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   2416篇
  免费   146篇
  国内免费   23篇
耳鼻咽喉   25篇
儿科学   95篇
妇产科学   130篇
基础医学   411篇
口腔科学   40篇
临床医学   174篇
内科学   622篇
皮肤病学   19篇
神经病学   135篇
特种医学   133篇
外科学   245篇
综合类   27篇
预防医学   181篇
眼科学   32篇
药学   109篇
中国医学   2篇
肿瘤学   205篇
  2023年   8篇
  2022年   17篇
  2021年   51篇
  2020年   20篇
  2019年   52篇
  2018年   49篇
  2017年   46篇
  2016年   47篇
  2015年   50篇
  2014年   52篇
  2013年   87篇
  2012年   124篇
  2011年   109篇
  2010年   75篇
  2009年   64篇
  2008年   114篇
  2007年   136篇
  2006年   146篇
  2005年   120篇
  2004年   100篇
  2003年   98篇
  2002年   98篇
  2001年   82篇
  2000年   96篇
  1999年   76篇
  1998年   52篇
  1997年   60篇
  1996年   43篇
  1995年   40篇
  1994年   31篇
  1993年   19篇
  1992年   43篇
  1991年   38篇
  1990年   25篇
  1989年   49篇
  1988年   41篇
  1987年   19篇
  1986年   28篇
  1985年   32篇
  1984年   21篇
  1983年   28篇
  1982年   19篇
  1981年   9篇
  1980年   12篇
  1978年   5篇
  1977年   13篇
  1974年   7篇
  1973年   5篇
  1972年   5篇
  1966年   4篇
排序方式: 共有2585条查询结果,搜索用时 15 毫秒
991.
Bovine papillomavirus type 4 (BPV-4) morphologically transforms primary bovine cells in vitro only in the presence of an activated ras gene. The transformed cells are capable of anchorage-independent growth, but are not immortal and are incapable of inducing tumors in nude mice, suggesting that other events are needed to convert the cells to the fully transformed phenotype. We show here that treatment of the cells with a single dose of the flavonoid quercetin leads to full oncogenic transformation of cells transfected with BPV-4 and ras. Quercetin is one of the most potent mutagens found in bracken fern, the environmental cofactor in BPV-4-associated carcinogenesis of the upper alimentary canal of cattle. Our results point to quercetin as the probable in vivo cocarcinogen synergizing with BPV-4 in malignant progression.  相似文献   
992.
993.
Whole cell patch-clamp recordings of calcium-activated chloride current [ICl(Ca)] were made from adult sensory neurons of naive and axotomized mouse L4-L6 lumbar dorsal root ganglia after 1 day of culture in vitro. A basal ICl(Ca) was specifically expressed in a subset of naive medium-diameter neurons (30-40 microm). Prior nerve injury, induced by sciatic nerve transection 5 days before experiments, increased both ICl(Ca) amplitude and its expression in medium-diameter neurons. Moreover, nerve injury also induced ICl(Ca) expression in a new subpopulation of neurons, the large-diameter neurons (40-50 microm). Small-diameter neurons (inferior to 30 microm) never expressed ICl(Ca). Regulated ICl(Ca) expression was strongly correlated with injury-induced regenerative growth of sensory neurons in vitro and nerve regeneration in vivo. Cell culture on a substrate not permissive for growth, D,L-polyornithine, prevented both elongation growth and ICl(Ca) expression in axotomized neurons. Regenerative growth and the induction of ICl(Ca) expression take place 2 days after injury, peak after 5 days of conditioning in vivo, slowly declining thereafter to control values. The selective expression of ICl(Ca) within medium- and large-diameter neurons conditioned for rapid, efficient growth suggests that these channels play a specific role in postinjury behavior of sensory neuron subpopulations such as neuropathic pain and/or axonal regeneration.  相似文献   
994.
Increasing use of unbiased genomic sequencing in critically ill infants can expand understanding of rare diseases such as Kabuki syndrome (KS). Infants diagnosed with KS through genome-wide sequencing performed during the initial hospitalization underwent retrospective review of medical records. Human phenotype ontology terms used in genomic analysis were aggregated and analyzed. Clinicians were surveyed regarding changes in management and other care changes. Fifteen infants met inclusion criteria. KS was not suspected prior to genomic sequencing. Variants were classified as Pathogenic (n = 10) or Likely Pathogenic (n = 5) by American College of Medical Genetics and Genomics Guidelines. Fourteen variants were de novo (KMT2D, n = 12, KDM6A, n = 2). One infant inherited a likely pathogenic variant in KMT2D from an affected father. Frequent findings involved cardiovascular (14/15) and renal (7/15) systems, with palatal defects also identified (6/15). Three infants had non-immune hydrops. No minor anomalies were universally documented; ear anomalies, micrognathia, redundant nuchal skin, and hypoplastic nails were common. Changes in management were reported in 14 infants. Early use of unbiased genome-wide sequencing enabled a molecular diagnosis prior to clinical recognition including infants with atypical or rarely reported features of KS while also expanding the phenotypic spectrum of this rare disorder.  相似文献   
995.
Ophthalmological and molecular genetic studies were performed in a consanguineous family with individuals showing either retinitis pigmentosa (RP) or cone-rod dystrophy (CRD). Assuming pseudodominant (recessive) inheritance of allelic defects, linkage analysis positioned the causal gene at 1p21-p13 (lod score 4.22), a genomic segment known to harbor the ABCR gene involved in Stargardt's disease (STGD) and age- related macular degeneration (AMD). We completed the exon-intron structure of the ABCR gene and detected a severe homozygous 5[prime] splice site mutation, IVS30+1G->T, in the four RP patients. The five CRD patients in this family are compound heterozygotes for the IVS30+1G- >T mutation and a 5[prime] splice site mutation in intron 40 (IVS40+5G- >A). Both splice site mutations were found heterozygously in two unrelated STGD patients, but not in 100 control individuals. In these patients the second mutation was either a missense mutation or unknown. Since thus far no STGD patients have been reported to carry two ABCR null alleles and taking into account that the RP phenotype is more severe than the STGD phenotype, we hypothesize that the intron 30 splice site mutation represents a true null allele. Since the intron 30 mutation is found heterozygously in the CRD patients, the IVS40+5G->A mutation probably renders the exon 40 5[prime] splice site partially functional. These results show that mutations in the ABCR gene not only result in STGD and AMD, but can also cause autosomal recessive RP and CRD. Since the heterozygote frequency for ABCR mutations is estimated at 0.02, mutations in ABCR might be an important cause of autosomal recessive and sporadic forms of RP and CRD.   相似文献   
996.
A new technique called transvaginal hydrolaparoscopy is described for the exploration of the tubo-ovarian structures in infertile patients without obvious pelvic pathology. It aims to be an acceptable alternative to diagnostic laparoscopy, a standard but not innocuous procedure which infrequently reveals pathology in the asymptomatic patient. Transvaginal hydrolaparoscopy copy is performed under local anaesthesia using a small diameter optic with the patient in the dorsal position. Cavity distension is achieved with normal saline. Transvaginal hydrolaparoscopy does not provide the familiar and panoramic view of the pelvis given by laparoscopy, but it does have several advantages. These include accurate and atraumatic inspection of adnexal structures without manipulation, with the opportunity to perform dye hydrotubation and salpingoscopy. The risks of a general anaesthetic are avoided, and there is less risk of trauma to major vessels. The high patient acceptability makes transvaginal hydrolaparoscopy suitable as an early stage procedure in the investigation of infertility and as a repeat or second look procedure. Minor operative procedures such as biopsy and adhesiolysis can also be performed. In patients with obvious pelvic pathology, diagnostic laparoscopy will obviously remain the procedure of choice. Transvaginal hydrolaparoscopy deserves full evaluation of its accuracy, risks and benefits before it can be accepted as a new first line technique in gynaecological practice.   相似文献   
997.
998.

Background  

The success rate of IVF treatment is low. A recent systematic review and meta-analysis found that the outcome of IVF treatment could be improved in patients who have experienced recurrent implantation failure if an outpatient hysteroscopy (OH) is performed before starting the new treatment cycle. However, the trials were of variable quality, leading to a call for a large and high-quality randomised trial. This protocol describes a multi-centre randomised controlled trial to test the hypothesis that performing an OH prior to starting an IVF cycle improves the live birth rate of the subsequent IVF cycle in women who have experienced two to four failed IVF cycles.  相似文献   
999.
Despite high rates of unintended pregnancy among women aged 18 to 30 years, little research has been conducted to understand the factors associated with their contraceptive use. Eighteen focus groups were conducted with young adult women (N = 106) who were mostly white, non-Hispanic. Results suggested that contraceptive use was negatively affected by low contraceptive knowledge; use of alcohol; a lack of planning for sex; a misperception of the likelihood of pregnancy; forgetting to use contraceptives; and concerns about side effects, cost, and confidentiality. Women liked the peace of mind that using contraceptives gave them and the benefits of regular periods from some hormonal methods. Implications for reducing unintended pregnancies through interventions are offered.  相似文献   
1000.
A lifetime experiment using 4279 CBA/J mice was carried out to investigate whether the pre-conceptual exposure of sperm cells to X-ray radiation or urethane would result in an increased cancer risk in the untreated progeny, and/or increased susceptibility to cancer following exposure to a promoting agent. The study consisted of four main groups, namely a control group (saline), a urethane group (1 mg/g body wt) and two X-ray radiation groups (1 Gy, 2 Gy). At 1, 3 and 9 weeks after treatment, the males of these four parental groups were mated with untreated virgin females. The offspring of each parental group was divided into two subgroups: one received s.c. urethane (0.1 mg/g body wt once) as a promoter, the other saline, at the age of 6 weeks. All animals were evaluated for the occurrence of tumours. K-ras oncogene and p53 tumour suppressor gene mutations were investigated in frozen lung tumour samples. The female offspring of male parents exposed to X-rays 1 week before their mating showed a trend towards a higher tumour incidence of the haematopoietic system than the F1 controls. In addition, a higher percentage of bronchioloalveolar adenocarcinomas in male offspring born to irradiated paternals mated 1 week after X-ray treatment points to a plausible increased sensitivity of post-meiotic germ cell stages towards transgenerational carcinogenic effects. On the other hand, no increased tumour incidence and malignancy were observed in the offspring born to irradiated paternals mated 3 and 9 weeks after X-ray treatment. Paternal urethane treatment 1, 3 and 9 weeks prior to conception did not result in significantly altered incidence or malignancy of tumours of the lung, liver and haematopoietic tissue in the offspring. K-ras mutations increased during tumour progression from bronchioloalveolar hyperplasia to adenoma. Codon 61 K-ras mutations were more frequent in lung tumours of urethane-promoted progeny from irradiated parents than from control parents. P53 mutations were absent from these lung alterations.  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