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   10796篇
  免费   604篇
  国内免费   31篇
耳鼻咽喉   127篇
儿科学   324篇
妇产科学   199篇
基础医学   1328篇
口腔科学   286篇
临床医学   1059篇
内科学   2157篇
皮肤病学   147篇
神经病学   1166篇
特种医学   292篇
外科学   1495篇
综合类   52篇
一般理论   6篇
预防医学   874篇
眼科学   205篇
药学   817篇
中国医学   23篇
肿瘤学   874篇
  2023年   58篇
  2022年   85篇
  2021年   166篇
  2020年   161篇
  2019年   195篇
  2018年   254篇
  2017年   202篇
  2016年   238篇
  2015年   255篇
  2014年   327篇
  2013年   567篇
  2012年   685篇
  2011年   708篇
  2010年   414篇
  2009年   392篇
  2008年   687篇
  2007年   661篇
  2006年   690篇
  2005年   638篇
  2004年   596篇
  2003年   570篇
  2002年   551篇
  2001年   125篇
  2000年   79篇
  1999年   120篇
  1998年   121篇
  1997年   115篇
  1996年   104篇
  1995年   120篇
  1994年   93篇
  1993年   96篇
  1992年   79篇
  1991年   99篇
  1990年   66篇
  1989年   79篇
  1988年   61篇
  1987年   54篇
  1986年   52篇
  1985年   75篇
  1984年   82篇
  1983年   56篇
  1982年   85篇
  1981年   78篇
  1980年   41篇
  1979年   35篇
  1978年   43篇
  1977年   55篇
  1975年   35篇
  1974年   31篇
  1973年   32篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
The contribution of peritoneal B cells to the intestinal lamina propria plasma cell population is well documented in mice, but unknown in humans. We have analyzed immunoglobulin (Ig) genes of human peritoneal B cells, because such genes show distinctive characteristics in mucosal B cells, particularly highly mutated variable regions. Here, we report the characteristics of variable region genes used by IgM, IgA and IgG in peritoneal cells. We focused on the properties of IgV(H)4-34 to allow comparisons of like-with-like between different isotypes and cells from different immune compartments. We observed that the IgM genes were mostly unmutated, and that the mutated subset had less mutations than would be expected in a mucosal B cell population. Likewise, the IgV(H)4-34 genes used by IgA and IgG from peritoneal B cells had significantly lower numbers of mutations than observed in the mucosal counterparts. Other trends observed, while not reaching statistical significance, followed the trend of peripheral B cells. The peritoneal B cell population had more IgA1 than IgA2 sequences, and there was no dominance of J(H)4 in the IgA from peritoneum or spleen, in contrast to the mucosal sequences. Overall, this study suggested that human peritoneal B cell are either peripheral or mixed in origin; they are unlikely to represent an inductive compartment for the mucosal B cell system.  相似文献   
82.
BACKGROUND AND AIM: Electronic patient-provider communication promises to improve efficiency and effectiveness of clinical care. This study aims to explore whether a secure web-based messaging system is an effective way of providing patient care in general practices. METHOD: We conducted a randomised controlled trail and recruited 200 patients from the waiting area in one primary clinic in Norway. Participants were randomised to either the intervention group, which received access to a secure messaging system, or the control group receiving standard care without such access. Primary outcome measures were number of online consultations, telephone consultations and office visits in the two groups. Data were derived from patient records and collected 1 year prior to (baseline), and 1 year after the intervention. RESULTS: Forty-six percent of the patients who were given access to the messaging system (n=99) used the online communication system on at least one occasion (ranging from 1 to 17 messages per patient per year). A total of 147 electronic messages were sent to six general practitioners during a 1-year trial period. Eleven percent of the messages were to schedule an appointment. In 10% of the messages, the GP was unable to respond adequately and recommended an office visit. The reduction in office visits over time was greater for the intervention group than for the control group (P=0.034). There was however no significant difference in the number of telephone consultations between the groups during the study (P=0.258). CONCLUSION: The use of a secure electronic messaging system reduced the number of office visits at the general practice, but not phone consultations.  相似文献   
83.
84.
In this study, the desensitization of acetylcholine-induced inositol 1,4,5-trisphosphate [I(1,4,5)P3] formation, upon short-time prestimulations, was investigated in cultures of human neuroblastoma SH-SY5Y cells. Four repeated stimulations for 10 seconds with 10 μM acetylcholine were necessary to induce a desensitization of the I(1,4,5)P3 formation. The desensitization was observed 4 hours after the initiation of repetitive stimulations. The same effect was obtained by a single prestimulation with 1 mM acetylcholine. Preincubation of the cells with phorbol 12-myristate 13-acetate (PMA) markedly down-regulated the acetylcholine-induced I(1,4,5)P3 formation. However, the protein kinase C (PKC) inhibitors H7 and staurosporine did not influence the desensitization induced by four repeated stimulations with 20 μM acetylcholine. These results indicate that the signal transduction can be desensitized following repeated stimulations with sub-maximal concentrations of receptor agonist and although activation of PKC can induce the same down-regulation, PKC is most likely not involved in the desensitization induced by repetitive acetylcholine-stimulations.  相似文献   
85.
Isolation of HIV from cultures of CD4+ lymphocytes purified from peripheral blood by indirect panning was optimized and evaluated. Infectious HIV was isolated by single isolation attempts in 98% of 102 HIV-antibody-positive patients (55 had AIDS or ARC and 47 were clinically healthy). The average culture time required for positive cultures was largely independent of the CD4 count of the patients and 87% of the positive isolation cultures from both groups of patients became positive within 14 days of culture. An evaluation of the possible influence of media additives on propagation of HIV showed that: amphotericin-B had a suppressive effect on HIV replication at concentrations recommended for anti-fungal activity; recombinant and human interleukin-2 were equally suitable for both isolation cultures and for propagation of HIV, and polybrene, at a concentration of 2 micrograms/ml in the culture medium had a beneficial effect.  相似文献   
86.
Ebbe  Taudorf  Allan  Bundgaard  Per Olof  Fagerstrom  Eva  Weeke Bent  Weeke 《Allergy》1981,36(7):495-500
A sustained release preparation of terbutaline sulphate has been formulated (Bricanyl® depot tablets) in order to extend the duration and accordingly change the dosage regimen to twice a day. This presentation gives a summary of a clinical trial performed in order to study effect and side effects of terbutaline depot tablets 7.5 mg twice a day compared to terbutaline tablets 5 mg three times a day.
Patients suffering from perennial asthma and with daily requirement of asthma medicine were accepted for the study. The trial was a double-blind cross-over, double dummy and randomized. The tablets were given in two consecutive periods of 7 day's duration each. The effect of terbutaline depot tablets was equal to the effect of the ordinary terbutaline tablets. The indication for using depot tablets in the basic treatment of bronchial asthma is a better patient compliance due to medication twice a day. Furthermore in patients with unstable bronchial asthma and in patients with morning dips in PEF the more stable plasma concentration may perhaps keep the patients in a more steady state.  相似文献   
87.
Oocytes collected in stimulated cycles are more readily fertilizedafter preincubation than are oocytes inseminated immediatelyafter collection. It has not been ascertained, however, whetherthis increase in the fertilization rate is due to extrusionof the first polar body (meiotic maturation) during this period,or to some conclusive cytoplasmic maturation subsequent to thepolar body extrusion. When analysing oocytes with a polar body(n = 14) by transmission electron microscopy, differences wereobserved in the appearance of cytoplasmic features which werecorrelated to the total durations both of systemic human chorionicgonadotrophin influence before collection and of oocyte culture.These differences were manifested as a delayed formation inaggregates of the smooth endoplamic reticulum in the ooplasmof oocytes having a polar body and might have signified a cytoplasmicmaturation. The degree of synchrony in the oocytes varied andthis could explain why some oocytes can be fertilized when inseminatedshortly after collection and others not until 8 h or even moreafter collection. Thus, although meiotic and cytoplasmic maturationis likely to be synchronized at ovulation of an oocyte in anatural cycle, they appear to be mainly asynchronous in oocytescollected in stimulated cycles.  相似文献   
88.
Genetics of the low density lipoprotein receptor:   总被引:1,自引:0,他引:1  
Fibroblast association (plasma membrane binding plus intracellular accumulation) and degradation of radioiodinated low density lipoprotein (125I-LDL) index plasma membrane LDL receptor activity. Cultured fibroblasts from 23 subjects affected with familial hypercholesterolemia (HC) and from 95 subjects without HC (non-HCs) were tested for 125I-LDL association and degradation. Both LDL receptor activity indices were twice as high in non-HC and HC heterozygous cell strains. This is compatible with a major gene effect on LDL receptor activity. However, a considerable overlap between non-HC and HC heterozygous values was found in the 125I-LDL association assay [median (range) 970 (330-2500), and 450 (250-490), respectively] and in the degradation assay [median (range) 810 (280-2020), and 470 (160-790), respectively]. The values are expressed as ng 125I-LDL X mg cell protein-1 X 4.5 h-1. These great overlaps in the LDL receptor activity indices support the view that the influence of LDL receptor activity on the HC phenotype may be smaller than believed previously. Furthermore, for the diagnosis of HC, these LDL receptor activity assays are far more expensive and have less sensitivity and specificity than simple serum cholesterol determination. The LDL receptor-dependent 125I-LDL association values for the HC heterozygous individuals clustered into four groups. Family data supported the hypothesis that this variation could be due to four different LDL receptor variants, each coded for by different alleles at the LDL receptor locus. If confirmed, this finding may have implications for the understanding of the variable expression of HC and also of the genetic impact on lipoprotein metabolism and susceptibility to atherosclerosis in non-HCs.  相似文献   
89.
OBJECTIVE: To describe the clinical picture, pathophysiology, and treatment of concomitant lesions of the peroneus brevis tendon and lateral ligament injuries to the ankle. BACKGROUND: In some cases, chronic lateral ankle instability is associated with a longitudinal partial tear in the peroneus brevis tendon. Patients who suffer from this lesion usually have atypical posterolateral ankle pain combined with signs of recurrent ligament instability ("giving way"). The tendon injury is often overlooked because it is combined with the ligament injury, and the injury mechanisms are similar. DESCRIPTION: Tears or laxity in the superior peroneal retinaculum allow the anterior part of the injured peroneus brevis tendon to ride over the sharp posterior edge of the fibula, leading to a longitudinal tear in the tendon. This combined injury should be suspected in patients with recurrent giving way of the ankle joint and retromalleolar pain. The diagnosis can be established using either ultrasonography or magnetic resonance imaging. DIFFERENTIAL DIAGNOSIS: Ligament injury, tenosynovitis, peroneus longus tendon lesion, os peroneum fracture, distal peroneus brevis tendon tear, or anomalous peroneus tertius tendon. TREATMENT: The tendon injury and the ligament insufficiency should be repaired at the same time. CONCLUSIONS: We recommend reconstruction of the superior peroneal retinaculum, combined with repair of the tendon, using side-to-side sutures and anatomical reconstruction of the lateral ankle ligaments.  相似文献   
90.
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