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   15750篇
  免费   704篇
  国内免费   80篇
耳鼻咽喉   92篇
儿科学   320篇
妇产科学   131篇
基础医学   2075篇
口腔科学   449篇
临床医学   1042篇
内科学   3774篇
皮肤病学   301篇
神经病学   1130篇
特种医学   737篇
外科学   2577篇
综合类   125篇
一般理论   2篇
预防医学   455篇
眼科学   326篇
药学   989篇
中国医学   27篇
肿瘤学   1982篇
  2023年   107篇
  2022年   178篇
  2021年   322篇
  2020年   171篇
  2019年   236篇
  2018年   299篇
  2017年   215篇
  2016年   289篇
  2015年   279篇
  2014年   435篇
  2013年   560篇
  2012年   830篇
  2011年   915篇
  2010年   511篇
  2009年   410篇
  2008年   756篇
  2007年   837篇
  2006年   773篇
  2005年   786篇
  2004年   754篇
  2003年   701篇
  2002年   741篇
  2001年   428篇
  2000年   405篇
  1999年   371篇
  1998年   226篇
  1997年   168篇
  1996年   188篇
  1995年   144篇
  1994年   116篇
  1993年   116篇
  1992年   257篇
  1991年   282篇
  1990年   258篇
  1989年   347篇
  1988年   254篇
  1987年   222篇
  1986年   194篇
  1985年   191篇
  1984年   126篇
  1983年   128篇
  1982年   70篇
  1979年   91篇
  1977年   60篇
  1975年   57篇
  1974年   67篇
  1973年   64篇
  1972年   68篇
  1970年   61篇
  1969年   64篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Summary To clarify the biological features of primitive gliomas in the cerebrum and clearly distinguish them from malignant or anaplastic gliomas and glioblastomas, we studied eight cases clinically and pathologically. Our evaluations included immunohistochemical and electron microscopic observations. We divided the patients into two groups, children and young adults. Most tumours appeared as ring-like, enhanced masses on computed tomography and avascular or ring-like, vascular masses on angiography. Macroscopically, the tumours were well demarcated and contained cysts. Ocassionally we found tumour dissemination. Microscopically, the tumours were composed of small, round cells without remarkable structural features. Ependymal, astroglial, and oligodendroglial differentiation was evident, in varying proportions; tumours in which the differentiated areas constituted more than half of the mass were classified as poorly differentiated gliomas. By these criteria, this series comprised four undifferentiated and four poorly differentiated gliomas. Cell anaplasia and polymorphism were rare in both undifferentiated and differentiated areas of the tumours. Immunohistochemical and electron microscopic examinations also revealed glial differentiation. These primitive gliomas appear to be biologically similar, but not identical, to cerebellar medulloblastomas. In this series, five patients died because of recurrence or dissemination. Whole brain and spinal irradiation should be considered after total or subtotal surgical removal.  相似文献   
72.
A rare case of lentigo maligna in the oral cavity was investigated by light and electron microscopy. Cutaneous lentigo malignas often develop to malignant melanomas. However, the electron microscopic examination revealed that even though there were a large number of melanosomes, most of them were late stage and had membrane structure, and positive staining with HMB-45 was not recognized. From our findings, it is difficult to conclude that oral lentigo malignas develop malignant melanomas, and thus further studies are needed.  相似文献   
73.
Neurons survive when their activity is maintained. An influential hypothesis on the cellular mechanism underlying this phenomenon is that there is an appropriate range of intracellular Ca2+ concentration ([Ca2+]i) for survival. The rat cerebellar granule neuron in culture serves as the most often used model system for the analysis of activity-dependent survival, since it does not survive unless an excitant (KCl or glutamate) is added to the culture medium. Against the above-mentioned hypothesis, we found in our previous examination no difference between steady-state [Ca2+]i in granule neurons cultured under high KCl (i.e., survival) and low KCl (i.e., death) conditions. In this report, we present the quantitative background of unchanged [Ca2+]i between the two culture conditions. Influx of Ca2+ due predominantly to L-type voltage-dependent calcium channels was higher in high KCl cultures than in low KCl cultures. At the same time, efflux of Ca2+ due to the activity of Ca2+/Na+ antiport was also higher in high KCl cultures. Additionally, we found that the endocytotic activity was greater in high KCl cultures than in low KCl cultures, as monitored by the rate of uptake of horseradish peroxidase added to medium. Since the uptake was blocked by an internal Ca2+ chelator, the increased endocytotic activity in high KCl cultures might be a consequence of the enhanced Ca2+ turnover.  相似文献   
74.
Pneumatic ventricular assist device (VAD) was utilized for cardiogenic shock after intracardiac operation in two children with complex cardiac anomalies based with single ventricle. In the first case (a 10-year-old), after a modified Fontan operation, VAD was placed between the functional left atrium and ascending aorta, serving as a "artificial single ventricle" with neither pumping chamber nor artificial support in the right side of the heart. The systemic circulation was maintained by keeping relatively high central venous pressure. In another child (a 3-year-old) who underwent repair of incompetent atrioventricular valve leaving intracardiac lesions, VAD was placed between the common atrium and ascending aorta, serving as a pump for both pulmonary and systemic circulation with regulation of pulmonary blood flow through an aortopulmonary Gore-Tex shunt. The circulatory assist with VAD was utilized for 5 and 6 days, respectively. Although weaning from the device was not feasible in both patients because of the pulmonary dysfunction, these experience showed the possible use of VAD for cardiogenic shock after surgery in patients with complex cardiac anomalies.  相似文献   
75.
Regional cerebral blood flow (CBF) in eight patients in a persistent vegetative state was measured and compared with that in five healthy volunteers. The patients were classified into three groups: Group 1 (locked-in syndrome) consisted of a single patient, Group 2 (typical vegetative state) of five patients, and Group 3 (prolonged coma) of two patients. CBF was measured early after onset by single photon emission computed tomography with 123I-N-isopropyl-p-iodo-amphetamine and/or 99mTc-hexamethyl-propyleneamine oxime. The regions of interest (ROIs) were the bilateral frontal, temporal, parietal, occipital, and cerebellar areas and basal ganglia. The values obtained in these areas were averaged, and the ratio for each ROI [(the value in the ROI/the mean value) x 100] was calculated. "Hyperfrontal distribution" of CBF was found to be rare in both the normal condition and the vegetative state. Higher CBF values were noted in the left than in the right frontal area in four of the five volunteers but in only four of the eight patients. CBF distribution in the frontal lobe was characteristic for each group: Group 1 showed high CBF bilaterally, although the elevation was statistically significant only on the right side, and Group 3 exhibited significantly low values. In Group 2, CBF was variable but, for the most part, within normal limits. Awareness was closely correlated with frontal lobe function and alteration of CBF in the frontal region.  相似文献   
76.
Key words  intractable pain - celiac plexus neurolysis - ultrasonography  相似文献   
77.
Transient induction of single GST-P positive hepatocytes by DEN   总被引:12,自引:3,他引:9  
The single cells positive for placental glutathione S-transferase(GST-P), detectable in livers of rats soon after treatment withhepatocarcinogens, are possible ‘initiated cells’,the hypothesis tested in the present series of experiments.No low dose threshold was observed in male Sprague-Dawley ratsat different single doses of diethylnitrosamine (DEM) althougha plateau was reached between 160 and 200 mg/kg body weight.At the latter single dose 12 400 positive cells/cm3 were observedimmunohistochemically in rat livers after one week, the numbersthen decreasing to week 8 and thereafter rising again. In thenumbers then decreasing to week 8 and thereafter rising again.In the early stages single cells predominated but with timea gradual increase in mini-foci and larger lesions became evident.Application of selection pressure (feeding of diet containing0.02% 2-AAF plus partial hepatectomy) to rats 2–24 weeksafter single DEN-treatment resulted in the formation of largefoci positive for GST-P, especially in the early stages, thegrowth response being less pronounced with time. The numberof foci, on the other hand. was correlated with the number offoci, on the other hand, was correlated with the number ofsingle cells/mini-foci detected inhepatectomy tissue of thesame individuals. These results suggest that the early GST-Ppositive populations could be the precursor for preneoplasticfoci and nodules.  相似文献   
78.
An inappropriate antidiuretic hormone secretion (SIADH) has been recognized as the cause of hypotonic hyponatremia, and the occurrence of this syndrome, accompanied by an ADH-producing adenocarcinoma in the nasal cavity, is reported. In February, 1987, a 50-year-old male, showing sights of delirium, disorientation, and irritability was admitted to the hospital. The patient was observed to be healthy, except for a neck lymphnode metastasis that was present up to the time of his hospitalization. The hyponatremia was incidentally found, although dehydration or intravascular volume depletion were not noted. These neuropsychiatric symptoms were considered to be associated with hyponatremia due to SIADH. He had had a partial maxillectomy, a neck dissection, and irradiation to the nose and nasal cavity 32 months earlier, and then underwent a surgical resection of the neck metastasis; he had a total of 10 other operations before the onset of the symptoms. Upon initial inspection, since neither an intracranial invasion nor a brain metastasis was found, we diagnosed that his symptoms were due to an autonomic disturbance caused by surgical and mental "stress". When he died of cardiac failure due to a mediastinal invasion 8 months after the onset of SIADH, tumor tissues was extirpated in an autopsy and was then cultured. In this manner, it was proved that the tumor cells had been producing ADH. This procedure clarified that the syndrome had resulted from an ADH-producing tumor of the nasal cavity.  相似文献   
79.
Ligation of the chemokine receptor CCR2 on monocytes and macrophages with its ligand CCL2 results in activation of the cascade consisting of phosphatidylinositol-3-OH kinase (PI(3)K), the small G protein Rac and lamellipodium protrusion. We show here that a unique clathrin heavy-chain repeat homology protein, FROUNT, directly bound activated CCR2 and formed clusters at the cell front during chemotaxis. Overexpression of FROUNT amplified the chemokine-elicited PI(3)K-Rac-lamellipodium protrusion cascade and subsequent chemotaxis. Blocking FROUNT function by using a truncated mutant or antisense strategy substantially diminished signaling via CCR2. In a mouse peritonitis model, suppression of endogenous FROUNT markedly prevented macrophage infiltration. Thus, FROUNT links activated CCR2 to the PI(3)K-Rac-lamellipodium protrusion cascade and could be a therapeutic target in chronic inflammatory immune diseases associated with macrophage infiltration.  相似文献   
80.
Recent data have shown the existence of specific changes in mRNAs in thyroid carcinomas. It has not been clarified, however, why these changes clearly distinguish benign tissues from carcinomas, while genomic alternation such as mutations in the RAS or P53 genes do not. Further, the widely believed hypothesis, multi-step carcinogenesis, does not explain some clinical and experimental evidence of thyroid carcinomas. Considering these facts, we propose a new idea for thyroid carcinogenesis called "germ-cell carcinogenesis", in which cancer cells are derived from the remnant of fetal thyroid germ cells(thyroblasts) instead of normal thyroid follicular cells. Utilizing such mRNAs, we have established a new method for preoperative molecular-based diagnosis of thyroid carcinomas, Aspiration Biopsy Nucleic Acid Diagnosis(ABND). ABND allows us to perform preoperative nucleic acid analyses of the tumors by extracting RNAs or DNAs from tumor cells obtained by fine needle aspiration biopsies(FNABs). Pathological diagnosis of thyroid follicular carcinoma is quite difficult, and the establishment of preoperative molecular-based diagnosis of follicular carcinoma has been long expected. We found that quantification of the trefoil factor 3(TFF3)/galectin-3 mRNA ratio in thyroid tumor cells is a useful tool for distinction between follicular adenomas and carcinomas. Because ABND can be performed without any severe invasion to the patients, in the near future, when more reliable systems of quantitative RNA analysis have been developed, ABND will probably become one of the standard tests for preoperative diagnosis of thyroid carcinoma.  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