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   4715篇
  免费   45篇
  国内免费   3篇
电工技术   49篇
化学工业   715篇
金属工艺   65篇
机械仪表   65篇
建筑科学   143篇
矿业工程   6篇
能源动力   60篇
轻工业   274篇
水利工程   29篇
石油天然气   10篇
无线电   363篇
一般工业技术   565篇
冶金工业   2109篇
原子能技术   20篇
自动化技术   290篇
  2021年   24篇
  2020年   24篇
  2019年   27篇
  2018年   24篇
  2017年   24篇
  2016年   38篇
  2015年   24篇
  2014年   49篇
  2013年   158篇
  2012年   81篇
  2011年   127篇
  2010年   73篇
  2009年   83篇
  2008年   117篇
  2007年   99篇
  2006年   75篇
  2005年   106篇
  2004年   98篇
  2003年   95篇
  2002年   96篇
  2001年   85篇
  2000年   63篇
  1999年   95篇
  1998年   563篇
  1997年   349篇
  1996年   239篇
  1995年   184篇
  1994年   126篇
  1993年   163篇
  1992年   75篇
  1991年   50篇
  1990年   68篇
  1989年   58篇
  1988年   66篇
  1987年   54篇
  1986年   45篇
  1985年   59篇
  1984年   47篇
  1983年   43篇
  1982年   54篇
  1981年   58篇
  1980年   51篇
  1979年   43篇
  1978年   37篇
  1977年   82篇
  1976年   172篇
  1975年   52篇
  1974年   38篇
  1973年   40篇
  1972年   21篇
排序方式: 共有4763条查询结果,搜索用时 15 毫秒
41.
42.
Experiment 1 was to test effect of three ratios of energy to protein in complete mixed diets for 36 lactating cows in three, 28-d periods. Energy was varied with cottonseed hulls, pelleted ground corrugated boxes, and a mixture of the two. Crude protein was varied with soybean meal to give energy:crude protein of 5.7, 5.0, and 4.6 for each energy amount. Cottonseed meal was compared with soybean meal in corrugated box diets. Feed intake was much higher with cottonseed hulls, and appreciable feedlot bloat resulted from pelleted ground corrugated box diets. Data adjusted to equal feed intake showed significant effect of energy to crude protein ratio on milk yield and improved digestion of organic matter with soybean meal vs. cottonseed meal. Experiment 2 tested the hypothesis that lactating cows consuming high-protein alfalfa may benefit from supplemental protein. Diets were 50% forage. Six diets were 14 or 18% crude protein in three ratios of alfalfa hay to corn silage (0:100, 50:50, 100:0). Additional corn silage diets were to compare: 14 versus 18% protein from distiller's dried grains with solubles only and with .5 or .9% urea (four diets); two 14% protein diets compared .6% added potassium chloride with or without .5% urea. Thirty-six Holstein cows in early lactation received one of the 12 diets in each of three 28-d periods. Distiller's grains with solubles markedly depressed milk yield (2.2 kg/d) and milk protein (.22%); heat damage of distiller's grains was evident. Protein interacted with alfalfa so gain in milk from 18 versus 14% increased from .55 to 1.36 to 2.66 kg/d as alfalfa changed from 0 to 50 to 100%. Thus, crude protein of alfalfa was not as effective as that from soybean meal in supporting milk yield.  相似文献   
43.
The absolute right to refuse medical treatment, even if the reasons are irrational, is confined to competent adults. Children under 16 years can give legal consent to treatment in the absence of consent from those with parental responsibility. Children under 18 years do not, however, have an absolute right to consent, or refuse to consent, to treatment. The views of children assume increasing importance with age and maturity. Accident and emergency medical and nursing staff may face difficult decisions when children, or those with parental responsibility, refuse to consent to medical treatment. This paper presents guidelines designed to guide the decision making process in immediately or potentially life threatening conditions and in non-life-threatening conditions.  相似文献   
44.
The design of a single-chip VLSI system to implement the Zigangirov-Jelinek sequential decoding algorithm for bit-error-correction is described and the dependence of performance on design parameters is discussed. By virtue of being self-contained, having few input and output pins, and processing stack elements once each clock cycle, the system should be capable of high-speed decoding. For constraint length 21, rate 1/2 codes, and 3-b soft decision detection, it is found that a system containing approximately 25000 stack cells reduces errors in a 3-dB signal-to-noise level environment, corresponding to 7.8% hard decision error rate, by two orders of magnitude. Higher decoding gain is obtained at lower noise levels through the use of a relatively long constraint length. The constraint length is not limited by the architecture. Chip area estimates needed to obtain prescribed decoded error rates and average decoding rates are also described and indicate that an effective system is potentially achievable with current technology  相似文献   
45.
The high prevalence of multiple chronic medical conditions in the elderly and the likelihood of multiple drug therapies dramatically increase the chance of drug-specific adverse effects and drug-drug interactions. This article reviews the age-associated alterations in pharmacokinetics and pharmacodynamics along with the most frequently prescribed medications for the elderly. Adverse drug reactions, drug-drug interactions and oral side effects are reviewed along with the impact these medications may have on dental treatment planning and management.  相似文献   
46.
47.
Reviews challenges associated with behavioral training approaches for individuals with mental retardation and mental illness in the community. Family and non-family facilitated training are considered. Professional practice issues are reviewed, and justification for multifactor behavioral assessment is offered. Future research directions are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
48.
Intramuscular phenol neurolysis is a well-known procedure used to decrease spasticity and improve function in patients who have failed to respond to more conservative forms of intervention. Traditionally, this approach has been limited to spasticity reduction in limb muscles, and its use in managing spasticity of the facial muscles has not been described in the literature. This case report describes a new and previously unreported application of intramuscular neurolysis for managing severe unrelenting facial muscle spasticity in a postanoxic encephalopathic patient. Prior to the procedure, hypertonicity in the orbicularis oris muscle was so profound that it limited speech and affected cosmetic, hygienic, and nutritional status. After intramuscular phenol neurolysis of the orbicularis oris muscle, the patient's level of functioning improved.  相似文献   
49.
The 29Si MAS NMR spectra of the 2H, 4H, 6H, and 3C polytypes of silicon carbide are presented. An attempt is made to correlate differences in the chemical shifts with local atomic environment. The results of the analysis of the spectra of pure polytypes are used as a basic for the interpretation of the spectra of mixed polytypes and a discussion of the crystallinity and impurity levels of different samples. Carbon-13 chemical shifts obtained from spectra of the same polytypes are also tabulated.  相似文献   
50.
Chronic caloric restriction has been shown to inhibit mammary tumor promotion in the 7,12-dimethyl-benz[a]anthracene (DMBA) rat mammary tumor model. The objectives of this study were to determine (i) the effects of chronic caloric cycling (yo-yo dieting) on mammary tumor promotion by high fat diets and (ii) the effect of three dietary regimens +/- superimposed mammary tumor burden on plasma endothelin-1,2 (ET) levels. Female Sprague-Dawley rats were treated with DMBA (5 mg/rat) and divided into three dietary groups: ad libitum (AL) (containing 15% corn oil); 40% calorie restricted (CR) (containing 20% corn oil so consumption of fat was equivalent between AL and CR); a calorie cycled (CC) group fed alternatively AL and CR diets each 48 h period. After 10 weeks, tumor incidences were: AL, 63%; CR, 27%; CC, 57% (AL versus CR, P < 0.05; CC versus CR, P < 0.05; AL versus CC, NSD). ET levels (pg/ml plasma) were: AL, 16.0 +/- 6.54; CR, 32.31 +/- 0.34; CC, 23.44 +/- 5.04 (AL versus CR, P < 0.01; CC versus CR, P < 0.01; AL versus CC, P < 0.05). Plasma ET levels were independent of tumor incidence and tumor burden, but plasma ET levels were significantly increased in rats with a prior history of calorie restriction. As expected, maintained caloric restriction reduced mammary tumor incidence but intermittent caloric restriction (caloric cycling or yo-yo dieting) was without similar benefit.  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