全文获取类型
收费全文 | 26973篇 |
免费 | 2690篇 |
国内免费 | 1786篇 |
专业分类
电工技术 | 2086篇 |
综合类 | 2547篇 |
化学工业 | 3462篇 |
金属工艺 | 1529篇 |
机械仪表 | 1703篇 |
建筑科学 | 1846篇 |
矿业工程 | 934篇 |
能源动力 | 822篇 |
轻工业 | 2804篇 |
水利工程 | 862篇 |
石油天然气 | 699篇 |
武器工业 | 407篇 |
无线电 | 2772篇 |
一般工业技术 | 2285篇 |
冶金工业 | 2700篇 |
原子能技术 | 354篇 |
自动化技术 | 3637篇 |
出版年
2024年 | 117篇 |
2023年 | 333篇 |
2022年 | 946篇 |
2021年 | 1179篇 |
2020年 | 838篇 |
2019年 | 622篇 |
2018年 | 675篇 |
2017年 | 717篇 |
2016年 | 676篇 |
2015年 | 1042篇 |
2014年 | 1313篇 |
2013年 | 1700篇 |
2012年 | 1996篇 |
2011年 | 2054篇 |
2010年 | 2090篇 |
2009年 | 1877篇 |
2008年 | 1943篇 |
2007年 | 1891篇 |
2006年 | 1622篇 |
2005年 | 1313篇 |
2004年 | 942篇 |
2003年 | 662篇 |
2002年 | 585篇 |
2001年 | 600篇 |
2000年 | 429篇 |
1999年 | 225篇 |
1998年 | 491篇 |
1997年 | 342篇 |
1996年 | 233篇 |
1995年 | 151篇 |
1994年 | 152篇 |
1993年 | 142篇 |
1992年 | 79篇 |
1991年 | 79篇 |
1990年 | 78篇 |
1989年 | 75篇 |
1988年 | 73篇 |
1987年 | 56篇 |
1986年 | 64篇 |
1985年 | 67篇 |
1984年 | 73篇 |
1983年 | 53篇 |
1982年 | 59篇 |
1981年 | 70篇 |
1980年 | 59篇 |
1979年 | 45篇 |
1977年 | 87篇 |
1976年 | 120篇 |
1975年 | 61篇 |
1972年 | 42篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
51.
JD Adachi WG Bensen F Bianchi A Cividino S Pillersdorf RJ Sebaldt P Tugwell M Gordon M Steele C Webber CH Goldsmith 《Canadian Metallurgical Quarterly》1996,23(6):995-1000
OBJECTIVE: To determine the efficacy and safety of vitamin D 50,000 units/week and calcium 1,000 mg/day in the prevention of corticosteroid induced osteoporosis. METHODS: A minimized double blind, placebo controlled trial in corticosteroid treated subjects in a tertiary care university affiliated hospital. The sample was 62 subjects with polymyalgia rheumatica, temporal arteritis, asthma, vasculitis, or systemic lupus erythematosus. The primary outcome measure was the percentage change in bone mineral density (BMD) of the lumbar spine in the 2 treatment groups from baseline to 36 mo followup. RESULTS: BMD of the lumbar spine in the vitamin D and calcium treated group decreased by a mean (SD) of 2.6% (4.1%) at 12 mo, 3.7% (4.5%) at 24 mo, and 2.2% (5.8%) at 36 mo. In the placebo group there was a decrease of 4.1% (4.1%) at 12 mo, 3.8% (5.6%) at 24 mo, and 1.5% (8.8%) at 36 mo. The observed differences between groups were not statistically significant. The difference at 36 mo was-0.693% (95% CI -5.34, 3.95). CONCLUSION: Vitamin D and calcium may help prevent the early loss of bone seen in the lumbar spine as measured by densitometry of the lumbar spine. Longterm vitamin D and calcium in those undergoing extended therapy with corticosteroids does not appear to be beneficial. 相似文献
52.
53.
54.
55.
Many companies are using Just-In-Time (JIT) control systems in their mixed-model multi-level production facilities. When scheduling these facilities the most important objective is to keep a constant rate of usage for every part used by the system. In this paper a mathematical model for scheduling these facilities is studied and techniques for determining good schedules are developed. Procedures for solving very large problems are given. 相似文献
56.
57.
58.
Capacity and power control issues are considered for urban CDMA microcells that operate on channels characterized by log-normal shadowing and Nakagami fading. The effects of fading on the desired and interfering signals, variations in the shadow standard deviation, imperfect power control, and the requiredE
b
/N
o
for satisfactory link operation are investigated. It is shown that the reverse channel is relatively insensitive, and the forward channel very sensitive, to shadow and fading variations. Power control error is shown to significantly degrade reverse channel capacity. Twobiased forward channel power control strategies are introduced to enhance existing unbiasedbalancing forward channel power control algorithms.This research has been supported by BNR Inc. 相似文献
59.
60.