全文获取类型
收费全文 | 126240篇 |
免费 | 9571篇 |
国内免费 | 235篇 |
专业分类
耳鼻咽喉 | 1140篇 |
儿科学 | 3568篇 |
妇产科学 | 2610篇 |
基础医学 | 19754篇 |
口腔科学 | 3374篇 |
临床医学 | 10704篇 |
内科学 | 25637篇 |
皮肤病学 | 2212篇 |
神经病学 | 12110篇 |
特种医学 | 5281篇 |
外国民族医学 | 9篇 |
外科学 | 15941篇 |
综合类 | 559篇 |
现状与发展 | 1篇 |
一般理论 | 106篇 |
预防医学 | 14417篇 |
眼科学 | 2001篇 |
药学 | 7398篇 |
中国医学 | 237篇 |
肿瘤学 | 8987篇 |
出版年
2023年 | 513篇 |
2022年 | 774篇 |
2021年 | 1958篇 |
2020年 | 1427篇 |
2019年 | 2063篇 |
2018年 | 2622篇 |
2017年 | 2237篇 |
2016年 | 2421篇 |
2015年 | 2718篇 |
2014年 | 3727篇 |
2013年 | 4860篇 |
2012年 | 7402篇 |
2011年 | 7457篇 |
2010年 | 3903篇 |
2009年 | 4112篇 |
2008年 | 6599篇 |
2007年 | 6837篇 |
2006年 | 6576篇 |
2005年 | 6211篇 |
2004年 | 5307篇 |
2003年 | 4998篇 |
2002年 | 4553篇 |
2001年 | 4444篇 |
2000年 | 4387篇 |
1999年 | 3924篇 |
1998年 | 1687篇 |
1997年 | 1390篇 |
1996年 | 1474篇 |
1995年 | 1186篇 |
1994年 | 1125篇 |
1993年 | 996篇 |
1992年 | 2687篇 |
1991年 | 2417篇 |
1990年 | 2286篇 |
1989年 | 2154篇 |
1988年 | 1974篇 |
1987年 | 1727篇 |
1986年 | 1642篇 |
1985年 | 1572篇 |
1984年 | 1119篇 |
1983年 | 972篇 |
1982年 | 538篇 |
1981年 | 468篇 |
1980年 | 405篇 |
1979年 | 862篇 |
1978年 | 525篇 |
1977年 | 433篇 |
1974年 | 417篇 |
1973年 | 410篇 |
1972年 | 366篇 |
排序方式: 共有10000条查询结果,搜索用时 734 毫秒
991.
Shadlen MF Larson EB Wang L Phelan EA McCormick WC Jolley L Teri L van Belle G 《Neurobiology of aging》2005,26(1):17-24
OBJECTIVES: To assess the influence of education on the association between apolipoprotein E and cognitive change. DESIGN: Prospective cohort. PARTICIPANTS: HMO-based sample of 2168 non-demented community-dwelling elderly followed over 6 years. MEASUREMENTS: Generalized estimating equations were used with the difference between baseline and follow-up cognitive abilities screening instrument (CASI) as the outcome variable. RESULTS: At follow-up, 6% of the sample had a decline of 1.5 S.D. or greater on the CASI. Compared to individuals without an APOE4 allele, individuals with a single APOE4 allele did not have greater CASI decline. By contrast, individuals with two APOE4 alleles experienced greater decline in cognitive performance and the magnitude of that decline decreased as years of educational attainment increased. These relationships held after adjusting for age, gender, ethnicity, depression, diabetes, and history of vascular disease. CONCLUSION: Lower education was associated with steep 4-year cognitive decline for APOE4 homozygotes but not for APOE4 heterozygotes. Potentially modifiable host factors such as education could influence the association of high-risk genotypes and cognitive decline. 相似文献
992.
Performance of CHROMagar MRSA medium for detection of methicillin-resistant Staphylococcus aureus 总被引:2,自引:0,他引:2 下载免费PDF全文
Diederen B van Duijn I van Belkum A Willemse P van Keulen P Kluytmans J 《Journal of clinical microbiology》2005,43(4):1925-1927
CHROMagar MRSA was evaluated for its ability to identify methicillin-resistant Staphylococcus aureus (MRSA). A well-defined collection consisting of 216 MRSA strains and 241 methicillin-susceptible Staphylococcus aureus isolates was used. The sensitivity of CHROMagar MRSA after 24 h of incubation was 95.4%, increasing to 100% after 48 h. The specificity was already 100% after 24 h. 相似文献
993.
Oostra RJ van der Wolk S Maas M Hennekam RC 《American journal of medical genetics. Part A》2005,(4):327-342
The Museum Vrolik collection of anatomical specimens in Amsterdam, The Netherlands, comprises over 5,000 specimens of human and animal anatomy, embryology, pathology, and congenital anomalies. Recently, we rediagnosed a subset of the collection comprising dried infantile, juvenile, and adult human skulls with congenital and acquired conditions. On external examination and additional radiography, we found 58 skulls with craniosynostosis (CS) involving one or more sutures and 40 skulls with a presumed suture related condition. Most of these were part of the material collected and described by Louis Bolk (1866-1930). Analysis of his observations suggests that skull deformation because of premature suture closure depends not only on the identity of the sutures involved but also on the timing and progression of their closure and the extent of their involvement. Moreover, premature closure of the sagittal suture after 3-6 years of age appeared to be much more common than expected because it is not accompanied by skull deformation. Many of the skulls with single-suture CS were microcephalic, which may be the cause of the premature synostosis. By contrast, microcephaly may be a resulting phenomenon in multi-suture CS. We noticed that the quotient between height of the cranial vault (vertex-porion distance) and head circumference, multiplied by 100, was 26 or higher only in those CS cases with multi-suture involvement. We therefore consider this parameter, which we named "acrocephalic index", to be an indicator of multi-suture involvement in individual CS cases. In two adult skulls, the skull had a quadrangular shape, which we assumed to be correlated to the presence of an unusually interdigitated open metopic suture. We propose to name this anomaly: tetragonocephaly. Another presumed suture-related condition, bathrocephaly, was found concomitantly with basilar invagination in several cases. We hypothesize that the chronically raised intracranial pressure in these cases caused the still open lambdoidal sutures to distend and the occipital bone to protrude. 相似文献
994.
In the present study, serotonin (5-HT) responses of hippocampal pyramidal cornu ammonis 1 (CA1) neurons were studied in rats subjected twice daily for 21 days to unpredictable stressors. In hippocampal tissue from thus stressed rats mRNA expression of the 5-HT(1A) receptor and mineralo- as well as glucocorticoid receptors were examined with in situ hybridization. On average, stressed rats displayed increased adrenal weight and attenuated body weight gain compared with controls, supporting that the animals had experienced increased corticosterone levels due to the stress exposure. One day after the last stressor, under conditions that corticosterone levels were low (predominant mineralocorticoid receptor activation), the 5-HT(1A) receptor mediated hyperpolarization of CA1 neurons in response to 10 microM 5-HT was significantly reduced compared with controls. Basal membrane properties of CA1 cells in stressed rats were comparable to those of controls. The 5-HT(1A) receptor mRNA expression was not changed after chronic stress exposure, in any of the hippocampal areas. A small but significant increase in mineralocorticoid receptor mRNA expression was observed after stress in the dentate gyrus, while glucocorticoid receptor expression was unchanged. The data indicate that unpredictable stress exposure for 3 weeks results in suppression of 5-HT(1A) receptor-mediated responses, possibly due to posttranslational modification of the receptor. 相似文献
995.
Many biochemical, physiological, and behavioral processes display daily rhythms generated by an internal timekeeping mechanism referred to as the circadian clock. The core oscillator driving this clock is located in the ventral part of the hypothalamus, the so called suprachiasmatic nuclei (SCN). At the molecular level, this oscillator is thought to be composed of interlocking autoregulatory feedback loops involving a set of clock genes. Among the components driving the mammalian circadian clock are the Period 1 and 2 (mPer1 and mPer2) and Cryptochrome 1 and 2 (mCry1 and mCry2) genes. A mutation in the mPer2 gene leads to a gradual loss of circadian rhythmicity in mice kept in constant darkness (DD). Here we show that inactivation of the mCry2 gene in mPer2 mutant mice restores circadian rhythmicity and normal clock gene expression patterns. Thus, mCry2 can act as a nonallelic suppressor of mPer2, which points to direct or indirect interactions of PER2 and CRY2 proteins. In marked contrast, inactivation of mCry1 in mPer2 mutant mice does not restore circadian rhythmicity but instead results in complete behavioral arrhythmicity in DD, indicating different effects of mCry1 and mCry2 in the clock mechanism 相似文献
996.
Mutations in the pre-mRNA splicing factor gene PRPC8 in autosomal dominant retinitis pigmentosa (RP13) 总被引:7,自引:0,他引:7
997.
Colonization of in vitro-formed cervical human papillomavirus- associated (pre)neoplastic lesions with dendritic cells: role of granulocyte/macrophage colony-stimulating factor 总被引:3,自引:0,他引:3 下载免费PDF全文
Hubert P van den Brüle F Giannini SL Franzen-Detrooz E Boniver J Delvenne P 《The American journal of pathology》1999,154(3):775-784
The purpose of this study was to investigate the ability of CD1a+ Langerhans/dendritic cells (LCs/DCs) to infiltrate human papillomavirus (HPV)-associated (pre)neoplastic lesions of the uterine cervix. Migration of LCs/DCs in the presence of keratinocytes derived from normal cervix and HPV-transformed cell lines was evaluated in Boyden chambers and in organotypic cultures and correlated with granulocyte/macrophage colony-stimulating factor (GM-CSF) production by the cells, as determined by ELISA. Conditioned media of HPV-transformed keratinocytes contained lower amounts of GM-CSF and induced a decreased motile response of LCs/DCs in the Boyden chamber assay compared with those of normal cervical keratinocytes. The migration of LCs/DCs in the presence of conditioned media from normal keratinocytes could be blocked by an anti-GM-CSF antibody, and the migration of LCs/DCs in the presence of conditioned media from HPV-transformed keratinocytes could be increased by supplementing the media with recombinant GM-CSF. GM-CSF was also a potent factor in enhancing the colonization of LCs/DCs into organotypic cultures of HPV-transformed keratinocytes, as the infiltration of LCs/DCs in the in vitro-formed (pre)neoplastic epithelium was minimal under basal conditions and dramatically increased after the addition of GM-CSF to the cultures. These results suggest that GM-CSF could play an important role in the recruitment of LCs/DCs into the HPV-transformed (pre)neoplastic cervical epithelium and be useful as a new immunotherapeutic approach for cervical (pre)cancers. 相似文献
998.
Dr. B. K. van Kreel N. Cox-Reyven P. Soeters 《Medical & biological engineering & computing》1998,36(3):337-345
Multifrequency bio-electronic impedance analysis (MF BIA) measurements are taken from a heterogeneous group of patients, varying
in size between obese and slim. The measuring system uses four electrodes: two current and two potential electrodes. Three
new models are developed to calculate total body water (TBW) from the BIA data, and the resulting TBW values are compared
with TBW determined by D2O dilution. The results demonstrate that the most simple model provides the best TBW values. For individual patients, TBW
can be determined by means of bioimpedance measurement with an accuracy of 3 litres. In the most simple model (model 1), the
body is electrically represented by a cylinder, and corrections are made for the amount of fat. This is an extension of the
model used by Xitron. In the more advanced models (2 and 3), the body is represented by a cylinder for the trunk, and truncated
cones represent the arms and legs. In model 2, ΔTBW amounts to 3 litres. It is shown that the resistance of the trunk is proportional
to the square root of the length. In model 3, it is assumed that subcutaneous fat is a poor conductor if electric current.
An equation is developed that describes the partition of subcutaneous fat, and the fat layer is then removed from the cones
representing arms and legs and from the cylinder that models the trunk. 相似文献
999.
In vivo and in vitro degradation of poly(ether ester) block copolymers based on poly(ethylene glycol) and poly(butylene terephthalate) 总被引:2,自引:0,他引:2
Deschamps AA van Apeldoorn AA Hayen H de Bruijn JD Karst U Grijpma DW Feijen J 《Biomaterials》2004,25(2):247-258
Two in vivo degradation studies were performed on segmented poly(ether ester)s based on polyethylene glycol (PEG) and poly(butylene terephthalate) (PBT) (PEOT/PBT). In a first series of experiments, the in vivo degradation of melt-pressed discs of different copolymer compositions were followed up for 24 weeks after subcutaneous implantation in rats. The second series of experiments aimed to simulate long-term in vivo degradation. For this, PEOT/PBT samples were pre-degraded in phosphate buffer saline (PBS) at 100 degrees C and subsequently implanted. In both series, explanted materials were characterized by intrinsic viscosity measurements, mass loss, proton nuclear magnetic resonance spectroscopy (1H-NMR) and differential scanning calorimetry (DSC). In both studies the copolymer with the higher PEO content degraded the fastest, although all materials degraded relatively slowly. To determine the nature of the degradation products formed during hydrolysis of the copolymers, 1000 PEOT71PBT29 (a copolymer based on PEG with a molecular weight of 1000 g/mol and 71 wt% of PEO-containing soft segments) was degraded in vitro at 100 degrees C in phosphate buffer saline (PBS) during 14 days. The degradation products present in PBS were analyzed by 1H-NMR and high performance liquid chromatography/mass spectroscopy (HPLC/MS). These degradation products consisted of a fraction with high contents of PEO that was soluble in PBS and a PEOT/PBT fraction that was insoluble at room temperature. From the different in vitro and in vivo degradation experiments performed, it can be concluded that PEOT/PBT degradation is a slow process and generates insoluble polymeric residues with high PBT contents. 相似文献
1000.
van Muiswinkel FL de Vos RA Bol JG Andringa G Jansen Steur EN Ross D Siegel D Drukarch B 《Neurobiology of aging》2004,25(9):1253-1262
Dopamine (DA) autooxidation, and consequent formation of neurotoxic DA-derived quinones and reactive oxygen species, has been implicated in dopaminergic cell death and, hence, in the pathogenesis of Parkinson's disease (PD). Stimulation of pathways involved in the detoxication of DA-quinones in the brain is hypothesized to be an effective means to limit oxidative stress and to confer neuroprotection in PD. In this respect, the inducible flavoprotein NAD(P)H:quinone oxidoreductase (NQO1) is of particular interest as it is directly implicated in the detoxication of DA-quinones and, in addition, has broad spectrum anti-oxidant properties. To study the potential pathophysiological role of NQO1 in PD, the cellular expression of NQO1 was examined in the mesencephalon of PD patients and age-matched controls. In the substantia nigra pars compacta (SNpc), NQO1 was found to be expressed in astroglial and endothelial cells and, albeit less frequently, also in dopaminergic neurons. Moreover, while overt NQO1 immunoreactivity was absent in the surrounding nervous tissue, in the Parkinsonian SNpc a marked increase in the astroglial and neuronal expression of NQO1 was consistently observed. 相似文献