全文获取类型
收费全文 | 5033篇 |
免费 | 207篇 |
国内免费 | 33篇 |
专业分类
化学 | 3597篇 |
晶体学 | 17篇 |
力学 | 123篇 |
数学 | 865篇 |
物理学 | 671篇 |
出版年
2023年 | 41篇 |
2022年 | 52篇 |
2021年 | 91篇 |
2020年 | 116篇 |
2019年 | 110篇 |
2018年 | 68篇 |
2017年 | 55篇 |
2016年 | 154篇 |
2015年 | 139篇 |
2014年 | 177篇 |
2013年 | 277篇 |
2012年 | 312篇 |
2011年 | 358篇 |
2010年 | 252篇 |
2009年 | 199篇 |
2008年 | 314篇 |
2007年 | 314篇 |
2006年 | 301篇 |
2005年 | 300篇 |
2004年 | 236篇 |
2003年 | 207篇 |
2002年 | 212篇 |
2001年 | 82篇 |
2000年 | 69篇 |
1999年 | 70篇 |
1998年 | 59篇 |
1997年 | 64篇 |
1996年 | 69篇 |
1995年 | 44篇 |
1994年 | 38篇 |
1993年 | 23篇 |
1992年 | 19篇 |
1991年 | 31篇 |
1990年 | 19篇 |
1989年 | 30篇 |
1988年 | 18篇 |
1986年 | 19篇 |
1985年 | 28篇 |
1984年 | 30篇 |
1983年 | 27篇 |
1982年 | 33篇 |
1981年 | 23篇 |
1980年 | 25篇 |
1979年 | 18篇 |
1978年 | 33篇 |
1977年 | 20篇 |
1976年 | 15篇 |
1975年 | 12篇 |
1974年 | 18篇 |
1973年 | 10篇 |
排序方式: 共有5273条查询结果,搜索用时 15 毫秒
61.
Kristiane M. Van Lierde Sofie Claeys Marc De Bodt Paul Van Cauwenberge 《Journal of voice》2004,18(1):97-106
A relatively new management strategy for the treatment of voice disorders is the use of laryngeal (LB) and velopharyngeal biofeedback (VB). The main purpose of the present pilot study is to document the outcome of vocal and velopharyngeal performances after a well-defined LB and VB treatment. Four subjects were studied pretreatment (1 week before LB or VB treatment) and posttreatment (1 week after the LB or VB treatment). To measure and compare the effect of LB and VB, objective and subjective assessment techniques were used. Perceptual voice assessment included a perceptual rating of the voice using the GRBAS scale. Furthermore, the vocal quality in this population is modeled by means of the Dysphonia Severity Index. For the objective assessment of nasal resonance, the Nasometer and the Glatzel test were used. A perceptual evaluation of speech, the Gutzmann test, and the tests from Bzoch were used as subjective assessment techniques. Both patients selected for LB and VB treatment showed improvement of their performances. The resulting improvement, as measured by means of an objective approach, is in agreement with the perceived (auditory) improvement of voice and resonance. The use of LB and VB treatment in patients, especially in some subjects who are not responding to traditional voice or velopharyngeal therapy, must be encouraged. 相似文献
62.
Wijnand Hoitinga Roel de Groot Marcel Kwakkel Marc Gerritsma 《Journal of computational physics》2008,227(4):2411-2429
This paper describes an equivalent but improved least-squares formulation for the numerical approximation of the solution of partial differential equations. Instead of using variational analysis to impose the conditions for minimizing the residual, the residuals are minimized directly, thus leading to a method we will denote by Direct Minimization (DM). DM circumvents setting up the normal equations which consists of matrix–matrix multiplications. Matrix–matrix multiplications are expensive, may lead to loss of accuracy and destroy the sparsity pattern present in the original system. The condition number of the DM formulation is the square root of the condition number which would be obtained if variational analysis was employed. An element-by-element procedure will be presented which allows for parallelization of DM. A computational comparison between DM and the conventional least-squares formulation based on variational analysis will be presented. 相似文献
63.
Ultraviolet and infrared conical emissions were observed during the filamentation in air of powerful femtosecond laser pulses produced by a portable terawatt laser system. The broadband spectrum was measured from 200 nm up to 14 microm and covered the complete optical transmission window of the atmosphere. The angularly resolved spectrum showed some X-wave structure across the frequency range analyzed. However, we demonstrated that the strong conical emission observed in the mid- and far-infrared is mainly owing to the four-wave mixing between the pump pulse and its blueshifted conical emission. 相似文献
64.
Unique continuation results are proved for metrics with prescribed Ricci curvature in the setting of bounded metrics on compact manifolds with boundary, and in the setting of complete conformally compact metrics on such manifolds. Related to this issue, an isometry extension property is proved: continuous groups of isometries at conformal infinity extend into the bulk of any complete conformally compact Einstein metric. Relations of this property with the invariance of the Gauss–Codazzi constraint equations under deformations are also discussed. 相似文献
65.
Modeling urban street patterns 总被引:3,自引:0,他引:3
Urban street patterns form planar networks whose empirical properties cannot be accounted for by simple models such as regular grids or Voronoi tesselations. Striking statistical regularities across different cities have been recently empirically found, suggesting that a general and detail-independent mechanism may be in action. We propose a simple model based on a local optimization process combined with ideas previously proposed in studies of leaf pattern formation. The statistical properties of this model are in good agreement with the observed empirical patterns. Our results thus suggest that in the absence of a global design strategy, the evolution of many different transportation networks indeed follows a simple universal mechanism. 相似文献
66.
There has been growing interest in the possibility of testing more precisely the assumption of statistical isotropy of primordial density perturbations. If it is to be tested with galaxy surveys at distance scales < or = 10 Mpc, then nonlinear evolution of anisotropic power must be understood. To this end, we calculate the angular dependence of the power spectrum to third order in perturbation theory for a primordial power spectrum with a quadrupole dependence on the wave vector direction. Our results suggest that primordial power anisotropies will be suppressed by < or = 7% in the quasilinear regime. We also show that the skewness in the statistically anisotropic theory differs by no more than 1% from that in the isotropic theory. 相似文献
67.
We present new hairy black hole solutions of SU(N) Einstein-Yang-Mills (EYM) theory in asymptotically anti-de Sitter (AdS) space. These black holes are described by N+1 independent parameters and have N-1 independent gauge field degrees of freedom. Solutions in which all gauge field functions have no zeros exist for all N, and for a sufficiently large (and negative) cosmological constant. At least some of these solutions are shown to be stable under classical, linear, spherically symmetric perturbations. Therefore there is no upper bound on the amount of stable gauge field hair with which a black hole in AdS can be endowed. 相似文献
68.
Using atomic force microscopy with nonconventional carbon tips, the pinning of a liquid contact line on individual nanometric defects was studied. This mechanism is responsible for the occurrence of the contact angle hysteresis. The presence of weak defects which do not contribute to the hysteresis is evidenced for the first time. The dissipated energy associated with strong defects is also measured down to values in the range of kT, which correspond to defect sizes in the order of 1 nm. 相似文献
69.
Vigreux C Barthélémy E Bastard L Broquin JE Barillot M Ménard S Parent G Pradel A 《Optics letters》2011,36(15):2922-2924
The feasibility of all-telluride integrated optics devices based on waveguides presenting a single-mode behavior in the spectral range (10-20 μm) is demonstrated. These waveguides are constituted of a several micrometer thick Te(82)Ge(18) film deposited onto a Te(75)Ge(15)Ga(10) bulk glass substrate by thermal coevaporation and further etched by reactive ion etching under the CHF(3)/O(2)/Ar atmosphere. The obtained structures were proven to behave as channel waveguides with a good single-mode transmission over the whole spectral range. These results allowed validating our technological solution for the fabrication of integrated optics modal filters for spatial interferometry. 相似文献
70.
Nanotextured multicrystalline Al‐BSF solar cells reaching 18% conversion efficiency using industrially viable solar cell processes 下载免费PDF全文
Bishal Kafle Abdul Mannan Timo Freund Laurent Clochard Edward Duffy Marc Hofmann Jochen Rentsch Ralf Preu 《固体物理学:研究快报》2015,9(8):448-452
We report recent achievements in adapting industrially used solar cell processes on nanotextured surfaces. Nanostructures were etched into c‐Si surfaces by dry exothermic plasma‐less reaction of F species with Si in atmospheric pressure conditions and then modified using a short post‐etching process. Nanotextured multicrystalline wafers are used to prepare Al‐BSF solar cells using industrially feasible solar cell proc‐ essing steps. In comparison to the reference acidic textured solar cells, the nanostructured cells showed gain in short circuit current (Jsc) of up to 0.8 mA/cm2 and absolute gain in conversion efficiency of up to 0.3%. The best nanotextured solar cell was independently certified to reach the conversion efficiency of 18.0%. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) 相似文献