全文获取类型
收费全文 | 106296篇 |
免费 | 10538篇 |
国内免费 | 3324篇 |
专业分类
耳鼻咽喉 | 862篇 |
儿科学 | 1284篇 |
妇产科学 | 1166篇 |
基础医学 | 13262篇 |
口腔科学 | 3753篇 |
临床医学 | 10833篇 |
内科学 | 11032篇 |
皮肤病学 | 1336篇 |
神经病学 | 6816篇 |
特种医学 | 3246篇 |
外国民族医学 | 12篇 |
外科学 | 7388篇 |
综合类 | 15590篇 |
现状与发展 | 10篇 |
一般理论 | 3篇 |
预防医学 | 16889篇 |
眼科学 | 1228篇 |
药学 | 14067篇 |
114篇 | |
中国医学 | 5855篇 |
肿瘤学 | 5412篇 |
出版年
2024年 | 355篇 |
2023年 | 1823篇 |
2022年 | 3637篇 |
2021年 | 5064篇 |
2020年 | 4805篇 |
2019年 | 4201篇 |
2018年 | 3835篇 |
2017年 | 4153篇 |
2016年 | 4191篇 |
2015年 | 4202篇 |
2014年 | 7324篇 |
2013年 | 7926篇 |
2012年 | 7100篇 |
2011年 | 7473篇 |
2010年 | 5651篇 |
2009年 | 5316篇 |
2008年 | 5146篇 |
2007年 | 5154篇 |
2006年 | 4444篇 |
2005年 | 3916篇 |
2004年 | 3238篇 |
2003年 | 2897篇 |
2002年 | 2211篇 |
2001年 | 2038篇 |
2000年 | 1574篇 |
1999年 | 1364篇 |
1998年 | 1303篇 |
1997年 | 1182篇 |
1996年 | 1020篇 |
1995年 | 926篇 |
1994年 | 889篇 |
1993年 | 694篇 |
1992年 | 655篇 |
1991年 | 551篇 |
1990年 | 471篇 |
1989年 | 490篇 |
1988年 | 419篇 |
1987年 | 371篇 |
1986年 | 296篇 |
1985年 | 386篇 |
1984年 | 301篇 |
1983年 | 175篇 |
1982年 | 209篇 |
1981年 | 159篇 |
1980年 | 160篇 |
1979年 | 121篇 |
1978年 | 81篇 |
1977年 | 52篇 |
1976年 | 73篇 |
1974年 | 42篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
独立成分分析是一种新的信号处理统计方法。被广泛用于各个领域。在信号分析中面临的难题是:源信号的不同特性(既包括超高斯信号又包括亚高斯信号);未知的独立源数目;传感器信号受到较大的加性噪声污染。针对以上难题,本文提出了一种独立成分分析的鲁棒算法。该方法先对观测数据作预处理,将包含噪声的高维传感器观测信号降维分解到信号子空间和噪声子空间。利用交叉验证法估计出独立源的数目(解决了独立成分分析本身不能确定源数目的缺陷);然后利用快速稳定的FastICA算法分离独立成分。通过人工合成的数据和实际的脑磁图数据分析。验证了这种方法的功效。 相似文献
992.
Felix Eckstein Beat Merz Magdalena Müller-Gerbl Nikolaus Holzknecht Markus Pleier Reinhard Putz 《Anatomical record (Hoboken, N.J. : 2007)》1995,243(3):327-335
Background: A deeper joint socket (concave incongruity) is found at most angles of flexion of the humero-ulnar joint and maintained over a wide range of physiological loading. It is, however, unclear how far this incongruity affects the distribution of load and subchondral mineralization of this joint as compared with a congruous configuration. Methods: Two nonlinear, axisymmetrical finite element models with two cartilage layers were constructed, one congruous and one incongruous, with a joint space of realistic magnitude. The distribution of subchondral mineralization was determined by computed tomography osteoabsorptiometry in the same six specimens that were investigated in the first part of the study, and compared with the biomechanical data obtained there and the predictions of the models. Results: In the congruous case, the center of the socket is highly loaded, whereas the periphery does not experience mechanical stimulation. A central bone density maximum is predicted. With concave incongruity the position of the contact areas shifts from the joint margin towards the center as the load increases, and the peak stresses are considerably lower. A bicentric ventro-dorsal distribution pattern of subchondral mineralization is predicted, and this is actually found in the six specimens. Conclusions: Concave incongruity is shown to determine load transmission and subchondral mineralization of the humero-ulnar joint. It is suggested that this shape leads to a more even distribution of stress, provides intermittent stimulation of the cartilaginous tissue, and has beneficial effects on the metabolism, nutrition, and lubrication of the articular cartilage during cyclic loading. © 1995 Wiley-Liss, Inc. 相似文献
993.
Sabine Nick Piero Pileri Stefania Tongiani Yasushi Uematsu Ludwig Kappos Gennaro De Libero 《European journal of immunology》1995,25(2):355-363
To study the relevance of γδ T cells in multiple sclerosis (MS) we analyzed the T cell receptor (TCR) γδ repertoire and the antigen reactivity of γδ clones isolated from cerebrospinal fluid (CSF). In T cell cultures derived from CSF we found an increased percentage of Vδ1+ cells as compared to peripheral blood of the same donors. Phenotypic analysis of cells from MS CSF with Vγ- and Vγ-specific monoclonal antibodies (mAb) showed that the Vγ1 chain is most frequently associated with γ chains belonging to the VγI family. Sequence analysis of TCR genes revealed heterogeneity of junctional regions in both δ and γ genes indicating polyclonal expansion. γδ clones were established and some recognized glioblastoma, astrocytoma or monocytic cell lines. Stimulation with these targets induced serine esterase release and lymphokine expression characteristic of the TH0-like phenotype. Remarkably, these tumor-reactive γδ cells were not detected in the peripheral blood using PCR oligotyping, but were found in other CSF lines independently established from the same MS patient. Altogether, these results demonstrate that in the CSF there is a skewed TCR γδ repertoire and suggest that γδ cells reacting against brain-derived antigens might have been locally expanded. 相似文献
994.
John S. Pirolo Stephen J. Bresina Lawrence L. Creswell Kent W. Myers Barna A. Szabó Michael W. Vannier Michael K. Pasque 《Annals of biomedical engineering》1993,21(3):199-219
The characterization of regional myocardial stress distribution has been limited by the use of idealized mathematical representations
of biventricular geometry. State-of-the-art computer-aided design and engineering (CAD/CAE) techniques can be used to create
complete, unambiguous mathematical representations (solid models) of complex object geometry that are suitable for a variety
of applications, including stress-strain analyses. We have used advanced CAD/CAE software to create a 3-D solid model of the
biventricular unit using planar geometric data extracted from anex vivo canine heart. Volumetric analysis revealed global volume errors of 4.7%, −1.3%, −1.6%, and −1.1% for the left ventricular
cavity, right ventricular cavity, myocardial wall, and total enclosed volumes, respectively. Model errors for 34 in-plane
area and circumference determinations (mean ±SD) were 5.3±6.7% and 3.8±2.7%. Error analysis suggested that model volume errors
may be due to operator variability. These results demonstrate that solid modeling of theex vivo biventricular unit yields an accurate mathematical representation of myocardial geometry which is suitable for meshing and
subsequent finite element analysis. The use of CAD/CAE solid modeling in the representation of biventricular geometry may
thereby facilitate the characterization of regional myocardial stress distribution. 相似文献
995.
996.
通过对<心理发展与教育)2004~2006年所发表论文的引文、语种、作者群、作者地区分布、发表论文作者机构、载文栏目等指标进行文献计量学分析,该刊三年共发表论文258篇.引文率99.61%,篇均15.25条.主要引文类型以期刊为主.占总引文量的94.71%,图书5.18%,自引率3.00%;作者合作论文222篇,合作率88.45%.作者地区分布主要在北京、广州、天津、重庆四个地区.其中北京居首,共发表173篇.栏目设置发文量最多的是认知与社会性发展119篇.论文多产机构为北京师范大学122篇.结果 表明:该刊论文作者人群众多、分布范围广、涉猎文献面广、研究课题引用文献比较高,专业人员利用新文献能力强、作者能紧跟本学科的研究发展方向.该刊是心理学领域具有权威性和代表性的刊物. 文率99.61%,篇均15.25条.主要引文类型以期刊为主.占总引文量的94.71%,图书5.18%,自引率3.00%;作者合作论文222篇,合作率88.45%.作者地区分布主要在北京、广州、天津、重庆四个地区.其中北京居首,共发表173篇.栏目设置发文量最多的是认知与社会性发展119篇.论文多产机构为北京师范大学122篇.结果 表明:该 论文作者人群众多、分布范围广、涉猎文献面广、研究课题引用文献比较高,专业人员利用新文献能力强、作者能紧跟本学科的研究发展方向.该刊是心理学领域具有权威性和代表性的刊物. 文率99.6 相似文献
997.
Alena Jiroutova Rastislav Slavkovsky Martina Cermakova Lenka Majdiakova Irena Hanovcova Radka Bolehovska Milena Hajzlerova Hana Radilova Ema Ruszova Jiri Kanta 《Experimental and toxicologic pathology》2007,58(4):263-273
Hepatic stellate cells (HSC) and liver myofibroblasts (MFB) are two cell populations most likely responsible for the synthesis of most connective tissue components in fibrotic liver. They differ in their origin and location, and possibly in patterns of gene expression. Normal and carbon tetrachloride-cirrhotic livers from rats were used to isolate HSC. Liver was perfused with pronase and collagenase solutions, followed by centrifugation of the cell suspension on a density gradient. HSC were quiescent 2 days after plating on plastic but they became activated after another 5 days in culture. When the culture was passaged 5 times, its character changed profoundly as HSC were replaced by MFB. Microarray analysis was used to determine gene expression in quiescent HSC, activated HSC and MFB. The expression of 49 genes coding for connective tissue proteins, proteoglycans, metalloproteinases and their inhibitors, growth factors and cellular markers was determined. The pattern of gene expression changed during HSC activation and there were distinct differences between HSC and MFB. Little difference between normal cells and cells isolated from cirrhotic liver was found. 相似文献
998.
血管内皮生长因子在子宫内膜异位症发病中的作用 总被引:4,自引:1,他引:4
目的探讨血管内皮生长因子(vascularendothelialgrowthfactor,VEGF)在子宫内膜异位症(endometriosis,EM)发病中的作用。方法应用免疫组织化学方法并结合图像分析技术。结果正常子宫内膜和EM在位内膜腺上皮细胞的VEGF随月经周期呈现规律性变化,分泌期腺上皮VEGF蛋白表达量显著高于增殖期(P<0.05)。在增殖期,EM在位子宫内膜腺上皮VEGF的表达与正常子宫内膜相比无明显差别,但在分泌期,EM在位子宫内膜腺上皮细胞中VEGF的表达强度明显高于正常子宫内膜(P<0.01)。EM在位内膜腺上皮的VEGF含量显著高于同组卵巢子宫内膜异位囊肿的异位腺上皮(P<0.01)。结论表明VEGF的表达异常与EM的发病有关。 相似文献
999.
Summary Ionic channel properties of acetylcholine receptors located in, in the vicinity of, or far away from a frog neuromuscular
junction were investigated by noise analysis of drug induced current fluctuations. For drugs applied to the junction, in certain
cases two Lorentzian curves were necessary to describe the data. It is postulated that the reason for this observation is
that a contribution from perijunctional receptors was being observed. The conductance of a single channel in the junction
was independent of the nature of the agonist and had an average value of 17.9 pS (temperature range 8–25°C, solution buffered
with Tris). After denervation for 21 days the conductance γ was 7.5 pS at extrajunctional locations. In the close neighbourhood
of the junction (perijunctional receptors) values were found between 4 and 19 pS.
The mean value of the open channel life-time τ in the endplate exposed to acetylcholine was 2.4 ms at 8–11°C. This value was
0.90 ms with carbachol, 0.50 ms with succinylcholine, 0.28 ms with decamethonium and 0.45 ms with nicotine. The receptors
outside the endplate exhibited τ-values which at a given temperature were 2–3 times larger than those at the endplate. Raising
the temperature to 23°C reduced all τ-values by factors of 2–3. It is concluded that at least two types of ACh-receptors with
different properties exist in the muscle membrane, possibly produced by ACh-receptive units in different states of aggregation.
This work was supported by the Deutsche Forschungsgemeinschaft, SFB 38, Project N 相似文献
1000.
Sowiska-Klencka D Klencki M Dedecjus M Lewiski A Pawlikowski M 《Endocrine pathology》2000,11(2):173-178
Nucleolar organizer regions (NORs) are segments of DNA, encoding for ribosomal RNA. They are associated with argyrophilic
proteins and, thus, they can be localized through silver staining. A correlation has been shown between the number, the size,
or the intranuclear localization of AgNORs, and the proliferative activity of cells. The aim of this study was to examine
numerous features of AgNORs in pituitary adenomas and to relate them to immunohistochemical typing of tumor. Histologic slides
from 32 pituitary tumors and one normal pituitary were silver-stained and analyzed with a computerized system for microscopic
image analysis, supported by an AgNORmeter95 program. All the tumors were also immunocyto chemically characterized. We have
found that gonadotropinomas, when compared with plurihormonal adenomas, revealed a lower proportion of nuclei with a single
AgNOR and a higher percentage of marginal dots. Recurrent adenomas, when compared with primary adenomas, showed a higher proportion
of nuclei with three AgNOR dots, a larger total area of dots in the nuclei, and a higher standard deviation of the AgNOR dot
area in the nucleus. Adenomas immunopositive for prolactin, when compared with immunonegative ones, showed a larger mean area
of the AgNOR dot, a larger area of the biggest dot in the nucleus, and a higher proportion of nuclei within a single dot.
These results suggest that the estimated parameters of AgNOR dots differ according to tumor aggressiveness and to the hormone
immunopositivity of pituitary adenomas. 相似文献