全文获取类型
收费全文 | 2158篇 |
免费 | 41篇 |
国内免费 | 11篇 |
专业分类
电工技术 | 92篇 |
综合类 | 1篇 |
化学工业 | 443篇 |
金属工艺 | 77篇 |
机械仪表 | 52篇 |
建筑科学 | 34篇 |
能源动力 | 86篇 |
轻工业 | 130篇 |
水利工程 | 9篇 |
无线电 | 225篇 |
一般工业技术 | 443篇 |
冶金工业 | 430篇 |
原子能技术 | 52篇 |
自动化技术 | 136篇 |
出版年
2023年 | 9篇 |
2022年 | 22篇 |
2021年 | 30篇 |
2020年 | 11篇 |
2019年 | 26篇 |
2018年 | 25篇 |
2017年 | 22篇 |
2016年 | 33篇 |
2015年 | 23篇 |
2014年 | 43篇 |
2013年 | 101篇 |
2012年 | 69篇 |
2011年 | 107篇 |
2010年 | 77篇 |
2009年 | 102篇 |
2008年 | 87篇 |
2007年 | 81篇 |
2006年 | 67篇 |
2005年 | 66篇 |
2004年 | 55篇 |
2003年 | 64篇 |
2002年 | 57篇 |
2001年 | 46篇 |
2000年 | 47篇 |
1999年 | 50篇 |
1998年 | 184篇 |
1997年 | 109篇 |
1996年 | 66篇 |
1995年 | 55篇 |
1994年 | 52篇 |
1993年 | 43篇 |
1992年 | 21篇 |
1991年 | 31篇 |
1990年 | 23篇 |
1989年 | 30篇 |
1988年 | 23篇 |
1987年 | 16篇 |
1986年 | 27篇 |
1985年 | 30篇 |
1984年 | 17篇 |
1983年 | 13篇 |
1982年 | 19篇 |
1981年 | 14篇 |
1980年 | 19篇 |
1979年 | 12篇 |
1978年 | 6篇 |
1977年 | 17篇 |
1976年 | 34篇 |
1975年 | 8篇 |
1973年 | 8篇 |
排序方式: 共有2210条查询结果,搜索用时 15 毫秒
11.
Y. Nakamura Ichiro Tanaka N. Takeuchi S. Koshiba H. Sakaki 《Journal of Electronic Materials》1998,27(11):1240-1243
We studied morphology of GaAs surfaces and the transport properties of two-dimensional electron gas (2DEG) on vicinal (111)B
planes. Multi-atomic steps (MASs) are found on the vicinal (111)B facet grown by molecular beam epitaxy, which will affect
electron transport on the facet. We also studied how the morphology of GaAs epilayers on vicinal (111)B substrates depends
on growth conditions, especially on the As4 flux. The uniformity of MASs on the substrates have been improved and smooth surfaces were obtained when the GaAs was grown
with high As4 flux, providing step periodicity of 20 nm. The channel resistance of the 2DEG perpendicular to the MASs is reduced drastically
with this smooth morphology. These findings are valuable not only for fabricating quantum devices on the (111)B facets but
also those on the vicinal (111)B substrates. 相似文献
12.
Tohru Morii Hiroyuki Hamada Muriel Desaeger Akihiko Gotoh Atsushi Yokoyama Ignaas Verpoest Zen-ichiro Maekawa 《Composite Structures》1995,32(1-4):133-139
This study deals with the impact property and damage tolerance of matrix hybrid composite laminates with different laminate constitution. The matrix hybrid composite laminates consisted of the laminae with a conventional epoxy resin and the laminae with a flexible epoxy resin modified from the conventional resin to avoid the interlaminar delamination. The impact energy absorption ratio greatly depended on the matrix resin placed at the impact face. The energy absorption was almost constant if the conventional resin was placed at the impact surface layer, while it increased exponentially with the increasing fraction of the flexible resin if the flexible resin was placed at the impact face. The impact energy was absorbed by the damage development and propagation in the laminate with conventional resin laminae as the impacted face, while it was absorbed by both the recoverable deformation of the flexible resin and the damage propagation in the laminate with flexible resin laminae as the impacted face. 相似文献
13.
Development of accurate schemes is a technical issue related to calculation of electromagnetic fields. This study uses constrained interpolation profile (CIP) method to analyze electromagnetic fields created by line current. This is a novel method proposed by Yabe. Comparison of results obtained using finite difference time domain (FDTD) analysis and CIP analysis indicates that CIP analysis provides higher accuracy using identical discretization. In addition, given the same level of accuracy, CIP analysis requires less memory and less calculation time 相似文献
14.
Wakabayashi H. Ueki M. Narihiro M. Fukai T. Ikezawa N. Matsuda T. Yoshida K. Takeuchi K. Ochiai Y. Mogami T. Kunio T. 《Electron Devices, IEEE Transactions on》2002,49(1):89-95
Sub-50-nm CMOS devices are investigated using steep halo and shallow source/drain extensions. By using a high-ramp-rate spike annealing (HRR-SA) process and high-dose halo, 45-nm CMOS devices are fabricated with drive currents of 650 and 300 μA/μm for an off current of less than 10 nA/μm at 1.2 V with Toxinv =2.5 nm. For an off current less than 300 nA/μm, 33-nm pMOSFETs have a high drive current of 400 uA/μm. Short-channel effect and reverse short-channel effect are suppressed simultaneously by using the HRR-SA process to activate a source/drain extension (SDE) after forming a deep source/drain (S/D). This process sequence is defined as a reverse-order S/D (R-S/D) formation. By using this formation, 24-nm nMOSFETs are achieved with a high drive current of 800 μA/μm for an off current of less than 300 μA/μm at 1.2 V. This high drive current might be a result of a steep halo structure reducing the spreading resistance of source/drain extensions 相似文献
15.
T Yoshida M Satoh Y Nakagaito H Kuno M Takeuchi 《Canadian Metallurgical Quarterly》1993,76(1):147-150
The effects of various cytokines on survival and differentiation of an astrocyte progenitor cell line (AP-16) were examined. Epidermal growth factor (EGF) deprivation caused death of AP-16 cells by apoptosis. Transforming growth factor-alpha (TGF-alpha) and basic fibroblast growth factor (bFGF) prevented the apoptosis occurring in the absence of EGF. Leukemia inhibitory factor (LIF) and ciliary neurotrophic factor (CNTF) induced glial fibrillary acidic protein (GFAP) and decreased A2B5 antigen in AP-16 cells, indicating that these cytokines induced AP-16 cells to differentiate into astrocytes. 相似文献
16.
A simple, accurate and universal relationship between MOSFET drain current in saturation, effective channel length, and gate drive has been found. It can be explained by a simple analytical model, whose validity is supported by numerical simulation. The model shows that the length of a velocity saturated region is a crucial parameter for describing MOSFET performance, particularly for short channel devices. The shrinkage of the length deteriorates the merit of channel length scaling 相似文献
17.
18.
Highly transparent cellulose hydrogels with physical crosslinkage were prepared from nonaqueous organic cellulose solutions and viscose by coagulating and regenerating cellulose in an aqueous solution containing a water‐miscible organic solvent. Nonaqueous organic cellulose solutions used were LiCl/dimethylacetamide, paraformaldehyde/dimethyl sulfoxide, and triethylammonium chloride/dimethyl sulfoxide. Preparation conditions and physical properties of the transparent cellulose hydrogels were studied. The transparency of the cellulose hydrogels depended on the composition of the aqueous solution containing the organic solvent. Furthermore, transparent cellulose hydrogels from viscose showed high tensile strength. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3020–3025, 2003 相似文献
19.
S Kondo BP Barna T Morimura J Takeuchi J Yuan A Akbasak GH Barnett 《Canadian Metallurgical Quarterly》1995,55(24):6166-6171
Increasing the susceptibility of tumor cells to apoptotic cell death following chemotherapy is of importance to the outcome of cancer treatment. Although the tumor suppressor gene p53 is required for efficient induction of apoptosis by chemotherapeutic agents, it is not the only apoptosis mediator gene. The molecular mechanisms mediating apoptosis following chemotherapy via p53-dependent or p53-independent pathways remain unclear. We show here that cis-diamminedichloroplatinum (cisplatin) induces the expression of interleukin-1 beta-converting enzyme (ICE), a mammalian homologue of the Caenorhabditis elegans cell death gene ced-3, in murine and human malignant glioma cells during apoptosis regardless of their p53 status. Furthermore, overexpression of the murine ICE gene induces apoptosis in these tumor cells. The apoptosis induced by cisplatin treatment or murine ICE overexpression can be suppressed by the tetrapeptide ICE inhibitor Ac-YVAD-CMK or the apoptosis inhibitors bcl-2 or bcl-2-related bcl-XL gene. These findings suggest that ICE may mediate apoptosis induced by chemotherapy, and its induction could represent a novel approach for the effective treatment of malignant glioma. 相似文献
20.
In recent years, ultra-precision micromachining technology has been used in a variety of fields such as optical instruments, electronic devices, medical equipments, etc. At present, it is essential to meet the requirement of producing various shapes, one of which is a structure with a high aspect ratio. Such structures are applied, for example, to a shaft of micro robot, a long part of microactuator and micromachine, a microneedle for syringe, etc. However, due to its fragile nature, it is extremely difficult to fabricate the structure with a high aspect ratio since it is easily damaged during cutting. It is intended to produce micro towers with high aspect ratios by applying the ultra-precision milling technology using a single crystal diamond cutting tool. The method enables accurate creation of a variety of microstructures with high aspect ratios. In addition, the study also proposes a new machining method to create microneedle arrays, avoiding the contact of cutting edge with already machined parts again. As a result, it is concluded that the proposed method has the potential of producing a variety of microstructures with high aspect ratios. 相似文献