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   8631篇
  免费   818篇
  国内免费   586篇
电工技术   860篇
综合类   660篇
化学工业   1312篇
金属工艺   543篇
机械仪表   519篇
建筑科学   548篇
矿业工程   222篇
能源动力   245篇
轻工业   1170篇
水利工程   225篇
石油天然气   138篇
武器工业   80篇
无线电   733篇
一般工业技术   761篇
冶金工业   643篇
原子能技术   194篇
自动化技术   1182篇
  2024年   38篇
  2023年   95篇
  2022年   265篇
  2021年   354篇
  2020年   225篇
  2019年   224篇
  2018年   215篇
  2017年   247篇
  2016年   232篇
  2015年   319篇
  2014年   440篇
  2013年   555篇
  2012年   673篇
  2011年   669篇
  2010年   589篇
  2009年   613篇
  2008年   631篇
  2007年   534篇
  2006年   489篇
  2005年   433篇
  2004年   354篇
  2003年   299篇
  2002年   291篇
  2001年   250篇
  2000年   180篇
  1999年   96篇
  1998年   144篇
  1997年   103篇
  1996年   56篇
  1995年   40篇
  1994年   60篇
  1993年   52篇
  1992年   23篇
  1991年   15篇
  1990年   23篇
  1989年   20篇
  1988年   16篇
  1987年   9篇
  1986年   11篇
  1985年   15篇
  1984年   11篇
  1983年   11篇
  1982年   16篇
  1981年   8篇
  1980年   10篇
  1979年   6篇
  1977年   11篇
  1976年   19篇
  1975年   7篇
  1974年   7篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
952.
To search the relationships between urinary albumin excretion and blood vessel lesion in non-insulin-dependent diabetics, we compared the differences of blood-lipid, blood pressure, coronary heart disease and retina disease between 58 patients. The group with microalbuminuria had significantly lower concentration of apolipoprotein A, and apolipoprotein A1/apolipoprotein B100 than that of the group with normal albuminuria, but there was no significant change in concentrations of trigly cerides, total cholesterol, high density lipoprotein, and apolipoprotein B100. Coronary heart disease and retina disease were significantly increased in group with microalbuminuria. There was negative correlation with apolipoprotein A1 and value of apolipoprotein A1/apolipoprotein B100, but positive correlation with systolic blood pressure by linear regression analysis for urinary albumin excretion.  相似文献   
953.
Studies of severe hypoxemic events, defined as an arterial oxygen saturation < 80% greater than 4 s in spontaneously breathing infants, have been limited. The purpose of our study was to examine the distribution of respiratory events that lead to a fall in oximetrically measured oxygen saturation by using breathing patterns, heart rate, and validated pulse oximetry analysis. A total of 161 hypoxemic events were detected in 18 of 30 premature infants studied. Using an inductive plethysmographic based monitor, a total of 460 h of cardiorespiratory monitor recordings were analyzed. Hypoxemic events were categorized as being the direct result of apnea (duration longer than 15 s) or pauses (duration 4-14 s) with either unchanged or lower end-expiratory lung volumes compared with the preevent breaths. The breaths in the preevent period were analyzed for volume, timing, and thoracoabdominal coordination indices. Forty of the 161 events (25%) were associated with apnea of which 80% (31/40) had a mixed/obstructive basis. Ninety-four of the 161 severe hypoxemic events (58%) were associated with pauses with unchanged end-expiratory lung volume. Twenty-two of the 161 events (14%) showed pauses with lower end-expiratory lung volume. There were 5/161 events (3%) with severe hypoxemia in which no pause was observed. Comparison of the preevent periods in each category showed significant differences for only percent tidal volume from initial calibration and arterial oxygen saturation. Sixty-two percent (100/161) of severe hypoxemic events were preceded by hypopneic values of percent tidal volume. Seventy-five percent (40/161) of these hypoxemic events and their etiology would have gone undetected using respiratory monitoring from impedance pneumograms and ECGs. The varied basis for these events underscores the importance of analyzing detailed respiratory wave forms along with movement-free signal of arterial oxygen saturation and ECG, to formulate appropriate intervention strategies.  相似文献   
954.
BN纤维补强ZrO_2材料的显微结构   总被引:1,自引:0,他引:1  
研究了 BN 纤维补强 ZrO_2 材料中显微结构及界面特性,BN 纤维与 ZrO_2基体之间有一扩散区,经烧结后复合材料中 BN 以多晶形式存在。在 BN 纤维内扩散入较多 Y_2O_3 和 SiO_2,这些组分在纤维内形成玻璃相。聚集在 ZrO_2之间的 BN 形成细长结晶体,该晶体内有较多刃位错和反相畴区域。与 BN 相邻的 ZrO_2仍为四方相。  相似文献   
955.
阮文忠 《山西建筑》2005,31(15):39-40
对小半径预应力混凝土曲线侨的受力特点进行了简要分析,并通过工程实例,从桥跨选择、支座设置、预应力钢索设计等多方面,提出了设计中的一些细节的处理方法。  相似文献   
956.
现代战争中导弹和导弹系统在战场中都将受到各种电子干扰 ,导弹系统中的雷达在受噪声等干扰后 ,可能导致各种参数测量误差的增大、发现概率的降低等。研究地空导弹系统中的雷达在受噪声干扰情况下 ,其发现概率、测角精度、测距精度等所受的影响  相似文献   
957.
长江口深水航道的选择及其治理原则   总被引:3,自引:0,他引:3       下载免费PDF全文
在长期系统研究的基础上,分析对比了长江口的水流动力、泥沙运动和河床演变等各种条件,选择了北槽作为长江口深水航道先予治理,确立了符合长江口实际情况的治理原则.长江口深水航道一、二期治理工程的实施,已取得了良好的治理效果和巨大的经济效益.  相似文献   
958.
阮一凡  白晓东  周洪直 《微波学报》2005,21(Z1):130-133
针对现代通信中线性功率放大器的补偿要求,介绍一种利用反射理论设计可调移相器,实现大范围移相,同时幅度波动很小,并详细讨论了它的工作原理和实验结果。  相似文献   
959.
Electricity sector has grown substantially in Turkey since the early 1960s as a result of rapid industrialization and urbanization. The vertically integrated state-owned company had a legally established monopoly on the generation, transmission and distribution of electricity in Turkey. With the support and encouragement of international organizations like the World Bank, Turkey has initiated a comprehensive program to liberalize and privatize the electricity market in 2001. The liberalization of the electricity market in Turkey started in the distribution side of the market. The distribution network was divided into 21 distribution regions and in each of these, separate – initially state-owned – distribution companies have been authorized to distribute and sell electricity. The plan envisaged to complete privatization of all distribution companies until the end of 2006. This study compares the welfare implication of privatization of the distribution networks by comparing two extreme cases, a pure regional distributional monopoly case and a representative pure “free” consumer case, with a benchmark case of administered price regulation. For this purpose, we develop a simulation model of the Turkish electricity system, and use the data on generation and distribution costs. Our simulation analysis shows that substantial welfare losses occur if the distributional companies behave as regional monopolists. Our findings reiterate the importance of regulation and market design.  相似文献   
960.
In this work we study the time-stepping schemes for shell models, which describe the shell-director vector motion by the finite rotations. Different possibilities for choosing director rotations are examined and their relationships are cast in terms of the commutative diagram. The Newmark time-stepping schemes, making use of different rotation parameters, are then developed. The mid-point scheme modified to either conserve or dissipate the total energy is further examined. Several numerical simulations are presented to illustrate the performance of each developed scheme.  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