全文获取类型
收费全文 | 39700篇 |
免费 | 3650篇 |
国内免费 | 2719篇 |
专业分类
耳鼻咽喉 | 200篇 |
儿科学 | 540篇 |
妇产科学 | 562篇 |
基础医学 | 4903篇 |
口腔科学 | 712篇 |
临床医学 | 4841篇 |
内科学 | 6520篇 |
皮肤病学 | 375篇 |
神经病学 | 2340篇 |
特种医学 | 1565篇 |
外国民族医学 | 23篇 |
外科学 | 4293篇 |
综合类 | 5864篇 |
现状与发展 | 12篇 |
一般理论 | 3篇 |
预防医学 | 2287篇 |
眼科学 | 977篇 |
药学 | 4119篇 |
15篇 | |
中国医学 | 1898篇 |
肿瘤学 | 4020篇 |
出版年
2024年 | 105篇 |
2023年 | 567篇 |
2022年 | 1323篇 |
2021年 | 1694篇 |
2020年 | 1378篇 |
2019年 | 1224篇 |
2018年 | 1300篇 |
2017年 | 1199篇 |
2016年 | 1142篇 |
2015年 | 1769篇 |
2014年 | 2096篇 |
2013年 | 1834篇 |
2012年 | 2903篇 |
2011年 | 3049篇 |
2010年 | 1866篇 |
2009年 | 1511篇 |
2008年 | 2097篇 |
2007年 | 2141篇 |
2006年 | 1942篇 |
2005年 | 2040篇 |
2004年 | 1389篇 |
2003年 | 1332篇 |
2002年 | 1095篇 |
2001年 | 906篇 |
2000年 | 1026篇 |
1999年 | 1096篇 |
1998年 | 697篇 |
1997年 | 752篇 |
1996年 | 566篇 |
1995年 | 539篇 |
1994年 | 472篇 |
1993年 | 341篇 |
1992年 | 328篇 |
1991年 | 343篇 |
1990年 | 308篇 |
1989年 | 297篇 |
1988年 | 250篇 |
1987年 | 243篇 |
1986年 | 198篇 |
1985年 | 157篇 |
1984年 | 112篇 |
1983年 | 85篇 |
1982年 | 47篇 |
1981年 | 61篇 |
1980年 | 47篇 |
1979年 | 43篇 |
1978年 | 30篇 |
1977年 | 33篇 |
1976年 | 28篇 |
1975年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
根据下頜光弹的等倾线图,描绘出主应力迹线规迹。在下颌侧位X线照片和去除唇侧及颊侧密质骨板的标本上,观察骨密质和松质的配布,以及骨小梁的排列和方向,试行探讨骨小梁方向与主应力迹线的关系。用光弹法求得的主应力迹线有两个系列:S_1系在下颌体近水平方向,在下颌支近垂直方向分布;S_2系力线与S_1系诸力线呈正交。在标本和X线照片上,主应力迹线规迹不同程度地在骨小梁的排列上有所反映。 相似文献
72.
Armando A. Lagrutta Ke-Zhong Shen André Rivard R. Alan North J. P. Adelman 《Pflügers Archiv : European journal of physiology》1998,435(5):731-739
Structural determinants of permeation in large unit conductance calcium-activated potassium channels (BK channels) were investigated.
Y293 and F294 in the P-region of dSlo were substituted by tryptophans. Compared to wild-type channels, Y293W channels displayed reduced inward unitary currents
while F294W channels exhibited normal inward current amplitudes but flickery kinetics. Both mutations produced changes in
current/voltage relations under bi-ionic conditions. Sensitivity to block by external tetraethylammonium (TEA) was affected
in both channels, and the voltage dependence of TEA block was increased in F294W channels. Both mutations also affected gating
by shifting the half-maximal activation voltage of macroscopic conductance/voltage relations to more positive potentials,
and eliminating a slow component of deactivation. The double mutant did not produce ionic currents. These data are consistent
with a model in which Y293 contributes to a potassium-binding site close to the outer mouth of the dSlo pore, while F294 contributes to an energy barrier near this site.
Received: 16 September 1997 / Received after revision: 20 November 1997 / Accepted: 21 November 1997 相似文献
73.
鉴于热休克蛋白90β(hsp90β)基因内含子中含有维生素D3受体(VDR)结合位点,为探讨作为核受体家族成员的VDR是否对核受体特异分子伴侣的hsp90β基因的表达具有调控作用,我们开展了本项研究。分别将野生型VDR、含N端(1~133氨基酸残基)及C端(281~427氨基酸残基)片段的VDR突变体真核表达质粒与人hsp90β基因调控片段(-1039/+1531)介导的氯霉素乙酰基转移酶(CAT)报告基因质粒共转染Jurkat细胞,检测正常及经热休克(42℃,1h)处理后细胞裂解液中CAT活性。结果表明VDRN端增强、而C端抑制hsp90β的组成性表达;在热诱导条件下野生型VDR对hsp90β的表达有一定的抑制作用,而其C端片段的抑制较强。为进一步研究VDR对细胞内源性热休克基因表达的影响,我们用RTPCR方法研究了VDR的对细胞内hsp90β基因mRNA水平的影响,发现VDR过表达对hsp90β的热诱导表达明显抑制。结果提示VDR对hsp90β基因的组成性和热诱导表达的调控机制不同。 相似文献
74.
Carcinoma of the cervix is typically treated with a combination of intracavitary brachytherapy and external beam radiation. The external beam dose is delivered with whole pelvis fields followed by split fields that protect midline organs at risk (bladder and rectum) while treating the parametria. Three approaches have been developed to shield midline structures: a simple rectangular block, a block customized to a single brachytherapy isodose line, and a step wedge filter constructed to conform to multiple brachytherapy isodose lines. A customized step wedge filter has the potential to produce a more homogeneous dose distribution but has not achieved widespread use due to labor intensive construction. We have developed a simple, novel method to produce a custom midline step wedge using dynamic multileaf collimation (dMLC). A comparison of film measurements in a phantom with the dose calculated by a commercial treatment planning system demonstrated agreement within 3% or 3 mm. The technique requires delivery times comparable to conventional techniques. 相似文献
75.
Jasmin Shen Robert Brackett Thomas Fischer Alan Holder Frank Kellogg J. Gabriel Michael 《Infection and immunity》1981,32(2):967-968
Immunoglobulin E antibodies to Psuedomonas aeruginosa were demonstrated in patients with cystic fibrosis colonized with the bacterium. 相似文献
76.
Human mini-chromosomes in mouse embryonal stem cells 总被引:3,自引:2,他引:3
We have introduced human mini-chromosomes of 4 Mb and approximately 15 Mb
in size into mouse embryonal stem cells. Although these human mini-
chromosomes are stable in hamster and chicken cells, they re-arrange or
segregate aberrantly in the embryonal stem cells and are rapidly lost in
the absence of selection. However, one of the mini-chromosomes re-
arranged, acquired mouse centromeric sequences and was then stably
maintained for at least 60 population doublings in culture. This mini-
chromosome, which is 4 Mb in size, is a candidate for a mouse germ line
chromosome vector.
相似文献
77.
Roberts-Thomson PJ Male DA Walker JG Cox SR Shen X Smith MD Ahern MJ Turner DR 《Asian Pacific journal of allergy and immunology / launched by the Allergy and Immunology Society of Thailand》2004,22(2-3):153-158
Scleroderma is an enigmatic rheumatic disorder of uncertain etio-pathogenesis. Cancer has an approximately two-fold higher incidence in scleroderma patients than in the general population. There are preliminary data of acquired genetic damage in scleroderma but the significance of these observations are uncertain. To determine somatic mutation frequency at the glycophorin-A (GPA) locus in patients with limited and diffuse cutaneous scleroderma. The GPA assay measures the total somatic mutation frequency (Vf), composed of gene inactivating mutations (NO) and mutations arising from mitotic recombination (NN) in individuals heterozygous for the GPA MN blood group. Mutation frequency was determined using a validated GPA flow cytometric assay using fluorescent labeled monoclonal antibodies specific for the GPA blood groups M and N. This assay detects and enumerates progeny of red blood cell (rbc) precursor cells which have acquired genetic damage resulting in a loss of expression of one of the GPA alleles. It was found that patients with scleroderma (n = 23) had significantly elevated Vf as compared with young healthy controls (p < 0.001) and elderly controls (p = 0.03). Patients with diffuse scleroderma had higher mean Vf as compared with limited scleroderma (p = 0.055). In comparison with controls, patients with scleroderma exhibit a higher proportion of mitotic recombinant mutations than inactivating mutations (p < 0.002). There was no correlation between Vf and disease duration, age at onset or autoantibody status. We have documented evidence of acquired genetic damage at the GPA locus in scleroderma. Evidence of acquired genetic damage in this disorder may be importance in explaining both the etio-pathogenesis of scleroderma and the association of scleroderma with cancer. 相似文献
78.
Unlike the penetrating monoenergetic 662 keV gamma rays emitted by 137Cs LDR sources, the spectrum of 192Ir used in HDR brachytherapy contains low-energy components. Since these are selectively absorbed by the high-atomic number materials of which intracavitary applicators are made, the traditional neglect of applicator attenuation can lead to appreciable dose errors. We investigated the attenuation effects of a uterine applicator, and of a set of commonly used vaginal cylinders. The uterine applicator consists of a stainless steel source guide tube with a wall thickness of 0.5 mm and a density of 8.02 g/cm3, whereas the vaginal cylinders consist of the same stainless steel tube plus concentric polysulfone cylinders with a radius of 1 or 2 cm and a density of 1.40 g/cm3. Monte Carlo simulations were performed to compute dose distributions for a bare 192Ir-HDR source, and for the same source located within the applicators. Relative measurements of applicator attenuation using ion-chambers (0.125 cm3) confirmed the Monte Carlo results within 0.5%. We found that the neglect of the applicator attenuation overestimates the dose along the transverse plane by up to 3.5%. At oblique angles, the longer photon path within applicators worsens the error. We defined attenuation-corrected radial dose and anisotropy functions, and applied them to a treatment having multiple dwell positions inside a vaginal cylinder. 相似文献
79.
Snapper CM Shen Y Khan AQ Colino J Zelazowski P Mond JJ Gause WC Wu ZQ 《Trends in immunology》2001,22(6):308-311
Studies have indicated that purified soluble polysaccharide antigens can elicit T cell-independent Ig responses in vivo, although these responses can be modulated by T cells in a noncognate manner. Relatively little is known, however, concerning the parameters that regulate polysaccharide-specific, as well as protein-specific, Ig isotype responses to an intact extracellular bacterium. Using the murine in vivo humoral response to intact Streptococcus pneumoniae as a model it can be shown that CD4+ T-cell receptor alphabeta+ T cells deliver help for both polysaccharide- and protein-specific Ig responses. However, these responses differ fundamentally in their mechanism of action. 相似文献
80.