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   15686篇
  免费   1330篇
  国内免费   68篇
耳鼻咽喉   205篇
儿科学   358篇
妇产科学   229篇
基础医学   2036篇
口腔科学   239篇
临床医学   1716篇
内科学   3385篇
皮肤病学   381篇
神经病学   946篇
特种医学   667篇
外科学   2582篇
综合类   116篇
现状与发展   1篇
一般理论   4篇
预防医学   1306篇
眼科学   516篇
药学   1132篇
中国医学   83篇
肿瘤学   1182篇
  2024年   16篇
  2023年   181篇
  2022年   442篇
  2021年   842篇
  2020年   451篇
  2019年   551篇
  2018年   640篇
  2017年   424篇
  2016年   503篇
  2015年   520篇
  2014年   656篇
  2013年   706篇
  2012年   1120篇
  2011年   1087篇
  2010年   650篇
  2009年   523篇
  2008年   903篇
  2007年   883篇
  2006年   750篇
  2005年   702篇
  2004年   617篇
  2003年   542篇
  2002年   494篇
  2001年   494篇
  2000年   452篇
  1999年   370篇
  1998年   129篇
  1997年   113篇
  1996年   101篇
  1995年   81篇
  1994年   74篇
  1993年   64篇
  1992年   150篇
  1991年   105篇
  1990年   120篇
  1989年   114篇
  1988年   97篇
  1987年   83篇
  1986年   68篇
  1985年   54篇
  1984年   49篇
  1983年   35篇
  1982年   20篇
  1981年   12篇
  1980年   18篇
  1979年   17篇
  1977年   11篇
  1976年   9篇
  1975年   7篇
  1974年   6篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Repair and regeneration are mutually exclusive responses to injury. Previous studies have shown that wound fluids promote proliferation, but not differentiation, of myoblasts in vitro. This study explored the ability of the repair environment within polyvinyl alcohol sponges to support cellular events of skeletal muscle regeneration in vivo. Neonatal rat L8 myoblasts were modified to express beta-galactosidase then inoculated into plain sponges or sponges containing minced muscle. Labeled myoblasts were found in myotubes within minced muscle. In contrast, myoblasts inoculated into sponges lacking muscle remained mononucleate. Occurrence of labeled myoblasts within myotubes, which required fusion, represents differentiation of inoculated myoblasts to participate in regeneration. Failure of myoblasts to form myotubes in sponges lacking muscle suggests that this wound repair environment cannot support morphologic differentiation of myoblasts. Although this repair environment can support the survival of myoblasts, it did not support myogenesis, an event necessary to complete skeletal muscle regeneration. Data from this study reinforce earlier studies in vitro and suggest that the properties attributed to wound fluids are inherent in the wound environment. Whether the inability of this environment to support myogenesis is the consequence of the absence of essential factors or the presence of inhibitors remains to be determined.  相似文献   
32.
Effect of photodynamic therapy on blood flow in normal and tumor vessels   总被引:1,自引:0,他引:1  
The aim of this series of experiments was to determine the dynamic blood flow changes that occur in normal and neoplastic tissues during photodynamic therapy. Mice bearing SMT-F tumors and rats with transplanted chondrosarcomas were injected with graded doses of dihematoporphyrin ether. Studies of changes in single-vessel and whole-tumor blood flow were carried out with 630 nm light activation. A helium neon laser Doppler velocimeter was used to stimulate dihematoporphyrin ether, as well as to measure changes in flow velocity in both single-vessel and whole-tumor models. There was a reduction of flow velocity in all vessels and tumors in animals injected with 1 to 40 mg/kg dihematoporphyrin ether intraperitoneally. The extent of flow reduction was related to drug dose administered. Decreases in blood flow began within 10 seconds of light stimulation and were maximal within 5 minutes. Both normal and tumor vessels responded similarly. We conclude that photodynamic therapy leads to significant microcirculatory changes that may be pertinent to the mechanism of tumor necrosis.  相似文献   
33.
BACKGROUND: Congenital absence of the inferior rectus muscle is a rare cause of apparent inferior rectus palsy especially in the absence of associated cranial facial anomalies. METHODS: We report three cases of isolated congenital absence of the inferior rectus muscle and its successful surgical management. RESULTS: Failure of the normal embryologic development of the mesodermal complex around the eye can lead to agenesis of the extraocular muscles. In apparent palsies of the inferior rectus muscle and no definite cause, a high index of suspicion and orbital imaging can confirm the diagnosis of congenitally absent inferior rectus preoperatively. Surgical correction may involve inferior transposition of the horizontal rectus muscles. CONCLUSIONS: Although rare, congenital absence of the inferior rectus muscle is a possible cause of apparent inferior rectus muscle palsy particularly in the absence of another identifiable cause. Strabismus surgery in conjunction with intramuscular botulinum toxin injection can offer significant improvement in function and cosmesis of these patients.  相似文献   
34.
A turkey red blood cell haemagglutination assay (TRBC HA) allowing rapid measurement of the antibodies against tetanus has been set recently. Its feasibility was evaluated in injured patients admitted into an emergency unit during summer 1987. TRBC HA was performed by the same physician who questioned the patient on his/her previous vaccinations and evaluated his/her immunization status. The rapid HA test practiced in emergency was controlled by TRBC HA and ELISA measurement of antibodies carried out in the laboratory. Each method was compared to the others: the results were fitted and no significant difference was found. The preventive procedures which would have followed the antibody measurement by immediate TRBC HA were compared to the decision resulting from clinical evaluation. The immunoprophylactic attitude would have been the same in 82% of cases. TRBC HA is a reliable test, and feasible in an emergency: it could help in making the appropriate decision for immunoprophylaxis to be applied to the injured and other patients at risk of tetanus.  相似文献   
35.
The aims of this study were to ascertain vertebral deformity prevalence in elderly men and women and to describe the association between bone mineral density (BMD) at the lumbar spine and femoral neck, severity of spinal degenerative disease and vertebral deformity prevalence. We performed standardized spinal radiographs in a random sample of 300 elderly men and women participating in the Dubbo Osteoporosis Epidemiology Study, a population-based study of fracture risk factors. Radiographs were read independently by masked observers for the prevalence of vertebral deformity and severity of osteophytosis. BMD was measured by dual-energy X-ray absorptiometry. The prevalence of vertebral deformities was critically dependent on the criterion used. The less strict criteria seemed to overestimate deformities at either end of the spine region analysed. However, irrespective of the criterion used, prevalence of deformity was higher in men than in women (25% vs 20% for the 3 SD criterion, 17% vs 12% for the 4 SD criterion and 27% vs 25% for the 25% criterion). Femoral neck BMD was more strongly associated with vertebral deformities than spinal BMD for the 25% criterion (OR/SD change in BMD 1.39 (p=0.02) vs 1.20 (p=0.19)), 3 SD criterion (OR/SD change in BMD 1.45 (p=0.01) vs 1.10 (p=0.34)) and 4 SD criterion (OR/SD change in BMD 1.98 (p=0.0002) vs 1.68 (p=0.008)). BMD was also more strongly associated with biconcave deformities than either wedge or crush deformities and more so in men than in women. Severity of spinal osteophytosis was not associated with vertebral deformity. In conclusion, femoral neck BMD is at least equivalent to the lumbar spine BMD in strength of association with prevalent vertebral fractures. Spinal osteophytosis falsely elevates BMD without a concomitant decrease in fracture risk, indicating that any interpretation of spinal BMD needs to be adjusted for osteophytosis. These findings support the use of femoral neck bone densitometry in older men and women. Moreover, these data indicate that current criteria for radiological assessment of vertebral deformity are sufficiently loose to include a substantial proportion of non-fractures in the elderly, with important implications for the design of clinical trials. However, irrespective of the criterion used, vertebral deformities in men are at least as common, if not more so, than in women, suggesting that vertebral osteoporotic fractures are overlooked in men.  相似文献   
36.
37.
38.
Polymerizations of 2-methylpropene (MP) initiated by the system 1,4-bis(1-azido-1-methylethyl)benzene (DAMEB)/BCl3 in the presence of DMSO were carried out by “all monomer in” (AMI) technique at ?70°C in CH2Cl2 solution. FT-IR, 1H NMR and SEC analyses of polymers (PMP) showed that the M n versus weight of PMP plot is a straight line without intercept and azide Fn3 and aromatic ring F? functionalities are close to the theoretical values of 2 and 1, respectively. A polymerization of MP initiated by the system α,ω-diazido-PMP/BCl3/DMSO led to a final poly(2-methylpropene) (PMP) with an increase of M n corresponding to the amount of MP introduced and presenting the same functionalities FN3 and F? as the starting PMP. These results indicate that the polymerization system MP/DAMEB/BCl3/DMSO is a “living” one, because in an acceptably large range of molecular weight (M n < 50000) the Mayo plot 1/DP versus 1/DP 0 is a straight line. The intercept gives ktrM/kp = 4 · 10?5, showing the transfer reaction proceeds at very low rate.  相似文献   
39.
Transsynaptic degeneration of motoneurones caudal to spinal cord lesions   总被引:2,自引:0,他引:2  
We studied the effects of complete transversal section of the spinal cord, at T8-10, in adult rats, upon the number and morphology of identified motoneurones in lumbar segments L4 and L5. In observations by light and electron microscopy many lumbar motoneurones had structural abnormalities when the interval between surgery and perfusion ranged between a few hours and one week. We found also that as many as 25% of the motoneurones distal to a cord transection disappeared as a consequence of the lesions. We did not find comparable changes in the spinal cord at C6 after transection at T8-10. Complete removal of the cerebellum did not reduce the lumbar motoneurone counts. Bilateral ablation of the "motor" cortex did cause a reduction of motoneurone counts at L4-5; these animals showed normal or near normal spontaneous locomotor activity beginning a few days after the lesion was placed. Motoneurone counts were significantly reduced after partial cord lesions that spared the dorsal funiculi (where the corticospinal tract travels in the rat), but in this case the rats were paraplegic as a result of the lesion. Cord transection at 7 days of postnatal age resulted in reduced motoneurone counts when the rats reached adulthood. Intraspinal or subarachnoid administration of colchicine led to reduced motoneurone counts. Prolonged infusion of a GABA agonist, muscimol, into the lumbar CSF did not prevent the loss of motoneurones produced by cord transection. Pretreatment of animals with a Ca2+ channel blocker (nimodipine) did not prevent the effects of cord transection.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
40.
The retinal nerve fiber layer is different in normal and glaucomatous eyes. We correlated semi-quantitative data of the retinal nerve fiber layer of 398 eyes with chronic primary open-angle glaucoma and of 234 normal eyes with the intra- and parapapillary morphometric signs and with the perimetric indices. The three parameters "sequence of the fundus sectors concerning the best visibility of the retinal nerve fiber bundles", "visibility of the nerve fiber bundles", and "localized defects" were significantly (p less than 0.001) correlated to 1) area of the neuroretinal rim as a whole and in four different optic disc sectors, 2) neuroretinal rim width determined every 30 degrees, 3) optic cup area, diameters and form, 4) horizontal and vertical cup/disc ratios and the quotient of the horizontal to vertical cup/disc ratio, 5) area and width of zone "Alpha", zone "Beta", and the total parapapillary chorio-retinal atrophy, 6) diameter of the retinal vessels, 7) grade of a "tesselated fundus", and 8) the visual field loss. If only the inferior temporal and the superior temporal sectors were considered, the retinal nerve fiber bundles were less visible in that sector with the largest notch in the neuroretinal rim, the smaller neuroretinal rim area and width, the thinner retinal vessels, and the larger zone "Alpha", zone "Beta", and total parapapillary chorio-retinal atrophy. The glaucomatous changes in the retinal nerve fiber layer are correlated in time and location with the intra- and parapapillary and the perimetric alterations. Evaluation of the retinal nerve fiber layer is a useful method to detect a glaucomatous optic nerve damage.(ABSTRACT TRUNCATED AT 250 WORDS)  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