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   20934篇
  免费   1202篇
  国内免费   224篇
耳鼻咽喉   205篇
儿科学   528篇
妇产科学   427篇
基础医学   2200篇
口腔科学   638篇
临床医学   1600篇
内科学   5634篇
皮肤病学   453篇
神经病学   2047篇
特种医学   964篇
外科学   3675篇
综合类   63篇
一般理论   6篇
预防医学   781篇
眼科学   252篇
药学   1115篇
中国医学   22篇
肿瘤学   1750篇
  2024年   20篇
  2023年   261篇
  2022年   523篇
  2021年   941篇
  2020年   535篇
  2019年   677篇
  2018年   829篇
  2017年   655篇
  2016年   675篇
  2015年   769篇
  2014年   911篇
  2013年   1166篇
  2012年   1679篇
  2011年   1646篇
  2010年   895篇
  2009年   849篇
  2008年   1342篇
  2007年   1245篇
  2006年   1114篇
  2005年   1081篇
  2004年   937篇
  2003年   783篇
  2002年   725篇
  2001年   225篇
  2000年   200篇
  1999年   186篇
  1998年   150篇
  1997年   107篇
  1996年   105篇
  1995年   99篇
  1994年   67篇
  1993年   67篇
  1992年   102篇
  1991年   78篇
  1990年   88篇
  1989年   67篇
  1988年   56篇
  1987年   71篇
  1986年   55篇
  1985年   48篇
  1984年   49篇
  1983年   18篇
  1982年   19篇
  1981年   19篇
  1979年   32篇
  1978年   16篇
  1977年   23篇
  1976年   17篇
  1975年   21篇
  1968年   15篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
Cystic lesions of the thyroid are common findings. Although many thyroid cysts are of benign, some cases of hemorrhagic degenerative changes occur in neoplastic nodules, mostly follicular neoplasms and papillary carcinomas. The occurrence of hemorrhagic changes in medullary carcinomas has never been documented with aspirative cytological and histological pictures to the best of our knowledge. A case of medullary thyroid carcinoma with a large central hemorrhagic cyst is described, and the literature regarding the pathogenesis of this regression and the occurrence of cystic neoplasms in the thyroid is reviewed.  相似文献   
82.
Folate receptor family members (FOLRs) mediate the delivery of 5-methyltetrahydrofolate to the interior of, out of within, or between cells in a process known as potocytosis. Three FOLRs and a pseudogene map to 11q13.4. The aim of this study was to verify whether FOLRs could be responsible for the onset of nonsyndromic cleft lip with or without cleft palate (CL/P). Linkage and linkage disequilibrium between genetic markers and disorder were analyzed. Patients and their mothers from 71 familial CL/P pedigrees and 75 sporadic cases from Italian population were investigated by PCR-SSCP analysis. Data from mutation scanning allowed us to find only a silent mutation in FOLR1 present in a mother and her child. Our findings do not support FOLR1 and FOLR2 genes in the onset of CL/P.  相似文献   
83.
Histopathologic parameters in predicting lymph node metastasis of supraglottic laryngeal carcinoma. A systematic clinical-pathological study was performed on fifty-three resected cases of supraglottic laryngeal squamous cell carcinoma, followed up for at least 5 years. The aim of the research was to evaluate histopathologic parameters in predicting lymph node metastasis (N+) as expression of biological malignancy of the neoplasm. The following neoplastic microscopical features were studied: histopathologic and cytologic grading, pattern of growth, peritumoral inflammatory infiltrate, stromal reaction, tumoral necrosis. The results are as follows: stromal reaction and cytologic grading are not useful to identify N+ and N- cases. Cases with high and low degree of differentiation (Broder's grading) are significantly correlated respectively to low (14.3%) and high (70%) incidence of lymph node metastasis (p less than 0.03). A clear correlation is present between the pattern of growth "pushing" and lacking of node metastasis (84.6%). A favorable prognosis significance seems to be linked with the presence of peritumoral lymphoplasmocytic infiltrate, which results to be a marker of cases in which lymph node metastasis incidence is very low (5.5%; p less than 0.001). On the contrary lymph node metastasis incidence increase when tumoral necrosis is present (76.5%; p less than 0.001).  相似文献   
84.
The objective of this study was to assess the association betweenalcohol drinking before and during pregnancy and the risk ofspontaneous abortion using data from a case-control study conductedin Milan, Italy. A total of 462 women (median age 30 years)were admitted for spontaneous abortion (within the 12th weekof gestation) to a network of obstetrics departments in thegreater Milan area. Of these, 148 (32%) were between the fourthand the eighth week of gestation and 314 (68%) between the ninthand the 12th week. A control group was made up of 814 women(median age 29 years) who gave birth at term (>37 weeks gestation)to healthy infants (Apgar 5th minute 8, weight 3000 g) on randomlyselected days at the same hospitals where cases had been identified.A total of 212 cases (46%) and 355 controls (47%) reported alcoholdrinking before conception. Considering non-drinkers as thereference category, the relative risks (RR) of spontaneous abortionwere 1.2 (95% confidence interval (CI), 0.9–1.6] and 0.8(95% CI, 0.6–1.1), respectively, in drinkers of one toseven and more than seven drinks per week before conception.No association emerged between the duration of alcohol drinkingand the risk of spontaneous abortion. A total of 166 cases (35.9%)and 263 (32.3%) controls reported any alcohol drinking duringthe first trimester of pregnancy. The corresponding relativerisk was 1.1 (95% CI, 0.9–1.4) and no relationship emergedbetween the number of drinks per week and the risk of abortion.Likewise, maternal wine and beer drinking in the first trimesterof pregnancy was not associated with the risk of spontaneousabortion. Evidence available from this and previous studies,although partially controversial, indicates that moderate (oneor two drinks per day) alcohol consumption does not increasemarkedly the risk of miscarriage.  相似文献   
85.
Telomerase is the enzyme responsible for synthesizing telomeric repeats at the ends of chromosomes to maintain telomere length. Recent studies have suggested that telomere shortening may serve as a surrogate marker of the progression of malignant disorders and seems to be accelerated in allogeneic bone marrow transplant recipients. In this study, the results of the telomere length of nine cord blood mononuclear cell samples are presented. Telomere length was measured by the flow-FISH method, using a peptide nucleic acid probe. The proportion of cord blood cell subsets (CD19/CD34/CD3) was also evaluated. The telomere length of the internal control 1301 cell line was estimated to be 100%. The mean telomere length of cord blood cells was 18.5 +/- 3.9%, compared with the internal control. The progenitor CD34+ cells were detected as 2.6 +/- 0.7% in the lymphoid gate measured. Linear correlation analysis did not find any connection between the cell subsets (CD3+, CD34+, CD19+) and the telomere length. The findings confirm that the telomere flow-FISH method is sufficient for estimation of the telomere length. Assessment of the current procedures of collection, manipulation, and ex vivo expansion of cord blood cells in terms of their effect on telomere shortening might be important.  相似文献   
86.
Human oocyte development was evaluated after a reduced timeexposure to spermatozoa in vitro. A total of 119 patients wereassigned to two study groups in a randomized prospective studyin which each patient‘s oocytes were exposed to spermatozoafor either 1 h (group 1 – 58 patients) or the standard16 h incubation period (group 2 – 61 patients). The fertilizationrate obtained in group 1 was higher than in group 2 (285/393,73%, and 272/410, 66% respectively), suggesting that the spermatozoa-oocyteinteraction occurs within 1 h. This was confirmed in a studyin vitro using fluorescently labelled spermatozoa and normaloocyte-cumulus complexes. Spermatozoa enter the cumulus complexwithin 15 min, traverse the cumulus layer within 3 h, and firstappear in the oocyte cortex at 4 h post-insemination. The incidenceof polyspermy was higher in oocytes exposed to spermatozoa for16 h (3%) than for 1 h (1%). There was no difference in thecleavage rate or morphological characteristics of embryos fromboth study groups. However, when evaluating the timing of embryodevelopment, group 1 generated a significantly higher percentageof four to five cell embryos when compared to group 2 (55 versus39%; P < 0.001), documented at 40 h post-insemination. Theimplantation and pregnancy rates for group 1 were 11 and 28%,while the corresponding rates for group 2 were 8 and 15%. Thissuggests that a reduced exposure of oocyte to spermatozoa favoursembryo viability, possibly due to a decrease in potential damagefrom sperm metabolic waste products.  相似文献   
87.
Lipoprotein(a) [Lp(a)] is an atherogenic and prothrombotic molecule formed by the covalent binding of the highly polymorphic apolipoprotein(a) [apo(a)] to apoprotein B-100 of LDL. High Lp(a) concentrations are a recognized genetic risk factor for coronary heart disease (CHD) and have been shown to be related with a familial clustering of ischemic cardiac events. Nevertheless, the association between apolipoprotein(a) isoforms and a positive familial history of CHD has received far less attention. In this report, we explored the distribution of apo(a) phenotypes in 127 CHD subjects with a family history of coronary events and in 92 CHD patients without such a history. Twenty-two apo(a) isoforms were detected by a high-resolution immunoblotting method. In univariate analysis, the percentage of subjects with at least one small sized apo(a) isoform was significantly higher in CHD patients with a positive family history than in those without (P<0.01). Multivariate analysis showed that apo(a) isoforms of low molecular weight were the best predictors of familial aggregation of cardiac ischemia. We conclude that apo(a) size polymorphism is strongly associated with a familial history of CHD and is more efficient than Lp(a) plasma concentrations in predicting the familial clustering of coronary disease. When detected by high-resolution techniques, apo(a) phenotypes are objective laboratory markers that can substitute for a knowledge of a positive family history of CHD and should be used, together with Lp(a) levels, to better assess the familial predisposition to coronary events.  相似文献   
88.
The present study was performed to investigate the effect of treatment with furosemide on the pressor response induced by intracerebroventricular (i.c.v.) injections of cholinergic (carbachol) and adrenergic (norepinephrine) agonists, angiotensin II (ANGII) and hypertonic saline (HS, 2 M NaCl). The changes induced by furosemide treatment on the pressor response to intravenous (i.v.) norepinephrine, ANGII and arginine vasopressin (AVP) were also studied. Rats with a stainless-steel cannula implanted into the lateral ventricle (LV) were used. Two injections of furosemide (30 mg/kg b.wt. each) were performed 12 and 1 h before the experiments. Treatment with furosemide reduced the pressor response induced by carbachol, norepinephrine and ANGII i.c.v., but no change was observed in the pressor response to i.c.v. 2 M NaCl. The pressor response to i.v. ANGII and norepinephrine, but not AVP, was also reduced after treatment with furosemide. These results show that the treatment with furosemide impairs the pressor responses induced by central or peripheral administration of adrenergic agonist or ANGII, as well as those induced by central cholinergic activation. The results suggest that the treatment with furosemide impairs central and peripheral pressor responses mediated by sympathetic activation and ANGII, but not those produced by AVP.  相似文献   
89.
Thirty sera reacting by IFL technique in titres greater than or equal to 100 with smooth muscle fibres of rat stomach, rat renal glomeruli, and with the membrane region of thyroid cells were randomly chosen among sera sent in for routine testing of tissue antibodies. All sera but one were found to be derived from patients with chronic active hepatitis. The smooth muscle and other relevant cell staining were abolished after absorption of sera with actin, prepared from rabbit skeletal muscle and found to be homogeneous by SDS gel-electrophoresis and by electron microscopy. The actin anti-bodies were purified by precipitation of sera with F-actin and elution of the precipitates at acid pH. The purified antibodies stained all tissues in the same way as the original sera. In double immunodiffusion tests all thirty sera gave precipitation with actin. Thus, it was concluded that these broad-reacting SMA are directed against actin. The finding of high-titred SMA is of diagnostic value and supports the clinical diagnosis of active chronic hepatitis. In addition, anti-actin antibodies eluted from human sera are a suitable tool for studying actin-containing cellular structures.  相似文献   
90.
Several lines of evidence from neuroimaging, pharmacology and genetics support the involvement of the dopaminergic system in the etiology of Attention Deficit Hyperactivity Disorder (ADHD). Previous candidate gene studies have investigated the association between a dinucleotide (CA)n repeat polymorphism, located 18.5 kb from the start codon of the DRD5 gene, and ADHD. Association between the 148 bp allele and ADHD has been reported in some studies, however replication of the finding has not been consistent. We tested for an association between the (CA)n repeat and adult ADHD in a sample comprised of 119 families with adult ADHD probands and 88 unrelated adult ADHD cases with a corresponding number of controls matched for age, ethnicity and sex. In the family sample we found a non-significant trend for association between the 148 bp allele and ADHD (Z = 1.91, p = 0.055). An excess of non-transmissions was detected for the 150 and 152 bp alleles (Z = −2.26, p = 0.023; Z = −2.20, p = 0.028). Quantitative analysis performed using the Brown Attention Deficit Disorder Scale (BADDS) showed association between the 150 bp allele and lower total score (p = 0.011), and lower effort (p = 0.008), activation (p = 0.008) and attention (p = 0.01) cluster scores. We did not replicate association findings in the case–control group, likely due to the lack of statistical power of this sample. Our findings add to the literature suggesting DRD5 (CA)n repeat has a modest effect in modulating susceptibility to adult ADHD but further studies are required.  相似文献   
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