全文获取类型
收费全文 | 3133篇 |
免费 | 34篇 |
国内免费 | 14篇 |
专业分类
电工技术 | 41篇 |
综合类 | 28篇 |
化学工业 | 58篇 |
金属工艺 | 4篇 |
机械仪表 | 104篇 |
建筑科学 | 15篇 |
矿业工程 | 6篇 |
能源动力 | 6篇 |
轻工业 | 355篇 |
水利工程 | 2篇 |
无线电 | 15篇 |
一般工业技术 | 99篇 |
冶金工业 | 2329篇 |
原子能技术 | 3篇 |
自动化技术 | 116篇 |
出版年
2022年 | 17篇 |
2020年 | 18篇 |
2019年 | 30篇 |
2018年 | 5篇 |
2014年 | 6篇 |
2013年 | 155篇 |
2012年 | 31篇 |
2011年 | 22篇 |
2010年 | 31篇 |
2009年 | 28篇 |
2008年 | 30篇 |
2007年 | 34篇 |
2006年 | 22篇 |
2005年 | 24篇 |
2004年 | 23篇 |
2003年 | 21篇 |
2002年 | 15篇 |
2001年 | 4篇 |
2000年 | 10篇 |
1999年 | 80篇 |
1998年 | 760篇 |
1997年 | 436篇 |
1996年 | 287篇 |
1995年 | 156篇 |
1994年 | 126篇 |
1993年 | 150篇 |
1992年 | 26篇 |
1991年 | 31篇 |
1990年 | 41篇 |
1989年 | 40篇 |
1988年 | 39篇 |
1987年 | 54篇 |
1986年 | 38篇 |
1985年 | 38篇 |
1984年 | 10篇 |
1983年 | 6篇 |
1982年 | 13篇 |
1981年 | 22篇 |
1980年 | 19篇 |
1979年 | 8篇 |
1978年 | 5篇 |
1977年 | 60篇 |
1976年 | 126篇 |
1975年 | 6篇 |
1974年 | 3篇 |
1973年 | 5篇 |
1969年 | 5篇 |
1958年 | 4篇 |
1955年 | 18篇 |
1954年 | 16篇 |
排序方式: 共有3181条查询结果,搜索用时 15 毫秒
31.
KE Ensrud DM Black L Palermo DC Bauer E Barrett-Connor SA Quandt DE Thompson DB Karpf 《Canadian Metallurgical Quarterly》1997,157(22):2617-2624
BACKGROUND: The efficacy of antiresorptive therapy in preventing fractures in women at highest fracture risk, such as very elderly women or those with severe osteoporosis, is uncertain. PARTICIPANTS AND METHODS: Using data from a double-blind, randomized, placebo-controlled clinical trial that enrolled 2027 postmenopausal women aged 55 to 81 years with low femoral neck bone mineral density (BMD) and existing vertebral fractures, we examined the consistency of the effect of treatment with alendronate sodium in preventing fractures within a priori-specified risk subgroups defined at baseline by age, bone density, number of preexisting vertebral fractures, and history of postmenopausal fracture. The women were randomized to oral administration of alendronate or placebo and followed up for an average of 2.9 years. The initial dose of alendronate sodium was 5 mg/d; the dosage was increased from 5 to 10 mg/d at 24 months. New vertebral fractures, the primary end point of this arm of the trial, were defined by morphometry as a decrease of 20% and at least 4 mm in any vertebral height between baseline and a follow-up radiograph at 36 months. Incident clinical fractures, the secondary end point, included nonspine and clinical (symptomatic) vertebral fractures. All clinical fractures were confirmed with x-ray film reports or, in the case of clinical vertebral fractures, x-ray films. RESULTS: Overall, there was a 47% significant reduction in risk of new vertebral fractures in the alendronate group compared with the placebo group. The reduction in risk of new vertebral fracture was consistent across fracture risk categories including age (relative risk [RR], 0.49 in women < 75 years compared with 0.62 in those > or = 75 years), BMD (RR, 0.54 in women with a femoral neck BMD < 0.59 g/cm2 [median] compared with 0.53 in those with a BMD > or = 0.59 g/cm2), and number of preexisting vertebral fractures (RR, 0.58 in women with 1 vertebral fracture compared with 0.52 in those with > or = 2). The overall significant 28% reduction in risk of incident clinical fractures in the alendronate group compared with the placebo group was also observed within these subgroups. Compared with the number of lower-risk women, a similar or smaller number of high-risk women needed to be treated to prevent 1 fracture. For example, 8 women aged 75 years or older compared with 9 women younger than 75 years, or 4 women with 2 or more existing vertebral fractures compared with 16 women with 1 existing vertebral fracture, needed to be treated with alendronate for 5 years to prevent 1 new vertebral fracture. CONCLUSIONS: Alendronate effectively reduces fracture risk in postmenopausal women with vertebral fractures and low BMD, including those women at highest risk because of advanced age or severe osteoporosis. Since the risk reductions observed with alendronate treatment were consistent within fracture risk categories, more fractures were prevented by treating women at highest risk. 相似文献
32.
DE Stewart 《Canadian Metallurgical Quarterly》2003,191(9):561-562
33.
34.
E. WITTIG DE PENNA P. CARREñO X. URRUTIA L. LOPEZ D. BALLESTER 《Journal of food science》1987,52(5):1434-1435
Cookies enriched with 0, 5, 10, 15, 20, and 25% full-fat sweet lupine flour (FFSL) were evaluated by a sensory panel using the rank of preference and paired comparison tests. Cookies with 0, 5, and 10% FFSL were preferred while those containing 20 and 25% FFSL were rejected (p≤0.01). Studies conducted with school children showed similar acceptability for 0 and 10% FFSL-containing cookies which was different (p = 0.05) from those containing 20% FFSL. Fortification of the basic formula with 10% FFSL was recommended on the basis of acceptability. 相似文献
35.
36.
Burkholderia pseudomallei is the causative agent of melioidosis, a disease increasingly recognized as an important cause of morbidity and mortality in many regions of the world. B. pseudomallei is a facultative intracellular pathogen capable of invading eukaryotic cells. We used Tn5-OT182 mutagenesis to generate mutants deficient in the ability to invade a human type II pneumocyte cell line (A549 cells). One of these mutants, AJ1D8, exhibited approximately 10% of the ability of the parental strain, 1026b, to invade A549 cells. There was no difference in the abilities of 1026b and AJ1D8 to resist killing by RAW macrophages or the human defensin HNP-1. The nucleotide sequence flanking the Tn5-OT182 integration in AJ1D8 was determined, and two open reading frames were identified. The predicted proteins shared considerable homology with two-component regulatory systems involved in the regulation of heavy-metal resistance in other organisms. AJ1D8 was 16-fold more sensitive to Cd2+ and twofold more sensitive to Zn2+ than was 1026b but was not sensitive to any of the other heavy metals examined. The B. pseudomallei two-component regulatory system, termed irlRS, complemented the invasion-deficient and heavy-metal-sensitive phenotype of AJ1D8 in trans. There was no significant difference between the virulence of AJ1D8 and that of 1026b in infant diabetic rats and Syrian hamsters, suggesting that the irlRS locus is probably not a virulence determinant in these animal models of acute B. pseudomallei infection. 相似文献
37.
38.
39.
40.