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   323596篇
  免费   26193篇
  国内免费   13752篇
耳鼻咽喉   3387篇
儿科学   5376篇
妇产科学   6930篇
基础医学   43595篇
口腔科学   7511篇
临床医学   35288篇
内科学   52602篇
皮肤病学   5017篇
神经病学   19727篇
特种医学   11324篇
外国民族医学   102篇
外科学   38395篇
综合类   35863篇
现状与发展   39篇
一般理论   63篇
预防医学   22351篇
眼科学   8102篇
药学   31871篇
  190篇
中国医学   11953篇
肿瘤学   23855篇
  2023年   3330篇
  2022年   8441篇
  2021年   11109篇
  2020年   8098篇
  2019年   7595篇
  2018年   8640篇
  2017年   7586篇
  2016年   7217篇
  2015年   10552篇
  2014年   12978篇
  2013年   12954篇
  2012年   18797篇
  2011年   20188篇
  2010年   12734篇
  2009年   10118篇
  2008年   14331篇
  2007年   14145篇
  2006年   13648篇
  2005年   12839篇
  2004年   9402篇
  2003年   8611篇
  2002年   7489篇
  2001年   11894篇
  2000年   12217篇
  1999年   10802篇
  1998年   4513篇
  1997年   3984篇
  1996年   2976篇
  1995年   2814篇
  1994年   2497篇
  1993年   1854篇
  1992年   5716篇
  1991年   5524篇
  1990年   4996篇
  1989年   4925篇
  1988年   4672篇
  1987年   4313篇
  1986年   3966篇
  1985年   3733篇
  1984年   2494篇
  1983年   2158篇
  1979年   2183篇
  1978年   1316篇
  1975年   1299篇
  1974年   1482篇
  1973年   1532篇
  1972年   1468篇
  1971年   1359篇
  1970年   1235篇
  1969年   1191篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Coronary flow reserve (CFR) has been used toassess coronary microcirculation and epicardial coro-nary stenoses[1— 3 ] . CFR is defined as the ratio ofcoronary flow under maximal coronary vasodilatationto coronary flow under resting conditions[4 ] .Whenthe cross- sectional area of epicardial coronary arteriesis constant,coronary flow velocity (CFV) ratios areequal to volume flow ratios.The most common method used clinically formeasuring CFVR is intracoronary Doppler flow(ICD) analysis re…  相似文献   
42.
43.
We report spectrophotometric methods for quantifying sodium and potassium in serum and plasma without sample pretreatment or solvent-extraction steps. The methods are based on novel chromogenic ionophores characterized by molecular structures highly preorganized for binding, which result in exceptionally high sensitivity and selectivity (negligible responses to sodium at 80 to 200 mmol/L in the potassium assay and to potassium at 0 to 10 mmol/L in the sodium assay). The within-run imprecisions are comparable with those for ion-selective electrodes (for K, 1.0% at 4.5 mmol/L; for Na, 1.1% at 136 mmol/L); the analytical range is 2-10 mmol/L for potassium, 80-170 mmol/L for sodium. The results for greater than 100 patients' samples correlated well with results obtained with ion-selective electrodes (r = 0.99 for K, 0.97 for Na). The ready-to-use aqueous reagents will be available under the trade name of ChromoLyte for use with Technicon's RA family of clinical analyzers.  相似文献   
44.
试论医院药师的业务标准   总被引:3,自引:0,他引:3  
作者依据医药卫生事业发展对药学人员的要求,在调查了80家综合医院药师工作现状的基础上,提出了药师在调剂、制剂、药品检验、药学科研、药品储存供应、药学综合知识与技能6个方面应具备的业务标准,为我国实行医院药师资格准入控制提供参考。  相似文献   
45.
表皮生长因子对牛眼小梁细胞c—fos基因表达的诱导   总被引:4,自引:0,他引:4  
目的研究表皮生长因子(epidermalgrowthfactor,EGF)对小梁细胞的作用。方法应用分子杂交技术研究EGF对体外培养的牛眼小梁细胞c-fos基因表达的诱导和3H胸腺核苷酸(3H-thymidineincorparation,3H-TdR)掺入法观察细胞DNA的合成。结果小梁细胞的3H-TdR掺入率随着EGF浓度不同而变化,浓度为20~150ng/ml时,细胞掺入率随浓度增加升高(P<0.01)。与对照组相比,EGF刺激停止生长的小梁细胞0.5小时后,c-fos基因开始表达,1小时后达高峰,至2小时后消失。不同浓度EGF刺激小梁细胞1小时后,c-fos基因表达呈浓度依赖性。结论实验结果表明EGF刺激小梁细胞增殖或进入生长状态,可能与c-fos基因产物的信号传递作用有关。  相似文献   
46.
PURPOSETo use functional MR imaging to measure the effect of frequency (pitch), intensity (loudness), and complexity of auditory stimuli on activation in the primary and secondary auditory cortexes.METHODSMultiplanar echo-planar images were acquired in healthy subjects with normal hearing to whom auditory stimuli were presented intermittently. Functional images were processed from the echo-planar images with conventional postprocessing methods. The stimuli included pure tones with a single frequency and intensity, pure tones with the frequency stepped between 1,000, 2,000, 3,000, or 4,000 Hz, and spoken text. The pixels activated by each task in the transverse temporal gyrus (TTG) and the auditory association areas were tabulated.RESULTSThe pure tone task activated the TTG. The 1,000-Hz tone activated significantly more pixels in the TTG than did the 4,000-Hz tone. The 4,000-Hz tone activated pixels primarily in the medial TTG, whereas the 1,000-Hz tone activated more pixels in the lateral TTG. Higher intensity tones activated significantly more pixels than did lower intensity tones at the same frequency. The stepped tones activated more pixels than the pure tones, but the difference was not significant. The text task produced significantly more activation than did the pure tones in the TTG and in the auditory association areas. The more complex tasks (stepped tones and listening to text) tended to activate more pixels in the left hemisphere than in the right, whereas the simpler tasks activated similar numbers of pixels in each hemisphere.CONCLUSIONAuditory stimuli activate the TTG and the association areas. Activation in the primary auditory cortex depends on frequency, intensity, and complexity of the auditory stimulus. Activation of the auditory association areas requires more complex auditory stimuli, such as the stepped tone task or text reading.  相似文献   
47.
为探讨钙调素在慢性缺氧性肺动脉高压发病中的作用,将40只Wistar大鼠随机分为四组,I组为正常对照组,不接受任何处理。Ⅱ、Ⅲ、Ⅳ组为实验组,分别间断缺氧1、2、3周,而后采用火焰原子吸收分光光度法及磷酸二酯酶法测定四组大鼠肺组织Ca^2+含量及CaM活性。  相似文献   
48.
Nephrotoxic cysteine conjugates derived from a variety of halogenated alkenes are enzymatically activated via the beta-lyase pathway to yield reactive sulfur-containing metabolites which bind covalently to cellular macromolecules. Mitochondria contain beta-lyase enzymes and are primary targets for binding and toxicity. Previously, mitochondrial protein and/or DNA have been considered as molecular targets for cysteine conjugate metabolite binding. We now report that metabolites of nephrotoxic cysteine conjugates form covalent adducts with rat kidney mitochondrial phospholipids. Rat kidney mitochondria were incubated with the 35S-labeled conjugates S-(1,1,2,2-tetrafluoroethyl)-L-cysteine (TFEC), S-(2-chloro-1,1,2-trifluoroethyl)-L-cysteine (CTFC), S-(1,2-dichlorovinyl)-L-cysteine, and S-(1,2,3,4,4-pentachlorobutadienyl)-L-cysteine. Quantitation of metabolite binding to whole mitochondria and to mitochondrial protein and lipid fractions revealed that as much as 42% of the 35S-label associated with the mitochondria was found in the lipid fraction. Total lipids were also extracted from 35S-treated mitochondria and separated by thin-layer chromatography. 35S-Containing metabolites were found in the lipid fractions from mitochondria treated with each of the conjugates. Lipids from both [35S]CTFC- and [35S]-TFEC-treated mitochondria contained major 35S-labeled lipid adducts which had similar mobility by thin-layer chromatography. Fatty acid analysis, 19F and 31P NMR spectroscopy, and mass spectrometric analyses confirmed that the major TFEC and CTFC adducts are thioamides of phosphatidylethanolamine.  相似文献   
49.
Birth weight on 12,644 singleton infants from 6,196 sibships born in Maryland between 1980 and 1984 were used to estimate the effects of nine maternal and infant covariates on the sibship correlation in birth weight. Assuming a homogeneous correlation across all families, the estimated intraclass correlation was 0.4664 (+/- 0.0099). This high sibship correlation makes it possible to predict, with reasonable accuracy, the birth weight of a child given information on previous sibs, as well as covariates on the mother and/or infant pertinent to a given pregnancy. The reduction in variance associated with incorporating information on the nine covariates used here was approximately equal to that obtained by conditioning on a single previous sib. Testing for heterogeneity in correlation among different groups of families showed that a crude measure of parity (first live birth vs. other), time between births, mother's marital status, and maternal age at the birth of the last child significantly influenced the sibship correlation in birth weight.  相似文献   
50.
Eighty-nine cases of chronic bronchitis were matched against167 asymptomatic controls from the glass bangle industry ofFirozabad. Factors of age, social status, smoking habit andduration of exposure were studied. Duration of exposure wasfound to be a factor contributing significantly to the causationof disease. Requests for reprints should be addressed to: Dr B. N. Gupta, Division of Epidemilogy, Industrial Toxicology Research Centre, Mahatma Gandhi Marg, Lucknow P.O. Box 80, 226001, India  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