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   3315篇
  免费   161篇
  国内免费   20篇
耳鼻咽喉   11篇
儿科学   65篇
妇产科学   169篇
基础医学   542篇
口腔科学   18篇
临床医学   302篇
内科学   710篇
皮肤病学   38篇
神经病学   490篇
特种医学   72篇
外科学   286篇
综合类   6篇
预防医学   158篇
眼科学   18篇
药学   258篇
中国医学   3篇
肿瘤学   350篇
  2024年   6篇
  2023年   24篇
  2022年   39篇
  2021年   92篇
  2020年   61篇
  2019年   69篇
  2018年   84篇
  2017年   70篇
  2016年   66篇
  2015年   91篇
  2014年   116篇
  2013年   153篇
  2012年   229篇
  2011年   235篇
  2010年   111篇
  2009年   141篇
  2008年   214篇
  2007年   212篇
  2006年   235篇
  2005年   255篇
  2004年   200篇
  2003年   195篇
  2002年   151篇
  2001年   41篇
  2000年   46篇
  1999年   46篇
  1998年   39篇
  1997年   22篇
  1996年   31篇
  1995年   22篇
  1994年   19篇
  1993年   16篇
  1992年   20篇
  1991年   14篇
  1990年   17篇
  1989年   8篇
  1988年   12篇
  1987年   10篇
  1986年   5篇
  1985年   7篇
  1984年   9篇
  1983年   11篇
  1982年   4篇
  1981年   5篇
  1979年   6篇
  1978年   4篇
  1976年   3篇
  1971年   4篇
  1947年   3篇
  1907年   2篇
排序方式: 共有3496条查询结果,搜索用时 15 毫秒
1.
BACKGROUND: The HOXA1 gene plays a major role in brainstem and cranial morphogenesis. The G allele of the HOXA1 A218G polymorphism has been previously found associated with autism. METHODS: We performed case-control and family-based association analyses, contrasting 127 autistic patients with 174 ethnically matched controls, and assessing for allelic transmission disequilibrium in 189 complete trios. RESULTS: A, and not G, alleles were associated with autism using both case-control (chi(2) = 8.96 and 5.71, 1 df, p <.005 and <.025 for genotypes and alleles, respectively), and family-based (transmission/disequilibrium test chi(2) = 8.80, 1 df, p <.005) association analyses. The head circumference of 31 patients carrying one or two copies of the G allele displayed significantly larger median values (95.0th vs. 82.5th percentile, p <.05) and dramatically reduced interindividual variability (p <.0001), compared with 166 patients carrying the A/A genotype. CONCLUSIONS: The HOXA1 A218G polymorphism explains approximately 5% of the variance in the head circumference of autistic patients and represents to our knowledge the first known gene variant providing sizable contributions to cranial morphology. The disease specificity of this finding is currently being investigated. Nonreplications in genetic linkage/association studies could partly stem from the dyshomogeneous distribution of an endophenotype morphologically defined by cranial circumference.  相似文献   
2.
Underlining the importance of Profundus Femoral Artery and its capacity to make up for lower limb's haemodynamics during obliterative arteriopathy, the Authors conceive a funnel-shaped intravascular prosthesis, Goretex constructed (PTFE), to introduce, in case of obstruction, in the artery lumen with a suitable instrument. The research is performed through ten oldster dogs whose average weight is twenty-four kilograms. Isolated the deep Femoral Artery and carried out an arteriotomy of about two centimetres on the Common Femoral Artery, we bring the prothesis in Profundis Femoral Artery and we fix it to the wall of the Common Femoral Artery with 8/O microsurgical dots. After thirty days, the arteriographic test shows the patency of the endoprosthesis with normal peripheral flow in nine animals out of ten. By virtue of this preliminary experiment, the Authors point out the semplicity of this intervention, also feasible in local anaesthesia, the good tolerability of the prosthesis and its perfect integration with the surrounding arterious wall, without shifts or dissecting laminar flows between the external prosthesis wall and the vessel lumen of the animal.  相似文献   
3.
Demonstration of malignant cells in blood specimens collected during transurethral resection of the prostate (TURP) has implicated TURP in the dissemination of prostatic cancer. Of 153 patients who underwent radiation therapy for prostate cancer between January 1977 and June 1990 and were retrospectively analyzed, 93 were evaluable. Fifty-nine patients required TURP before radiation therapy for prostatic obstruction (BPH and/or cancer); the remaining 34 patients underwent radiation therapy after fine-needle aspiration biopsy. No statistically significant difference in failure rate could be detected between these groups, with a failure rate of 47% (28 of 59 patients) at a median follow-up time of 49 months (range, 8 to 146 months) in the TURP group versus a failure rate of 47% (16 of 34 patients) at a median follow-up time of 50 months (range, 3 to 122 months) in the group who underwent biopsy only (Fisher's exact test, P = 0.23). Within the confines of this retrospective study, it appeared that TURP did not enhance the development of metastatic disease.  相似文献   
4.
Given current clinical use of phospholipid bilayer structures (liposomes/vesicles) as nontoxic drug delivery vehicles, we have addressed the possibility of employing the phospholipids themselves as MRI contrast agents. To this end we have synthesized phosphatidylcholine with a nitroxide spin label replacing one methyl residue of the choline headgroup. This material was mixed with natural phosphatidylcholine in mole ratios from 1:50 to 1:1 and used to prepare sonicated unilamellar vesicles in saline. Expected structural features of these vesicles were verified by freeze-fracture electron microscopy. Proton T1 values of saline were readily decreased to less than 0.3 s by such preparations, yielding a net relaxivity of 0.6 M-1 s-1. The approach seems to be a realistic way of firmly associating a contrast agent of minimal toxicity with ordinary liposomes/vesicles in a manner that is not subject to leakage.  相似文献   
5.
6.
AIM: A positive correlation between maternal and cord-blood IgE levels is well documented for total IgEs, but not for specific IgEs. The difficulty in detecting specific cord-blood IgEs is due to their low concentrations, which hinder their dosage by low-sensitivity methods. The study aimed to correlate maternal and foetal specific IgEs against individual cow's milk proteins, detected by highly sensitive and specific techniques. METHODS: Cow's milk specific IgE detection was performed by chemiluminescence on 52 specimens of maternal and cord blood after cow's milk protein separation by 1D and 2D gel electrophoresis. Cow's milk protein (CMP) antigens were identified by mass spectrometry techniques. RESULTS: Specific IgEs for CMPs were found in 25/52 (48.1%) of maternal sera and in 19/52 (37%) of cord-blood sera. In order of decreasing frequency, the proteins found were BSA, IgG heavy chain, caseins and, in a single case, b-lactoglobulin. Positive cord-blood sera in all cases corresponded to a positive maternal result, and maternal and foetal immunoreactivity patterns were closely correlated. Moreover, in no case was there a positive cord-blood response with a negative maternal response. CONCLUSION: The study demonstrates a close relationship between maternal and cord-blood specific IgE patterns. The phenomenon observed could provide a model to elucidate the general production method of foetal IgEs, which might only be produced in the presence of both the corresponding maternal IgE and the related allergen.  相似文献   
7.
BACKGROUND: The hydrogen breath test (H(2)BT) is the most widely used procedure in the diagnostic workup of lactose malabsorption and lactose intolerance. AIM: To establish whether a simplified two- or three-sample test may reduce time, costs and staff resources without reducing the sensitivity of the procedure. PATIENTS AND METHODS: Data from 1,112 patients (292 men, 820 women) with a positive 4 h, nine-sample H(2)BT were retrospectively analyzed. Patients were stratified according to the degree of lactose malabsorption, the occurrence and type of symptoms. Loss of sensitivity in the procedure was evaluated taking into account two-sample tests (0 min and 120 min or 0 min and 210 min) or three-sample tests (0 min, 120 min and 180 min or 0 min, 120 min and 210 min). RESULTS: Using a two-sample test (0 min and 120 min or 0 min and 210 min) the false-negative rate was 33.4% and 22.7%, respectively. With a three-sample test (0 min, 120 min and 180 min or 0 min, 120 min or 210 min), lactose malabsorption was diagnosed in 91.2% (1,014 of 1,112) patients and in 96.1% (1,068 of 1,112) patients, respectively. Of 594 patients with abdominal symptoms, 158 (26.6%) and 73 (12.2%) would have false-negative results with 0 min and 120 min or 0 min and 210 min two-sample tests, respectively. The three-sample tests, 0 min, 120 min and 180 min or 0 min, 120 min and 210 min, have a false-negative rate of 5.9% and 2.1%, respectively. CONCLUSIONS: A three-sample H(2)BT is time- and cost-sparing without significant loss of sensitivity for the diagnosis both of lactose malabsorption and lactose intolerance.  相似文献   
8.
Sixty-seven insulinomas were investigated by immunohistochemistry using site-directed antibodies against insulin, proinsulin, chromogranin A, HISL-19, and four proteins directly or indirectly involved in the proteolytic processing of proinsulin: the prohormone convertases PC2 and PC3, carboxypeptidase H (CPH) and 7B2. Results were expressed in a six-grade score according to the frequency of immunoreactive tumour cells. Insulin was expressed by all tumours, appearing in either a diffuse or a polarized pattern and being detected in more than 30% of tumour cells in all cases but three. Proinsulin was also expressed in all tumours, with more than 50% of tumour cells immunoreactive in all cases but 5. It was consistently localized in the Golgi apparatus. In about half the cases, moreover, it also showed diffuse cytoplasmic staining, usually with a very sparse distribution. Trabecular and solid insulinomas did not present specific, homogeneous patterns of insulin immunostaining. However, insulin immunoreactivity was much more abundant in trabecular than in solid neoplasms, being present in virtually all tumour cells (score 6) in 50% and 8% of cases, respectively. Virtually all insulinomas expressed PC2, PC3, CPH and 7B2, usually in 30–100% of tumour cells, with a frequency significantly related to that of insulin. However, detection of PC2 and 7B2 was slightly less frequent than that of PC3 and CPH. In consecutive sections these proteins were found to be mostly co-localized with insulin and chromogranin A but not with proinsulin. They were heavily expressed in all 10 tumours with more than 10% of cells showing cytoplasmic proinsulin immunoreactivity, indicating that the leakage of proinsulin from the Golgi compartment is not associated with faulty expression of converting enzymes and possibly reflects a saturated processing capacity. HISL-19 immunoreactivity was found in both Golgi apparatus and insulin stores, indicating that the relevant antigen is different from all other proteins investigated. These results do not support a defect in expression or localization of proinsulin-processing enzymes in most insulinomas.  相似文献   
9.
A series of 21 neuroleptics with different chemical structures (phenothiazines, thioxanthenes, dibenzodiazepines, butyrophenones, benzamides, etc.) was examined for their in vitro interactions with 12 neurotransmitter binding sites in the rat brain (alpha- and beta-noradrenergic, dopaminergic, muscarinic, serotoninergic, histaminic, and opioid receptors, calcium channels, and serotonin uptake binding sites). The biochemical profile obtained from the binding data was compared with reported pharmacological and clinical profiles for this class of compounds by cluster analysis. Cluster analysis on binding data classified the compounds in three main subgroups: benzamides, compounds with an affinity mainly for DA2 and 5-HT2 receptors and inactive at muscarinic receptors, and compounds with a high affinity for alpha 1-adrenergic receptors and muscarinic receptors. The main subgroups resulting from cluster analysis of previously published pharmacological and clinical data for neuroleptics contain compounds common to the present study, with some correlations. The results extend previous observations that a complete binding profile corresponds to the pharmacological and clinical profile of this class of compounds.  相似文献   
10.
BACKGROUND: Infertile women positive for thyroid antibodies suffer from a poor pregnancy/delivery outcome, although conflicting data have been published. Our objective was to investigate if levothyroxine (LT4) exerts any effect on pregnancy and/or delivery rates in thyroid peroxidase antibody (TPOAb)-positive (+) women undergoing assisted reproductive technologies. METHODS: Patients undergoing treatment were screened for TPOAb, thyroid-stimulating hormone (TSH) and free thyroxine (FT4). A total of 72 (15%) out of the 484 euthyroid women selected were TPOAb (+). These 72 patients were randomly divided into two groups: group A (n = 36) underwent LT4 treatment, group B (n = 36) placebo. Group C consisted of 412 women (85%) who were TPOAb negative (-). All patients received controlled ovarian stimulation. The endpoints of treatment were pregnancy rate, miscarriage rate and delivery rate. RESULTS: No differences in pregnancy rate were observed between the three groups. Miscarriage rate was higher in TPOAb (+) in comparison to TPOAb (-) [relative risk: 2.01 (95% CI = 1.13-3.56), P = 0.028]. CONCLUSIONS: The pregnancy rate is not affected either by presence of TPOAb or treatment with LT4. However, TPOAb (+) women show a poorer delivery rate compared to TPOAb (-). LT4 treatment in TPOAb (+) does not affect the delivery rate.  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