全文获取类型
收费全文 | 302954篇 |
免费 | 4725篇 |
国内免费 | 822篇 |
专业分类
电工技术 | 5344篇 |
综合类 | 212篇 |
化学工业 | 48767篇 |
金属工艺 | 12394篇 |
机械仪表 | 9040篇 |
建筑科学 | 7613篇 |
矿业工程 | 1940篇 |
能源动力 | 7058篇 |
轻工业 | 28149篇 |
水利工程 | 3291篇 |
石油天然气 | 7116篇 |
武器工业 | 16篇 |
无线电 | 32640篇 |
一般工业技术 | 61131篇 |
冶金工业 | 51690篇 |
原子能技术 | 7661篇 |
自动化技术 | 24439篇 |
出版年
2021年 | 2494篇 |
2019年 | 2275篇 |
2018年 | 4318篇 |
2017年 | 4228篇 |
2016年 | 4603篇 |
2015年 | 3019篇 |
2014年 | 4951篇 |
2013年 | 13590篇 |
2012年 | 7627篇 |
2011年 | 10164篇 |
2010年 | 8383篇 |
2009年 | 9401篇 |
2008年 | 9717篇 |
2007年 | 9572篇 |
2006年 | 8387篇 |
2005年 | 7750篇 |
2004年 | 7149篇 |
2003年 | 6921篇 |
2002年 | 6999篇 |
2001年 | 6838篇 |
2000年 | 6487篇 |
1999年 | 6466篇 |
1998年 | 14950篇 |
1997年 | 11242篇 |
1996年 | 8714篇 |
1995年 | 6663篇 |
1994年 | 6039篇 |
1993年 | 5884篇 |
1992年 | 4574篇 |
1991年 | 4515篇 |
1990年 | 4347篇 |
1989年 | 4356篇 |
1988年 | 4313篇 |
1987年 | 3661篇 |
1986年 | 3642篇 |
1985年 | 4279篇 |
1984年 | 4093篇 |
1983年 | 3703篇 |
1982年 | 3506篇 |
1981年 | 3664篇 |
1980年 | 3504篇 |
1979年 | 3432篇 |
1978年 | 3515篇 |
1977年 | 3981篇 |
1976年 | 5088篇 |
1975年 | 3231篇 |
1974年 | 3053篇 |
1973年 | 3078篇 |
1972年 | 2673篇 |
1971年 | 2497篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
161.
162.
163.
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
164.
Radiochemistry - Azathioprine, an antitumor agent, was labeled with 99mTc using stannous chloride dihydrate as a reducing agent. Factors such as the amounts of the reducing agent and substrate, pH,... 相似文献
165.
166.
The investigation of phase transformations in metastable ceramic systems such as zirconia often requires local phase analysis within the areas of interest. Electron backscatter diffraction is a suitable method in combination with focused ion beam sample preparation. The interaction between ion beam and sample has to be carefully considered. In case of metastable Y-PSZ and Mg-PSZ, phase transformations were observed after FIB preparation with 30?kV, 30?nA and 5° incidence angle. Damage was the dominating effect for angles of 72°. The expected local temperature increase due to the ion bombardment with 30?kV and 30?nA is 700?K for ZrO2. Thus, the observed phase transformations can be explained on the basis of the temperature increase in the corresponding Y-PSZ phase diagram. In case of Mg-PSZ, the transition temperature is 1083?°C. The local temperature increase was obviously lower. The excitation energy for the observed phase transformation was smaller than expected from the phase diagrams of the thermodynamic equilibrium. Using 5?kV, 4.8?nA and 5° incidence angle, no phase transformations and no damage were observed. Thus, these conditions are well suited for the FIB preparation of metastable zirconia. 相似文献
167.
168.
Bulge is a defect that causes geometrical inaccuracy and premature failure in the innovative incremental sheet forming (ISF) process. This study has two-fold objectives: (1) knowing the bulging behavior of a Cu clad tri-layered steel sheet as a function of forming conditions, and (2) analyzing the bending effect on bulging in an attempt to identify the associated mechanism. A series of ISF tests and bending analysis are performed to realize these objectives. From the cause-effect analysis, it is found that bulge formation in the layered sheet is sensitive to forming conditions in a way that bulging can be minimized utilizing annealed material and performing ISF with larger tool diameter and step size. The bending under tension analysis reveals that the formation of bulge is an outgrowth of bending moment that the forming tool applies on the sheet during ISF. Furthermore, the magnitude of bending moment depending upon the forming conditions varies from 0.046 to 10.24 N·m/m and causes a corresponding change in the mean bulge height from 0.07 to 0.91 mm. The bending moment governs bulging in layered sheet through a linear law. These findings lead to a conclusion that the bulge defect can be overcome by controlling the bending moment and the formula proposed can be helpful in this regards. 相似文献
169.
170.
Dr. Vlastimil Jirasko Dr. Nils-Alexander Lakomek Dr. Susanne Penzel Dr. Marie-Laure Fogeron Prof. Dr. Ralf Bartenschlager Prof. Dr. Beat H. Meier Dr. Anja Böckmann 《Chembiochem : a European journal of chemical biology》2020,21(10):1453-1460
Proton-detected 100 kHz magic-angle-spinning (MAS) solid-state NMR is an emerging analysis method for proteins with only hundreds of microgram quantities, and thus allows structural investigation of eukaryotic membrane proteins. This is the case for the cell-free synthesized hepatitis C virus (HCV) nonstructural membrane protein 4B (NS4B). We demonstrate NS4B sample optimization using fast reconstitution schemes that enable lipid-environment screening directly by NMR. 2D spectra and relaxation properties guide the choice of the best sample preparation to record 2D 1H-detected 1H,15N and 3D 1H,13C,15N correlation experiments with linewidths and sensitivity suitable to initiate sequential assignments. Amino-acid-selectively labeled NS4B can be readily obtained using cell-free synthesis, opening the door to combinatorial labeling approaches which should enable structural studies. 相似文献