全文获取类型
收费全文 | 253257篇 |
免费 | 3037篇 |
国内免费 | 867篇 |
专业分类
电工技术 | 4810篇 |
综合类 | 193篇 |
化学工业 | 36241篇 |
金属工艺 | 9520篇 |
机械仪表 | 7553篇 |
建筑科学 | 6079篇 |
矿业工程 | 880篇 |
能源动力 | 7262篇 |
轻工业 | 21123篇 |
水利工程 | 2204篇 |
石油天然气 | 3233篇 |
武器工业 | 15篇 |
无线电 | 34388篇 |
一般工业技术 | 50104篇 |
冶金工业 | 48634篇 |
原子能技术 | 5079篇 |
自动化技术 | 19843篇 |
出版年
2021年 | 2179篇 |
2020年 | 1568篇 |
2019年 | 1924篇 |
2018年 | 3286篇 |
2017年 | 3319篇 |
2016年 | 3414篇 |
2015年 | 2226篇 |
2014年 | 3974篇 |
2013年 | 11506篇 |
2012年 | 6257篇 |
2011年 | 8596篇 |
2010年 | 6932篇 |
2009年 | 7903篇 |
2008年 | 8431篇 |
2007年 | 8320篇 |
2006年 | 7392篇 |
2005年 | 6523篇 |
2004年 | 6306篇 |
2003年 | 6566篇 |
2002年 | 6051篇 |
2001年 | 6529篇 |
2000年 | 5984篇 |
1999年 | 6406篇 |
1998年 | 16504篇 |
1997年 | 11427篇 |
1996年 | 8818篇 |
1995年 | 6621篇 |
1994年 | 5919篇 |
1993年 | 5870篇 |
1992年 | 4140篇 |
1991年 | 4030篇 |
1990年 | 3863篇 |
1989年 | 3661篇 |
1988年 | 3562篇 |
1987年 | 3022篇 |
1986年 | 2944篇 |
1985年 | 3211篇 |
1984年 | 2930篇 |
1983年 | 2831篇 |
1982年 | 2645篇 |
1981年 | 2546篇 |
1980年 | 2463篇 |
1979年 | 2308篇 |
1978年 | 2110篇 |
1977年 | 2610篇 |
1976年 | 3565篇 |
1975年 | 1767篇 |
1974年 | 1729篇 |
1973年 | 1669篇 |
1972年 | 1465篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
92.
Konstantin V. Dergilev Evgeny K. Shevchenko Zoya I. Tsokolaeva Irina B. Beloglazova Ekaterina S. Zubkova Maria A. Boldyreva Mikhail Yu. Menshikov Elizaveta I. Ratner Dmitry Penkov Yelena V. Parfyonova 《International journal of molecular sciences》2020,21(24)
Cell therapy of the post-infarcted myocardium is still far from clinical use. Poor survival of transplanted cells, insufficient regeneration, and replacement of the damaged tissue limit the potential of currently available cell-based techniques. In this study, we generated a multilayered construct from adipose-derived mesenchymal stromal cells (MSCs) modified to secrete stem cell factor, SCF. In a rat model of myocardium infarction, we show that transplantation of SCF producing cell sheet induced activation of the epicardium and promoted the accumulation of c-kit positive cells in ischemic muscle. Morphometry showed the reduction of infarct size (16%) and a left ventricle expansion index (0.12) in the treatment group compared to controls (24–28%; 0.17–0.32). The ratio of viable myocardium was more than 1.5-fold higher, reaching 49% compared to the control (28%) or unmodified cell sheet group (30%). Finally, by day 30 after myocardium infarction, SCF-producing cell sheet transplantation increased left ventricle ejection fraction from 37% in the control sham-operated group to 53%. Our results suggest that, combining the genetic modification of MSCs and their assembly into a multilayered construct, we can provide prolonged pleiotropic effects to the damaged heart, induce endogenous regenerative processes, and improve cardiac function. 相似文献
93.
In order to improve the process effectiveness and joint quality, ultrasonic vibrations were integrated with friction stir lap welding. Effect of ultrasonic exertion on the process and joint quality of AA 6061-T6 were investigated. Upon ultrasonic exertion, joints owned larger effective lap width, shorter hooks and improved strength. Weld fracture mode changed from a ductile–brittle mixed mode to a more ductile mode while the fracture path shifted from lap interface to beyond the stir zone. Material flow and interface defects were characterised using lap welded dissimilar aluminium alloy joints. Ultrasonic vibration improved the material flow and reduced the interfacial defects. Variations in failure load of joints were found in accordance with the variations in material flow and interfacial defects. 相似文献
94.
95.
Senthilkumar M. Vasundhara M. G. Kalavathi G. K. 《International Journal of Mechanics and Materials in Design》2019,15(3):611-627
International Journal of Mechanics and Materials in Design - The resonant frequency of electromechanical energy harvester should be tuned to ambient frequency so as to maximize the harvester power.... 相似文献
96.
ABSTRACTIn recent times, the applications of multimedia are rising in a greedy mode and hence the amount of video transactions is also increasing exponentially. This has shouted great demands on effective models on video encoding and also for reducing the transmission channel congestion. This research work introduces a managing technique termed weighted encoding for High-Efficiency Video Coding (HEVC). HEVC, also termed as MPEG-H Part 2 and H.265 is a video compression standard that is widely utilized AVC (H.264 or MPEG-4 Part 10). When compared to AVC, HEVC grants double the ratio of data compression at a similar level of quality of the video or considerably enhanced video quality at a similar bit rate. This work intends to optimize the weight that adopted in HEVC for encoding. For this, this paper proposes a new Iterative based propagation update in the water wave Optimization Algorithm (IPU-WWO), which is the improved form of Water wave Optimization (WWO). The performance of proposed IPU-WWO is compared over other conventional methods like Artificial Bee Colony (ABC), Firefly (FF), Particle Swarm Optimization (PSO) and Genetic Algorithm (GA) with respect to Peak Signal to Noise Ratio (PSNR). By doing the encoding process, it minimizes the video size with perceptually better quality video or PSNR. 相似文献
97.
98.
Burdin D. A. Savel’ev D. V. Ekonomov N. A. Chashin D. V. Fetisov Yu. K. 《Technical Physics Letters》2020,46(5):487-490
Technical Physics Letters - The magnetoelectric (ME) effect in a planar amorphous ferromagnet–piezoelectric lead zirconate titanate (PZT) composite structure can be effectively excited by... 相似文献
99.
I. Ansia H.H. Stein C. Brøkner C.A. Hayes J.K. Drackley 《Journal of dairy science》2021,104(3):2979-2995
The aims of this experiment were (1) to compare the effects of a soybean meal with an enzymatic treatment (ESBM) to reduce the concentration of antinutritional factors versus a standard soybean meal (SBM) on foregut and small intestine digestion in weaned dairy calves and (2) to estimate the endogenous losses of crude protein (CP) in the small intestine. Our hypothesis was that a diet containing ESBM instead of SBM would improve ruminal and small intestine digestion and absorption of nutrients. A T-cannula was placed in the duodenum, and a second T-cannula was installed in the distal ileum of 12 Holstein calves at approximately 3 wk of age. Calves were weaned on d 42, and on d 50 they were assigned randomly to a quadruplicated 3 × 3 Latin square with 10-d periods. Digesta samples were collected on d 7 and 8 from the ileum and d 9 and 10 from the duodenum. The diets were fed for ad libitum intake and consisted of a calf starter (CS) of 20% CP with SBM as the main source of protein (CTRL), and an isonitrogenous CS with an ESBM instead of SBM (ENZT). A third diet with a low content of CP (10%) and no soy protein was fed to estimate endogenous N losses and digestibilities of test ingredients. Flows and digestibilities of nutrients were compared between CTRL and ENZT and their test ingredients (SBM vs. ESBM, respectively). Duodenal net flows of CP and total AA as well as ruminal microbial protein synthesis per kilogram of digested CP were greater, and flow of nonprotein N and CP true (corrected by endogenous and microbial flows) foregut digestibility were lower with ENZT than CTRL. The apparent small intestine digestibilities of CP and total AA were greater for ESBM than SBM, but there were no differences between the CTRL and ENZT diets. We observed no differences in digestibilities at the duodenum or ileum of starch or NDF, but true small intestine digestibilities of CP and all AA were greater with ENZT than CTRL. Total endogenous protein losses in the small intestine estimated from calves fed the low-CP with no soy protein diet were 37 ± 1.5 g of CP and 29 ± 1.4 g of AA/kg of DMI. These values may be considered the basal endogenous losses as they are similar to values obtained with the regression method, which estimates N losses when dietary N is null. Our results indicated that the inclusion of an ESBM improved the efficiency of ruminal microbial protein synthesis per digested kilogram of organic matter and CP, and increased CP and AA absorption in the small intestine despite a greater proportion of undigested dietary protein entering the duodenum. 相似文献
100.
Morampudi Mahesh Kumar Prasad Munaga V. N. K. Raju U. S. N. 《Multimedia Tools and Applications》2020,79(27-28):19215-19237
Multimedia Tools and Applications - Rapid advancement in technology has led to the use of biometric authentication in every field. In particular, from the past few years, iris recognition systems... 相似文献