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   1153篇
  免费   66篇
耳鼻咽喉   23篇
儿科学   49篇
妇产科学   122篇
基础医学   118篇
口腔科学   38篇
临床医学   65篇
内科学   252篇
皮肤病学   4篇
神经病学   85篇
特种医学   14篇
外科学   193篇
综合类   6篇
预防医学   32篇
眼科学   13篇
药学   48篇
中国医学   3篇
肿瘤学   154篇
  2023年   7篇
  2022年   13篇
  2021年   24篇
  2020年   15篇
  2019年   25篇
  2018年   24篇
  2017年   16篇
  2016年   24篇
  2015年   27篇
  2014年   39篇
  2013年   45篇
  2012年   81篇
  2011年   75篇
  2010年   32篇
  2009年   47篇
  2008年   57篇
  2007年   76篇
  2006年   60篇
  2005年   58篇
  2004年   82篇
  2003年   41篇
  2002年   60篇
  2001年   11篇
  2000年   16篇
  1999年   20篇
  1998年   5篇
  1997年   10篇
  1996年   11篇
  1995年   11篇
  1994年   11篇
  1993年   7篇
  1992年   19篇
  1991年   5篇
  1990年   11篇
  1989年   11篇
  1988年   14篇
  1987年   22篇
  1986年   12篇
  1985年   6篇
  1984年   10篇
  1983年   8篇
  1982年   7篇
  1981年   7篇
  1980年   4篇
  1979年   6篇
  1978年   5篇
  1977年   5篇
  1976年   4篇
  1967年   11篇
  1966年   3篇
排序方式: 共有1219条查询结果,搜索用时 0 毫秒
1.
A variation in the bioactivity of different production lots of human menopausal gonadotropin (hMG) has been suggested. Therefore, we evaluated ovarian response to hMG in 14 women during three separate IVF cycles. The first two cycles were performed with the same lot (#03310027; Cycles A1 and A2); the third cycle utilized different lots of hMG (Cycle B). In all cycles, hMG was administered 3 ampules/day beginning cycle Day 3 and continued for at least 6 days. Estradiol and ultrasound evaluations were performed on Day 3, and then daily, beginning on cycle Day 8. Fourteen women completed all three cycles. There were no significant differences in baseline estradiol and ultrasound. Estradiol levels on Day 8 (A1, 754 +/- 130; A2, 700 +/- 107; B, 520 +/- 80 pg/ml, analysis of variance p greater than 0.5) and on Day 9 (A1, 1051 +/- 144; A2, 1140 +/- 155; B, 840 +/- 124 pg/ml, p greater than 0.05) were similar as well. The number of small (1.0-1.4 cm) follicles, large (greater than or equal to 1.5 cm) follicles, and total follicles (Day 8: total A1, 5.5 +/- 0.9; A2, 4.0 +/- 0.7; B, 4.5 +/- 0.9, p greater than 0.05; Day 9: total A1, 6.7 +/- 0.9; A2, 6.9 +/- 0.8; B, 6.9 +/- 0.9, p greater than 0.05) in all three cycles were also similar.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
2.
Human seminal plasma from normal or patients with abnormal parameters of the ejaculates contains an inhibitory material that expresses potent in vitro inhibitory activity on PHA-M-induced blast transformation and NK activity. Using the test of inhibition of NK activity, the semen samples from individuals with higher concentrations of fructose had higher inhibitory activity. The results described herein suggest that inhibitory activity for blast transformation may be present in the prostatic fluid while the NK inhibition aspects are correlated with the vesicle-marker (fructose). Inhibition of the immune responses by human seminal plasma of the effector functions indicates the interesting implication that soluble factors may indirectly protect against or promote human autoimmune infertility disease.  相似文献   
3.
4.
Testosterone biosynthesis was examined in three pairs of twin male Saanen goats. In each pair, one goat was a phenotypically normal male of XY chromosome constitution; the other showed testicular hypoplasia of the sort typically associated with homozygosity for the dominant gene for polledness in genetic females, and was of XX chromosome constitution.
The histological and hormonal situations in the hypoplastic male goats resembled those found in Kleinfelter and XX human males, both in their nature and in their variability. Histological examination of the testes of the hypoplastic XX males showed various degrees of degeneration. In one case a "sperm pocket" full of spermatozoa was observed, and in this case sperm cells with heads separated from tails were observed in the semen. In the other two cases semen was devoid of sperm cells. In two cases plasma testosterone levels of the hypoplastic goats were lower than those of their normal counterparts, in one of the cases much lower. When testicular microsomal fractions of these goats were tested for their in vitro ability to bring about the conversion of androstenedione to testosterone, it was observed that 17β-hydroxysteroid dehydrogenase activity was either absent or lower in the hypoplastic goats than in their normal twins. In the third pair of animals, plasma testosterone levels were similar in both normal and hypoplastic animals. In this case, however, the increase in testosterone levels following HCG administration was lower in the hypoplastic than in the normal goats. 3β-hydroxysteroid dehydrogenase was the same in normal and hypoplastic goats. The variable effects on testosterone biosynthesis support the notion that the sex chromosomes, while affecting steroid biosynthesis in the testis, do so indirectly.  相似文献   
5.
Primary infertility is a key issue in the developed world, while the developing world has high rates of secondary infertility. The impact of HIV/AIDS on fertility is insufficiently explored. One of the most important barriers to access to infertility treatment is cost; at the same time the role of social and cultural factors in restricting access should not be underestimated. IVF has become the standard therapy for female infertility, and ICSI for infertility of the male partner. However, the use of these therapies should not be initiated without a thorough investigation and, whenever possible, individual diagnosis of the underlying causes of infertility. Multiple gestation remains one of the most challenging and controversial issues in the treatment of infertility. Current IVF practices are often blamed for this; in this respect, attention should also be focused on the role of ovarian stimulation in ovulation induction. National guidelines and national registries for assisted reproductive technology (ART) are becoming more widespread and are expected to play an important role in promoting best practice in ART in the future.  相似文献   
6.
BACKGROUND: Laparoscopic cholecystectomy is now used in the management of acute cholecystitis. Under these circumstances unfavorable conditions may result in conversion and complications. Information about these conditions may help in planning the laparoscopic approach or in proceeding directly to open cholecystectomy. This study was initiated to evaluate perioperative factors associated with conversion and complications of laparoscopic cholecystectomy in acute cholecystitis. Special attention was paid to the duration of complaints until surgery, to the delay on the part of the patient, and to the delay on the part of the physician. METHODS: Between January 1994 and December 1997, we attempted to perform laparoscopic cholecystectomy on 348 patients with acute cholecystitis. All perioperative data were collected on standardized forms. RESULTS: There were 182 cases (52%) of acute uncomplicated cholecystitis, 90 (26%) of gangrenous cholecystitis, 33 of hydrops (9.5%), and 43 of empyema of the gallbladder (12.5%). Seventy six patients (22%) needed conversion to open cholecystectomy and complications occurred in 57 cases. Advanced cholecystitis was associated with significant patient delay (P = 0.01), and it had a significantly higher conversion rate (39%) compared with early cholecystitis (14.5%); (P <0.00001). Conversion rates were also associated with male gender (P = 0.0017), a history of biliary disease (P = 0.0085), and a patient delay of >48 hours (P = 0.028). The total and infectious complication rates were associated with an age older than 60 years (P = 0.023 and 0.007, respectively) and male gender (P = 0.026 and 0.014, respectively). CONCLUSIONS: In acute cholecystitis, patient delay is associated with a high conversion rate. Early timing of laparoscopic cholecystectomy tends to reduce the conversion rate, as well as the total and the infectious complication rates. Male gender, a history of biliary disease, and advanced cholecystitis are associated with conversion. Male and older patients are associated with a high total and infectious complication rates.  相似文献   
7.
The use of a large synthetic mesh for laparoscopic repair of significant ventral abdominal wall defects may be accompanied by technical difficulties resulting from improper orientation and positioning of the mesh over the defect. We suggest a technique based on initial fixation of the mesh center to the central point of the defect, and subsequent centrifugal attachment of the mesh to the abdominal wall. This technique is advantageous because it leads to precise orientation and positioning of the synthetic patch and to significant reduction of the time needed for its reinforcement over and around the defect. Received: 25 September 1998/Accepted: 27 November 1998  相似文献   
8.
9.
Purpose: Carbogen has long been under investigation as an adjuvant to radiotherapy of tumors. A major factor confounding its evaluation is its inconsistency in raising blood partial pressure of CO2 (pCO2). We investigated whether a new partial rebreathing method would provide better control of pCO2 than carbogen.

Methods and materials: We compared the efficacy of each method in 10 healthy volunteers. Volunteers breathed 1.5, 3 and 5% carbogen in 5-min stages via the usual non-rebreathing circuit. All the volunteers then breathed 100% O2 through a commercial sequential gas delivery (SGD) circuit modified by attaching a reservoir to its exhalation port. Hypercarbia was induced by step reductions in oxygen flow to the SGD circuit. We monitored minute ventilation and end-tidal pCO2 (ETpCO2) as a surrogate for its arterial value.

Results: Inhalation of 1.5 and 3% carbogen did not increase ETpCO2 from baseline (40 ± 1.5 mmHg); 5% carbogen increased ETpCO2 to 45 ± 1.6 mmHg (p < 0.001). With the SGD circuit, reducing O2 flow to 4.3 ± 0.7 l/min increased ETpCO2 in all subjects from 41 ± 2.0 mmHg (baseline) to 46 ± 2.1 mmHg (p < 0.001). Voluntary hyperventilation reduced ETpCO2 with 5% carbogen but not with SGD (p = 0.379).

Conclusions: We confirm previous observations that carbogen inhalation does not result in a predictable rise in ETpCO2 and suggest that a precise and stable target ETpCO2 can instead be induced by simply controlling O2 flow into a modified SGD circuit. We hoped that the reliable control of pCO2 will enable studies that address first, the efficacy of raising ETpCO2 on specific tumor blood flow, and eventually, its benefit as an adjuvant to radiotherapy.  相似文献   
10.
Liver diseases and regeneration are associated with hemodynamic changes denoting pathological alterations. Determining and monitoring physiological and pathological liver changes is essential for diagnostic and therapeutic objectives. Our aim was to determine the feasibility of functional magnetic resonance imaging (fMRI) during hypercapnia and hyperoxia for monitoring liver pathology. Liver fMRI images were acquired in rodents following acute bleeding, partial hepatectomy, and fibrosis. Results were quantitated and confirmed by histology. Changes induced by hyperoxia and hypercapnia following hemorrhage significantly correlated with the percentage of blood loss, reflecting lower liver perfusion and diminished vessel responsiveness to gas saturation. Hepatectomy resulted in an early decline in signal intensity changes due to hyperoxia, suggesting a decrease in liver perfusion and blood content. Following hepatectomy, signal intensity changes due to hypercapnia increased, signifying a change in liver perfusion from a mainly portal to a more arterial source. Two weeks after induction of fibrosis, signal intensity changes due to hypercapnia became much lower and those due to hyperoxia were much higher than those in normal livers, reflecting the increased perfusion due to the inflammatory process as confirmed by histologic analysis. With fibrosis progression, signal intensity changes induced by hypercapnia and hyperoxia were gradually attenuated, indicating structural and functional alterations of the liver vasculature during fibrosis. CONCLUSION: In various liver pathologies, fMRI response to hypercapnia and hyperoxia is sensitive to changes in liver hemodynamic status involved in hepatic damage or recovery; thus, this technique may offer an additional noninvasive diagnostic tool for evaluation and follow-up of liver diseases by means of examining perfusion-related alterations.  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