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   47124篇
  免费   3151篇
  国内免费   66篇
电工技术   301篇
综合类   130篇
化学工业   10575篇
金属工艺   888篇
机械仪表   955篇
建筑科学   1426篇
矿业工程   112篇
能源动力   1136篇
轻工业   9096篇
水利工程   513篇
石油天然气   275篇
武器工业   4篇
无线电   1972篇
一般工业技术   7383篇
冶金工业   9054篇
原子能技术   208篇
自动化技术   6313篇
  2024年   76篇
  2023年   397篇
  2022年   778篇
  2021年   1521篇
  2020年   1126篇
  2019年   1246篇
  2018年   1893篇
  2017年   1857篇
  2016年   1943篇
  2015年   1427篇
  2014年   1895篇
  2013年   3783篇
  2012年   3015篇
  2011年   2892篇
  2010年   2340篇
  2009年   2126篇
  2008年   2038篇
  2007年   1809篇
  2006年   1349篇
  2005年   1078篇
  2004年   1005篇
  2003年   960篇
  2002年   810篇
  2001年   626篇
  2000年   530篇
  1999年   625篇
  1998年   3077篇
  1997年   2042篇
  1996年   1300篇
  1995年   702篇
  1994年   582篇
  1993年   594篇
  1992年   211篇
  1991年   176篇
  1990年   148篇
  1989年   161篇
  1988年   175篇
  1987年   162篇
  1986年   133篇
  1985年   157篇
  1984年   122篇
  1983年   89篇
  1982年   99篇
  1981年   127篇
  1980年   123篇
  1979年   60篇
  1978年   62篇
  1977年   203篇
  1976年   392篇
  1973年   56篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
111.
112.
In this study chick embryo optic cups at HH stage 13 of development were analyzed under normal conditions and after inoculation with colchicine for 1, 2, 4, and 8 h. Several changes were seen after these periods of treatment: 1) modifications of the structure, with thicker regions in the cup and a general decrease in the total volume according to the duration of exposure to the drug (about 4 times less than normal, 5,035 x 10(3) microns 3 vs 1,334 x 10(3) microns 3 after 8 h of treatment); 2) enlargement of the ventricular cavity and its closure, due to failure of approximation of retinal and pigmentary layers; 3) failure of lens development, with delay and impairment of pit formation and deformation of all structures; lens volume was less than normal (about 4 times less, 2,148 x 10(3) microns 3 vs 658 x 10(3) microns 3 after 8 h of treatment); 4) a general segregation of the cells making up the structure, principally in the more active proliferating zones. The local alterations found are described.  相似文献   
113.
114.
Pericardial effusion (PE) as a hypothyroidism associated sign, is something that can be found with relative frequency; nevertheless, cardiac tamponade (CT) as the first sign of this disease may be considered exceptional especially in young patients. We report a 31 years old woman with clinical symptoms and signs of CT that in the forward workshop was diagnosed of primary hypothyroidism as cause of the CT. We shortly describe the case and review the literature, emphasizing the importance of the knowledge of CT trigger factors in myxedematous PE, as well as its usual benign evolution with hormonal treatment, without recurrences of the CT after pericardiocentesis is performed. This justify a conservative approach, in spite of the slow resolution of the PE what can take as long as 1.5 years.  相似文献   
115.
116.
Data from the past few years have shown that as caffeine metabolizes solely in the liver, caffeine elimination can serve as a liver function test. We have collected data by monitoring 40 persons with liver diseases (11 chronic alcoholic hepatitis, 24 liver cirrhosis, 5 non-cirrhotic liver disease). Eight subjects served as controls. The patients with liver cirrhosis were classified according to the Child--Pugh scoring system. To determine caffeine elimination blood samples were collected before and at 3, 6, 9 and 12 hours after oral administration of 0.2 g caffeine. Fasting serum caffeine concentration and concentration 12 hours after administration, serum clearance, half life, peak concentration and volume of distribution have been compared. The respective values measured in patients with non-cirrhotic liver diseases did not differ significantly from the controls. The disappearance of caffeine was significantly decreased in cirrhotics. Our results demonstrated a good correlation between impairment of caffeine elimination and assessment of severity of liver disease by the Child--Pugh classification. Measuring serum levels in samples taken 12 hours after caffeine administration is a simple and useful method in the diagnosis of liver diseases at cirrhotic stage.  相似文献   
117.
118.
A review of isolates of Neisseria meningitidis and other laboratory evidence of meningococcal infection was carried out for the period 1990-1995. Thirty-three patients with evidence of meningococcal disease were identified over the six year period. Group B organisms were the most commonly identified, but an increase in Group C has occurred and is almost equal in number. Data from clinical, laboratory and public health sources should be centralized in a National Surveillance Centre.  相似文献   
119.
Reaction of bacterial adhesins with complementary receptors on the surfaces of mucosal respiratory, gastrointestinal and genitourinary cells leads to bacterial adhesion to the human body. This is the first step in the sequence of events leading to infection. It has been observed that subinhibitory concentrations (sub-MICs) of some antibiotics are able to reduce bacterial adhesion. The pharmacokinetic curves of antibiotics show that these sub-MICs are present in tissues during a typical course of therapy. This study investigated the ability of sub-MICs of seven macrolides and four fluoroquinolones to reduce adhesiveness of Staphylococcus aureus to human buccal cells. The literature generally reports data for only one antibiotic at a time. To obtain an overall view of the findings of eleven antibiotics together, the data have been normalized according to the molecular weight of each antibiotic and the dose-effect curves determined.  相似文献   
120.
INTRODUCTION: Even though there are few epidemiological studies evaluating the birth weights of different groups of malformed babies with chromosomal abnormalities, it is widely known that infants with trisomy 18, and to a lesser degree those with trisomy 13 and other chromosomal alterations, have low birth weights. PATIENTS AND METHODS: In this study we present the analysis of the birth weights and gestational ages of a large sample of babies (23,155 malformed and a similar number of nonmalformed babies), separating the different groups of chromosomal anomalies and comparing the weight in the clinical groups of malformed infants. RESULTS: Most of the groups with chromosomal abnormalities present lower birth weights in comparison to the other groups. CONCLUSIONS: The results of our study support the conclusion that the relationship between chromosomal alterations and low birth weight is sufficiently important that such a low birth weight in children with minor or major anomalies should be considered as one more indication to perform chromosomal analysis.  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