全文获取类型
收费全文 | 39901篇 |
免费 | 2738篇 |
国内免费 | 1463篇 |
专业分类
电工技术 | 1839篇 |
技术理论 | 2篇 |
综合类 | 2236篇 |
化学工业 | 6417篇 |
金属工艺 | 2117篇 |
机械仪表 | 2258篇 |
建筑科学 | 2940篇 |
矿业工程 | 917篇 |
能源动力 | 880篇 |
轻工业 | 2288篇 |
水利工程 | 516篇 |
石油天然气 | 2595篇 |
武器工业 | 201篇 |
无线电 | 4576篇 |
一般工业技术 | 4756篇 |
冶金工业 | 4249篇 |
原子能技术 | 402篇 |
自动化技术 | 4913篇 |
出版年
2024年 | 141篇 |
2023年 | 623篇 |
2022年 | 928篇 |
2021年 | 1398篇 |
2020年 | 1054篇 |
2019年 | 882篇 |
2018年 | 961篇 |
2017年 | 1146篇 |
2016年 | 1036篇 |
2015年 | 1348篇 |
2014年 | 1718篇 |
2013年 | 2199篇 |
2012年 | 2145篇 |
2011年 | 2447篇 |
2010年 | 2206篇 |
2009年 | 2028篇 |
2008年 | 2021篇 |
2007年 | 2007篇 |
2006年 | 2030篇 |
2005年 | 1766篇 |
2004年 | 1204篇 |
2003年 | 1049篇 |
2002年 | 1011篇 |
2001年 | 868篇 |
2000年 | 898篇 |
1999年 | 1160篇 |
1998年 | 1684篇 |
1997年 | 1252篇 |
1996年 | 1086篇 |
1995年 | 782篇 |
1994年 | 658篇 |
1993年 | 495篇 |
1992年 | 353篇 |
1991年 | 275篇 |
1990年 | 209篇 |
1989年 | 196篇 |
1988年 | 153篇 |
1987年 | 123篇 |
1986年 | 98篇 |
1985年 | 80篇 |
1984年 | 57篇 |
1983年 | 31篇 |
1982年 | 45篇 |
1981年 | 37篇 |
1980年 | 29篇 |
1979年 | 13篇 |
1977年 | 40篇 |
1976年 | 73篇 |
1975年 | 6篇 |
1970年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
With greater need for treating root surface lesions, dentinal adhesives are more in demand. For successful treatment, all factors--dentin, tooth, patient and materials--must be considered. 相似文献
72.
73.
Hamsters were fed high fiber diets containing cellulose, wheat bran or psyllium. The psyllium was incorporated into high fiber, ready-to-eat (RTE) flakes that were used to formulate the test diet. All the diets contained 0.125% cholesterol. The study was terminated after three weeks. Food intake, weight gain and feed efficiency were not significantly different in the three groups. Serum total and HDL cholesterol levels were reduced significantly by the psyllium diet. Serum triglycerides were 26% lower in the hamsters fed psyllium but because of the large variation the difference did not reach statistical significance. Liver total cholesterol and cholesteryl ester levels were significantly lower in the hamsters fed psyllium. Liver triglycerides were highest in the psyllium-fed hamsters and liver phospholipid levels were similar in the three groups. Liver cholesterol and triglyceride levels were higher in hamsters fed cellulose than in those fed wheat bran. Psyllium formulated into an RTE cereal was effective in reducing serum and liver cholesterol levels in hamsters. 相似文献
74.
Jet injection can be used to introduce genes into the cells of differentiated tissues of living animals and organ cultures. When a solution of plasmid DNA is jet injected into a selected tissue or organ, cells lying in or near the path of the jet injection are transfected with the DNA and the introduced gene(s) are expressed. Since there is minimal morbidity from each jet injection, multiple injections can be performed at the same or nearby sites. Both mRNA and protein expression from transfected genes can be quantitated using standard methods. In addition, the technique is an efficient means of DNA immunization. Methodology for using jet injection to transfer plasmid DNA into the cells of skin, fat, mammary gland, and muscle are described. 相似文献
75.
76.
Resurgence has been shown in human and nonhuman operant behavior, but not in derived relational responses. The present study examined this issue. Twenty-three undergraduates were trained to make conditional discriminations in a three-choice matching-to-sample paradigm. The training resulted in three equivalence classes, each consisting of four arbitrarily configured visual stimuli. The same 12 stimuli were then reorganized, and the conditional discrimination training was repeated such that three new classes were possible. In a subsequent test of derived relations, most subjects showed response patterns that were consistent with the altered conditional discriminations. Subjects were then exposed to conditional discrimination trials under extinction. Most subjects continued to respond consistently with the most recently reinforced conditional discrimination trials. During the next phase, subjects were exposed to symmetry and equivalence trials. Responses consistent with the most recent training produced feedback saying that the responses were incorrect, whereas other responses produced no feedback. Most subjects showed a resurgence of responding that was consistent with their earlier training. Finally, subjects were exposed to conditional discrimination trials carried out in extinction. Most subjects continued to show a resurgence of responding that was consistent with their early training. 相似文献
77.
DC Sutton R Kluger SU Ahmed SC Reimold JB Mark 《Canadian Metallurgical Quarterly》1994,108(3):576-582
This study assessed the value of biplane transesophageal echocardiographic assessment of diastolic flow reversal in the descending aorta as an alternative to Doppler color flow imaging in determining severity of aortic regurgitation. In 45 patients undergoing cardiac operations, the severity of aortic regurgitation was assessed by semiquantitative grading of the width of the Doppler color flow regurgitant jet relative to the left ventricular outflow tract, and the presence of diastolic flow reversal was assessed with pulsed-wave Doppler measurements at three sites in the descending aorta. In four patients, the diastolic flow reversal method was the only available form of assessment because of inadequate visualization of the left ventricular outflow tract beneath a mitral valve prosthesis. Diastolic flow reversal in the descending aorta was not observed in patients without aortic regurgitation and was always present in patients with severe aortic regurgitation. Aortic valve replacement successfully eliminated descending aortic flow reversal in all 19 patients in whom it was present before valve replacement. Identification of diastolic flow reversal at multiple sites in the descending aorta with biplane transesophageal echocardiography helps to confirm the presence of severe aortic regurgitation and can serve as an alternative method of assessment when visualization of the left ventricular outflow tract is impaired. 相似文献
78.
79.
80.