全文获取类型
收费全文 | 2618篇 |
免费 | 3篇 |
国内免费 | 1篇 |
专业分类
综合类 | 1篇 |
化学工业 | 8篇 |
金属工艺 | 1篇 |
建筑科学 | 1篇 |
轻工业 | 19篇 |
石油天然气 | 1篇 |
武器工业 | 1篇 |
一般工业技术 | 6篇 |
冶金工业 | 2578篇 |
自动化技术 | 6篇 |
出版年
2018年 | 1篇 |
2017年 | 2篇 |
2016年 | 1篇 |
2014年 | 1篇 |
2012年 | 2篇 |
2011年 | 4篇 |
2010年 | 1篇 |
2009年 | 2篇 |
2008年 | 5篇 |
2004年 | 4篇 |
2003年 | 5篇 |
2002年 | 2篇 |
2001年 | 3篇 |
2000年 | 4篇 |
1999年 | 78篇 |
1998年 | 795篇 |
1997年 | 458篇 |
1996年 | 281篇 |
1995年 | 146篇 |
1994年 | 135篇 |
1993年 | 151篇 |
1992年 | 26篇 |
1991年 | 32篇 |
1990年 | 30篇 |
1989年 | 39篇 |
1988年 | 35篇 |
1987年 | 30篇 |
1986年 | 25篇 |
1985年 | 29篇 |
1983年 | 7篇 |
1982年 | 16篇 |
1981年 | 13篇 |
1980年 | 15篇 |
1978年 | 7篇 |
1977年 | 58篇 |
1976年 | 175篇 |
1975年 | 2篇 |
1973年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有2622条查询结果,搜索用时 15 毫秒
81.
RS Kirby 《Canadian Metallurgical Quarterly》1995,110(6):649-650
82.
A new method was developed for binding poly-(ethylene oxide) (PEO) to polymer surfaces that involves the use of electron beam irradiation in two steps. In the first, methacrylic acid was grafted and polymerized to a polymer surface, changing it from hydrophobic to hydrophilic. Exposure of this surface to aqueous PEO solutions resulted in strong hydrogen bonding of the PEO, which was covalently grafted in a second radiation step. The PEO grafts were stable; they could not be removed with extensive washing with water, soaking in basic solution, or gentle mechanical scraping. Both monolayers and multilayers of PEO were formed. The density of the monolayers were found to have little dependence on the molecular weight or concentration of the PEO solution; multilayers could be controlled by varying the viscosity of the PEO solution and the method of application. The PEO-grafted monolayers were tested for their ability to prevent protein adsorption of cytochrome-c, albumin, and fibronectin. Monolayers of star PEO were the most effective, at best showing a 60% decrease in adsorption from untreated controls. One million molecular wight linear PEO monolayers were almost as effective as star monolayers, and 35,000 g/mol linear PEO was bound too closely to the surface, owing to its small size, to have much impact in preventing protein adsorption. The reason for the continued protein adsorption was believed to be due to a close grafting of the PEO to the surface, as well as the grafted methacrylic acid chains being long enough to extend through the PEO monolayer, thus being accessible on the surface. 相似文献
83.
DJ Drake RS Jensen J Busch-Petersen JK Kawakami M Concepcion Fernandez-Garcia P Fan A Makriyannis MA Tius 《Canadian Metallurgical Quarterly》1998,41(19):3596-3608
The stereoelectronic requirements for interaction of the southern aliphatic hydroxyl of cannabimimetic pharmacophores with the CB1 and CB2 receptors are explored. The stereoselective syntheses of three series of classical/nonclassical hybrid cannabinoids are described. These compounds were designed to investigate the importance of the southern aliphatic hydroxyl (SAH) pharmacophore for cannabimimetic activity. Variation in the chain length of the SAH moiety in these 6beta-(hydroxyalkyl)dihydrobenzopyran analogues, from 6beta-hydroxymethyl to 6beta-(omega-hydroxyethyl) and 6beta-(omega-hydroxypropyl), and the effects of replacing the hydroxyl functionality by hydride and iodide are reported. Our results indicate that the SAH pharmacophore has less pronounced effects than the C-3 aliphatic chain on cannabinoid activity. Furthermore, it appears that this southern molecular component is capable of interacting with two different subsites on the receptor and that the nature of this interaction is determined by the terminal substituent on the C-6beta alkyl group. One of the subsites can accommodate the relatively polar SAH pharmacophore, while the second subsite interacts with more hydrophobic C-6beta substituents and can accommodate large spherical pharmacophores separated by three methylene carbons from the tricyclic cannabinoid template. 相似文献
84.
Modular polyketide synthases (PKSs), such as the 6-deoxyerythronolide B synthase (DEBS), catalyze the biosynthesis of structurally complex and medicinally important natural products. These large multienzymes are organized into a series of functional units known as modules. Each dimeric module contains two catalytically independent clusters of active sites homologous to those of vertebrate fatty acid synthases. Earlier studies have shown that modules consist of head-to-tail homodimers in which ketosynthase (KS) and acyl carrier protein (ACP) domains are contributed by opposite subunits to form a catalytic center. Here, we probe the functional topology of the acyltransferase (AT) domain which transfers the methylmalonyl moiety of methylmalonyl-CoA onto the phosphopantetheine arm of the ACP domain. Using a bimodular derivative of DEBS, the AT domain of module 2 (AT2) was inactivated by site-directed mutagenesis. Heterodimeric protein pairs were generated in vitro between the inactivated AT2 (AT2 degrees) polypeptide and an inactive KS1 (KS1 degrees) or KS2 (KS2 degrees) protein. Both of these hybrid proteins supported polyketide synthesis, suggesting that AT2 can perform its function from either subunit. The apparent catalytic rate constants for each of the two hybrid protein pairs, KS1 degrees/AT2 degrees and KS2 degrees/AT2 degrees, were identical, indicating that no significant kinetic preference exists for a particular AT2-ACP2 combination. These results suggest that the AT domain can be shared between the two clusters of active sites within the same dimeric module. Such a novel structural organization might provide a functional advantage for the efficient biosynthesis of polyketides. 相似文献
85.
We describe two unusual cases in sheep of subclinical mastitis caused by Streptococcus parasanguinis. This bacterium has been associated with the development of experimental endocarditis; its presence at relatively high concentrations in apparently healthy sheep milk may pose a health risk in persons with predisposing heart lesions. 相似文献
86.
L Madlensky TC Berk BV Bapat RS McLeod J Couture D Baron T Hiruki M Redston Z Cohen S Gallinger 《Canadian Metallurgical Quarterly》1995,5(2):355-360
Hereditary nonpolyposis colorectal cancer (HNPCC) is a genetic disorder characterized by a strong family history of colorectal and extracolonic cancers, usually at a young age. This article presents a new provincial service for families with HNPCC. The Steve Atanas Stavro Familial Gastrointestinal Cancer Registry at Mount Sinai Hospital is accruing patients that meet a set of criteria establishing a putative diagnosis of HNPCC. The objectives of the Registry are to develop and assess patient pedigrees, to coordinate screening procedures for at-risk persons, to maintain a prospective database of patient information, to provide education and support for families and to contribute to research. To date, surgeons and patients are the most common referral sources, while oncologists and geneticists are the least common. The ultimate goal of the HNPCC service is the secondary prevention of cancer and a corresponding decrease in mortality for HNPCC family members. 相似文献
87.
JG Wilcox FZ Stanczyk RS Morris E Gentzschein RA Lobo 《Canadian Metallurgical Quarterly》1996,66(5):748-752
OBJECTIVE: To determine the independent biologic effects of 17 alpha-dihydroequilin sulfate. DESIGN: Prospective randomized study. SETTING: University of Southern California Medical Center. PATIENTS(S): Twenty-one postmenopausal women, mean age 50 +/- 2 (+/-SEM) years, and mean body mass index 27 +/- 2. INTERVENTION(S): Women were randomized to receive daily oral doses of either 1.25 mg of estrone sulfate (E1S), 0.2 mg of 17 alpha-dihydroequilin sulfate, or a combination. Three blood and urine samples were obtained before and after 30 and 90 days of treatment. RESULT(S): After 30 and 90 days of treatment, E1S alone increased sex hormone-binding globulin (SHBG) levels significantly, 19.7% +/- 6.0% and 61.3% +/- 13.0%, whereas 17 alpha-dihydroequilin sulfate reduced SHBG levels, 20.8% +/- 68% and 12.4% +/- 7.5%, respectively. Nevertheless, the combination of E1S and 17 alpha-dihydroequilin sulfate significantly increased SHBG levels, 103% +/- 27.9% and 98.2% +/- 19.1%, compared with baseline at 30 and 90 days. Fewer changes were evident with corticosteroid-binding globulin (CBG). After 90 days of treatment, CBG levels significantly increased 30.9% +/- 5.5% with E1S, decreased by 7.2% +/- 5.0% with 17 alpha-dihydroequilin sulfate, and, with the combination, significantly increased by 10.5% +/- 2.4% compared with baseline. Changes in lipids and lipoproteins were more variable. However, high-density-lipoprotein cholesterol increased significantly with E1S at 30 and 90 days compared with baseline, 96.5% +/- 39% and 91.5% +/- 22.6%, and with the combination increased 66.4% +/- 13.3% and 79.2% +/- 24.4%, respectively. Fewer changes were evident with 17 alpha-dihydroequilin sulfate alone, decreasing 4.4% +/- 22% and 2.6% +/- 21.3%. Urinary ratios of bone collagen equivalents-creatinine and calcium-creatinine decreased in all three groups. However, the combination group resulted in a significantly greater percentage decrease in bone collagen equivalents-creatinine than with E1S alone. CONCLUSIONS(S): 17 alpha-Dihydroequilin sulfate could modify some of the first-pass effects of conjugated equine estrogens and act synergistically with other conjugated equine estrogens to reduce bone resorption. 相似文献
88.
IK Temple RJ Gardner DO Robinson MS Kibirige AW Ferguson JD Baum JC Barber RS James JP Shield 《Canadian Metallurgical Quarterly》1996,5(8):1117-1121
Transient neonatal diabetes mellitus (TNDM) is a rare form of childhood diabetes which usually resolves in the first 6 months of life but which predisposes to type 2 diabetes of adult onset. We recently reported paternal uniparental isodisomy of chromosome 6 (UPD6) in two children with TNDM and proposed that there may be an imprinted gene important in the aetiology of diabetes on chromosome 6. We now describe two unrelated families which independently suggest that the gene is imprinted, is paternally expressed and maps to 6q22-q23. One family has a duplication while the other, with familial TNDM, shows linkage to a marker in this region. 相似文献
89.
Objective. To assess the role of coronal and sagittal vertebral clefts in diagnosing skeletal dysplasias. Material and Methods. A search in the database at the International Skeletal Dysplasia Registry revealed 40 different diagnoses in which coronal or sagittal clefts were present, the major groups being: atelosteogenesis, chondrodysplasia punctata, dyssegmental dysplasia, Kniest dysplasia and short rib polydactyly syndrome. We reviewed all firm cases with both AP and lateral films of the spine in these major groups (n = 143), with patients' ages ranging from 20 weeks of gestation up to 26 years of age. Results. Ninety-four percent of all clefts were found in children less than 1 year of age, mainly located in the thoracolumbar region. Fifty-six percent of the clefts were observed in boys. Coronal clefts were more common than sagittal clefts. Clefts were most frequently observed in atelosteogenesis (88%), followed by chondrodysplasia punctata (79%), dyssegmental dysplasia (73%), Kniest dysplasia (63%) and short rib polydactyly syndrome (53%). Conclusion. Vertebral clefts are of major diagnostic value in the groups mentioned above, especially before 1 year of age. The search did not come up with new entities in which vertebral clefts are of major diagnostic value. 相似文献
90.
CA Porr DS Kronfeld LA Lawrence RS Pleasant PA Harris 《Canadian Metallurgical Quarterly》1998,76(7):1875-1879
Diet and exercise are two management factors that affect bone density and strength. We proposed that bone density and calcium status would be affected by deconditioning for 12 wk and by dietary Ca concentration. Eleven highly conditioned Arabian horses were taken out of training and placed in stalls for 12 wk. Horses were walked on a mechanical walker in two 30-min sessions, 7 d/wk. Diets were designated CC (.36% Ca) and HC (.62% Ca). Data were collected every 21 d. Serum or plasma were analyzed for total and ionized Ca, parathyroid hormone, osteocalcin, hydroxyproline, electrolytes, and blood gases. Bone mineral content (BMC) of the left third metacarpal bone was estimated by radiographic photometry using an aluminum step wedge, which was exposed in each radiograph, as a reference standard for an image analysis system. During deconditioning, BMC decreased by approximately 1.1 g/2 cm, or .45% per week. This decrease was unaffected by dietary Ca. Serum Ca concentration increased with deconditioning. The results suggest that dietary Ca at twice the currently recommended level did not prevent the loss of BMC in response to deconditioning. Loss of BMC during 12 wk of stall confinement may weaken bones, increasing the risk of skeletal injuries when training is resumed. 相似文献