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   644798篇
  免费   7130篇
  国内免费   1399篇
电工技术   11217篇
综合类   2764篇
化学工业   100238篇
金属工艺   27810篇
机械仪表   21423篇
建筑科学   14574篇
矿业工程   4847篇
能源动力   15482篇
轻工业   49038篇
水利工程   8110篇
石油天然气   15283篇
武器工业   39篇
无线电   68991篇
一般工业技术   130995篇
冶金工业   97943篇
原子能技术   14906篇
自动化技术   69667篇
  2021年   5483篇
  2019年   5271篇
  2018年   22836篇
  2017年   21970篇
  2016年   19267篇
  2015年   6585篇
  2014年   10433篇
  2013年   26242篇
  2012年   18653篇
  2011年   29810篇
  2010年   24653篇
  2009年   23980篇
  2008年   25406篇
  2007年   25969篇
  2006年   16387篇
  2005年   15818篇
  2004年   15025篇
  2003年   14776篇
  2002年   13734篇
  2001年   12945篇
  2000年   12489篇
  1999年   12063篇
  1998年   27694篇
  1997年   20063篇
  1996年   15669篇
  1995年   12013篇
  1994年   10868篇
  1993年   10621篇
  1992年   8343篇
  1991年   8123篇
  1990年   7990篇
  1989年   7764篇
  1988年   7486篇
  1987年   6747篇
  1986年   6533篇
  1985年   7391篇
  1984年   6700篇
  1983年   6437篇
  1982年   5777篇
  1981年   5898篇
  1980年   5632篇
  1979年   5733篇
  1978年   5664篇
  1977年   6181篇
  1976年   7690篇
  1975年   5108篇
  1974年   4904篇
  1973年   4980篇
  1972年   4280篇
  1971年   4038篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Poly(vinyl alcohol) is crosslinked in dilute solution (c=0.1 wt%) with glutaraldehyde. The reaction product is characterized by viscometry and gel permeation chromatography (g.p.c.). The intrinsic viscosity decreases with increasing degree of crosslinking and does not depend on temperature. G.p.c. reveals that the reaction product is not homogeneous, but consists of a mixture of particles with different sizes, possibly both intra- and intermolecularly crosslinked molecules. The intramolecularly crosslinked molecules are smaller in size than the initial polymer molecules and their size depends on the degree of crosslinking. They possess a narrow particle size distribution even if the initial polymer sample had a broad molecular weight distribution.  相似文献   
102.
103.
Translated from Atomnaya Énergiya, Vol. 67, No. 2, pp. 111–113, August, 1989.  相似文献   
104.
Translated from Khimiya i Tekhnologiya Topliv i Masel, No. 2, pp. 14–15, February, 1989.  相似文献   
105.
We investigate the saturation effects of power broadening, Stark shifting, and population transfer on Stokes conversion in stimulated Raman scattering. We do not make the usual rotating wave approximation because the detuning from the next electronic state is assumed to be in the optical regime. Retaining the counter-rotating terms allows an exact determination of the pump and Stokes indexes of refraction. Steady-state solutions for the Stokes intensity and phase are obtained and the effects of making the rotating wave approximation (RWA) are discussed. Finally, we examine the behavior of these solutions for Stokes conversion in hydrogen gas when geometric propagation is appropriate.  相似文献   
106.
The usefulness of selected PCR-protocols for the detection of Salmonella in 117 samples of animal origin (17 raw minced meat, 27 raw chicken meat, 8 raw sausages, and 25 egg samples, as well as 18 poultry faecal, and caecal swabs samples) and DNA-fingerprinting typing is shown. To establish an accurate PCR-procedure for Salmonella detection the following parameters were evaluated: two pre-PCR concentration procedures, centrifugation and immunomagnetic separation (IMS) using Dynabeads anti- Salmonella; the specificity and sensitivity of 10 sets of primers; and different conditions of the amplification reaction. In light of the results obtained from the use of PCR-based procedures alone or in combination with conventional methods, the following findings can be underlined: First, IMS is more efficient than centrifugation in the recovery of Salmonella. Second, the selected IMS/PCR-detection protocol is less time-consuming (45 h) than the IMS/culture procedure (90 h), and a good concordance between them was found when the Kappa coefficient was calculated (0·87). Third, PCR-ribotyping technique showed a very low discrimination power, being able to differentiate only three profiles. Fourth, RAPD technique using specific primers supports previous works in which it was proposed as a simple and useful tool for discriminating isolates between and within serotypes. Fifth, The efficiency, rapidity, and flexibility of the PCR-protocols applied were high, and they can be performed using two PCR-programs and the same basic equipment.  相似文献   
107.
108.
This study empirically examined the organisational learning effects of the nonfinancial performance information provided by management accounting information systems (MAISs) under advanced manufacturing technology (AMT). In this study, a target costing system and the frequent and quick reporting of information were considered the facilitators of learning. First, we examined the relationships between AMT level and the amount of nonfinancial performance information produced by MAISs. The empirical results showed that there are significant positive relationships between the level of AMT and nonfinancial performance information. With a systems approach, we also proved the impact of the relationships among AMT levels, nonfinancial performance information and learning facilitators on the organisational performance of a firm. The results of our research suggest that under a high level of AMT, for the provision of information to result in an increase of performance through organisational learning, a target costing system must be introduced and a large amount of information should be provided frequently and quickly. The results of this study also showed that although AMT level may be low, fairly well-arranged facilitators and a moderately large amount of information may be necessary for the improvement of performance. In conclusion, effective organisational learning depends on the provision of relevant information as well as efficient learning support mechanisms.  相似文献   
109.
Consideration was given to the decision making procedures based on the fuzzy messages of experts whose preferences on the set of collective decisions can also be fuzzy.  相似文献   
110.
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