全文获取类型
收费全文 | 24737篇 |
免费 | 1826篇 |
国内免费 | 76篇 |
专业分类
耳鼻咽喉 | 377篇 |
儿科学 | 672篇 |
妇产科学 | 526篇 |
基础医学 | 3066篇 |
口腔科学 | 274篇 |
临床医学 | 2533篇 |
内科学 | 5285篇 |
皮肤病学 | 484篇 |
神经病学 | 2241篇 |
特种医学 | 1196篇 |
外科学 | 4058篇 |
综合类 | 254篇 |
一般理论 | 23篇 |
预防医学 | 1777篇 |
眼科学 | 404篇 |
药学 | 1755篇 |
中国医学 | 28篇 |
肿瘤学 | 1686篇 |
出版年
2023年 | 292篇 |
2022年 | 555篇 |
2021年 | 1123篇 |
2020年 | 628篇 |
2019年 | 943篇 |
2018年 | 1044篇 |
2017年 | 705篇 |
2016年 | 734篇 |
2015年 | 919篇 |
2014年 | 1170篇 |
2013年 | 1454篇 |
2012年 | 2104篇 |
2011年 | 2141篇 |
2010年 | 1139篇 |
2009年 | 906篇 |
2008年 | 1404篇 |
2007年 | 1409篇 |
2006年 | 1325篇 |
2005年 | 1165篇 |
2004年 | 1028篇 |
2003年 | 875篇 |
2002年 | 779篇 |
2001年 | 237篇 |
2000年 | 153篇 |
1999年 | 188篇 |
1998年 | 143篇 |
1997年 | 108篇 |
1996年 | 108篇 |
1995年 | 78篇 |
1994年 | 62篇 |
1993年 | 58篇 |
1992年 | 112篇 |
1991年 | 97篇 |
1990年 | 88篇 |
1989年 | 98篇 |
1988年 | 70篇 |
1987年 | 83篇 |
1986年 | 73篇 |
1985年 | 73篇 |
1984年 | 65篇 |
1983年 | 52篇 |
1982年 | 54篇 |
1981年 | 60篇 |
1980年 | 41篇 |
1979年 | 52篇 |
1978年 | 45篇 |
1974年 | 37篇 |
1973年 | 47篇 |
1972年 | 49篇 |
1970年 | 39篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
In vitro degradation of silk fibroin 总被引:14,自引:0,他引:14
Horan RL Antle K Collette AL Wang Y Huang J Moreau JE Volloch V Kaplan DL Altman GH 《Biomaterials》2005,26(17):3385-3393
A significant need exists for long-term degradable biomaterials which can slowly and predictably transfer a load-bearing burden to developing biological tissue. In this study Bombyx mori silk fibroin yarns were incubated in 1mg/ml Protease XIV at 37 degrees C to create an in vitro model system of proteolytic degradation. Samples were harvested at designated time points up to 12 weeks and (1) prepared for scanning electron microscopy (SEM), (2) lyophilized and weighed, (3) mechanical properties determined using a servohydraulic Instron 8511, (4) dissolved and run on a SDS-PAGE gel, and (5) characterized with Fourier transform infrared spectroscopy. Control samples were incubated in phosphate-buffered saline. Fibroin was shown to proteolytically degrade with predictable rates of change in fibroin diameter, failure strength, cycles to failure, and mass. SEM indicated increasing fragmentation of individual fibroin filaments from protease-digested samples with time of exposure to the enzyme; particulate debris was present within 7 days of incubation. Gel electrophoresis indicated a decreasing amount of the silk 25 kDa light chain and a shift in the molecular weight of the heavy chain with increasing incubation time in protease. Results support that silk is a mechanically robust biomaterial with predictable long-term degradation characteristics. 相似文献
62.
Paul K. Hildebrandt James D. Conroy Adam E. McKee M. B. A. Nyindo David L. Huxsoll 《Infection and immunity》1973,7(2):265-271
The ultrastructure of Ehrlichia canis was examined in both pulmonary mononuclear cells and in monocytes cultured from an infected dog. The cytoplasmic inclusions, or morulae, of E. canis consisted of a membrane-lined vacuole-containing elementary bodies which varied in size and number. The elementary bodies were bound by two trilamellar membranes. The organism shared morphological properties of both the genus Rickettsia and genus Chlamydia. 相似文献
63.
The complete sequence of the coding region of the ATM gene reveals similarity to cell cycle regulators in different species 总被引:30,自引:3,他引:30
Savitsky Kinneret; Sfez Sharon; Tagle Danilo A.; Ziv Yael; Sartiel Adam; Collins Francis S.; Shiloh Yosef; Rotman Gallt 《Human molecular genetics》1995,4(11):2025-2032
Ataxia-telangiectasia (A-T) is an autosomal recessive disorderinvolving cerebellar degeneration, immunodeficiency, radiationsensitivity, and cancer predisposition. A-T heterozygotes aremoderately cancer prone. The A-T gene, designated ATM, was recentlyidentified in our laboratory by positional cloning, and a partialcDNA clone was found to encode a polypeptide with a PI-3 kinasedomain. We report here the molecular cloning of a cDNA contigspanning the complete open reading frame of the ATM gene. Thepredicted protein of 3056 amino acids shows significant sequencesimilarities to several large proteins in yeast, Drosophilaand mammals, all of which share the PI-3 kinase domain. Manyof these proteins are involved in the detection of DNA damageand the control of cell cycle progression. Mutations in theirgenes confer a variety of phenotypes with features similar tothose observed in human A-T cells. The complete sequence ofthe ATM gene product provides useful clues to the function ofthis protein, and furthers understanding of the pleiotropicnature of the A-T mutations. 相似文献
64.
H. Seibold E. Henze J. Kohler J. Roth A. Schmidt W. Adam 《Journal of molecular medicine (Berlin, Germany)》1985,63(20):1041-1047
Summary Simultaneous right heart catheterization and radionuclide ventriculography were performed in 27 patients with a wide range of chronic obstructive pulmonary disease. Central hemodynamics and radionuclide studies were done at rest and during exercise. In the resting state the right ventricular ejection fraction (RVEF) was in the normal range (43.3±6%). During exercise a significant (p<0.001) decrease of RVEF to 38.8±6.7% occurred. The pumonary artery mean pressures were 19.9±3.8 at rest. During exercise a significant (p<0.001) increase to 41±9.8 mm Hg occurred. There was a linear relationship between pulmonary pressures and RVEF during exercise in patients with pulmonary artery pressures not exceeding 35 mm Hg. In patients with right ventricular end-diastolic wall thickness 6 mm a curvilinear relationship between these parameters could be observed with a flattening of the curve at higher pressures (>35 mm Hg) and lower ejection fractions (<35% RVEF). Radionuclide venticulography cannot substitute for right heart catheterization. Echocardiography is useful for interpretation of right ventricular ejection fractions in advanced chronic obstructive pulmonary disease.Abbreviations CI
Cardiac index (l/min/m2)
- CO
Cardiac output (l/min)
- COPD
Chronic obstructive pulmonary disease
- FEV1
Forced expiratory volume in the first second (ml)
- HR
Heart rate (B/min)
- PAd
Pulmonary artery diastolic pressure (mm Hg)
- PAP
Pulmonary artery mean pressure (mm Hg)
- PAs
Pulmonary artery peak pressure (mm Hg)
- PVR
Pulmonary vascular resistance (dyn·s·cm–5)
- PwP
Pulmonary capillary wedge pressure (mm Hg)
- RAP
Right arterial pressure (mm Hg)
- Raw
Airway resistance (cm H2/l/s)
- RNV
Radionuclide ventriculogram
- RV
Residual volume (l)
- RVEF
Right ventricular ejection fraction (%)
- RVEDVI
Right ventricular enddiastolic volume index (ml/m2)
- RVEDVI
SVI RVEF (ml/m2)
- RVESVI
Right ventricular endsystolic index (m2/m2)
- SVI
Stroke volume index (ml/m2)
- TLC
Total lung capacity (l)
- VC
Vital capacity (l) 相似文献
65.
Pelisek J Engelmann MG Golda A Fuchs A Armeanu S Shimizu M Mekkaoui C Rolland PH Nikol S 《Journal of molecular medicine (Berlin, Germany)》2002,80(11):724-736
Cationic liposomes/DNA complexes are widely used vectors for delivering genes in clinical and experimental trials. Relatively low transfer efficiencies in vivo compared with viral gene transfer may be improved using local application. In addition, markedly increased transfer efficiency may be achieved in vitro and in vivo via optimization of known variables influencing liposomal transfection. Lipofection under different conditions was performed in various cell lines and primary porcine smooth muscle cells. Optimized conditions found in vitro were verified in vivo using a porcine restenosis model. Toxicity was monitored analyzing cell metabolism. Transfer efficiency and safety were determined using morphometry, histology, galactosidase assays, PCR, and RT-PCR. The most important variables enabling maximum transfer efficiency were firstly the appropriate selection of cationic lipids for the cell type to be transfected, secondly the DNA/liposome ratio chosen, which depended on the cell type and cationic lipids used, and thirdly the state of proliferation of the targeted cells. Transfection in vivo demonstrated two- to fivefold higher transfer efficiencies when transfer conditions were extrapolated from optimization experiments in stationary cells compared with the use of conditions established in proliferating cells. Application of the therapeutic gene for cecropin using optimized transfer conditions resulted in a significantly reduced neointima formation compared with the transfection using a control gene for ss-galactosidase. Thus, in this vascular model, initial optimization of lipofection in stationary cells in culture followed by local delivery in vivo and with selection of a suitable therapeutic gene led to markedly improved transfer efficiencies, gene expression, and biological effect. Stationary cell cultures simulate more realistically the in vivo situation and may therefore represent a better model for future in vivo experiments. In addition, the advantages of liposomes are easy handling, low toxicity, and the lack of carcinogenicity or immunogenic reactions. 相似文献
66.
67.
Fast implementation of the single scatter simulation algorithm and its use in iterative image reconstruction of PET data 总被引:1,自引:0,他引:1
In positron emission tomography (PET), scatter correction is usually performed prior to image reconstruction using a more or less exact model of the scatter processes. These models require estimates of the true activity and object density distributions of the imaged object. The problem is that these estimates are computed from measured data and, therefore, already contain scattered events. The purpose of this work was to overcome this problem by incorporating scatter characteristics directly into the process of iterative image reconstruction. This could be achieved by an optimized implementation of the single scatter simulation (SSS) algorithm, which results in a significant speed-up of the scatter estimation procedure. The scatter simulation was then included in the forward projection step of maximum likelihood image reconstruction. The results demonstrate that this approach leads to a more exact estimation of the scatter component which cannot be obtained by a simple sequential data processing strategy. 相似文献
68.
4E-binding protein phosphorylation and eukaryotic initiation factor-4E release are required for airway smooth muscle hypertrophy 总被引:1,自引:0,他引:1
Zhou L Goldsmith AM Bentley JK Jia Y Rodriguez ML Abe MK Fingar DC Hershenson MB 《American journal of respiratory cell and molecular biology》2005,33(2):195-202
The molecular mechanisms of airway smooth muscle hypertrophy, a feature of severe asthma, are poorly understood. We previously established a conditionally immortalized human bronchial smooth muscle cell line with a temperature-sensitive SV40 large T antigen. Temperature shift and loss of large T cause G1-phase cell cycle arrest that is accompanied by increased airway smooth muscle cell size. In the present study, we hypothesized that phosphorylation of eukaryotic initiation factor-4E (eIF4E)-binding protein (4E-BP), which subsequently releases eIF4E and initiates cap-dependent mRNA translation, was required for airway smooth muscle hypertrophy. Treatment of cells with chemical inhibitors of PI 3-kinase and mammalian target of rapamycin blocked protein synthesis and cell growth while decreasing the phosphorylation of 4E-BP and increasing the binding of 4E-BP to eIF4E, consistent with the notion that 4E-BP1 phosphorylation and eIF4E function are required for hypertrophy. To test this directly, we infected cells with a retrovirus encoding a phosphorylation site mutant of 4E-BP1 (AA-4E-BP-1) that dominantly inhibits eIF4E. Upon temperature shift, cells infected with AA-4E-BP-1, but not empty vector, failed to undergo hypertrophic growth. We conclude that phosphorylation of 4E-BP, eIF4E release, and cap-dependent protein synthesis are required for hypertrophy of human airway smooth muscle cells. 相似文献
69.
Opolski A Laskowska A Madej J Wietrzyk J Kłopocki A Radzikowski C Ugorski M 《Clinical & experimental metastasis》1998,16(8):673-681
Several lines of evidence indicate that sialosyl Le a , tumor-associated carbohydrate antigen present on human colon carcinoma cells, is involved in formation of metastases. To study the role of this carbohydrate structure in development of metastases, we have used the clone of human colon carcinoma CX-1 cells transfected with antisense expression vector containing fragment of cDNA for a1,3/4-fucosyltransferase (FT III), which is involved in synthesis of sialosyl Le a tetrasaccharide. It has been reported previously that, in contrast to the parental cells, the antisense-transfected CX-1.1AS5 cells do not express sialosyl Le a and do not adhere to E-selectin-expressing CHO cells. In the present work we have studied the formation of liver metastases by CX-1.1AS5 cells after their orthotopic or intrasplenic implantation into athymic nu/nu mice. After orthotopic implantation of sialosyl Le a -negative colon carcinoma CX-1.1AS5 cells, the number of mice with liver metas-tases was markedly lower (21% of mice) in comparison with their number after implantation of the parental CX-1.1 cells (86% of mice). However, no differences in ability to form colonies in liver were observed between parental CX-1.1 cells and antisense-transfected CX-1.1AS5 cells after intrasplenic inoculation. The liver metastases were formed in 89% and 84% of mice, respectively. Our data support the thesis on the importance of sialosyl Le a antigen expression in the development of liver metastases by colon cancer cells, and indicate the role of transplantation route and primary tumor localization in formation of metastases.© Kluwer Academic Publishers 1998 相似文献
70.
Adam R Clarke Robert J Barry Rory McCarthy Mark Selikowitz Christopher R Brown Rodney J Croft 《International journal of psychophysiology》2003,47(2):129-137
Stimulant medications are the most commonly-used treatments for Attention-Deficit/Hyperactivity Disorder (ADHD) in North America and Australia, although it is still not entirely known how these medications work. This study investigated the effects of stimulant medications on the EEG of children with the Inattentive type of ADHD. An initial EEG was recorded during an eyes-closed resting condition and Fourier transformed to provide absolute and relative power estimates for the delta, theta, alpha and beta bands. Theta/alpha and theta/beta ratios were also calculated. Subjects were placed on a 6-month trial of a stimulant and a second EEG was recorded at the end of the trial. Subjects were included in this study only if they showed a good clinical response during the trial. The unmedicated ADHD group had significantly greater absolute and relative theta, less relative alpha, and higher theta/alpha and theta/beta ratios than the control group. The stimulant medications resulted in a normalisation of the EEG, with changes in the theta, alpha and beta bands being most evident. These results suggest that stimulants act to increase cortical arousal in children with ADHD, normalising their EEG. 相似文献