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   1099篇
  免费   1篇
电工技术   1篇
化学工业   2篇
机械仪表   1篇
轻工业   137篇
无线电   1篇
冶金工业   957篇
自动化技术   1篇
  2022年   1篇
  2019年   2篇
  2016年   1篇
  2014年   1篇
  2013年   3篇
  2012年   2篇
  2011年   3篇
  2010年   2篇
  2008年   5篇
  2007年   7篇
  2006年   7篇
  2005年   9篇
  2004年   17篇
  2003年   19篇
  2002年   11篇
  2001年   15篇
  2000年   9篇
  1999年   29篇
  1998年   285篇
  1997年   171篇
  1996年   105篇
  1995年   51篇
  1994年   62篇
  1993年   57篇
  1992年   8篇
  1991年   10篇
  1990年   16篇
  1989年   11篇
  1988年   12篇
  1987年   7篇
  1986年   1篇
  1985年   8篇
  1984年   2篇
  1983年   3篇
  1982年   5篇
  1981年   6篇
  1980年   10篇
  1979年   1篇
  1978年   5篇
  1977年   35篇
  1976年   81篇
  1975年   2篇
  1974年   1篇
  1955年   2篇
排序方式: 共有1100条查询结果,搜索用时 15 毫秒
41.
A neostriatal habit learning system in humans   总被引:1,自引:0,他引:1  
Amnesic patients and nondemented patients with Parkinson's disease were given a probabilistic classification task in which they learned which of two outcomes would occur on each trial, given the particular combination of cues that appeared. Amnesic patients exhibited normal learning of the task but had severely impaired declarative memory for the training episode. In contrast, patients with Parkinson's disease failed to learn the probabilistic classification task, despite having intact memory for the training episode. This double dissociation shows that the limbic-diencephalic regions damaged in amnesia and the neostriatum damaged in Parkinson's disease support separate and parallel learning systems. In humans, the neostriatum (caudate nucleus and putamen) is essential for the gradual, incremental learning of associations that is characteristic of habit learning. The neostriatum is important not just for motor behavior and motor learning but also for acquiring nonmotor dispositions and tendencies that depend on new associations.  相似文献   
42.
Nonsyndromic cleft lip with or without cleft palate (CL/P) and nonsyndromic cleft palate only (CPO) are common congenital anomalies with significant medical, psychological, social, and economic ramifications. Both CL/P and CPO are examples of complex genetic traits. There exists sufficient evidence to hypothesize that disease loci for CL/P and CPO can be identified by a candidate-gene linkage-disequilibrium (LD) strategy. Candidate genes for clefting, including TGFA, BCL3, DLX2, MSX1, and TGFB3, were screened for LD with either CL/P or CPO in a predominantly Caucasian population, with both case-control- and nuclear-family-based approaches. Previously reported LD for TGFA with both CL/P and CPO could not be confirmed, except in CL/P patients with a positive family history. Also, in contrast to previous studies, no LD was found between BCL3 and either CL/P or CPO. Significant LD was found between CL/P and both MSX1 and TGFB3 and between CPO and MSX1, suggesting that these genes are involved in the pathogenesis of clefting. In addition, a mutation search in the genes DLX2, MSX1, and TGFB3 was performed in 69 CPO patients and in a subset of the CL/P patients. No common mutations were found in the coding regions of these genes; however, several rare variants of MSX1 and TGFB3 were found that may alter the latters' normal function. These results form the basis for future research, including (a) mutation searches in the MSX1 and TGFB3 genes in Caucasian CL/P patients and (b) extension of the search for MSX1 mutations in CPO patients to the noncoding regions.  相似文献   
43.
44.
It is proposed that both polar and radical reactions should be considered when discussing radical ion reactivity. The fact that only the polar reactivity has dominated previous discussions is pointed out. It is argued that if the configuration mixing model is applicable for the estimation of radical cation-nucleophile (or cation-nucleophile) combination reaction barriers, the theory should also explain the reactivity of the proton toward anionic nucleophiles. The model severely overestimates reaction barriers for the latter reactions. The discussion is centered around the following hypothesis: In the absence of severe steric effects, the reactivity of radical ions, especially evident in the reactions with radicals (for example very few radical cations react with dioxygen at measurable rates), is dominated by the degree of coupling between charge and radical centers. Evidence from the literature supporting the hypothesis is presented for a number of different classes of radical ion reactions. Further work to test the validity of the hypothesis is proposed for many of the reaction types. Triarylmethyl radicals and carbenium ions are suggested as models to which the radical and polar reactivities of 9,10-diarylanthracene radical cations may be compared. It is concluded that the radical cation/carbenium ion comparison (for the reaction with acetate ion) would show similar reactivities while the radical cation/free radical comparison (for the reaction with dioxygen) would fail, since no reaction at all would be observed with the radical cation while the free radical reacts rapidly.  相似文献   
45.
46.
To establish an animal model for the controlled study of enteral nutrition by tube, five adult chair-adapted primates (Macaca fasicularis) had gastrostomy and jejunostomy tubes placed for the delivery of a modified protein isolate diet. Following 7 days of postoperative depletion with a hypocaloric infusion of dextrose (20 kcal, 0 g N/kg/day), the animals were repleted for 10 days with tube feedings (124 kcal, 0.73 g N/kg/day). There was no operative mortality or morbidity and each animal demonstrated conversion to anabolism by significant weight gain, positive nitrogen balance, and net protein synthesis as determined by [15N]glycine protein turnover rates. Significant correlation was found between caloric intake and nitrogen balance at the level of nitrogen provided in this diet (r = 0.88, p less than 0.05). This model was found to be well suited for the surgical and nutritional techniques required for the long-term study of enteral nutrition by tube.  相似文献   
47.
Aspiration of hydrochloric acid in rabbits resulted in an increased P(A-a)O2 together with increases in both lung water volume and lung extravascular albumin. This finding suggests lung damage following acid aspiration is related to changes in capillary permeability, with pulmonary edema resulting from the movement of albumin and water into the interstitial space. Therapy with albumin and furosemide together reduced the lung water and albumin accumulation and decreased P(A-a)O2. Treatment with albumin or furosemide alone was ineffective. Caution should be exercised in administering albumin alone for therapy of pulmonary edema when plasma protein is not clearly decreased, or when increased pulmonary capillary permeability is suspected.  相似文献   
48.
Thirteen autistic children were compared to 13 normal children matched to them in mental age, on performance of a visual discrimination task. Form, color, and size were relevant and redundant cues. The groups did not differ significantly in mean trials to reach criterion or in breadth of learning, and both groups increased their breadth of learning after 50 trials of overtraining. Form was preferred to color and size by both autistic and normal children. Within each group, rank on mental age was highly correlated with rank in breadth of learning. Verbal and nonverbal autistic children did not differ in breadth of learning or in dimensional preference. Even nonverbal autistics equaled the performance of their normal controls. Our results suggest that overselective attention is better understood as part of a general developmental lag in cognition in autistic children than as a specific deficit underlying psychotic behavior.  相似文献   
49.
A negative temperature differential between fruits or vegetables and the water in which they are immersed theoretically enhances infiltration of water and any microorganisms it might contain into tissues. The effect of temperature differentials between cantaloupes and wash water, each at 4 and 30 degrees C, on changes in cantaloupe weight and populations of Salmonella enterica Poona recovered from rinds and stem scar tissues of Eastern and Western (shipper) types of cantaloupes was assessed. The percent weight increase in Western cantaloupes was significantly greater (P < or = 0.05) than that in Eastern cantaloupes for all cantaloupe and inoculum temperature combinations. Salmonella Poona attachment to or infiltration of Eastern but not Western cantaloupe rind is enhanced when the fruit is at 4 degrees C, compared with 30 degrees C, regardless of the temperature of the immersion suspension. The number of Salmonella Poona cells recovered from rind tissue of Western cantaloupes at 30 degrees C immersed in inoculum at 30 degrees C was significantly less (P < or = 0.05) than that recovered from rind tissues of cantaloupes at 4 or 30 degrees C that were immersed in inoculum at 4 degrees C. Salmonella Poona in immersion water can adhere to or infiltrate surface tissues of cantaloupes. The populations of Salmonella Poona recovered from stem scar tissues of Eastern and Western types of cantaloupes were not significantly (P > 0.05) affected by cantaloupe and inoculum temperature combinations. Populations of cells adhering to or infiltrating various cantaloupe tissues is not dictated entirely by temperature differentials between fruits and immersion suspensions: rather, it also apparently is influenced by structures unique to surface tissues.  相似文献   
50.
Arachis hypogaea L. ‘Tifspan’ and ‘Florunner’ peanuts (groundnuts) were treated with selected foliar fungicides for control of Cercospora leafspot. Peanut fruits were harvested on three different dates and analysed for aflatoxin, oil and protein content and degree of maturity. No significant differences (P = <0.05) in aflatoxin incidence were associated with either fungicide treatments or harvest dates. Significant differences were observed, however, in the percentage protein and oil content of the peanut kernels, depending upon the fungicide treatment. Delayed maturity was caused by specific fungicide treatments.  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