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   22776篇
  免费   1012篇
  国内免费   317篇
电工技术   489篇
综合类   551篇
化学工业   4243篇
金属工艺   558篇
机械仪表   802篇
建筑科学   949篇
矿业工程   179篇
能源动力   651篇
轻工业   2339篇
水利工程   253篇
石油天然气   182篇
武器工业   28篇
无线电   2567篇
一般工业技术   3188篇
冶金工业   3766篇
原子能技术   186篇
自动化技术   3174篇
  2023年   111篇
  2022年   355篇
  2021年   611篇
  2020年   322篇
  2019年   396篇
  2018年   462篇
  2017年   430篇
  2016年   471篇
  2015年   418篇
  2014年   634篇
  2013年   1178篇
  2012年   892篇
  2011年   1138篇
  2010年   870篇
  2009年   922篇
  2008年   909篇
  2007年   911篇
  2006年   789篇
  2005年   663篇
  2004年   742篇
  2003年   952篇
  2002年   1234篇
  2001年   1044篇
  2000年   610篇
  1999年   558篇
  1998年   1361篇
  1997年   892篇
  1996年   655篇
  1995年   446篇
  1994年   332篇
  1993年   363篇
  1992年   200篇
  1991年   156篇
  1990年   151篇
  1989年   142篇
  1988年   137篇
  1987年   112篇
  1986年   115篇
  1985年   155篇
  1984年   97篇
  1983年   97篇
  1982年   87篇
  1981年   107篇
  1980年   101篇
  1979年   68篇
  1978年   51篇
  1977年   106篇
  1976年   196篇
  1975年   53篇
  1973年   52篇
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
71.
This study analyses the relationship between the use of rotating instruments, the production of a smear layer and the presence of alterations to enamel microstructures. The rotating instruments used were carbide (8-12 blade) and diamond tipped (30-15 m) cutters. Cavities were made in extracted teeth. Subsequently, half the sample was analysed using the rugosimeter before and after the application of ortophosphoric acid at 35% for 15 and the other half suing a Scansion Electronic microscope (SEM). The results obtained showed on the one hand that carbide cutters leave a smoother surfacer than diamond tipped cutters, and on the other that the smear layer is eliminated better by carbide cutters compared to diamond tipped cutters. Moreover, there are no major traumatic-type alterations at the level of the enamel affecting the microstructure after the use of carbide cutters.  相似文献   
72.
Analysis of Combined Systems of Two Endoreversible Engines   总被引:3,自引:0,他引:3  
A single endoreversible engine can operate as a cooler, a true heat engine, a heat pump, or a refrigerator. We investigate how many different modes of operation a combined system of two endoreversible engines may display. Special attention is paid to the independent combined system which neither consumes nor supplies power.  相似文献   
73.
74.
We report a 20-year-old man affected by glycogenosis type III with distal muscle weakness, more severe in distal leg muscles. The electromyogram showed myopathic features. Nerve conduction studies and central motor conduction after magnetic stimulation of the brain were normal. Our results suggest that there is no involvement of central motor pathways in this disease.  相似文献   
75.
76.
77.
To determine if cardiac allograft outcome is improved among patients with fewer HLA-DR mismatches with their donors, we studied 132 recipients of a primary cardiac allograft who were transplanted between December 1985 and December 1991. These recipients and their donors all had high-confidence-level serological HLA-DR typing, previously shown to correlate highly with DNA DR typing. Patients were divided in two groups based on the HLA-DR mismatch with their donors. Group I consisted of 78 patients with 1 or zero DR mismatch and group II of 54 patients with 2 DR mismatches. Allograft outcome measurements included incidence of moderate rejection, incidence of allograft vasculopathy at 12 months, cardiac function measured as left ventricular ejection fraction (LVEF) and cardiac index (CI), and actuarial graft survival up to 7 years. Groups I and group II were not different with regard to recipient age, donor age, ischemia time, pulmonary vascular resistance, sex, or PRA greater than 0%. Group II had a higher incidence of moderate rejection on the first-week biopsy (47% vs. 25%, P = 0.019), and during the first month (84% vs. 58%, P = 0.006), but no difference was found in frequency of rejection from months 2 to 12. LVEF was not different in the groups at any point. CI was better in group I at 12 months (2.76 vs. 2.5, P = 0.03). No statistically significant difference was found in incidence of allograft vasculopathy (17% vs. 26%, P = 0.204). Actual graft survival at 1 year was better for group I (91% vs. 74%, P = 0.008), and actuarial graft survival at 6 years also favored group I (76% vs. 56%, P = 0.04). Using high-confidence-level serological HLA-DR typing assignments we demonstrated that HLA-DR mismatching correlates highly with cardiac allograft outcome. Implications are that heart transplant survival could be improved if prospective matching were feasible and prioritized or if immunosuppression were tailored to the HLA-DR match.  相似文献   
78.
钠冷快堆中喷雾钠火的计算分析   总被引:5,自引:0,他引:5  
根据钠冷快堆中喷雾钠火的特点建立了理论模型,编制了SSPRAY程序。该程序模拟钠喷雾燃料过程中钠滴的运动、钠和氧气的燃烧反应、热量传递和质量传递等瞬态过程。用该程序计算了气体和墙壁温度、气体压力、氧气摩尔份额、喷雾流燃烧速率和热量热递速率等主要参数。利用AI实验数据和美国SPRAY-3A的计算结果对程序进行了验证,结果符合较好。  相似文献   
79.
采用X射线光电子能谱(XPS)对电沉积Ni-W合金镀层表面膜进行了分析。研究结果表明,Ni-W合金镀层表面存在一层薄的氧化膜,而钨的氧化作用远大于镍,Ni-W合金镀层中W含量的提高对耐蚀性起决定作用。  相似文献   
80.
In this paper we describe a framework for analysing the creation and justification of Research & Development. The 4S framework is developed for analysing the scope, scale, skills and social network aspects of Research & Development value. The framework is based on social system theory, a process contingency model, and recent Research & Development metrics. We present a first empirical assessment based on a workshop using the 4S framework for leveraging Research & Development. Results that assist in the assessment of value creation utilising R & D within networks are very relevant in high tech industries. The multi–dimensional process approach of this framework seems promising for understanding and managing R&D value creation, but needs further operationalisation. Case studies are described and a Dutch network on leveraging R&D has been initiated.  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