全文获取类型
收费全文 | 37352篇 |
免费 | 2945篇 |
国内免费 | 114篇 |
专业分类
耳鼻咽喉 | 403篇 |
儿科学 | 975篇 |
妇产科学 | 668篇 |
基础医学 | 4901篇 |
口腔科学 | 775篇 |
临床医学 | 3583篇 |
内科学 | 7745篇 |
皮肤病学 | 531篇 |
神经病学 | 4290篇 |
特种医学 | 1501篇 |
外国民族医学 | 4篇 |
外科学 | 5259篇 |
综合类 | 801篇 |
一般理论 | 71篇 |
预防医学 | 3272篇 |
眼科学 | 783篇 |
药学 | 2209篇 |
中国医学 | 59篇 |
肿瘤学 | 2581篇 |
出版年
2023年 | 153篇 |
2022年 | 232篇 |
2021年 | 559篇 |
2020年 | 318篇 |
2019年 | 561篇 |
2018年 | 701篇 |
2017年 | 538篇 |
2016年 | 585篇 |
2015年 | 660篇 |
2014年 | 988篇 |
2013年 | 1556篇 |
2012年 | 2323篇 |
2011年 | 2502篇 |
2010年 | 1329篇 |
2009年 | 1253篇 |
2008年 | 2381篇 |
2007年 | 2460篇 |
2006年 | 2404篇 |
2005年 | 2641篇 |
2004年 | 2327篇 |
2003年 | 2160篇 |
2002年 | 2163篇 |
2001年 | 541篇 |
2000年 | 457篇 |
1999年 | 493篇 |
1998年 | 515篇 |
1997年 | 457篇 |
1996年 | 435篇 |
1995年 | 420篇 |
1994年 | 335篇 |
1993年 | 318篇 |
1992年 | 379篇 |
1991年 | 358篇 |
1990年 | 346篇 |
1989年 | 308篇 |
1988年 | 304篇 |
1987年 | 295篇 |
1986年 | 259篇 |
1985年 | 270篇 |
1984年 | 301篇 |
1983年 | 263篇 |
1982年 | 307篇 |
1981年 | 303篇 |
1980年 | 250篇 |
1979年 | 179篇 |
1978年 | 175篇 |
1977年 | 126篇 |
1976年 | 137篇 |
1974年 | 128篇 |
1973年 | 103篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Celia F Hybels Dan G Blazer Carl F Pieper Bruce M Burchett Judith C Hays Gerda G Fillenbaum Laura D Kubzansky Lisa F Berkman 《The American journal of geriatric psychiatry》2006,14(6):498-506
OBJECTIVE: Neighborhood sociodemographic characteristics may be important to the mental health of older adults who have decreased mobility and fewer resources. Our objective was to examine the association between neighborhood context and level of depressive symptomatology in older adults in a diverse geographic region of central North Carolina. METHODS: The sample included 2,998 adults 65 or older residing in 91 census tracts. Depressive symptoms were measured using the Center for Epidemiologic Studies-Depression scale (CES-D). Neighborhoods were characterized by five census-based characteristics: socioeconomic disadvantage, socioeconomic advantage, racial/ethnic heterogeneity, residential stability, and age structure. RESULTS: In ecologic level analyses, level of census tract socioeconomic disadvantage was associated with increased depressive symptoms. To determine whether neighborhood context was associated with depressive symptoms independently of individual characteristics, the authors used multilevel modeling. The authors examined the ability of each of five neighborhood (level 2) characteristics to predict a level 1 outcome (CES-D symptoms) controlling for the effects of individual (level 1) characteristics. Younger age, being widowed, lower income, and having some functional limitations were associated with increased depression symptoms conditional on census tract random effects. However, none of the neighborhood characteristics was significantly associated with depression symptoms, conditional on census tract random effects, either unadjusted or adjusted for individual characteristics. CONCLUSION: Any observed association between neighborhood sociodemographic characteristics and individual depressive symptoms in our sample may reflect the characteristics of the individuals who reside in the neighborhood rather than the neighborhood characteristics themselves. The use of multilevel modeling is important to separate these effects. 相似文献
12.
The effect of bracing on proprioception of knees with anterior cruciate ligament injury. 总被引:2,自引:0,他引:2
Bruce D Beynnon Lars Good May Arna Risberg 《The Journal of orthopaedic and sports physical therapy》2002,32(1):11-15
This paper is a comprehensive review on the effect of bandaging, bracing, and neoprene sleeves on knee proprioception following anterior cruciate ligament (ACL) injury and reconstruction with a focus on studies that have measured joint position sense and threshold to detection of passive knee motion. Disruption of the ACL does not appear to alter joint position sense soon after injury, although there is evidence that in some subjects deterioration may occur over time. An ACL tear creates a deficit in the threshold to detection of passive knee motion soon after injury and in those with chronic tears. The magnitude of worsening is less then 1.0 degree of movement in flexion-extension and of questionable concern from a clinical and functional perspective. Application of a functional brace or neoprene sleeve to the ACL-deficient limb does not improve the threshold to detection of passive knee motion; however, application of an elastic bandage to a knee with an ACL tear improves joint position sense. Reconstruction of a torn ACL is associated with a deficit in the threshold to detection of passive knee motion, and during the first year of healing the use of a neoprene sleeve provides improvement. Two years following ACL reconstruction there is no deficit in the threshold to detection of passive knee motion and the use of a brace has no effect on this outcome. 相似文献
13.
Multilocus DNA fingerprinting reveals high rate of heritable genetic mutation in herring gulls nesting in an industrialized urban site. 总被引:4,自引:0,他引:4
下载免费PDF全文
![点击此处可从《Proceedings of the National Academy of Sciences of the United States of America》网站下载免费的PDF全文](/ch/ext_images/free.gif)
C L Yauk J S Quinn 《Proceedings of the National Academy of Sciences of the United States of America》1996,93(22):12137-12141
Genotoxins, such as polycyclic aromatic compounds, are ubiquitous in urban and industrial environments. Our understanding of the role that these chemicals play in generating DNA sequence mutations is predominantly derived from laboratory studies with specific genotoxins or extracts of contaminants from environmental media. Most assays are not indicative of the germinal effects of exposure in situ to complex mixtures of common environmental mutagens. Using multilocus DNA fingerprinting, we found the mutation rate in herring gulls inhabiting a heavily industrialized urban harbor (Hamilton Harbour, Ontario) to be more than twice as high as three rural sites: Kent Island, Bay of Fundy; Chantry Island, Lake Huron; and Presqu'ile Provincial Park in Lake Ontario. Overall we found a mutation rate of 0.017 +/- 0.004 per offspring band in Hamilton, 0.006 +/- 0.002 at Kent Island, 0.002 +/- 0.002 from Chantry Island, and 0.004 +/- 0.002 from Presqu'ile Provincial Park. The mutation rate from the rural sites (pooled) was significantly lower than the rate observed in Hamilton Harbour (Fisher's exact test, two-tailed; P = 0.0006). These minisatellite DNA mutations may be important biomarkers for heritable genetic changes resulting from in situ exposure to environmental genotoxins in a free-living vertebrate species. 相似文献
14.
N A Athanasou C A Wells J Quinn D P Ferguson A Heryet J O McGee 《British journal of cancer》1989,59(4):491-498
The origin and nature of osteoclast-like multinucleated giant cells (OMGCs), in extraskeletal neoplasms, is uncertain. The ultrastructure, antigenic phenotype and function of OMGCsm in a breast carcinoma were studied in order to clarify the relationship between OMGCs, osteoclasts and other cells of the mononuclear phagocyte system (MPS). OMGCs resorbed cortical bone in a manner similar to osteoclasts. However, unlike osteoclasts, OMGCs did not possess a ruffled border or clear zone, and expressed HLA-DR and Fc receptors and CD14, CD16, CD18 and CD11 (p150,95) antigens. In addition, OMGCs failed to respond morphologically to calcitonin and were directly stimulated by parathyroid hormone (PTH) to increase bone resorption. These findings suggest that OMGCs are a specific type of macrophage polykaryon distinct from both osteoclasts and other types of inflammatory polykaryon. Occasional smaller (20-25 microns) macrophage-like cells were also associated with resorption pits. Bone resorption by OMGCs isolated from the breast indicates that a cell of the MPS can be transplanted to a new tissue location and perform a highly specialised function appropriate to an MPS cell of that tissue (i.e. the osteoclast). PTH stimulation of bone resorption by OMGCs suggests that PTH or a PTH-like protein, may be involved in the bone resorption and consequent hypercalcaemia associated with metastatic breast cancer. 相似文献
15.
16.
The Broad Spectrum of Quality in Deceased Donor Kidneys 总被引:7,自引:6,他引:1
Jesse D. Schold Bruce Kaplan Rajendra S. Baliga Herwig-Ulf Meier-Kriesche 《American journal of transplantation》2005,5(4):757-765
The quality of the deceased donor organ clearly is one of the most crucial factors in determining graft survival and function in recipients of a kidney transplant. There has been considerable effort made towards evaluating these organs culminating in an amendment to allocation policy with the introduction of the expanded criteria donor (ECD) policy.
Our study, from first solitary adult deceased donor transplant recipients from 1996 to 2002 in the National Scientific Transplant Registry database, presents a donor kidney risk grade based on significant donor characteristics, donor–recipient matches and cold ischemia time, generated directly from their risk for graft loss. We investigated the impact of our donor risk grade in a naïve cohort on short- and long-term graft survival, as well as in subgroups of the population.
The projected half-lives for overall graft survival in recipients by donor risk grade were I (10.7 years), II (10.0 years), III (7.9 years), IV (5.7 years) and V (4.5 years). This study indicates that there is great variability in the quality of deceased donor kidneys and that the assessment of risk might be enhanced by this scoring system as compared to the simple two-tiered system of the current ECD classification. 相似文献
Our study, from first solitary adult deceased donor transplant recipients from 1996 to 2002 in the National Scientific Transplant Registry database, presents a donor kidney risk grade based on significant donor characteristics, donor–recipient matches and cold ischemia time, generated directly from their risk for graft loss. We investigated the impact of our donor risk grade in a naïve cohort on short- and long-term graft survival, as well as in subgroups of the population.
The projected half-lives for overall graft survival in recipients by donor risk grade were I (10.7 years), II (10.0 years), III (7.9 years), IV (5.7 years) and V (4.5 years). This study indicates that there is great variability in the quality of deceased donor kidneys and that the assessment of risk might be enhanced by this scoring system as compared to the simple two-tiered system of the current ECD classification. 相似文献
17.
18.
Comparison of 2-dimensional and 3-dimensional acquisition for 18F-FDG PET oncology studies performed on an LSO-based scanner. 总被引:1,自引:0,他引:1
Martin A Lodge Ramsey D Badawi Richard Gilbert Pablo E Dibos Bruce R Line 《Journal of nuclear medicine》2006,47(1):23-31
Three-dimensional (3D) PET acquisition has the potential to reduce image noise but the advantage of 3D PET for studies outside the brain has not been well established. To compare the performance of 2-dimensional (2D) and 3D acquisition for whole-body (18)F-FDG applications, a series of patient studies were performed using a lutetium oxyorthosilicate (LSO)-based tomograph. METHODS: Comparative 2D and 3D images were acquired for 27 oncology patients using an LSO-based tomograph. Data acquisition (350-650 keV, 6 ns) started 99 +/- 12 min (mean +/- SD) after injection of 624 +/- 76 MBq (18)F-FDG. Bias caused by tracer redistribution and decay was eliminated by acquiring dynamic data over a single-bed position using a protocol that alternated between septa-in and septa-out modes (2D, 3D, 2D, 3D, 2D, 3D). Frames were combined to form 8 statistically independent sinograms: four 2D replicates (105 s) and four 3D replicates (90 s). The different frame durations in 2D and 3D compensated for the different number of overlapping bed positions required for an 85-cm whole-body study. Images were reconstructed with either 2D or fully 3D ordered-subsets expectation maximization (2 iterations and 8 subsets; 2D 6-mm gaussian, 3D 5- and 6-mm gaussian). Image target-to-background ratio was assessed by dividing the lesion maximum by the mean within a neighboring background region. Image noise was assessed by applying background regions of interest to the replicate images and calculating the within-patient coefficient of variation. RESULTS: The difference in target-to-background ratio between the 2D and 3D images, when they were filtered with 6-mm and 5-mm gaussian filters, respectively, was not highly statistically significant (P = 0.16). The mean ratio of 3D to 2D image values was 0.94 with 95% limits of agreement of 0.63-1.41. The within-patient coefficients of variation for the 2D and 3D images were 13% +/- 15% and 9% +/- 10%, respectively (P = 0.0005). CONCLUSION: Under conditions of matched target to-to-background ratios, the 3D mode was found to produce images with significantly less variability than the 2D mode. These data provide support for the use of 3D acquisition with LSO detectors to reduce scan times in whole-body (18)F-FDG applications. 相似文献
19.
Yubin Miao Said D Figueroa Darrell R Fisher Herbert A Moore Richard F Testa Timothy J Hoffman Thomas P Quinn 《Journal of nuclear medicine》2008,49(5):823-829
Peptide-targeted alpha-therapy with 7.4 MBq of (212)Pb-[1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid]-ReO-[Cys(3,4,10),d-Phe(7),Arg(11)]alpha-MSH(3-13) ((212)Pb-DOTA-Re(Arg(11))CCMSH) cured 45% of B16/F1 murine melanoma-bearing C57 mice in a 120-d study, highlighting its melanoma treatment potential. However, there is a need to develop an imaging surrogate for patient-specific dosimetry and to monitor the tumor response to (212)Pb-DOTA-Re(Arg(11))CCMSH therapy. The purpose of this study was to evaluate the potential of (203)Pb-DOTA-Re(Arg(11))CCMSH as a matched-pair SPECT agent for (212)Pb-DOTA-Re(Arg(11))CCMSH. METHODS: DOTA-Re(Arg(11))CCMSH was labeled with (203)Pb in 0.5 M NH(4)OAc buffer at pH 5.4. The internalization and efflux of (203)Pb-DOTA-Re(Arg(11))CCMSH were determined in B16/F1 melanoma cells. The pharmacokinetics of (203)Pb-DOTA-Re(Arg(11))CCMSH was examined in B16/F1 melanoma-bearing C57 mice. A micro-SPECT/CT study was performed with (203)Pb-DOTA-Re(Arg(11))CCMSH in a B16/F1 melanoma-bearing C57 mouse at 2 h after injection. RESULTS: (203)Pb-DOTA-Re(Arg(11))CCMSH was easily prepared in NH(4)OAc buffer and completely separated from the excess nonradiolabeled peptide by reversed-phase high-performance liquid chromatography (RP-HPLC). (203)Pb-DOTA-Re(Arg(11))CCMSH displayed fast internalization and extended retention in B16/F1 cells. Approximately 73% of (203)Pb-DOTA-Re(Arg(11))CCMSH activity internalized after a 20-min incubation at 25 degrees C. After incubation of the cells in culture medium for 20 min, 78% of internalized activity remained in the cells. (203)Pb-DOTA-Re(Arg(11))CCMSH exhibited a biodistribution pattern similar to that of (212)Pb-DOTA-Re(Arg(11))CCMSH in B16/F1 melanoma-bearing mice. (203)Pb-DOTA-Re(Arg(11))CCMSH exhibited a peak tumor uptake of 12.00+/-3.20 percentage injected dose per gram (%ID/g) at 1 h after injection. The tumor uptake gradually decreased to 3.43+/-1.12 %ID/g at 48 h after injection. (203)Pb-DOTA-Re(Arg(11))CCMSH exhibited a peak tumor-to-kidney uptake ratio of 1.53 at 2 h after injection. The absorbed doses to the tumor and kidneys were 4.32 and 4.35 Gy, respectively, per 37 MBq. Whole-body clearance of (203)Pb-DOTA-Re(Arg(11))CCMSH was fast, with approximately 89% of the injected activity cleared through the urinary system by 2 h after injection. (203)Pb showed 1.6-mm SPECT resolution, which was comparable to (99m)Tc. Melanoma lesions were visualized through SPECT/CT images of (203)Pb-DOTA-Re(Arg(11))CCMSH at 2 h after injection. CONCLUSION: (203)Pb-DOTA-Re(Arg(11))CCMSH exhibited favorable pharmacokinetic and tumor imaging properties, highlighting its potential as a matched-pair SPECT agent for (212)Pb-DOTA-Re(Arg(11))CCMSH melanoma treatment. 相似文献
20.