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   22294篇
  免费   2071篇
  国内免费   935篇
电工技术   1206篇
综合类   1032篇
化学工业   3748篇
金属工艺   1488篇
机械仪表   1681篇
建筑科学   1275篇
矿业工程   610篇
能源动力   816篇
轻工业   1524篇
水利工程   314篇
石油天然气   973篇
武器工业   116篇
无线电   2977篇
一般工业技术   3592篇
冶金工业   1246篇
原子能技术   185篇
自动化技术   2517篇
  2024年   113篇
  2023年   469篇
  2022年   785篇
  2021年   1116篇
  2020年   827篇
  2019年   683篇
  2018年   825篇
  2017年   783篇
  2016年   806篇
  2015年   917篇
  2014年   1114篇
  2013年   1351篇
  2012年   1454篇
  2011年   1612篇
  2010年   1385篇
  2009年   1356篇
  2008年   1232篇
  2007年   1022篇
  2006年   979篇
  2005年   855篇
  2004年   654篇
  2003年   635篇
  2002年   590篇
  2001年   498篇
  2000年   466篇
  1999年   472篇
  1998年   456篇
  1997年   353篇
  1996年   326篇
  1995年   262篇
  1994年   209篇
  1993年   137篇
  1992年   111篇
  1991年   77篇
  1990年   74篇
  1989年   63篇
  1988年   43篇
  1987年   34篇
  1986年   33篇
  1985年   22篇
  1984年   17篇
  1983年   10篇
  1982年   8篇
  1981年   16篇
  1980年   10篇
  1979年   5篇
  1978年   6篇
  1977年   7篇
  1976年   10篇
  1973年   2篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
The phase behavior of a hybrid polymer network (HPN) composed of poly[(propylene glycol maleate)-co-(propylene glycol phthalate)] crosslinked with styrene and polyester–urethane crosslinked with methylene-bis-ortho-chloroaniline was examined. The correlation between phase separation and impact strength of the HPNs is discussed. The composition of HPNs has an effect on their properties.  相似文献   
92.
In this letter, we examined whether the parasitic bipolar junction transistors (BJTs) in the MOSFET fabricated by the standard CMOS process can play a role as a fluorescence detector. To suppress the action of two vertical parasitic BJTs, the gate and n-well were tied in the parasitic BJTs, and the body node was connected to the drain. The proposed device was compared with the inherent and the parasitic diodes in the MOSFET. It had 100 times higher photocurrents than the diodes in the MOSFET. In addition, it was applied for the detection of the fluorescent signal, and could detect near 10 nM of Alexa 546. Therefore, CMOS-process-compatible parasitic BJTs can be used as a photodetector in an integrated fluorescence detector.  相似文献   
93.
A novel bidirectional complementary metal-oxide-semiconductor (CMOS) transceiver for chip-to-chip optical interconnects operating at 2.5 Gb/s is proposed, which shares the common block of a receiver and a transmitter on a single chip. The share of the common block of two circuits makes it possible to save 55% or 20% of power dissipation, depending on the operating mode. The chip in 0.18-/spl mu/m CMOS technology occupies an area of 0.82/spl times/0.82 mm/sup 2/, 70% of the total area of a typical unshared transceiver chip. The transmitting and receiving modes of operation show -3-dB bandwidths of 2.2 and 2.4 GHz and electrical isolations of -28 and -40 dB, respectively.  相似文献   
94.
    
“悟”是一种对客观的事和物的一种感知,是对事和物获取了解、获取知效,是人们求得理解的一种启示、一种认识的过程。一般地说,“我对事和物,意在彻悟”,是指人们得到充分的悟性,特别对意、意义的悟,有的很快领会,有的要耗费时日,有的要经过一定的时间乃至终身。悟性就是理解的  相似文献   
95.
“对于建筑事业,没有什么比让全民的建筑意识提高更重要的事情了。”五十多年前,年轻的齐康对此深信不疑,如今已是古稀之年的齐老对此仍然耿耿于怀。对于青年一代的教育,他从未放松;传统与现代的比较、东方与西方差异的研究,他从未停止。从本期起,我们将连续刊登齐康系列文章《建筑课》。  相似文献   
96.
力量空间     
设计师做自己办公空间设计往往想法很多,也很苛求。这种设计状态会令将来的作品显得杂乱、稚嫩, 容易出现“昏招”,或者流于刻板、拘谨、不灵动。我懂得调整自己的状态:有时记住自己是甲方,可以任意发挥,有时把它忘了,也就不必太苛求,以致经常改动设计,不坚决。由于急于搬迁的缘故,加之那时我正好出差在外,所以本案设计周期较短。几天时间在宾馆里伏案设计,倒给出了一个好的状态:略去许多泉涌的想法, 只抓住最好的,好比画者在做速写,把控大局。凭我个人的喜好和习惯,以及对设计公司办公空间的理解与思考,我在凝神中拔高自己,发现塑造一种力量空间会比较接近于表达设计师这种群体的周遭环境,无需过多地出招,无需捕捉人的眼球。力量是潜在的,它无处不在,闭着眼也能抓住你的心。我就这样确立了设计主旨。  相似文献   
97.
Fresh persimmons were subjected to two different processes: sun-drying during 1 month and dehydration at 60 °C during 12 h. To assess the effect of this process on nutritional and health-related properties of persimmons dietary fibers, minerals, trace elements, polyphenols and the total radical scavenging activities (TRSAs) were determined before and after processing. It was found that the contents of dietary fibers, minerals and trace elements in fresh and dried persimmons fruits were comparable. Total polyphenols in fresh persimmons was higher than in dried fruits (1.3 vs. 0.9 and 0.8 mg/100 g FW, respectively) and percentage of inhibition was higher than in dried fruits (70% vs. 59% and 55% and 58% vs. 53% and 46% for 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2′-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) [ABTS] radicals, respectively (P>0.05 in all cases). In conclusion: (1) the differences in the contents of dietary fibers, minerals and trace elements in fresh and dried persimmons are not significant; (2) the contents of polyphenols and the level of the TRSA are higher in fresh persimmons than in dried fruits; however, both variables are also high in dried persimmons; (3) when fresh fruits are not available, proper dried persimmons could be used as a valuable substitute.  相似文献   
98.
With the increase of cellular users, traffic hot spots and unbalanced call distributions are common in wireless networks. As a solution to this problem, code-division multiple-access techniques enable a base transceiver station to connect microcells with optical fibers and to control the channels by sectorizing the microcells. To solve the load balancing among microcells, we dynamically sectorize the microcells depending on the time-varying traffic. The microcell sectorization problem is formulated as an integer linear programming that minimizes the blocked and handoff calls in the network. In the proposed sectorization, proper, connected, and compact sectors are considered to keep the handoffs as small as possible while satisfying the channel capacity at each sector. Three genetic algorithms (GAs) are proposed to solve the problem: standard GA, grouping GA, and parallel GA. Computational results show that the proposed GAs are highly effective. All three GAs illustrate outstanding performance for small size problems. The parallel GA, which is based on the operators used in grouping GA, demonstrates excellent solution quality in a reasonable time  相似文献   
99.
The braking system of a high-speed train has a crucial role for the safety of human mass transportation. However, it is hard to acquire design parameters of the braking system in the development stage of a new high-speed train. In this paper, we build a Hardware-In-the-Loop (HIL) system for the braking system of the Korean High-Speed Train (KHST) that is supposed to reach 350 km/h, and analyze the characteristics of the braking system of KHST (composed of 7 cars) via real-time simulations. In the HIL system that is built using a DSP board of dSPACE, the dynamics of the 7 car bodies and several bogies and characteristics of connecting devices between cars are considered individually. Simulation results show that the designed braking system of KHST is valid and satisfies design specifications.  相似文献   
100.
Accurate assessment and replacement of blood loss and fluid-electrolyte deficit during craniosynostosis repair is difficult owing to patient size and the diversity of surgical technique. Forty-three patients undergoing primary craniosynostosis repair over a 10-year period were studied retrospectively to determine blood loss and fluid deficit and to assess blood transfusion practices during both intraoperative and postoperative periods. Blood loss was calculated on the basis of estimated red cell mass (ERCM) and fluid-electrolyte imbalance was investigated with blood samplings. Blood transfusion was considered appropriate if the postoperative or posttransfusion ERCM was within 12% of the preoperative value. Estimated fluid requirement (EFR) was used in 4 ml kg(-1) h(-1) except for neonates. Intraoperatively, 80% of all patients were appropriately managed with respect to blood transfusion and EFR. Postoperatively only 20% of the patients receiving transfusions were transfused appropriately. In 23.3% of these patients (10/43) unexpected respiratory distress developed immediately after their recovery from the anesthesia. With the measurement of estimated blood volume and allowable blood loss, appropriate transfusion could be achieved for the successful treatment of the primary craniosynostosis.  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