首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   994篇
  免费   68篇
  国内免费   23篇
耳鼻咽喉   4篇
儿科学   19篇
妇产科学   5篇
基础医学   275篇
口腔科学   6篇
临床医学   47篇
内科学   249篇
皮肤病学   17篇
神经病学   140篇
特种医学   11篇
外科学   40篇
综合类   44篇
预防医学   57篇
眼科学   2篇
药学   135篇
中国医学   2篇
肿瘤学   32篇
  2024年   2篇
  2023年   28篇
  2022年   32篇
  2021年   47篇
  2020年   32篇
  2019年   39篇
  2018年   32篇
  2017年   31篇
  2016年   21篇
  2015年   22篇
  2014年   52篇
  2013年   55篇
  2012年   34篇
  2011年   47篇
  2010年   44篇
  2009年   39篇
  2008年   25篇
  2007年   31篇
  2006年   32篇
  2005年   31篇
  2004年   20篇
  2003年   26篇
  2002年   18篇
  2001年   20篇
  2000年   20篇
  1999年   17篇
  1998年   13篇
  1997年   17篇
  1996年   22篇
  1995年   28篇
  1994年   12篇
  1993年   22篇
  1992年   18篇
  1991年   11篇
  1990年   13篇
  1989年   20篇
  1988年   8篇
  1987年   10篇
  1986年   10篇
  1985年   7篇
  1984年   14篇
  1983年   5篇
  1982年   7篇
  1981年   4篇
  1979年   3篇
  1977年   3篇
  1975年   6篇
  1974年   12篇
  1973年   11篇
  1972年   8篇
排序方式: 共有1085条查询结果,搜索用时 15 毫秒
1.
长江北三角平原上所遗存的二十余种记及明代倭患和抗倭战争的古代的碑石文献 ,在数量上据全国各抗倭战区所存的同类文献之首。在内容上 ,对补充旧史的阙失、订正传误、佐证史实、深化研究也有诸多帮助 ,尤其是对廓正对倭寇与倭患问题的认识有着积极的意义  相似文献   
2.
The seroepidemiological profile of HBV and HDV was investigated in 640 male haemophiliacs. Twenty-seven of forty-four HBsAg carriers were anti-HDV-IgG positive, 22 were also anti-HDV-IgM positive. A markedly lower prevalence of HDV infection was found in patients with anti-HBc in the absence of HBsAg and anti-HBs (6/41). Repeated detection of anti-HDV-IgM in 5/41 individuals of this group indicates that circulating HBsAg is not an absolute prerequisite for chronic HDV infection. Overall, chronically active HDV infection was detected more frequently in quiescent than in active chronic HBV infections. Anti-HDV-IgM was not detected in the absence of anti-HDV-IgG antibodies. Anti-HDV-IgG may disappear after resolution of HDV infection, as indicated by the low prevalence (1/42) in such individuals with past HBV infection as well as by loss of anti-HDV-IgG observed in two patients.  相似文献   
3.
取乙型肝炎患者Delta抗体(抗—HD)阳性血清,经硫酸铵盐析和DE—52柱层析,得到纯化的抗—HD抗体,用辣根过氧化物酶标记。用丁型肝炎病毒(HDV)感染慢性携带土拨鼠肝炎病毒的东方土拨鼠(Woodchuck)后,取其肝组织制成匀浆,离心后经Sepharose 4B柱,免疫亲和层析柱,获得高丰度的HDAg。双抗体夹心法测定其滴度高达1∶10~6。制备成ELISA竞争抑制法检测抗HD试剂盒,其特异性、敏感性、重复性与爱尔兰同种试剂比较结果一致。  相似文献   
4.
The previously described cyclic delta opioid receptor-selective tetrapeptide H-Tyr-d -Cys-Phe-d -Pen-OH (JOM-13) was modified at residue 3 by incorporation of both natural and unnatural amino acids with varying steric, electronic, and lipophilic properties. Effects on mu and delta opioid receptor binding affinities were evaluated by testing the compounds for displacement of radiolabeled receptor-selective ligands in a guinea pig brain receptor binding assay. Results obtained with the bulky aromatic 1-Nal3 and 2-Nal3 substitutions suggest that the shape of the receptor subsite with which the side chain of the internal aromatic residue interacts differs for delta and mu receptors. This subsite of either receptor can accommodate the transverse steric bulk of the 1-Nal3 side chain but only the delta receptor can readily accept the more elongated 2-Nal3 side chain. Several analogs with pi-excessive heteroaromatic side chains in residue 3 were examined. In general, these analogs display diminished binding to mu and delta receptors, consistent with previous findings for analogs with residue 3 substitutions of modified electronic character. Several analogs with alkyl side chains in residue 3 were also examined. While delta receptor binding affinity is severely diminished with Val3, Ile3, and Leu3 substitutions, Cha3 substitution is very well tolerated, indicating that, contrary to the widely held belief, an aromatic side chain in this portion of the ligand is not required for delta receptor binding. Where possible, comparison of results in this delta-selective tetrapeptide series with those reported for analogous modification in the cyclic delta-selective pentapeptide [d -Pen2, d -Pen5]enkephalin (DPDPE) and linear pentapeptide enkephalins reveals similar trends.  相似文献   
5.
We investigated non-rapid eye movement (non-REM) sleep in patients with newly diagnosed Parkinson's disease (PD) who had never previously received dopaminergic medication. There were no significant differences in the conventional sleep parameters between de novo patients with PD and a healthy control group, but the length of stage 1 sleep and the number of awakenings increased significantly upon administration of dopaminergic drugs. Analyzing the quantitative electroencephalogram (EEG), we observed a significant reduction in the low-delta frequency range and a nonsignificant increase in the sigma frequency range in de novo patients with PD. The dopaminergic medication also nonsignificantly reduced the low-delta and sigma frequencies, the latter to the level of the controls. Possible mechanisms that may account for the observed differences are discussed. It is suggested that Parkinson's disease as well as the application of dopaminergic drugs exerts a desynchronizing effect on the sleep EEG that is reflected in a disruption of sleep continuity.  相似文献   
6.
The behavioural effects of selective -, - and delta" align="BASELINE" BORDER="0">-opioid agonists in 5-, 10- and 20-day-old rats were investigated by observational analysis. The predominant response to -agonists was behavioural depression. High doses (10 mg/kg IP) of morphine and DAGO (d-Ala2, NMe-Phe4, Glyol5-enkephalin) produced overt sedation in all the age groups and also induced catalepsy which was particularly apparent in the 5- and 10-day-old animals. These compounds did not produce any signs of behavioural activation in the neonatal rats. In contrast, rat pups treated with the -agonists U50,488H and PD 117,302 (1,10 mg/kg IP) exhibited marked hyperactivity with increases in wall-climbing and locomotion. Sedative effects of the highest dose of the -agonists began to emerge, however, as the animals grew older, resulting in significant decreases in behaviours such as gnawing and grooming at 20 days of age. The -agonist (+)-tifluadom (0.1–10 mg/kg), but not its corresponding (-)-isomer, produced an increase in activity in 5-day-old rats, thus extending the observations made with U50,488H and PD 117,302 and establishing the stereoselective nature of the response. The involvement of -receptors in opioid-induced hyperactivity was further substantiated by using a variety of opioid antagonists. In this context, the increase in activity induced by U50,488H (10 mg/kg) in 5-day-old neonates was attenuated by naltrexone (1 mg/kg IP) but not by larger doses (10 mg/kg) of either M8008 (which has low affinity for -receptors) or the selective delta" align="BASELINE" BORDER="0">-receptor antagonist ICI 174,864. Finally, DPDPE (d-Pen2, d-Pen5-enkephalin) which acts selectively at delta" align="BASELINE" BORDER="0">-opioid receptors, did not exert any behavioural effects in either the 5-, 10- or 20-day-old rat pups at doses of up to 10 mg/kg. These results demonstrate behavioural effects of - and -but not delta" align="BASELINE" BORDER="0">-agonists in neonatal rats. There is a clear differentiation between - and -receptor effects and both - and -mediated behaviours show dissimilarities from the adult profile.  相似文献   
7.
We have studied the influence of a temperature-sensitive cdc2-1 mutation in DNA polymerase delta" align="BASELINE" BORDER="0"> on the selection-induced mutation occurring at the LYS-2 locus in the yeast Saccharomyces cerevisiae. It was found that in cells plated on synthetic complete medium lacking only lysine, the numbers of Lys+ revertant colonies accumulated in a time-dependent manner in the absence of any detectable increase in cell number. When cdc2-1 mutant cells, after selective plating, were incubated at the restrictive temperature of 37°C for 5 h daily for 7 days, the frequency of an adaptive reversion of lys - Lys+ was significantly higher than the frequency in cells incubated only at the permissive temperature, or in wild-type cells incubated either at 23°C or 37°C. Therefore, when the proof-reading activity of DNA polymerase delta" align="BASELINE" BORDER="0"> is impaired under restrictive conditions, the frequency of adaptive mutations is markedly enhanced.  相似文献   
8.
Heavy-ion radiation accounts for the major component of absorbed cosmic radiation and is thus regarded as a significant risk during long-term manned space missions. To evaluate the genetic damage induced by heavy particle radiation, gpt delta transgenic mice were exposed to carbon particle irradiation and the induced mutations were compared with those induced by reference radiations, i.e., X-rays and gamma-rays. In the transgenic mouse model, deletions and point mutations were individually identified as Spi(-) and gpt mutations, respectively. Two days after 10 Gy of whole-body irradiation, the mutant frequencies (MFs) of Spi(-) and gpt were determined. Carbon particle irradiation significantly increased Spi(-) MF in the liver, spleen, and kidney but not in the testis, suggesting an organ-specific induction of mutations by heavy-ion irradiation. In the liver, the potency of inducing Spi(-) mutation was highest for carbon particles (3.3-fold increase) followed by X-rays (2.1-fold increase) and gamma-rays (1.3-fold increase), while the potency of inducing gpt mutations was highest for gamma-rays (3.3-fold increase) followed by X-rays (2.1-fold increase) and carbon particles (1.6-fold increase). DNA sequence analysis revealed that carbon particles induced deletions that were mainly more than 1,000 base pairs in size, whereas gamma-rays induced deletions of less than 100 base pairs and base substitutions. X-rays induced various-sized deletions and base substitutions. These results suggest that heavy-ion beam irradiation is effective at inducing deletions via DNA double-strand breaks but less effective than X-ray and gamma-ray irradiation at producing oxidative DNA damage by free radicals.  相似文献   
9.
TCR gamma delta(+) cells constitute <5% of all circulating T cells in healthy, adult Caucasians, and V(delta)1(+) cells constitute a minority of these cells. In contrast to TCR alpha beta(+) cells, their repertoire is selected extrathymically by environmental antigens. Although increased frequencies of V(delta)1(+) cells are found in several diseases, their function remains obscure. Here we show that the frequency of peripheral blood gamma delta T cells in healthy West Africans is about twice that of Caucasians, mainly due to a 5-fold increase in V(delta)1(+) cells, which is consequently the dominant subset. No age dependency of V(delta)1 frequencies was identified and the V(delta)1(+) cells in the African donors did not show preferential V(gamma) chain usage. Analysis of the CDR3 region size did not reveal any particular skewing of the V(delta)1 repertoire, although oligoclonality was more pronounced in adults compared to children. The proportions of CD8(+), CD38(+) and CD45RA(hi)CD45RO(-) cells within the V(delta)1(+) subset were higher in the African than in the European donors, without obvious differences in expression of activation markers. No significant correlations between levels of V(delta)1(+) cells and environmental antigens or immunological parameters were identified. Taken together, the evidence argues against a CDR3-restricted, antigen-driven expansion of V(delta)1(+) cells in the African study population. Our study shows that high frequencies of TCR gamma delta(+) cells with dominance of the V(delta)1(+) subset can occur at the population level in healthy people, raising questions about the physiological role of V(delta)1(+) T cells in the function and regulation of the immune system.  相似文献   
10.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号