the functional domains of TNSALP. RESULTS: Although reported ultrasound signs were heterogeneous, two mutated alleles were found in 18 of the 19 cases studied, indicating recessive transmission of the disease. Functional domains of TNSALP were affected by 74% of missense mutations. In all the cases, including one with only a heterozygous mutation, molecular, biological, and familial data do not corroborate the hypothesis of prenatal benign HP. The mutation c.1133A>T observed in the prenatal benign form of HP and common in USA was not found in this series. CONCLUSION: The results point out the prenatally detectable allelic heterogeneity of HP. The nature of the detected mutations and the evidence of recessive inheritance do not support these cases being affected with prenatal benign HP.  相似文献   
86.
87.
88.
The Global Health Research Initiative (GHRI) involving the Canadian International Development Agency, the Canadian Institutes of Health Research, Health Canada and the International Development Research Centre seeks to coordinate Canada's research response to global health challenges. In light of numerous calls to action both nationally and internationally, an orientation to applied health policy and systems research, and to public health research and its application is required to redress global inequalities in wealth and health and to tackle well-documented constraints to achieving the United Nations Millennium Development Goals. Over the last four years, the GHRI has funded close to 70 research program development and pilot projects. However, longer-term investment is needed. The proposed dollars 100 million Teasdale-Corti Global Health Research Partnership Program is such a response, and is intended to support teams of researchers and research users to develop, test and implement innovative approaches to strengthening institutional capacity, especially in low- and middle-income countries; to generating knowledge and its effective application to improve the health of populations, especially those most vulnerable; and to strengthen health systems in those countries. While Canada stands poised to act, concerted leadership and resources are still required to support "research that matters" for health and development in low- and middle-income countries.  相似文献   
89.
Understanding the evaporation process of binary sessile droplets is essential for optimizing various technical processes, such as inkjet printing or heat transfer. Liquid mixtures whose evaporation and wetting properties may differ significantly from those of pure liquids are particularly interesting. Concentration gradients may occur in these binary droplets. The challenge is to measure concentration gradients without affecting the evaporation process. Here, spectroscopic methods with spatial resolution can discriminate between the components of a liquid mixture. We show that confocal Raman microscopy and spatially resolved NMR spectroscopy can be used as complementary methods to measure concentration gradients in evaporating 1-butanol/1-hexanol droplets on a hydrophobic surface. Deuterating one of the liquids allows analysis of the local composition through the comparison of the intensities of the C–H and C–D stretching bands in Raman spectra. Thus, a concentration gradient in the evaporating droplet was established. Spatially resolved NMR spectroscopy revealed the composition at different positions of a droplet evaporating in the NMR tube, an environment in which air exchange is less pronounced. While not being perfectly comparable, both methods—confocal Raman and spatially resolved NMR experiments—show the presence of a vertical concentration gradient as 1-butanol/1-hexanol droplets evaporate.

Evaporating droplets occur in various contexts such as inkjet printing (1, 2), heat transfer, or daily phenomena such as drying coffee stains (3, 4). In many applications, such as painting (5), cleaning, gluing, or printing (6), where liquid mixtures are used, the evaporation of a droplet is a complex process because the concentration profile within the droplet varies over time. To improve the controllability and predictability of the technical processes, it is essential to characterize the transport phenomena during the drying process. The measurement of the droplet composition is a crucial element and has to be carried out with sufficient spatial and temporal resolution. In particular, spectroscopic methods are promising tools for contactless concentration measurements of liquid mixtures.The evaporation of a droplet is governed by physical properties such as surface tension (7), density (810), vapor pressure (11), and boiling temperature. Additionally, concentration gradients can evolve in liquid mixtures (12). These gradients are driven by thermal gradients due to the enthalpy of evaporation (droplet cooling) or on heated surfaces, by surface tension gradients induced by preferential evaporation of one component or by density gradients for droplets composed of liquids with different densities like water and glycerol (13). The evaporation rates of the components can vary over the droplet surface. For sessile droplets with contact angles smaller than 90°, for example, the evaporation rates are higher at the three-phase contact line (14). These thermal or surface tension gradients can induce flow inside the droplet called Marangoni flow. This flow leads to concentration gradients across the droplet (710). The direction of the gradient depends on the density and surface tension. A direct application of this principle is, for instance, Marangoni cleaning in semiconductor technology (15).The investigation of the composition of sessile drops on the microliter scale, as they occur in inkjet printing or other technical processes, poses a challenge because the typical length scales of interest are smaller than the capillary length. In bulk samples, the composition can be examined in a straightforward manner with chromatographic methods such as gas chromatography and high-performance liquid chromatography or spectroscopic methods such as NMR spectroscopy, infrared spectroscopy, and Raman spectroscopy. However, for the investigation of sessile droplets, a high spatial and temporal resolution is required. For this purpose, confocal Raman spectroscopy and spatially resolved NMR spectroscopy are powerful tools. For both techniques, concentration determination is straightforward if at least two signals of the components of interest are baseline-separated. NMR is intrinsically calibration-free, whereas Raman spectroscopy requires calibration through reference experiments (1618). Both approaches allow the quantification of concentration gradients in sessile droplets, as is shown here.In Raman microscopy, good spatial resolution can be achieved in a confocal setup. The components of mixtures can be distinguished via specific vibrations for different functional groups or through a careful analysis of the Raman signals in the fingerprint region (<1,500 cm−1). For example, binary mixtures of ethanol and water can be characterized in a straightforward manner (17). If, however, both liquids have a similar chemical structure, the discrimination of the components might be hampered by signal overlap in the C–H stretching region (2,800 to 3,000 cm−1); e.g., in such cases, Raman signals in the fingerprint region (<1,500 cm−1) might be used for the identification of the species. However, these signals often provide a poor signal-to-noise ratio, which makes large integration times necessary. Thus, the image rate or resolution is so low that even slow diffusion processes are hardly resolved. Here, Raman stable isotope probing (SIP), which has been developed to monitor metabolic processes in microbiology, offers a solution (19). The basic idea of Raman SIP is to replace the proton in the C–H with deuterium in one of the mixture components such that the C–D stretching region occurs at roughly 1/2 times the C–H stretching and falls into a region with very weak or even without signals from the protonated liquid component. Thus, the concentration in a binary mixture can be calculated in a straightforward manner from the ratio of the integrated Raman intensities ICD/ICH of the respective stretching vibrations.Compared to Raman microscopy, where localization is achieved by scanning the focal point across the region of interest, in NMR experiments localization is achieved by using magnetic field gradients. Usually, one avoids phase boundaries (especially liquid–gas interfaces) in NMR experiments because they disturb the magnetic field homogeneity and reduce the spectral quality in terms of line shape and baseline separation of the resonances. Nevertheless, it has been shown that MRI can be used to characterize freezing water droplets (20), the infiltration of water into asphalts (21), and the evaporation of sessile droplets from porous surfaces (2224). Additionally, NMR can be used to quantify the composition of binary droplets during evaporation (25).Thus, the use of both complementary approaches to characterize evaporating binary droplets may be beneficial. In this article, we discuss the capabilities of Raman SIP and NMR techniques to analyze the evolution of the composition of an evaporating sessile binary droplet. As a model system, a binary mixture of 1-butanol and 1-hexanol was used. This mixture shows a low volatility such that the evaporation process can be captured with both Raman and NMR spectroscopies. With Raman spectroscopy, it was possible to observe concentration gradients of 1-butan-d9-ol over the height of the droplet during evaporation. NMR techniques were examined in terms of the capability to observe the evaporation of 1-butanol and yield time-dependent droplet composition with spatially resolved 1H-NMR spectra. Furthermore, the contours of the evaporating droplets were tracked by optical measurements to characterize the time-dependent changes in the droplet dimensions. Flows induced by the concentration gradients were confirmed by astigmatic particle tracking velocimetry.  相似文献   
90.
Collagen peptide mass fingerprinting by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry, also known as zooarchaeology by mass spectrometry (ZooMS), is a rapidly growing analytical technique in the fields of archaeology, ecology, and cultural heritage. Minimally destructive and cost effective, ZooMS enables rapid taxonomic identification of large bone assemblages, cultural heritage objects, and other organic materials of animal origin. As its importance grows as both a research and a conservation tool, it is critical to ensure that its expanding body of users understands its fundamental principles, strengths, and limitations. Here, we outline the basic functionality of ZooMS and provide guidance on interpreting collagen spectra from archaeological bones. We further examine the growing potential of applying ZooMS to nonmammalian assemblages, discuss available options for minimally and nondestructive analyses, and explore the potential for peptide mass fingerprinting to be expanded to noncollagenous proteins. We describe the current limitations of the method regarding accessibility, and we propose solutions for the future. Finally, we review the explosive growth of ZooMS over the past decade and highlight the remarkably diverse applications for which the technique is suited.  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