全文获取类型
收费全文 | 63997篇 |
免费 | 5969篇 |
国内免费 | 3484篇 |
专业分类
耳鼻咽喉 | 561篇 |
儿科学 | 1046篇 |
妇产科学 | 489篇 |
基础医学 | 5755篇 |
口腔科学 | 1190篇 |
临床医学 | 7937篇 |
内科学 | 7263篇 |
皮肤病学 | 889篇 |
神经病学 | 2073篇 |
特种医学 | 2327篇 |
外国民族医学 | 7篇 |
外科学 | 5209篇 |
综合类 | 14602篇 |
现状与发展 | 14篇 |
一般理论 | 2篇 |
预防医学 | 6629篇 |
眼科学 | 990篇 |
药学 | 7838篇 |
71篇 | |
中国医学 | 5008篇 |
肿瘤学 | 3550篇 |
出版年
2024年 | 252篇 |
2023年 | 755篇 |
2022年 | 2043篇 |
2021年 | 2672篇 |
2020年 | 2167篇 |
2019年 | 1543篇 |
2018年 | 1616篇 |
2017年 | 1876篇 |
2016年 | 1651篇 |
2015年 | 2749篇 |
2014年 | 3554篇 |
2013年 | 4116篇 |
2012年 | 5777篇 |
2011年 | 6151篇 |
2010年 | 4935篇 |
2009年 | 4269篇 |
2008年 | 4619篇 |
2007年 | 4477篇 |
2006年 | 4018篇 |
2005年 | 3267篇 |
2004年 | 2416篇 |
2003年 | 2204篇 |
2002年 | 1811篇 |
2001年 | 1430篇 |
2000年 | 1044篇 |
1999年 | 558篇 |
1998年 | 271篇 |
1997年 | 222篇 |
1996年 | 179篇 |
1995年 | 158篇 |
1994年 | 134篇 |
1993年 | 78篇 |
1992年 | 96篇 |
1991年 | 73篇 |
1990年 | 46篇 |
1989年 | 43篇 |
1988年 | 27篇 |
1987年 | 31篇 |
1986年 | 21篇 |
1985年 | 14篇 |
1984年 | 11篇 |
1983年 | 11篇 |
1981年 | 4篇 |
1979年 | 21篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1970年 | 4篇 |
1969年 | 6篇 |
1968年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
钟向真 《中国优生与遗传杂志》2006,14(11):70-71,74
目的探讨三种不同方法治疗自身免疫型习惯性流产的临床效果。方法选取78例确诊为自身免疫异常引起的习惯性流产患者,分为4组,1为阿司匹林+泼尼松组(22例),2为阿司匹林+肝素组(18例),3为静丙组(20例),4为对照组(18例),不接受任何治疗,用卡方检验比较各组妊娠成功率。结果1、2、3组与对照组分别比较,差异均有统计学意义(P〈0.05),但3种治疗方法之间无显著差异(P〉0.05);1组出现了胎膜早破、妊娠期高血压疾病等妊娠合并症,2组出现了早产和消化道出血,但各组发生率无统计学差异(P〉0.05)。结论传统的激素、抗凝剂和被动免疫疗法均有一定疗效,但三者之间疗效无差异。 相似文献
32.
To optimize fitness under conditions of varying Darwinian opportunity, organisms demonstrate tremendous plasticity in their life-history strategies based on their perception of available resources. Higher-energy environments generally promote more aggressive life-history strategies, such as faster growth, larger adult size, greater genetic variation, shorter lifespan, larger brood sizes, and offspring ratio skewed towards the larger-sized gender. While numerous mechanisms regulate life-history plasticity including genetic imprinting, methylation, and growth factors, evidence suggests that thyroid hormone plays a central role. Given the pivotal adaptive role of thyroid hormone, the teleology of its dependence on dietary iodine for production remains unexplained. We hypothesize that iodine may have emerged as a substrate for production of thyroid hormone in prehistoric ecosystems because the former represented a reliable proxy for ecologic potential that enabled the latter to modulate growth, reproduction, metabolic rate, and lifespan. Such a scenario may have existed in early marine ecosystems where ocean-surface vegetation, which concentrates iodine for its antimicrobial and antioxidant properties, formed the basis of the food chain. Teleologic parallels can be drawn to the food-chain accumulation of antimicrobials that also exhibit antioxidant properties and promote adult size, brood size, and offspring quality by modulating central hormonal axes. As each higher species in the food chain tunes its life-history strategy based on iodine intake, the coupling of this functional role of iodine with its value as a resource signal to the next member of the food-chain may promote runaway evolution. Whereas predators in prehistoric ecosystems successfully tuned their life-history strategy using iodine as a major input, the strategy may prove maladaptive in modern humans for whom the pattern of iodine intake is decoupled from resource availability. Iodine acquired through sodium iodide supplementation may independently contribute to some biologic dysfunctions currently attributed to sodium. 相似文献
33.
为了探讨趋化性细胞因子在体外对人Tc1和Tc2亚群细胞内Ca2 + 浓度变化的影响 ,从PBMC中分离纯化CD8+ T细胞 ,在特定细胞因子及细胞因子抗体作用下 ,体外定向诱导出能长期培养的Tc1和Tc2细胞系 ,用免疫荧光染色结合流式细胞术分析对其进行鉴定后 ,通过流式细胞术检测在趋化性细胞因子刺激前后 ,细胞内Ca2 + 浓度的变化。发现受SDF 1作用后 ,Tc1及Tc2细胞内Ca2 + 浓度变化均不明显 ,而IP 10刺激后 ,Tc1及Tc2细胞内Ca2 + 水平在短时间内明显上调 ,且在Tc1胞内的上升幅度远高于Tc2细胞 ,在MIP 1β刺激后 ,也观察到类似趋势 ;受Eotaxin刺激后 ,Tc1及Tc2细胞内Ca2 + 水平均有微小上升 ,在Tc2细胞内的上升幅度略高于Tc1细胞。说明Tc1和Tc2细胞受趋化性细胞因子作用后 ,细胞内Ca2 + 浓度有不同程度的变化 ,且与趋化性细胞因子受体的表达呈现一定的相关性。 相似文献
34.
Single nucleotide variation analysis in 65 candidate genes for CNS disorders in a representative sample of the European population 下载免费PDF全文
Freudenberg-Hua Y Freudenberg J Kluck N Cichon S Propping P Nöthen MM 《Genome research》2003,13(10):2271-2276
The detailed investigation of variation in functionally important regions of the human genome is expected to promote understanding of genetically complex diseases. We resequenced 65 candidate genes for CNS disorders in an average of 85 European individuals. The minor allele frequency (MAF), an indicator of weak purifying selection, was lowest in radical amino acid alterations, whereas similar MAF was observed for synonymous variants and conservative amino acid alterations. In noncoding sequences, variants located in CpG islands tended to have a lower MAF than those outside CpG islands. The transition/transversion ratio was increased among both synonymous and conservative variants compared with noncoding variants. Conversely, the transition/transversion ratio was lowest among radical amino acid alterations. Furthermore, among nonsynonymous variants, transversions displayed lower MAF than did transitions. This suggests that transversions are associated with functionally important amino acid alterations. By comparing our data with public SNP databases, we found that variants with lower allele frequency are underrepresented in these databases. Therefore, radical variants obtain distinctively lower database coverage. However, those variants appear to be under weak purifying selection and thus could play a role in the etiology of genetically complex diseases. 相似文献
35.
重复电刺激前肢神经引起成年大鼠运动皮层的可塑性改变 总被引:2,自引:0,他引:2
为了了解成年大鼠运动皮层的功能可塑性,利用皮层内微刺激方法测定MI代表区并观察重复电刺激前肢神经对MI代表区的影响。实验组大鼠(9例)持续1.2-2小时的前肢神经电刺激导致前肢运动区与面部触须运动区边界向VI方向,移动263.3±90.9μm并同时伴有运动阈值的改变;FL内MT降低5.0±13.3μA,而在VI内MT升高9.6±11.6μA对照组大鼠间隔1.5-2小时的两次测定结果,FL-VI边界 相似文献
36.
用抗CD59单抗2A7与CNBr-Sepharose4B偶联制备亲和层析柱,从正常人红细胞膜蛋白抽提物中分离纯化出CD59分子。本法纯化的CD59分子量为18-20KDa对还原剂敏感,与McAbssMEM43和1F5有高亲和性,再掺入豚鼠红细胞后,能够抑制人体补体的反应性溶血,本文还对三株抗CD59单抗2A7,MEM43及1F5的抗原特异性进行了初步分析。 相似文献
37.
Effects of transgenes for human and bovine growth hormones on age-related changes in ovarian morphology in mice 总被引:1,自引:0,他引:1
The expression of human growth hormone (GH) in female transgenic mice (TM) is accompanied by sterility, whereas females expressing the bovine GH gene are fertile. A light and electron microscopic study was conducted to examine whether expression of these foreign GH genes in mice is associated with structural changes in the ovaries of young adult (3-month-old) or middle-aged (7-month-old) mice. One ovary was serially sectioned for light microscopy, and the contralateral ovary was used for electron microscopy. The numbers of preantral (PAF) and antral (AF) follicles, with and without signs of atresia, as well as the number of corpora lutea (CL), were determined. As expected, body weights of both young and middle-aged TM of either kind were significantly increased over those of their normal littermates. However, the ovarian weights of TM and control mice did not differ. In the 3-month-old TM, the ovaries were grossly normal at the light microscopic level. However, significantly more CL were counted in the ovaries of human GH-TM than in those of the other two groups. The percentage of PAF with signs of atresia was significantly reduced in ovaries of bovine GH-TM compared with the other groups, while the percentages of AF undergoing atresia were significantly different in all groups, with the highest values in normal animals, intermediate ones in human GH-TM, and the lowest in bovine GH-TM. In the ovaries of 7-month-old human GH-TM, conspicuous clusters of large, foamy light cells were present in the cortex and the medulla. Ultrastructurally, these cells appeared as interstitial cells in various stages of degeneration, accumulating cholesterol crystal-like inclusions. Although degeneration of interstitial cells was observed also in the other types of animals, it involved usually only single cells and no cytoplasmic crystal inclusions. Moreover, in the ovaries of 7-month-old human GH-TM the percentages of PAF were significantly reduced and the percentages of AF significantly increased compared with those in the two other groups, which did not differ from each other with respect to these parameters. No significant differences in the numbers of CL were found between the groups. Percentages of atretic PAF were significantly reduced in bovine GH-TM and comparable in the other two groups, while percentages of atretic AF were not different between normal and bovine GH-TM, but were significantly increased in human GH-TM.(ABSTRACT TRUNCATED AT 400 WORDS) 相似文献
38.
为获取有功能的IV型II类反式激活因子基因 (CIITA IV ) ,诱导肿瘤细胞表达MHCII类分子 ,从IFN γ刺激的THP 1细胞中以RT PCR获得CIITA IV ,将其连接到pGEMT easy载体。对所构建的pcDNA3 1 CIITA IV型表达载体进行反复测序后发现 ,所获得的CIITA IV基因存在结构变异 ,在 2 87位插入了 3个核苷酸TAG ,使 2 86 2 88位的AAG改变成为ATAGAG(2 86 2 90 ) ,并引起其他 8个座位核苷酸 (及推导的氨基酸残基 )发生改变。将表达载体转入原先不表达MHCII类分子的HeLa细胞中 ,检测到所获得的IV型CIITA变异体具有诱导人II类分子HLA DR表达的能力。空载体和CIITA IV基因导入的HeLa细胞中 ,DR阳性细胞百分率分别为 0 0 1 %和 37 6 4 %。该基因已从GenBank得到登录号 ,表明这是一个具有诱导HLA DR分子表达功能的IV型CIITA新基因。 相似文献
39.
Lymphoproliferative disorders comprise a heterogeneous group of neoplasms whose behaviors range from indolent to very aggressive. The increased incidence seen in the context of immunodeficiency provides evidence that the host immune system plays a vital role in their pathogenesis. We believe that T-helper (Th)-2 dominant states favor development of lymphoproliferative disorders, including lymphoma, and conversely T-helper (Th)-1 immunity protects against lymphoproliferative disease. The age distribution of lymphomas favors childhood and post-reproductive senescence, suggesting that exposure to these periods of Th-2 bias constitutes a key risk factor for developing the disease. The tendency of lymphomas to arise in Th-2 biased locations such as mucosal interfaces, immunoprivileged sites, and regions of B-cell differentiation may likewise reflect a corresponding spatial predilection. Various clinical conditions or treatments that shift Th1/Th2 balance, including HIV infection, transplant-related immune suppression, and autoimmune disorders, can also influence the status of lymphoproliferative diseases. 相似文献
40.
近年来 ,脑功能成像技术发展迅速 ,已在脑科学研究中占有重要地位。研究中通常需要将同一被试的多种模式成像结果或同一模式的时间序列结果结合起来分析 ,首先要解决的问题就是几幅图像的严格对齐问题 ,即所谓的图像配准。在模拟退火算法和其它工作的基础之上 ,较好的解决了图像配准中的连续变量全局优化问题 ,通过基于点的配准方法 ,实现了时间序列脑功能图像的高精度配准。 相似文献