全文获取类型
收费全文 | 30735篇 |
免费 | 557篇 |
国内免费 | 745篇 |
专业分类
电工技术 | 640篇 |
综合类 | 68篇 |
化学工业 | 4202篇 |
金属工艺 | 2389篇 |
机械仪表 | 1354篇 |
建筑科学 | 606篇 |
矿业工程 | 119篇 |
能源动力 | 901篇 |
轻工业 | 1448篇 |
水利工程 | 207篇 |
石油天然气 | 384篇 |
武器工业 | 5篇 |
无线电 | 3125篇 |
一般工业技术 | 8501篇 |
冶金工业 | 4245篇 |
原子能技术 | 336篇 |
自动化技术 | 3507篇 |
出版年
2023年 | 51篇 |
2022年 | 105篇 |
2021年 | 184篇 |
2020年 | 140篇 |
2019年 | 251篇 |
2018年 | 1076篇 |
2017年 | 1084篇 |
2016年 | 962篇 |
2015年 | 580篇 |
2014年 | 663篇 |
2013年 | 1567篇 |
2012年 | 1190篇 |
2011年 | 1793篇 |
2010年 | 1134篇 |
2009年 | 1344篇 |
2008年 | 1362篇 |
2007年 | 1374篇 |
2006年 | 1162篇 |
2005年 | 3201篇 |
2004年 | 2101篇 |
2003年 | 1666篇 |
2002年 | 855篇 |
2001年 | 687篇 |
2000年 | 654篇 |
1999年 | 696篇 |
1998年 | 1455篇 |
1997年 | 1033篇 |
1996年 | 892篇 |
1995年 | 569篇 |
1994年 | 456篇 |
1993年 | 377篇 |
1992年 | 240篇 |
1991年 | 242篇 |
1990年 | 156篇 |
1989年 | 168篇 |
1988年 | 119篇 |
1987年 | 82篇 |
1986年 | 57篇 |
1985年 | 62篇 |
1984年 | 37篇 |
1983年 | 31篇 |
1982年 | 26篇 |
1981年 | 30篇 |
1980年 | 17篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1977年 | 9篇 |
1976年 | 20篇 |
1975年 | 11篇 |
1973年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
1.
Strength of Materials - In order to study the failure process of a large-scale spherical bearing, the finite element simulation method was used to establish the full-scale finite element model of... 相似文献
2.
Vasanth Winston X. Sankar D. SenthilKannan K. Vimalan M. Rajesh Kumar T. 《Journal of Materials Science: Materials in Electronics》2022,33(26):20616-20630
Journal of Materials Science: Materials in Electronics - Nonlinear optical organometallic single crystal of manganese mercury thiocyanate (MMTC) has been grown by SR method in aqueous solution. The... 相似文献
3.
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
4.
Currently, there is little information pertaining to the airborne bacterial communities of green buildings. In this case study, the air bacterial community of a zero carbon building (ZCB) in Hong Kong was characterized by targeting the bacterial 16S rRNA gene. Bacteria associated with the outdoor environment dominated the indoor airborne bacterial assemblage, with a modest contribution from bacteria associated with human skin. Differences in overall community diversity, membership, and composition associated with short (day‐to‐day) and long‐term temporal properties were detected, which may have been driven by specific environmental genera and taxa. Furthermore, time‐decay relationships in community membership (based on unweighted UniFrac distances) and composition (based on weighted UniFrac distances) differed depending on the season and sampling location. A Bayesian source‐tracking approach further supported the importance of adjacent outdoor air bacterial assemblage in sourcing the ZCB indoor bioaerosol. Despite the unique building attributes, the ZCB microbial assemblage detected and its temporal characteristics were not dissimilar to that of conventional built environments investigated previously. Future controlled experiments and microbial assemblage investigations of other ZCBs will undoubtedly uncover additional knowledge related to how airborne bacteria in green buildings may be influenced by their distinctive architectural attributes. 相似文献
5.
Strength of Materials - The development of bimetallic materials is one of the modern lines of research. The differences in the properties of components can impart special mechanical characteristics... 相似文献
6.
Strength of Materials - The tribological tests are carried out to assess the effect of pin diameters on wear characteristics via changing contact stresses and sliding speeds to provide support for... 相似文献
7.
In the present work Ba(Ti1-xCex)O3 ceramics are prepared through a standard solid-state sintering process. Crystal structures, dielectric properties, ferroelectric properties and electrocaloric... 相似文献
8.
The objective of this study was to extend a stable isotope-based assessment of AA absorption from rumen-degradable protein (RDP) sources to include determination of essential AA (EAA) availability from microbial protein (MCP). To demonstrate the technique, a study using a 2 × 2 factorial arrangement of treatments applied in a repeated 4 × 4 Latin square design was undertaken. Factors were high and low rumen-degradable protein and high and low starch. Twelve lactating cows were blocked into 3 groups according to days in milk and randomly assigned to the 4 treatment sequences. Each period was 14 d in length with 10 d of adaption followed by 4 d of ruminal infusions of 15N-labeled ammonium sulfate. On the last day of each period, a 13C-labeled AA mixture was infused into the jugular vein over a 6-h period to assess total AA entry. Rumen, blood, urine, and milk samples were collected during the infusions. Ruminal bacteria and blood samples were assessed for AA enrichment. Total plasma AA absorption rates were derived for 6 EAA from plasma 13C AA enrichment. Absorption of 6 EAA from MCP was calculated from total AA absorption based on 15N enrichment in blood and rumen bacteria. Essential AA absorption rates from total protein, MCP, and rumen-undegradable protein were derived with standard errors of the mean of 6, 14, and 14%, respectively. An average of 45% of absorbed EAA were from MCP, which varied among 6 EAA and was interactively affected by starch and RDP in diets. Microbial AA availability measured by isotope dilution method increased with the high RDP diets and was unaffected by starch level, except for Met, which decreased with high starch. Microbial protein outflow, estimated from urinary purine derivatives, increased with RDP and was not significantly affected by starch. This was consistent with measurements from the isotope dilution method. Total AA absorption rates measured from isotope dilution were similar to estimates from CNCPS (v. 6.55), but a lower proportion of absorbed AA was derived from MCP for the former method. Compared with the isotope and CNCPS estimates, the Fleming model underestimated microbial EAA and total EAA availability. An average of 58% of the absorbed EAA was converted into milk, which varied among individual AA and was interactively affected by starch and RDP in diets. The isotope dilution approach is advantageous because it provides estimates of EAA availability for individual EAA from rumen-undegradable protein and MCP directly with fewer errors of measurement than can be achieved with intestinal disappearance methods. 相似文献
9.
Yin Ma X.R. Wang Tong Li Jiawei Zhang Ji Gao Z.Y. Sun 《International Journal of Hydrogen Energy》2021,46(54):27330-27348
The present paper provides insights into the feasibility of using hydrogen and bioethanol blends as energy carriers in the foreseeable future upon discussions on the advantages and the disadvantages. The comprehensive overviews on the production, storage, and transportation of hydrogen and bioethanol have been made; and the current problems and potential solutions for the three stages have been summarized. Finally, the prospections on hydrogen and bioethanol could be expect optimistically. 相似文献
10.
Association of size‐fractionated indoor particulate matter and black carbon with heart rate variability in healthy elderly women in Beijing 下载免费PDF全文
W. Dong L. Pan H. Li M. R. Miller M. Loh S. Wu J. Xu X. Yang J. Shan Y. Chen F. Deng X. Guo 《Indoor air》2018,28(3):373-382
Associations between size‐fractionated indoor particulate matter (PM) and black carbon (BC) and heart rate variability (HRV) and heart rate (HR) in elderly women remain unclear. Twenty‐nine healthy elderly women were measured for 24‐hour HRV/HR indices. Real‐time size‐fractionated indoor PM and BC were monitored on the same day and on the preceding day. Mixed‐effects models were applied to investigate the associations between pollutants and HRV/HR indices. Increases in size‐fractionated indoor PM were significantly associated with declines in power in the high‐frequency band (HF), power in the low‐frequency band (LF), and standard deviation of all NN intervals (SDNN). The largest decline in HF was 19% at 5‐minute moving average for an interquartile range (IQR) increase (24 μg/m3) in PM0.5. The results showed that smaller particles could lead to greater reductions in HRV indices. The reported associations were modified by body mass index (BMI): Declines in HF at 5‐minute average for an IQR increase in PM0.5 were 34.5% and 1.0% for overweight (BMI ≥25 kg/m2) and normal‐weight (BMI <25 kg/m2) participants, respectively. Moreover, negative associations between BC and HRV indices were found to be significant in overweight participants. Increases in size‐fractionated indoor PM and BC were associated with compromised cardiac autonomic function in healthy elderly women, especially overweight ones. 相似文献