全文获取类型
收费全文 | 2278篇 |
免费 | 3篇 |
国内免费 | 1篇 |
专业分类
化学工业 | 13篇 |
金属工艺 | 1篇 |
矿业工程 | 1篇 |
能源动力 | 1篇 |
轻工业 | 3篇 |
无线电 | 6篇 |
一般工业技术 | 2篇 |
冶金工业 | 2245篇 |
原子能技术 | 6篇 |
自动化技术 | 4篇 |
出版年
2023年 | 1篇 |
2017年 | 2篇 |
2012年 | 2篇 |
2011年 | 2篇 |
2006年 | 3篇 |
2003年 | 5篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1999年 | 71篇 |
1998年 | 737篇 |
1997年 | 372篇 |
1996年 | 267篇 |
1995年 | 132篇 |
1994年 | 112篇 |
1993年 | 120篇 |
1992年 | 19篇 |
1991年 | 29篇 |
1990年 | 18篇 |
1989年 | 21篇 |
1988年 | 19篇 |
1987年 | 22篇 |
1986年 | 15篇 |
1985年 | 17篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 12篇 |
1981年 | 13篇 |
1980年 | 17篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 72篇 |
1976年 | 160篇 |
1975年 | 4篇 |
1964年 | 1篇 |
1955年 | 2篇 |
排序方式: 共有2282条查询结果,搜索用时 15 毫秒
101.
Bierman Karen L.; Nix Robert L.; Maples Jerry J.; Murphy Susan A. 《Canadian Metallurgical Quarterly》2006,74(3):468
Although clinical judgment is often used in assessment and treatment planning, rarely has research examined its reliability, validity, or impact in practice settings. This study tailored the frequency of home visits in a prevention program for aggressive- disruptive children (n = 410; 56% minority) on the basis of 2 kinds of clinical judgment: ratings of parental functioning using a standardized multi-item scale and global assessments of family need for services. Stronger reliability and better concurrent and predictive validity emerged for the 1st kind of clinical judgment than for the 2nd. Exploratory analyses suggested that using ratings of parental functioning to tailor treatment recommendations improved the impact of the intervention by the end of 3rd grade but using more global assessments of family need did not. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
102.
103.
LL Kiefer OR Ittoop K Bunce AT Truesdale DH Willard JS Nichols SG Blanchard K Mountjoy WJ Chen WO Wilkison 《Canadian Metallurgical Quarterly》1997,36(8):2084-2090
Several mutations that cause ectopic expression of the agouti gene result in obesity, hyperinsulinemia, and yellow coat color. A candidate pathway for agouti induced obesity and hyperinsulinemia is through altered signaling by melanocortin receptors, as agouti normally regulates coat coloration through antagonism of melanocortin receptor 1. Furthermore, melanocortin peptides mediate functions including steroidogenesis, lipolysis, and thermoregulation. We report apparent inhibition dissociation constants for mouse and human agouti protein inhibition of ligand binding to the melanocortin receptors, to determine which of these receptors might be involved in agouti induced diabetes. The similarity in the apparent K(I) values for agouti inhibition of ligand binding to the brain melanocortin receptors 3 and 4 (mouse: K(I) app = 190 +/- 74 and 54 +/- 18 nM; human: K(I) app = 140 +/- 56 and 70 +/- 18 nM, respectively) suggests that the MC3-R is a potential candidate for a receptor mediating the effects of agouti protein overexpression. Agouti residues important for melanocortin receptor inhibition were identified through the analysis of deletion constructs and site-specific variants. Val83 is important for inhibition of binding to MC1-R (K(I) app for Val83Ala agouti increased 13-fold relative to wild-type protein). Arg85, Pro86, and Pro89 are important for selective inhibition of binding between MC1-R and MC3-R and MC4-R as their apparent K(I) values are essentially unchanged at MC1-R, while they have increased 6-10-fold relative to wild-type protein at MC3-R and MC4-R. 相似文献
104.
Annual nitrogen (N), phosphorus (P), and potassium (K) flows in agriculture in The Netherlands were identified and quantified in 1990, with special emphasis on pig production. Also, the effects that various management strategies in pig production have on NPK emission in 1990 were compared using a static deterministic simulation model. Ammonia emission from pig production in 1990 (60.9 Gg N) exceeded the defined target for the year 2000 (12.7 Gg N). Measures that affect volatilization of ammonia directly (i.e., introduction of low-emission stables, manure storage facilities, or manure application techniques) reduced ammonia emission most effectively. These measures, however, should be combined with a reduction in application of artificial N fertilizer to avoid an increase in N losses through leaching, run-off, or denitrification. Targets for ammonia emission in the year 2010 require a reduction in the pig population of 24 to 62%, in addition to implications of measures described in this article. National NPK losses in 1990 through leaching, run-off, or denitrification, predicted at 223.5 kg/ha for N, 32.7 kg/ha for P, and 67 kg/ha for K, exceeded government targets for the year 2010 (185 kg N/ha; 8.7 kg P/ha; norm not set for K). Reducing application of artificial NPK fertilizer reduced national NPK losses most effectively. For P, use of phytase and feeding pigs in accordance with their P requirements is required, in addition to limited use of artificial P fertilizer to meet targets for the year 2010. Hence, from an environmental point of view, pig production in The Netherlands is limited primarily by ammonia emission targets for the year 2010. 相似文献
105.
AJ Vidal-Puig RV Considine M Jimenez-Li?an A Werman WJ Pories JF Caro JS Flier 《Canadian Metallurgical Quarterly》1997,99(10):2416-2422
The peroxisome proliferator activated receptor (PPAR gamma) plays a key role in adipogenesis and adipocyte gene expression and is the receptor for the thiazolidinedione class of insulin-sensitizing drugs. The tissue expression and potential for regulation of human PPAR gamma gene expression in vivo are unknown. We have cloned a partial human PPAR gamma cDNA, and established an RNase protection assay that permits simultaneous measurements of both PPAR gamma1 and PPAR gamma2 splice variants. Both gamma1 and gamma2 mRNAs were abundantly expressed in adipose tissue. PPAR gamma1 was detected at lower levels in liver and heart, whereas both gamma1 and gamma2 mRNAs were expressed at low levels in skeletal muscle. To examine the hypothesis that obesity is associated with abnormal adipose tissue expression of PPAR gamma, we quantitated PPARgamma mRNA splice variants in subcutaneous adipose tissue of 14 lean and 24 obese subjects. Adipose expression of PPARgamma 2 mRNA was increased in human obesity (14.25 attomol PPAR gamma2/18S in obese females vs 9.9 in lean, P = 0.003). This increase was observed in both male and females. In contrast, no differences were observed in PPAR gamma1/18S mRNA expression. There was a strong positive correlation (r = 0.70, P < 0.001) between the ratio of PPAR gamma2/gamma1 and the body mass index of these patients. We also observed sexually dimorphic expression with increased expression of both PPAR gamma1 and PPAR gamma2 mRNAs in the subcutaneous adipose tissue of women compared with men. To determine the effect of weight loss on PPAR gamma mRNA expression, seven additional obese subjects were fed a low calorie diet (800 Kcal) until 10% weight loss was achieved. Mean expression of adipose PPAR gamma2 mRNA fell 25% (P = 0.0250 after a 10% reduction in body weight), but then increased to pretreatment levels after 4 wk of weight maintenance. Nutritional regulation of PPAR gamma1 was not seen. In vitro experiments revealed a synergistic effect of insulin and corticosteroids to induce PPAR gamma expression in isolated human adipocytes in culture. We conclude that: (a) human PPAR gamma mRNA expression is most abundant in adipose tissue, but lower level expression of both splice variants is seen in skeletal muscle; to an extent that is unlikely to be due to adipose contamination. (b) RNA derived from adipose tissue of obese humans has increased expression of PPAR gamma 2 mRNA, as well as an increased ratio of PPAR gamma2/gamma1 splice variants that is proportional to the BMI; (c) a low calorie diet specifically down-regulates the expression of PPAR gamma2 mRNA in adipose tissue of obese humans; (d) insulin and corticosteroids synergistically induce PPAR gamma mRNA after in vitro exposure to isolated human adipocytes; and (e) the in vivo modulation of PPAR gamma2 mRNA levels is an additional level of regulation for the control of adipocyte development and function, and could provide a molecular mechanism for alterations in adipocyte number and function in obesity. 相似文献
106.
A Madan M Sluzewski WJ van Rooij CC Tijssen JL Teepen 《Canadian Metallurgical Quarterly》1997,39(11):777-780
Deep cerebral vein thrombosis can present with acute, severe neurological symptoms and may be rapidly fatal as in the 20-year-old woman reported here. Although MRI is superior for establishing the diagnosis, CT is usually the first examination performed in the clinical setting. It is therefore important to recognise certain indicators such as extensive bithalamic low density. These and certain other less specific signs are correlated with the MRI and autopsy findings. 相似文献
107.
WJ Chodzko-Zajko 《Canadian Metallurgical Quarterly》1997,18(2):95-104; quiz 104-5
This article discusses the physiological changes that accompany normal aging and current understandings of how environmental factors interact with a person's genetic mechanisms to slow or speed up the aging process. Chronological age is contrasted with biological age to illustrate the different rates and extent of anatomical changes and functional declines observed in older people of the same age, behaviors that appear to delay or reduce the inevitable progression of sensescence, the extraordinary heterogeneity of the aging population, and the complexity of the processes responsible for the consequences of human aging. 相似文献
108.
CJ Bouma WJ Niessen KJ Zuiderveld EJ Gussenhoven MA Viergever 《Canadian Metallurgical Quarterly》1997,1(4):363-377
One prerequisite for standard clinical use of intravascular ultrasound imaging is rapid evaluation of the data. The main quantities to be extracted from the data are the size and the shape of the lumen. Until now, no accurate, robust and reproducible method to obtain the lumen boundaries from intravascular ultrasound images has been described. In this study, 21 different (semi-)automated binary-segmentation methods for determining the lumen are compared with manual segmentation to find an alternative for the laborious and subjective procedure of manual editing. After a preprocessing step in which the catheter area is filled with lumen-like grey values, all approaches consist of two steps: (i) smoothing the images with different filtering methods and (ii) extracting the lumen by an object definition method. The combination of different filtering methods and object definition methods results in a total of 21 methods and 80 experiments. The results are compared with a reference image, obtained from manual editing, by use of four different quality parameters--two based on squared distances and two based on Mahalanobis distances. The evaluation has been carried out on 15 images, of which seven are obtained before balloon dilation and eight after balloon dilation. While for the post-dilation images no definite conclusions can be drawn, an automated contour model applied to images smoothed with a large kernel appears to be a good alternative to manual contouring. For pre-dilation images a fully automated active contour model, initialized by thresholding, preceded by filtering with a small-scale median filter is the best alternative for manual delineation. The results of this method are even better than manual segmentation, i.e. they are consistently closer to the reference image than the average distance of all individual manual segmentations. 相似文献
109.
Apoptosis is a form of programmed cell death serving physiologic and homeostatic functions. However, recent evidence implicating apoptosis in the etiology and pathophysiology of known human diseases, such as heart diseases, cancer, AIDS, and neurodegenerative and autoimmune diseases are continually surfacing. This has spawned the need for identifying which methods are the most effective and well accepted to decipher its presence in a variety of research settings. We have therefore detailed the morphology and biochemical features of apoptotic cell death, with an emphasis on discriminating it from necrosis. In addition, we describe specific and selective techniques which are optimal to target hallmark apoptotic features, such as microscopy, Annexin V labeling, in situ nick-end labeling (TUNEL), and DNA fragmentation analysis by gel electrophoresis and ELISA for oligonucleosome-sized DNA. The advantages and disadvantages of each technique are discussed, as well as their experimental importance relative to one another. The methods have been described in a stepwise fashion, and can readily be applied in the majority of cell systems. Whether working on the tissue or single cell level, these methods are highly effective in qualifying and quantifying apoptosis. The application of these methods in conjunction with molecular techniques can further delineate the underlying mechanisms of apoptosis. 相似文献
110.
Acute bronchitis is a lower respiratory tract infection that causes reversible bronchial inflammation. In up to 95 percent of cases, the cause, is viral. While antibiotics are often prescribed for patients with acute bronchitis, little evidence shows that these agents provide significant symptomatic relief or shorten the course of the illness. In a few small studies, bronchodilators such as albuterol have been found to relieve some symptoms of acute bronchitis. Increased attention is being given to the role of Chlamydia species in acute bronchitis and adult-onset asthma. Studies in progress may help to clarify the importance of these organisms in acute bronchitis and to determine whether early treatment can prevent or ameliorate asthma. 相似文献