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   711190篇
  免费   44844篇
  国内免费   1255篇
耳鼻咽喉   9216篇
儿科学   23288篇
妇产科学   17620篇
基础医学   110486篇
口腔科学   19987篇
临床医学   63887篇
内科学   134628篇
皮肤病学   16176篇
神经病学   49564篇
特种医学   25763篇
外国民族医学   76篇
外科学   104591篇
综合类   14835篇
现状与发展   2篇
一般理论   160篇
预防医学   51443篇
眼科学   16364篇
药学   54026篇
  13篇
中国医学   2374篇
肿瘤学   42790篇
  2019年   5591篇
  2018年   7881篇
  2017年   6139篇
  2016年   6863篇
  2015年   7558篇
  2014年   10278篇
  2013年   15396篇
  2012年   20503篇
  2011年   21491篇
  2010年   12721篇
  2009年   11934篇
  2008年   19995篇
  2007年   21514篇
  2006年   21911篇
  2005年   20449篇
  2004年   19991篇
  2003年   18945篇
  2002年   18457篇
  2001年   36328篇
  2000年   36896篇
  1999年   30378篇
  1998年   7878篇
  1997年   6662篇
  1996年   6969篇
  1995年   6627篇
  1994年   6096篇
  1993年   5589篇
  1992年   22968篇
  1991年   22925篇
  1990年   22309篇
  1989年   22077篇
  1988年   20035篇
  1987年   19418篇
  1986年   18467篇
  1985年   17305篇
  1984年   12697篇
  1983年   10741篇
  1982年   5922篇
  1979年   11519篇
  1978年   8129篇
  1977年   6832篇
  1976年   6594篇
  1975年   7268篇
  1974年   8498篇
  1973年   8141篇
  1972年   7658篇
  1971年   7127篇
  1970年   6877篇
  1969年   6306篇
  1968年   5780篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
Objective. To develop and test a new cerclage wire tightening technique, yielding reproducibly maximal pre-tension, load to failure and minimal elongation to failure of the wire junction.

Design. Laboratory bench study.

Background. Cerclage wire fixation is difficult to perform by hand with reproducible quality and tightening tension, which are required for optimal performance.

Methods. With the new technique, 1, 1.25 and 1.5 mm steel wires were passed through a 9 × 18 mm steel tube, grasped using a modified ASIF wire-tightener and tightened by twisting until spontaneous failure of the wires in the tube. These fixations were compared to wires pre-tightened by hand to controlled high or low pre-tension using the simple twist, the knot twist and twist secured against untwisting, loaded to failure on a testing machine. The tests assessed pre-tension, ultimate failure load and elongation to failure.

Results. Wire twists performed with the new technique were always perfectly symmetrical and may be tightened to maximal pre-tension without weakening of the wire. The twist secured against untwisting combined high stiffness with high failure load.

The knot twist elongates to an unacceptable degree, unlike the secured twist. The simple twist untwists under little tension.

Conclusions. The new technique allows to obtain maximal pre-tension and thus minimal elongation to failure of simple wire twists, without having to worry about breaking the wire at the base of the twist due to over-tightening.Relevance

Cerclage wire fixation is an effective and cheap method to perform osteosynthesis. For adequate performance, maximal pre-tension, symmetrical twisting and high load to failure are necessary. The here presented technique combines all of these pre-requisites in a simple fashion.  相似文献   

942.
Previous research indicates that physical examination cannot diagnose sacroiliac joint (SIJ) pathology. Earlier studies have not reported sensitivities and specificities of composites of provocation tests known to have acceptable inter-examiner reliability. This study examined the diagnostic power of pain provocation SIJ tests singly and in various combinations, in relation to an accepted criterion standard. In a blinded criterion-related validity design, 48 patients were examined by physiotherapists using pain provocation SIJ tests and received an injection of local anaesthetic into the SIJ. The tests were evaluated singly and in various combinations (composites) for diagnostic power. All patients with a positive response to diagnostic injection reported pain with at least one SIJ test. Sensitivity and specificity for three or more of six positive SIJ tests were 94% and 78%, respectively. Receiver operator characteristic curves and areas under the curve were constructed for various composites. The greatest area under the curve for any two of the best four tests was 0.842. In conclusion, composites of provocation SIJ tests are of value in clinical diagnosis of symptomatic SIJ. Three or more out of six tests or any two of four selected tests have the best predictive power in relation to results of intra-articular anaesthetic block injections. When all six provocation tests do not provoke familiar pain, the SIJ can be ruled out as a source of current LBP.  相似文献   
943.
A study of prostaglandins (PGE2 and PGF2) and cyclic nucleotides (cAMP, cGMP) in the blood and gastric mucosa biopsies was carried out. In peptic ulcer the level of cyclic nucleotides in the blood and gastric mucosa was on an increase. The level of prostaglandins increased in the blood and decreased in the gastric mucosa. A decrease in the level of prostaglandins and cAMP in the blood and gastric mucosa was noted in patients with chronic atrophic histamine refractory gastritis with a simultaneous rise of the cAMP level. It was shown that stable stimulation of cyclic nucleotides resulting in an increase of gastric acid production, might cause ulcer development and exacerbation of disease. In patients with chronic atrophic gastritis changes of prostaglandins and cyclic nucleotides as compared to those in patients with peptic ulcer, were contrary.  相似文献   
944.
A 55-year-old man was admitted to our hospital because of myelopathy. He had a history of chronic renal failure due to polycystic kidney disease at the age of 39, being treated by hemodialysis for 9 years with several blood transfusions for the treatment of renal anemia. After cadaver renal transplantation at the age of 48, he discontinued hemodialysis. At 50 years of age, he had pulmonary tuberculosis and tuberculous arthritis of the left elbow joint. He has experienced difficulty in walking since he was 48 years old, with mild dysuria. Gait disturbance gradually aggravated after that, and urinary retention was observed. When he was 55 years old, being human T-cell lymphotropic virus type-1 (HTLV-1)-positive in the serum and cerebrospinal fluid, he was diagnosed as having HTLV-1-associated myelopathy (HAM). As active steroid therapy was unapplicable because of the history of pulmonary tuberculosis and immunosuppression for transplanted kidney, a series of plasma exchanges (PE) was performed with fresh frozen plasma as a replacement fluid. After PE, dyskinesia of the left leg and dysuria subjectively and objectively improved. These results suggest that PE seems to be one of the therapeutic tools for the treatment of HAM.  相似文献   
945.
Background: The effect of an α‐melanocyte stimulating hormone (α‐MSH) analogue (AP214) on experimentally endotoxin‐induced systemic inflammatory response syndrome (SIRS) was studied, because α‐MSH in rodent models has shown promise in attenuating inflammatory response markers and associated organ damage in SIRS. SIRS is associated with considerable morbidity and mortality. Consequently, new treatment modalities are still warranted to address the different aspects of the pathophysiological process. Methods: SIRS was induced by lipopolysaccharide (LPS) (Escherichia coli endotoxin) infusion in anaesthetized Danish Landrace pigs (20–25 kg). The pigs received an α‐MSH analogue (AP214) or saline as a bolus at the initiation of the LPS infusion. The hemodynamic response was registered as well as echocardiographic indices of left ventricular function. Results: The cardiovascular response was recorded together with echocardiographic indices of left ventricular function in control and in intervention animals. AP214 reduced the early peak in pulmonary pressure and pulmonary vascular resistance by approximately 33%. Furthermore, AP214 prevented the decline in left ventricular fractional shortening as observed in the control group. Mean change and standard deviation in fractional shortening (ΔFS) in control group: ‐ 7·3 (4·7), AP214 (low dose): 0·9 (8·2) and AP214 (high dose) 4·1 (6·0), P < 0·05 for both intervention groups versus control. Conclusions: In the porcine model, the peak increase in pulmonary pressure was attenuated, and the LPS‐induced decline in left ventricular function was prevented.  相似文献   
946.
The activity of serum type IV collagen-degrading enzyme was measured in 21 patients with hepatocellular carcinoma, and the changes in the enzyme activity were investigated with respect to metastasis. The activity of serum type IV collagen-degrading enzyme did not increase until tumor invasion to the portal vein and intrahepatic metastasis were clearly detected ultrasonographically. Activities did not increase during the observation period in patients whose tumor grew slowly and did not invade the portal vein. Thus, the enzyme activity increases in relation to the metastasis of hepatocellular carcinoma and may be useful to detect ongoing metastases.  相似文献   
947.
Three separate approaches were applied to examine the general relationship between R, the rate of induction of specific enzymes (mitochondrial alpha-glycero-phosphate dehydrogenase and cytosolic malic enzyme) and q, the fractional nuclear occupancy by triiodothyronine in male Sprague-Dawley rats. Daily 200-microgram injections of triiodothyronine per 10u g body wt for 7 days resulted in saturation of the hepatic nuclear sites and the achievement of an apparent new steady state of enzyme levels. The increase achieved over base-line hypothyroid levels was then compared with the increment over hypothyroid base line characteristic of intact euthyroid animals with 47% of nuclear sites occupied. The maximal theoretical reate of steady-state enzyme induction could be protected on the basis of the observed maximal increase in enzyme activity observed 1 day after the injection of graded doses of hormone and lambda, the known fractional rate of enzyme dissipation. The 24-h dose-response studies were used to generate R as a continuous function of q, both in hypothyroid as well as in euthyroid animals. This approach involved the numerical solution of an ordinary differential equation describing the rate of change of enzyme as a function of R, which was assumed to be uniquely related to q. Results of these analyses indicated that the ratio of the maximal rate of induction of enzyme at full occupancy to the rate of induction under euthyroid conditions assumes a value between 9.0 and 19.5, depending on the precise analytic and experimental approach applied. This value is far in excess of the theoretical ratio 2.13 which on would anticipate if R were linearly related to q and 47% of the nuclear sites occupied under physiological conditions. Thus, the signal for enzyme induction appears to undergo progressjive amplification with increasing nuclear occupancy. Moreover, the curve describing the relationship between R and q appears highly nonlinear throughout (concave upwards). Although the molecular mechanism responsible for amplification is unknown, recognition of this phenomenon may be helpful in understanding tissue effects of thyroid hormone excess. Moreover, the analytic technique for determining R as a function of q may be of general applicability in studying hormonal response systems under nonsteady-state conditions.  相似文献   
948.
A rare sepsis-like hypersensitivity reaction has been observed in persons with human immunodeficiency virus (HIV) after exposure to trimethoprim-sulfamethoxazole. This reaction most commonly occurs on rechallenge with the drug and is manifested by a syndrome resembling bacterial sepsis. The mechanism of this unusual reaction remains unclear. We describe the first case in which this severe hypersensitivity reaction was the initial manifestation of HIV.  相似文献   
949.
Scoring systems provide a means for comparing results, ensuring consistent standards and evaluating changes in therapy. The APACHE II system depends partly on the results of laboratory tests which are not normally available in Central Africa. The aim of this study was to develop a scoring system based only on clinical observations. Six hundred and twenty-four consecutive admissions to the intensive care unit (ICU) were allocated a clinical sickness score (CSS) according to pulse rate, blood pressure, respiration rate, urine output, Glasgow Coma Scale, temperature and age. CSS was significantly associated with outcome, there being no significant difference between actual and predicted outcomes calculated by logistic regression analysis. There was a significant difference between mean scores for survivors and non-survivors in all diagnostic groups except diabetes. The proportional change in score from admission was also significantly associated with outcome on each subsequent day in ICU. The CSS provides an objective measure of illness severity for critically ill patients in Africa.  相似文献   
950.
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