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   9443篇
  免费   716篇
  国内免费   34篇
耳鼻咽喉   78篇
儿科学   340篇
妇产科学   261篇
基础医学   1232篇
口腔科学   121篇
临床医学   1172篇
内科学   1667篇
皮肤病学   164篇
神经病学   977篇
特种医学   239篇
外科学   1190篇
综合类   73篇
一般理论   9篇
预防医学   1165篇
眼科学   125篇
药学   612篇
中国医学   5篇
肿瘤学   763篇
  2024年   15篇
  2023年   100篇
  2022年   148篇
  2021年   347篇
  2020年   216篇
  2019年   330篇
  2018年   388篇
  2017年   245篇
  2016年   257篇
  2015年   310篇
  2014年   411篇
  2013年   544篇
  2012年   812篇
  2011年   802篇
  2010年   426篇
  2009年   361篇
  2008年   605篇
  2007年   624篇
  2006年   557篇
  2005年   524篇
  2004年   400篇
  2003年   352篇
  2002年   307篇
  2001年   93篇
  2000年   91篇
  1999年   66篇
  1998年   83篇
  1997年   56篇
  1996年   41篇
  1995年   33篇
  1994年   36篇
  1993年   32篇
  1992年   72篇
  1991年   54篇
  1990年   46篇
  1989年   43篇
  1988年   26篇
  1987年   23篇
  1986年   36篇
  1985年   27篇
  1984年   27篇
  1983年   24篇
  1982年   14篇
  1979年   16篇
  1978年   17篇
  1977年   13篇
  1975年   12篇
  1974年   19篇
  1968年   12篇
  1967年   13篇
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
1.
2.
The use of multifunctional materials for water remediation is a modern approach where adsorption phenomena and heterogeneous photocatalysis can be applied for the removal of pollutants. Since the ideal remediation system should be able to remove both organic and inorganic pollutants, a crucial aspect to consider is the knowledge of operational parameters affecting the removal process, especially when heavy metal ions are present in concoction as in real systems. Given the proven efficiency of multifunctional TiO2/Alg/FeNPs magnetic beads for the removal of model organic pollutants, this study investigated the possibility to exploit such system also for the removal of mixed heavy metals (MHM), specifically Cr(III), Cu(II), and Pb(II) ions, under ultraviolet irradiation at a wavelength of 254 nm. After a preliminary screening on the optimal catalyst loading, operating parameters such as the initial concentration of metal ions, contact and irradiation time, and pH were investigated to optimize the removal of metal ions using response surface methodology (RSM) via Box–Behnken design. Starting from a MHM solution containing 44 ppm of each metal ion, the removal of Pb(II), Cr(III), and Cu(II) ions in the aqueous solution was nearly completed (>98.4%) for all three ions within 72 min of irradiation at almost neutral pH (pH = 6.8). The stability of TiO2/Alg/FeNPs was confirmed by retrieving and reusing the beads in three consecutive cycles of heavy metals removal without observing significant changes in catalyst efficiency.  相似文献   
3.
4.
5.
6.
OBJECTIVE: Cervical nerve root stimulation (CRS) is a technique of assessing the proximal segments of motor axons destined to upper extremity muscles. Few studies report normal values. The objective was to determine CMAP onset-latencies and CMAP amplitude, area, and duration changes in healthy controls for the abductor pollicis brevis (APB), abductor digiti minimi (ADM), biceps, and riceps muscles. In addition, to determine the tolerability of CRS, as measured by the visual analog scale (VAS). METHODS: We studied 21 healthy volunteers prospectively with CRS using four target muscles (APB, ADM, biceps, and triceps) bilaterally. Collision studies were used in all APB recordings. VAS was obtained in all subjects. RESULTS: Mean CMAP onset-latencies were: APB 14 +/- 1.5 ms; ADM 14.2 +/- 1.5 ms; biceps 5.4 +/- 0.6 ms; triceps 5.4 +/- 1.0 ms. Onset-latency significantly correlated with height for all nerves. The mean change in CMAP amplitude and area (%) between most distal stimulation and CRS was: APB reduction of 15.1 +/- 11.6 and 4.9 +/- 3.6%; ADM reduction of 21.1 +/- 10.7 and 17.2 +/- 8.8; biceps reduction of 10 +/- 11.5 and reduction of 8.7 +/- 6.8; triceps increase of 3.3 +/- 5.2 and 11.0 +/- 9.9% respectively. Mean CMAP duration change between most distal stimulation and CRS was: APB, increase of 20.4 +/- 7.4%; ADM, increase of 14.4 +/- 8.5%; biceps, increase of 13.9 +/- 10.8%; triceps, increase of 7.7 +/- 6.7%. The mean VAS score was 3.8 +/- 1.2, and all subjects completed the study. CONCLUSIONS: The present study establishes normative data and indicates that CRS is a well-tolerated technique. SIGNIFICANCE: The normal values may be used as reference data for the needle CRS technique in the assessment of proximal conduction abnormalities.  相似文献   
7.
Renal transplant recipients suffering from persistent diarrhea have been repeatedly reported to have increased tacrolimus (Tac) trough levels. This study aimed to explore this phenomenon in detail in 15 renal transplant recipients with diarrhea, whose immunosuppression consisted of corticosteroids, mofetil mycophenolate and Tac. Both hepatic and intestinal CYP3A4 and PGP activity, important determinants of Tac bioavailability, were assessed, together with global CYP activity and investigations for gastrointestinal infection, function and morphology. Global CYP, CYP3A4, PGP and trough/dose levels of Tac were compared with diarrhea-free controls. In addition, a pharmacokinetic study of Tac was performed in 11 patients affected by diarrhea versus 9 controls. As expected, diarrhea was associated with increased Tac trough levels. An even stronger, significant increase of dose-normalized Tac levels was observed between 90 and 360 min after Tac intake. Time to peak concentration and drug half-life, however, were not altered. In addition, a concomitant decrease (+/-50%) of intestinal PGP activity was noticed in patients with diarrhea. For global CYP, CYP3A4 and hepatic PGP activity no such differences were noted. This pattern was not influenced by the specific cause of diarrhea. These data strongly suggest that persistent diarrhea is associated with an increased oral bioavailability of Tac.  相似文献   
8.
BACKGROUND: Perfusion functional magnetic resonance imaging (fMRI) was used to investigate the effect of genetic variation of the human serotonin transporter (5-HTT) gene (5-HTTLPR, SLC6A4) on resting brain function of healthy individuals. METHODS: Twenty-six healthy subjects, half homozygous for the 5-HTTLPR short allele (s/s group) and half homozygous for the long allele (l/l group), underwent perfusion functional and structural magnetic resonance imaging during a resting state. The two genotype groups had no psychiatric illness and were similar in age, gender, and personality scores. RESULTS: Compared with the l/l group, the s/s group showed significantly increased resting cerebral blood flow (CBF) in the amygdala and decreased CBF in the ventromedial prefrontal cortex. The effect of functional modulation in these regions by 5-HTTLPR genotype cannot be accounted for by variations in brain anatomy, personality, or self-reported mood. CONCLUSIONS: The 5-HTTLPR genotype alters resting brain function in emotion-related regions in healthy individuals, including the amygdala and ventromedial prefrontal cortex. Such alterations suggest a broad role of the 5-HTT gene in brain function that may be associated with the genetic susceptibility for mood disorders such as depression.  相似文献   
9.
Epidemiologic studies have demonstrated that trans fat intake increases the risk of some chronic diseases. We hypothesize that trans fat intake would increase the risk of cardiovascular disease and type 2 diabetes mellitus by changing the lipid profile in plasma, the secretion of adipokines in adipose tissue, and the insulin sensitivity. Accordingly, the major objective of present study was to investigate the effect of dietary intake of trans fat on lipid profile, insulin sensitivity, and adipokine levels in plasma. Two groups of Wistar rats were fed a diet containing 4.5% trans fat or a control diet containing no trans fat for 16 weeks. Fasting glucose level was monitored every 2 weeks. At the end of feeding experiment, blood, heart, kidney, liver, omental adipose tissue, and semitendinosus muscle were collected. The trans fat content in organs, lipid profile, adipokine, insulin, and glucose levels in plasma were analyzed. The trans fat content in adipose tissue, heart, kidney, liver, and muscle of rats fed trans fat were 169.9, 0.6, 1.2, 1.7, and 2.5 mg/g samples, respectively. The trans fat content in these organs contributed to 15.9%, 1.2%, 2.3%, 4.3%, and 6.1% of the total fat, respectively. The plasma glucose level, insulin level, and insulin sensitivity index were not significantly different between the trans fat and control groups. The results indicated that trans fat intake might not be related to insulin resistance. However, lipid profile and plasma adipokine levels were significantly changed after trans fat feeding. The trans fat fed group showed significantly lower total cholesterol and high-density lipoprotein cholesterol levels than the control group. The decreased high-density lipoprotein cholesterol level may indicate the detrimental effect of trans fat intake on lipid profile. Adiponectin and resistin levels were significantly higher in the trans fat group than the control group. Leptin levels were significantly lower in the trans fat group than the control group. The results indicated that dietary intake of trans fat can significantly change the adipokine levels, but the possible links between adipokine level change caused by trans fat intake and metabolic effects of this change need further investigations.  相似文献   
10.
Incisional hernias occur in up to 17% of patients after liver transplantation. Laparoscopic ventral hernia repair is associated with fewer wound complications and a decreased incidence of recurrence when compared to open hernia repair in nontransplant patients. This is a retrospective review of 13 patients who underwent laparoscopic incisional hernia repair (LAP group) after liver transplantation compared to 14 patients who had open repairs (OP group; all but one with mesh). Primary immunosuppression in both groups at the time of transplantation was tacrolimus, but more patients in the LAP group were on sirolimus at the time of hernia, while more patients in the OP group were on prednisone at the time of hernia repair. All operations were completed with a laparoscopic approach; there were no conversions to open. Length of stay differed significantly between the 2 groups, with a mean of 5.4 days for the LAP group compared to 2.7 days in the OP group (0.0059). Complications occurred in 2 (15%) of the patients in the LAP group and 5 (36%) in the OP group. One patient in the LAP group required mesh removal to exclude causes of recurrent ascites, and 1 in the OP group for mesh infection. One (7.6%) of the patients in the LAP group developed a recurrence, compared to 29% (4) of the OP group (P =0.3259). In conclusion, laparoscopic incisional hernia repair is safe in patients after liver transplantation, with a low risk of infection or recurrence.  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