全文获取类型
收费全文 | 299816篇 |
免费 | 2380篇 |
国内免费 | 683篇 |
专业分类
化学 | 142697篇 |
晶体学 | 4167篇 |
力学 | 11926篇 |
综合类 | 9篇 |
数学 | 29510篇 |
物理学 | 82937篇 |
无线电 | 31633篇 |
出版年
2019年 | 2519篇 |
2018年 | 3388篇 |
2017年 | 3349篇 |
2016年 | 4823篇 |
2015年 | 2816篇 |
2014年 | 4663篇 |
2013年 | 11298篇 |
2012年 | 8495篇 |
2011年 | 10425篇 |
2010年 | 7634篇 |
2009年 | 7804篇 |
2008年 | 10517篇 |
2007年 | 11033篇 |
2006年 | 10282篇 |
2005年 | 9473篇 |
2004年 | 8784篇 |
2003年 | 7977篇 |
2002年 | 7907篇 |
2001年 | 8515篇 |
2000年 | 6874篇 |
1999年 | 5427篇 |
1998年 | 4961篇 |
1997年 | 4925篇 |
1996年 | 4534篇 |
1995年 | 4251篇 |
1994年 | 4350篇 |
1993年 | 4036篇 |
1992年 | 4457篇 |
1991年 | 4528篇 |
1990年 | 4399篇 |
1989年 | 4166篇 |
1988年 | 4198篇 |
1987年 | 3829篇 |
1986年 | 3629篇 |
1985年 | 4699篇 |
1984年 | 4990篇 |
1983年 | 4177篇 |
1982年 | 4266篇 |
1981年 | 4211篇 |
1980年 | 4156篇 |
1979年 | 4088篇 |
1978年 | 4402篇 |
1977年 | 4322篇 |
1976年 | 4383篇 |
1975年 | 4025篇 |
1974年 | 4103篇 |
1973年 | 4254篇 |
1972年 | 3014篇 |
1971年 | 2507篇 |
1970年 | 2312篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
In recent years there has emerged significant interest in low pressure radio frequency (rf) glow discharges which are used widely particulary in IC fabrication. Various parameters of the rf glow discharge have been found to be useful for its electrical characterization; however, there is no uniformity and agreement. Extensive experimental investigations on various discharge systems have shown, that the self-bias on the rf driven electrode, the complex conductivity and the breakdown characteristic are preferable parameters of rf discharges. Advantageously the self-bias and the complex conductivity should be presented in dependence on the pressure and the applied rf voltage. The discharge current cannot be measured quite accurately due to currents via leaky capacitors and the deviations from a sinusoidal form of the current due to nonlinearities. 相似文献
122.
Nagle H.T. Fritzemeier R.R. Van Well J.E. McNamer M.G. 《Industrial Electronics, IEEE Transactions on》1989,36(2):151-163
As the level of microprocessor complexity increases to several hundred thousand transistors for a single-chip machine, it is becoming very difficult to test commercially available designs to the level of fault coverage desired by some customers. In order to achieve near 100-percent coverage of single stuck-at faults, future microprocessors must be designed with special testing features (designed for testability). The authors describe the testing problem for microprocessors, including the various methods of generating test sets and their application by the user. A survey of the testability features of some of today's commercially available microprocessors is presented. Suggestions for testability features for future-generation microprocessors are also discussed 相似文献
123.
124.
V. I. Naryshkin G. M. Strelkov A. M. Ryazantsev 《Journal of Communications Technology and Electronics》2008,53(7):782-787
Deformation and attenuation of an ultrawideband radio pulse propagating along a single-wire line are analyzed as functions of the pulse initial duration. Variations in the longitudinal and transverse components of the pulse electric field with the distance from the line are determined. Features of the spatial distribution of the energy carried by the pulse near the line are revealed. 相似文献
125.
Russomanno D.J. de Jongh Curry A.L. Atanasova G.S. Hunt L.C. Goodwin J.C. 《IEEE transactions on information technology in biomedicine》2008,12(1):76-86
DefibViz is a software application developed for defibrillation simulation and visualization. It exploits both surface techniques and methods for the interactive exploration of volumetric datasets for the analysis of transthoracic defibrillation simulation results. DefibViz has a graphical user interface for the specification of the shape, size, position, and applied voltage of a defibrillator's electrodes. An option is provided for using 3D slice plane widgets, which operate on the volumetric datasets, such that the distribution of the voltage gradient induced by an electric shock can be visually inspected in various tissues throughout the myocardium and torso. One goal of DefibViz is to enhance understanding of how electrode parameters relate to the change of the voltage gradient distribution throughout the heart, which may help lead to optimal defibrillator design. DefibViz is significant, in that, it is built by using an open-source graphics and visualization framework providing a platform for subsequent modifiability and extensibility. Moreover, it integrates simulation and visualization techniques, which previously required the running of several independent software executables, into an enhanced, seamless, and comprehensive software application. 相似文献
126.
The article proposes an analytical method for determining occupancy distribution and blocking probability in systems which are offered overflow traffic composed of multi-service traffic streams. The described analytical model enables determination of parameters of traffic overflowed from primary groups in hierarchically constructed telecommunication networks. The proposed method is based on an appropriate modification of the Kaufman-Roberts recursion for the full-availability group with multi-rate traffic and uses the modified Fredericks & Hayward’s approximation. Additionally, an approximate method for dimensioning systems with multi-service overflow traffic is also presented. The analytical results of the blocking probability and the results obtained in the dimensioning processes calculated using the presented methodology are compared with the data obtained from the system simulation process. 相似文献
127.
Franck D'Agosto Marie‐Thrse Charreyre Christian Pichot Robert G. Gilbert 《Journal of polymer science. Part A, Polymer chemistry》2003,41(9):1188-1195
A method is described for synthesizing latex particles with anchored hairs by the grafting of hydrophilic chains, synthesized by reversible addition–fragmentation chain transfer, onto functionalized latex particles. These have the potential to bind biologically active species. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1188–1195, 2003 相似文献
128.
Salimgareeva V. N. Polevoi R. M. Kolesov S. V. Ostakhov S. S. Ponomareva V. A. Leplyanin G. V. 《Russian Journal of Applied Chemistry》2003,76(5):804-808
The luminescence and scintillation properties of poly(methyl methacrylate) containing 1,1,3-trimethyl-3-phenylindan were studied. 相似文献
129.
María G. Armentano Ricardo G. Durn 《Numerical Methods for Partial Differential Equations》2003,19(5):653-664
In this article we analyze the effect of mass‐lumping in the linear triangular finite element approximation of second‐order elliptic eigenvalue problems. We prove that the eigenvalue obtained by using mass‐lumping is always below the one obtained with exact integration. For singular eigenfunctions, as those arising in non convex polygons, we prove that the eigenvalue obtained with mass‐lumping is above the exact eigenvalue when the mesh size is small enough. So, we conclude that the use of mass‐lumping is convenient in the singular case. When the eigenfunction is smooth several numerical experiments suggest that the eigenvalue computed with mass‐lumping is below the exact one if the mesh is not too coarse. © 2003 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 19: 653–664, 2003 相似文献
130.
The sub-millisecond protonation dynamics of the chromophore in S65T mutant form of the green fluorescent protein (GFP) was
tracked after a rapid pH jump following laser-induced proton release from the caged photolabile compoundo-nitrobenzaldehyde. Following a jump in pH from 8 to 5 (which is achieved within 2 μs), the fluorescence of S65T GFP decreased
as a single exponential with a time constant of ∼90 μs. This decay is interpreted as the conversion of the deprotonated fluorescent
GFP chromophore to a protonated non-fluorescent species. The protonation kinetics showed dependence on the bulk viscosity
of the solvent, and therefore implicates bulk solvent-controlled protein dynamics in the protonation process. The protonation
is proposed to be a sequential process involving two steps: (a) proton transfer from solvent to the chromophore, and (b) internal
structural rearrangements to stabilize a protonated chromophore. The possible implications of these observations to protein
dynamics in general is discussed 相似文献