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   7894篇
  免费   429篇
  国内免费   37篇
耳鼻咽喉   44篇
儿科学   66篇
妇产科学   86篇
基础医学   1137篇
口腔科学   251篇
临床医学   534篇
内科学   1887篇
皮肤病学   88篇
神经病学   552篇
特种医学   256篇
外科学   1269篇
综合类   49篇
预防医学   324篇
眼科学   66篇
药学   765篇
中国医学   18篇
肿瘤学   968篇
  2022年   77篇
  2021年   134篇
  2020年   59篇
  2019年   80篇
  2018年   107篇
  2017年   82篇
  2016年   104篇
  2015年   97篇
  2014年   135篇
  2013年   162篇
  2012年   264篇
  2011年   361篇
  2010年   175篇
  2009年   202篇
  2008年   317篇
  2007年   312篇
  2006年   320篇
  2005年   336篇
  2004年   313篇
  2003年   320篇
  2002年   321篇
  2001年   272篇
  2000年   309篇
  1999年   283篇
  1998年   98篇
  1997年   66篇
  1996年   86篇
  1995年   79篇
  1994年   57篇
  1993年   56篇
  1992年   239篇
  1991年   244篇
  1990年   244篇
  1989年   240篇
  1988年   196篇
  1987年   183篇
  1986年   210篇
  1985年   161篇
  1984年   111篇
  1983年   101篇
  1982年   59篇
  1979年   82篇
  1978年   51篇
  1977年   58篇
  1975年   41篇
  1974年   55篇
  1973年   53篇
  1969年   63篇
  1968年   51篇
  1967年   47篇
排序方式: 共有8360条查询结果,搜索用时 15 毫秒
31.
Among the routes of gaseous I transfer to rice grains, direct deposition to the hull of rice plants and the subsequent transfer to brown rice and polished rice should be more critical than leaf absorption-translocation. A grain number normalized deposition velocity (Vs) is recommended as a key parameter to assess the amount of gaseous I deposited on the rough rice. This parameter is given as "iodine content per unit number of grain per unit time" divided by "iodine concentration per unit volume of the air." After the heading period the surface area of rough rice is almost constant but weight increases with time. Therefore, mass normalized deposition velocity (VD) varies with time. By introducing Vs instead of VD, the variations could be converged into narrow ranges. The contribution of gaseous I from the atmosphere to rough rice, brown rice and polished rice were estimated using Vs values obtained experimentally and gaseous I concentration in the air.  相似文献   
32.
Summary Changes in capillary walls between human glial, non-glial and metastatic brain tumors were studied with conventional ultrathin section and freeze-fracture replica techniques. The following results were obtained. (1) In glial tumors, ultrathin section studies showed cell junctions of the capillaries were either short or elongate. Moreover, endothelial hyperplasia, surface infolding of endothelial cells, irregularity of the basal lamina and a large extravascular space were observed. Freeze-fracture replicas of capillary endothelium showed tight junctions as two to seven strands. In addition, pinocytotic vesicles had increased markedly and were an average of 25 per m2. Both ultrathin and freeze fracture studies showed that, in contrast to malignant gliomas, there were only slight changes in benign astrocytomas. (2) In non-glial tumors, ultrathin sections showed surface infoldings, increased vesicles, many fenestrations of endothelial cells, irregularity of basal lamina and enlarged perivascular space. Freeze-fracture replicas of vascular endothelium, showed that the average number of pinocytotic vesicles and fenestrations were 25 and 22 per m2, respectively. Moreover, the tight junction was composed of one or two strands which appeared to be a discontinuous array of particles. (3) In metastatic brain tumors, ultrathin studies showed capillary endothelia were proliferated, had marked infolding, and showed an increased number of pinocytotic vesicles and many fenestrations. Moreover, short and elongate intercellular junctions were presented but no open junction was detected. Finally the basal lamina lost its three-layered appearance and was irregular in width. Freeze-fracture replicas showed pinocytotic vesicles had increased and were 24 per m2 on average in four cases, but fenestrations and tight junctions could not be detected. The most fundamental feature of vessels in these three different kinds of tumors was whether they were fenestrated or not. Glial tumors were non-fenestrated, whereas non-glial and metastatic tumors were fenestrated.  相似文献   
33.
34.
35.
The aim of this study was to determine the in-phantom thermal neutron distribution derived from neutron beams for intraoperative boron neutron capture therapy (IOBNCT). Gold activation wires arranged in a cylindrical water phantom with (void-in-phantom) or without (standard phantom) a cylinder styrene form placed inside were irradiated by using the epithermal beam (ENB) and the mixed thermal-epithermal beam (TNB-1) at the Japan Research Reactor No 4. With ENB, we observed a flattened distribution of thermal neutron flux and a significantly enhanced thermal flux delivery at a depth compared with the results of using TNB-1. The thermal neutron distribution derived from both the ENB and TNB-1 was significantly improved in the void-in-phantom, and a double high dose area was formed lateral to the void. The flattened distribution in the circumference of the void was observed with the combination of ENB and the void-in-phantom. The measurement data suggest that the ENB may provide a clinical advantage in the form of an enhanced and flattened dose delivery to the marginal tissue of a post-operative cavity in which a residual and/or microscopically infiltrating tumour often occurs. The combination of the epithermal neutron beam and IOBNCT will improve the clinical results of BNCT for brain tumours.  相似文献   
36.
Relationship between SIRS and CARS in the pathologic condition of acute pancreatitis was discussed. SIRS promotes excessive inflammatory reaction and CARS induces the susceptibility to infection. Both conditions can develop into organ failure in acute pancreatitis. Hence, countermeasures for both conditions are mandatory in the care of patients with acute pancreatitis.  相似文献   
37.
Somatic mitochondrial mutation in gastric cancer.   总被引:11,自引:1,他引:11       下载免费PDF全文
Likely hot spots for mutations are mitochondrial sequences as there is less repair and more damage by carcinogens compared with nuclear sequences. A somatic 50-bp mitochondrial D-loop deletion was detected in four gastric adenocarcinomas. The deletion included the CSB2 region and was flanked by 9-bp direct repeats. The deletion was more frequent in adenocarcinomas arising from the gastroesophageal junction (4/32, 12.5%) compared with more distal tumors (0/45). Topographical analysis revealed the absence of the deletion from normal tissues except in focal portions of smooth muscle in one case. In two cases, apparent mutant homoplasmy was present throughout two tumors, including their metastases. In the two other cases, the mutation was present in only minor focal portions ( < 5%) of their primary tumors. These findings document the presence of somatic mitochondrial alterations in gastric cancer, which may reflect the environmental and genetic influences operative during tumor progression.  相似文献   
38.
The effects of electrical stimulation of ventral subiculum (VSB) of the hippocampus of the thermosensitive neurons in the preoptic area were studied in urethane-anesthetized rats. VSB stimulation affected thermosensitive neurons more frequently (92.1%, 58 of 63) than thermally insensitive neurons (71.4%, 55 of 77). The majority of the VSB-responsive thermosensitive neurons (33 of 44 warm-units and 11 of 14 cold-units) were initially inhibited following stimulation. The result provides further support for the involvement of hippocampus in the central control of thermoregulation.  相似文献   
39.
New Zealand Black (NZB) mice spontaneously develop a severe autoimmune hemolytic anemia due to the production of anti-mouse red blood cell (MRBC) autoantibodies. The contribution of variable region genes and somatic mutations in the pathogenicity of anti-MRBC autoantibodies was investigated by mRNA sequencing of eight NZB anti-MRBC monoclonal autoantibodies, among which five are capable of inducing anemia in BALB/c mice. Here we report that at least three VH gene families (J558, J606 and 3609) and five Vchi subgroups (V chi 8, 9, 19, 21 and 28), in combination with several D, JH and Jchi gene segments, encode anti-MRBC autoantibodies. Thus, the NZB anti-MRBC autoantibodies, whether pathogenic or not, are encoded by a large number of immunoglobulin gene elements and by members of known VH and Vchi gene families with preferential usage of VH gene families most distal to the D regions. The presence of several mutations in the JH gene segments of both IgM and IgG anti-MRBC autoantibodies, whether pathogenic or not, strongly suggests that their VH regions may be highly mutated and that the mechanism of somatic diversification might be important in the generation of anti-MRBC autoantibodies. Our results support the idea that anti-MRBC autoimmune responses are likely to be generated by an antigen-driven mechanism.  相似文献   
40.
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