全文获取类型
收费全文 | 5473篇 |
免费 | 303篇 |
国内免费 | 42篇 |
专业分类
耳鼻咽喉 | 48篇 |
儿科学 | 147篇 |
妇产科学 | 71篇 |
基础医学 | 729篇 |
口腔科学 | 155篇 |
临床医学 | 514篇 |
内科学 | 1350篇 |
皮肤病学 | 147篇 |
神经病学 | 670篇 |
特种医学 | 348篇 |
外科学 | 655篇 |
综合类 | 52篇 |
一般理论 | 1篇 |
预防医学 | 270篇 |
眼科学 | 24篇 |
药学 | 268篇 |
中国医学 | 3篇 |
肿瘤学 | 366篇 |
出版年
2020年 | 38篇 |
2019年 | 46篇 |
2018年 | 51篇 |
2017年 | 47篇 |
2016年 | 69篇 |
2015年 | 87篇 |
2014年 | 85篇 |
2013年 | 185篇 |
2012年 | 145篇 |
2011年 | 173篇 |
2010年 | 137篇 |
2009年 | 155篇 |
2008年 | 168篇 |
2007年 | 194篇 |
2006年 | 171篇 |
2005年 | 206篇 |
2004年 | 187篇 |
2003年 | 173篇 |
2002年 | 165篇 |
2001年 | 166篇 |
2000年 | 150篇 |
1999年 | 166篇 |
1998年 | 152篇 |
1997年 | 123篇 |
1996年 | 151篇 |
1995年 | 96篇 |
1994年 | 95篇 |
1993年 | 95篇 |
1992年 | 106篇 |
1991年 | 125篇 |
1990年 | 130篇 |
1989年 | 131篇 |
1988年 | 138篇 |
1987年 | 138篇 |
1986年 | 115篇 |
1985年 | 111篇 |
1984年 | 97篇 |
1983年 | 77篇 |
1982年 | 71篇 |
1981年 | 52篇 |
1980年 | 46篇 |
1979年 | 75篇 |
1978年 | 69篇 |
1977年 | 62篇 |
1976年 | 59篇 |
1975年 | 58篇 |
1974年 | 63篇 |
1973年 | 56篇 |
1972年 | 55篇 |
1971年 | 59篇 |
排序方式: 共有5818条查询结果,搜索用时 15 毫秒
51.
Swartling J Pålsson S Platonov P Olsson SB Andersson-Engels S 《Medical & biological engineering & computing》2003,41(4):403-409
The optical properties of pig heart tissue were measured after in vivo ablation therapy had been performed during open-heart
surgery. In vitro samples of normal and ablated tissue were subjected to measurements with an optically integrating sphere
set-up in the region 470–900 nm. Three independent measurements were made: total transmittance, total reflectance and collimated
transmittance, which made it possible to extract the absorption and scattering coefficients and the scattering anisotropy
factor g, using an inverse Monte Carlo model. Between 470 and 700 nm, only the reduced scattering coefficient and absorption
could be evaluated. The absorption spectra were fitted to known tissue chromophore spectra, so that the concentrations of
haemoglobin and myoglobin could be estimated. The reduced scattering coefficient was compared with Mie computations to provide
Mie equivalent average radii. Most of the absorption was from myoglobin, whereas haemoglobin absorption was negligible. Metmyoglobin
was formed in the ablated tissue, which could yield a spectral signature to distinguish the ablated tissue with a simple optical
probe to monitor the ablation therapy. The reduced scattering coefficient increased by, on average, 50% in the ablated tissue,
which corresponded to a slight decrease in the Mie equivalent radius. 相似文献
52.
Yau JL Rasmuson S Andrew R Graham M Noble J Olsson T Fuchs E Lathe R Seckl JR 《Neuroscience》2003,121(2):307-314
Neurosteroids such as dehydroepiandrosterone (DHEA), pregnenolone and 17beta-estradiol are synthesized by cytochrome P450s from endogenous cholesterol. We previously reported a new cytochrome P450 enzyme, CYP7B, highly expressed in rat and mouse brain that metabolizes DHEA and related steroids by hydroxylation at the 7alpha position. Such 7-hydroxylation can enhance DHEA bioactivity in vivo. Here we show that the reaction is conserved across mammalian species: in addition to mouse and rat, DHEA hydroxylation activity was present in brain extracts from sheep, marmoset and human. Northern blotting using a human CYP7B complementary deoxyribonucleic acid (cDNA) probe confirmed the presence of CYP7B mRNA in marmoset and human hippocampus; CYP7B mRNA was present in marmoset cerebellum and brainstem, with lower levels in hypothalamus and cortex. In situ hybridization to human brain revealed higher levels of CYP7B mRNA in the hippocampus than in cerebellum, cortex, or other brain regions. We also measured CYP7B expression in Alzheimer's disease (AD). CYP7B mRNA was significantly decreased (approximately 50% decline; P<0.05) in dentate neurons from AD subjects compared with controls. A decline in CYP7B activity may contribute the loss of effects of DHEA with ageing and perhaps to the pathophysiology of AD. 相似文献
53.
Alterations in female gonadal hormones are associated with anxiety and mood changes. The aim of the present study was to determine influences of chronic gonadal hormone supplementation on 5-HT(2A) and 5-HT(2C) receptor mRNA levels in the ventral hippocampus and the frontal cerebral cortex. Ovariectomized adult female Sprague-Dawley rats (n=37) received implantation of subcutaneous pellets containing different dosages of 17beta-estradiol alone or in combination with progesterone, or placebo pellets, for 2 weeks. Serotonin receptor mRNA levels were analyzed by in situ hybridization in the ventral hippocampus and 5-HT(2A) receptor mRNA also in the frontal cortex. Estradiol treatment in combination with low-dose progesterone increased 5-HT(2A) receptor mRNA by 43% in the CA2 region of the ventral hippocampus, while estradiol combined with high-dose progesterone increased the expression of this gene by 84% in ventral CA1. 5-HT(2A) mRNA expression in the frontal cortex was not influenced by hormone manipulation. 5-HT(2C) receptor gene expression was in the ventral hippocampus decreased in the CA2, ventral CA1 and the subiculum subregions by high-dose estradiol treatment (8-20% decreases). Effects on mood by gonadal hormones can be mediated, at least partly, through influences on 5-HT(2A) and 5-HT(2C) receptor expression. 相似文献
54.
Radiation dose measurements with alanine/agarose gel and thin alanine films around a 192Ir brachytherapy source,using ESR spectroscopy 总被引:6,自引:0,他引:6
Olsson S Bergstrand ES Carlsson AK Hole EO Lund E 《Physics in medicine and biology》2002,47(8):1333-1356
Alanine/agarose gel and alanine films in stacks have been used for measurements of absorbed dose around an HDR 192Ir source in a vaginal cylinder-applicator, with and without a 180 degrees tungsten shield. The gel and the films were analysed by means of ESR spectroscopy and calibrated against an ion chamber in a 4 MV photon beam to obtain absolute dose values. The gel serves as both dosimeter and phantom material, and the thin (130 microm) films are used to achieve an improved spatial resolution in the dose estimations. Experimental values were compared with Monte Carlo simulations using two different codes. Results from the measurements generally agree with the simulations to within 5%, for both the alanine/agarose gel and the alanine films. 相似文献
55.
The effects of ageing and of chronic antidepressant treatment upon 5-HT transporter sites ([3H]paroxetine binding) in the rat hippocampus was examined. [3H]paroxetine binding to transporter sites was decreased with ageing in the hippocampus of control rats (38% decrease in dentate gyrus and CA4). Amitriptyline (10 mg/kg, i.p.) had no significant effect on [3H]paroxetine binding in 10 months old rats, but increased binding sites in 24 months rats in all hippocampal subregions (greatest increase of 109% in CA1 compared to saline controls). These data indicate an age-related decrease in hippocampal serotonin transporter sites and upregulation of these sites following 10 weeks of amitriptyline. The observed increase in transporter sites following amitriptyline may contribute to the general lower effectiveness of tricyclic antidepressants with ageing. 相似文献
56.
57.
Missense mutation in a von Willebrand factor type A domain of the alpha 3(VI) collagen gene (COL6A3) in a family with Bethlem myopathy 总被引:2,自引:0,他引:2
Pan TC; Zhang RZ; Pericak-Vance MA; Tandan R; Fries T; Stajich JM; Viles K; Vance JM; Chu ML; Speer MC 《Human molecular genetics》1998,7(5):807-812
The Bethlem myopathy is a rare autosomal dominant proximal myopathy
characterized by early childhood onset and joint contractures. Evidence for
linkage and genetic heterogeneity has been established, with the majority
of families linked to 21q22.3 and one large family linked to 2q37,
implicating the three type VI collagen subunit genes, COL6A1 (chromosome
21), COL6A2 (chromosome 21) and COL6A3 (chromosome 2) as candidate genes.
Mutations of the invariant glycine residues in the triple-helical
domain-coding region of COL6A1 and COL6A2 have been reported previously in
the chromosome 21-linked families. We report here the identification of a
G-->A mutation in the N-terminal globular domain-coding region of COL6A3
in a large American pedigree (19 affected, 12 unaffected), leading to the
substitution of glycine by glutamic acid in the N2 motif, which is
homologous to the type A domains of the von Willebrand factor. This
mutation segregated to all affected family members, to no unaffected family
members, and was not identified in 338 unrelated Caucasian control
chromosomes. Thus mutations in either the triple-helical domain or the
globular domain of type VI collagen appear to cause Bethlem myopathy.
相似文献
58.
An allergic reaction following intrauterine insemination 总被引:1,自引:0,他引:1
Intrauterine insemination is a common procedure used for the treatment of
different causes of infertility. Adverse reactions associated with this
procedure are very rare and usually the procedure is well tolerated by the
patient. We report a case of an allergic reaction after intrauterine
insemination. The patient developed fever, difficulty breathing and
wheezing in both lung fields. Although a low concentration of penicillin in
the medium was used, it caused a significant allergic reaction. When
intrauterine insemination was performed in subsequent cycles with an
antibiotic-free medium, no allergic reaction occurred, and the procedure
was well tolerated by the patient. A careful allergy history is essential
in patients pursuing infertility treatment where antibiotics are utilized.
Patients who are known to be allergic to penicillin should have semen
prepared by an antibiotic-free medium.
相似文献
59.
Guang-Xian Zhang Cun-Gen Ma Bao-Guo Xiao Moiz Bakhiet Hans Link Tomas Olsson 《European journal of immunology》1995,25(5):1191-1198
To understand the role of CD8+ T cells in experimental autoimmune myasthenia gravis (EAMG), CD8+ T cells were depleted by injecting a monoclonal anti-rat CD8 antibody (OX8) into Lewis rats immunized with Torpedo acetylcholine receptor (AChR) in complete Freund's adjuvant (CFA). CD8-depleted EAMG rats showed strikingly less muscle weakness and lower anti-AChR IgG antibody levels compared to Hy2-15-injected control EAMG rats. Moreover, the numbers of AChR-specific IgG antibody-secreting cells, AChR-reactive interferony-γ-secreting T helper type 1-like cells and lymphocyte proliferation to AChR were lower in the CD8-depleted group than in control EAMG rats. These differences were significant among mononuclear cells from inguinal and popliteal lymph nodes, mesenteric lymph nodes and spleen, but not from thymus when examined 3, 5 and 7 weeks post-immunization. We suggest that CD8+ T cells are involved in the induction and persistance of EAMG by directly or indirectly affecting AChR-reactive T cells and anti-AChR IgG antibody-secreting cells. 相似文献
60.