全文获取类型
收费全文 | 500170篇 |
免费 | 5817篇 |
国内免费 | 1459篇 |
专业分类
电工技术 | 9210篇 |
综合类 | 480篇 |
化学工业 | 75719篇 |
金属工艺 | 20165篇 |
机械仪表 | 15332篇 |
建筑科学 | 12007篇 |
矿业工程 | 2711篇 |
能源动力 | 12070篇 |
轻工业 | 44080篇 |
水利工程 | 5240篇 |
石油天然气 | 9967篇 |
武器工业 | 83篇 |
无线电 | 59392篇 |
一般工业技术 | 97016篇 |
冶金工业 | 90852篇 |
原子能技术 | 11488篇 |
自动化技术 | 41634篇 |
出版年
2021年 | 3784篇 |
2019年 | 3644篇 |
2018年 | 6448篇 |
2017年 | 6459篇 |
2016年 | 6887篇 |
2015年 | 4424篇 |
2014年 | 7519篇 |
2013年 | 21449篇 |
2012年 | 12096篇 |
2011年 | 16438篇 |
2010年 | 13254篇 |
2009年 | 14999篇 |
2008年 | 15890篇 |
2007年 | 15723篇 |
2006年 | 14160篇 |
2005年 | 13090篇 |
2004年 | 12375篇 |
2003年 | 12064篇 |
2002年 | 11887篇 |
2001年 | 11746篇 |
2000年 | 11198篇 |
1999年 | 11327篇 |
1998年 | 26618篇 |
1997年 | 19460篇 |
1996年 | 15349篇 |
1995年 | 11822篇 |
1994年 | 10628篇 |
1993年 | 10451篇 |
1992年 | 8223篇 |
1991年 | 7830篇 |
1990年 | 7519篇 |
1989年 | 7399篇 |
1988年 | 7215篇 |
1987年 | 6215篇 |
1986年 | 6130篇 |
1985年 | 7161篇 |
1984年 | 6766篇 |
1983年 | 6114篇 |
1982年 | 5779篇 |
1981年 | 6013篇 |
1980年 | 5713篇 |
1979年 | 5486篇 |
1978年 | 5444篇 |
1977年 | 6308篇 |
1976年 | 7995篇 |
1975年 | 5008篇 |
1974年 | 4850篇 |
1973年 | 4889篇 |
1972年 | 4094篇 |
1971年 | 3846篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
142.
143.
144.
145.
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
146.
147.
In order to observe the transport ability of peritoneum to small molecular substances, peritoneal equilibration test (PET) was performed in 52 CAPD patients. By analysing the relationship between peritoneal transport function and dialysis adequacy, we found the average urea KT/V and Cr were significantly lower in high and low transport groups (n = 6 and n = 2) than in high average and low average groups (n = 35 and n = 9). According to the results of PET, we adjusted the dialysis program of 11 patients and the dialysis adequacy was markedly improved. We concluded that PET was helpful for selecting and adjusting CAPD program, and discussed some questions which should be payed more attention in PET operation. 相似文献
148.
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
149.
For part I see, ibid., p. 134, 1998. The basic approach outlined in the previous article is applied to the difficult problem of computing the optical modes of a vertical-cavity surface-emitting laser. The formulation utilizes a finite difference equation based upon the lowest order term of an infinite series solution of the scalar Helmholtz equation in a local region. This difference equation becomes exact in the one-dimensional (1-D) limit, and is thus ideally suited for nearly 1-D devices such as vertical-cavity lasers. The performance of the resulting code is tested on both a simple cylindrical cavity with known solutions and an oxide-confined vertical-cavity laser structure, and the results compared against second-order-accurate code based upon Crank-Nicolson differencing 相似文献
150.