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   163284篇
  免费   3283篇
  国内免费   1221篇
电工技术   3896篇
技术理论   1篇
综合类   1033篇
化学工业   25912篇
金属工艺   6352篇
机械仪表   5607篇
建筑科学   5386篇
矿业工程   773篇
能源动力   4169篇
轻工业   18547篇
水利工程   1397篇
石油天然气   1172篇
武器工业   120篇
无线电   21756篇
一般工业技术   30183篇
冶金工业   24209篇
原子能技术   2465篇
自动化技术   14810篇
  2021年   1441篇
  2019年   1202篇
  2018年   1477篇
  2017年   1593篇
  2016年   1684篇
  2015年   1686篇
  2014年   2477篇
  2013年   7339篇
  2012年   4032篇
  2011年   5514篇
  2010年   4386篇
  2009年   4833篇
  2008年   5339篇
  2007年   5528篇
  2006年   4986篇
  2005年   4610篇
  2004年   4309篇
  2003年   4153篇
  2002年   4135篇
  2001年   4156篇
  2000年   3922篇
  1999年   3872篇
  1998年   6770篇
  1997年   5334篇
  1996年   4555篇
  1995年   3782篇
  1994年   3413篇
  1993年   3231篇
  1992年   2828篇
  1991年   2713篇
  1990年   2649篇
  1989年   2628篇
  1988年   2469篇
  1987年   2173篇
  1986年   2118篇
  1985年   2561篇
  1984年   2324篇
  1983年   2197篇
  1982年   2073篇
  1981年   1993篇
  1980年   1862篇
  1979年   1875篇
  1978年   1770篇
  1977年   2085篇
  1976年   2562篇
  1975年   1583篇
  1974年   1430篇
  1973年   1453篇
  1972年   1196篇
  1971年   1115篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
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   
82.
83.
A multivariate mixed linear model for meta-analysis.   总被引:1,自引:0,他引:1  
A multivariate mixed-effects approach for meta-analysis is presented. The approach (a) incorporates as outcomes multiple effect sizes per study; (b) allows different studies to have different subsets of effect sizes; and (c) treats each study's effect sizes as random realizations from a population of possible effect sizes. Application is illustrated via reanalysis of data from studies assessing the effects of coaching on verbal and mathematical subtests of the Scholastic Aptitude Test. Covariance components are estimated via restricted maximum likelihood (REML); inferences about regression coefficients and specific study effect sizes are based on their joint conditional distribution given the REML covariance component estimates. The approach can be implemented via now-standard software for unbalanced hierarchical data. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
84.
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   
85.
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   
86.
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   
87.
14 medicated hypertensive, 15 nonmedicated mild hypertensive, 39 normotensive, and 13 hypotensive adults participated in a 1–2 hr laboratory experiment that assessed each S's symptoms, moods, and estimates of systolic blood pressure (SBP) relative to actual SBP levels. Several self-reports and autonomic measures were collected during and after each of 22 tasks. Within-S correlations indicated that all Ss could estimate SBP at levels greater than chance. Further, 68% of the Ss evidenced at least 1 significant symptom–SBP correlation. Although medicated hypertensives believed they could estimate their BP more accurately than other groups, they were actually no more accurate than the other Ss. They also evidenced far fewer empirically derived symptom–SBP and emotion–SBP correlations than any other group. Overall, blood pressure (BP) beliefs were largely inaccurate. If these erroneous beliefs can be eliminated, Ss may be able to estimate BP fluctuations more accurately. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
88.
89.
In this paper, a physics-based mismatch model is presented. It is demonstrated on a 0.18-/spl mu/m technology that a simple mismatch model can still be used to characterize deep-submicron technologies. The accuracy of the model is examined and found to be within 20% in the strong inversion region. Bulk bias dependence is modeled in a physical way. To extract the mismatch parameters, a weighted fit is introduced. It is shown that the width and length dependence of the mismatch parameters is given by the Pelgrom model.  相似文献   
90.
An attack on the public key cryptosystem Polly Cracker is described, that reveals the complete secret key σ ∈ Fq n by means of n (nonadaptively) chosen "fake" ciphertexts  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