全文获取类型
收费全文 | 12784篇 |
免费 | 1225篇 |
国内免费 | 367篇 |
专业分类
耳鼻咽喉 | 39篇 |
儿科学 | 106篇 |
妇产科学 | 67篇 |
基础医学 | 1261篇 |
口腔科学 | 291篇 |
临床医学 | 922篇 |
内科学 | 1353篇 |
皮肤病学 | 118篇 |
神经病学 | 636篇 |
特种医学 | 800篇 |
外科学 | 543篇 |
综合类 | 1617篇 |
一般理论 | 1篇 |
预防医学 | 2226篇 |
眼科学 | 103篇 |
药学 | 2479篇 |
5篇 | |
中国医学 | 717篇 |
肿瘤学 | 1092篇 |
出版年
2024年 | 24篇 |
2023年 | 160篇 |
2022年 | 282篇 |
2021年 | 594篇 |
2020年 | 526篇 |
2019年 | 458篇 |
2018年 | 451篇 |
2017年 | 463篇 |
2016年 | 512篇 |
2015年 | 494篇 |
2014年 | 874篇 |
2013年 | 958篇 |
2012年 | 722篇 |
2011年 | 810篇 |
2010年 | 599篇 |
2009年 | 614篇 |
2008年 | 550篇 |
2007年 | 490篇 |
2006年 | 481篇 |
2005年 | 390篇 |
2004年 | 342篇 |
2003年 | 346篇 |
2002年 | 286篇 |
2001年 | 258篇 |
2000年 | 192篇 |
1999年 | 220篇 |
1998年 | 179篇 |
1997年 | 178篇 |
1996年 | 151篇 |
1995年 | 143篇 |
1994年 | 141篇 |
1993年 | 109篇 |
1992年 | 119篇 |
1991年 | 105篇 |
1990年 | 101篇 |
1989年 | 104篇 |
1988年 | 96篇 |
1987年 | 80篇 |
1986年 | 77篇 |
1985年 | 106篇 |
1984年 | 88篇 |
1983年 | 69篇 |
1982年 | 70篇 |
1981年 | 54篇 |
1980年 | 56篇 |
1979年 | 61篇 |
1978年 | 39篇 |
1977年 | 47篇 |
1976年 | 32篇 |
1975年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
91.
Dendritic spines in the visual cortex of the mouse: Introduction to a mathematical model 总被引:1,自引:0,他引:1
F. Valverde A. Ruiz-Marcos 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1969,8(3):269-283
Summary The spines of apical dendrites of the layer V pyramidal cells of the area striata in the mouse represent a sequence of post-synaptic structures receiving a variety of contacts from terminal fibers derived fundamentally from short axon cells and superficial pyramidal cells. The study of Golgi preparations of mice 180 days old shows the existence of the most complicated terminal structures over portions of apical dendrites at the levels of layers III and IV. Observations on young mice reveals the terminations of the specific afferent fibers on the dendrites of short axon cells. A mathematical model which defines the distribution of spines along the apical dendrites is introduced. The principal equation of the model has been adjusted from the data processing of microscope countings through a series of programs written for an IBM 7070. The equation defines satisfactorily the different distributions of dendritic spines in mice 10–180 days old raised in normal conditions and in complete darkness. The equation defines also the distribution of dendritic spines in the visual cortex of mice enucleated at birth on one side, and the distribution along the apical dendrites of various cortical areas of the hamster, cat and man. The number of dendritic spines increases with the age of the subject and their distribution varies significantly according to the values of the parameters of the model. 相似文献
92.
Z Zhao F Kong X Zeng H F Gidding J Morgan G L Gilbert 《Clinical microbiology and infection》2008,14(3):260-267
Serotype distribution and antibiotic resistance (AR) among group B streptococci (GBS) affect GBS disease prevention strategies, but vary among patient groups. A multiplex PCR-based reverse line blot (mPCR/RLB) hybridisation assay was used to compare the distributions of GBS serotypes, serotype III subtypes and AR-associated genes among 666 invasive isolates from 663 patients, divided into five age groups: infants, early-onset (EO; 0-6 days) and late-onset (LO; 7-90 days); children (aged 3 months to 14 years); women of childbearing age (WCBA; aged 15-45 years); and other adults (males aged >15 years; females aged >45 years). Serotypes Ia and V and serosubtype III-1 accounted for 60% of infections. Serosubtype III-2, which corresponds to a virulent clone belonging to sequence type (ST)17, was relatively uncommon overall (7%), but was associated strongly with LO infant infections, in which it was significantly more common than in adult infections (25/104 (24%) vs. 9/392 (2%), p <0.0001) or in EO infections (25/104 (24%) vs. 14/155 (9%), p <0.005). Erythromycin resistance genes were found in 8% of all isolates (ermB 3%, ermA 2.5% and mefA/E 2%), in 11-15% of isolates of serotypes II and V and subtype III-1, but in none of the isolates of serosubtype III-2 (III-2, 0/49 vs. all others, 54/618 (9%), p <0.04). In summary, the virulent serosubtype III-2 was associated strongly with LO infant GBS infection, but was less likely than other serotypes or serosubtype III-1 to carry AR genes. 相似文献
93.
Yasushi Nakayama Junji Saito Hideki Bando Terunori Fujita 《Macromolecular chemistry and physics.》2005,206(18):1847-1852
Summary: Fluorinated bis(phenoxy‐imine)Ti complexes 1 – 3 combined with MgCl2/i‐BunAl(OR)3−n (MgCl2‐supported catalysts) were able to polymerize propylene in a living fashion at room temperature to provide slightly to highly syndiotactic poly(propylenes) (PPs) with extremely narrow distributions of molecular weight. These represent the first examples of MAO‐ and borate‐free group 4 metal‐based living catalysts. The supported complexes 2 and 3 formed PPs with higher syndiotacticity and Tm's than the corresponding homogeneous MAO‐activation systems (e.g., 3 : rr 97%, Tm 155 °C; MAO activation: rr 93%, Tm 152 °C). The measured Tm of 155 °C represents the highest known Tm for syndiotactic PPs synthesized at room temperature.
94.
在心室晚电位的研究中,我们引入了信号的时间一频率表示法,并根据晚电位的具体特性用Wigner分布法(维格纳分布)把信号表示为在时间及频率空间中的能量分布。由于Wigner分布的优异性质使我们有可能更准确表示出心室晚电位的存在。但当输入信号是两个信号的线性叠加时,Wigner分布的结果会出现一个交叉项,相当于引入干扰。针对此不足,作者介绍改进方案,消除部分交叉项,收到较好的效果,并给出一些仿真及应用实例。 相似文献
95.
K. J. Ullrich G. Rumrich K. Neiteler G. Fritzsch 《Pflügers Archiv : European journal of physiology》1992,420(1):29-38
In order to study the quantitative structure/activity relationship of organic cation transport across the contraluminal side of the proximal renal tubule cell, the stopped-flow capillary microperfusion method was applied and the inhibitory potency (apparent K
i values) of different homologous series of substrates against N
1-[3H]methylnicotinamide (NMeN+) transport was evaluated. Aniline and its ring- or N-substituted analogues as well as the aminonaphthalines do not interact with the contraluminal NMeN+ transporter except for the quaternary trimethylphenylammonium and pararosaniline, which bear a permanent positive charge, and for 1,8-bis-(dimethylamino)naphthaline, which forms an intramolecular hydrogen bond. If, however, one or more than one methylene group is interposed between the benzene ring and the amino group, the compounds interact with the contraluminal NMeN+ transporter in proportion to their hydrophobicity parameter, i.e. the octanol/water partition coefficient (log octanol). The catecholamines and other hydroxyl-substituted phenylethyl analogues also follow this rule. In addition, the N-heterocyclic pyridine, quinoline, isoquinoline and acridine analogues also interact with the contraluminal NMeN+ transporter, when their pK
a values are higher than 5.0, and, an inverse correlation between pK
a and log K
i, NMeN was observed. An exception to this rule are those hydroxy compounds of pyridine, quinoline and isoquinoline that show tautomerism. These compounds slightly inhibit NMeN+ transport despite low pK
a values. The quaternary nitrogen compounds of aniline and the N-heterocyclic analogues, as far as tested, all interact with the contraluminal NMeN+ transporter in relation to their hydrophobicity. The data indicate that the contraluminal NMeN+ transporter interacts with N-compounds according to their hydrophobicity and/or according to their basicity (affinity to protons). The reason for deviation of the aniline analogues and the OH-tautomeric heterocyclic N-compounds from this behaviour is discussed. 相似文献
96.
97.
本文提出了一个计算高能重带电粒子束平衡能量的简单公式。在计算重带电粒子放射治疗剂量时,用此公式可获得与平均能量有关的物理量的解析表达式,用此公式计算了入射铝内10-MeV的质子束的平均能量,并与相应的实验数据作了比较,比较表明,本文提出的公式在相当大的能量范围内能够精确地预言重带电粒子的平均能量,此外,还计算了在水中在100-MeV、150-MeV和200-MeV的质子束的平均能量。 相似文献
98.
Neoplastic cells generally present profound changes in glucose metabolism. The mechanisms underlying such process are numerous and all may involve altered cellular hormonal responses. Here we report the first evidence that cellular location of phosphofructokinase activity in human breast cancer tissues is different from the one observed in control tissues and that this phenomenon may be involved in the increased glycolytic flux observed in those cells. Through co-sedimentation techniques, we observed that 60% of phosphofructokinase activity in neoplastic tissues is located in an actin-enriched fraction, against 36% in control tissues. Additionally, metastatic tumor tissues presented a two fold increase in this particulate activity when compared to non-metastatic tumor samples. We propose that the alteration in cellular distribution of phosphofructokinase activity in human breast cancer tissues is a mechanism associated to the process of cell transformation and may be a consequence of the altered hormonal milieu observed in several types of cancer. 相似文献
99.
L. Jakobsen D. Sandvang V. F. Jensen A. M. Seyfarth N. Frimodt-Møller A. M. Hammerum 《Clinical microbiology and infection》2007,13(8):830-832
In total, 120 Escherichia coli isolates positive for one of the gentamicin resistance (GEN(R)) genes aac(3)-II, aac(3)-IV or ant(2')-I were tested for gentamicin susceptibility by the agar dilution method. Isolates positive for aac(3)-IV or ant(2')-I had an MIC distribution of 8-64 mg/L, whereas isolates positive for aac(3)-II had MICs of 32 to >512 mg/L, suggesting a relationship between the distribution of MICs and the specific GEN(R) mechanism. The MIC distribution, regardless of the GEN(R) mechanism, was 8 - >512 mg/L, which supports the clinical breakpoint of MIC >4 mg/L suggested by EUCAST and questions the breakpoint recommended by the CLSI (> or =16 mg/L). 相似文献
100.
Rybnikova EA Pelto-Huikko M Rakitskaya VV Shalyapina VG 《Neuroscience and behavioral physiology》2003,33(4):399-404
In situ hybridization was used to study the distribution of corticoliberin receptors of subtypes 1 and 2 (CL-R1 and CL-R2 respectively) in different structures of the rat brain. Levels of CL-R1 mRNA in the brain were significantly greater than levels of CL-R2 mRNA, and the most intense expression of the CL-R1 gene was seen in forebrain structures, especially various neocortical, archicortical, and paleocortical regions in the cerebellar cortex. In addition, significant levels of CL-R1 mRNA expression were noted in the red nucleus and the reticular nucleus of the tegmentum. Intense expression of CL-R2 mRNA was observed in structures of the olfactory system, corticomedial parts of the amygdala, fields CA1–CA4 of the hippocampus, the ventromedial hypothalamus, and several brain stem nuclei. Moderate levels of CL-R2 mRNA were seen in the dorsolateral neostriatum. These results provide evidence that corticoliberin receptors of both subtypes are widespread in the brain. The different patterns of expression of CL-R1 and CL-R2 in the brain probably provide the basis for the functional specificity of action of corticoliberin in brain structures. 相似文献