全文获取类型
收费全文 | 4027篇 |
免费 | 298篇 |
国内免费 | 39篇 |
专业分类
耳鼻咽喉 | 65篇 |
儿科学 | 121篇 |
妇产科学 | 141篇 |
基础医学 | 473篇 |
口腔科学 | 101篇 |
临床医学 | 510篇 |
内科学 | 753篇 |
皮肤病学 | 82篇 |
神经病学 | 213篇 |
特种医学 | 258篇 |
外国民族医学 | 1篇 |
外科学 | 668篇 |
综合类 | 166篇 |
一般理论 | 1篇 |
预防医学 | 229篇 |
眼科学 | 90篇 |
药学 | 228篇 |
中国医学 | 5篇 |
肿瘤学 | 259篇 |
出版年
2021年 | 48篇 |
2020年 | 31篇 |
2019年 | 52篇 |
2018年 | 71篇 |
2017年 | 45篇 |
2016年 | 56篇 |
2015年 | 62篇 |
2014年 | 111篇 |
2013年 | 133篇 |
2012年 | 185篇 |
2011年 | 172篇 |
2010年 | 125篇 |
2009年 | 129篇 |
2008年 | 193篇 |
2007年 | 171篇 |
2006年 | 199篇 |
2005年 | 157篇 |
2004年 | 130篇 |
2003年 | 160篇 |
2002年 | 174篇 |
2001年 | 117篇 |
2000年 | 146篇 |
1999年 | 109篇 |
1998年 | 65篇 |
1997年 | 51篇 |
1996年 | 45篇 |
1995年 | 51篇 |
1994年 | 35篇 |
1993年 | 33篇 |
1992年 | 75篇 |
1991年 | 79篇 |
1990年 | 79篇 |
1989年 | 93篇 |
1988年 | 83篇 |
1987年 | 86篇 |
1986年 | 78篇 |
1985年 | 70篇 |
1984年 | 57篇 |
1983年 | 68篇 |
1982年 | 42篇 |
1981年 | 47篇 |
1980年 | 42篇 |
1979年 | 52篇 |
1978年 | 28篇 |
1977年 | 26篇 |
1975年 | 23篇 |
1974年 | 40篇 |
1973年 | 25篇 |
1972年 | 32篇 |
1969年 | 27篇 |
排序方式: 共有4364条查询结果,搜索用时 339 毫秒
21.
22.
Two systems allowing quantitative, objective analysis of sperm movement were compared: 1) the Hamilton-Thorn Motility Analyzer (HTM), in which sperm images are digitized automatically, and 2) the Image-80, a modified image-analysis system in which sperm movement is digitized manually by hand tracing from videotape (Tessler and Olds-Clarke, 1985). Videotapes were made of human spermatozoa obtained by a swim-up procedure. The same videotape frames were analyzed by both systems. The mean percentage of motile spermatozoa was similar as judged by eye with either the HTM or Image-80 monitors and as reported by the HTM. For every motile spermatozoon, two motility parameters were calculated: linearity (a measure of track shape) and curvilinear velocity at 30 frames/second (a measure of track speed). When samples from five donors were averaged, there were no significant differences in mean linearity between automatic and manual systems. Also, linearity as reported by the HTM and Image-80 systems for the same track was significantly correlated (r = 0.72; N = 80). Whereas the absolute values for curvilinear velocity were slightly but significantly higher for the Image-80 system than for the HTM system, their correlation was also significant (r = 0.91). Since the two systems provide comparable data on percentage of motile sperm as well as speed and path shape parameters, this suggests that the HTM automatic digitization is accurate for images of human spermatozoa. 相似文献
23.
24.
Despite sufficient iodine supply, goiter continues to be of considerable surgical significance in formerly endemic countries. It now appears that iodine deficiency and increased thyrotropin stimulation are not the only causes of goiter. Xenotransplantation of human thyroid tissue onto nude mice allowed study of the regulation of growth and function in human goiter tissue. Grafts of human thyroid tissue growing in nude mice could be shown to react to endogenous mouse thyrotropic stimulation and suppression. 131I autoradiographs of xenotransplanted goiter tissue showed as marked a heterogeneity as did the original goitrous tissue prior to transplantation. There was no firm correlation between the morphologic appearance of a follicle and its iodine metabolism. Scintigraphically "cold" and "hot" goiter tissue differed from each other quantitatively but not qualitatively; i.e., both "hot" and "cold" tissue were composed of metabolically active and nonactive follicles. Iodine organification was not completely suppressible by thyroxine treatment; this indicates autonomous functional activity. The distribution of proliferating tissue labeled by 3-H-thymidine did not parallel the distribution of functionally active tissue labelled by 131I. Thyroxine treatment did not completely inhibit 3-H-thymidine incorporation, indicating autonomous growth. Thus, our pathogenetic concept of goiter formation is based on three mainstays: (1) goiter heterogeneity, (2) autonomy of growth and function, and (3) dissociation of growth and function in human goiter tissue. Thus, the surgeon dealing with goiter ought to remove all pathologically altered tissue, i.e., nodular tissue, irrespective of its appearance on scintiscans. 相似文献
25.
Based on a study of 105 patients and a comprehensive literature review we recommend a prophylactic regimen for orthopaedic procedures which is easily adaptable to the needs of individual clinics. The regimen is especially designed for joint replacements and includes basically the following four points: 1. parenteral prophylaxis with cefazolin 1 g every 6 hours for 24 hours; the first dose is given between 10 and 30 minutes before surgery (for knee-replacement the initial dose is 2 g); 2. use of bone cement impregnated with antibiotics, e.g. Palacos-Gentamycin-cement; 3. when possible the operation should be performed in a theater equipped with "ultra-clean-air" laminar air-flow and the surgeon should wear "whole-body-exhaust" suits or suits made of "Fabric 450"; 4. antibiotic selection as outlined in points one and two must be adjusted over time based on ongoing monitoring of antimicrobial resistance in the individual clinic. 相似文献
26.
Although commercial rapid antigen detection tests (RADTs) are more expensive than blood agar plate (BAP) cultures, the advantage they offer is the speed with which they provide results. Rapid identification and consequent prompt treatment of patients with pharyngitis due to group A beta-hemolytic streptococci (GABHS) can reduce the risk of spread of GABHS, can allow patients to return to school or work sooner, and may reduce the acute morbidity of this illness. In most studies, RADTs have been compared with BAP cultures as the criterion standard. However, these comparisons are complicated by the fact that there is no universally accepted procedure for performing a BAP culture. The great majority of the RADTs that are currently available have a high specificity (i.e., 95% or greater) and a sensitivity of between 70 and 90% compared with BAP cultures. Few published studies have compared the performance of various RADTs to each other or examined the performance of various RADTs in the office setting. There is also relatively little published information about how physicians in practice actually use RADTs, but the available information suggests that many physicians do not follow recommended guidelines. While the development of easy-to-perform RADTs for the diagnosis of GABHS pharyngitis has altered clinical practice substantially, only limited data about cost-effectiveness are currently available. 相似文献
27.
Recent reports of human immunodeficiency virus-1 (HIV-1) infection of astrocytes suggest a role for astrocytes in HIV encephalitis. In this study, we infected a human astrocytoma cell line with a pathogenic simian HIV (SHIV50OLNV) and examined growth patterns and immunomodulatory genes. Approximately 1% of uninfected cells in culture expressed glial fibrillary acid protein (GFAP) whereas 40% of the cells expressed GFAP at 7 days post-inoculation along altered growth patterns. Using targeted cytokine cDNA arrays, we found that SHIV50OLNV infection resulted in the up-regulation of several genes including metalloproteinase bone morphogenic protein 1 and chemokines monocyte chemoattractant protein 1 and stromal cell derived factor 1. These data suggest that astrocytic activation, altered morphology and up-regulation of immunomodulatory genes in response to SHIV infection may participate in initiation of inflammation and trafficking of infected monocytes/macrophages into the central nervous system, potentiating the development of HIV encephalitis. 相似文献
28.
Synaptically released glutamate activates ionotropic and metabotropic receptors at central synapses. Metabotropic glutamate receptors (mGluRs) are thought to modulate membrane conductances through transduction cascades involving G proteins. Here we show, in CA3 pyramidal cells from rat hippocampus, that synaptic activation of type 1 mGluRs by mossy fiber stimulation evokes an excitatory postsynaptic response independent of G-protein function, while inhibiting an afterhyperpolarization current through a G-protein-coupled mechanism. Experiments using peptide activators and specific inhibitors identified a Src-family protein tyrosine kinase as a component of the G-protein-independent transduction pathway. These results represent the first functional evidence for a dual signaling mechanism associated with a heptahelical receptor such as mGluR1, in which intracellular transduction involves activation of either G proteins or tyrosine kinases. 相似文献
29.
Decreased virulence of a pneumolysin-deficient strain of Streptococcus pneumoniae in murine meningitis 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《Infection and immunity》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Wellmer A Zysk G Gerber J Kunst T Von Mering M Bunkowski S Eiffert H Nau R 《Infection and immunity》2002,70(11):6504-6508
Pneumolysin, neuraminidases A and B, and hyaluronidase are virulence factors of Streptococcus pneumoniae that appear to be involved in the pathogenesis of meningitis. In a murine model of meningitis after intracerebral infection using mutants of S. pneumoniae D39, only mice infected with a pneumolysin-deficient strain were healthier at 32 and 36 h, had lower bacterial titers in blood at 36 h, and survived longer than the D39 parent strain. Cerebellar and spleen bacterial titers, meningeal inflammation, and neuronal damage scores remained uninfluenced by the lack of any of the virulence factors. 相似文献
30.
Androgen receptor YAC transgenic mice carrying CAG 45 alleles show trinucleotide repeat instability 总被引:1,自引:15,他引:1
La Spada AR; Peterson KR; Meadows SA; McClain ME; Jeng G; Chmelar RS; Haugen HA; Chen K; Singer MJ; Moore D; Trask BJ; Fischbeck KH; Clegg CH; McKnight GS 《Human molecular genetics》1998,7(6):959-967
X-linked spinal and bulbar muscular atrophy (SBMA) is caused by a CAG
repeat expansion in the first exon of the androgen receptor (AR) gene.
Disease-associated alleles (37-66 CAGs) change in length when transmitted
from parents to offspring, with a significantly greater tendency to shift
size when inherited paternally. As transgenic mice carrying human AR cDNAs
with 45 and 66 CAG repeats do not display repeat instability, we attempted
to model trinucleotide repeat instability by generating transgenic mice
with yeast artificial chromosomes (YACs) carrying AR CAG repeat expansions
in their genomic context. Studies of independent lines of AR YAC transgenic
mice with CAG 45 alleles reveal intergenerational instability at an overall
rate of approximately 10%. We also find that the 45 CAG repeat tracts are
significantly more unstable with maternal transmission and as the
transmitting mother ages. Of all the CAG/CTG repeat transgenic mice
produced to date the AR YAC CAG 45 mice are unstable with the smallest
trinucleotide repeat mutations, suggesting that the length threshold for
repeat instability in the mouse may be lowered by including the appropriate
flanking human DNA sequences. By sequence-tagged site content analysis and
long range mapping we determined that one unstable transgenic line has
integrated an approximately 70 kb segment of the AR locus due to
fragmentation of the AR YAC. Identification of the cis - acting elements
that permit CAG tract instability and the trans -acting factors that
modulate repeat instability in the AR YAC CAG 45 mice may provide insights
into the molecular basis of trinucleotide repeat instability in humans.
相似文献