全文获取类型
收费全文 | 42328篇 |
免费 | 3954篇 |
国内免费 | 1906篇 |
专业分类
电工技术 | 2450篇 |
技术理论 | 3篇 |
综合类 | 2681篇 |
化学工业 | 6550篇 |
金属工艺 | 2193篇 |
机械仪表 | 2417篇 |
建筑科学 | 2965篇 |
矿业工程 | 1132篇 |
能源动力 | 1117篇 |
轻工业 | 2621篇 |
水利工程 | 773篇 |
石油天然气 | 2510篇 |
武器工业 | 379篇 |
无线电 | 4898篇 |
一般工业技术 | 4743篇 |
冶金工业 | 4198篇 |
原子能技术 | 404篇 |
自动化技术 | 6154篇 |
出版年
2024年 | 239篇 |
2023年 | 827篇 |
2022年 | 1511篇 |
2021年 | 2050篇 |
2020年 | 1519篇 |
2019年 | 1147篇 |
2018年 | 1365篇 |
2017年 | 1422篇 |
2016年 | 1177篇 |
2015年 | 1669篇 |
2014年 | 2152篇 |
2013年 | 2407篇 |
2012年 | 2721篇 |
2011年 | 2938篇 |
2010年 | 2610篇 |
2009年 | 2180篇 |
2008年 | 2316篇 |
2007年 | 2075篇 |
2006年 | 2007篇 |
2005年 | 1741篇 |
2004年 | 1135篇 |
2003年 | 962篇 |
2002年 | 927篇 |
2001年 | 803篇 |
2000年 | 799篇 |
1999年 | 1031篇 |
1998年 | 1498篇 |
1997年 | 1008篇 |
1996年 | 859篇 |
1995年 | 617篇 |
1994年 | 517篇 |
1993年 | 402篇 |
1992年 | 250篇 |
1991年 | 197篇 |
1990年 | 153篇 |
1989年 | 120篇 |
1988年 | 108篇 |
1987年 | 73篇 |
1986年 | 63篇 |
1985年 | 50篇 |
1984年 | 32篇 |
1983年 | 35篇 |
1982年 | 37篇 |
1981年 | 36篇 |
1980年 | 46篇 |
1979年 | 15篇 |
1978年 | 21篇 |
1977年 | 72篇 |
1976年 | 184篇 |
1973年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
报道了一种新型毫米波天线—衍射天线的测量结果.经分析讨论说明,这种天线具有良好的电性能. 相似文献
92.
着重阐述了河北冶金实验厂8MN快锻液压机电控系统的选择过程。经过反复考察,论证,对比,最终所选的压机电控系统为目前国产快锻液压机中自动化水平最高的锻造设备。 相似文献
93.
C Wang ME Nicol MK Chakrabarti A Holdcroft JG Whitwam 《Canadian Metallurgical Quarterly》1993,16(6):354-357
We compared high frequency ventilation (HFV) to conventional mechanical ventilation (CMV) under normoxic and normocapnic condition in surfactant depleted rabbits with bilateral pneumothoraces. We hypothesized that lower airway pressures would be required with HFV under these conditions. We applied CMV and HFV in 8 anaesthetized rabbits with a prototype ventilator at frequencies of 30, 100, 200, and 300 cycles/min. A positive end-expiratory pressure (PEEP) just below the pressure sufficient to open the air leak from the pneumothoraces was applied at all frequencies. Airway pressures, gas exchange, heart rate, and mean arterial pressure were recorded. Peak airway pressure decreased significantly from 2.50 to 2.10 kPa when the frequency of ventilation was increased from 30 to 300 cycles/min. There were no significant changes in mean airway pressure, PaO2, arterial pH, heart rate, and mean arterial pressure when HFV was compared to CMV. In conclusion, during HFV peak airway pressures measured at the mouth were decreased. Our ability to maintain adequate gas exchange in the face of ongoing pulmonary air leaks may reflect lower alveolar pressures. 相似文献
94.
95.
96.
ST O'Sullivan GT McGreal A Lyons L Burke JG Geoghegan MP Brady 《Canadian Metallurgical Quarterly》1994,47(9):851-852
A case of histologically confirmed Paget's disease of the breast in a 72 year old man, without underlying breast carcinoma, is reported. This report raises questions about the pathogenesis of this condition and suggests that Paget's disease is an independent, intraepidermal carcinoma rather than a direct extension of intraductal carcinoma of the breast to the nipple and areola. 相似文献
97.
采用电子表格软件EXCEL5.0可以方便地解决许多选煤生产中的线性规划问题。本文通过选煤过程线性规划实例介绍EXCEL5.0在此领域的应用方法。 相似文献
98.
BACKGROUND: Previous studies have documented greater use of health services by depressed persons and have postulated that health care costs could be reduced overall through better recognition and treatment of depression. OBJECTIVE: To determine whether a greater burden of medical illness contributes to excess charges for diagnostic tests among older adults with symptoms of depression. DESIGN: Prospective cohort study. SETTING: A primary care group practice at an academic institution. PATIENTS: 3767 patients 60 years of age and older who completed testing on the Centers for Epidemiologic Studies Depression Scale (CES-D) during routine office visits. MEASUREMENTS: Charges for all inpatient and ambulatory diagnostic testing for 2 years, including clinical pathology, diagnostic imaging, and special procedures; number of visits to the ambulatory care center or emergency department; and number of hospitalizations. The Ambulatory Care Group case-mix approach, which is based on ambulatory diagnoses, was used as a measure of health status and expected resource consumption. RESULTS: Patients with symptoms of depression (CES-D scores > or = 16) were significantly younger (66.6 compared with 68.1 years; P < 0.001), more likely to be white (50.5% compared with 33.9%; P = 0.001), and more likely to be female (75.8% compared with 67.6%; P = 0.001) than were those without these symptoms (CES-D scores < 16). They also had more nonpsychiatric comorbid conditions, had more visits to the ambulatory care center (9.2 compared with 7.8; P < 0.001), were more likely to use the emergency department (52.3% compared with 40%; P = 0.001), were more likely to be hospitalized (22.4% compared with 17%; P = 0.002), and had greater median total diagnostic test charges for a period of 1 year ($583 compared with $387; P < 0.001). The difference in charges, most of which were clinical pathology charges (54.2%), persisted into the second year. Ambulatory Care Group assignment was independently associated with diagnostic test charges. The CES-D summary score was not independently associated with diagnostic test charges when controlling for Ambulatory Care Group assignment. CONCLUSIONS: Patients with symptoms of depression accrue greater average diagnostic test charges. However, these data suggest that such patients also have a greater burden of comorbid nonpsychiatric illness. Efforts to improve outcome and decrease cost for patients who have late-life depression must target interventions to improve the care of psychiatric and medical illness concurrently. 相似文献
99.
本文研究短程透镜的焦点位于端面外的球差特性。对焦点位于波导外部(包括端面)的情况给出了一种精确测量焦距新方法,采用这种方法简单易行,测量精度取决于读数显微镜的读数精度(0.01mm)。 相似文献
100.