全文获取类型
收费全文 | 11337篇 |
免费 | 293篇 |
国内免费 | 39篇 |
专业分类
化学 | 5782篇 |
晶体学 | 162篇 |
力学 | 267篇 |
数学 | 733篇 |
物理学 | 3109篇 |
无线电 | 1616篇 |
出版年
2023年 | 127篇 |
2022年 | 235篇 |
2021年 | 251篇 |
2020年 | 283篇 |
2019年 | 312篇 |
2018年 | 292篇 |
2017年 | 295篇 |
2016年 | 385篇 |
2015年 | 233篇 |
2014年 | 453篇 |
2013年 | 879篇 |
2012年 | 598篇 |
2011年 | 685篇 |
2010年 | 441篇 |
2009年 | 441篇 |
2008年 | 495篇 |
2007年 | 483篇 |
2006年 | 372篇 |
2005年 | 324篇 |
2004年 | 259篇 |
2003年 | 199篇 |
2002年 | 201篇 |
2001年 | 139篇 |
2000年 | 145篇 |
1999年 | 103篇 |
1998年 | 76篇 |
1997年 | 83篇 |
1996年 | 124篇 |
1995年 | 131篇 |
1994年 | 132篇 |
1993年 | 120篇 |
1992年 | 143篇 |
1991年 | 112篇 |
1990年 | 97篇 |
1989年 | 104篇 |
1988年 | 104篇 |
1987年 | 101篇 |
1986年 | 80篇 |
1985年 | 124篇 |
1984年 | 136篇 |
1983年 | 103篇 |
1982年 | 108篇 |
1981年 | 106篇 |
1980年 | 119篇 |
1979年 | 96篇 |
1978年 | 103篇 |
1977年 | 88篇 |
1976年 | 63篇 |
1975年 | 66篇 |
1974年 | 81篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
41.
42.
S. C. Joshi M. P. Singh V. P. Pandey B. S. Rajput 《International Journal of Theoretical Physics》2002,41(6):1107-1125
In four-dimensional N = 4 supersymmetric gauge theory, we obtain an exact metric on the moduli space of quantum vacua and analyze the spectra of BPS states in weak as well as in strong coupling regions. Identifying the hypermultiplet of the dyonic state as a string stretched between D3-brane probe and a 7-brane, we demonstrate that the two hypermultiplets, which become massless at two singularities in supersymmetric theory, correspond to open strings beginning on the D3-brane and ending on the respective 7-brane. 相似文献
43.
Electron emission from insulator-semiconductor interface in ZnS:Mn ac thin film electroluminescent (ACTFEL) display devices was investigated by studying the current and field waveforms. A new technique for measuring the interface electron energy distribution at insulator-semiconductor interfaces was developed. The technique involves the measurement of tunnel current transients and can be used to study the interface electron energy distribution between any insulator-semiconductor pair with which an ac thin film test structure can be fabricated. It was applied to a ZnS:Mn display device at two temperatures of 10 K and 300 K and to a metal interface device structure 相似文献
44.
Barada S. Singh H. 《IEEE transactions on systems, man and cybernetics. Part C, Applications and reviews》1998,28(3):371-391
The paper describes an approach to generating optimal adaptive fuzzy neural models from I/O data. This approach combines structure and parameter identification of Takagi-Sugeno-Kang (TSK) fuzzy models. We propose to achieve structure determination via a combination of modified mountain clustering (MMC) algorithm, recursive least squares estimation (RLSE), and group method of data handling (GMDH). Parameter adjustment is achieved by training the initial TSK model using the algorithm of an adaptive network based fuzzy inference system (ANFIS), which employs backpropagation (BP) and RLSE. Further, a procedure for generating locally optimal model structures is suggested. The structure optimization procedure is composed of two phases: 1) locally optimal rule premise variables subsets (LOPVS) are identified using MMC, GMDH, and a search tree (ST); and 2) locally optimal numbers of model rules (LONOR) are determined using MMC/RLSE along with parallel simulation mean square error (PSMSE) as a performance index. The effectiveness of the proposed approach is verified by a variety of simulation examples. The examples include modeling of a nonlinear dynamical process from I/O data and modeling nonlinear components of dynamical plants, followed by tracking control based on a model reference adaptive scheme (MRAC). Simulation results show that this approach is fast and accurate and leads to several optimal models 相似文献
45.
Singh R. Fakhruddin M. Poole K.F. 《Semiconductor Manufacturing, IEEE Transactions on》2003,16(2):96-101
In this paper, we have described the importance of single-wafer processing (SWP) in semiconductor manufacturing. As compared to batch processing, reduced cycle time, better control of surface and interface properties, and reduced defect densities are some of the attractive features of SWP. We have provided the example of new SWP tools that have the answers to address virtually all process integration issues in dealing with new materials as well as conventional materials in ultra small dimensions. Driven by reduced I/O pitches, and emergence of system-on-chip, system-in-package or system-on-package as the driver of semiconductor growth, SWP tools have started to play an important role in the surface cleaning in IC assembly and packaging. Global acceptance of SWP in manufacturing can address the supply chain problem of the semiconductor industry. 相似文献
46.
R.A. Gunasekaran M. Agarwal A. Singh P. Dubasi P. Coane K. Varahramyan 《Optics and Lasers in Engineering》2005,43(6):1086
A novel small fluid controlled optical lens system that is capable of displaying dynamic variation of its focal length and field-of-view (FOV) is designed and fabricated. In this active lens system, appropriate volume of the optical fluid can be pumped into or out of the lens chamber to provide double-convex (DCX) or double-concave (DCV) lens effect. Simple optical imaging experiments were performed using different sets of glass lenses with fixed focal lengths to determine the optimum lens configuration required for designing a dynamic optical lens system. The experimental results obtained from the glass lenses demonstrate that a combination of a single DCX lens with three DCV lenses provides a wider FOV. The flexible membranes for fluid controlled lenses were fabricated using polydimethylsiloxane polymer material, which has good optical transparency and elasticity. A simple fluid injection system is used to vary the radius of curvature of the lenses, and thereby to change the focal length. A dynamic optical lens system with a combination of one DCX and multiple variable focal length DCV lenses as designed here can image an object with a wide range of focal length and FOV. With this fluid controlled optical system, the FOV and focal length could be continuously varied and a maximum FOV of 118.3° could be achieved. The smallest f-number (f/#) for this fluid controlled single lens system was found to be 1.3, which corresponds to the numerical aperture value of 0.35. 相似文献
47.
48.
Conductivity, viscosity, turbidity, and NMR measurements were performed over most of the mole fraction range for sodium deoxycholate (SDC) with hexadecyltrimethylammonium bromide (HTAB), hexadecylpyridinium bromide (HPyBr), and hexadecylpyridinium chloride (HPyCl). All studies demonstrate that the mixed-micelle formation is more favorable in SDC plus HTAB rather than SDC plus HPyBr or SDC plus HPyCl mixtures. The results showed that the bulky pyridinium head groups of HPyBr or HPyCl create steric incompatibility with rigid SDC monomers in the mixed state. 相似文献
49.
E. A. Davis A. Singh S. F. J. Cox S. R. Kreitzman T. L. Estle B. Hitti R. L. Lichti R. DuVarney 《Hyperfine Interactions》1994,86(1):705-710
Studies of the muonium fractions in the amorphous oxide a-SiO have been carried out by RF resonance at TRIUMF, Canada and LF repolarization techniques at RAL, U.K. The resonance measurements confirm the presence of the interstitial Mu centre in this intermediate oxide of silicon. Analysis of the data gathered at RAL, using a recently-developed fitting technique, reveals that the Mu* state is present here as well, but with lower relative fractions than in a-Si. However, as in the latter material, but in contrast to c-Si, this bond-centre species appears to be stable up to room temperature. 相似文献
50.
M. Singh 《Journal of the Iranian Chemical Society》2006,3(4):334-339
Using upper consolute temperatures (UCT) and corresponding consolute compositions (CC) of water-phenol systems with each of 0.1 mol kg?1 salts and acids, 1.0% polyethylene glycol 200, 0.01 mol kg?1 surfactant and aromatic compounds, we obtained 0.01 mol kg?1 CaF2 and CrCl3 compositions. Focusing on UCT and CC, the role of valence electrons and shell number, basicity, hydrophilic, hydrophobic and π conjugated electrons of corresponding additives are reported. The surfactants and π conjugation electrons are noted to decrease the UCT in a constant ratio that depicts the state and inherent strength of ionic and molecular-water interactions. The data are useful in the investigation of cloud points of immiscible solutions based on the Hofmeister series. 相似文献