全文获取类型
收费全文 | 11062篇 |
免费 | 644篇 |
国内免费 | 397篇 |
专业分类
电工技术 | 399篇 |
综合类 | 479篇 |
化学工业 | 1239篇 |
金属工艺 | 509篇 |
机械仪表 | 399篇 |
建筑科学 | 611篇 |
矿业工程 | 362篇 |
能源动力 | 176篇 |
轻工业 | 457篇 |
水利工程 | 147篇 |
石油天然气 | 663篇 |
武器工业 | 56篇 |
无线电 | 964篇 |
一般工业技术 | 954篇 |
冶金工业 | 3594篇 |
原子能技术 | 54篇 |
自动化技术 | 1040篇 |
出版年
2024年 | 50篇 |
2023年 | 148篇 |
2022年 | 285篇 |
2021年 | 358篇 |
2020年 | 303篇 |
2019年 | 268篇 |
2018年 | 261篇 |
2017年 | 290篇 |
2016年 | 252篇 |
2015年 | 354篇 |
2014年 | 399篇 |
2013年 | 517篇 |
2012年 | 500篇 |
2011年 | 537篇 |
2010年 | 464篇 |
2009年 | 446篇 |
2008年 | 385篇 |
2007年 | 423篇 |
2006年 | 410篇 |
2005年 | 354篇 |
2004年 | 219篇 |
2003年 | 194篇 |
2002年 | 152篇 |
2001年 | 142篇 |
2000年 | 156篇 |
1999年 | 309篇 |
1998年 | 1239篇 |
1997年 | 714篇 |
1996年 | 527篇 |
1995年 | 310篇 |
1994年 | 248篇 |
1993年 | 250篇 |
1992年 | 58篇 |
1991年 | 75篇 |
1990年 | 65篇 |
1989年 | 55篇 |
1988年 | 48篇 |
1987年 | 36篇 |
1986年 | 26篇 |
1985年 | 23篇 |
1984年 | 2篇 |
1983年 | 5篇 |
1982年 | 13篇 |
1981年 | 5篇 |
1980年 | 29篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 66篇 |
1976年 | 125篇 |
1975年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
Reliable joints of Ti3SiC2 ceramic and TC11 alloy were diffusion bonded with a 50 μm thick Cu interlayer. The typical interfacial structure of the diffusion boned joint, which was dependent on the interdiffusion and chemical reactions between Al, Si and Ti atoms from the base materials and Cu interlayer, was TC11/α-Ti + β-Ti + Ti2Cu + TiCu/Ti5Si4 + TiSiCu/Cu(s, s)/Ti3SiC2. The influence of bonding temperature and time on the interfacial structure and mechanical properties of Ti3SiC2/Cu/TC11 joint was analyzed. With the increase of bonding temperature and time, the joint shear strength was gradually increased due to enhanced atomic diffusion. However, the thickness of Ti5Si4 and TiSiCu layers with high microhardness increased for a long holding time, resulting in the reduction of bonding strength. The maximum shear strength of 251 ± 6 MPa was obtained for the joint diffusion bonded at 850 °C for 60 min, and fracture primarily occurred at the diffusion layer adjacent to the Ti3SiC2 substrate. This work provided an economical and convenient solution for broadening the engineering application of Ti3SiC2 ceramic. 相似文献
2.
4.
In this paper, we first re-examine the previous protocol of controlled quantum secure direct communication of Zhang et al.’s scheme, which was found insecure under two kinds of attacks, fake entangled particles attack and disentanglement attack. Then, by changing the party of the preparation of cluster states and using unitary operations, we present an improved protocol which can avoid these two kinds of attacks. Moreover, the protocol is proposed using the three-qubit partially entangled set of states. It is more efficient by only using three particles rather than four or even more to transmit one bit secret information. Given our using state is much easier to prepare for multiqubit states and our protocol needs less measurement resource, it makes this protocol more convenient from an applied point of view. 相似文献
5.
6.
7.
Siqi Yu Qin Wang Jianwei Wang Yong Xiang Xiaobin Niu Tingshuai Li 《International Journal of Hydrogen Energy》2021,46(27):14331-14337
Artificial nitrogen fixation is emerging as a promising approach for synthesis of ammonia at mild conditions. Inspired by biological nitrogen fixation based on bacteria containing iron, zinc doped Fe2O3 nanoparticles are proposed as an efficient and earth abundant electrocatalyst for converting N2 to NH3. In neutral media, it achieves a maximum Faradaic efficiency (FE) of 10.4% and a large NH3 yield rate of 15.1 μg h?1 mg?1cat. at ?0.5 V vs. reversible hydrogen electrode. This catalyst also exhibits excellent selectivity and stability. Theoretical calculations suggest the reaction follows the associative enzymatic mechanism and it has a barrier of as low as 0.68 eV. 相似文献
8.
Simultaneous determination of six ephedrines in urine sample has been achieved by high performance liquid chromatography on a Lichrospher RP-18 column, using methylamphetamine as internal standard. The 6 ephedrines are well separated in 25 minutes with resolution better than 1.8. This method has high recovery, selectivity and reproducibility, and the linearity is satisfactory from 1.5 micrograms/ml to 25 micrograms/ml with correlation coefficients better than 0.999. 相似文献
9.
10.
BACKGROUND: To determine the best cutoff values of aspartate aminotransferase (AST) and alanine amino-transferase (ALT) in detecting viral hepatitis C infection among patients of continuous ambulatory peritoneal dialysis (CAPD). METHODS: 90 (44 male and 46 female) CAPD patients and 526 adult controls (266 male, 260 female) were enrolled. Serum AST and ALT were measured by an auto-analyser monthly. Serum HBsAg was examined using a RIA method and anti-HCV by an second-generation EIA method. The best cutoff values of AST and ALT for detecting viral hepatitis were obtained from the ROC (receiver-operating characteristic) curve. RESULTS: The prevalence of anti-HCV(+) was significantly higher in CAPD patients (16.7%) than in normal controls (4.9%), while that of HBsAg(+) was similar in both groups. CAPD patients had significantly lower levels of serum aminotransferases compared to normal controls. Mean AST were 23.8 IU/l in normal control and 18.8 IU/l in the CAPD patients (P < 0.001). Mean ALT were 21.9 IU/l in normal controls and 15.3 IU/l in the CAPD patients (P < 0.001). CAPD patients with HCV infection had higher serum AST and ALT levels than those without. However, HBV infection did not cause significant serum aminotransferase elevation in patients. The conventional cutoff values of AST (40 IU/l) and ALT (40 IU/l) for detecting viral hepatitis yielded only a sensitivity of 27.3 and 18.2% respectively; on the contrary, our revised cutoff values of AST (24 IU/l) and ALT (17 IU/l) had better sensitivities (AST, 72.7%; ALT, 63.6%). For serial aminotransferase values, the sensitivity of AST and ALT for detecting HCV were 36.4 and 27.3% by conventional criteria, and were both 81.8%, by our newly revised criteria. CONCLUSIONS: Serum aminotransferase cutoff values should be modified for screening viral hepatitis in a CAPD population. Our new cutoff criteria had important clinical implications in providing benefits of earlier detection and possible prevention from chronic hepatic deteriorations. 相似文献