全文获取类型
收费全文 | 544篇 |
免费 | 39篇 |
国内免费 | 12篇 |
专业分类
化学 | 340篇 |
晶体学 | 6篇 |
力学 | 8篇 |
数学 | 18篇 |
物理学 | 127篇 |
无线电 | 96篇 |
出版年
2024年 | 3篇 |
2023年 | 12篇 |
2022年 | 53篇 |
2021年 | 72篇 |
2020年 | 47篇 |
2019年 | 40篇 |
2018年 | 32篇 |
2017年 | 21篇 |
2016年 | 41篇 |
2015年 | 18篇 |
2014年 | 38篇 |
2013年 | 37篇 |
2012年 | 24篇 |
2011年 | 25篇 |
2010年 | 18篇 |
2009年 | 11篇 |
2008年 | 11篇 |
2007年 | 9篇 |
2006年 | 4篇 |
2005年 | 5篇 |
2004年 | 8篇 |
2003年 | 2篇 |
2002年 | 5篇 |
2001年 | 3篇 |
2000年 | 6篇 |
1999年 | 3篇 |
1998年 | 1篇 |
1994年 | 5篇 |
1993年 | 4篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1970年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有595条查询结果,搜索用时 15 毫秒
1.
Wireless Networks - Wireless sensor network (WSN) consists of small sized devices containing different sensors to monitor physical, environmental and medical conditions during surveillance of... 相似文献
2.
Inam Ridha Ali Basiri Sudhakar Godeshala Md Zubair Ebne Rafique Deepanjan Ghosh Jason Williams Nikhilesh Chawla Jung Keun Lee Jacquelyn Kilbourne Yu Yao Kaushal Rege 《Advanced functional materials》2021,31(6):2007811
Poor strength, infection, leakage, long procedure times, and inflammation limit the efficacy of common tissue sealing devices in surgeries and trauma. Light-activated sealing is attractive for tissue sealing and repair, and can be facilitated by the generation of local heat following absorption of nonionizing laser energy by chromophores. Here, the inherent ability of biomaterials is exploited to absorb nonionizing, mid-infrared (midIR) light in order to engender rapid photothermal sealing and repair of soft tissue wounds. In this approach, the biomaterial simultaneously acts as a photothermal convertor as well as a biosealant, which dispenses the need for exogeneous light-absorbing nanoparticles or dyes. Biomechanical recovery, mathematical modeling, histopathology analyses, tissue strain mapping using digital imaging correlation, and visualization of the biosealant-tissue interface using hyperspectral imaging indicate superior performance of midIR sealing in live mice compared to conventional sutures and glue. The midIR-biosealant approach demonstrates rapid sealing of soft tissues, improves cosmesis, lowers potential for scarring, obviates safety concerns because of the nonionizing light used, and allows adoption of a wide diversity of biomaterials. Taken together, the studies demonstrate a novel advance both in biomaterials for surgical sealing along with the use of nonionizing midIR light, with high potential for clinical translation. 相似文献
3.
4.
Bakhtar Ullah Yuli Zhou Jingwen Chen Zongbi Bao Yiwen Yang Qiwei Yang Qilong Ren Zhiguo Zhang 《Tetrahedron letters》2019,60(4):348-351
Thiourea itself has been introduced as a mild and efficient organocatalyst for the oxidative α -cyanation of N-aryltetrahydroisoquinolines (THIQs) with trimethylsilyl cyanide (TMSCN), giving the corresponding products in good to excellent yields. Experimental investigations demonstrated that thiourea acts as a radical initiator by abstracting hydroxyl radical (OH) from tert-butyl hydroperoxide (TBHP) directly instead of non-covalent hydrogen bondings (H-bondings) activation. The use of thiourea as a radical initiator offers a new avenue for innovative chemical transformations in organocatalyzed radical chemistry. 相似文献
5.
Md Sharif Ullah Vladimir V. Zhivonitko Anatoliy Samoylenko Artem Zhyvolozhnyi Sirja Viitala Santeri Kankaanp Sanna Komulainen Leif Schrder Seppo J. Vainio Ville-Veikko Telkki 《Chemical science》2021,12(24):8311
Exosomes are a subset of secreted lipid envelope-encapsulated extracellular vesicles (EVs) of 50–150 nm diameter that can transfer cargo from donor to acceptor cells. In the current purification protocols of exosomes, many smaller and larger nanoparticles such as lipoproteins, exomers and microvesicles are typically co-isolated as well. Particle size distribution is one important characteristics of EV samples, as it reflects the cellular origin of EVs and the purity of the isolation. However, most of the physicochemical analytical methods today cannot illustrate the smallest exosomes and other small particles like the exomers. Here, we demonstrate that diffusion ordered spectroscopy (DOSY) nuclear magnetic resonance (NMR) method enables the determination of a very broad distribution of extracellular nanoparticles, ranging from 1 to 500 nm. The range covers sizes of all particles included in EV samples after isolation. The method is non-invasive, as it does not require any labelling or other chemical modification. We investigated EVs secreted from milk as well as embryonic kidney and renal carcinoma cells. Western blot analysis and immuno-electron microscopy confirmed expression of exosomal markers such as ALIX, TSG101, CD81, CD9, and CD63 in the EV samples. In addition to the larger particles observed by nanoparticle tracking analysis (NTA) in the range of 70–500 nm, the DOSY distributions include a significant number of smaller particles in the range of 10–70 nm, which are visible also in transmission electron microscopy images but invisible in NTA. Furthermore, we demonstrate that hyperpolarized chemical exchange saturation transfer (Hyper-CEST) with 129Xe NMR indicates also the existence of smaller and larger nanoparticles in the EV samples, providing also additional support for DOSY results. The method implies also that the Xe exchange is significantly faster in the EV pool than in the lipoprotein/exomer pool.Diffusion and xenon NMR based methods to determine a very broad range of sizes and sub-sets of extracellular vesicles. 相似文献
6.
Bose G Nguyen VT Ullah E Lahiri S Görls H Langer P 《The Journal of organic chemistry》2004,69(26):9128-9134
The Lewis acid mediated domino "[3+3]-cyclization-homo-Michael" reaction of 1,3-bissilyl enol ethers with 1,1-diacylcyclopropanes allows an efficient one-pot synthesis of functionalized salicylates containing a halogenated side chain. A great variety of substitution patterns could be realized by variation of the starting materials and of the Lewis acid. The mechanism of the domino process was studied. 相似文献
7.
A variational analysis of the spiked harmonic oscillator Hamiltonian –d
2/dr2 +r
2 +/r
5/2,>0, is reported. A trial function automatically satisfying both the Dirichlet boundary condition at the origin and the boundary condition at infinity is introduced. The results are excellent for a very large range of values of the coupling parameter, suggesting that the present variational function is appropriate for the treatment of the spiked oscillator in all its regimes (strong, moderate, and weak interactions). 相似文献
8.
Ali Raza Hala A. Hejazi Sami Ullah Khan M. Ijaz Khan Kamel Smida Iskander Tlili 《印度化学会志》2022,99(7):100568
In this investigation, a mixed convective nanoparticles fluid flow over an inclined plate is deliberated. The effects of slip boundary wall and magnetic field are also considered. The dimensionless governing system for the considered problem is attained by implementing recent definitions of fractional derivatives (FD). The generalized solution is obtained through the Laplace Transformation Scheme (LTS) for the momentum and thermal expressions. To improve the novelty and to demonstrate some more physical perception of the stated research work, some remarkable special cases of velocity distribution through CF and AB-fractional derivative concept are addressed, whose daily life implication is well known in the existing literature. Moreover, to evaluate the physical interest of the stated problem, the outcomes of the obtained system graphical illustrations are made by utilizing MATHEMATICA. As a result, we concluded that the aluminium oxide nanoparticles show more decaying behavior as compared to titanium oxide nanoparticles for temperature and velocity profile. Furthermore, both fields i.e., momentum and thermal distributions are increased with the help of rising estimations parameter. Current results report novel applications in enhancement of heat transfer, thermal engineering, chemical processes, engineering and electronics devices, solar systems, extrusion processes, fission reactions etc. 相似文献
9.
Kamel Guedri Tahmoor Bashir A. Abbasi Waseh Farooq Sami Ullah Khan M. Ijaz Khan Mohammed Jameel Ahmed M. Galal 《印度化学会志》2022,99(9):100614
The electroosmotic peristaltic flow of modified hybrid nanofluid in presence of entropy generation has been presented in this thermal model. The Hall impact and thermal radiation with help of nonlinear relations has also been used to modify the analysis. The assumed flow is considered due to a non-uniform trapped channel. The properties of modified hybrid nanofluid model are focused with interaction of three distinct types of nanoparticles namely copper (, silver () and aluminum oxide ( The mathematical modeling and significances of entropy generation and Bejan number are identified. With certain flow assumptions, the governing equations are attained for optimized peristaltic electroosmotic problem. Widely used assumptions of long wave length and low Reynolds number reduced the governing equations in ordinary differential equations. The ND solver is flowed for the solution process. The physical significant of results is observed by assigning the numerical values to parameters. 相似文献
10.
In the presence of selenium(IV) and molybdenum(VI) a new polarographic peak appears which corresponds to a hydrogen catalytic wave. By differential pulse polarography a single, sharp peak at about -1.1 V is obtained, allowing trace determination of selenium(IV) and molybdenum(VI) in the range 1x10(-6)-5.0x10(-9) M with a linear calibration and a detection limit of 1.5x10(-9) M. The optimum conditions are found to be 0.1 M KNO(3) and a pH of about 3.2 (Britton-Robinson buffer). There is no serious interference from some ions when present at 1.0-40 times that of molybdenum. At higher amounts of interfering ions the interference is eliminated by the addition of EDTA. 相似文献