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   996746篇
  免费   76879篇
  国内免费   2623篇
耳鼻咽喉   13010篇
儿科学   34484篇
妇产科学   28472篇
基础医学   145461篇
口腔科学   27751篇
临床医学   90361篇
内科学   193376篇
皮肤病学   22956篇
神经病学   79233篇
特种医学   38543篇
外国民族医学   305篇
外科学   149850篇
综合类   23730篇
一般理论   385篇
预防医学   77708篇
眼科学   22592篇
药学   72060篇
  3篇
中国医学   2031篇
肿瘤学   53937篇
  2018年   10589篇
  2017年   8260篇
  2016年   9415篇
  2015年   10643篇
  2014年   14476篇
  2013年   22085篇
  2012年   29115篇
  2011年   30970篇
  2010年   18564篇
  2009年   17495篇
  2008年   28903篇
  2007年   30574篇
  2006年   31063篇
  2005年   29727篇
  2004年   29001篇
  2003年   27903篇
  2002年   26915篇
  2001年   46975篇
  2000年   48107篇
  1999年   40334篇
  1998年   11211篇
  1997年   10123篇
  1996年   10173篇
  1995年   9791篇
  1994年   9108篇
  1993年   8493篇
  1992年   32289篇
  1991年   31487篇
  1990年   31040篇
  1989年   29924篇
  1988年   27202篇
  1987年   27361篇
  1986年   25468篇
  1985年   24633篇
  1984年   18426篇
  1983年   15541篇
  1982年   9299篇
  1981年   8344篇
  1979年   16846篇
  1978年   12211篇
  1977年   10299篇
  1976年   9727篇
  1975年   10175篇
  1974年   12312篇
  1973年   11855篇
  1972年   10907篇
  1971年   10127篇
  1970年   9381篇
  1969年   8730篇
  1968年   8102篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
This study was conducted to determine if lower steroid secretion by the small white follicles in incubating turkey hens contributes to lower circulating steroid concentrations during this time. Turkey hens were grouped as either laying or incubating. Serum samples and the ovarian small white follicles (SWF; 2-7 mm diameter) were collected from each hen. The SWF were pooled for each group and their cells were dispersed by trypsin digestion. Serum-luteinizing hormone (LH), progesterone (P), testosterone (T), and estradiol (E) concentrations were lower and serum prolactin concentration was higher during incubation than during egg laying. SWF cells from incubating hens secreted more P and T and less E in response to ovine luteinizing hormone (oLH) than did similar cell suspensions from laying hens. The incubating hens' SWF cells' capacity to secrete E but not their capacity to secrete P or T in vitro is consistent with the observed circulating levels. It is hypothesized that lower levels of circulating LH and/or higher levels of prolactin found in incubating hens may have a depressing effect on aromatase activity and/or an up-regulating effect on LH-induced P and T secretion by the SWF cells.  相似文献   
994.
Forty-six patients with cholangitis were randomized to receive therapy with mezlocillin sodium (24 patients) or a combination of ampicillin sodium--gentamicin sulfate (22 patients). The biliary concentration of mezlocillin was 112 times higher than that of ampicillin and 778 times higher than that of gentamicin. The ratio of the concentration in serum or bile over the minimum inhibitory concentration against aerobic gram-negative bacilli (therapeutic index) was higher for mezlocillin than for either ampicillin or gentamicin. Twenty (83%) of 24 patients were cured following mezlocillin therapy compared with 9 (41%) of 22 patients after ampicillin-gentamicin therapy. The 3 patients with superinfection were in the ampicillin-gentamicin arm of the study. Fewer toxic or adverse effects occurred in association with mezlocillin treatment than with ampicillin-gentamicin treatment. Mezlocillin therapy was more effective, less toxic, and less expensive than treatment with ampicillin and gentamicin for patients with cholangitis.  相似文献   
995.
There is evidence that leukocyte contaminating red blood cells and platelet concentrates are responsible for refractoriness to platelet transfusions. The efficacy of a cotton-wool filter to remove leukocytes from red blood cells has been documented previously. The present study was designed to evaluate whether the cotton-wool filters can effectively remove leukocytes from platelet concentrates. Sixty pools of random-donor platelets and single-donor plateletpheresis products were filtered through a cotton-wool filter. The efficacy of filtration was determined by measuring the absolute numbers of leukocytes and platelets and subpopulations of mononuclear cells. The average platelet loss was 8% per pool of random platelets and 10% per plateletpheresis product. The average leukocyte removal was 99% from a pool of random platelets and plateletpheresis concentrates collected by CS-3000 and 90% from plateletpheresis concentrates harvested by single-stage COBE/IBM-2997. The filtration removed 100% of granulocytes, 95% of monocytes, 90% of B-lymphocytes, and 85% of T-lymphocytes. We conclude that filtration through a cotton-wool filter is an efficient and cost-effective method for preparation of leukocyte-poor platelets.  相似文献   
996.
997.
This article reviews the utility of noninvasive echocardiography in the detection of early cardiac transplant rejection before and after the use of cyclosporine. It addresses the use of Doppler and two-dimensional echocardiography in the routine cardiac evaluation of the heart-transplant patient, including the use of two-dimensional echocardiography in guiding the endomyocardial biopsy procedure.  相似文献   
998.
A giant aneurysm of the right common iliac artery presenting with an arteriovenous fistula (AVF) between the iliac artery and iliac vein and deep venous thrombosis of the right lower extremity is reported. The clinical signs and the radiologic and surgical management of the condition are discussed. In addition a brief review of the literature is given.  相似文献   
999.
In the present study, we present physiological evidence for rate-sensitive, fast feedback inhibition of secretion of ACTH and beta-endorphin (beta END)-related peptides. We used a 2 min restraint stress to physiologically increase plasma corticosterone, then examined the plasma responses of immunoreactive ACTH and beta END plus beta-lipotropin (beta END/beta LPH) to a subsequent restraint stress. After onset of this stress, plasma corticosterone increased from 2.5-10 min at a rate of 120 nM min-1, then remained at a peak from 10-15 min. A single 2 min restraint stress produced peak plasma levels of ACTH and beta END/beta LPH 2.5 min after onset of the stress, and these plasma concentrations declined after this initial stress at rates of 2.7 and 7.4 pM min-1, respectively. Application of a second restraint stress at the time of the peak corticosterone response produced plasma ACTH and beta END/beta LPH responses similar to those after the first stress. Application of a second stress during the period of significant rate-rise of corticosterone in plasma did not result in decreased incremental responses of plasma ACTH or beta END/beta LPH. However, the rates of decline of plasma ACTH and beta END/beta LPH of 7.6 and 32 pM min-1, respectively, from peak levels, were significantly greater after this second stress applied during the period of significant increase in plasma corticosterone concentration than the corresponding rates of decline observed after the initial stress or after a subsequent stress applied at the peak of plasma corticosterone. These differences in rates of decline of plasma ACTH or beta END/beta LPH appear to reflect differences in secretion rate rather than clearance, since disappearance of [125I]ACTH1-24 was not different after an initial vs. subsequent stress. In contrast to these data from intact rats, initial and subsequent stresses did not show different rates of decline of plasma ACTH or beta END/beta LPH in adrenalectomized rats. In conclusion, the stress-induced rate rise of glucocorticoid provides a negative feedback signal which serves to terminate and limit the duration, but not the peak, of the responses of POMC-derived peptides to subsequent stress.  相似文献   
1000.
A case is presented of severe pregnancy-induced hypertension that was complicated by oliguria and managed with the aid of a pulmonary artery catheter. This case illustrates that urinary diagnostic indices may be unreliable in predicting the etiology of oliguria. Although urinary diagnostic tests are advocated routinely as reliable in the nonobstetric literature, possible misinterpretation of these values in severe pre-eclampsia with oliguria may require confirmation with hemodynamic data obtained from a pulmonary artery catheter.  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