全文获取类型
收费全文 | 262篇 |
免费 | 11篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 13篇 |
综合类 | 3篇 |
化学工业 | 75篇 |
金属工艺 | 12篇 |
机械仪表 | 4篇 |
建筑科学 | 3篇 |
能源动力 | 12篇 |
轻工业 | 18篇 |
无线电 | 9篇 |
一般工业技术 | 57篇 |
冶金工业 | 24篇 |
原子能技术 | 6篇 |
自动化技术 | 38篇 |
出版年
2023年 | 3篇 |
2022年 | 5篇 |
2021年 | 13篇 |
2020年 | 6篇 |
2019年 | 5篇 |
2018年 | 11篇 |
2017年 | 5篇 |
2016年 | 8篇 |
2015年 | 2篇 |
2014年 | 8篇 |
2013年 | 19篇 |
2012年 | 20篇 |
2011年 | 14篇 |
2010年 | 19篇 |
2009年 | 17篇 |
2008年 | 18篇 |
2007年 | 7篇 |
2006年 | 9篇 |
2005年 | 10篇 |
2004年 | 4篇 |
2003年 | 4篇 |
2002年 | 3篇 |
2001年 | 5篇 |
2000年 | 2篇 |
1999年 | 4篇 |
1998年 | 9篇 |
1997年 | 8篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 2篇 |
排序方式: 共有274条查询结果,搜索用时 31 毫秒
91.
Kazuya Tajiri Yuichiro Tabuchi Fumio Kagami Shinichi Takahashi Koudai Yoshizawa Chao-Yang Wang 《Journal of power sources》2007
During startup from subzero temperatures the water produced in a polymer electrolyte fuel cell (PEFC) forms ice/frost in the cathode catalyst layer (CL), blocking the oxygen transport and causing cell shutdown once all CL pores are plugged with ice. This paper describes an experimental study on the effects of operating and design parameters on PEFC cold-start capability. The amount of total product water in mg cm−2 during startup is used as an index to quantify the cold-start capability. The newly developed isothermal cold-start protocol is used to explore the basic physics of cold start, and the effects of purge methods prior to cold start, startup temperature and current density, and the membrane thickness are shown. The experimental data also confirm the current density effect predicted earlier by a multiphase model of PEFC cold start. 相似文献
92.
Ding X Takahata M Akazawa T Iwasaki N Abe Y Komatsu M Murata M Ito M Abumi K Minami A 《Journal of materials science. Materials in medicine》2011,22(5):1247-1255
Even though synthetic hydroxyapatite (HAp) has a chemical composition similar to the mineral phase of bone, it is minimally
absorbed and replaced by bone tissue. This could be because HAp is composed of compactly arranged apatite crystals with homogenously
large grains. In this study, the surface and non-stoichiometry of the synthetic HAp crystals was modified by partial dissolution
and precipitation (PDP) to improve bioabsorbability of HAp. In vitro cell culture demonstrated that more osteoclasts were
activated on PDP-HAp compared with HAp. In vivo implantation using a rabbit bone defect model revealed that PDP-HAp was gradually
degraded and was replaced by bone tissue. Consistent with the in vitro results, more osteoclasts were activated in PDP-HAp
than in HAp, indicating that the former was absorbed through the stimulation of osteoclastic activity. These results suggest
that the PDP technique may have clinical utility for modifying synthetic HAp for use as superior bone graft substitutes. 相似文献
93.
Ulla König Anja Lode Petra B. Welzel Yuichiro Ueda Sven Knaack Anja Henß Anke Hauswald Michael Gelinsky 《Journal of materials science. Materials in medicine》2014,25(3):607-621
This study intended to evaluate a contemporary concept of scaffolding in bone tissue engineering in order to mimic functions of the extracellular matrix. The investigated approach considered the effect of the glycosaminoglycan heparin on structural and biological properties of a synthetic biomimetic bone graft material consisting of mineralized collagen. Two strategies for heparin functionalization were explored in order to receive a three-component bone substitute material. Heparin was either incorporated during matrix synthesis by mixing with collagen prior to simultaneous fibril reassembly and mineralization (in situ) or added to the matrix after fabrication (a posteriori). Both methods resulted in an incorporation of comparable amounts of heparin, though its distribution in the matrix varied as indicated by TOF-SIMS analyses, and a similar modulation of their protein binding properties. Differential scanning calorimetry revealed that the thermal stability and thereby the degree of crosslinking of the heparinized matrices was increased. However, in contrast to the a posteriori modification, the in situ integration of heparin led to considerable changes of morphology and composition of the matrix: a more open network of collagen fibers yielding a more porous surface and a reduced mineral content were observed. Cell culture experiments with human mesenchymal stem cells (hMSC) revealed a strong influence of the mode of heparin functionalization on cellular processes, as demonstrated for proliferation and osteogenic differentiation of hMSC. Our results indicate that not only heparin per se but also the way of its incorporation into a collagenous matrix determines the cell response. In conclusion, the a posteriori modification was beneficial to support adhesion, proliferation and differentiation of hMSC. 相似文献
94.
A new approach to cutting state monitoring in end-mill machining 总被引:2,自引:1,他引:1
Dong-Yeul Song Nobuo Otani Takayuki Aoki Yuichiro Kamakoshi Yasuhiro Ohara Haruo Tamaki 《International Journal of Machine Tools and Manufacture》2005,45(7-8):909-921
A new cutting state monitoring approach is proposed for the real-time predicting of the machining trouble and the surface quality of the machined products. In this approach, the relationships among the mechanical model of cutting process and its corresponding time series model, the surface roughness of the machined workpiece are evaluated through theoretical analysis and experimental investigation. It is therefore revealed that there is the linear relationships among the AR parameter a1, the stiffness k3 of cutting model and surface roughness Pz, and consequently the cutting process state can be estimated by only monitoring time series parameter a1 of vibration signal measured during machining operation. In particular, it was found that the variation in the surface roughness of Pz=3–5 μm can be fully monitored. 相似文献
95.
Yasushi Nakasaki Izumi Hirano Koichi Kato Yuichiro Mitani 《Microelectronic Engineering》2009,86(7-9):1901-1904
An atomic-scale model for current-assisted field-accelerated thermochemical degradation via charge capturing by O vacancy (VO) is proposed based on first-principles calculations. We found that the electron current enhances the VO formation around the VO itself and the hole current makes the VO transform into the puckered structure. The calculated activation enthalpy for breakdown and the effective dipole moment agree well with the experimental values. We also found that the subordinate carriers in the generated subordinate carrier injection (GSCI) model play critical roles through a disproportion reaction of positively charged VOs. 相似文献
96.
H Kimoto H Nagaoka Y Adachi T Mizuochi T Azuma T Yagi T Sata S Yonehara Y Tsunetsugu-Yokota M Taniguchi T Takemori 《Canadian Metallurgical Quarterly》1997,27(1):268-279
Well-developed germinal centers (GC) contain rapidly dividing surface immunoglobulin-negative (sIg-) B cells (centroblasts), and most of their progeny are sIg+ B cells (centrocytes) in a resting state. It has been predicted that somatic hypermutation occurs in centroblasts, whereas antigen-driven selection takes place in centrocytes. The present analysis indicates that murine GC B cells bearing sIg with specificity for an immunizing antigen are in a rapidly cycling state and increase exponentially in number to occupy spleen GC at high frequency during the 1st week after primary immunization; however, the number of these cells is significantly reduced in the 2nd week of immunization. During that period, these proliferating sIg+ GC B cells accumulate somatic hypermutations with nucleotide exchanges indicative of affinity maturation. These sIg+ GC B cells co-express B7-2, ICAM-1, and LFA-1, and have potent antigen-presenting activity which results in T cell activation in vitro. These observations indicate that the sIg+ GC B cells accumulate somatic hypermutations and undergo antigen-driven selection through proliferation, probably upon activation by T cells. This sIg+ GC B cell population may represent cell cycling centrocytes; however, the possibility that these may represent centroblasts undergoing re-expression of sIg could not be excluded. 相似文献
97.
Sakae Muto Takafumi Anegawa Shinichi Morooka Seiichi Yokobori Yukio Takigawa Shigeo Ebata Yuichiro Yoshimoto Shuzi Suzuki 《Nuclear Engineering and Design》1990,120(2-3):311-321
It is known that rod temperature rise after boiling transition (BT) is not excursive and that the peak cladding temperature (PCT) is suppressed by rewetting to return to nucleate boiling, even if BT occurs under severe conditions exceeding abnormal operational transients for a BWR. The purpose of this study is to develop and verify the rewetting correlation. The rewetting correlation was developed based on single rod data, as a function of quality, mass flux, pressure and heat flux. The transient thermal-hydraulic code used in the BWR design analysis (SCAT) with this rewetting correlation was compared with transient rod temperature result after the occurence of BT obtianed by the 8×8 and 4×4 rod bundle. It is concluded that the transient code with the developed rewetting correlation predicts the PCT conservatively, and the rewetting time well. 相似文献
98.
M Baba Y Kikuchi S Mori H Kimoto S Inui N Sakaguchi J Inoue T Yamamoto T Takemori M Howard K Takatsu 《Canadian Metallurgical Quarterly》1997,9(10):1463-1473
The germinal center (GC) develops in secondary lymphoid tissues in response to thymus-dependent (TD) antigens. To investigate the molecular mechanism of B cell differentiation in GC, we enriched GC B cells from spleen of TD antigen-immunized wild-type and X-linked immunodeficient (XID) mice, and examined the differentiation of GC B cells into antigen-specific IgG1 antibody-forming cells (AFC) in response to anti-CD40 mAb and cytokines. A significant proportion of freshly purified GC B cells expressed receptors for IL-4 and IL-5. Anti-CD40 mAb sustained the viability of GC B cells and IL-4 co-operated with anti-CD40 mAb for further enhancement of the cell viability. Anti-CD40 mAb and IL-4 were essential for inducing differentiation of GC B cells into antigen-specific IgG1-AFC and IL-5 efficiently enhanced their differentiation. GC B cells with the xid mutation responded for proliferation to CD40 ligation to a lesser extent and for the IgG1-AFC response to anti-CD40 mAb together with IL-4, but they showed impaired responsiveness to IL-5, regardless of enhanced expression of IL-5R in response to anti-CD40 mAb and IL-4. These results suggest that anti-CD40 mAb, IL-4 and IL-5 play a critical role in the differentiation of mouse GC B cells. The GC B cells from XID mice show a functional defect with respect to IL-5-mediated differentiation. 相似文献
99.
Brittle failures of large plastic structures observed in the field may have occurred at much higher loads than implied from the fracture surfaces, indeed, as if very ductile failures had occurred. It has been demonstrated that these brittle failures may be a direct result of high energy storage upon impact in large compliant systems. A rubber-toughened blend of polybutylene terephthalate (PBT) and polycarbonate (PC) was highlighted in this study. Soft steel springs were used in series with compact tension samples to simulate the high energy-storing capability of large compliant structures, Ductile and stable fractures of compact tension samples of the blend were observed at all of the temperatures tested down through ?30°C. With the insertion of springs to simulate large compliant structures, however, unstable failures resulted. At 25°C, initial ductile crack growth was followed by ductile but unstable failure. At ?30°C, initial ductile crack growth was followed by brittle unstable failure. These instabilities resulted from the excessive amount of stored energy released by the system during initial crack growth. A higher rubber variant of the PBT/PC blend as well as acrylonitrile-butadiene-styrene (ABS) and polycarbonate exhibited similar behavior. 相似文献
100.
Reactive miscible viscous fingering occurs when a reactive and miscible less-viscous liquid displaces a more-viscous liquid. Effects of bulk finger-growth velocity on reaction characteristics of miscible viscous fingering with a chemical reaction were studied analytically by using a convection-diffusion-reaction model. The model assumes the existence of a distinct interface between both liquids, assumes the existence of a two-dimensional, steady, stagnated flow field in the less-viscous liquid, and assumes an infinite chemical reaction rate. The model was then used to determine the reaction characteristics, such as the location of the reaction surface and the profile of the product, as functions of the velocity and initial reactant concentrations. The results reveal that the effects of the velocity on the reaction characteristics can be divided into low-, intermediate-, and high-velocity regions. In the low-velocity region, the reaction characteristics strongly depend on the reactant concentrations. In the intermediate-velocity region, the dependence of the reaction characteristics on the reactant concentrations decreases with increasing velocity. In the high-velocity region, the reaction characteristics are nearly independent of the reactant concentrations. Experiments confirm the existence of these three velocity regions predicted by the model. 相似文献