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   11608篇
  免费   833篇
  国内免费   261篇
耳鼻咽喉   70篇
儿科学   478篇
妇产科学   182篇
基础医学   2473篇
口腔科学   164篇
临床医学   734篇
内科学   2216篇
皮肤病学   120篇
神经病学   1333篇
特种医学   422篇
外科学   552篇
综合类   909篇
现状与发展   3篇
一般理论   4篇
预防医学   1504篇
眼科学   291篇
药学   514篇
中国医学   38篇
肿瘤学   695篇
  2024年   11篇
  2023年   210篇
  2022年   222篇
  2021年   372篇
  2020年   426篇
  2019年   474篇
  2018年   381篇
  2017年   361篇
  2016年   353篇
  2015年   406篇
  2014年   610篇
  2013年   814篇
  2012年   510篇
  2011年   642篇
  2010年   517篇
  2009年   535篇
  2008年   592篇
  2007年   581篇
  2006年   576篇
  2005年   477篇
  2004年   433篇
  2003年   405篇
  2002年   308篇
  2001年   384篇
  2000年   218篇
  1999年   224篇
  1998年   235篇
  1997年   219篇
  1996年   185篇
  1995年   141篇
  1994年   131篇
  1993年   99篇
  1992年   65篇
  1991年   63篇
  1990年   58篇
  1989年   42篇
  1988年   40篇
  1987年   44篇
  1986年   34篇
  1985年   39篇
  1984年   41篇
  1983年   19篇
  1982年   31篇
  1981年   46篇
  1980年   29篇
  1979年   17篇
  1978年   24篇
  1977年   12篇
  1976年   15篇
  1974年   7篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Aims Cardiovascular disease (CVD) is a major complication of Type 2 diabetes mellitus. The renin‐angiotensin system (RAS) and nitric oxide production are both important regulators of vascular function and blood pressure. Genes encoding proteins involved in these pathways are candidates for a contribution to CVD in diabetic patients. We have investigated variants of the angiotensinogen (AGT), angiotensin converting enzyme (ACE), angiotensin type 1 receptor (AT1R) and endothelial nitric oxide synthase (NOS3) genes for association with subclinical measures of CVD in families with Type 2 diabetes mellitus (T2DM). Methods Atherosclerosis was measured by carotid intima‐media thickness and calcification of the carotid and coronary arteries in 620 European Americans and 117 African Americans in the Diabetes Heart Study. Because of the role of these systems in blood pressure regulation, blood pressure was also investigated. Results Compelling evidence of association was not detected with any of the SNPs with any outcome measures after adjustments for covariates despite sufficient power to detect relatively small differences in traits for specific genotype combinations. Conclusions Genetic variation of the RAS and NOS3 genes do not appear to strongly influence subclinical cardiovascular disease or blood pressure in this diabetic population.  相似文献   
32.
目的探讨钙通道α1亚基(Cav1.1)基因26内含子-67A/G多态性与男性甲状腺功能亢进(简称甲亢)性周期性瘫痪(TPP)的相关性。方法采用多聚酶链反应-单链构象多态性(PCR-SSCP)方法检测46例男性TPP患者(TPP组)、68例男性甲亢患者(GD组)和72名男性健康对照者(CON组)Cav1.1基因26内含子-67A/G多态性。分析比较此多态位点基因型和等位基因在不同人群中分布的差异。结果(1)TPP组、GD组及CON组AG+GG基因型频率分别为47.83%、14.71%、29.17%,G等位基因频率分别为44.57%、13.24%、27.78%。(2)TPP组AG+GG基因型频率明显高于GD组和CON组(OR=5.32,P〈0.01;OR=2.23,P=0.04),TPP组G等位基因频率明显高于GD组和CON组(OR=5.27,P〈0.01;OR=2.09,P=0.008)。结论Cav1.1基因26内含子-67位点A/G多态性与男性TPP有相关性。  相似文献   
33.
目的克隆和鉴定日本血吸虫磷酸丙糖异构酶(SjTPI)编码基因,为寻找血吸虫病的候选疫苗联合应用打基础.方法设计合成引物,抽提日本血吸虫成虫总RNA,用RT-PCR法从中扩增出SjTPI基因编码序列,将其克隆入pGEM-T载体,用双酶切、以重组质粒为模板进行PCR扩增和测序进行鉴定.结果 RT-PCR法从成虫总RNA中扩增出大小为759 bp SjTPI基因编码序列,重组质粒pGEM-SjTPI经双酶切、PCR扩增,均可获得一条与RT-PCR产物一致的DNA片段,序列测定结果表明具有一个长度为759 bp的完整开放阅读框,与日本血吸虫(菲律宾株)和曼氏血吸虫磷酸丙糖异构酶核苷酸序列有高度同源性(分别为99%和88%).结论该实验成功地克隆了SjTPI编码基因,为进一步研究提供了条件.  相似文献   
34.
The objective of this study was to report a novel exon-1 mutation in the myelin protein zero (MPZ) gene, resulting in axonal Charcot–Marie–Tooth neuropathy with recurrent hyper-CK-emia. In a 64-year-old woman slowly progressive distal lower limb weakness, muscle cramps in the lower limb muscles, and stocking-type numbness had developed from the age of 61. Neurologic examination revealed discrete hip flexor weakness, weakness for foot extension, diffuse wasting of the distal lower limb muscles, reduced patella tendon reflexes, and absent Achilles tendon reflexes. There was recurrently elevated creatine kinase with a maximum of 607 U/l ( n , <145 U/l). Stimulation of the peroneal and tibial nerves did not evoke a muscular response. Electromyography was neurogenic. Biopsy of the right sural nerve showed diffuse axonal degeneration and loss of axons of all diameters. Muscle biopsy showed increased fiber-size variability, angulated fibers, internalized nuclei, accumulations of nuclei, grouped atrophic muscle fibers, and fiber splitting. Molecular genetic analysis by PCR and direct nucleotide sequencing revealed the heterozygous C59T exon-1 MPZ gene mutation, resulting in the amino acid exchange S20F of the MPZ signal protein domain (leader peptide). The novel C59T mutation in the leader peptide of the MPZ gene is pathogenic and manifests as severe, late-onset, axonal, symmetric sensorimotor polyneuropathy (CMT2) and hyper-CK-emia.  相似文献   
35.
The renin-angiotensin system is involved in control of blood pressure and salt and fluid homeostasis. Genes for components of this system have been of major focus in research on the causation of the common, complex, polygenic trait, essential hypertension (HT). Association of an A→C variant at nucleotide 1166 of the angiotensin II type 1 receptor (AT1R) gene with HT, but an absence of linkage of this locus with this disease, has been reported recently. Since confirmation in a different setting is imperative, we performed a cross-sectional case-control study of the A1166C variant in a well-characterized group of 108 Caucasian HT subjects with a strong family history (two affected parents) and early onset disease. Genotyping was by mismatch polymerase chain reaction/ Bfr I restriction fragment length polymorphism analysis. Frequency of the C1166allele was 0.40 in HTs and 0.29 in normotensives. The difference in genotype (χ2= 13, P = 0.0015) and allele (χ2= 5.3, P = 0.02) frequencies between the two groups was significant (odds ratio for CC vs AA+AC = 7.3 [95% CI, 1.9–31.9). The present results implicate the AT1R gene, or a locus in linkage disequilibrium with the variant tested, in the causation of essential HT.  相似文献   
36.
The expressed human κ light chain gene repertoire utilized by healthy individuals was studied by two different single-sided specific PCR techniques to avoid bias for certain V genes. A total of 103 rearranged κ sequences from peripheral blood mononuclear cells from healthy individuals were cloned from cDNA and assigned to the Vκ and Jκ germ-line genes with the closest overall homology. The use of cDNA rather than genomic DNA focused the analysis on activated B cells rich in mRNA. Accordingly, the sequences represented the applied repertoire and almost all were somatically mutated. V genes from the Jκ-proximal duplication unit of the κ locus were almost exclusively used. A total of 65% of the sequences could be assigned to four or five genes: A27 (humkv325), L6 (Vg), L2 (humkv328), and A3 and/or A19. N additions and P nucleotides were quite common and found in 32% and 21% of the sequences, respectively. Extended CDR3s more than nine residues in length were found in 18% of the sequences, and in 71% of cases this was due to insertion of an extra proline residue. This proline was usually explained from the germ-line sequences involved. These results are in good agreement with those of previous repertoire studies using potentially V-gene-biased techniques. Thus, it is clear that restricted V-gene usage, common N and P additions, and extended CDR3 regions are normal features and not, as has been claimed, characteristics of pathological autoantibodies.  相似文献   
37.
The genes of the major histocompatibility complex (MHC) are amongst the most polymorphic loci known in the human population. The population genetics of the MHC encoded HLA loci of sub-Saharan Africa are of major interest because of their particular genetic diversity. Here we report on the HLA-DR 52- and 51-associated determinants of the DRB1 loci observed in 165 East African individuals studied in Nairobi, Kenya. The HLA-DR typing was done by serologic and by molecular DNA techniques (PCR-SSOP). The most frequent allele identified was DRB1*1101, followed by DRB1*1503 and DRB1*1302. Some unexpected alleles were repeatedly identified: DRB1*1108, DRB1*1316 and DRB1*1421. Most oftheDR 52-and 51-associated DRB1 alleles were correctly identified by serology as part of the DR3, DR5, DR6 and DR2 groups respectively. The HLA-DRB1 profile reported here corroborates previous genetic and linguistic data supporting the concept that the Eastern African Black population is genetically distinct from other African Black populations. This has important implications in public health issues related to the genetic profile of a population (transplantation, vaccine design for example).  相似文献   
38.
Fifty couples and their children with Down syndrome (D.S.) were typed for HLA-A and HLA-B antigens and compared to 50 control families and 464 blood donors. The parental origin of the extra chromosome 21 was determined by cytogenetic methods. All individuals were caucasians and there was no history of consanguinity. No excessive HLA sharing was present in D.S. parents. The mothers of D.S. shared no more HLA antigens with their D.S. children than the control mothers with their normal children (14% vs. 18%). Thirteen of the fifty pairs (26%) (parent in whom the nondisjunction occurred and D.S. child) shared three HLA antigens at the A and/or B locus. This was not significantly higher than the proportion in the control group (12/50 or 24%). These data suggest that it is not the sharing of HLA-A and HLA-B antigens between the parents or between the parent who was the origin of the nondisjunction and the D.S. child that is related either to the occurrence of trisomy 21 zygotes or to prenatal survival of affected embryos and fetuses.  相似文献   
39.
Summary In the last decades back pain has reached dramatic proportions in industrialized countries. Disorders of the back are nowadays the leading cause of direct and indirect health care costs. Accurate prevalence estimates are needed to serve as a basis for health care evaluations. A review of epidemiologic studies in the general population reveals that back pain has reached a prevalence of 40 % for current pain. 7 to 18 % are “frequently”, “often”, “daily” or “constantly” affected. 75 % of the adult population suffers from back pain during the last year. 80 to 90 % of the adult population in industrialized countries experience back pain ever. Gender specific differences are only present in severe, chronic forms which are more often experienced by women. Back pain has a prevalence maximum at 50 to 64 years. Older persons display lower prevalence estimates. The prevalence maximum in men is one decade earlier than in women. There are several potential explanations for this prevalence pattern that are discussed in the article. Back pain can be classified by location, temporal characteristics, pain intensity and pain history. Currently, for none of these dimensions generally accepted, uniformly employed and validated definitions are available. In most of the industrialized countries back pain is one of the most expensive symptoms. 75–90 % of the direct and indirect health care costs were caused by those 5–10 % of patients who are disabled. As predictors of back pain a history of back pain and job satisfaction play by far a more important role than the extensively studied mechanical factors. For a first episode of back pain the prognosis is favorable. If the pain persist for more than three months the prognosis is unfavorable. After six months of absenteeism because of back pain more than half of the afflicted never return to work. Rarely back pain is present as a single symptom. In more than 80 % back pain is associated with pain in at least one joint. It remains to be studied if back pain may be viewed as an entity or as part of a more complex pain syndrome.   相似文献   
40.
上海市闵行区流动人口中的孕产妇保健状况   总被引:3,自引:0,他引:3  
通过对上海市闵行区580名外来孕产妇及580名作为对照的本地孕产妇的孕产期保健现况调查分析,表明外来孕产妇缺乏必要的孕产期保健措施,有47.6%的外来孕产妇从未做产前检查,产后保健则完全没有,并由此而造成外来产妇在急产、死产、甚至孕产妇死亡等方面令人忧虑的现状。为适应和促进当前经济发展的新形势,改善流动人口的孕产妇保健状况,应对流动人口中孕产妇保健状况深入研究,并采取相应的措施。  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