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   1076篇
  免费   50篇
  国内免费   11篇
耳鼻咽喉   10篇
儿科学   11篇
妇产科学   7篇
基础医学   182篇
口腔科学   70篇
临床医学   84篇
内科学   188篇
皮肤病学   13篇
神经病学   133篇
特种医学   52篇
外科学   160篇
综合类   4篇
一般理论   1篇
预防医学   64篇
眼科学   5篇
药学   87篇
中国医学   4篇
肿瘤学   62篇
  2024年   2篇
  2023年   12篇
  2022年   35篇
  2021年   51篇
  2020年   39篇
  2019年   32篇
  2018年   45篇
  2017年   23篇
  2016年   32篇
  2015年   39篇
  2014年   42篇
  2013年   77篇
  2012年   105篇
  2011年   85篇
  2010年   44篇
  2009年   26篇
  2008年   44篇
  2007年   59篇
  2006年   50篇
  2005年   54篇
  2004年   57篇
  2003年   53篇
  2002年   33篇
  2001年   4篇
  2000年   4篇
  1999年   5篇
  1998年   8篇
  1997年   4篇
  1996年   5篇
  1995年   3篇
  1994年   2篇
  1992年   3篇
  1991年   4篇
  1990年   3篇
  1989年   4篇
  1988年   4篇
  1984年   3篇
  1983年   2篇
  1982年   3篇
  1979年   2篇
  1977年   3篇
  1973年   2篇
  1971年   4篇
  1970年   4篇
  1966年   2篇
  1943年   2篇
  1942年   6篇
  1941年   1篇
  1937年   1篇
  1934年   1篇
排序方式: 共有1137条查询结果,搜索用时 15 毫秒
1.
The aim of this study was to investigate the effect of a moderate soft tissue trauma to the course of fracture healing in a standardized animal model. Thirty-eight Wistar rats were randomly divided into a fracture group (F, n = 19) and a group with a fracture and a soft tissue trauma (F + STT, n = 19). The fracture and the soft tissue trauma were created using an impact device with a standardized energy. All fractures were stabilized by two Kirschner wires. Three rats were measured for blood flow and sacrificed at days 1, 3, 7, and 14, and seven rats at day 28, from both groups. A three-point bending test was performed on the healed tibia after 28 days. During the first 24 h there was a reduction in blood flow, which was more pronounced in the F + STT group than in the F group. From histological sections, the shape of the callus formation, as well as the tissue distribution of newly formed bone, fibrous cartilage and fibrous connective tissue were determined. Distinctly more periosteal new bone formed and a larger callus formed at days 3 and 7 in group F compared to group F + STT. However, by days 14 and 28, the ossification and overall callus size no longer showed differences between the two groups. A fast recovery of blood flow and callus formation took place in the F + STT group, which led to similar histological and biomechanical results in fracture healing observed after 28 days between the two groups.  相似文献   
2.
Ultrasonography in the detection of cervical incompetency   总被引:2,自引:0,他引:2  
In 80 pregnancies with clinical and ultrasonic signs of cervical incompetency, the length of the cervix and the thickness of the anterior wall of a lower uterine segment have been evaluated ultrasonically. We have also measured the width of the endocervical canal and studied the prolapse of fetal membranes (with fetal parts) into the endocervical canal. We evaluated these same parameters in 80 healthy pregnancies. The length of the cervix, the thickness of the anterior wall of a lower uterine segment, and the width of the endocervical canal were followed longitudinally in the patients from the 10th to the 36th gestation week. No statistically significant differences between age groups were found. In four age groups at risk for cervical incompetency, cervical lengths and wall thickness were significantly different (p less than 0.001) from those in comparable controls. Forty-five percent of the patients in the at-risk group, with cervical cerclage, delivered at 37.3 (range: 32 to 41) weeks and 6.25% of pregnancies ended in abortion when the amniotic membrane herniated into the cervical canal, with or without some part of the fetus.  相似文献   
3.
Lipopolysaccharide (LPS) preconditioning provides neuroprotection against subsequent cerebral ischemic injury. Tumor necrosis factor-alpha (TNFalpha) is protective in LPS-induced preconditioning yet exacerbates neuronal injury in ischemia. Here, we define dual roles of TNFalpha in LPS-induced ischemic tolerance in a murine model of stroke and in primary neuronal cultures in vitro, and show that the cytotoxic effects of TNFalpha are attenuated by LPS preconditioning. We show that LPS preconditioning significantly increases circulating levels of TNFalpha before middle cerebral artery occlusion in mice and show that TNFalpha is required to establish subsequent neuroprotection against ischemia, as mice lacking TNFalpha are not protected from ischemic injury by LPS preconditioning. After stroke, LPS preconditioned mice have a significant reduction in the levels of TNFalpha (approximately threefold) and the proximal TNFalpha signaling molecules, neuronal TNF-receptor 1 (TNFR1), and TNFR-associated death domain (TRADD). Soluble TNFR1 (s-TNFR1) levels were significantly increased after stroke in LPS-preconditioned mice (approximately 2.5-fold), which may neutralize the effect of TNFalpha and reduce TNFalpha-mediated injury in ischemia. Importantly, LPS-preconditioned mice show marked resistance to brain injury caused by intracerebral administration of exogenous TNFalpha after stroke. We establish an in vitro model of LPS preconditioning in primary cortical neuronal cultures and show that LPS preconditioning causes significant protection against injurious TNFalpha in the setting of ischemia. Our studies suggest that TNFalpha is a twin-edged sword in the setting of stroke: TNFalpha upregulation is needed to establish LPS-induced tolerance before ischemia, whereas suppression of TNFalpha signaling during ischemia confers neuroprotection after LPS preconditioning.  相似文献   
4.
Proto-oncogenes, growth factors/receptors, and tumour suppressor genes were analysed in malignant metastatic insulinomas. Normal pancreas showed only a moderate immunoreaction for c-myc proto-oncogene and a strong reaction for insulin. Benign insulinomas were slightly or moderately positive for transforming growth factor a (TGFα), weakly positive for epidermal growth factor receptor (EGF-R), and strongly positive for c-myc and insulin. In malignant insulinomas, besides a strong immunoreaction for c-myc and TGFα, activation of c-K-ras and overexpression of p53 protein were found. Insulin reaction was moderate or strong. Three out of six malignant insulinomas displayed a c-K-ras point mutation at codon 12. All mutations were guanine to cytosine transversion, resulting in amino acid substitution, glycine to arginine. Mutations were present in metastatic insulinomas only. Patients with mutated c-K-ras oncogene had overexpression of p53 protein as well as c-myc and TGFα overexpression. Our results support the view that malignant progression is a consequence of more than one genetic lesion and suggest that activation of myc, TGFα, and ras genesα plays a role in a multistep process of tumour progression, perhaps serving as an initiating event.  相似文献   
5.
A major challenge in reconstructive surgery is flap ischemia, which might benefit from induction of therapeutic angiogenesis. Here we demonstrate the effect of an adeno-associated virus (AAV) vector delivering vascular endothelial growth factor (VEGF)165 in two widely recognized in vivo flap models. For the epigastric flap model, animals were injected subcutaneously with 1.5 x 10(11) particles of AAV-VEGF at day 0, 7, or 14 before flap dissection. In the transverse rectus abdominis musculocutaneous flap model, AAV-VEGF was injected intramuscularly. The delivery of AAV-VEGF significantly improved flap survival in both models, reducing necrosis in all treatment groups compared to controls. The most notable results were obtained by administering the vector 14 days before flap dissection. In the transverse rectus abdominis musculocutaneous flap model, AAV-VEGF reduced the necrotic area by >50% at 1 week after surgery, with a highly significant improvement in the healing process throughout the following 2 weeks. The therapeutic effect of AAV-VEGF on flap survival was confirmed by histological evidence of neoangiogenesis in the formation of large numbers of CD31-positive capillaries and alpha-smooth muscle actin-positive arteriolae, particularly evident at the border between viable and necrotic tissue. These results underscore the efficacy of VEGF-induced neovascularization for the prevention of tissue ischemia and the improvement of flap survival in reconstructive surgery.  相似文献   
6.
The left chorda tympani nerve was interrupted through meatus acusticus externus in ten dogs. In total, 40 dog salivary glands (20 submandibular and 20 sublingual) innervated via chorda tympani were examined. Twenty glands (10 submandibular and 10 sublingual) on the left side were deprived of parasympathetic innervation by chordectomy, whereas contraleteral glands, on the right side, served as controls. Biochemical analysis showed that the interruption of chorda tympani did not cause any significant changes in the concentrations of eight enzymes investigated, i.e. lactate dehydrogenase, alkaline phosphatase, acid phosphatase, amylase, aspartate aminotransferase, alanine aminotransferase, gamma-glutamyltransferase and creatine kinase. There were no significant changes in the concentrations of most important extracellular ions (sodium, potassium, chloride and phosphorus) in the right glands, but the loss of parasympathetic innervation in the left glands was found to cause a statistically significant decrease in the concentration of potassium as intracellular cation and of phosphorus as extracellular anion.  相似文献   
7.
Two outbreaks of typhoid fever caused by Salmonella typhi of the same phagotype (A, biotype II) and antibiotic susceptibility are reported. Both occurred during the war in Bosnia and Herzegovina. The first outbreak appeared among the refugees from the town of Jajce. The second outbreak appeared among the inhabitants in the village of Vidosi near Livno. This report describes main clinical, epidemioloigcal and laboratory findings for 22 patients treated in Split University Hospital, Croatia, in the period November 1992–January 1993. Possible epidemiological connections between those two outbreaks are discussed.  相似文献   
8.
IntroductionPublic health measures enacted to reduce COVID-19 transmission have affected individuals'' lifestyles, mental health, and psychological well-being. To date, little is known how stay-at-home orders have influenced the eating behaviors, weight development, and alcohol consumption of quarantined persons. The CoCo-Fakt cohort study analyzed these parameters and their association with psychological distress and coping strategies.MethodsAn online survey was conducted of all persons who tested positive for SARS-CoV-2 (infected persons [IP]) between December 12, 2020, and January 6, 2021, as well as their close contacts (contact persons [CP]) registered by the public health department of Cologne. 8,075 of 33,699 individuals were included in the analysis. In addition to demographic data, psychological distress, and coping strategies, information on changes in body weight, eating, and drinking behaviors was collected.ResultsIP lost 1.2 ± 4.4 kg during the quarantine period, and CP gained 1.6 ± 4.1 kg. The reasons given by IP for weight change were mainly loss of taste and feeling sick, whereas CP were more likely than IP to eat out of boredom. Higher psychological burden and lower coping strategies were associated with both weight gain and loss. Of the 30.8% of participants who changed their alcohol consumption during the quarantine period, CP in particular drank more alcohol (IP 15.2%; CP 47.7%). Significantly less alcohol was consumed by individuals with higher coping scores.ConclusionIn this short but psychologically stressful period of stay-at-home orders, changes in eating and drinking behavior as well as weight development are evident, mainly in high-risk contacts. To avoid possible long-term sequelae, health authorities should take these findings into account during the quarantine period; in particular, general practitioners should consider these findings during follow-up.  相似文献   
9.
This paper deals with the selection of the optimal material for railway wagons, from among three different steel and three aluminium based materials, by using four different Multicriteria Decision Making Methods (MCDM) and comparing their ranking of the materials. We analysed: Dual-Phase 600 steel, Transformation-Induced Plasticity (TRIP) 700 steel, Twinning-Induced Plasticity (TWIP) steel, Aluminium (Al) alloys, Al 6005-T6, and Al 6082-T6, and porous Al structure with closed cells. Four different MCDM methods were used: VIKOR, TOPSIS, PROMETTHEE and the Weighted aggregated sum product assessment method (WASPAS). Key material properties that were used in the MCDM analysis were: density, yield strength (Y.S.), tensile strength (T.S.), Y.S./T.S. ratio, Youngs modulus (Y.M.), cost and corrosion resistance (C.R.). Research results indicate that aluminium and its alloys prove to be the most suitable material, based on setup criteria. Advanced steels also achieved good ranking, making them a valid option, immediately behind lightweight aluminium alloys. Porous aluminium did not perform well, according to the used MDCM methods, mainly due to the significantly lower strength exhibited by the porous structures in general.  相似文献   
10.
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