全文获取类型
收费全文 | 17162篇 |
免费 | 1462篇 |
国内免费 | 741篇 |
专业分类
电工技术 | 917篇 |
技术理论 | 3篇 |
综合类 | 1174篇 |
化学工业 | 3025篇 |
金属工艺 | 831篇 |
机械仪表 | 936篇 |
建筑科学 | 1413篇 |
矿业工程 | 463篇 |
能源动力 | 497篇 |
轻工业 | 970篇 |
水利工程 | 285篇 |
石油天然气 | 1135篇 |
武器工业 | 111篇 |
无线电 | 2048篇 |
一般工业技术 | 2434篇 |
冶金工业 | 761篇 |
原子能技术 | 183篇 |
自动化技术 | 2179篇 |
出版年
2024年 | 65篇 |
2023年 | 288篇 |
2022年 | 456篇 |
2021年 | 675篇 |
2020年 | 466篇 |
2019年 | 456篇 |
2018年 | 493篇 |
2017年 | 495篇 |
2016年 | 444篇 |
2015年 | 603篇 |
2014年 | 772篇 |
2013年 | 881篇 |
2012年 | 1031篇 |
2011年 | 1120篇 |
2010年 | 996篇 |
2009年 | 994篇 |
2008年 | 950篇 |
2007年 | 902篇 |
2006年 | 948篇 |
2005年 | 830篇 |
2004年 | 554篇 |
2003年 | 546篇 |
2002年 | 480篇 |
2001年 | 408篇 |
2000年 | 452篇 |
1999年 | 469篇 |
1998年 | 419篇 |
1997年 | 401篇 |
1996年 | 360篇 |
1995年 | 327篇 |
1994年 | 237篇 |
1993年 | 191篇 |
1992年 | 154篇 |
1991年 | 90篇 |
1990年 | 102篇 |
1989年 | 104篇 |
1988年 | 67篇 |
1987年 | 31篇 |
1986年 | 28篇 |
1985年 | 22篇 |
1984年 | 13篇 |
1983年 | 9篇 |
1982年 | 16篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1976年 | 2篇 |
1959年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
利用引进的制造技术和设备,制作出了 APT(STLRI)—1.78型系列化光纤连接器。 相似文献
33.
34.
35.
36.
Enhanced light output in nitride-based light-emitting diodes by roughening the mesa sidewall 总被引:1,自引:0,他引:1
Chia-Feng Lin Zhong-Jie Yang Jing-Hui Zheng Jing-Jie Dai 《Photonics Technology Letters, IEEE》2005,17(10):2038-2040
In this letter, we will report on a nitride-based light emitting diode with a mesa sidewall roughening process that increases light output power. The fabricated GaN-based light-emitting diode (LED) wafers were first treated through a photoelectrochemical (PEC) process. The Ga/sub 2/O/sub 3/ layers then formed around the GaN : Si n-type mesa sidewalls and the bottoms mesa etching regions. Selective wet oxidation occurred at the mesa sidewall between the p- and the n-type GaN interface. The light output power of the PEC treated LED was seen to increase by about 82% which was caused by a reduced index reflectance of GaN-Ga/sub 2/O/sub 3/-air layers, by a rough Ga/sub 2/O/sub 3/ surface, by a microroughening of the GaN sidewall surface, and by a selective oxidation step profile of the mesa sidewall that increases the light-extraction efficiency from the mesa sidewall direction. Consequently, this wet PEC treated process is suitable for high powered nitride-based LEDs lighting applications. 相似文献
37.
A high‐melt‐strength polypropylene (HMSPP) was prepared using a twin‐screw reactive extruder from a commercial isotactic polypropylene through two stages, first, maleic anhydride is grafted to polypropylene to obtain a maleic anhydride‐grafted polypropylene (PP‐g‐MA), and then the grafted polymer is reacted with epoxy to extend the branched chain. Fourier transformed infrared spectroscopy indicated that maleic anhydride was grafted on polypropylene and reacted with epoxy. Melt flow rate and sag resistance test showed that the melt strength of the HMSPP improved considerably. Differential scanning calorimetry test showed that the long chain branches (LCBs) act as a nucleating agent in the crystallization of the HMSPP, which leads to a high crystallization temperature and crystallinity. Furthermore, the LCB efficiency of the HMSPP can also be calculated by analyzing its rheological property. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers 相似文献
38.
39.
In this paper, we study a three-dimensional axisymmetric boundary-value problem of a slender cylinder composed of a nonlinearly elastic material subjected to an axial force. Starting from the field equations, after a transformation and proper scalings, we identify a small variable and two small parameters, which characterize the present problem. Then, by an approach involving compound series-asymptotic expansions, a nonlinear ODE is derived, which governs the axial strain (the first-term in the series expansion). By imposing the zero radial displacement conditions at two ends, we manage to get the analytical solution of the axial strain, from which all other physical quantities can be deduced and thus the three-dimensional displacement field can be determined. Graphical results are presented, which show that there are two boundary layers near the two ends while the middle part is in a state of almost uniform extension. The asymptotic structure of the analytical solution is derived, which offers clear explanations to the structure of the deformed configuration and shows that the thickness of both boundary layers is of the order of the radius. We also point out the relevance of the present results to the St. Venant’s problem. In particular, we obtain the explicit uniformly-valid exponentially small error term, when the obtained deformed configuration is compared to the configuration of a uniform extension. 相似文献
40.
OBJECTIVE: To identify the influence of the increased level of serum cholyglycine (CG) on lipid metabolism and hemorrheology in patients with intrahepatic cholestasis during pregnancy (ICP). METHODS: The concentrations of serum CG, total cholesterol (CH), triglycerides (TG), high density lipoprotein-cholesterol (HDL-C), low density lipoprotein-cholesterol (LDL-C), high shear and low shear of blood specific viscosity (HS and LS), plasma specific viscosity (PV) and hematocrit (HCT) were measured in 68 cases of primiparas with single pregnancy and 30 healthy nonpregnant women respectively. The group of ICP was composed of 35 cases with CG > 6 mumol/L, the group of normal pregnancy, 33 cases with CG < 6 mumol/L. RESULTS: The means of CG and the lipidic parameters in the two pregnant groups were significantly higher than those in the non-pregnancy group (P < 0.02-0.001) except the means of HDL-C between the groups of ICP and non-pregnancy. The levels of LDL-C, LDL-C/HDL-C, LS, PV and HCT in the ICP were significantly higher than those in the normal pregnancy group (P < 0.02-0.001). CONCLUSIONS: There are significant changes of lipid metabolism and hemorrheology in patients with ICP. However, these changes could be corrected after pregnancy termination, when the level of serum CG returned to normal. The results suggest that the pathophysiologic changes of ICP are associated with increased level of serum CG. 相似文献