全文获取类型
收费全文 | 234928篇 |
免费 | 27640篇 |
国内免费 | 25767篇 |
专业分类
电工技术 | 29178篇 |
技术理论 | 9篇 |
综合类 | 16550篇 |
化学工业 | 43092篇 |
金属工艺 | 12580篇 |
机械仪表 | 14525篇 |
建筑科学 | 10068篇 |
矿业工程 | 3594篇 |
能源动力 | 8441篇 |
轻工业 | 15341篇 |
水利工程 | 2824篇 |
石油天然气 | 5827篇 |
武器工业 | 2247篇 |
无线电 | 32513篇 |
一般工业技术 | 22930篇 |
冶金工业 | 13512篇 |
原子能技术 | 3556篇 |
自动化技术 | 51548篇 |
出版年
2024年 | 1231篇 |
2023年 | 3990篇 |
2022年 | 7233篇 |
2021年 | 8258篇 |
2020年 | 8101篇 |
2019年 | 7171篇 |
2018年 | 6736篇 |
2017年 | 9154篇 |
2016年 | 9914篇 |
2015年 | 11082篇 |
2014年 | 12308篇 |
2013年 | 14892篇 |
2012年 | 17557篇 |
2011年 | 19436篇 |
2010年 | 13948篇 |
2009年 | 13870篇 |
2008年 | 14731篇 |
2007年 | 16988篇 |
2006年 | 16193篇 |
2005年 | 13977篇 |
2004年 | 11858篇 |
2003年 | 9679篇 |
2002年 | 7495篇 |
2001年 | 5940篇 |
2000年 | 4933篇 |
1999年 | 4199篇 |
1998年 | 3293篇 |
1997年 | 2741篇 |
1996年 | 2173篇 |
1995年 | 1869篇 |
1994年 | 1576篇 |
1993年 | 1120篇 |
1992年 | 925篇 |
1991年 | 724篇 |
1990年 | 603篇 |
1989年 | 459篇 |
1988年 | 334篇 |
1987年 | 215篇 |
1986年 | 192篇 |
1985年 | 233篇 |
1984年 | 222篇 |
1983年 | 177篇 |
1982年 | 213篇 |
1981年 | 99篇 |
1980年 | 97篇 |
1979年 | 25篇 |
1978年 | 16篇 |
1977年 | 24篇 |
1959年 | 19篇 |
1957年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
993.
R-卡尼丁的合成和改进 总被引:2,自引:2,他引:2
以环氧氯丙烷为原料合成了 ( R,S) -卡尼丁 ,用二苯甲酰 - L-酒石酸对其进行了拆分 ,对反应和拆分条件进行了优化 ,并用氧化还原法实现了 S-卡尼丁的消旋化 ,使其可以回收利用。 相似文献
994.
Although user experience and personal innovativeness are two important factors in new technology adoption, there has been no prior study to test these factors with the Enterprise Resource Planning (ERP) adoption. This paper investigates moderating roles of user experience on the relationship between the personal innovativeness and the ERP adoption motivations. This issue is important because if the user has more experience with the systems then the power of influence of personal innovativeness on ERP adoption motivation would be different. Thus, this paper tests these important insights of ERP systems adoption with the two different field samples with high (more than three years) and low (less than three years) user experience, based on the innovation diffusion theory, self determination theory, and different types of motivations such as intrinsic and extrinsic motivations. The findings, based on the PLS analysis of the model using 107 ERP end users, show that there are clear moderating effects of user experience—such as impacts of personal innovativeness on ERP systems adoption motivations are higher in case of low user experience samples, as expected. Academic and practical implications are discussed in the paper based on these empirical findings. 相似文献
995.
996.
Hydrogen evolution during formaldehyde oxidation in alkaline solution has been monitored by Differential Electrochemical Mass Spectrometry on Au(111) and polycrystalline gold. The current efficiency for hydrogen evolution increases with higher concentration and is in the same range on both, polycrystalline Au and Au(111) electrode. The onset potentials and half-wave potentials are higher on Au(111). Reaction orders for the faradaic current on the bare gold electrodes have been determined as 0.21 for higher and 0.76 for lower concentrations. Reaction orders for hydrogen evolution during formaldehyde oxidation are 1.4 times higher in each case. Tafel slopes in the range of 140-160 mV are found. This signifies that the first reaction step involving the formation of adsorbed hydrogen is largely determining the overall reaction rate. In the presence of thallium adlayers hydrogen evolution from formaldehyde oxidation is largely suppressed. On the thallium modified polycrystalline Au, formaldehyde oxidation is shifted for 100 mV to higher potentials where Tl is partially desorbed and hydroxide is coadsorbed on the modified surface. On thallium modified Au(111), a similar process takes place, but in the same potential region as the onset of formaldehyde oxidation on the bare surface and therefore the formaldehyde oxidation is only slightly shifted. Tafel slopes are decreased to 80 mV/dec in the presence of thallium. In the presence of adsorbed thallium, the first reaction step is in equilibrium, the coverage with adsorbed hydrogen is smaller and its recombination to H2 is largely suppressed. 相似文献
997.
998.
The processing–property relationship of a model cryogenically mechanically alloyed polymer–polymer system [polycarbonate (PC) and poly(aryl ether ether ketone) (PEEK)] was investigated. PC and PEEK powders were cryogenically mechanically alloyed for 10 h, and the resulting two‐phase powder particles were processed into testable coupons with a miniature ram‐injection molder. The bulk mechanical properties of the coupons made from the mechanically alloyed powders and nonmechanically alloyed powders were investigated as a function of mechanical alloying and injection‐molding parameters. The injection‐molded coupons were mechanically tested in the three‐point‐bending mode. The results demonstrated that no measurable improvement was achieved in the energy to break, strain at failure, or failure strength in the coupons made from the mechanically alloyed materials in comparison with those of the coupons made from the nonmechanically alloyed powders. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1196–1202, 2003 相似文献
999.
Muhammad Nor Omar Humphrey A. Moynihan Richard J. Hamilton 《European Journal of Lipid Science and Technology》2003,105(1):43-44
The asymmetric Sharpless epoxidation of methyl 13S‐hydroxy‐9Z, 11E‐octadeca‐dienoate (13S‐HODE, 1 ) with tert‐butyl hydroperoxide (TBHP) catalysed by titanium tetraisopropoxide {Ti(iOPr)4} in the presence of L(+)‐diisopropyl tartrate (L‐DIPT) gave methyl 13S‐hydroxy‐11S, 12S‐epoxy‐9Z‐octadecenoate 2 (erythro isomer) in 84% diastereomeric excess (de). The epoxidation of 1 with TBHP catalysed by Ti(iOPr)4 in the presence of D(‐)‐DIPT yielded methyl 13S‐hydroxy‐11RR12R‐epoxy‐9Z‐octadecenoate (threo isomer) 3 in 76% de. 相似文献
1000.
橡胶/蒙脱土纳米复合材料的优异性能使其成为橡胶工业中富有潜力的一类新型材料。笔者综述了三元乙丙橡胶(EPDM)/蒙脱土纳米复合材料的制备方法、性能和工业应用领域等,讨论了蒙脱土片层的表面修饰、插层剂的选择以及复合材料的制备方法对材料性能的影响,并提出了三元乙丙橡胶/蒙脱土纳米复合材料这一新型橡胶材料在轮胎工业上的应用前景。 相似文献