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   8358篇
  免费   376篇
  国内免费   76篇
耳鼻咽喉   73篇
儿科学   137篇
妇产科学   174篇
基础医学   929篇
口腔科学   151篇
临床医学   507篇
内科学   2210篇
皮肤病学   157篇
神经病学   517篇
特种医学   300篇
外科学   1669篇
综合类   18篇
一般理论   1篇
预防医学   214篇
眼科学   197篇
药学   456篇
中国医学   14篇
肿瘤学   1086篇
  2023年   67篇
  2022年   137篇
  2021年   204篇
  2020年   120篇
  2019年   140篇
  2018年   217篇
  2017年   150篇
  2016年   170篇
  2015年   208篇
  2014年   261篇
  2013年   323篇
  2012年   550篇
  2011年   643篇
  2010年   351篇
  2009年   313篇
  2008年   576篇
  2007年   596篇
  2006年   533篇
  2005年   525篇
  2004年   475篇
  2003年   489篇
  2002年   433篇
  2001年   107篇
  2000年   85篇
  1999年   95篇
  1998年   117篇
  1997年   80篇
  1996年   77篇
  1995年   55篇
  1994年   65篇
  1993年   48篇
  1992年   63篇
  1991年   53篇
  1990年   40篇
  1989年   55篇
  1988年   52篇
  1987年   43篇
  1986年   32篇
  1985年   23篇
  1984年   25篇
  1983年   26篇
  1982年   17篇
  1981年   21篇
  1980年   13篇
  1979年   9篇
  1978年   15篇
  1977年   20篇
  1976年   11篇
  1975年   13篇
  1974年   13篇
排序方式: 共有8810条查询结果,搜索用时 15 毫秒
51.
PROBLEM: The presence of antisperm antibodies (ASA) in males can reduce fecundity, however, relationship between the two is disputed. This study was performed to investigate if there is diversity of ASA bound to sperm surface using immunobead test (IBT) combined with complement dependent sperm immobilization test (SIT). METHODS: The ASA bound to sperm surface were detected using the direct IBT (D-IBT) in 275 semen samples. In some cases with ASA detected by D-IBT, sperm immobilizing antibodies bound to sperm surface were also evaluated using direct SIT (D-SIT). RESULTS: The incidence of the immunoglobulin G (IgG), IgA, and IgM classes of ASA detected by D-IBT were 2.5, 1.8, and 0.4%, respectively. Totally, nine (3.3%) infertile men had ASA on the sperm surface. D-SIT was tested positive in four (66.7%) of six cases with ASA assessed by D-IBT. CONCLUSIONS: Some of the sperm-bound antibodies are associated with complement dependent sperm immobilizing antibodies, indicating that there exists a heterogeneity of sperm-bound antibodies. This result might be one of the reasons for the controversy about the relationship between ASA and immunological infertility in men.  相似文献   
52.
Mutations of either PKD1 or PKD2 are associated with autosomal dominant polycystic kidney disease (ADPKD). The molecular function of the gene product of PKD1, polycystin-1, in vitro has been elucidated recently, but the molecular pathological consequences of the loss of polycystin-1 in vivo have remained unclear. We have generated a mouse with a targeted deletion of exons 2-6 of Pkd1 to study the molecular defects in Pkd1 mutants. Homozygote embryos (Pkd1(-/-)) developed hydrops, cardiac conotruncal defects and renal cystogenesis. Total protein levels of beta-catenin in heart and kidney and c-MYC in heart were decreased in Pkd1(-/-) embryos. In the kidneys of Pkd1(-/-), the expression of E-cadherin and PECAM in basolateral membranes of renal tubules was attenuated, and tyrosine phosphorylation of epidermal growth factor receptor and Gab1 were constitutively enhanced when cystogenesis started on embryonic day (E) 15.5-16.5. Maternally administered pioglitazone, a thiazolidinedione compound, resolved these molecular defects of Pkd1(-/-). Treatment with pioglitazone improved survival of Pkd1(-/-) embryos and ameliorated the cardiac defects and the degree of renal cystogenesis. Long-term treatment with pioglitazone improved the endothelial function of adult Pkd1(+/-). These data indicated that molecular defects observed in Pkd1(-/-) embryos contributed to the pathogenesis of ADPKD and that thiazolidinediones had a compensatory effect on the pathway affected by the loss of polycystin-1. Pathways activated by thiazolidinediones may provide new therapeutic targets in ADPKD.  相似文献   
53.
54.
The effects of L-arginine on spontaneous contraction of endothelium-denuded longitudinal preparations of the rat portal vein were studied. L-arginine increased the frequency of spontaneous contraction concentration-dependently between 10 microM and 1 mM. Changes in contraction amplitude and duration were not remarkable. D-arginine had a negligible effect on spontaneous contraction. N(omega)-nitro-L-arginine (1 mM) did not affect spontaneous contraction or the response to L-arginine. Addition of N(G)-monomethyl-L-arginine (1 mM), l-lysine (1 mM) or N-ethymaleimide (0.1 mM) increased the frequency of spontaneous contractions and inhibited the effect of L-arginine. Glibenclamide (10 microM) did not affect spontaneous contraction or the response to L-arginine. Spontaneous increase in concentration of intracellular Ca2+, estimated as the ratio of Fura-PE3 fluorescence occurred synchronously with spontaneous contraction. Spontaneous increase in concentration of intracellular Ca2+ occurred more frequently in the presence of L-arginine (1 mM). L-arginine (1 mM) also increased the number of action potential bursts/min in the longitudinal smooth muscle layer. L-arginine (1 mM) also depolarized cell membranes. This study indicates that L-arginine increases the frequency of spontaneous contraction of longitudinal muscle in the rat portal vein by membrane depolarization through mechanisms that do not involve nitric oxide or the inhibition of ATP-sensitive K+ channels.  相似文献   
55.
Hiyama S  Tsuiki S  Ono T  Kuroda T  Ohyama K 《Sleep》2003,26(4):440-445
STUDY OBJECTIVES: To examine changes in the upper-airway dimension and its surrounding structures induced by mandibular advancement during sleep. DESIGN: Eleven nonapneic adult males participated in the study. A set of supine lateral cephalograms was taken for each subject at the end of expiration during stage 1 and 2 non-rapid-eye-movement sleep with and without a Klearway appliance (Great Lakes Orthodontics, NY, USA), which was adjusted to 67% of the maximum protrusion position. The Wilcoxon signed-rank test was used to compare changes in the anteroposterior width of the upper airway and the positions of the hyoid bone and third cervical vertebra with and without the appliance. SETTING: N/A. PATIENTS OR PARTICIPANTS: N/A. INTERVENTIONS: N/A. MEASUREMENTS AND RESULTS: The amount of jaw opening was significantly increased by wearing the titratable oral appliance, and the mandibular symphysis moved backward. The sagittal dimension of the superior pharyngeal airway was significantly increased; however, no significant changes were found in the middle and inferior pharyngeal airway. Significant posterior displacement of the hyoid bone and third cervical vertebra was seen. Moreover, significant inferior displacement of the hyoid bone was also seen. The relationship among the mandibular symphysis, the hyoid bone, and the third cervical vertebra remained constant. CONCLUSIONS: Mandibular advancement significantly increases the size of the upper airway in the velopharynx and results in posteroinferior displacement of the hyoid bone and posterior displacement of the third cervical vertebra during sleep.  相似文献   
56.
A case of the syndrome of sea-blue histiocyte is presented in a 53-year-old Japanese woman, which is the first recorded case in Japan. The patient had hepatosplenomegaly, bleeding manifestations, mild thrombocytopenia, fatty metamorphosis and cirrhosis of the liver, as well as abnormal serum lipid profiles. Her parents were consanguineous and her maternal grandmother with hepatomegaly died of hepatic failure. Histologically, peculiar histiocytes containing numerous, intracytoplasmic sea-blue stained granules on May-Giemsa stain were demonstrated in biopsy materials of the bone marrow, lymph node and liver. The sea-blue granules in these histiocytes proved to have histochemical staining characteristics of lipogenic ceroid-like pigment. Ultrastructurally, these granules showed membrane-bound, pleomorphic inclusions of heterogeneous nature, including electron-dense amorphous or variegatedly osmiophilic, frequently laminated materials. Enzyme cyto-chemically, localization of acid phosphatase activity was demonstrated in and around the intracytoplasmic inclusions. With regard to the pathogenesis of the sea-blue histiocytes in this case, it may be suggested that the existence of the abnormality in lipid metabolism plays an imporant role in intralysosomal ceroidogenesis in these histiocytes.  相似文献   
57.
58.
Japanese encephalitis virus-specific IgM is a reliable indicator for serodiagnosis of Japanese encephalitis. A particle agglutination (PA) assay system was developed to detect anti-Japanese encephalitis virus IgM in human serum samples. The newly developed PA assay consisted of hydroxyapatite-coated nylon beads and V-bottom 96-well microplates. Hydroxyapatite-coated nylon beads were coated with Japanese encephalitis virus antigens. Japanese encephalitis virus antigen-coated, hydroxyapatite-coated nylon beads agglutinated in the IgM-captured wells when anti-Japanese encephalitis virus IgM-positive serum samples were used. A button pattern was formed at the bottom of the wells when anti-Japanese encephalitis virus IgM-negative serum samples were used. Thirty anti-Japanese encephalitis virus IgM-positive serum samples from Japanese encephalitis-confirmed cases were tested by the PA assay. All these serum samples were determined to be Japanese encephalitis virus IgM-positive. IgM titers determined by the PA assay corresponded to those determined by enzyme-linked immunosorbent assay. The titers were consistent in two independent PA assays. These results indicate that the newly developed PA assay is a reliable method for detecting anti-Japanese encephalitis virus IgM in human serum samples and that this assay will be a suitable diagnostic system especially in rural areas of Asia.  相似文献   
59.
60.
Diverse functions of the p75 neurotrophin receptor   总被引:5,自引:0,他引:5  
The pan-neurotrophin receptor p75NTR belongs to a large family of receptors, which includes tumor necrosis factor receptors, Fas and approximately 25 other members. The p75NTR is the first receptor to be cloned molecularly. Recent years have seen the emergence of a consensus regarding the signaling pathways activated by p75NTR and its potential biological function, although receptor characterization had not been targeted for some years. We now know that p75NTR has surprisingly diverse effects, ranging from cell death to regulation of axon elongation. This diversity can be explained by the complex formation of p75NTR with other receptors and multiple signaling molecules that interact with the intracellular domain of p75NTR.  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