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   27953篇
  免费   1852篇
  国内免费   584篇
耳鼻咽喉   210篇
儿科学   615篇
妇产科学   323篇
基础医学   3590篇
口腔科学   1719篇
临床医学   3965篇
内科学   5015篇
皮肤病学   175篇
神经病学   2033篇
特种医学   2014篇
外国民族医学   3篇
外科学   2853篇
综合类   3168篇
现状与发展   1篇
预防医学   897篇
眼科学   489篇
药学   1841篇
  4篇
中国医学   706篇
肿瘤学   768篇
  2024年   30篇
  2023年   284篇
  2022年   398篇
  2021年   802篇
  2020年   798篇
  2019年   728篇
  2018年   786篇
  2017年   659篇
  2016年   628篇
  2015年   769篇
  2014年   1169篇
  2013年   1503篇
  2012年   1090篇
  2011年   1237篇
  2010年   1027篇
  2009年   1031篇
  2008年   1177篇
  2007年   1237篇
  2006年   1129篇
  2005年   1099篇
  2004年   1065篇
  2003年   944篇
  2002年   946篇
  2001年   925篇
  2000年   746篇
  1999年   683篇
  1998年   709篇
  1997年   707篇
  1996年   660篇
  1995年   650篇
  1994年   580篇
  1993年   464篇
  1992年   454篇
  1991年   376篇
  1990年   330篇
  1989年   295篇
  1988年   259篇
  1987年   229篇
  1986年   200篇
  1985年   287篇
  1984年   203篇
  1983年   145篇
  1982年   184篇
  1981年   147篇
  1980年   135篇
  1979年   96篇
  1978年   86篇
  1977年   86篇
  1976年   79篇
  1974年   38篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
This study was conducted to determine the occurrence of menstrual-linked asthma (MLA) in India in 100 consecutive female asthmatics in the reproductive age group. The patients were required to respond to a questionnaire concerning the relationship between their asthma and the menstrual cycle. Twenty-three patients had subjective perception of deterioration in symptoms of asthma in relation to the menstrual cycle. Ten patients from both groups were also required to maintain a daily peak expiratory flow rate (PEFR) diary for 2 consecutive menstrual cycles. The mean total duration of illness in patients with MLA was significantly longer than in patients without cyclic exacerbation. Cough and breathlessness were also significantly more severe as was the disease. This was evidenced by the more frequent emergency room visits and hospitalizations in these patients. Menstrual-linked worsening of asthma was most common in the premenstrual week (17 patients). In 8 of these 17 patients, this phenomenon continued to occur during the menstrual week also. Interestingly, 1 patient complained of deterioration of asthma 2 days after menstruation was over. Such an observation is yet to be recorded. Fourteen patients reported an increase in symptoms with almost every cycle while 3 had worsening related to specific season only. Sixteen patients often required extra medication during the premenstrual and/or menstrual weeks. A significant association was also observed between severity of premenstrual syndrome and MLA. The mean PEFR values over 2 cycles revealed a significant fall in the morning as well as evening values in the premenstrual and menstrual weeks as compared to the midcycle week in patients with MLA. This fall was maximal in the premenstrual week. Such a fall was not observed in asthmatics without menstrual exacerbation of symptoms. MLA was detected in about a fourth of the female asthmatics in India and it appears to represent a more severe form of the disease. This study also documented that MLA was associated with an increase in airway resistance and was not simply due to an increased perception of symptoms during the premenstrual or menstrual weeks.  相似文献   
92.
为了探讨动脉分支处及小动脉端侧吻合处的血液流动方式,采用微循环电视显微镜成像技术,活体观察大鼠肠系膜微动脉分支区域血液流动方式和红细胞流变行为,研究动脉血流方向的改变对血流方式的影响。实验中观察到,在形态各异的大鼠肠系膜微动脉分支区域血液流态为稳定层流;红细胞通过不规则变形能很好地适应血管腔不同的几何形态,以保持血液流态的稳定。结果表明,微小动脉血流方向的改变未能在分支区域导致湍流发生,小动脉端侧吻合只是人为增加了侧支循环,同样不会导致血流紊乱和增加血栓形成的危险  相似文献   
93.
Summary Changes in regional cerebral blood flow in anaesthetized pigs with an induced focal cerebral contusion were studied before and after two grades of hyperventilation. A reduction in arterial tension of CO2 with 0.70mmHg and a further reduction of 0.55mmHg did not change the CO2 reactivity. Reactivity in both injured and macroscopically normal regions was the same, revealing an average of 39.3% flow change per kPa change in CO2 tension. Regions with low flow after the contusion had an equally big reduction apparently leading to hypoxia because global metabolic rate was unchanged.  相似文献   
94.
Global and regional cerebral blood flow (CBF) were evaluated with single photon emission computerized tomography (SPECT) utilizing both 133Xenon (133Xe) (47 subjects, 47–82 years old) and 99Tc-hexamethylpropyleneamine oxime (99Tc-HMPAO) (27 subjects, 47–80 years old). The 133Xe results showed: among total subjects, no age-related decline in global CBF, but a significant regional decline in the occipital lobe (p < 0.05); among men, significant age-related declines in global, frontal, temporal, occipital and right hemisphere CBF (all p < 0.05); among women, no age-related decline in global or regional CBF. The 99Tc-HMPAO results showed no age-related decline in either global or regional perfusion among total subjects, men or women. These results suggest that age-related global and regional (including frontal lobe) CBF declines do not occur in healthy control subjects after the age of 45 years. However, gender differences in age-related CBF changes warrant further study.  相似文献   
95.
目的 研究易卒中型肾血管性高血压大鼠 (RHRSP)的脑血流 (CBF)自动调节下限及其最低耐受压。  方法 用氢清除法测定RHRSP和正常SD大鼠在不同低血压水平时 ,一侧顶枕交界区皮质和海马的局部CBF(rCBF) ;72小时后计算RHRSP和SD大鼠海马CA1 区神经细胞 (CA1 NC)线粒体的体密度 (Vv)、比表面 (δ)、平均体积 ( V)和数密度 (Nv) ,   结果 正常SD大鼠在平均动脉压 (MABP)为 1 0 67kPa、9 3 3kPa和 8kPa时 ,rCBF值无显著减少。在MABP为 1 0 67kPa时 ,RHRSP的rCBF值显著减少 ;超微结构观察发现CA1 NC无明显缺血改变 ,当MABP为 9 3 3kPa时 ,CA1 NC缺血明显 ;细胞形态分析发现 9 3 3kPa组与 1 0 67kPa组比较 ,前者线粒体的Vv和 V显著增大 ,δ和Nv显著减小。  结论 RHRSP的CBF自动调节下限上移至 1 0 67kPa,并与其最低耐受压十分接近 ,表明RHRSP是一种研究高血压脑血管损害较理想的动物模型  相似文献   
96.
In order to assess the suitability of DNA flow cytometry of fine-needle aspirates for quantiftring spermatogenesis, the results from DNA flow cytometry were compared to histological evaluation of testicular biopsies taken concomitantly from 171 previously maldescended testes. In 137 of 171 cases, sufficient material for flow cytometric as well as histological evaluation was obtained.
Histological analysis of surgical biopsy specimens revealed spermatogenesis including the spermatid stage in 117 of the 137 gonads. In six of the 117 gonads no haploid cells were found using flow cytometry. On the other hand, surgical biopsies failed to reveal spermatogenesis in five cases in which the corresponding aspirates contained haploid cells. Both methods therefore seem equally sensitive in detection of spermatogenesis.
Other types of histological patterns also corresponded to distinct DNA histograms.
Thus, in 11 of 12 cases with Sertoli-cell-only pattern in all tubules, at least 95% of the cells had a diploid DNA content. Furthermore, predominance of tubules with maturation arrest at the primary spermatocyte level corresponded to an increased proportion of tetraploid cells.
When compared to surgical biopsy, DNA flow cytometry of testiclar fine-needle aspirates is a more objective, easy and rapid method, which is more convenient for the patient. This study has indicatedthat DNA flow cytometry is a suitable method of quantitative assessment of spermatogenesis. One of the first target groups might be men with azoospermia. In such men, DNA flow cytometric analysis of fine-needle aspirates and surgical biopsy are apparently of equal sensitivity in detecting gonads with spermatogenesis. We conclude that DNA flow cytometry may become an alternative method for the quantification of spermatogenesis.  相似文献   
97.
目的:观察缺氧及停止缺氧后对大鼠心肌血流量的影响。方法:34只Wistar大鼠,随机分为4组:①平原对照组;②急性缺氧组;③慢性缺氧组;④返回平原组。以放射性生物微球法测定心肌血流量。结果:急性缺氧引起PaO2、心输出量及氧运送量降低,但左、右心室心肌血流量明显增加;慢性缺氧时右心室收缩压、血球压积、血液粘滞性及右心室生理指数明显增加,而心肌血流量接近正常。停止缺氧30d后,上述所有指标均与平原以  相似文献   
98.
In this study, human umbilical vein and human saphenous vein endothelial cells were seeded on glass and exposed to fluid shear in a parallel-plate flow chamber. Cell retention, morphology and migration were studied as a function of shear stress and of adhesion time prior to exposure to shear. Three-hour and 24-h adhesion times gave rise to comparable cell retention values after 2 h of flow for both cell types. Cell retention decreased from 85 to 20% as shear stress increased from 88 to 264 dynes cm−2 (8.8 to 26 Pa). Mean spreading areas decreased after the onset of flow, but subsequently stabilized to plateau values, which were smaller at higher shear stresses. Shape factors increased faster to higher values as cells were exposed to higher shear stresses, without any obvious preference in orientation of the cells with respect to the direction of flow. Migration was unidirectional with flow and linear with time. Migration was faster for cells which had adhered for 24 h than for cells which had adhered for 3 h and was accompanied by the presence of fibrillar structures left behind on the surface upstream of migrating cells. It is concluded that after 3 h adhesion to glass, cells have adhered with an adhesion strength that does not substantially increase during the next 21 h. However, during this time changes in cell-substratum interactions seem to occur judging by the differences in, e.g., migration rates.  相似文献   
99.
Summary A duplex ultrasound system was used to examine the blood flow of the common femoral artery in ten young patients with fractures of the lower extremities. Two patients had fractures of both legs. In eight patients the blood flow in the injuried leg was comparable with that in the not injured leg. The flow alterations were measured on 3–7 different days over a period of 6–224 days after trauma. All patients showed a significant (to twice or three times that before injury) increase in blood flow in the injured leg a few days after trauma and/or operation, whereas the blood flow in the uninjured leg remained the same or even decreased a little. In the case of undisturbed fracture healing the change in blood flow disappeared within 8–12 weeks, corresponding to fracture consolidation. When fracture healing was delayed and/or further operations on the injured leg were necessary, the blood flow was increased for much longer. The hemodynamics of an injured extremity are compared with those reported elsewhere in the literature. The increased demand for oxygen or energy can explain the changes only in part. Another function of the reflective increase in blood flow could be the temperature increase in the extremity.
Doppler-sonographische durchblutungsmessungen der unteren extremität des menschenII. Hämodynamik nach trauma und operation
Zusammenfassung Mittels Doppler-sonographischer Durchblutungsmessung wurde die Hämodynamik der verletzten Extremität an 10 jungen Patienten mit Frakturen der unteren Extremität untersucht. Bei 8 Patienten konnte die Durchblutung des verletzten Beins mit der unverletzten Gegenseite verglichen werden. Die Messungen erfolgten an 3–7 verschiedenen Tagen in einem Zeitraum von 6–224 Tagen nach dem Unfall. An allen verletzten Extremitäten steigt die Durchblutung wenige Tage nach dem Unfall und/oder der Operation deutlich um das 2- bis 3fache an, während die Durchblutung des unverletzten Beins niedrig bleibt. Bei einem ungestörten klinischen Verlauf sinkt die Durchblutung in 8–12 Wochen wieder. Heilungsstörungen und weitere Operationen an dem Bein verzögern diese Normalisierung deutlich. Diese Ergebnisse werden mit anderen Untersuchungen der Literatur verglichen. Ursache und Funktion der hämodynamischen Änderungen könnte u. a. in einer reflektorischen Temperaturerhöhung zu sehen sein.
  相似文献   
100.
为给临床心脏术后监测心淋巴管损伤程度及可能出现的并发症提供参考指标,以手术方法阻断羊心淋巴流并对其血清相关成份进行了测定。实验发现,实验组术后谷草转氨酶(SGOT)、谷丙转氨酶(SGPT)、碱性磷酸酶(AKP)、乳酸脱氢酶(LDH)均有不同程度的增高,以SGOT增高最为明显,术前均值为47.53U,术后2天增至104.20U,高峰出现时间最早,多在术后24小时。血清离子改变中低钾最为突出,血钾在术后2天明显降低(P<0.01),术后7天逐渐恢复,术后14天恢复至术前水平。血清蛋白改变以球蛋白降低、白蛋白/球蛋白比值升高为主。提示心淋巴循环郁滞可导致心肌细胞损伤、毛细血管通透性和结构的改变。不同酶活性的变化对郁滞的敏感度存在着差异。  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