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   448篇
  免费   15篇
  国内免费   44篇
儿科学   10篇
妇产科学   26篇
基础医学   36篇
口腔科学   6篇
临床医学   47篇
内科学   95篇
皮肤病学   1篇
神经病学   20篇
特种医学   77篇
外科学   36篇
综合类   14篇
预防医学   47篇
眼科学   6篇
药学   69篇
中国医学   1篇
肿瘤学   16篇
  2023年   3篇
  2021年   5篇
  2020年   2篇
  2019年   1篇
  2018年   3篇
  2017年   3篇
  2016年   3篇
  2015年   6篇
  2014年   7篇
  2013年   5篇
  2012年   12篇
  2011年   5篇
  2010年   13篇
  2009年   9篇
  2008年   12篇
  2007年   38篇
  2006年   13篇
  2005年   21篇
  2004年   13篇
  2003年   17篇
  2002年   13篇
  2001年   16篇
  2000年   14篇
  1999年   18篇
  1998年   19篇
  1997年   16篇
  1996年   9篇
  1995年   13篇
  1994年   11篇
  1993年   14篇
  1992年   11篇
  1991年   13篇
  1990年   8篇
  1989年   23篇
  1988年   22篇
  1987年   8篇
  1986年   12篇
  1985年   11篇
  1984年   4篇
  1983年   7篇
  1982年   8篇
  1981年   6篇
  1980年   8篇
  1979年   4篇
  1978年   6篇
  1977年   10篇
  1976年   6篇
  1975年   5篇
  1970年   1篇
排序方式: 共有507条查询结果,搜索用时 0 毫秒
41.
OBJECTIVE: Our purpose was to determine whether the incidence of postoperative endometritis and wound infection is associated with the method of placental removal at the time of cesarean section.STUDY DESIGN: Parturients undergoing cesarean delivery were prospectively randomized to have the placenta removed manually or spontaneously. Patients were excluded from participation if they had received intrapartum prophylactic antibiotics or had been determined to have chorioamnionitis. After delivery of the infant women in the manual group had the placenta extracted by the primary surgeon, whereas women in the spontaneous group had the placenta delivered by gentle traction on the umbilical cord. All study subjects received perioperative prophylactic antibiotics. The primary outcome variable was a postcesarean infection, defined as postcesarean endometritis or wound cellulitis requiring drainage and antibiotic therapy.RESULTS: A total of 333 women were enrolled in the investigation, with 165 assigned to the manual removal group and 168 allocated to have spontaneous removal. There were no statistically significant differences in mean gestational age, frequency or duration of ruptured membranes, frequency or duration of labor, or mean number of vaginal examinations between the two study groups. Postoperative infections occurred in 25 of 168 (15%) women in the spontaneous delivery group compared with 44 of 165 (27%) women in which the placenta was manually extracted (relative risk 0.6, 95% confidence interval 0.4 to 0.9, p = 0.01). Subset analysis of patients delivered with ruptured membranes similarly demonstrated a statistically significant reduction in the incidence of postoperative infections with spontaneous placental removal compared with manual extraction (20% vs. 38%, relative risk 0.5, 95% confidence interval 0.3 to 0.9, p = 0.02). There was a similar trend toward a reduction in postdelivery infections associated with spontaneous placental removal in women with intact membranes; however, this difference did not attain statistical significance.CONCLUSIONS: Spontaneous delivery of the placenta after cesarean delivery is associated with a decrease in the incidence of postcesarean infections. (Am J Obstet Gynecol 1997;176:1250-4.)  相似文献   
42.
43.
The purpose of this study was to determine whether aged myocardium exhibits decreased responsiveness to adenosine A1 and A(2a) receptor activation. Studies were conducted in adult (4-6 months) and aged (24-26 months) Fischer 344 x Brown Norway hybrid (F344 x BN) rats. Effects of the adenosine A1/A(2a) agonist AMP579 were measured in isolated hearts and in rats submitted to in vivo regional myocardial ischemia. Aged isolated hearts exhibited lower spontaneous heart rates and higher coronary resistance, as well as normal A1- and A(2a)-mediated responses. There was no difference in control infarct size between adult and aged rats; however, AMP579 treatment resulted in a 50% greater infarct size reduction in aged rats (18 +/- 4% of risk area) compared to adult rats (37 +/- 3%). These findings suggest that adenosine A1 and A(2a) receptor-mediated effects are not diminished in normal aged myocardium, and that aged hearts exhibit increased adenosine agonist-induced infarct reduction.  相似文献   
44.
Recent precipitous population declines in northern fur seal (Callorhinus ursinus) and other Alaskan pinniped populations are due in part to reduced fecundity and have emphasized deficits in basic reproductive knowledge of these species. Following estrus and mating, fertilized female pinnipeds experience an obligatory delayed implantation lasting several months and non-pregnant (pseudopregnant) females are indistinguishable by sex steroid levels during this time. The current study examined circulating steroid concentrations and ovarian expression of key steroid-synthesizing enzymes in northern fur seals to identify changes associated with embryonic implantation, data necessary for estimating early pregnancy rates of the population. Blood samples were collected from 84 female fur seals captured on an Alaskan rookery from October 15 to November 30, a period spanning the end of the delay and subsequent uterine implantation of the fertilized blastocyst in this species. Concentrations of progesterone, estradiol, and estrone measured in blood collected during boreal fall were contrasted with samples collected during late summer from post-ovulatory females and males. Serum sex steroids were also related to ovarian expression of key enzymes responsible for androgen (17alpha-hydroxylase/17,20-lyase, cytochrome b5, and 3beta-hydroxysteroid dehydrogenase) and estrogen (aromatase cytochrome P450) synthesis. Enzymes necessary for androgen synthesis were highly expressed in ovaries, and accordingly, endocrine profiles were expanded to include DHEA, androstenediol, androstenedione, and testosterone. Estradiol concentrations were universally low and free and conjugated estrone were the primary circulating estrogens in fur seal sera. No implantation-associated peak was identified for estrogens or progesterone and mean values of progesterone and estrone were actually greater in female serum samples collected during summer than fall. However, there was a significant positive relationship between fall sampling date and testosterone concentration. Additionally, DHEA concentrations in females were lower in samples collected during the implantation period than during the summer embryonic delay. These data suggest androgens may play a substantial regulatory role in the embryonic delay of northern fur seals.  相似文献   
45.
During their annual musth cycle, adult African and Asian bull elephants have increased gonadal androgens (testosterone [T], dihydrotestosterone [DHT], androstenedione [A4]). Because musth is a physiologically and psychologically stressful time, this study was conducted to investigate whether the adrenal glands (stimulated by stress) increase production of both glucocorticoids and androgens during musth. Weekly serum samples were taken for 11-15 months from four intact adult Asian bull elephants, and from a castrate African bull elephant who exhibits musth. Testosterone, androstenediol (A5), A4, luteinizing hormone (LH), cortisol, and dehydroepiandrosterone (DHEA) were measured in each sample. In three of the four intact bulls, all hormones measured increased during musth. Adrenal androgens were strongly correlated with LH and testicular androgens, though not to cortisol. None of the hormones measured in the castrate bull increased during his musth cycles. While the significance of adrenal activity in the elephant during musth has yet to be determined, this study provides evidence that the adrenal gland actively produces both glucocorticoids and androgens during musth in the Asian elephant.  相似文献   
46.
47.
Exercising women with amenorrhea exhibit a hypometabolic state. The purpose of this study was to evaluate the relationship of luteal phase deficient (LPD) menstrual cycles to metabolic hormones, including thyroid, insulin, human GH (hGH), leptin, and IGF-I and its binding protein levels in recreational runners. Menstrual cycle status was determined for three consecutive cycles in sedentary and moderately active women. Menstrual status was defined as ovulatory or LPD. Subjects were either sedentary (n = 10) or moderately active (n = 20) and were matched for age (27.7 +/- 1.2 yr), body mass (60.2 +/- 3.3 kg), menstrual cycle length (28.4 +/- 0.9 d), and reproductive age (14.4 +/- 1.2 yr). Daily urine samples for the determination of estrone conjugates, pregnanediol 3-glucuronide, and urinary levels of LH were collected. Blood was collected on a single day during the follicular phase (d 2-6) of each menstrual cycle for analysis of TSH, insulin, total T3, total T4, free T4, leptin, hGH, IGF-I, and IGF binding protein (IGFBP)-1 and IGFBP-3. Among the 10 sedentary subjects, 28 of 31 menstrual cycles were categorized as ovulatory (SedOvul). Among the 20 exercising subjects, 24 menstrual cycles were included in the ovulatory category (ExOvul), and 21 menstrual cycles were included in the LPD category (ExLPD). TSH, total T4, and free T4 levels were not significantly different among the three categories of cycles. Total T3 was suppressed (P = 0.035) in the ExLPD (1.63 +/- 0.07 nmol/liter) and the ExOvul categories of cycles (1.75 +/- 0.8 nmol/liter) compared with the SedOvul category of cycles (2.15 +/- 0.1 nmol/liter). Leptin levels were lower (P < 0.001) in both the ExOvul (5.2 +/- 0.4 microg/liter) and the ExLPD categories of cycles (5.1 +/- 0.4 microg/liter) when compared with the SedOvul category of cycles (13.7 +/- 1.7 microg/liter). Insulin was lower (P = 0.009) only in the ExLPD category of cycles (31.9 +/- 2.8 pmol/liter) compared with the SedOvul (60.4 +/- 8.3 pmol/liter) and ExOvul (61.8 +/- 10.4 pmol/liter) categories of cycles. IGF-I, IGFBP-1, IGFBP-3, IGF-I/IGFBP-1, IGF-I/IGFBP-3, and hGH were comparable among the different categories of cycles. These data suggest that exercising women with LPD menstrual cycles exhibit hormonal alterations consistent with a hypometabolic state that is similar to that observed in amenorrheic athletes and other energy-deprived states, although not as comprehensive. These alterations may represent a metabolic adaptation to an intermittent short-term negative energy balance.  相似文献   
48.
Breast cancer is the most common cause of cancer death in women in this country. Until recently, the traditional treatment has been radical surgery with or without radiation therapy for patients with primary breast cancer, and palliative endocrine therapy followed by chemotherapy for patients with advanced disease. These treatments have met with limited effectiveness in terms of eradicating the disease. Studies in the past decade have given cause for optimism for breast cancer patients. Adjuvant systemic therapy after local treatment appears promising for certain subsets of patients with primary breast cancer. The development of estrogen receptor assays has markedly changed our approach to the disease and improved patient care. Estrogen receptor is an important prognostic factor and is useful in planning appropriate therapy for patients with primary breast cancer as well as those with advanced disease. Further research is urgently needed to improve the dismal survival of certain women with this common malignancy.  相似文献   
49.
Samples from prospectively followed recipients, their respective donors, and a cohort of random donors were used to evaluate the specificity and efficacy of a recombinant immunoblot assay (RIBA) as an adjunct to anti-hepatitis C virus (HCV) testing by enzyme immunoassay (EIA). RIBA reacted (RIBA+) in 100 percent of patients who developed hepatitis associated with anti-HCV seroconversion documented by EIA and in 100 percent of the EIA-positive (EIA+) donors implicated in these cases. In contrast, RIBA reacted in none of 10 recipients who were EIA+ but did not develop hepatitis, in none of 7 EIA+ patients with hepatitis B or cytomegalovirus infection, in 33 percent of EIA+ donors who were not implicated in hepatitis transmission, and in 37 percent of EIA+ random donors. Hence, the vast majority of EIA+ individuals who have ancillary evidence of HCV infection react on RIBA, whereas the majority of EIA+ individuals in low-risk settings do not react (RIBA-negative, or RIBA-). There was a strong association between RIBA reactivity and the presence of a surrogate marker (elevated alanine aminotransferase [ALT] and/or antibody to hepatitis B core antigen); 43 percent of RIBA+ implicated donors had a surrogate marker as compared to none of 14 EIA+, RIBA- donors. Among EIA+ random donors, 77 percent of those with a surrogate marker were RIBA+, as compared with 29 percent of those without a surrogate marker. In addition, in EIA+ donors, RIBA reactivity correlated with the extent of ALT elevation; 86 percent of those with an ALT greater than 135 IU per L were RIBA+ compared with 18 percent of those with an ALT less than 30 IU per L.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
50.
Intravaginal administration of an anti-microbial agent, (Ala8,13,18)-magainin II amide, during blastocyst implantation inhibits pregnancy establishment in a dose-related manner in the rhesus monkey (Macaca mulatta). In the present study, mated female rhesus monkeys were vaginally inserted with tampons containing vehicle (Group 1; N = 5) and test agent (magainin, 0.5 mg/animal; Group 2; N = 6) on cycle day 20. Endometrial tissue samples were collected on Cycle Day 24 from all monkeys and processed for morphometric and ultrastructural analysis. Concentrations of estradiol-17β, progesterone, and chorionic gonadotrophin in peripheral circulation were determined, which revealed that two monkeys in Group 1 were pregnant while no animals were pregnant in Group 2. Endometrial morphology, however, revealed histologic evidence of pregnancy in three out of the six magainin-treated animals. It appears that intra-vaginal administration of magainin II amide had a marginal effect on the implantation stage endometrium and the initiation of the implantation process in the rhesus monkey.  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