全文获取类型
收费全文 | 53673篇 |
免费 | 13652篇 |
国内免费 | 3067篇 |
专业分类
化学 | 47768篇 |
晶体学 | 463篇 |
力学 | 1176篇 |
综合类 | 94篇 |
数学 | 3315篇 |
物理学 | 5974篇 |
无线电 | 11602篇 |
出版年
2024年 | 54篇 |
2023年 | 338篇 |
2022年 | 452篇 |
2021年 | 714篇 |
2020年 | 2181篇 |
2019年 | 3538篇 |
2018年 | 1837篇 |
2017年 | 1427篇 |
2016年 | 4441篇 |
2015年 | 4627篇 |
2014年 | 4727篇 |
2013年 | 5437篇 |
2012年 | 4504篇 |
2011年 | 3659篇 |
2010年 | 4001篇 |
2009年 | 4023篇 |
2008年 | 3521篇 |
2007年 | 2778篇 |
2006年 | 2345篇 |
2005年 | 2471篇 |
2004年 | 2147篇 |
2003年 | 2002篇 |
2002年 | 2821篇 |
2001年 | 2028篇 |
2000年 | 1716篇 |
1999年 | 708篇 |
1998年 | 349篇 |
1997年 | 249篇 |
1996年 | 204篇 |
1995年 | 180篇 |
1994年 | 142篇 |
1993年 | 113篇 |
1992年 | 90篇 |
1991年 | 95篇 |
1990年 | 64篇 |
1989年 | 51篇 |
1988年 | 40篇 |
1987年 | 39篇 |
1986年 | 22篇 |
1985年 | 31篇 |
1984年 | 24篇 |
1983年 | 25篇 |
1982年 | 14篇 |
1981年 | 24篇 |
1980年 | 17篇 |
1979年 | 17篇 |
1978年 | 14篇 |
1977年 | 14篇 |
1976年 | 14篇 |
1974年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
241.
242.
This paper proposes a new LDMOSFET structure with a trenched sinker for high‐power RF amplifiers. Using a low‐temperature, deep‐trench technology, we succeeded in drastically shrinking the sinker area to one‐third the size of the conventional diffusion‐type structure. The RF performance of the proposed device with a channel width of 5 mm showed a small signal gain of 16.5 dB and a maximum peak power of 32 dBm with a power‐added efficiency of 25% at 2 GHz. Furthermore, the trench sinker, which was applied to the guard ring to suppress coupling between inductors, showed an excellent blocking performance below ?40 dB at a frequency of up to 20 GHz. These results confirm that the proposed trenched sinker should be an effective technology both as a compact sinker for RF power devices and as a guard ring against coupling. 相似文献
243.
244.
245.
We propose an efficient scheme for camera motion characterization in MPEG‐compressed video. The proposed scheme detects six types of basic camera motions through threshold‐based qualitative interpretation, in which fixed thresholds are applied to motion model parameters estimated from MPEG motion vectors (MVs). The efficiency and robustness of the scheme are validated by the experiment with real compressed video sequences. 相似文献
246.
The 193 nm photochemistry of (aminoethylaminomethyl)phenethylsiloxane (PEDA) self‐assembled monolayers (SAMs) under ambient conditions is described. The primary photodegradation pathways at low exposure doses (< 100 mJ cm–2) are benzylic C–N bond cleavage (ca. 68 %), with oxidation of the benzyl C to the aldehyde, and Si–C bond cleavage (ca. 32 %). Amine‐containing photoproducts released from the SAM during exposure remain physisorbed on the surface, where they undergo secondary photolysis leading to their complete degradation and removal after ca. 1200 mJ cm–2. NaCl(aq) post‐exposure rinsing removes the physisorbed materials, showing that degradation of the original PEDA species (leaving Si–OH) is substantially complete after ca. 450 mJ cm–2. Consequently, patterned, rinsed PEDA SAMs function as efficient templates for fabrication of high‐resolution, negative‐tone, electroless metal and DNA features with good selectivity at low dose (i.e., ca. 400 mJ cm–2) via materials grafting to the intact amines remaining in the unirradiated PEDA SAM regions. 相似文献
247.
248.
非线性编辑实验室的构建与实验教学 总被引:2,自引:2,他引:0
以计算机为操作平台的非线性编辑系统广泛应用于电视节目的制作 ,学校相关专业开设非线性编辑课程也需要配置非线性编辑系统作为学生实验用机。主要介绍一种学生实验用非线性编辑系统及实验室的配置方案以及该非线性编辑系统在实验教学中的性能特征。 相似文献
249.
In this paper, we report on a novel family of monodisperse thermo‐sensitive core–shell hydrogel microspheres that is featured with high monodispersity and positively thermo‐responsive volume phase transition characteristics with tunable swelling kinetics, i.e., the particle swelling is induced by an increase rather than a decrease in temperature. The microspheres were fabricated in a three‐step process. In the first step, monodisperse poly(acrylamide‐co‐styrene) seeds were prepared by emulsifier‐free emulsion polymerization. In the second step, poly(acrylamide) or poly[acrylamide‐co‐(butyl methacrylate)] shells were fabricated on the microsphere seeds by free radical polymerization. In the third step, the core–shell microspheres with poly‐ (acrylamide)/poly(acrylic acid) based interpenetrating polymer network (IPN) shells were finished by a method of sequential IPN synthesis. The proposed monodisperse core–shell microspheres provide a new mode of the phase transition behavior for thermo‐sensitive “smart” or “intelligent” monodisperse micro‐actuators that is highly attractive for targeting drug delivery systems, chemical separations, sensors, and so on. 相似文献
250.
New polyaniline (PANI) asymmetric membranes were fabricated using a phase‐inversion technique with hexane as the coagulation bath. These membranes exhibit a dense structure with macrovoids distributed asymmetrically throughout the cross‐section. A stress–strain study demonstrated that the Young's modulus (1.421 GPa) and strain at break (7.6 %) of the new PANI asymmetric membranes prepared from hexane are approximately 12 and 4 times higher, respectively, than the values reported previously for the PANI integrally skinned asymmetric membranes (ISAMs) (123 MPa Young's modulus and 1.8 % strain at break). Furthermore, monolithic electrochemical actuators based on a single PANI asymmetric membrane were constructed, and a bending movement of up to 20 Hz was experimentally recorded in a hydrochloric acid aqueous solution. A lifetime of over 329 500 cycles was determined for these actuators at a ± 2° angular displacement (5 Hz). The lifetime is limited by a bending fatigue that creates a transversal crack on the PANI membrane at the air–water interface. Control over the actuator movement is also manifested by the linear dependences of the bending angle on the charge and of the angular velocity on the current. These relationships are independent of both the kind of applied electric signal and the frequency used. 相似文献