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   16479篇
  免费   1339篇
  国内免费   305篇
耳鼻咽喉   125篇
儿科学   392篇
妇产科学   280篇
基础医学   1677篇
口腔科学   220篇
临床医学   2280篇
内科学   2893篇
皮肤病学   92篇
神经病学   1112篇
特种医学   1319篇
外国民族医学   1篇
外科学   2157篇
综合类   1733篇
预防医学   686篇
眼科学   164篇
药学   1278篇
  11篇
中国医学   335篇
肿瘤学   1368篇
  2024年   27篇
  2023年   299篇
  2022年   474篇
  2021年   851篇
  2020年   796篇
  2019年   697篇
  2018年   718篇
  2017年   615篇
  2016年   576篇
  2015年   578篇
  2014年   1125篇
  2013年   1100篇
  2012年   829篇
  2011年   986篇
  2010年   746篇
  2009年   800篇
  2008年   705篇
  2007年   739篇
  2006年   609篇
  2005年   502篇
  2004年   433篇
  2003年   342篇
  2002年   275篇
  2001年   260篇
  2000年   212篇
  1999年   199篇
  1998年   202篇
  1997年   199篇
  1996年   170篇
  1995年   164篇
  1994年   160篇
  1993年   154篇
  1992年   143篇
  1991年   111篇
  1990年   130篇
  1989年   117篇
  1988年   122篇
  1987年   78篇
  1986年   93篇
  1985年   102篇
  1984年   102篇
  1983年   82篇
  1982年   106篇
  1981年   64篇
  1980年   42篇
  1979年   50篇
  1978年   52篇
  1977年   44篇
  1976年   42篇
  1975年   22篇
排序方式: 共有10000条查询结果,搜索用时 40 毫秒
71.
用放射免疫法测定产后40天和60天乳母血清泌乳素基础水平和吸吮后泌乳素最大反应性增值,发现其与乳母泌乳量、婴儿吸吮频率、吸吮时间之间均不存在正相关关系,推测引起泌乳素分泌除吸吮外,还存在其他机理。  相似文献   
72.
Twenty-four mongrel dogs were anaesthetized and ventilated mechanically in the supine position. Extravascular lung water (EVLW) and central blood volume (CBV) were measured with a double indicator (dye/cold) dilution technique. Both indicators were detected intravascularly in the aortic root with a fibreoptic thermistor catheter. Seven dogs ventilated with a positive end-expiratory pressure (PEEP) of 1.0 kPa (10 cmH2O) for a short period of time (less than 20 min) displayed no significant change in EVLW as measured with the indicator dilution technique (= EVLWi), while reductions were seen in both CBV (15%, P less than 0.01) and cardiac output (CO-thermodilution technique) (10%, P less than 0.05). Another seven dogs ventilated with a PEEP of 1.0 kPa for 8 h showed a gradual increase in EVLWi. After 8 h, a mean increase of 34% (P less than 0.01) was recorded, and the increase was also verified by post-mortem gravimetric determination of EVLW (= EVLWg), displaying an increase of 61% (P less than 0.01). In five dogs ventilated with zero end-expiratory pressure (ZEEP) for 8 h, no changes in EVLWi, CO, and CBV were observed, and EVLWg was mean 4.39 g/kg body weight (BW). Five additional dogs were sacrificed after 15 min of anaesthesia without catheterization and EVLWg was found to be 4.24 g/kg BW. It is concluded that EVLWi does not change measurably during ZEEP or short periods of PEEP. However, long periods (8 h) of PEEP result in elevated EVLWi values. Gravimetry supports these conclusions.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
73.
目的 :用彩色速度显像定量 (CVI Q)技术测定颈动脉血流量并给出青年组正常参考值。方法 :应用传统的多普勒法及CVI Q法对正常 5 0名在校四年级大学生进行左、右颈总动脉血流量的测定比较。结果 :单侧颈总动脉血流量传统法测定为 (789.49± 15 3 .40 )ml·min-1,CVI Q法为 (3 92 .85± 63 .95 )ml·min-1,两者有显著性差异 (P <0 .0 0 1) ,男女之间、左右之间无明显差异 ,S/D、RI和PI 3组数据两两之间亦无显著性差异。结论 :CVI Q是一种实用、无创、简便、可靠的测量方法 ,具有良好的临床应用价值  相似文献   
74.
75.
M. Sekimoto  M. Fukui  & K. Fujita 《Anaesthesia》1997,52(12):1166-1172
We studied seven analytical methods of estimating the plasma volume from the decay curves of indocyanine green. Fifteen volunteers received 1.0 mgkg−1 of the dye by intravenous injection and the plasma concentration was measured continuously using spectrophotometry. Plasma volumes were calculated using three single-regression methods (1-a, 1-b, 1-c) and four biexponential regression methods (2-a, 2-b, 2-c, 2-d). The means (SD) of 1-a, 1-b and 1-c were 39 (5.0), 44 (5.7) and 54 (11.5) mlkg−1, respectively, and these were significantly different from each other (p < 0.05). The values for methods 2-b, 2-c and 2-d were similar to each other: 39 (4.6), 40 (4.1) and 40 (4.0) mlkg−1, respectively. These required more than 3 min circulation or mixing time. When the time allowed for mixing was less than 3 min (method 2-a) the plasma volume was underestimated. We conclude that plasma volume estimation using indocyanine green and spectrophotometry is most accurate when the mixing time is adequate (3–5 min) and the decay curves are analysed using biexponential regression.  相似文献   
76.
Summary. The aim of the present study was to establish a more differentiating indicator of plasma membrane integrity of spermatozoa than the classic version of the hypoosmotic swelling test according to Jeyendraan. Spermatozoa were prepared by density gradient centrifugation (90% Percoll) to select 'fertilization competent' spermatozoa only. After a second washing procedure sufficiently pure sperm cell suspensions were obtained. The volume distributions of these sperm cells were measured with a Coulter Counter at 25 °C after adaptation in 300 mosmolar NaCl solution resp. 150 mosmolar NaCl solution for 5 min. These volume distributions showed significantly different patterns for the isotonic and hypotonic stress situation in the simple salt solution. Moreover, the comparison of the response to hypoosmotic stress showed more than four reproducible characteristic patterns, promising well differentiated results for different sperm populations. The new method for the detection of hypoosmotic swelling effect might be a real and valuable functional parameter.  相似文献   
77.
McConaghy (1989) argued that the validity of penile circumference responses (PCRs) is at best unestablished and that penile volume responses (PVRs) have been demonstrated to be clearly superior indices of sexual arousal and orientation. In his critique, McConaghy stated that (i) penile erection has been incorrectly identified with sexual arousal, (ii) that PCRs have not been shown to accurately discriminate between divergent patterns of sexual arousal (including paraphilias), (iii) that the methodologies used to compare the two types of transducers are inappropriate, and (iv) that PCRs should not be used for diagnostic and treatment decisions. In this paper, McConaghy's criticisms are reviewed in the context of the existing literature on the subject. Although PCRs and PVRs involve different methodologies, they generally yield results that bear more similarities than differences. Furthermore, there is an extensive and growing literature on the use of PCR measures with various paraphilias. Several of McConaghy's arguments should be considered tentative while others are clearly unsubstantiated. Most of McConaghy's concerns over the validity and uses of PCR measures are empirical questions. Suggestions for future research are offered.  相似文献   
78.
目的 探讨维汉民族前列腺增生患前列腺的体积、症状积分和膀胱排尿症状的相关性。方法 对71例住院手术的维汉不同民族前列腺增生症(BPH)患进行国际前列腺症状评分(BPSS),生活质量评分(L),前列腺体积(V),重量(M),患年龄(age),尿流动力学指标的直线相关分析。结果 40例汉族及31例维族BPH患的前列腺体积与膀胱颈压,膀胱颈压与膀胱顺应性,最大尿流率与膀胱顺应性均呈正相关。结论 最大尿流率、前列腺体积、膀胱顺应性、膀胱颈压四个参数不但能了解膀胱排尿功能和形态改变,也可做为临床上手术切除增生前列腺组织,解除梗阻,缓解症状,评价治疗效果的指标。  相似文献   
79.
The aim of this study was to evaluate the contribution of a low calcium diet to the cortical and trabecular osteoporosis seen in ovariectomized rats after 7 weeks on a low calcium diet and to investigate the effects of the bisphosphonate clodronate on this development of osteoporosis. Thirty-six mature, female Wistar rats were randomized into four groups: Ovx−B (bisphosphonate) and Ovx−C (control) were ovariectomized, and Sham−Ca (low calcium) and Sham+Ca (normal calcium) were sham operated. The first three groups were fed a low calcium diet (0.01%) and Sham+Ca normal rat chow (Ca 1.1%). The Ovx−B received 10 mg/kg s.c. clodronate daily for nine weeks, and Ovx−C, Sham−Ca, and Sham+Ca received the same volumes of saline. Bone mineral turnover measured as 85Sr-uptake was increased in all low calcium groups compared to Sham+Ca. The Sham+Ca femora had higher dry weight and ash weight than the other groups, and Ovx−C had higher dry weight compared with Ovx−B and Sham−Ca. Calcium content was lower in both Ovx groups compared to both Sham groups. Magnesium was lower in all groups compared to Sham+Ca and higher in Ovx−B compared with Ovx−C. In the femoral shaft, Sham+Ca had significantly higher ultimate bending moment, energy absorption, and deflection compared to the other three groups. Ultimate bending moment was higher in Sham−Ca than in Ovx−C. Stiffness was increased in both Sham+Ca and Ovx−B compared to Ovx−C. The maximum stress in the femoral midshaft was higher in Sham+Ca than in the other groups, and higher in Ovx−B than in Ovx−C. Histomorphometry showed increased medullary area in all low calcium groups compared to Sham+Ca and larger cortical area in Sham+Ca and Ovx−B compared to Ovx−C. Compared to Sham+Ca the trabecular bone volume was decreased to 30% in Sham−Ca and to 9% in Ovx−C, but was unchanged in Ovx−B. The low calcium diet generally increased bone mineral turnover and reduced the tibial bone volume. Femoral changes led to a reduction of cortical fracture strength and maximal stress. Ovariectomy in addition to a low calcium diet reduced femoral strength even more. Daily injections of clodronate to ovariectomized rats on a low calcium diet increased femoral shaft stiffness and maximum stress, and clodronate preserved both trabecular and cortical tibial bone volume completely. Received: 11 June 1996 / Accepted: 5 March 1997  相似文献   
80.
Assuming that type I atrial flutter is a macroreentrant circuit, its cycle length should vary with the atrial dimensions. In order to test this hypothesis, flutter cycle length was measured while inducing atrial volume and pressure changes by postural and pharmacological means in seven patients undergoing a therapeutic programmed stimulation for type 1 atrial flutter conversion. Right atrial volume was estimated from B-mode echocardiography data. Basal values were compared with those obtained during inspiration, expiration, Valsalva maneuver, negative tilt (head down), and positive tilt (head up) with 0.8–1.6 mg p.o. nitroglycerin. The right atrial size increased slightly from 17.8 to 18.3 cm2 (P = 0.04) during the pressure load induced by negative tilt (+ 3 mmHg), with a corresponding lengthening of the flutter cycle length from 228 to 233 msec (P = 0.02). Similarly, pressure unloading of -2 mmHg by positive tilting and nitrates was accompanied by a decrease in right atrial size to 16.6 cm2 (P = 0.04), with a corresponding decrease in cycle length from 228 to 219 msec (P = 0.03). Respiratory maneuver yielded similar results with an inspiratory cycle lengthening, expiratory shortening, and further shortening during Valsalva maneuver. These experiments demonstrate a direct relation between cycle length and atrial volume in human type I atrial flutter. They underline the importance of the right heart preload and atrial size for the electrophysiological characteristics of type I atrial flutter. Beside its fundamental interest, this finding is important for the understanding of the mechanism of maintenance and therapeutic responses of this common arrhythmia.  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