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   324784篇
  免费   9328篇
  国内免费   183篇
耳鼻咽喉   3447篇
儿科学   11760篇
妇产科学   6552篇
基础医学   39446篇
口腔科学   6187篇
临床医学   24957篇
内科学   58428篇
皮肤病学   4968篇
神经病学   31916篇
特种医学   14819篇
外科学   50554篇
综合类   3018篇
一般理论   65篇
预防医学   26927篇
眼科学   5973篇
药学   19565篇
中国医学   859篇
肿瘤学   24854篇
  2023年   935篇
  2022年   800篇
  2021年   1832篇
  2020年   1544篇
  2019年   1996篇
  2018年   24949篇
  2017年   19843篇
  2016年   22740篇
  2015年   4260篇
  2014年   4590篇
  2013年   7211篇
  2012年   15171篇
  2011年   29691篇
  2010年   23638篇
  2009年   14846篇
  2008年   28125篇
  2007年   30556篇
  2006年   9676篇
  2005年   11154篇
  2004年   11727篇
  2003年   12736篇
  2002年   10646篇
  2001年   5639篇
  2000年   7170篇
  1999年   3961篇
  1998年   1819篇
  1997年   1543篇
  1996年   1138篇
  1995年   994篇
  1994年   955篇
  1993年   878篇
  1992年   814篇
  1991年   757篇
  1990年   760篇
  1989年   736篇
  1988年   596篇
  1987年   660篇
  1986年   551篇
  1985年   787篇
  1984年   735篇
  1983年   623篇
  1982年   694篇
  1981年   613篇
  1980年   607篇
  1979年   530篇
  1978年   490篇
  1977年   512篇
  1976年   444篇
  1975年   447篇
  1974年   441篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
962.
Neuronal regulation of smooth muscle tone in the female pig urethra has mainly been studied in vitro using electrical field stimulation (EFS) of nerves. Excitatory control is considered to be exerted by released noradrenaline, whereas inhibitory control is non-adrenergic non-cholinergic (NANC), and mediated by nitric oxide (NO), and an as yet unidentified agent. We investigated the functional and morphological effects of α-latrotoxin (αLTX), a spider neurotoxin believed to cause massive release of vesicle-stored neurotransmitters, on spontaneously developed urethral smooth muscle tone. The effects were compared to those of EFS and high potassium. In the presence of the NO-synthesis inhibitor Nω-nitro-L-arginine (L-NOARG: 0.3 mM) both αLTX and EFS evoked contractions. After treatment with scopolamine and phentolamine, no contraction was observed, and under these conditions αLTX and EFS induced relaxation. At low frequencies (<12 Hz), the EFS-induced relaxations were rapid, whereas at higher frequencies (>12 Hz), they were biphasic, consisting of a rapid first phase followed by a more long-lasting second phase. L-NOARG abolished the relaxations at low frequencies, as well as the first phase of the biphasic relaxation. The second phase was not affected by treatment with L-NOARG, but 0.1 μM ω-conotoxin GVIA, blocker of N-type voltage-operated calcium- channels (VOCCs), markedly reduced or abolished the response. In the presence of L-NOARG or ω-conotoxin GVIA, the αLTX-induced relaxation was significantly decreased, and the combination of L-NOARG and ω-conotoxin GVIA further reduced or abolished the relaxation. In preparationstreated with tetrodotoxin or scorpion venom, believed to inactivate nerves by acting on sodium channels, αLTX and EFS had no effects. αLTX-induced relaxation was not associated with changes in cyclic GMP or cyclic AMP content. High (80 mM) potassium solution induced a triphasic response of the preparation. A transient relaxation was followed by a restoration of tone, and then by a persistent relaxation. The persistent relaxation was slightly reduced by scorpion venom or L-NOARG, but reduced by 50% by a combination of L-NOARG and ω-conotoxin GVIA. Ultrastructural analysis of the urethral circular smooth muscle layer revealed a moderate amount of nerve profiles supplying the smooth muscle. In control preparations, the nerve profiles contained both small synaptic vesicles and large dense core vesicles. αLTX caused a major loss of both types of vesicle. The present data suggest that αLTX has the ability to release not only adrenergic and cholinergic transmitters, but also NANC mediators of relaxation, including NO, from nerve terminals in the urethra. Received: 13 January 1997 / Accepted: 17 April 1997  相似文献   
963.
We report the first case of a unilateral microcysticMeesmann‘s epithelial dystrophy, observed in the left cornea of a 43-year-old patient. The diagnosis was verified histologically by the unilateral occurrence of a ’peculiar substance‘ within epithelial cysts and within the cytoplasm of the corneal epithelial cells. In an attempt to resolve thepatient‘s frequent corneal erosions, we performed an autologous stem cell transplantation from the non-involved right eye. The results are, so far, satisfactory. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   
964.
965.
Purpose To evaluate the clinical results of percutaneous transluminal rotational atherectomy in the treatment of peripheral vascular disease. Methods Rotational atherectomy was performed in 39 patients aged 39–87 years (mean 66.6 years). A total of 71 lesions (43 stenoses and 28 occlusions) were treated in 40 limbs. Additional balloon angioplasty was required in 54% of lesions. Fifteen patients (37.5%) presented in Fontaine stage II, 10 patients (25%) in Fontaine stage III and 15 patients (37.5%) in Fontaine stage IV. Rotational atherectomy at 750 rpm was carried out over a 0.014-inch guidewire with continuous aspiration into a vacuum, bottle. Follow-up angiography and color flow Doppler examinations were performed in 22 patients (23 limbs) after a mean period of 6 months (range 2–14 months) Results There was one primary technical failure. In 36 of 40 lesions there was a good angiographic result with residual stenoses in less than 30%. In 70 lesions treated by rotational atherectomy, however, 54% showed residual stenoses of 30%–50% and these cases required additional balloon angioplasty. The mean ankle-brachial index improved significantly (p<0.001), from 0.49 before the procedure to 1.01 after the procedure. A single distal embolus, related to primary recanalization, occurred and there were two large inguinal hematomas. Cumulative clinical patency after 6 months was 83.8% and cumulative angiographic patency after 6 months was 79.1%. Conclusion Percutaneous rotational atherectomy is a promising approach for the treatment of chronic peripheral vascular disease. Further prospective, randomized studies are necessary to compare percutaneous transluminal angioplasty with this new technical approach.  相似文献   
966.
967.
A 50-year old male presented with swollen right eyelids, bleeding per nostrils and a vague left post-auricular swelling for 4 months. Posterior rhinoscopy revealed one pinkish polypoidal mass in the posterior nare and roof of nasopharynx. FNAC from the post-auricular swelling suggested metastatic undifferentiated carcinoma. Incisional biopsy was done form the nasopharynx and histopathological examination proved it to be a malignant paraganglioma. The case is reported for its rarity.  相似文献   
968.
Zusammenfassung In diesem Reviewartikel wird die sozial- und verhaltenswissenschaftliche Interventionsliteratur der letzten 20 Jahre im deutschsprachigen Raum kritisch resümiert. Es werden nur kontrollierte Studien mit ad?quater Erhebungsmethodologie berücksichtigt. Was Interventionen im kognitiven Bereich betrifft, so belegen die Arbeiten deutlich positive Trainingseffekte. Allerdings zeigen Studien auch die Grenzen der kognitiven Plastizit?t in deutlicher Weise auf. Anhand eines weiten Bündels von Studien zeigt sich die Potenz von Interventionen zur Bewahrung bzw. Wiedererlangung der Selbst?ndigkeit im Alltag, zur Erh?hung der sozialen Aktivit?t und des subjektiven Wohlbefindens. Ebenso finden sich positive Effekte im Bereich des Selbstkonzepts, der personalen Kontrolle und des Attributionsstils. Eine allgemeine Diskussion dieser Befunde mündet in Vorschl?ge für zukünftige Forschungspriorit?en. Eingegangen: 10. November 1997, Akzeptiert: 22. Januar 1998  相似文献   
969.
Alcohol and food items can compromise or contribute to health, depending on the quantity and frequency with which they are consumed. How much people consume may be influenced by product availability and promotion in local retail stores. We developed and tested an observational tool to objectively measure in-store availability and promotion of alcoholic beverages and selected food items that have an impact on health. Trained observers visited 51 alcohol outlets in Los Angeles and southeastern Louisiana. Using a standardized instrument, two independent observations were conducted documenting the type of outlet, the availability and shelf space for alcoholic beverages and selected food items, the purchase price of standard brands, the placement of beer and malt liquor, and the amount of in-store alcohol advertising. Reliability of the instrument was excellent for measures of item availability, shelf space, and placement of malt liquor. Reliability was lower for alcohol advertising, beer placement, and items that measured the “least price” of apples and oranges. The average kappa was 0.87 for categorical items and the average intraclass correlation coefficient was 0.83 for continuous items. Overall, systematic observation of the availability and promotion of alcoholic beverages and food items was feasible, acceptable, and reliable. Measurement tools such as the one we evaluated should be useful in studies of the impact of availability of food and beverages on consumption and on health outcomes.  相似文献   
970.
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