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   36949篇
  免费   3357篇
  国内免费   1430篇
耳鼻咽喉   120篇
儿科学   174篇
妇产科学   193篇
基础医学   2542篇
口腔科学   835篇
临床医学   3739篇
内科学   1936篇
皮肤病学   611篇
神经病学   794篇
特种医学   835篇
外科学   1970篇
综合类   8222篇
现状与发展   3篇
预防医学   4186篇
眼科学   316篇
药学   8285篇
  183篇
中国医学   6202篇
肿瘤学   590篇
  2024年   558篇
  2023年   562篇
  2022年   1365篇
  2021年   1623篇
  2020年   1421篇
  2019年   891篇
  2018年   791篇
  2017年   1105篇
  2016年   1232篇
  2015年   1271篇
  2014年   2451篇
  2013年   2463篇
  2012年   2609篇
  2011年   2731篇
  2010年   2131篇
  2009年   1692篇
  2008年   1783篇
  2007年   2043篇
  2006年   1591篇
  2005年   1381篇
  2004年   1191篇
  2003年   988篇
  2002年   849篇
  2001年   789篇
  2000年   669篇
  1999年   622篇
  1998年   511篇
  1997年   428篇
  1996年   462篇
  1995年   421篇
  1994年   415篇
  1993年   341篇
  1992年   311篇
  1991年   268篇
  1990年   248篇
  1989年   223篇
  1988年   214篇
  1987年   187篇
  1986年   172篇
  1985年   183篇
  1984年   117篇
  1983年   64篇
  1982年   101篇
  1981年   52篇
  1980年   44篇
  1979年   35篇
  1978年   31篇
  1977年   25篇
  1976年   26篇
  1974年   13篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Summary Melanosomes and isolated melanosomal fragments (melanin particles) originating from gangliocytes (substantia nigra), astroglia (melanosis cerebelli), and melanocytes (melanotic meningeoma; metastases of melanoblastoma; melanosis thalami of the goat) were compared with synthetic melanins prepared from dopamine and serotonin, respectively. Samples were examined by electron microscopy, X-ray diffraction analysis according to Debye-Scherrer and by infrared spectrophotometry, and the results were evaluated with regard to characteristic features as they may relate to specific cell types or chemical structures.On electron microscopy all three types of melanosomes could be differentiated unequivocally as could the two synthetic melanins. Thus, there were similarities between synthetic melanin from dopamine and the gliogenic melanins of the cerebellum; the synthetic melanin from serotonin resembled melanin of melanocytes.X-ray diffraction analysis yielded 2-4 Debye diffraction rings with all human and synthetic samples, suggesting short range orders between 3.8 to 5 Å the sample obtained from a goat with thalamic melanosis showed a specific reflex pattern. While diffraction patterns of some melanins were partially identical, in particular that of melanin from dopamine and melanin of substantia nigra and dentate nucleus, respectively, they were different for the various melanocytic melanins. Further investigations are required to determine whether these differences are due to disparities in basic chemical structures or conformations or else, to particular compositional features of the various types of melanocytes as they arise from benign or malignant tumors or a specific species.Infrared spectrophotometry at higher wave numbers revealed the well known patterns of melanins, which are not, however, very suitable, for their further differentiation. At lower wave numbers (fingerprinting) melanin of substantia nigra and the glial melanin in melanosis cerebelli yielded additional absorption bands of identical configuration. In contrast to melanin from dopamine, melanin from serotonin exhibited a closely similar absorption pattern in this spectral range, suggesting that the neuroectodermal melanins may contain a component possibly arising from serotonin.
Herrn Prof. Dr. Wilhelm Doerr zum 25. 8. 1979  相似文献   
82.
83.
目的:评价激光虹膜切除治疗闭角型青光眼临床疗效。方法:应用Nd:YAG激光于上方或下方作周边虹膜切除。结果:107例122眼闭角型青光眼术后经过2—106月随访观察,成功115眼,失败7眼。结论:激光虹膜切除术治疗闭角型青光眼安全、有效。  相似文献   
84.
夏玉凤  王强  濮祖茂 《中药材》2003,26(5):323-326
分别采用扫描电镜和紫外光谱法对地肤子、藜、小藜和扫帚菜四种药材进行了比较鉴别。结果表明:扫描电镜下四种药材的胞果、毛茸、气孔和种子形态特征有较为明显的区别;紫外光谱扫描结果表明地肤子和扫帚菜无明显区别,但与藜和小藜之间有显著区别。  相似文献   
85.
目的:建立口腔愈疡颗粒的质量标准。方法:采用高效液相色谱法对成品中芍药苷进行含量测定。结果:芍药香浓度线性范围为:0.104—0.520μg/ml,γ=0.9993。样品平均回收率为98.85%,RSD为1.27%(n=5)。结论:该方法适用于口腔愈疡颗粒的质量控制。  相似文献   
86.
OBJECTIVES: Presently, a design-based and practical method for measuring amniotic fluid volume (AFV) for routine clinical examinations has not been proposed. In this study we describe a new method, which combines the Cavalieri method with ultrasound imaging to estimate AFV. METHODS: We measured the AFVs of 14 women in the third trimester of pregnancy, and repeated our measurements three times for each woman. Parallel planimetric ultrasonographic images were obtained at every 2 cm along the longitudinal uterine axis. AFVs were calculated as the total of the multiples of the estimated cut surface areas by the section thickness. RESULTS: The mean estimated AFV was 380.5 cm3. The coefficient of error of each measurement was calculated and the mean was 0.108. The coefficient of correlation between the amniotic fluid index and our AFV estimations was 0.87. CONCLUSIONS: Design-based and efficient estimation of AFV is possible with the combination of consecutive ultrasound images and the Cavalieri method.  相似文献   
87.
The fact that certain ultraviolet (UV) filters used in cosmetics display estrogenic activity prompted us to study potential actions on androgen receptors (AR) in the human breast carcinoma cell line MDA-kb2, which expresses functional endogenous AR and glucocorticoid receptors (GR) and is stably transfected with a luciferase reporter plasmid. Dihydrotestosterone (DHT), methyltrienolone (R1881), methyltestosterone, danazol, and androstenedione increased luciferase activity, with EC50 values between 0.11 nM (R1881), 0.14 nM (DHT), and 73.5 nM (androstenedione). DHT-induced luciferase gene expression was inhibited by nonsteroidal antiandrogens, hydroxyflutamide, flutamide, bicalutamide, and vinclozolin. In contrast, the steroidal AR agonist/antagonist cyproterone actetate showed agonistic activity in the absence and presence of DHT, which was not blocked by hydroxyflutamide and thus seems not to be mediated by AR. GR-mediated activation of luciferase by dexamethasone was 100 times less potent than DHT and was not antagonized by hydroxyflutamide. The cell line was used for screening of UV filters, benzophenone-3 (Bp-3), benzophenone-4, 3-benzylidene camphor, 4-methylbenzylidene camphor, butyl-methoxy-dibenzoylmethane, homosalate (HMS), octyl-dimethyl-PABA, and octyl-methoxycinnamate. Two of these, Bp-3 and HMS, antagonized DHT-induced AR activation below cytotoxic concentrations, with IC50 of 5.57 10-6 M (HMS) and 4.98 10-6 M (Bp-3). None of the eight UV filters displayed agonistic activity when tested alone, but high concentrations of Bp-3 induced an increase of luciferase activity in the presence of dexamethasone, which was not blocked by hydroxyflutamide or the estrogen antagonist, ICI 182,780. These data indicate that the UV filters Bp-3 and HMS possess antiandrogenic activity in vitro in addition to estrogenic activity.  相似文献   
88.
离子抑制色谱法测定琥乙红霉素含量及其有关物质   总被引:3,自引:0,他引:3  
目的 建立离子抑制色谱法测定琥乙红霉素原料的含量及有关物质的方法 ,并研究其影响因素。方法 采用ZorbaxSB -C1 8色谱柱 ,以 0 .0 2mol·L- 1 KH2 PO4 乙腈 ( 4 5∶5 5 ,用氨试液调至pH 6 .8)为流动相 ,流速 1.2mL·min- 1 ,检测波长 2 10nm ,柱温 ( 30± 0 .5 )℃。结果 在选定固定相条件下 ,流动相对组分的洗脱和选择性影响最大 ,柱温次之 ,琥乙红霉素在乙腈中比较稳定。测定了有效主成分琥乙红霉素A的含量以及 7个有关物质的总含量 ,琥乙红霉素A的平均回收率为 99.4 5 %(RSD =2 .2 4 % ,n =5 )。结论 本方法可用于琥乙红霉素原料的含量测定和有关物质的检查。  相似文献   
89.
中医药治疗恶性肿瘤的研究进展   总被引:1,自引:0,他引:1  
阐述了中医对恶性肿瘤病因病机的认识及治则治法,对目前中医药治疗恶性肿瘤的几种新思路进行了探讨.在指出中医药治疗恶性肿瘤中存在的问题的同时,提出了笔者的几点建议。  相似文献   
90.
γ—干扰素对喉癌细胞株HEP—2增殖活性的影响   总被引:1,自引:0,他引:1  
用单克隆抗体Ki-67(抗PCNA),以链霉菌素-生物素技术(LSAB)检测喉癌细胞株HEP-2增殖细胞核抗原(PCNA)表达。人重组γ-干扰素(rhu-IFN-γ)抑制PCNA表达(即抗增殖活性)强弱与其剂量有关;雌激素对rhu-IFN-γ抗增殖作用无影响。提示:rhu-IFN-γ对喉癌细胞株HEP-2有抗增殖作用,因而在喉癌的治疗中具有应用价值的。  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