全文获取类型
收费全文 | 3849篇 |
免费 | 290篇 |
国内免费 | 87篇 |
专业分类
电工技术 | 188篇 |
综合类 | 164篇 |
化学工业 | 666篇 |
金属工艺 | 88篇 |
机械仪表 | 124篇 |
建筑科学 | 142篇 |
矿业工程 | 94篇 |
能源动力 | 94篇 |
轻工业 | 158篇 |
水利工程 | 36篇 |
石油天然气 | 63篇 |
武器工业 | 7篇 |
无线电 | 431篇 |
一般工业技术 | 487篇 |
冶金工业 | 1047篇 |
原子能技术 | 34篇 |
自动化技术 | 403篇 |
出版年
2024年 | 7篇 |
2023年 | 30篇 |
2022年 | 63篇 |
2021年 | 79篇 |
2020年 | 62篇 |
2019年 | 43篇 |
2018年 | 68篇 |
2017年 | 69篇 |
2016年 | 99篇 |
2015年 | 110篇 |
2014年 | 141篇 |
2013年 | 198篇 |
2012年 | 175篇 |
2011年 | 199篇 |
2010年 | 187篇 |
2009年 | 157篇 |
2008年 | 188篇 |
2007年 | 147篇 |
2006年 | 174篇 |
2005年 | 121篇 |
2004年 | 97篇 |
2003年 | 115篇 |
2002年 | 133篇 |
2001年 | 107篇 |
2000年 | 71篇 |
1999年 | 99篇 |
1998年 | 329篇 |
1997年 | 205篇 |
1996年 | 135篇 |
1995年 | 87篇 |
1994年 | 67篇 |
1993年 | 82篇 |
1992年 | 31篇 |
1991年 | 49篇 |
1990年 | 19篇 |
1989年 | 24篇 |
1988年 | 24篇 |
1987年 | 23篇 |
1986年 | 21篇 |
1985年 | 15篇 |
1984年 | 9篇 |
1983年 | 13篇 |
1982年 | 11篇 |
1981年 | 15篇 |
1980年 | 9篇 |
1979年 | 7篇 |
1978年 | 6篇 |
1977年 | 27篇 |
1976年 | 50篇 |
1975年 | 8篇 |
排序方式: 共有4226条查询结果,搜索用时 8 毫秒
1.
Sangmin Lee Biao Che Meiling Tai Wanzhao Li Shin-Hyun Kim 《Advanced functional materials》2021,31(42):2105477
Hydrogel shells that compartmentalize the water core from the aqueous surrounding provide molecular selectivity on size and charge in transmembrane transport. It is highly demanding to produce thin hydrogel shells to minimize diffusion length and maximize core volume. Here, internal osmosis in water-in-oil-in-water-in-oil (W/O/W/O) triple-emulsion droplets is used to produce thin hydrogel shells enclosing a large water core. The triple-emulsion droplets are prepared to have an ultrathin middle oil layer using a capillary microfluidic device. The innermost water droplet has a higher osmolarity than the outer water layer containing photopolymerizable hydrogel precursors, which pumps water from the outer layer to the core through the ultrathin oil layer by the osmosis. Therefore, the outer layer gets thinner and hydrogel precursors are enriched while the size of the triple-emulsion droplets remains unchanged. Through photopolymerization of precursors and phase transfer from oil to water, hydrogel shells enclosing water core are produced in the water environment; the oil layer is ruptured for molecular exchange through the shells. The thickness and composition of the hydrogel shells are precisely controllable by the osmotic conditions. The shells show a high permeation rate due to the thinness as well as controlled cut-off threshold of permeation for neutral and charged molecules. 相似文献
2.
Ming-Puu Chen Asta Y. Z. Lord Yu-Yao Cheng Ku-Chou Tai Wen-Harn Pan 《Journal of Computer Assisted Learning》2020,36(3):383-396
Reflective judgement is crucial for medical-related practitioners in dealing with controversial issues. However, the conformity phenomenon is likely to occur and interfere with reflective judgement learning during interactive activities. Effective strategies are required to moderate the conformity behaviour tendency (CBT) and improve reflective judgement performance (RJP). This study demonstrates two significant results: (a) Compared with the guided self-reflection learning strategy, the online collective reflection (OCR) learning strategy effectively weakened the learners' general CBT while dealing with professional controversial issues; and (b) a significantly negative correlation between the RJP achieved and the change of CBT in online environment was detected in the OCR group. The implications and potential applications in higher education were discussed. Further studies are needed to confirm the long-term effects and the extending application to other professional studies. 相似文献
3.
4.
5.
OBJECTIVE: To examine the relationship between pregnancy incidence and the level of serum E2 during danazol therapy. DESIGN: Danazol was given by 200 mg four times daily for 3 months. Serum E2 level was checked after completing the therapy, but before stopping medication. Patients then were advised to conceive at the appropriate time over a 6-month period. SETTING: Reproductive and Endocrine Laboratory of the Department of Obstetrics and Gynecology, Keelung Chang Gung Memorial Hospital, Keelung, Taiwan. PATIENTS: Infertile women with invasive endometriosis receiving conservative surgery and danazol treatment. INTERVENTIONS: Serum E2 is checked before medication and at the end of danazol therapy, but before stopping medication. MAIN OUTCOME MEASURES: Whether pregnancy is related to the change of serum E2 caused by danazol therapy. RESULTS: There were 24 pregnancies in 38 patients with invasive endometriosis after treatment. Pregnant patients had significantly lower serum E2 levels as compared with the nonpregnant patients. CONCLUSIONS: After conservative surgery for invasive endometriosis associated with infertility, the therapeutic period of danazol treatment could be shortened to 3 months. Because there is significant correlation of fecundability and serum E2 after danazol medication, serum E2 could be a guideline for predicting pregnancy or for prolonging or changing of treatment after danazol therapy. 相似文献
6.
DC Reynolds CE Leak KK Bajaj CE Stutz RL Jones KR Evans PW Yu WM Theis 《Canadian Metallurgical Quarterly》1989,40(9):6210-6217
7.
The photoelectrochemical behaviors of RuL2(NCS)2 dye-sensitized SnO2/TiO2 coupled solar cell was studied and compared with TiO2 single system. The coupled system shows higher incident photon-to-current conversion efficiency (IPCE) value than the single system. A maximum IPCE value in the coupled system with 3.5 μm-thick SnO2 and 7 μm-thick TiO2 attained 82.4% at 530 nm wavelength. The higher IPCE value in the coupled system is attributed to the charge separation by fast electron transfer process from the excited RuL2(NCS)2 dye to TiO2 to SnO2 in the system with different energy level. 相似文献
8.
阐述了企业人力资源投资财务评价应解决的两个重要问题:评价对象的分类和项目的财务现金流量的内容。 相似文献
9.
10.
Effects of surfactant/silica and silica/cerium ratios on the characteristics of mesoporous Ce-MCM-41
Se Ho Park Bo Yune Song Tai Gyu Lee 《Journal of Industrial and Engineering Chemistry》2008,14(2):261-264
Using the surfactant CTMABr (cetyltrimethyl ammonium bromide) and cerium(IV) sulfate, mesoporous Ce-MCM-41 molecular sieves were produced under a hydrothermal condition with various surfactant/silica (surfactant/Si) and silica/cerium (Si/Ce) ratios. Changes to the structural traits caused by changing the molar ratios of both surfactant/Si and Si/Ce were investigated. XRD (X-ray diffraction), FT-IR (fourier transform infrared spectroscopy), and SEM (scanning electro microscopy) were used for the characterization of prepared mesoporous samples. Among the tested molar ratios, surfactant/Si ratio of 0.5 and 0.2 showed highest values of d1 0 0 and intensity, respectively, for the Si-MCM-41. XRD analysis also identified a quintessential hexagonal structure of Ce-MCM-41 for the Si/Ce molar ratio higher than 40 (maintaining the surfactant/Si ratio at 0.2). When cerium content was increased to have the Si/Ce molar ratio of 20, the hexagonal structure of Ce-MCM-41 was collapsed due to the structural stress of substituted cerium. FT-IR results confirmed calcination of Ce-MCM-41 and the incorporation of Ce4+ ions of cerium sulfate into the silica surface with proper removal of the surfactant. Rod-like shape with rounded edges of the prepared Ce-MCM-41 samples was identified by SEM. These results suggest surfactant/Si ratio of 0.2 and Si/Ce ratio of 40 for the production of Ce-MCM-41 with the highest level of crystallinity. 相似文献