全文获取类型
收费全文 | 3106篇 |
免费 | 47篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 45篇 |
综合类 | 8篇 |
化学工业 | 337篇 |
金属工艺 | 58篇 |
机械仪表 | 43篇 |
建筑科学 | 35篇 |
矿业工程 | 8篇 |
能源动力 | 37篇 |
轻工业 | 166篇 |
水利工程 | 10篇 |
石油天然气 | 4篇 |
无线电 | 237篇 |
一般工业技术 | 379篇 |
冶金工业 | 1491篇 |
原子能技术 | 48篇 |
自动化技术 | 249篇 |
出版年
2023年 | 13篇 |
2022年 | 26篇 |
2021年 | 34篇 |
2020年 | 17篇 |
2019年 | 17篇 |
2018年 | 19篇 |
2017年 | 20篇 |
2016年 | 41篇 |
2015年 | 26篇 |
2014年 | 40篇 |
2013年 | 103篇 |
2012年 | 74篇 |
2011年 | 98篇 |
2010年 | 85篇 |
2009年 | 73篇 |
2008年 | 72篇 |
2007年 | 73篇 |
2006年 | 53篇 |
2005年 | 62篇 |
2004年 | 59篇 |
2003年 | 44篇 |
2002年 | 49篇 |
2001年 | 42篇 |
2000年 | 29篇 |
1999年 | 75篇 |
1998年 | 461篇 |
1997年 | 247篇 |
1996年 | 207篇 |
1995年 | 127篇 |
1994年 | 85篇 |
1993年 | 96篇 |
1992年 | 37篇 |
1991年 | 45篇 |
1990年 | 50篇 |
1989年 | 50篇 |
1988年 | 41篇 |
1987年 | 26篇 |
1986年 | 28篇 |
1985年 | 38篇 |
1984年 | 21篇 |
1983年 | 14篇 |
1982年 | 20篇 |
1981年 | 19篇 |
1980年 | 25篇 |
1978年 | 18篇 |
1977年 | 32篇 |
1976年 | 94篇 |
1975年 | 12篇 |
1974年 | 13篇 |
1973年 | 18篇 |
排序方式: 共有3155条查询结果,搜索用时 0 毫秒
41.
TS Bocanegra AL Weaver EA Tindall DH Sikes JA Ball CB Wallemark GS Geis JG Fort 《Canadian Metallurgical Quarterly》1998,25(8):1602-1611
42.
Kocur C.M. Rogers S.K. Myers L.R. Burns T. Kabrisky M. Hoffmeister J.W. Bauer K.W. Steppe J.M. 《IEEE engineering in medicine and biology magazine》1996,15(3)
This study focuses on improving microcalcification classification by establishing an efficient computer-aided diagnosis system that extracts Daubechies-4 and biorthogonal wavelet features. These wavelets were chosen because they have been used in military target recognition and fingerprint recognition research with images characterized by low contrast, similar to mammography. Feature selection techniques are employed to further increase classification performance. The artificial neural network feature selection techniques are complemented by a conventional decision boundary-based feature selection method. The results using the wavelet features are compared to more conventional measures of image texture, angular second moment, and Karhunen Loeve coefficients. The use of alternative signal processing to compare wavelet and neural techniques allows for a measure of the problem difficulty. It is concluded that advances and contributions have been made with the introduction of two novel feature extraction methods for breast cancer diagnosis, wavelets and eigenmasses. Additionally, feature selection techniques are demonstrated, compared, and validated, transforming adequate discrimination power into promising classification results 相似文献
43.
SA Klein JM Dobmeyer TS Dobmeyer M Pape OG Ottmann EB Helm D Hoelzer R Rossol 《Canadian Metallurgical Quarterly》1997,11(9):1111-1118
OBJECTIVE: To characterize changes of Th1/Th2 cytokine production by peripheral blood mononuclear cells (PBMC) that occur during the course of HIV infection by cytoplasmic cytokine staining on single cell level. DESIGN AND METHODS: Mitogen-stimulated PBMC from 16 healthy donors, 18 HIV-1-infected individuals without AIDS and 14 patients with AIDS were stained intracellularly with fluorescein-labelled MAb against interleukin (IL)-2, IL-4, IL-10 and interferon (IFN)-gamma. Additionally, co-staining of CD4+ T-cell, CD8+ T-cell, natural killer (NK) cell, B-cell and monocytic markers was performed. Fluorescence staining was analysed by three-colour flow-cytometry. RESULTS: A reduced percentage of IL-2 and IFN-gamma (Th1 type)-producing cells among CD4+ T cells from HIV-1-infected individuals could be demonstrated. There was a continuous decrease of IFN-gamma-producing CD4+ T cells in the course of HIV infection and a dramatic reduction of IL-2-expressing cells among CD4+ T cells in patients with AIDS. In contrast to Th1 cytokines, the frequency of Th2 cytokine expressing cells among CD4+ T cells increased in HIV-infected individuals. The maximum frequency of IL-4-expressing cells among CD4+ T cells was seen in HIV-infected individuals without AIDS, whereas the rate of IL-10-producing cells was highest in patients with AIDS. In HIV-infected individuals no significant proportion of Th0 cells expressing both Th1 and Th2 cytokines was detectable. In CD8+ T cells the percentage of IL-2 was expressing cells decreased continuously accompanied by a strong increase of the frequency of IFN-gamma-producing cells. CONCLUSION: The decreased percentage of cells expressing IL-2 and IFN-gamma in conjunction with an increased proportion of IL-4- and IL-10-producing cells among the CD4+ T cells in HIV-1-infected individuals demonstrate a Th1 to Th2 cytokine shift in the course of HIV infection on a single cell level. There was no evidence of a Th1 to Th0 cytokine shift. In addition to the loss of CD4+ T cells in HIV infection, the qualitative changes of Th1/Th2 cytokine expression may serve as a marker for progressive failure of cell-mediated immunity. 相似文献
44.
45.
Nadine Kretschmer Antje Hufner Christin Durchschein Katrin Popodi Beate Rinner Birgit Lohberger Rudolf Bauer 《International journal of molecular sciences》2021,22(5)
Melanoma is the deadliest form of skin cancer and accounts for about three quarters of all skin cancer deaths. Especially at an advanced stage, its treatment is challenging, and survival rates are very low. In previous studies, we showed that the constituents of the roots of Onosma paniculata as well as a synthetic derivative of the most active constituent showed promising results in metastatic melanoma cell lines. In the current study, we address the question whether we can generate further derivatives with optimized activity by synthesis. Therefore, we prepared 31, mainly novel shikonin derivatives and screened them in different melanoma cell lines (WM9, WM164, and MUG-Mel2 cells) using the XTT viability assay. We identified (R)-1-(1,4-dihydro-5,8-dihydroxy-1,4-dioxonaphthalen-2-yl)-4-methylpent-3-enyl 2-cyclopropyl-2-oxoacetate as a novel derivative with even higher activity. Furthermore, pharmacological investigations including the ApoToxGloTM Triplex assay, LDH assay, and cell cycle measurements revealed that this compound induced apoptosis and reduced cells in the G1 phase accompanied by an increase of cells in the G2/M phase. Moreover, it showed hardly any effects on the cell membrane integrity. However, it also exhibited cytotoxicity against non-tumorigenic cells. Nevertheless, in summary, we could show that shikonin derivatives might be promising drug leads in the treatment of melanoma. 相似文献
46.
The electrochemical behaviour of several natural ilmenites has been studied by cyclic voltammetry. From the analysis of the current-voltage curves it was concluded that the valences of the metal ions in FeTiO3 are FeII and TiIV. It was also found that little amounts of FeIII and excess of TiIV (probably TiO2) can enter into the composition of the ilmenites. 相似文献
47.
Ye Cai ré Zimmermann Arndt Bauer Fritz Aldinger 《Journal of the American Ceramic Society》2003,86(9):1598-1600
Precursor-derived Si-C-N ceramics after creep testing in air were characterized using X-ray diffractometry (XRD) and transmission electron microscopy (TEM). XRD analysis showed that the crept Si-C-N ceramics were covered by an α-cristobalite layer. TEM observations revealed that the precipitated nanocrystallites in the crept Si-C-N ceramics were β-SiC. Between α-cristobalite and crept Si-C-N ceramic, there was an intermediate zone in which Si2 N2 O nanocrystallites were distributed homogeneously. Moreover, Si2 N2 O nanocrystallites were often found covering the surface of nanosized gas channels in the crept Si-C-N ceramics, where no α-cristobalite phase was detected. Based on these observations, a two-step oxidation mechanism of Si-C-N ceramics during creep testing in air was proposed. 相似文献
48.
Three types of anode, Pb–Sb, Pb–Ca–Sn and Pb–Co3O4, for copper electrowinning were investigated. The corrosion resistance, as evaluated by cyclic voltammetric (CV) measurements was higher for Pb–Co3O4 than for Pb–Sb and Pb–Ca–Sn. During prolonged electrowinning under galvanostatic conditions, the anodic reaction on the Pb–Co3O4 anode was depolarized by 0.053 V as compared to Pb–Sb, and by 0.106 V with respect to Pb–Ca–Sn. The composition and structure of the anodic layer were determined by XPS, X-ray and SEM analyses. The surface layer on the three anodes examined was composed mainly of PbSO4, -PbO2 and -PbO2. Different structure of the surface layer was observed: loose and highly spread coral-like structure in the case of Pb–Sb; fibrous structure in the case of Pb–Ca–Sn and dense, fine-grained structure in the case of Pb–Co3O4. 相似文献
49.
50.
An axisymmetric model for thread forming in polycarbonate and polypropylene screw and boss fasteners
Plastic boss and screw fasteners are an economical means of securing automotive components, such as instrument or body panels. However, new materials and/or suboptimal design present challenges to the boss/screw effectiveness. Failure of a boss/screw can result is loss of functional performance or increased squeak and rattle. Failure is often controlled by what occurs during the initial thread‐forming process. Thus, the goal of this paper is to develop an FEA model to elucidate the thread‐forming process so that we can facilitate subsequent design and/or process optimization, and understand potential failure modes. The FEA must accommodate nonlinear couplings, such as large strain and heat transfer. Heat generation is present in the forms of interfacial shear heating and plastic work associated with the large deformation of the interface between the boss and screw. Strain rate‐dependent materials are included using the Eyring theory for plastic flow of polymeric materials. Results of the model are presented and compared to experimentally determined torque curves and temperatures. Polym. Eng. Sci. 44:1498–1508, 2004. © 2004 Society of Plastics Engineers. 相似文献