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   6035篇
  免费   525篇
  国内免费   62篇
耳鼻咽喉   103篇
儿科学   250篇
妇产科学   90篇
基础医学   817篇
口腔科学   81篇
临床医学   519篇
内科学   1213篇
皮肤病学   146篇
神经病学   305篇
特种医学   185篇
外科学   700篇
综合类   465篇
一般理论   4篇
预防医学   389篇
眼科学   89篇
药学   521篇
  1篇
中国医学   85篇
肿瘤学   659篇
  2023年   55篇
  2022年   131篇
  2021年   200篇
  2020年   128篇
  2019年   143篇
  2018年   162篇
  2017年   116篇
  2016年   135篇
  2015年   166篇
  2014年   225篇
  2013年   244篇
  2012年   404篇
  2011年   384篇
  2010年   231篇
  2009年   192篇
  2008年   304篇
  2007年   332篇
  2006年   246篇
  2005年   218篇
  2004年   211篇
  2003年   202篇
  2002年   165篇
  2001年   168篇
  2000年   170篇
  1999年   162篇
  1998年   66篇
  1997年   57篇
  1996年   52篇
  1995年   52篇
  1994年   52篇
  1993年   37篇
  1992年   121篇
  1991年   86篇
  1990年   79篇
  1989年   99篇
  1988年   57篇
  1987年   66篇
  1986年   52篇
  1985年   57篇
  1984年   34篇
  1983年   27篇
  1982年   28篇
  1979年   27篇
  1977年   43篇
  1976年   25篇
  1974年   32篇
  1973年   41篇
  1972年   34篇
  1971年   29篇
  1967年   33篇
排序方式: 共有6622条查询结果,搜索用时 15 毫秒
41.
42.
43.
44.
After a brief review of the AIDS virus, its transmission, and clinical aspects, the obstetric implications of HIV infections for a developing country like India are summarized. HIV, the virus that causes AIDS, is transmissible in utero with a 66% risk of infecting the fetus, and may cause intrauterine growth retardation or prematurity. HIV positive pregnant women may become immunosuppressed, so they should be offered pregnancy termination. A woman in labor infected with HIV should be managed like a woman with hepatitis B: intrauterine catheters, fetal scalp electrodes, and fetal blood sampling are contraindicated. Forceps and episiotomy should be used only if needed. Cesarean section to prevent intrapartum infection of the fetus is controversial. While breastfeeding is allowed, breast milk should not be donated to other infants. Nursing staff should be informed that HIV is much less transmissible than hepatitis.  相似文献   
45.
The current article describes the design and synthesis of a new series of phosphorus-containing fluoro-sulfonated polytriazoles through click polymerization. The synthesized copolytriazoles (PTPFDSH-70 to 90) with different degrees of sulfonation (DS) from 70% to 90% are structurally interpreted by various spectroscopic techniques (1H, 13C, and FTIR). The high molecular weight (weight average molecular weight as high as 77 500 g mol−1 with polydispersity index of 2.29) polymers exhibits excellent mechanical (elongation at break up to 95%), thermal (10% decomposition temperature: 266–317 °C), and oxidative (>14.5 h) stability. The PTPFDSH-70 to 90 possess outstanding water-holding ability in hydrated conditions (swelling ratio [in-plane]: 6.2–7.3% at 80 °C). The microstructural alterations by their thermal relaxations and transitions with increasing DS in the polymers have been thoroughly investigated by dynamic mechanical analysis. The atomic force microscopy and transmission electron microscope images of the PTPFDSH-70 to 90 polymer membranes demonstrated the phase segregated interconnected ionic cluster-like morphology between hydrophilic and hydrophobic domains. The PTPFDSH-90 (DEB:PFAZ:DSAZ = 100:10:90) polymer membrane displays the proton conductivity (176 and 190 ms cm−1 at 80 and 90 °C, respectively) higher than Nafion117 under similar test conditions.  相似文献   
46.
Presents an algorithm to align 2D images with similar densitometric patterns in the spatial domain. It performs automatic identification of control points through local maxima in normalized image cross correlations computed through projections of an image function on 2D orthonormal bases over a predefined circular domain. The image is subsequently subjected to translational and rotational corrections through an integrated transformation matrix obtained by the least-squares minimization technique. The algorithm restricts the corrections required for alignment to rotation and translation only, and care is taken to see that the image does not go through scaling (isotropic or anisotropic) or nonlinear distortions. The least-squares method results in implicit equations in three variables, theta , h, upsilon , representing rotation, and translations along x and y axes. The present algorithm, on the other hand, is based on an approximation that results in a set of explicit equations that are easy to solve. The mathematical validity of this approximation is proved and the results obtained show that the algorithm performs well with similar biological (histological, autoradiographic, and tomographic) images. The algorithm is iterative, and its computer implementation is discussed.  相似文献   
47.
48.
Of 613 children evaluated in a village in Haryana 94 (15.3%) were observed to have chronic suppurative otitis media (CSOM). Fifty eight (61.7%) children had hearing impairment. CSOM contributed to 71.6% of the hearing impaired (58/81). On analysis of association of CSOM with literacy and socio-economic status of mothers, and age, sex, and upper respiratory tract infections (URI) in children positive correlation was observed only with URIs (P<0.001). Literacy and socio-economic status of the mothers did not correlate significantly with knowledge about treatment seeking, and ear cleaning practices, probably due to the narrow range of incomes and literacy levels. An intervention program consisting of play, demonstrations, health charts and slogans, and aural cleaning and antibiotic drops was introduced.  相似文献   
49.
BACKGROUND: Tumor necrosis factor alpha (TNF-alpha) is an important mediator of septic shock. Endotoxin (LPS) signal transduction in human monocytes leads to activation of nuclear factor-kappa B (NF-kappaB) and TNF-alpha release. Previous studies have implicated activation of both protein kinase C (PKC) and protein tyrosine kinases (PTK) in LPS-induced NF-kappaB activation and TNF-alpha production. We hypothesized that inhibition of either PKC or PTK would decrease LPS-induced NF-kappaB DNA binding and TNF-alpha release in human monocytes. MATERIALS AND METHODS: Human monocytes were stimulated with PMA (50 ng/ml) alone or LPS (100 ng/ml) with and without a nonspecific serine/threonine protein kinase inhibitor staurosporine (Stauro), a specific pan-PKC inhibitor bisindolylmaleimide (Bis), or an inhibitor of PTK genistein (Gen). TNF-alpha release in culture supernatants was measured by an ELISA. NF-kappaB DNA binding was evaluated by electrophoretic mobility shift assay. RESULTS: LPS increased NF-kappaB DNA binding and TNF-alpha release in human monocytes. Nonspecific protein kinase inhibition inhibited NF-kappaB activation and TNF-alpha release, while specific PKC inhibition with Bis had no effect on LPS-induced NF-kappaB DNA binding or TNF-alpha release. PTK inhibition with Gen attenuated both LPS-induced NF-kappaB DNA binding and TNF-alpha production in human monocytes. Direct activation of PKC with PMA induced both NF-kappaB activation and TNF-alpha production by human monocytes. CONCLUSIONS: These results suggest that LPS-induced NF-kappaB activation and TNF-alpha release in human monocytes are independent of PKC activity. Furthermore, our results provide evidence that PTK plays a role in LPS-induced NF-kappaB activation and TNF-alpha release in human monocytes and thus could be a potential therapeutic target in inflammatory states.  相似文献   
50.
Ischemic preconditioning has been shown to ameliorate injury due to subsequent ischemia in several organs. However, relatively little is known about preconditioning and the kidney. To address this, rats were randomized to control (C, N = 14), 2 min of ischemic preconditioning (P2 N = 10), 3 periods of 2 min of ischemia separated by 5 min periods of reflow (P2,3 N = 7), or three 5 min periods of ischemia separated by 5 min of reflow (P5,3 N = 6) prior to 45 min of bilateral renal ischemia followed by 24 hours of reperfusion. We observed a lower serum creatinine after 24 hours of reflow in P2, P2, 3 but not P5, 3 rats compared with C. Histology was examined in the C and P2, 3 groups and demonstrated less severe injury in the P2, 3 group. To gain insight into the mechanism by which preconditioning ameliorated ischemic injury, we performed near IR spectroscopy and 31P NMR spectroscopy. Based on near IR spectroscopy, the P2, 3 group had closer coupling of cytochrome aa3 redox state with that of hemoglobin during reflow. In the 31P NMR studies, the changes in ATP and pHi were similar during ischemia, but the P2, 3 group recovered ATP and pHi faster than C. These data suggest that ischemic preconditioning may ameliorate ischemic renal injury as assessed by functional, metabolic and morphological methods. The mechanism(s) by which this occurs requires additional study.  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