全文获取类型
收费全文 | 50897篇 |
免费 | 1462篇 |
国内免费 | 205篇 |
专业分类
电工技术 | 652篇 |
综合类 | 636篇 |
化学工业 | 6174篇 |
金属工艺 | 893篇 |
机械仪表 | 1406篇 |
建筑科学 | 981篇 |
矿业工程 | 390篇 |
能源动力 | 764篇 |
轻工业 | 2650篇 |
水利工程 | 622篇 |
石油天然气 | 59篇 |
武器工业 | 4篇 |
无线电 | 3545篇 |
一般工业技术 | 5134篇 |
冶金工业 | 21997篇 |
原子能技术 | 331篇 |
自动化技术 | 6326篇 |
出版年
2023年 | 290篇 |
2022年 | 222篇 |
2021年 | 359篇 |
2020年 | 222篇 |
2019年 | 222篇 |
2018年 | 686篇 |
2017年 | 933篇 |
2016年 | 1350篇 |
2015年 | 992篇 |
2014年 | 745篇 |
2013年 | 930篇 |
2012年 | 2668篇 |
2011年 | 3073篇 |
2010年 | 1133篇 |
2009年 | 1238篇 |
2008年 | 1059篇 |
2007年 | 984篇 |
2006年 | 882篇 |
2005年 | 3625篇 |
2004年 | 2797篇 |
2003年 | 2255篇 |
2002年 | 1077篇 |
2001年 | 939篇 |
2000年 | 474篇 |
1999年 | 809篇 |
1998年 | 6444篇 |
1997年 | 3979篇 |
1996年 | 2634篇 |
1995年 | 1539篇 |
1994年 | 1161篇 |
1993年 | 1173篇 |
1992年 | 285篇 |
1991年 | 356篇 |
1990年 | 339篇 |
1989年 | 305篇 |
1988年 | 318篇 |
1987年 | 248篇 |
1986年 | 214篇 |
1985年 | 179篇 |
1984年 | 80篇 |
1983年 | 94篇 |
1982年 | 137篇 |
1981年 | 189篇 |
1980年 | 198篇 |
1979年 | 65篇 |
1978年 | 98篇 |
1977年 | 618篇 |
1976年 | 1329篇 |
1975年 | 101篇 |
1971年 | 51篇 |
排序方式: 共有10000条查询结果,搜索用时 890 毫秒
31.
A route to synthesize ZSM‐5 crystals with a bimodal micro/mesoscopic pore system has been developed in this study; the successful incorporation of the mesopores within the ZSM‐5 structure was performed using tetrapropylammonium hydroxide (TPAOH)‐impregnated mesoporous materials containing carbon nanotubes in the pores, which were encapsulated in the ZSM‐5 crystals during a solid rearrangement process within the framework. Such mesoporous ZSM‐5 zeolites can be readily obtained as powders, thin films, or monoliths. 相似文献
32.
Shi-Jin Ding Hang Hu Lim H.F. Kim S.J. Yu X.F. Chunxiang Zhu Li M.F. Byung Jin Cho Chan D.S.H. Rustagi S.C. Yu M.B. Chin A. Dim-Lee Kwong 《Electron Device Letters, IEEE》2003,24(12):730-732
For the first time, we successfully fabricated and demonstrated high performance metal-insulator-metal (MIM) capacitors with HfO/sub 2/-Al/sub 2/O/sub 3/ laminate dielectric using atomic layer deposition (ALD) technique. Our data indicates that the laminate MIM capacitor can provide high capacitance density of 12.8 fF//spl mu/m/sup 2/ from 10 kHz up to 20 GHz, very low leakage current of 3.2 /spl times/ 10/sup -8/ A/cm/sup 2/ at 3.3 V, small linear voltage coefficient of capacitance of 240 ppm/V together with quadratic one of 1830 ppm/V/sup 2/, temperature coefficient of capacitance of 182 ppm//spl deg/C, and high breakdown field of /spl sim/6 MV/cm as well as promising reliability. As a result, the HfO/sub 2/-Al/sub 2/O/sub 3/ laminate is a very promising candidate for next generation MIM capacitor for radio frequency and mixed signal integrated circuit applications. 相似文献
33.
34.
35.
36.
H.S. Seo Y.G. Choi B.J. Park D.H. Cho K.H. Kim 《Photonics Technology Letters, IEEE》2003,15(9):1198-1200
A flat signal gain over in the entire C- and L-bands by erbium (Er) ions' radiative transition and stimulated Raman scattering in an Er-doped germano-silica fiber can be obtained if proper values of the concentration of Er and background loss in a fiber core are obtained during the fiber fabrication process. The optimized conditions for the flat C- and L-band gain are analyzed as functions of Er concentrations. Even for a low-gain value provided by a germano-silica core fiber with a low Er concentration and an optimum fiber length, a relatively low pump is required to obtain the flat gain band. 相似文献
37.
Maenghyo Cho Hee Yuel Roh 《International journal for numerical methods in engineering》2003,56(1):81-115
In the present study first‐order shear deformable shell finite elements based on general curvilinear co‐ordinates are proposed. For the development of the present shell elements, a partial mixed variational functional with independently assumed strains is provided in order to avoid the severe locking troubles known as transverse shear and membrane lockings. Bubble functions are included in the shape function of displacement to improve the performance of the developed element. The proposed assumed strain four‐ and nine‐node elements based on the general tensor shell theory provide an efficient linkage framework for shell surface modelling and finite element analysis. In the several benchmark problems, the present shell elements with exact geometric representations demonstrate their performance compared to previously reported results. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
38.
The expression of cytokeratins (CK), involucrin, vimentin, CD34, and alpha-smooth-muscle actin was studied in fetal and adult hair follicles. The first stage of the developing hair follicle is characterized by palisaded, elongated epithelial cells budding from the epidermal basal layer. These cells express CK5/6, CK14, CK17, CK19, and vimentin. During the following weeks of gestation, different structures in the developing hair follicle can be identified and characterized. The matrical cells display only CK19. The keratinocytes of the outer root sheath express CK5/6, CK14, CK17, CK19, and involucrin; those of the inner root sheath, CK4, CK18, and involucrin; those of the isthmus, the same profile as the ORS. In the infundibulum, the basal-layer keratinocytes express CK5/6, CK14, CK17, and CK19, whereas in the suprabasal layers CK1, CK4, CK10, CK14, and CK17 are seen. The adult hair follicle in anagen fails to express CK19 in the matrical cells and isthmus and both CK17 and CK19 in the infundibulum. These profiles of intermediate filaments and other markers appear to be potentially useful in categorizing neoplasms with apparent follicular differentiation. 相似文献
39.
40.
Phospholamban (PLN) was expressed in Escherichia coli as a protein fusion with glutathione S-transferase (GST). GST-PLN was mostly present in the insoluble protein fraction and accounted for approximately 50% of total insoluble protein. Attempts to suppress inclusion body formation or to use GST as an affinity-purification tag failed. A successful purification method is based on preparative SDS/PAGE and electrodialysis. From 1 g cells we typically purified 13.5 mg fusion protein with a PLN content of 2.8 mg. We genetically inserted an enterokinase (EK) protease site just in front of the PLN sequence and demonstrated the proteolytical liberation of PLN from the carrier protein. The approach described represents a substantial advancement in PLN expression and purification. 相似文献