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   1003篇
  免费   75篇
  国内免费   2篇
耳鼻咽喉   19篇
儿科学   41篇
妇产科学   8篇
基础医学   151篇
口腔科学   6篇
临床医学   90篇
内科学   177篇
皮肤病学   9篇
神经病学   143篇
特种医学   42篇
外科学   74篇
综合类   8篇
预防医学   140篇
眼科学   7篇
药学   93篇
中国医学   1篇
肿瘤学   71篇
  2023年   12篇
  2022年   32篇
  2021年   51篇
  2020年   34篇
  2019年   29篇
  2018年   38篇
  2017年   31篇
  2016年   20篇
  2015年   33篇
  2014年   36篇
  2013年   58篇
  2012年   59篇
  2011年   86篇
  2010年   41篇
  2009年   41篇
  2008年   73篇
  2007年   54篇
  2006年   74篇
  2005年   47篇
  2004年   73篇
  2003年   46篇
  2002年   46篇
  2001年   1篇
  2000年   4篇
  1999年   2篇
  1998年   10篇
  1997年   5篇
  1996年   10篇
  1995年   2篇
  1994年   5篇
  1993年   11篇
  1992年   2篇
  1991年   1篇
  1989年   2篇
  1988年   1篇
  1986年   2篇
  1983年   1篇
  1982年   1篇
  1981年   2篇
  1978年   1篇
  1975年   1篇
  1963年   2篇
排序方式: 共有1080条查询结果,搜索用时 15 毫秒
41.
Chondrodysplastic dwarfism in Japanese brown cattle is an autosomal recessive disorder characterized by short limbs. Previously, we mapped the locus responsible for the disease on the distal end of bovine chromosome 6. Here, we narrowed the critical region to approximately 2 cM by using linkage analysis, constructed a BAC and YAC contig covering this region, and identified a gene, LIMBIN (LBN), that possessed disease-specific mutations in the affected calves. One mutation was a single nucleotide substitution leading to an activation of a cryptic splicing donor site and the other was a one-base deletion resulting in a frameshift mutation. Strong expression of the Lbn gene was observed in limb buds of developing mouse embryos and in proliferating chondrocytes and bone-forming osteoblasts in long bones. These findings indicate that LBN is responsible for bovine chondrodysplastic dwarfism and has a critical role in a skeletal development.  相似文献   
42.
Macrophage mannose receptor on lymphatics controls cell trafficking   总被引:2,自引:0,他引:2  
Macrophage mannose receptor (MR) participates in pathogen recognition, clearance of endogenous serum glycoproteins, and antigen presentation. MR is also present on lymphatic vessels, where its function is unknown. Here we show that migration of lymphocytes from the skin into the draining lymph nodes through the afferent lymphatics is reduced in MR-deficient mice, while the structure of lymphatic vasculature remains normal in these animals. Moreover, in a tumor model the primary tumors grow significantly bigger in MR–/– mice than in the wild-type (WT) controls, whereas the regional lymph node metastases are markedly smaller. Adhesion of both normal lymphocytes and tumor cells to lymphatic vessels is significantly decreased in MR-deficient mice. The ability of macrophages to present tumor antigens is indistinguishable between the 2 genotypes. Thus, MR on lymphatic endothelial cells is involved in leukocyte trafficking and contributes to the metastatic behavior of cancer cells. Blocking of MR may provide a new approach to controlling inflammation and cancer metastasis by targeting the lymphatic vasculature.  相似文献   
43.
Type 4 phosphodiesterase (PDE4) inhibitors reportedly induce apoptosis in chronic lymphocytic leukemia (CLL) cells. Following clinical improvement of one previously untreated CLL patient with sildenafil therapy, we evaluated the in vitro induction of apoptosis in CLL cells by 4 PDE5/6 inhibitors, including sildenafil, vardenafil, zaprinast, and methoxyquinazoline (MQZ). After 24 hours of culture, the various PDE inhibitors differed in their ability to induce apoptosis, with zaprinast displaying no killing effect. Normal B cells isolated from control donors were totally resistant to PDE-induced apoptosis. Vardenafil was 3 and 30 times more potent an inducer of apoptosis than sildenafil and MQZ, respectively. Both vardenafil and sildenafil failed to elevate adenosine 3'5' cyclic monophosphate (cAMP) levels, largely excluding an inhibitory effect on cAMP-PDE3, -PDE4, and -PDE7. Vardenafil- or sildenafil-treated B-CLL cells displayed up to 30% intracellular active caspase 3. Drug-induced apoptosis was inhibited by the caspase inhibitor z-VAD.fmk, prevented by interleukin-4 (IL-4), and significantly reduced by stromal-derived factor1-alpha (SDF-1alpha). We conclude that vardenafil and sildenafil induce caspase-dependent apoptosis of B-CLL cells in vitro and thus might be considered in the treatment of CLL patients. However, further in vivo investigations should be warranted.  相似文献   
44.
45.
46.
Severe cognitive impairment involving multiple cognitive domains can occur early during the course of multiple sclerosis (MS). We investigated resting state functional connectivity changes in large‐scale brain networks and related structural damage underlying cognitive dysfunction in patients with early MS. Patients with relapsing MS (3–5 years disease duration) were prospectively assigned to two groups based on a standardized neuropsychological evaluation: (1) cognitively impaired group (CI group, n = 15), with abnormal performances in at least 3 tests; (2) cognitively preserved group (CP group, n = 20) with normal performances in all tests. Patients and age‐matched healthy controls underwent a multimodal 3T magnetic resonance imaging (MRI) including anatomical T1 and T2 images, diffusion imaging and resting state functional MRI. Structural MRI analysis revealed that CI patients had a higher white matter lesion load compared to CP and a more severe atrophy in gray matter regions highly connected to networks involved in cognition. Functional connectivity measured by integration was increased in CP patients versus controls in attentional networks (ATT), while integration was decreased in CI patients compared to CP both in the default mode network (DMN) and ATT. An anatomofunctional study within the DMN revealed that functional connectivity was mostly altered between the medial prefrontal cortex (MPFC) and the posterior cingulate cortex (PCC) in CI patients compared to CP and controls. In a multilinear regression model, functional correlation between MPFC and PCC was best predicted by PCC atrophy. Disconnection in the DMN and ATT networks may deprive the brain of compensatory mechanisms required to face widespread structural damage. Hum Brain Mapp 35:4706–4717, 2014. © 2014 Wiley Periodicals, Inc .  相似文献   
47.
This paper focuses on the psychological benefits of caregiving in key relatives of patients with muscular dystrophies (MD), a group of rare diseases characterized by progressive weakness and restriction of the patient’s functional abilities. We describe whether relatives perceived caregiving to be a positive experience and test whether relatives’ perceptions vary in relation to their view of the patient as a valued person, the degree of involvement in care, and the level of support provided by social network and professionals. The study sample included 502 key relatives of patients aged 4–25 years, suffering from Duchenne, Becker, or limb-girdle MD, in treatment for at least 6 months to one of the eight participating centers, living with at least one relative aged 18–80 years. Of key relatives, 88 % stated that they had gotten something positive out of the situation, 96 % considered their patients to be sensitive, and 94 % viewed their patients as talented. Positive aspects of caregiving were more recognized by key relatives who were more convinced that the patient was sensitive and who perceived that they received higher level of professional help and psychological social support. These results suggest that most key relatives consider that their caregiving experience has had a positive impact on their lives, despite the practical difficulties of caring for patients with MD. Professionals should help relatives to identify the benefits of caregiving without denying its difficulties. Clinicians themselves should develop positive attitudes towards family involvement in the care of patients with long-term diseases.  相似文献   
48.
We hypothesized that bone resorption acts to increase bone strength through stimulation of periosteal expansion. Hence, we examined whether bone resorption, as reflected by serum β‐C‐telopeptides of type I collagen (CTX), is positively associated with periosteal circumference (PC), in contrast to inverse associations with parameters related to bone remodeling such as cortical bone mineral density (BMDC). CTX and mid‐tibial peripheral quantitative computed tomography (pQCT) scans were available in 1130 adolescents (mean age 15.5 years) from the Avon Longitudinal Study of Parents and Children (ALSPAC). Analyses were adjusted for age, gender, time of sampling, tanner stage, lean mass, fat mass, and height. CTX was positively related to PC (β = 0.19 [0.13, 0.24]) (coefficient = SD change per SD increase in CTX, 95% confidence interval)] but inversely associated with BMDC (β = –0.46 [–0.52,–0.40]) and cortical thickness [β = –0.11 (–0.18, –0.03)]. CTX was positively related to bone strength as reflected by the strength‐strain index (SSI) (β = 0.09 [0.03, 0.14]). To examine the causal nature of this relationship, we then analyzed whether single‐nucleotide polymorphisms (SNPs) within key osteoclast regulatory genes, known to reduce areal/cortical BMD, conversely increase PC. Fifteen such genetic variants within or proximal to genes encoding receptor activator of NF‐κB (RANK), RANK ligand (RANKL), and osteoprotegerin (OPG) were identified by literature search. Six of the 15 alleles that were inversely related to BMD were positively related to CTX (p < 0.05 cut‐off) (n = 2379). Subsequently, we performed a meta‐analysis of associations between these SNPs and PC in ALSPAC (n = 3382), Gothenburg Osteoporosis and Obesity Determinants (GOOD) (n = 938), and the Young Finns Study (YFS) (n = 1558). Five of the 15 alleles that were inversely related to BMD were positively related to PC (p < 0.05 cut‐off). We conclude that despite having lower BMD, individuals with a genetic predisposition to higher bone resorption have greater bone size, suggesting that higher bone resorption is permissive for greater periosteal expansion. © 2014 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals, Inc. on behalf of the American Society for Bone and Mineral Research. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.  相似文献   
49.
50.
Among the various methods for collecting oil spills and oil products, including from the water surface, one of the most effective is the use of sorbents. In this work, three-component bio-based composite granular adsorbents were produced and studied for oil products’ pollution collection. A bio-based binder made of peat, devulcanised crumb rubber from used tyres, and part fly ash as cenospheres were used for absorbent production. The structure, surface morphology, porosity, mechanical properties, and sorption kinetics of the obtained samples were studied. Composite hydrophobicity and sorption capacity to oil products, such as diesel fuel (DF) and motor oil (MO), were determined. The obtained pellets are characterised by a sufficiently pronounced ability to absorb oil products such as DF. As the amount of CR in the granules increases, the diesel absorption capacity increases significantly. The case of 30-70-0 is almost three times higher than the granules from homogenised peat. The increase in q is due to two factors: the pronounced surface hydrophobicity of the samples (Θ = 152°) and a heterogeneous porous granule structure. The presence of the cenosphere in the biocomposite reduces its surface hydrophobicity while increasing the diesel absorption capacity. Relatively rapid realisation of the maximum saturation by the MO was noted. In common, the designed absorbent shows up to 0.7 g·g−1 sorption capacity for MO and up to 1.55 g·g−1 sorption capacity for diesel. A possible mechanism of DF absorption and the limiting stages of the process approximated for different kinetic models are discussed. The Weber–Morris diffusion model is used to primarily distinguish the limiting effect of the external and internal diffusion of the adsorbate on the absorption process.  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