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   22287篇
  免费   1702篇
  国内免费   261篇
耳鼻咽喉   410篇
儿科学   342篇
妇产科学   301篇
基础医学   3951篇
口腔科学   226篇
临床医学   1993篇
内科学   4313篇
皮肤病学   1136篇
神经病学   1513篇
特种医学   1511篇
外科学   2322篇
综合类   74篇
现状与发展   1篇
一般理论   2篇
预防医学   928篇
眼科学   618篇
药学   2357篇
中国医学   354篇
肿瘤学   1898篇
  2024年   18篇
  2023年   182篇
  2022年   678篇
  2021年   920篇
  2020年   509篇
  2019年   677篇
  2018年   754篇
  2017年   678篇
  2016年   1029篇
  2015年   1403篇
  2014年   1602篇
  2013年   1689篇
  2012年   2390篇
  2011年   2133篇
  2010年   1405篇
  2009年   1082篇
  2008年   1360篇
  2007年   1244篇
  2006年   1036篇
  2005年   961篇
  2004年   716篇
  2003年   588篇
  2002年   486篇
  2001年   120篇
  2000年   95篇
  1999年   62篇
  1998年   63篇
  1997年   54篇
  1996年   34篇
  1995年   30篇
  1994年   25篇
  1993年   22篇
  1992年   24篇
  1991年   29篇
  1990年   19篇
  1989年   23篇
  1988年   19篇
  1987年   13篇
  1986年   12篇
  1985年   17篇
  1984年   9篇
  1983年   7篇
  1981年   4篇
  1980年   4篇
  1979年   8篇
  1978年   3篇
  1971年   4篇
  1969年   1篇
  1967年   1篇
  1962年   2篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
Rapid eye movement (REM) sleep deprivation has previously been shown to interfere with normal learning and memory and to inhibit long-term potentiation (LTP) in vitro. Previous studies on REM sleep deprivation and LTP have relied on in vitro analysis in isolated brain slices taken from animals following several days of sleep deprivation. LTP in the hippocampus in situ may differ from LTP in vitro due to modulatory inputs from other brain regions, which are altered after REM sleep deprivation. Here, we examined LTP in unanesthetized, behaving animals on the first and second recovery days following REM sleep deprivation to determine if similar effects are seen in vivo as previously reported in vitro. We found that LTP was significantly impaired in REM sleep-deprived animals on the second recovery day but not the first recovery day. Our results extend previous findings by showing that REM sleep deprivation continues to affect hippocampal function for more than 24h following the end of deprivation. Our results also suggest the presence of a modulatory process not present in vitro. Our findings are not explained by stress during REM sleep deprivation because equivalent circulating corticosterone levels (an index of stress) were found during both REM sleep deprivation and control treatment.  相似文献   
62.
To identify a major antigenic determinant for use in the development of a rapid serological diagnostic test for severe acute respiratory syndrome (SARS) coronavirus infection and to study the immune response during SARS coronavirus infection in humans, we cloned the full length and six truncated fragments of the nucleocapsid gene, expressed them, and purified them as glutathione S-transferase-tagged recombinant proteins. The reactivities of the recombinant proteins to a panel of antibodies containing 33 SARS coronavirus-positive sera and 66 negative sera and to antibodies against other animal coronaviruses were screened. A truncated 195-amino-acid fragment from the C terminus of the nucleocapsid protein (N195) was identified that had a strong ability to detect antibodies against SARS coronavirus. No cross-reaction was found between the N195 protein and antibodies against chicken, pig, and canine coronaviruses. The N195 protein was used to develop a Western blot assay to detect antibodies against SARS coronavirus in 274 clinically blinded samples. The specificity and sensitivity of this test were 98.3 and 90.9%, respectively. The correlation between our Western blotting assay and an immunofluorescence assay (IFA) was also analyzed. The results of our Western blot assay and IFA for the detection of SARS coronavirus-positive sera were the same. Thus, the N195 protein was identified as a suitable protein to be used as an antigen in Western blot and other possible assays for the detection of SARS coronavirus infection.  相似文献   
63.
Previous studies have suggested that glutathione S-transferase (GST) genotypes may play a role in determining susceptibility to cervical cancer, though the data have often been conflicting. The objective of this study was to examine the effect of GSTP1 polymorphism on cervical carcinogenesis. The studied subjects, patients who were pathologically diagnosed with invasive cervical cancer yielding positive results for human papillomavirus (HPV) (n=342), were compared to healthy, normal, female controls (n=707). DNA from peripheral blood samples from studied subjects whose GSTP1 specific sequences had been determined by PCR with allele-specific primers were reviewed in comparison with the normal controls. The genetic susceptibility of GSTP1 (11q 13.1) in cervical carcinogenesis was determined by examining the effect of gene and environmental factors by the different histopathologic types of invasive cervical cancers. In assessing polymorphism GSTP1, the percentages of individuals homozygous for the A allele, homozygous for the G allele, and heterozygous for the two alleles were 66.8%, 3.9%, and 29.3%, respectively, in the control group, and 64.3%, 4.1%, and 31.6%, respectively, among in women with cervical cancer. Compared with GSTP1 G allele positive (GA or G/G), the odds ratio (OR) (95% confidence interval) for GSTP1 A/A was 1.0 (0.7 - 1.4) for invasive cervical cancer. However, the risk increased with GSTP1 A/A among ever smokers (3.9, 1.7 - 8.9, p-value=0.0012) compared with GSTP1 G allele positive among nonsmokers. In particular, this risk was higher among women with squamous cell carcinoma (4.7, 2.0 - 10.8, p=0.0003). Polymorphism of GSTP1 among smoking women was associated with a higher risk of developing cervical cancer.  相似文献   
64.
Nonfunctioning islet cell tumors or pancreatic endocrine tumors are the most common type of malignant islet cell tumor. Although previously detected usually at an advanced stage because of mass effect, the early detection rate of small localized disease has been increasing. To date it has been difficult to predict the clinical behavior in localized regional nonfunctioning tumors. To investigate potential markers predicting malignancy and poor prognosis in nonfunctioning pancreatic endocrine tumors, we analyzed the expression of Ki-67, topoisomerase IIα (Topollα), and p27, as well as a variety of clinicopathologic parameters in 76 cases of nonfunctioning islet cell tumors (23 benign cases and 53 malignant cases). Ki-67, Topollα, and p27 labeling indices were significantly different between benign and malignant tumors. Expression of Ki-67, Topollα, and p27 were associated with survival in patients with a malignant tumor in a univariate setting. However, only p27 and Topollα were jointly associated with survival in multivariate analysis. Immunohistochemical staining for p27, Topollα, and Ki-67 can be helpful in the diagnosis of nonfunctioning pancreatic endocrine tumor. Analysis of p27 and Topollα may also have potential utility as prognostic factors for malignant tumors.  相似文献   
65.
Park SY  Kim HS  Hong EK  Kim WH 《Human pathology》2002,33(11):1078-1085
The expressions of cytokeratin (CK) 7 and 20 have been studied in various primary and metastatic carcinomas, and their determination may help distinguish the site of origin of metastatic carcinomas. However, little is known about the factors that determine variations in their expression patterns in primary gastric and colorectal carcinomas. We investigated the expressions of CK7 and CK20 in 289 cases of gastric carcinoma and 225 cases of colorectal carcinoma using a tissue microarray. To evaluate CK7 and CK20 expression patterns of ovarian metastases from gastric or colorectal carcinomas, 54 cases of metastatic carcinomas to the ovary were examined. It was found that 71% (207 of 289) of the gastric carcinomas stained positively for CK7, whereas only 9% (21 of 225) of the colorectal carcinomas proved to be CK7 positive, and that 41% (117 of 289) of the gastric carcinomas and 73% (165 of 225) of the colorectal carcinomas were CK20 positive. The proportion of CK7+/CK20- was highest in the gastric carcinomas at 46% (132 of 289), and was independent of the histologic classification of Lauren (46% of the intestinal type, 45% of the diffuse type). The CK7 and CK20 expression patterns were different in colorectal carcinomas according to histologic grade and location of the tumor. CK7-/CK20+ had the greatest proportion (68%) in colorectal carcinomas, and this was dependent on the tumor's histologic grade (75% of low-grade versus 52% of high-grade) and location (46% of right-sided versus 76% of left-sided). Moreover, 42% (18 of 43) of gastric carcinomas metastatic to the ovary were CK7+/CK20-, whereas 19% (8 of 43) were CK7-/CK20+. All colorectal cancers metastatic to the ovary were CK7-/CK20+, except 1 case that was CK7-/CK20-. In conclusion, the CK7 and CK20 expression patterns in primary gastric carcinomas vary considerably, and those in colorectal carcinomas are associated with histologic grade and tumor location. The CK7-/CK20+ expression pattern is specific for metastatic colorectal carcinomas to the ovary, but has low predictability for colorectal origin in metastatic ovarian carcinoma.  相似文献   
66.
67.
Loss of the cell adhesion molecule E-cadherin is suggested to promote tumor invasion and distant metastasis in tumor development. Recently, it has been proposed that E-cadherin function requires its linkage to the cytoskeleton through catenins. We evaluated the expression of E-cadherin and alpha-, beta-, gamma-catenins in tissues of human endometrial carcinoma, analyzed the patterns of cell adhesion molecules' expression in endometrial carcinoma and investigated the relationship between the statuses of cell adhesion molecules and various clinicopathological factors. This study investigated the immunohistochemical expression of E-cadherin and alpha-, beta-, gamma-catenins in 33 paraffin embedded formalin fixed tissues of endometrial carcinomas. Aberrant E-cadherin, and alpha-, beta-, gamma-catenin expression was observed in 33.3 (11 of 33), 27.3 (9 of 33), 18.2 (6 of 33), and 51.5 (17 of 33) % of the specimens, respectively. Statistically significant correlation was found between aberrant expression of E-cadherin and lymph node metastasis and cell types other than endometrioid adenocarcinoma. Aberrant pattern of gamma-catenin expression was also correlated with deep myometrial invasion. However, alpha-, and beta-catenin expression was not correlated with any clinicopathological parameters. Using the Kaplan-Meier method and log-rank comparison test, abnormal expression of E-cadherin was correlated closely with poor survival (p < 0.05), but cases with loss of both E-cadherin and catenin expression predicted even poorer survival than cases with only one or no aberrant expression in E-cadherin and catenins. We revealed aberrant expression of these cell adhesion molecules among patients with endometrial carcinoma. Aberrant expression of E-cadherin was correlated with lymph node metastasis and cell types other than endometrioid adenocarcinoma, while aberrant expression of gamma-catenin was related with deep myometrial invasion. The expression of E-cadherin might be a possible prognostic factor for endometrial cancer while the expression of catenins may help predict patient's survival.  相似文献   
68.
Localized in vivo proton magnetic resonance spectroscopy ((1)H-MRS) has been used to measure the metabolic status of the human brain in a non-invasive manner; thus, it is often called "a non-invasive biochemical assay". MRS is more sensitive than magnetic resonance imaging (MRI) in detecting ischemic damage by measuring the metabolic changes that occur prior to the anatomic changes. We report a patient who presented with innominate artery occlusion and symptoms of posterior circulation insufficiency and showed favorable metabolic changes by (1)H-MRS after revascularization. He showed no visible lesion in brain MRI, but in (1)H-MRS, decreased N-acetylaspartate (NAA) signal was noted in a resting state.After revascularization, both symptomatic improvement and recovery of NAA signal were observed. (1)H-MRS may provide valuable clinical information in diagnosis and management of cerebral hypoperfusion at a much earlier stage prior to the anatomic changes.  相似文献   
69.
We contrast naming from pictures, and reading words, for objects and verbs (actions relating to the objects) in a patient with a large, posterior left-hemisphere lesion. We present evidence for spared picture naming for verbs relative to objects, whilst the opposite pattern of sparing occurred in reading. Objects were also spared relative to verbs in tasks requiring that written words be matched to either pictures or auditory words, in the presence of semantically related or unrelated distractors. We conclude that verb semantics were more impaired than semantic knowledge for objects, and that the better semantic knowledge for object names supported word reading. With pictures, however, action verb retrieval was maintained through a nonsemantic route from vision to action, or though preserved right-hemisphere "action semantics."  相似文献   
70.
In genome scans of ankylosing spondylitis (AS), with the exception of the HLA loci, linkage has not been easy to replicate across studies. We applied the genome-search meta-analysis (GSMA) method to genome scans of AS and spondyloarthropathy (SpA) to assess evidence for linkage across studies. Three AS genome scans and one SpA scan including 430 families with 1,048 affected individuals were used. All four original genome scans mainly analyzed Caucasian families. Seven bins had both Psumrnk and Pord<0.05, suggesting these bins most likely contain AS-linked loci; bin 6.2, 6.1, 6.3, 16.3, 19.2, 17.1, and 16.4. The GSMA produced significant genome-wide evidence for linkage on chromosome 6p22.3–6p21.1 (Psumrnk=0.000003), including the HLA locus. In addition to the HLA-B27 locus, strong linkage evidence was found on chromosome 6p25.3–6p22.3 (Psumrnk=0.0013) and 6p21.1–6p15 (Psumrnk=0.043). In the GSMA of four genome scans including one SpA study, the bin 9.4 (9q21.32–9q33.1) was newly found for linkage (Psumrnk=0.043, Pord=0.013). This GSMA added the evidence of the HLA loci as the greatest susceptibility factor to AS and showed evidences of chromosome 6, 16q, 19, 17p, and 9q as non-HLA susceptibility loci.  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