全文获取类型
收费全文 | 36020篇 |
免费 | 1223篇 |
国内免费 | 1029篇 |
专业分类
电工技术 | 1569篇 |
技术理论 | 1篇 |
综合类 | 1323篇 |
化学工业 | 6363篇 |
金属工艺 | 3661篇 |
机械仪表 | 2698篇 |
建筑科学 | 2487篇 |
矿业工程 | 1301篇 |
能源动力 | 2131篇 |
轻工业 | 2197篇 |
水利工程 | 444篇 |
石油天然气 | 1459篇 |
武器工业 | 196篇 |
无线电 | 2958篇 |
一般工业技术 | 4229篇 |
冶金工业 | 1878篇 |
原子能技术 | 763篇 |
自动化技术 | 2614篇 |
出版年
2024年 | 60篇 |
2023年 | 393篇 |
2022年 | 620篇 |
2021年 | 881篇 |
2020年 | 849篇 |
2019年 | 855篇 |
2018年 | 804篇 |
2017年 | 911篇 |
2016年 | 965篇 |
2015年 | 1020篇 |
2014年 | 1871篇 |
2013年 | 2089篇 |
2012年 | 1867篇 |
2011年 | 2748篇 |
2010年 | 1895篇 |
2009年 | 1949篇 |
2008年 | 1785篇 |
2007年 | 2071篇 |
2006年 | 2026篇 |
2005年 | 1787篇 |
2004年 | 1500篇 |
2003年 | 1360篇 |
2002年 | 1168篇 |
2001年 | 991篇 |
2000年 | 869篇 |
1999年 | 927篇 |
1998年 | 764篇 |
1997年 | 666篇 |
1996年 | 558篇 |
1995年 | 469篇 |
1994年 | 356篇 |
1993年 | 238篇 |
1992年 | 209篇 |
1991年 | 154篇 |
1990年 | 106篇 |
1989年 | 100篇 |
1988年 | 90篇 |
1987年 | 48篇 |
1986年 | 49篇 |
1985年 | 33篇 |
1984年 | 39篇 |
1983年 | 16篇 |
1982年 | 15篇 |
1981年 | 36篇 |
1980年 | 14篇 |
1979年 | 9篇 |
1976年 | 4篇 |
1975年 | 12篇 |
1974年 | 4篇 |
1973年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
102.
A 1-D transient model (RESHEAT), developed by the writers, was used to study the thermal performance of a highly reflective paint applied sequentially to the outer walls and roof of a simulated residence in a hot and arid region of the southwestern United States. The model uses climatological inputs from a file that includes hourly data on ambient temperatures, insolation, cloud cover, and so on, at the particular location. The model focuses particularly on the potential cooling load reduction due to the reduced heat pickup from the inside attic surfaces to the outer surfaces of the supply duct. This simulation showed that a reduction of 33.6% (cooling load) on the average is achieved over the base case where no reflective paint is used when the outer surface of the roof and walls are painted. Alternatively, only a 11% reduction would be achieved if the reflective paint is applied only to the roof. Savings of $42 per month are conservatively estimated from calculations made when applying this technology to a typical residence (roof and walls) equipped with a 4 ton refrigeration unit in the Southwest. 相似文献
103.
Xin Song Xiaoyu Qi Bin Hao Yinbo Qu 《European Journal of Lipid Science and Technology》2008,110(12):1095-1101
Although lipases are widely applied in a wide variety of reactions, available information on the factors that are responsible for the substrate specificities of lipases from different sources is scarce. In this paper, nine lipase‐producing microorganism strains were isolated from oil‐containing samples. The properties of these enzymes, including pH optima, temperature optima, thermal stability, and pH stability, vary significantly with the different sources from which these lipases were isolated. The substrate specificities of the nine lipases, including fatty acid and positional specificities, were also studied. The fatty acid specificities of the nine lipases were observably different toward 15 substrates with different carbon chain lengths, different saturation degrees and different side chains. The lipases from S3 Penicillium citrinum (PCL), MJ1 Aspergillus niger (ANL), MJ2 Aspergillus oryzae (AOL), YM Bacillus coughing (BCL), S9 Geotrichum candidum (GCL), and S11 Candida lypolytica (CLL) showed the strongest specificities to short‐chain esters, and the other lipases showed strong selectivity for medium‐ or long‐chain and branched esters. The positional specificities were examined by analyzing the hydrolytic products of triolein catalyzed by the nine lipases, using TLC. The lipases can be mainly classified into two groups by their specificities for the ester bond at position 2 of triglycerides; one group can selectively hydrolyze the ester bond at position 2 of the triglycerides, the other group cannot. All these nine lipases were divided into four groups by hierarchical clustering analysis on the basis of the results of fatty acid and positional specificities. 相似文献
104.
The temperature programmed (palladium) hydride decomposition appeared very effective method for diagnosing the extent of alloying in Pd-Pt/SiO2 catalysts. Introduction of Pt to Pd catalysts moves the TPHD peak gradually towards lower temperatures and the shift in hydride decomposition peak is accompanied by a decrease in the amount of released hydrogen. The catalysts prepared the direct redox method showed much better alloy homogeneity than the samples prepared by coimpregnation. The results of probing with other techniques, i.e. catalytic probing with hydrodechlorination of CCl2F2 and XRD, were in line with TPHD data. The catalytic probing showed the presence of synergistic effect, a clear indication of Pd-Pt mixing. XRD data of post-reaction samples showed carbon incorporation into Pd-rich phase, whereas separate Pt-rich phase did not experience any bulk carbiding. 相似文献
105.
Mapping surface temperature in large lakes with MODIS data 总被引:1,自引:0,他引:1
Satellite sensor MODIS on two platforms can produce Sea Surface Temperature over certain regions about three to four times per day. Our objective was to test if the MODIS SST product can be applied for lakes whose surface areas are large enough to be observed at the MODIS spatial resolution and to compare the satellite-derived lake surface temperatures with in situ measurements. Surface temperatures for Lakes Vänern and Vättern in Sweden, two of the largest European lakes, are extracted from the MODIS/Terra images for period 2001-2003. The results are analyzed on different quality levels, as all MODIS L2 products are equipped with an additional quality flag. We present temperature development over 2001-2003, and show the capability of the MODIS SST product to couple the known thermodynamical features in the lakes under study, where temperature varies greatly with space and time. These results can complement lake monitoring programs anywhere. 相似文献
106.
107.
卸荷裂隙在水利水电工程建设中的危害 总被引:3,自引:0,他引:3
卸荷裂隙是对水工建筑物稳定最不利的软弱结构面之一。文中较系统地介绍了这种结构面的特点、分布规律、形成的力学机理、对工程的危害、勘查方法及处理措施。 相似文献
108.
109.
In arc welding processes, because of the complexity and nonlinearity of heat transfer phenomena, it is often difficult to design an effective control system based upon an exact mathematical model. In this paper, a self-organizing fuzzy control method is proposed to obtain a uniform weld quality by regulation of the surface temperature at a desired level. The proposed control system is designed to comprise a combined structure of the fuzzy SOC with conventional PD control for improving the system's stability. The control experiments show that the proposed controller guarantees a uniform weld quality for various welding conditions. 相似文献
110.
对新研制的两种电解防污开关恒流源所采用的不同逆变器、开关功率管、直流工作电源及取样方式的工作状态、工作特性进行了分析比较。在研制过程中,重点解决了恒流电源工作的安全可靠性、稳定性、抗干扰能力及输出范围宽等问题。 相似文献