全文获取类型
收费全文 | 4319篇 |
免费 | 60篇 |
国内免费 | 9篇 |
专业分类
电工技术 | 54篇 |
综合类 | 2篇 |
化学工业 | 445篇 |
金属工艺 | 78篇 |
机械仪表 | 49篇 |
建筑科学 | 29篇 |
矿业工程 | 1篇 |
能源动力 | 122篇 |
轻工业 | 105篇 |
水利工程 | 21篇 |
石油天然气 | 18篇 |
无线电 | 275篇 |
一般工业技术 | 564篇 |
冶金工业 | 2318篇 |
原子能技术 | 16篇 |
自动化技术 | 291篇 |
出版年
2023年 | 23篇 |
2022年 | 52篇 |
2021年 | 68篇 |
2020年 | 52篇 |
2019年 | 42篇 |
2018年 | 65篇 |
2017年 | 62篇 |
2016年 | 66篇 |
2015年 | 40篇 |
2014年 | 76篇 |
2013年 | 137篇 |
2012年 | 84篇 |
2011年 | 126篇 |
2010年 | 92篇 |
2009年 | 118篇 |
2008年 | 83篇 |
2007年 | 78篇 |
2006年 | 57篇 |
2005年 | 54篇 |
2004年 | 48篇 |
2003年 | 57篇 |
2002年 | 43篇 |
2001年 | 42篇 |
2000年 | 40篇 |
1999年 | 89篇 |
1998年 | 665篇 |
1997年 | 460篇 |
1996年 | 283篇 |
1995年 | 184篇 |
1994年 | 153篇 |
1993年 | 160篇 |
1992年 | 33篇 |
1991年 | 46篇 |
1990年 | 33篇 |
1989年 | 35篇 |
1988年 | 52篇 |
1987年 | 44篇 |
1986年 | 34篇 |
1985年 | 45篇 |
1984年 | 31篇 |
1983年 | 22篇 |
1982年 | 32篇 |
1981年 | 35篇 |
1980年 | 38篇 |
1979年 | 15篇 |
1978年 | 15篇 |
1977年 | 65篇 |
1976年 | 140篇 |
1975年 | 13篇 |
1973年 | 16篇 |
排序方式: 共有4388条查询结果,搜索用时 93 毫秒
51.
SS Gropper MC Naglak M Nardella A Plyler S Rarback S Yannicelli 《Canadian Metallurgical Quarterly》1993,12(2):108-114
Adequacy of nutrient intakes of adolescents with and without phenylketonuria (PKU) and infants and children with and without maple syrup urine disease (MSUD) were assessed using 3-day diet records sorted by disease and by age of the subject. Mean intakes of all nutrients were greater than two-thirds of the Recommended Dietary Allowances (RDA) or Estimated Safe and Adequate Daily Dietary Intakes (ESADDI) for all adolescents studied, with the exception of selenium (Se) in PKU adolescents, which averaged 27.8 micrograms. For adolescents with PKU, > 50% of the RDA or ESADDI for all nutrients was provided by elemental or modified protein hydrolysate medical foods, except for vitamin A in children aged 11-15 years and Se in children 11-18 years. Mean nutrient intakes of all infants and children were greater than two-thirds of the RDA or ESADDI for all nutrients except Se in MSUD children aged 1-11 years, where intakes ranged from 6.4 to 13.2 micrograms (21-66% of the RDA). The medical foods provided for most of the RDA and ESADDI recommendations, with the exception of Se in MSUD children. 相似文献
52.
For complex genetic diseases involving incomplete penetrance, genetic heterogeneity, and multiple disease genes, it is often difficult to determine the molecular variant(s) responsible for the disease pathogenesis. Linkage and association studies may help identify genetic regions and molecular variants suspected of being directly responsible for disease predisposition or protection, but, especially for complex diseases, they are less useful for determining when a predisposing molecular variant has been identified. In this paper, we expand upon the simple concept that if a genetic factor predisposing to disease has been fully identified, then a parent homozygous for this factor should transmit either of his/her copies at random to any affected children. Closely linked markers are used to determine identity by descent values in affected sib pairs from a parent homozygous for a putative disease predisposing factor. The expected deviation of haplotype sharing from 50%, when not all haplotypes carrying this factor are in fact equally predisposing, has been algebraically determined for a single locus general disease model. Equations to determine expected sharing for multiple disease alleles or multiple disease locus models have been formulated. The recessive case is in practice limiting and therefore can be used to estimate the maximum proportion of putative susceptibility haplotypes which are in fact predisposing to disease when the mode of inheritance of a disease is unknown. This method has been applied to 27 DR3/DR3 parents and 50 DR4/DR4 parents who have at least 2 children affected with insulin dependent diabetes mellitus (IDDM). The transmission of both DR3 and DR4 haplotypes is statistically different from 50% (P < 0.05 and P < 0.001, respectively). An upper estimate for the proportion of DR3 haplotypes associated with a high IDDM susceptibility is 49%, and for DR4 haplotypes 38%. Our results show that the joint presence of non-Asp at DQ beta position 57 and Arg at DQ alpha position 52, which has been proposed as a strong IDDM predisposing factor, is insufficient to explain the HLA component of IDDM predisposition. 相似文献
53.
S Sidney B Sternfeld SS Gidding DR Jacobs DE Bild A Oberman WL Haskell RS Crow JM Gardin 《Canadian Metallurgical Quarterly》1993,25(8):911-916
Symptom-limited, graded exercise treadmill testing was performed by 4,968 white and black adults, ages 18-30 yr, during the baseline examination for the Coronary Artery Risk Development in Young Adults (CARDIA) study. Compared with nonsmokers, the mean exercise test duration of smokers was 29-64 s shorter depending on race/gender group (all P < 0.001), but mean duration to heart rate 130 (beats.min-1) ranged from 20-50 s longer (P < 0.05). In each race/gender group, test duration to heart rates up to 150 was 15-35 s longer (P < 0.05) in smokers than in nonsmokers after adjustment for age, sum of skinfolds, hemoglobin, and physical activity score. The mean maximum heart rate was lower in smokers than in nonsmokers (difference ranging from 6.7 beats.min-1 in white men to 11.2 beats.min-1 lower in black women, P < 0.001), although maximum rating of perceived exertion was nearly identical in smokers and nonsmokers. Chronic smoking appears to blunt the heart rate response to exercise, so that exercise duration to submaximal heart rates is increased even though maximal performance is impaired. This may result from downloading of beta-receptors caused by smoking. Smoking status should be considered in the evaluation of physical fitness data utilizing submaximal test protocols, or else the fitness of smokers relative to nonsmokers is likely to be overestimated. 相似文献
54.
S Sawaguchi BY Yue JE Kawa IL Chang SS Twining B Meberg 《Canadian Metallurgical Quarterly》1994,35(1):251-261
PURPOSE: To examine in the human trabecular meshwork lysosomal enzymes and one inhibitor of serine proteases that actively participate in the degradation of macromolecules into low molecular weight constituents. METHODS: Using an avidin-biotin-peroxidase technique, lysosomal proteases and alpha 1-proteinase inhibitor were examined in the trabecular meshwork of 23 human eyes with donor ages ranging from 2 to 90 years. These eyes were categorized into three age groups (< or = 20, 21 to 49, and > or = 50 years). Histochemical staining for lysosomal hydrolases was also performed on frozen sections of 20 human eyes. The staining was analyzed by an image analyzer and the levels of lysosomal proteases were further measured by biochemical assays. RESULTS: The trabecular meshwork from all the eyes stained intensely against antibodies to cathepsins B and G and alpha 1-proteinase inhibitor. The staining for elastase was weaker but evident. Image analyses revealed that the staining intensity for each protease or inhibitor was similar in all age groups. The staining in the uveal meshwork appeared to be the strongest among all the trabecular meshwork regions. Biochemical assays of tissue extracts confirmed that the enzyme and inhibitor levels were comparable among the three donor age groups. Activities of two lysosomal hydrolases, acid phosphatase and acid esterase, were also found in trabecular meshwork cells of 20 eyes. No apparent difference in enzyme activities was found with increasing age, and variation related to region was not observed. CONCLUSIONS: This study demonstrated the age-independent distribution of a variety of lysosomal enzymes and a protease inhibitor in the human trabecular meshwork. The presence of these proteins suggests a possible role in the metabolic operation of the trabecular meshwork. 相似文献
55.
56.
57.
In recent years, the transition metal trichalcogenides (TX3) of Group IVB, VB and VIB have received much more attention because of the considerable diversity in their physical properties. The most striking feature of these compounds is that the structure here may be classified into three types depending on the number of different TX3 chains present in the unit cell. Thus ZrSe3, TaSe3 and NbSe3 are the representative compounds having one, two and three types of chain based on the different bond lengths for the (X2)2– pairs in the base of the TX3 trigonal prismatic framework. A similar model is also applicable in the case of NbS3, with the addition of a 2b-superstructure associated with the formation of niobium pairs. The chain structure also facilitates the process of intercalation which has been most effectively used in secondary batteries. These compounds exhibit the superconductivity phenomena and charge density wave, etc. and also find application in photoelectrochemical cells. An attempt has been made here to review the up-to-date chemistry of transition metal trichalcogenides related with their preparation, structure and properties such as physical and chemical, thermodynamic, electrical, magnetic and optical properties, intercalation and use in the photoelectrochemical cells. 93 相似文献
58.
59.
The radical copolymerization of acyclic terpene namely geraniol [GER] with acrylonitrile [AN] in DMF at (70 ± 0.1)°C for 1 h, using benzoylperoxide (BPO) as an initiator has been carried out under inert atmosphere of nitrogen. The kinetic expression for reaction is Rp ∝ [BPO]0.5 [AN]1.0 [GER]1.0. The IR spectrum of the copolymer shows bands at 3432 and at 2244 cm?1 due to ? OH group of GER and ? CN group of AN, respectively. The 13C‐NMR spectrum shows peaks at 73–75 δ ppm and 116–120 δ ppm due to ? OH group of GER and ? CN group of AN, respectively. The thermogravimetric analysis and differential scanning calorimetry study shows that copolymer is thermally stable up to 407°C and has glass transition temperatures (Tg) 56°C. The reactivity ratios r1 (AN) and r2 (GER) have been calculated as 0.05 and 0.005, respectively. The Alfrey‐Price Q‐e parameter for GER has been calculated as 0.094 and ?2.0, respectively. The molecular weights of the copolymers have been evaluated by gel‐permeation chromatography. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
60.
The dependence between the activity parameters of muscarine antagonists in the prevention of haloperidol catalepsy in rats and those in tests characterizing the interaction of ligands and various subtypes of m-cholinoceptors was studied. It was established by constructing the mathematical dependence that blockade of m1-cholinoceptors increases, while that of m2-cholinoceptors reduces the antiparkinsonian activity of the drugs. The activity of the muscarine antagonist pentiphan in the prevention of haloperidol-induced catalepsy in rats exceeds the activity of such traditional antiparkinsonian drugs as cyclodol and amedin. 相似文献