全文获取类型
收费全文 | 262篇 |
免费 | 4篇 |
专业分类
化学工业 | 20篇 |
建筑科学 | 7篇 |
能源动力 | 7篇 |
轻工业 | 17篇 |
无线电 | 13篇 |
一般工业技术 | 34篇 |
冶金工业 | 149篇 |
自动化技术 | 19篇 |
出版年
2022年 | 3篇 |
2021年 | 4篇 |
2019年 | 6篇 |
2018年 | 4篇 |
2017年 | 5篇 |
2016年 | 3篇 |
2015年 | 2篇 |
2014年 | 1篇 |
2013年 | 4篇 |
2012年 | 4篇 |
2011年 | 3篇 |
2010年 | 8篇 |
2009年 | 5篇 |
2008年 | 8篇 |
2007年 | 3篇 |
2006年 | 10篇 |
2005年 | 5篇 |
2004年 | 3篇 |
2003年 | 1篇 |
2002年 | 1篇 |
2001年 | 5篇 |
2000年 | 8篇 |
1999年 | 6篇 |
1998年 | 54篇 |
1997年 | 20篇 |
1996年 | 18篇 |
1995年 | 11篇 |
1994年 | 7篇 |
1993年 | 7篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1977年 | 5篇 |
1976年 | 12篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1970年 | 1篇 |
1969年 | 2篇 |
排序方式: 共有266条查询结果,搜索用时 15 毫秒
101.
COPD is an extremely common, chronic disorder characterized by a reduction in airflow after the administration of an inhaled bronchodilator as measured by the FEV1. The diagnosis is suspected in patients with a history of several decades of cigarette smoking who present with nonspecific respiratory symptoms. The diagnosis is established by simple forced expiratory spirometry. Baseline evaluation usually includes a chest radiograph and some assessment of functional capacity, either by history or with some form of exercise testing. In patients whose initial FEV1 is more severely reduced or who have significant dyspnea, an arterial blood gas is indicated at baseline. Dyspnea, hypoxemia, or hypercarbia that is out of proportion to the measured FEV1, at either presentation or follow-up, should prompt a thorough evaluation for complicating conditions. There are important roles in health care delivery and chronic disease management strategies for RCPs, primary care providers, and specialty trained pulmonary physicians. The need for repeated, extensive, or expensive testing will be largely driven by patients symptoms but disease monitoring with periodic assessments of dyspnea, functional capacity, and spirometry can be performed without great expense. 相似文献
102.
103.
OW Woltersdorf SJ deSolms EM Schultz EJ Cragoe 《Canadian Metallurgical Quarterly》1977,20(11):1400-1408
The discovery of the (acryloylaryloxy)acetic acids as a new class of potent diuretics prompted the investigation of related bicyclic compounds. Annelated analogues of the parent series, the (2-alkyl- and 2,2-dialkyl-1-oxo-5-indanyloxy)acetic acids, were the subjects of this study. Those compounds, unlike the monocyclic parent compound, lacked the double bond adjacent to the carbonyl group. More importantly, they possessed both saluretic and uricosuric properties. The optimal single 2-substituents for maximal saluretic and uricosuric activity were determined. In general, better activity was observed when a second 2-alkyl substituent (especially methyl) was present in the molecule. Replacement of the carboxy substituent by 5-tetrazolyl generally resulted in a reduction in activity. 相似文献
104.
The effect of diethylstilbestrol (DES) on the composition of tissue gain of Hereford steers was studied in a complete slaughter balance trial. Eight steers were slaughtered initially (IS) and, after 177 days on feed, eight control steers (C) and seven steers that had been fed 20 mg DES daily (DES) were slaughtered. Initial full body weight averaged 224.8 kg, and final full body weight averaged 403.0 kg for the C steers and 433.6 kg for the DES steers. Final empty body weight averaged 346.6 kg for the C steers and 368.0 kg for the DES steers. DES improved live weight gain by 17% and conversion of feed dry matter to live weight by 12%. Recovery of wet weight during slaughter averaged 99.6%. DES steers had larger rib cut weights and greater proportions of separable lean and bone plus connective tissue in the rib cuts than C steers, an ribeye area tended to be larger in DES steers. DES caused a small shift in relative body composition toward more protein, moisture and ash. Tissue gain in DES steers consisted of 28.3% more protein, 26.0% more moisture, 73.2% more ash, 1.5% less fat and 109.1% more residual (dry matter not accounted for by N x 6.25, ether extract and ash) than did tissue gain in C steers. Energy gain per unit of energy intake over the feeding period was not affected by DES treatment, but DES improved protein gain per unit of protein intake and per unit of energy intake by approximately 20% within the total empty body and by about 25% within the carcass fraction. Results confirm indirect estimates in the literature indicating that DES increases skeletal growth and lean tissue deposition in feedlot steers. 相似文献
105.
Johannes Moe 《Computers & Structures》1974,4(1):95-113
The structural design problem is formulated as a general nonlinear optimization problem with constraints. Characteristics of such problems and the solutions are discussed. Methods of solution for constrained as well as unconstrained problems are reviewed, with special emphasis on penalty function methods for constrained problems. A simple example on the solution of a design problem with discrete variables is shown, and a realistic example on the application of optimization methods in midship section design of OBO-carriers is presented. 相似文献
106.
Amniotic fluid testosterone levels were measured on specimens obtained between 12 and 25 weeks' gestation from 58 male-fetus and 77 female-fetus pregnancies. For the male fetuses the mean +/- SE amniotic fluid testosterone level of 223 +/- 10 pg/ml was significantly higher (P less than 0.001) than the concentration found for the female fetuses (40 +/- 2 pg/ml). The ranges were 104-424 and 18-82 pg/ml, respectively, for the same fetuses. In the male fetuses the highest mean level was found during the 17th gestational week, but the mean level observed during any 1 week was not significantly differenf from any other week for both sexes. These data are consistent with the concept that amniotic fluid testosterone levels may be a rapid and effective method for establishing fetal sex in utero during midgestation. 相似文献
107.
Only four instances of isolated chylopericardium following cardiac operation have been reported previously. We encountered this complication in a young patient who was operated on for infundibular pulmonary stenosis. The etiology appears to be related to a combination of intraoperative lymphatic injury and catheter-related subclavian vein thrombosis, the latter potentially elevating pressure within the thoracic duct and thereby resulting in an accumulation of chyle within the pericardial space. Therapy for this problem usually includes partial pericardiectomy with or without ligation of the thoracic duct. 相似文献
108.
The present work investigates the possibility of constructing a multivariate calibration model for predicting the composition of ground beef with respect to different meat quality types, based on intensity profiles from isoelectric focusing of water-soluble proteins. Beef mixtures containing various amounts of mechanically recovered meat, head meat and production meat from beef, were analysed by isoelectric focusing in immobilised pH-gradients. The gels were photographed and the images transferred to a digital format. By simple image processing procedures, background colour was virtually eliminated and signal strength was improved to a considerable degree. Multivariate analysis of protein profiles from the gels gave models explaining 75 to 90% of variance in sample composition. Manually deboned meat was explained to the highest degree, and with a precision of 7%. Two different qualities of mechanically recovered meat could be detected even when treated as one category. The present approach needs further refinement, but seems applicable for detecting intentional substitution of high quality meat products with low-price raw materials. One advantage of the approach is that evaluation of samples is not dependent on specific knowledge on the individual components to be analysed, so that such analytical methods are relatively easy to implement in any standard laboratory. 相似文献
109.
Tategu M Arauchi T Tanaka R Nakagawa H Yoshida K 《Molecular nutrition & food research》2008,52(4):439-446
Here, we attempted to identify novel target genes of genistein in human A549 cells. Using analysis of proteins related to cell cycle and apoptotic pathways, we confirmed an elevated level of p53 accompanying p21 Waf1/Cip1 protein in genistein-treated or genistin-treated A549 and WI-38 cells, but not in HeLa cells. In addition, a p53-upregulated modulator of apoptosis (Puma) protein accumulated significantly in genistein-treated A549 and WI-38 cells, but not in genistin-treated or beta-estradiol-treated cells, though the growth of any ingredient-treated cells was severely inhibited. Intriguingly, the caspase-3 activity of genistein-treated A549 cells, in which Puma or p53 expression was knocked-down by RNA interference (RNAi), remained unaltered compared to that in cells transfected with irrelevant RNAi. These results raise a concern that molecular targets identified by powerful omic approaches may not necessarily represent key molecules responsible for given cellular phenotypes and thus must be verified by conclusive assays. 相似文献
110.
Ertughrul OW; Errington N; Raza S; Sutcliffe MJ; Rowe AJ; Scrutton NS 《Protein engineering, design & selection : PEDS》1998,11(6):447-455
In trimethylamine dehydrogenase, a homodimeric iron-sulfur flavoprotein,the C-terminal 17 residues of each subunit (residues 713- 729) embraceresidues on the other subunit. The role of this unusual mode of interactionat the subunit interface was probed by isolating three mutant forms oftrimethylamine dehydrogenase in which the C- terminus of the enzyme wasdeleted by five residues [delta(725-729], 10 residues [delta(720-729)] and17 residues [delta(713-729)]. The solution properties and conformationalstates of the three mutant enzymes were investigated using optical,fluorescence and circular dichroism spectroscopies, ANS binding and a noveland conformationally sensitive hydrodynamic method. The data reveal thatsequential deletion of the C-terminus of trimethylamine dehydrogenase doesnot affect significantly dimer stability or the overall structuralintegrity of the enzyme. However, deletion of the C-terminus severelycompromises, but does not abolish, the ability of the enzyme to becomecovalently coupled with the redox cofactor FMN in the active site, locatedover 20 A from the C-terminus. Hydrodynamic studies reveal minorconformational changes in the deletion mutants that lead to a more compactenzyme structure. These conformational changes are probably transmitted tothe active site via altering the interaction of the C-terminus with thesecond helix in the beta/alpha barrel of trimethylamine dehydrogenase,leading to poor flavinylation during the folding of the enzyme and assemblywith FMN. 相似文献