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   153229篇
  免费   1950篇
  国内免费   663篇
电工技术   3129篇
综合类   193篇
化学工业   24324篇
金属工艺   5806篇
机械仪表   4962篇
建筑科学   4510篇
矿业工程   378篇
能源动力   3992篇
轻工业   17502篇
水利工程   1152篇
石油天然气   622篇
武器工业   5篇
无线电   20558篇
一般工业技术   29037篇
冶金工业   23983篇
原子能技术   2353篇
自动化技术   13336篇
  2019年   861篇
  2018年   1119篇
  2017年   1167篇
  2016年   1301篇
  2015年   1089篇
  2014年   1841篇
  2013年   6662篇
  2012年   3263篇
  2011年   4695篇
  2010年   3656篇
  2009年   4219篇
  2008年   4733篇
  2007年   5002篇
  2006年   4424篇
  2005年   4156篇
  2004年   4052篇
  2003年   3943篇
  2002年   3967篇
  2001年   4005篇
  2000年   3760篇
  1999年   3712篇
  1998年   6644篇
  1997年   5240篇
  1996年   4478篇
  1995年   3725篇
  1994年   3384篇
  1993年   3204篇
  1992年   2805篇
  1991年   2700篇
  1990年   2639篇
  1989年   2619篇
  1988年   2465篇
  1987年   2182篇
  1986年   2127篇
  1985年   2572篇
  1984年   2326篇
  1983年   2212篇
  1982年   2075篇
  1981年   2005篇
  1980年   1873篇
  1979年   1877篇
  1978年   1773篇
  1977年   2091篇
  1976年   2566篇
  1975年   1591篇
  1974年   1434篇
  1973年   1456篇
  1972年   1197篇
  1971年   1116篇
  1970年   948篇
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
21.
Efficient numerical solution techniques have been developed and used to examine the electromagnetic fields that can be developed in the working volume of the CW Ellipticus antenna operated at frequencies from 100 kHz to 1 GHz. An exponentially tapered transition section is designed to obtain the desired illumination pattern in the working volume. The input transition section is needed for impedance matching and to drive efficiently the Ellipticus antenna. A parametric study is performed to ascertain the performance of the Ellipticus antenna for frequencies up to 1 GHz  相似文献   
22.
23.
Heterostructure Acoustic Charge Transport (HACT) devices have been fabricated with a new nondestructive sense (NDS) electrode structure that provides for the recovery of base-band signals without the use of an integrating capacitor. This electrode structure provides an output signal comprising an RF carrier at the SAW frequency, amplitude modulated by the sampled input signal which has been delayed by a period proportional to the output electrodes distance from the input diode. The output of the NDS electrode structure is subsequently demodulated to provide the base-band signal  相似文献   
24.
25.
The immunological agglutination reactions of physically absorbed F(ab')2 molecules onto anionic and cationic latex particles have been investigated by means of optical absorbance measurements. These measurements have been conducted under different conditions to determine the most influential factors. Surface F(ab')2 and BSA densities, particle concentration in the reaction medium and polyethylene glycol concentration are some of these factors. Sensitized cationic and anionic latexes differ considerably with respect to their colloidal stability and reactivity. As a general rule, the sensitized cationic latex has a relatively higher colloidal stability and hence, it provides reagents with a better optical response. Less than 0.025 microgram/ml of C-reactive protein has been detected using this particle enhanced optical immunoassay.  相似文献   
26.
In a prospective study we found good results concerning postoperative complications (21%), perioperative lethality (3.2%) and lethality during hospital stay (6.5%) after implantation of dynamic hip screws (DHS) in patients with per- and subtrochanteric fractures of the femur. The ability to walk, as well as housing and social care postoperatively and follow-up for at least six months after dismissal demonstrates the importance of these fractures for the elderly. One of three patients needs professional care, 21% at home, 13% in nursing homes. Six months after operation the lethality is nearly 20%, i.e. three times higher than in hospital. These are the essential data for all techniques of osteosynthesis used in patients with these fractures, which could only be documented in prospective studies.  相似文献   
27.
28.
This paper focuses on the hydrodynamics of third sound on a superfluid 3 He film. We solve the hydrodynamical equations in the limit of thick films with weak interaction with the substrate. The surface tension at the free interface is shown to have a large effect on the third sound velocity and on the attenuation for frequencies larger than 1Hz. In the case of a diffusely scattering substrate a ripplon-like dispersion relation is found for this frequency range.  相似文献   
29.
In this study, the effect and side-effect of epidural injection with lappaconitine compound for post-operative analgesia was observed. One hundred and twenty patients were randomly divided into 4 groups. Lappaconitine compound (LB) consisted of 12 mg of lappaconitine and 22.5 mg of bupivacaine, was given to group A (the group of observation), and lappaconitine 12 mg, bupivacaine 22.5 mg and morphine 2 mg to group B, C and D respectively for control. All were given by epidural injection with single blind method during post-operative pain of incision operation. Result showed that the initiating of analgesia was quicker in group A and C than that in group B and D, and the efficacy was group D > A > C > B. There was significant difference between group A and B in the above two parameters, P < 0.01 and P < 0.05. The analgisia maintenence time of single injection was D > A > B > C, that of group D was significantly longer than that of group A (P < 0.01). It indicated that the epidural injection with LB was more rapid and potent than that with lappaconitine alone in post-operative analgesia, and the former had no side-effect, it was safer than morphine.  相似文献   
30.
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   
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