全文获取类型
收费全文 | 64284篇 |
免费 | 7032篇 |
国内免费 | 3546篇 |
专业分类
电工技术 | 4381篇 |
技术理论 | 2篇 |
综合类 | 4702篇 |
化学工业 | 10152篇 |
金属工艺 | 3867篇 |
机械仪表 | 4422篇 |
建筑科学 | 5400篇 |
矿业工程 | 1952篇 |
能源动力 | 1730篇 |
轻工业 | 4975篇 |
水利工程 | 1478篇 |
石油天然气 | 3324篇 |
武器工业 | 633篇 |
无线电 | 8028篇 |
一般工业技术 | 7204篇 |
冶金工业 | 2757篇 |
原子能技术 | 737篇 |
自动化技术 | 9118篇 |
出版年
2024年 | 372篇 |
2023年 | 1347篇 |
2022年 | 2587篇 |
2021年 | 3399篇 |
2020年 | 2552篇 |
2019年 | 1982篇 |
2018年 | 2099篇 |
2017年 | 2463篇 |
2016年 | 2191篇 |
2015年 | 3133篇 |
2014年 | 3789篇 |
2013年 | 4403篇 |
2012年 | 4673篇 |
2011年 | 5140篇 |
2010年 | 4478篇 |
2009年 | 4281篇 |
2008年 | 4179篇 |
2007年 | 3671篇 |
2006年 | 3366篇 |
2005年 | 2693篇 |
2004年 | 1733篇 |
2003年 | 1362篇 |
2002年 | 1282篇 |
2001年 | 1165篇 |
2000年 | 981篇 |
1999年 | 974篇 |
1998年 | 795篇 |
1997年 | 660篇 |
1996年 | 621篇 |
1995年 | 560篇 |
1994年 | 445篇 |
1993年 | 356篇 |
1992年 | 240篇 |
1991年 | 217篇 |
1990年 | 147篇 |
1989年 | 117篇 |
1988年 | 97篇 |
1987年 | 58篇 |
1986年 | 55篇 |
1985年 | 33篇 |
1984年 | 23篇 |
1983年 | 27篇 |
1982年 | 23篇 |
1981年 | 16篇 |
1980年 | 26篇 |
1979年 | 13篇 |
1976年 | 4篇 |
1967年 | 3篇 |
1959年 | 4篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
粉末材料中微夹杂缺陷的超声波检验 总被引:1,自引:0,他引:1
介绍了用超声波方法检测微夹杂缺陷的一些试验结果,比较了不同频率、不同试验方法检测能力的差异,并通过解剖试验对检出缺陷的性质、尺寸作了比较。 相似文献
122.
该文分析某微型起爆器引起的一起误爆事故,指出该起爆器设计上的缺陷及其对作业安全的威胁,提出防患建议。 相似文献
123.
本项预测采用概率方法,即首先根据广东省水利部门提出的55座土坝和59个重点的座标(见附图),进行概率地震危险性分析,给出它们在一定预测年限T(取50年和100年)的地震烈度Ⅰ的超越概率;其次根据近年我国发生的几次强震时处于不同烈度区内的土坝和堤防的震害资料,形成表示土坝和土堤地震易损性的震害概率矩阵;然后,根据上述两方面结果用概率公式评价各土坝和堤围点在预测年限内各震害等级的超越概率,并取10%超越概率为标准,估计震害等级。结果表明,珠江三角洲土工构筑物的地震危害性南部高于北部。 相似文献
124.
Da-Zhi Li Li Gan Zi-Qiang Yang Zheng Liang Jia-Yin Li 《Journal of Infrared, Millimeter and Terahertz Waves》1997,18(10):1885-1896
The dispersion characteristic of the plasma-loaded relativistic backward wave oscillator has been analyzed. The theoretical model has been established and the numerical calculations accord with the experimental results, which provides some useful suggestions on the designing of slow-wave structure of BWO. 相似文献
125.
This paper presents the dynamic performance analysis and closed-loop design of a new power supply system for a high-current magnet load. This new system introduces a series switch-mode ripple regulator (SMRR) into a phase-controlled rectifier to improve system dynamic response and to reduce the harmonic content in the magnet current. In this paper, the new system control configuration is explained. The small signal dynamic model is established. The function of the SMRR as a speed-up feed-forward path during dynamic transients is assessed. The criteria of the closed-loop regulator design are identified. The theoretical analyses are accompanied by computer simulation and experimental results. The systematical design procedure is outlined by an example which offers better performance than ever reported on high-current magnet power supplies in terms of fast dynamic response (closed-loop bandwidth several kHz) and low harmonic content (less than 10 ppm) in the magnet current 相似文献
126.
The cholesterolaemic effect of 2 hypercholesterolaemic diets was tested in 12 rat inbred strains. Diet I is a commercial diet supplemented with 2.0% (w/w) cholesterol and 5.0% (w/w) olive oil; diet II is identical to diet I with addition of 0.5% (w/w) sodium cholate. Strains with the highest plasma cholesterol response after diet I (BN and LEW) also had the highest cholesterol response after diet II (hyperresponders, mean response > 3.5 mmol/l). In the strains DA, SHR, BC, WAG, LOU, PVG and BUF the strain mean cholesterol response remained below 1.3 mmol/l after both diets (hyporesponders). Strains F344 and OM had an intermediate cholesterol response after both diets (normoresponders, mean response between 1.3 and 3.5 mmol/l). Only in the strains LOU, PVG and SHR there appeared to be a significant higher cholesterol response after diet II when compared with the cholesterol response after diet I. In the strain WKY this difference was of a borderline significance (P = 0.052) and this strain turned from a normoresponder after diet I into a hyperresponder after diet II. Liver cholesterol levels as measured after feeding diet II for two weeks also appeared to be strain-specific. No correlation was found between the plasma cholesterol response after diet II and the liver cholesterol levels. Changes in plasma phospholipid and triglyceride levels have been measured for both diet I and diet II. For group means a correlation between the cholesterol response and the change in phospholipid levels was found (r = 0.86 for diet I, P < 0.001 and r = 0.76 for diet II, P < 0.01). No such correlation was found for triglyceride levels. 相似文献
127.
128.
粘土矿物是低渗砂岩储层的主要胶结物,对储层物性及开发过程中储层物性变化趋势有着重要的影响和控制作用。另外,粘土矿物也蕴含着大量沉积环境介质的物理化学信息,认识其自然规律,可以有效地指导预测有利储层,认识和改造油层。以鄂尔多斯盆地砂岩储层中的粘土矿物为研究对象,探讨分析粘土矿物对低渗储层性质的影响,该研究对含油气盆地低渗储层有效开发具有一定的参考价值。 相似文献
129.
Grens C.M. Cressler J.D. Andrews J.M. Qingqing Liang Joseph A.J. 《Electron Devices, IEEE Transactions on》2007,54(7):1605-1616
This paper presents a comprehensive picture of operating-voltage constraints in SiGe heterojunction bipolar transistors, addressing breakdown-related issues as they relate to technology generation, bias configuration, and operating-current density. New definitions for breakdown voltage, adopted from standard measurements, are presented. Practical design implications and physical origins of breakdown are explored using calibrated 2-D simulations and quasi-3-D compact models. Device-level analysis of ac instabilities and power performance, which is relevant to mixed-signal circuit design, is presented, and implications of the relaxed voltage constraints for common-base operation are explored. 相似文献
130.