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   483544篇
  免费   6725篇
  国内免费   2554篇
电工技术   9691篇
技术理论   5篇
综合类   1348篇
化学工业   73459篇
金属工艺   19265篇
机械仪表   14267篇
建筑科学   12004篇
矿业工程   2456篇
能源动力   12157篇
轻工业   43217篇
水利工程   4823篇
石油天然气   8573篇
武器工业   258篇
无线电   57851篇
一般工业技术   92910篇
冶金工业   91860篇
原子能技术   9761篇
自动化技术   38918篇
  2021年   4373篇
  2020年   3080篇
  2019年   3831篇
  2018年   6265篇
  2017年   6273篇
  2016年   6720篇
  2015年   4784篇
  2014年   8011篇
  2013年   21579篇
  2012年   13045篇
  2011年   17616篇
  2010年   14160篇
  2009年   15614篇
  2008年   16775篇
  2007年   16806篇
  2006年   14814篇
  2005年   12973篇
  2004年   12018篇
  2003年   11913篇
  2002年   11451篇
  2001年   11950篇
  2000年   11055篇
  1999年   11531篇
  1998年   28020篇
  1997年   19942篇
  1996年   15236篇
  1995年   11441篇
  1994年   10411篇
  1993年   10227篇
  1992年   7543篇
  1991年   7264篇
  1990年   7175篇
  1989年   6938篇
  1988年   6665篇
  1987年   5688篇
  1986年   5611篇
  1985年   6218篇
  1984年   5900篇
  1983年   5577篇
  1982年   5024篇
  1981年   5115篇
  1980年   4815篇
  1979年   4836篇
  1978年   4540篇
  1977年   5161篇
  1976年   6885篇
  1975年   3951篇
  1974年   3776篇
  1973年   3752篇
  1972年   3228篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
61.
62.
This research was supported under project No. 6.02.02/128-93 as part of the state scientific-technical program on future information technologies and systems by the Ukrainian State Committee, of Science and Technology.  相似文献   
63.
64.
Nutrient uptake by the hindlimb was investigated utilising the arteriovenous difference technique in 5 Thoroughbred horses fed to maintenance a diet of 100% roughage or 52% oat grain and 48% roughage. Arterial blood was obtained from a catheter inserted into the carotid artery while venous blood was simultaneously collected from a catheter placed into the iliac vein via the medial saphenous vein. The arteriovenous difference for glucose was significant and represented a mean extraction of 10 +/- 1% with no effect of diet. If fully oxidised, glucose uptake (corrected for lactate and pyruvate arteriovenous difference) was sufficient to account for 78 +/- 13% or 107 +/- 15% of the oxygen consumed by the hindlimb in horses fed a roughage or 52% oat grain diet respectively. Acetate was also a major metabolite of the hindlimb, showing a 39 +/- 5% extraction with no effect of diet. However, the 52% oat grain diet did induce a significant decline in the concentration of acetate in arterial blood. The potential contribution to oxidation in the hindlimb was significantly reduced from 32 +/- 4% in horses fed roughage to 21 +/- 3% when fed 52% oat grain. D-3-Hydroxybutyrate uptake could account for 9 +/- 1% of the oxidation by the hindlimb with no effect of diet. The technique for measuring nutrient uptake across the hindlimb using the arteriovenous difference is relatively simple and would be valuable in investigating fuel use by muscle during exercise.  相似文献   
65.
66.
Carboxyl-terminated butadiene-acrylonitrile-rubber decreases modulus and yield stress of the studied epoxy but increases fracture toughness. The addition of glass bead compensates for the loss in modulus but has little effect on yield stress. However, it significantly contributes to the fracture toughness by providing additional mechanisms for toughening of both the unmodified and rubber-modified epoxy. For the toughened epoxies studied, fracture surfaces gave only limited information on fracture mechanisms since significant energy absorption also occurs in the material below the fracture surface. Suggestions for suitable material compositions for fiber composite matrices are given.  相似文献   
67.
This paper presents a model of heterogenous diffusion in capillary porous materials during the process of drying. The governing heat and mass transfer equations have been established using the liquid as well as vapor flow. Two models have been presented. Model 1 does not consider the heat conduction while the model 2 has been established by considering the conduction. The developed models and the numerical solutions of the resulting differential equations can take into account the moisture and temperature dependent thermophysical properties of the product. All equations have been established in spherical coordinates but the programme written for the purpose of calculations can be used for other geometries also. Numerical calculations have been performed for gas concrete and tiles using model 1, while model 2 has been used for gas concrete only because of the lack of data for thermophysical properties of the tile. For gas concrete it was seen that conduction has only marginal effect on the drying process and the numerical predictions of the drying process were reasonably accurate.  相似文献   
68.
The technological process of cold forging applied for the first time in the production of the casing of the internal joint with races is described. The process operations of cold forging and the annealing and carburizing regimes for this part me described.  相似文献   
69.
A CEC-funded project has been performed to tackle the problem of producing an advanced Life Monitoring System (LMS) which would calculate the creep and fatigue damage experienced by high temperature pipework components. Four areas were identified where existing Life Monitoring System technology could be improved:
1. 1. the inclusion of creep relaxation
2. 2. the inclusion of external loads on components
3. 3. a more accurate method of calculating thermal stresses due to temperature transients
4. 4. the inclusion of high cycle fatigue terms.

The creep relaxation problem was solved using stress reduction factors in an analytical in-elastic stress calculation. The stress reduction factors were produced for a number of common geometries and materials by means of non-linear finite element analysis. External loads were catered for by producing influence coefficients from in-elastic analysis of the particular piping system and using them to calculate bending moments at critical positions on the pipework from load and displacement measurements made at the convenient points at the pipework. The thermal stress problem was solved by producing a completely new solution based on Green's Function and Fast Fourier transforms. This allowed the thermal stress in a complex component to be calculated from simple non-intrusive thermocouple measurements made on the outside of the component. The high-cycle fatigue problem was dealt with precalculating the fatigue damage associated with standard transients and adding this damage to cumulative total when a transient occurred.

The site testing provided good practical experience and showed up problems which would not otherwise have been detected.  相似文献   

70.
Given the enormous size of the genome and that there are potentially many other types of measurements we need to do to understand it, it has become necessary to pick and choose one's targets to measure because it is still impossible to evaluate the entire genome all at once. What has emerged is a need to have rapidly customizable microarrays. There are two dominant methods to accomplish custom microarray synthesis, Affymetrix-like microarrays manufactured using light projection rather than semiconductor-like masks used by Affymetrix to mass manufacture their GeneChip/sup TM/ arrays now, or the ink-jet printing method employed by Agilent. The manufacture of these custom Affymetrix-like microarrays can now be done on a digital optical chemistry (DOC) machine developed at the University of Texas Southwestern Medical Center, and this method offers much higher feature numbers and feature density than is possible with ink-jet printed arrays. On a microarray, each feature contains a single genetic measurement. The initial DOC prototype has been described in several publications, but that has now led to a second-generation machine. This machine reliably produces a number of arrays daily, has been deployed against a number of biomedical questions, is being used in new ways and has also led to a number of spin-off technologies.  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