全文获取类型
收费全文 | 282474篇 |
免费 | 4009篇 |
国内免费 | 856篇 |
专业分类
电工技术 | 5414篇 |
综合类 | 366篇 |
化学工业 | 42464篇 |
金属工艺 | 10600篇 |
机械仪表 | 8908篇 |
建筑科学 | 7332篇 |
矿业工程 | 1174篇 |
能源动力 | 6962篇 |
轻工业 | 24488篇 |
水利工程 | 2768篇 |
石油天然气 | 3969篇 |
武器工业 | 68篇 |
无线电 | 36247篇 |
一般工业技术 | 54104篇 |
冶金工业 | 50563篇 |
原子能技术 | 5600篇 |
自动化技术 | 26312篇 |
出版年
2021年 | 2569篇 |
2020年 | 1836篇 |
2019年 | 2428篇 |
2018年 | 3959篇 |
2017年 | 3957篇 |
2016年 | 4318篇 |
2015年 | 2840篇 |
2014年 | 4740篇 |
2013年 | 12602篇 |
2012年 | 7624篇 |
2011年 | 10257篇 |
2010年 | 7957篇 |
2009年 | 8785篇 |
2008年 | 9721篇 |
2007年 | 9607篇 |
2006年 | 8661篇 |
2005年 | 7842篇 |
2004年 | 7560篇 |
2003年 | 7317篇 |
2002年 | 6875篇 |
2001年 | 6848篇 |
2000年 | 6493篇 |
1999年 | 6609篇 |
1998年 | 14914篇 |
1997年 | 10744篇 |
1996年 | 8496篇 |
1995年 | 6768篇 |
1994年 | 6046篇 |
1993年 | 5899篇 |
1992年 | 4775篇 |
1991年 | 4384篇 |
1990年 | 4284篇 |
1989年 | 4014篇 |
1988年 | 3820篇 |
1987年 | 3363篇 |
1986年 | 3267篇 |
1985年 | 3845篇 |
1984年 | 3583篇 |
1983年 | 3228篇 |
1982年 | 3023篇 |
1981年 | 3117篇 |
1980年 | 2907篇 |
1979年 | 2822篇 |
1978年 | 2650篇 |
1977年 | 3114篇 |
1976年 | 3756篇 |
1975年 | 2459篇 |
1974年 | 2421篇 |
1973年 | 2412篇 |
1972年 | 1929篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
A new method based on a two-wire line has been developed for noncontact diagnostics of a low-temperature plasma and its fluxes
in channels with complex profiles. This method provides good spatial and time resolution.
Pis’ma Zh. Tekh. Fiz. 23, 1–7 (July 26, 1997) 相似文献
122.
BACKGROUND: Home parenteral nutrition (HPN) is used to treat intestinal failure. A minority of HPN patients are dependent on opiates and benzodiazepines to control pain and anxiety. The aim of this study was to determine what effects such drug dependence had on patient outcomes. METHODS: Ten dependent patients were prospectively compared with 10 well-matched, nondependent HPN patients for the same 12-month period. Episodes of line sepsis and other complications were documented and the cost of treatment estimated. Health status was measured using the SF36 and EuroQol instruments. RESULTS: The dependent group had significantly more episodes of central line sepsis (p = .0007) as well as other complications (p = .0002). This led to significantly longer periods of inpatient care (p = .0004) and therefore higher costs of treatment. Health status was lower in the dependent group; they reported more pain (p = .04) and less energy (p = .04). CONCLUSIONS: The complication rate and increased cost of treatment for opiate- and sedative-dependent patients receiving HPN significantly detract from the overall outcome of this therapy. 相似文献
123.
Valenzuela R.A. Landron O. Jacobs D.L. 《Vehicular Technology, IEEE Transactions on》1997,46(1):203-212
We explore techniques for the measurement of local mean signal strength at 900 MHz and 2 GHz. In particular, we characterize the impact of transmitter and receiver antenna rotation on the estimated local mean. Then, we explore the collection of high resolution data while moving along a linear trajectory and using linear averaging techniques to estimate the local mean. With this information, the best measurement techniques can be chosen depending on the required speed versus accuracy tradeoff. Finally, we use a ray tracing propagation model to evaluate different methods of calculating the local mean signal strength for indoor environments 相似文献
124.
125.
126.
127.
ME Sutherlin I Nishimori T Caffrey EP Bennett H Hassan U Mandel D Mack T Iwamura H Clausen MA Hollingsworth 《Canadian Metallurgical Quarterly》1997,57(21):4744-4748
The levels of mRNA expression of three UDP-N-acetyl-alpha-D-galactosamine:polypeptide GalNAc N-acetylgalactosaminyltransferases (GalNAc-transferases) were quantified for human adenocarcinoma cell lines from pancreas, colon, stomach, and breast. Two of the GalNAc-transferases, GalNAc-T1 and GalNAc-T2, were expressed constitutively and at low levels in most or all cell lines examined. A third GalNAc-transferase, GalNAc-T3, was differentially expressed. Well-differentiated adenocarcinoma cell lines expressed high levels and moderately differentiated cell lines expressed lower levels of GalNAc-T3. Cell lines classified as poorly differentiated failed to express GalNAc-T3 mRNA at levels that could be detected by Northern blot analysis. Differential expression of the GalNAc-T3 protein was confirmed in these cell lines by Western blotting. We propose that glycosylation in tumor cell lines may be regulated in part by differential expression of GalNAc-transferases, and we suggest that GalNAc-T3 gene expression may be a molecular indicator of differentiated adenocarcinoma. 相似文献
128.
129.
CL Mesh BL Cmolik DW Van Heekeren JH Lee D Whittlesey LM Graham AS Geha SJ Bowlin 《Canadian Metallurgical Quarterly》1997,11(6):612-619
A premise of cardiac risk stratification is that the added risk of coronary artery bypass grafting (CABG) is offset by the improved safety of subsequent vascular reconstruction (VR). We questioned if elective CABG is patients with severe peripheral vascular disease (PVD) is a relatively high-risk procedure. A cohort study of 680 elective CABG patients from January 1993 to December 1994 was performed using three mutually exclusive outcomes of complication-free survival, morbidity, and mortality. Patient characteristic, operative, and outcome data were prospectively collected. Retrospective review determined that 58 patients had either a standard indication for or a history of VR. Overall CABG mortality was 2.5%, with statistically similar but relatively higher rates for PVD as compared to non-PVD patients. In contrast, major morbidity occurred at rates 3.6-fold higher in PVD patients (39.7%) than in disease-free patients (16.7%) after adjustment for the effects of patient and operative variables (odds ratio [OR] 3.67, 95% confidence interval [CI] 1.93-6.99). CABG morbidity in the PVD patient was most likely in those patients with aortoiliac (OR 9.51, CI 3.20-28.27) and aortic aneurysmal (OR 5.24, CI 1.28-21.41) disease types. CABG in PVD patients is associated with significant major morbidity. Such morbidity may preclude or alter the timing of subsequent VR. 相似文献
130.
John C. Hart Gordon W. Lescinsky Daniel J. Sandin Thomas A. DeFanti Louis H. Kauffman 《The Visual computer》1993,9(7):346-355
The pipelined architecture and parallel organization of the AT&T Pixel Machine image computer are described and demonstrated with applications for the visualization of multidimensional fractals, particularly linear fractals and quaternion/ stacked Julia sets. Techniques for pushing the Pixel Machine to its peak abilities are described and apply to more recent parallel image computers as well. 相似文献