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   7810篇
  免费   100篇
  国内免费   2篇
电工技术   47篇
综合类   1篇
化学工业   834篇
金属工艺   43篇
机械仪表   65篇
建筑科学   100篇
矿业工程   64篇
能源动力   84篇
轻工业   363篇
水利工程   33篇
石油天然气   7篇
无线电   452篇
一般工业技术   682篇
冶金工业   4750篇
原子能技术   43篇
自动化技术   344篇
  2021年   22篇
  2020年   25篇
  2019年   43篇
  2018年   50篇
  2017年   54篇
  2016年   51篇
  2015年   47篇
  2014年   71篇
  2013年   166篇
  2012年   91篇
  2011年   139篇
  2010年   101篇
  2009年   96篇
  2008年   144篇
  2007年   125篇
  2006年   102篇
  2005年   112篇
  2004年   97篇
  2003年   83篇
  2002年   91篇
  2001年   68篇
  2000年   96篇
  1999年   197篇
  1998年   1371篇
  1997年   819篇
  1996年   519篇
  1995年   316篇
  1994年   306篇
  1993年   307篇
  1992年   105篇
  1991年   107篇
  1990年   124篇
  1989年   140篇
  1988年   113篇
  1987年   138篇
  1986年   101篇
  1985年   123篇
  1984年   64篇
  1983年   64篇
  1982年   81篇
  1981年   70篇
  1980年   83篇
  1979年   43篇
  1978年   65篇
  1977年   167篇
  1976年   321篇
  1975年   44篇
  1974年   37篇
  1972年   34篇
  1971年   26篇
排序方式: 共有7912条查询结果,搜索用时 15 毫秒
101.
A review of the experience with 134 consecutive patients with germinal cell testicular neoplasia indicates that definitively accurate staging of the malignancy at presentation is the single most important prognostic factor. Nearly two-thirds of the patients with all types of germinal malignancies survived or died of other causes and the highest survival rates were seen among patients with earlier stages of seminoma. In recent years patients with all types of germinal malignancies of the testis have been treated by radical retroperitoneal lymphadenectomy with enhancement of survivals. Patients with seminoma and non-seminomatous tumors exhibited increased survival rates with node dissection. In 66 consecutive lymphadenectomies the complication rate was less than 14 per cent, with only 1 death related to the operation. Retroperitoneal lymphadenectomy not only affords therapeutic advantage but also provides an opportunity for accurate surgical staging of disease and allows for rational decision relative to additional treatment, radiation therapy or chemotherapy.  相似文献   
102.
Isotropic material can be made to exhibit piezoelectric effects by the application of a constant electric field. For insulators, the piezoelectric strain constant is proportional to the applied electric field and for semiconductors, an additional out-of-phase component of piezoelectricity is proportional to the electric current density in the sample. The two induced coefficients are proportional to the strain-dependent dielectric constant (depsilon/dS + epsilon) and resistivity (drho/dS - rho), respectively. The latter is more important at frequencies such that rhoepsilonomega less than 1, often the case in biopolymers. Signals from induced piezoelectricity in nature may be larger than those from true piezoelectricity.  相似文献   
103.
A case of acute pyelonephritis associated with venous encasement and amputation is described. Although venous encasement and amputation have been considered previously as specific signs of malignancy, it is now clear that these signs are non-specific, occurring also in inflammatory diseases of the kidney.  相似文献   
104.
Sudden infant death syndrome. A prospective study   总被引:1,自引:0,他引:1  
One hundred twenty-five sudden infant death syndrome (SIDS) victims followed up since birth from a large prospective study were compared with matched controls. Some of the future SIDS victims showed evidences of neonatal brain dysfunction including abnormalities in respiration, feeding, temperature regulation, and specific neurologic tests. These abnormalities could not be ralated to events in labor or delivery. A greater proportion of the future victims were mildly underweight for gestational age. The gestations that produced the SIDS victims were characterized by a greater frequency of mothers who smoked cigarettes and had anemia. The demographic profile of SIDS families proved to be indentical to the profile for families with excessive perinatal mortality. Many of the SIDS victims showed a retardation in postnatal growth prior to death.  相似文献   
105.
Based on the hitherto published population data of the human red cell PGM1 and acid phosphatase polymorphisms, the geographical distributions of their gene frequencies were analyzed. As far as the acid phosphatase alleles are concerned, a marked geographical gradient was found as the Pa and Pb alleles showed significant correlations with the mean annual temperatures of the various human biotopes (Pa:r = -0.706; Pb:r = +0.812). Against that, the world distribution of the PGM1 alleles did not show a comparable correlation (PGM1 1:R = +0.063; PGM2 1:R = -0.063). The possible reasons for the distribution pattern of the acid phosphatase alleles are discussed.  相似文献   
106.
As part of a multifactorial computer-assisted study of patients with asthma, the relationship between air pollution, animal dander and asthma symptoms was evaluated. No association was found between four major air pollutants (carbon monoxide, ozone, nitrogen oxides and sulfur dioxide) and asthma symptoms. Patients who owned cats and dogs reported more severe asthma symptoms (p less than .01) than patients who did not own cats and dogs. The evaluations completed to date indicate that daily exposure to cats and dogs accounts for more of the asthma symptoms differences between patients than daily exposure to air pollutants.  相似文献   
107.
When baseline red blood cell catechol O-methyltransferase (COMT) was measured in 15 unipolar depressive women, the authors found a linear correlation between COMT and response to imipramine (best outcome occurring at low COMT). The results of this study were not related to such variables as intensity of depression, family history, or psychiatric history. The authors suggest that this assay may be useful either as a predictor of response to the drug or as a guide in choosing the optimum dose.  相似文献   
108.
To test the hypothesis that regional cerebral blood flow (rCBF) is normally regulated by regional metabolic activity, rCBF and the regional cerebral metabolic rate for oxygen (rCMRO2) were compared in selected human subjects. In normal subjects and patients with chronic, stable diseases of brain, rCBF correlated well with rCMRO2. In one individual with mild dementia, rCBF and rCMRO2 were measured before and during exercise of the hand and forearm contralateral to the hemisphere studied. Appropriate parallel changes occurred in both rCBF and rCMRO2 during hand exercise. In patients with acute diseases affecting the hemisphere studied, however, the correlation between rCBF and rCMRO2 was unpredictable.  相似文献   
109.
Butorphanol (levo-N-cyclobutylmethyl-3, 14-dihydroxy morphinan), a potent analgetic agent of the narcotic antagonist type with a low abuse potential in laboratory animals, was evaluated for antitussive activity in unanesthetized guinea-pigs and dogs. Subcutaneously, it was over 100 times more active than codeine, dextromethorphan and dl-pentazocine and about 20 times more active than morphine in the guinea-pig, while in the dog it was 100, 10 and 4 times more active than codeine, dl-pentazocine and morphine, respectively. Orally, butorphanol was 15-20 times more active than either codeine or dextromethrophan in both species. Naloxone reversed the antitussive effects of butorphanol, codeine, morphine and dl-pentazocine while those of dextromethorphan were not antagonized. The antitussive effect of butorphanol and morphine lasted about 4 hr and both compounds were longer acting than codeine. Butorphanol was also shown to be as effective against cough of pathological origin as against experimentally induced cough in the dog.  相似文献   
110.
Beta adrenergic blockade was studied in vitro with human tracheal muscle strips and guinea pig tracheal chains. It was shown in isolated smooth muscle from both man and guinea pig that the order of potency for the three beta-blocking agents studied was: propranolol greater than sotalol greater than practolol. Under the conditions of this study, propranolol was about 30,000 times and sotalol about 30 times as potent as practolol. The order of potency suggests that the nature of adrenergic blockade induced by practolol on tracheal smooth muscle is only weakly beta2-relative to the blocking effects of propranolol and sotalol. Beta adrenergic blockade by propranolol, sotalol, and practolol produced different degrees of increased histamine lethality in mice. Whereas both propranolol at 0.01 mg/kg and sotalol at 1.0 mg/kg resulted in 100% histamine-induced lethality, practolol at 50 mg/kg resulted in only 50% histamine-induced lethality. These data, when added to those from our previous studies, suggest that the mechanisms responsible for resistance to the effects of histamine in untreated mice are at least partially mediated by the beta2-adrenergic system. Thus, in three different tissues, the blocking activity of practolol was shown to be less than that of sotalol or propranolol.  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