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   3942篇
  免费   245篇
  国内免费   100篇
耳鼻咽喉   24篇
儿科学   132篇
妇产科学   66篇
基础医学   350篇
口腔科学   183篇
临床医学   488篇
内科学   1004篇
皮肤病学   31篇
神经病学   246篇
特种医学   283篇
外科学   528篇
综合类   79篇
预防医学   349篇
眼科学   26篇
药学   234篇
中国医学   2篇
肿瘤学   262篇
  2021年   36篇
  2019年   38篇
  2018年   58篇
  2017年   33篇
  2016年   37篇
  2015年   61篇
  2014年   62篇
  2013年   141篇
  2012年   135篇
  2011年   129篇
  2010年   113篇
  2009年   94篇
  2008年   141篇
  2007年   169篇
  2006年   139篇
  2005年   158篇
  2004年   139篇
  2003年   124篇
  2002年   128篇
  2001年   130篇
  2000年   129篇
  1999年   102篇
  1998年   70篇
  1997年   69篇
  1996年   52篇
  1995年   60篇
  1994年   58篇
  1993年   63篇
  1992年   78篇
  1991年   97篇
  1990年   95篇
  1989年   105篇
  1988年   114篇
  1987年   88篇
  1986年   84篇
  1985年   80篇
  1984年   66篇
  1983年   35篇
  1982年   33篇
  1981年   37篇
  1980年   40篇
  1979年   56篇
  1978年   47篇
  1977年   51篇
  1976年   39篇
  1975年   35篇
  1974年   44篇
  1973年   40篇
  1972年   39篇
  1970年   33篇
排序方式: 共有4287条查询结果,搜索用时 0 毫秒
991.
Neisseria meningitidis is a leading cause of bacterial meningitis in the United States, with the highest case fatality rates reported for individuals ≥15 years of age. This study compares the safety and immunogenicity of the Novartis Vaccines investigational quadrivalent meningococcal CRM197 conjugate vaccine, MenACWY-CRM, to those of the licensed meningococcal conjugate vaccine, Menactra, when administered to healthy adults. In this phase III multicenter study, 1,359 adults 19 to 55 years of age were randomly assigned to one of four groups (1:1:1:1 ratio) to receive a single dose of one of three lots of MenACWY-CRM or a single dose of Menactra. Serum samples obtained at baseline and 1 month postvaccination were tested for serogroup-specific serum bactericidal activity using human complement (hSBA). The hSBA titers following vaccination with MenACWY-CRM and Menactra were compared in noninferiority and prespecified superiority analyses. Reactogenicity was similar in the MenACWY-CRM and Menactra groups, and neither vaccine was associated with a serious adverse event. When compared with Menactra, MenACWY-CRM met the superiority criteria for the proportions of recipients achieving a seroresponse against serogroups C, W-135, and Y and the proportion of subjects achieving postvaccination titers of ≥1:8 for serogroups C and Y. MenACWY-CRM''s immunogenicity was statistically noninferior (the lower limit of the two-sided 95% confidence interval was more than −10%) to that of Menactra for all four serogroups, with the postvaccination hSBA geometric mean titers being consistently higher for MenACWY-CRM than for Menactra. MenACWY-CRM is well tolerated in adults 19 to 55 years of age, with immune responses to each of the serogroups noninferior and, in some cases, statistically superior to those to Menactra.Neisseria meningitidis is a leading cause of bacterial meningitis in the United States (11). While the incidence of meningococcal disease is highest in infants, the highest case fatality rates are observed among older subjects: 4.6% in children <15 years of age, 22.5% in individuals 15 to 24 years of age, and 16.5% in adults >25 years of age (5). In 2007, approximately 72% of all cases of meningococcal disease in the United States were reported in individuals ≥18 years of age (4a).Two quadrivalent meningococcal vaccines, for prevention of meningococcal disease caused by serogroups A, C, W-135, and Y, are available in the United States: an unconjugated polysaccharide vaccine (MPSV4 [Menomune]; Sanofi Pasteur, Inc., Swiftwater, PA) and a diphtheria toxoid protein conjugated vaccine (Menactra; Sanofi Pasteur, Inc., Swiftwater, PA). In the United States, the quadrivalent meningococcal polysaccharide protein conjugate vaccine is currently recommended for all persons 11 to 18 years of age and for those persons 2 to 55 years of age who are at increased risk of meningococcal disease (4). This vaccine is only available in the United States and Canada. Outside North America, polysaccharide vaccines are the only quadrivalent meningococcal vaccines available.To expand the options for prevention of meningococcal disease, an investigational quadrivalent meningococcal CRM197 conjugate vaccine (MenACWY-CRM; Novartis Vaccines, Siena, Italy) was recently developed. Studies have shown that MenACWY-CRM is well tolerated and elicits robust immunogenicity when administered to infants as young as 2 months of age (10, 12), as well as children (2a) and adolescents (9). A large, randomized, controlled, direct comparative phase III study was recently completed, examining the safety and immunogenicity of MenACWY-CRM versus those of Menactra when administered to healthy subjects 11 to 55 years of age. Due to differences in expected immune responses between adolescents and adults, the predefined analyses were powered and analyzed separately for the 11- to 18-year-old and 19- to 55-year-old groups. The larger adolescent age stratum included in the study was powered to demonstrate the consistency of the immune response to three lots of MenACWY-CRM, and the results showed that MenACWY-CRM generated a significantly higher immune response to all four serogroups than Menactra (8). Here, we present the analysis of the safety and immunogenicity of MenACWY-CRM versus those of Menactra among the adult subjects 19 to 55 years of age.  相似文献   
992.
993.
994.
Microglial activation is implicated in the progressive nature of numerous neurodegenerative diseases, including Parkinson's disease. Using primary rat mesencephalic neuron-glia cultures, we found that pituitary adenylate cyclase-activating polypeptide (PACAP) 38, PACAP27, and its internal peptide, Gly-Ile-Phe (GIF; PACAP4-6), are neuroprotective at 10(-13) M against lipopolysaccharide (LPS)-induced dopaminergic (DA) neurotoxicity, as determined by [(3)H]DA uptake and the number of tyrosine hydroxylase-immunoreactive neurons. PACAP38 and GIF also protected against 1-methyl-4-phenylpyridinium(+)-induced neurotoxicity but only in cultures containing microglia. PACAP38 and GIF ameliorated the production of microglia-derived reactive oxygen species (ROS), where both LPS- and phorbol 12-myristate 13-acetate-induced superoxide and intracellular ROS were inhibited. The critical role of NADPH oxidase for GIF and PACAP38 neuroprotection against LPS-induced DA neurotoxicity was demonstrated using neuron-glia cultures from mice deficient in NADPH oxidase (PHOX(-/-)), where PACAP38 and GIF reduced tumor necrosis factor alpha production and were neuroprotective only in PHOX(+/+) cultures and not in PHOX(-/-) cultures. Pretreatment with PACAP6-38 (3 microM; PACAP-specific receptor antagonist) was unable to attenuate PACAP38, PACAP27, or GIF (10(-13) M) neuroprotection. PACAP38 and GIF (10(-13) M) failed to induce cAMP in neuronglia cultures, supporting that the neuroprotective effect was independent of traditional high-affinity PACAP receptors. Pharmacophore analysis revealed that GIF shares common chemical properties (hydrogen bond acceptor, positive ionizable, and hydrophobic regions) with other subpicomolar-acting compounds known to inhibit NADPH oxidase: naloxone, dextromethorphan, and Gly-Gly-Phe. These results indicate a common high-affinity site of action across numerous diverse peptides and compounds, revealing a basic neuropeptide regulatory mechanism that inhibits microglia-derived oxidative stress and promotes neuron survival.  相似文献   
995.
Despite the knowledge that many drugs affect men and women differently, few studies exploring the effects of marijuana use on cognition have included women. Findings from both animal and human studies suggest marijuana may have more marked effects in women. This study examined sex differences in the acute effects of marijuana on cognition in 70 (n=35 male, 35 female) occasional users of marijuana. Tasks were chosen to tap a wide variety of cognitive domains affected by sex and/or marijuana including attention, cognitive flexibility, time estimation, and visuospatial processing. As expected, acute marijuana use impaired performance on selective and divided attention, time estimation, and cognitive flexibility. While there did not appear to be sex differences in marijuana's effects on cognition, women requested to discontinue the smoking session more often than men, likely leading to an underestimation of differences. Further study of psychological differences in marijuana's effects on men and women following both acute and residual effects of marijuana is warranted.  相似文献   
996.
目的 探讨心肺转流(CPB)下行心脏不停跳冠状动脉搭桥术(OPBH)与非体外循环下冠状动脉搭桥术(OPCAB)治疗冠状动脉三支病变的临床效果.方法 210例单纯冠状动脉三支病变患者分为0PCAB组(105例)和OPBH组(105例),分别进行临床观察.结果 OPCAB组无一例需转成OPBH.所有患者均在心脏侧壁和后壁区域搭桥.两组人均冠状动脉远端吻合数和再血管化指数相似;手术后呼吸支持时间、胸腔引流量和输血量OPCAB组明显少于OPBH组;围手术期死亡率和并发症发生率两组比较差异无统计学意义.结论 对于低左室射血分数的患者,虽然出血和输血量较大,术后呼吸支持时间、ICU停留时间较长,但OPBH能取得与OPCAB相同的疗效.  相似文献   
997.
998.
999.
1000.
Inorganic arsenic (arsenite and arsenate) in drinking water has been associated with skin cancers and increased incidence of cardiovascular diseases. Additionally, studies have demonstrated the pro-angiogenic effect of arsenite and its potential promotion of tumor angiogenesis and tumor progression. Furthermore, recent reports demonstrated reversal of skin co-carcinogenesis by an organoselenium compound. The present study was undertaken to determine the effect and mechanism on angiogenesis of arsenite at low level and its potential reversal by various selenium-derived compounds. The pro-angiogenesis effects and mechanisms of sodium arsenite were determined using the chick chorioallantoic membrane (CAM) model over 3 days and compared with standard pro-angiogenesis factors, such as basic fibroblast growth factor (b-FGF). Additionally, the potential effect of various selenium-derived compounds--such as dimethyl selenone, diphenyl selenone, sodium selenite or Se-methyl selenocysteine--in reversing the pro-angiogenesis effect of arsenite or b-FGF was also determined in the CAM model. The pro-angiogenesis effect of arsenite or b-FGF was significantly (P < 0.01) blocked by dimethyl selenone, diphenyl selenone, sodium selenite or Se-methyl selenocysteine. The pro-angiogenesis effect of either sodium arsenite at 33 nM or b-FGF was blocked (P < 0.01) by the extracellular signal-regulated kinases 1 and 2 (ERK1/2) activation inhibitor, PD 98059. Additionally, the pro-angiogenic effect of arsenic or b-FGF was blocked as well (P < 0.01) by the alphavbeta3 antagonist, XT199. These data suggest that the pro-angiogenesis effect of arsenic is initiated at the plasma membrane integrin alphavbeta3, involves activation of the ERK1/2 pathway and is effectively reversed by various selenium-derived compounds.  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