全文获取类型
收费全文 | 3022篇 |
免费 | 103篇 |
国内免费 | 36篇 |
专业分类
化学 | 1713篇 |
晶体学 | 13篇 |
力学 | 52篇 |
数学 | 762篇 |
物理学 | 621篇 |
出版年
2023年 | 21篇 |
2022年 | 34篇 |
2021年 | 64篇 |
2020年 | 42篇 |
2019年 | 60篇 |
2018年 | 82篇 |
2017年 | 52篇 |
2016年 | 113篇 |
2015年 | 110篇 |
2014年 | 113篇 |
2013年 | 199篇 |
2012年 | 180篇 |
2011年 | 230篇 |
2010年 | 120篇 |
2009年 | 144篇 |
2008年 | 172篇 |
2007年 | 167篇 |
2006年 | 155篇 |
2005年 | 148篇 |
2004年 | 159篇 |
2003年 | 109篇 |
2002年 | 100篇 |
2001年 | 48篇 |
2000年 | 33篇 |
1999年 | 29篇 |
1998年 | 41篇 |
1997年 | 37篇 |
1996年 | 46篇 |
1995年 | 35篇 |
1994年 | 26篇 |
1993年 | 23篇 |
1992年 | 25篇 |
1991年 | 25篇 |
1990年 | 14篇 |
1989年 | 7篇 |
1988年 | 9篇 |
1986年 | 12篇 |
1985年 | 14篇 |
1984年 | 15篇 |
1983年 | 8篇 |
1982年 | 14篇 |
1981年 | 13篇 |
1980年 | 9篇 |
1979年 | 11篇 |
1978年 | 8篇 |
1977年 | 11篇 |
1976年 | 8篇 |
1975年 | 7篇 |
1971年 | 7篇 |
1930年 | 6篇 |
排序方式: 共有3161条查询结果,搜索用时 15 毫秒
101.
Boris Petrovichev Malcolm Gray David McClelland 《General Relativity and Gravitation》1998,30(7):1055-1074
We model the behaviour of single-bounce delay-line dual recycled Sagnac-based interferometer and compare its performance with that of single-bounce Michelson-based system. Geometric imperfections such as mirror tilt and curvature mismatch can strongly influence the performance of the Sagnac device due to the inherently smaller free spectral range (FSR) and higher order mode spacing. This leads to a greater number of higher order modes near, or within the signal band in the signal recycling cavity of the instrument. The important consequence of that is, in general, a greater sensitivity of a Sagnac system to nonideal parameters and imperfections of various kind affecting the performance of a real interferometer. A number of optical configurations have also been examined numerically to determine the best possible optical arrangement, in the presence of such geometric imperfections. We show that there is an optimum choice for the nominal radius of curvature of the end mirrors which results from balancing the loss due to mirror tilt against that due to curvature mismatch. 相似文献
102.
103.
The results of spectroscopic investigation of plane plasma discharge and sputtering processes in the triode system are presented. The forced electric discharge with currents of 1–4 A at an argon pressure of 1 mTorr was studied using the emission spectroscopy method. The spectra of plasma discharge were observed in the 200–1100 nm wavelength range. Two metal targets, gold and silver, were used for sputtering. It was found that a part of sputtered particles is ionized in plasma. The emission spectra of the ionized gold and silver species were observed as a function of target voltage while sputtering. It was shown that the number of ionized metal species depends on the energy of argon ions. 相似文献
104.
An experimentally realizable scheme of periodic sign-changing modulation of the scattering length is proposed for Bose-Einstein condensates similar to dispersion-management schemes in fiber optics. Because of controlling the scattering length via the Feshbach resonance, the scheme is named Feshbach-resonance management. The modulational-instability analysis of the quasiuniform condensate driven by this scheme leads to an analog of the Kronig-Penney model. The ensuing stable localized structures are found. These include breathers, which oscillate between the Thomas-Fermi and Gaussian configuration, or may be similar to the 2-soliton state of the nonlinear Schr?dinger equation, and a nearly static state ("odd soliton") with a nested dark soliton. An overall phase diagram for breathers is constructed, and full stability of the odd solitons is numerically established. 相似文献
105.
In 1910 E. Cartan constructed the canonical frame and found the most symmetric case for maximally nonholonomic rank 2 distributions in . We solve the analogous problems for rank 2 distributions in for arbitrary . Our method is a kind of symplectification of the problem and it is completely different from the Cartan method of equivalence. To cite this article: B. Doubrov, I. Zelenko, C. R. Acad. Sci. Paris, Ser. I 342 (2006). 相似文献
106.
Boris Martinac 《Applied magnetic resonance》2009,36(2-4):171-179
MscL, the bacterial mechanosensitive (MS) channel of large conductance, has become a prototype channel to study structure–function relationship of the MS class of ion channels. Within a few years of cloning the mscL gene, the three-dimensional structure of the MscL protein was determined by X-ray crystallography, which allowed for detailed molecular studies of its structure and function. A combination of the (1) patch-clamp recording examining the function of MscL channels reconstituted into artificial liposomes, and (2) electron paramagnetic resonance (EPR) and fluorescence resonance energy transfer (FRET) spectroscopy examining structural changes occurring during gating of the reconstituted channels, provided a plausible molecular mechanism of gating of MS channels. This experimental approach helped to establish two physical mechanisms as triggers of the MscL channel gating by lipid bilayer deformation forces: (1) the energetic cost of protein-bilayer hydrophobic mismatch and (2) the geometric consequences of bilayer intrinsic curvature. The results of the EPR and FRET spectroscopic studies showed that the open state of MscL is highly dynamic, supporting a water-filled pore of at least 25 Å in diameter corresponding to an overall change in diameter of the channel protein of about 15 Å. 相似文献
107.
We present a data structure for ray-shooting queries in a set of convex fat polyhedra of total complexity n in . The data structure uses O(n2+ε) storage and preprocessing time, and queries can be answered in O(log2n) time. A trade-off between storage and query time is also possible: for any m with n<m<n2, we can construct a structure that uses O(m1+ε) storage and preprocessing time such that queries take time.We also describe a data structure for simplex intersection queries in a set of n convex fat constant-complexity polyhedra in . For any m with n<m<n3, we can construct a structure that uses O(m1+ε) storage and preprocessing time such that all polyhedra intersecting a query simplex can be reported in O((n/m1/3)logn+k) time, where k is the number of answers. 相似文献
108.
We prove that the dynamical system defined by the hydrodynamical Euler equation on any closed Riemannian 3-manifold M is not mixing in the Ck topology (k>4 and non-integer) for any prescribed value of helicity and sufficiently large values of energy. This can be regarded as a 3D version of Nadirashvili's and Shnirelman's theorems showing the existence of wandering solutions for the 2D Euler equation. Moreover, we obtain an obstruction for the mixing under the Euler flow of Ck-neighborhoods of divergence-free vectorfields on M . On the way we construct a family of functionals on the space of divergence-free C1 vectorfields on the manifold, which are integrals of motion of the 3D Euler equation. Given a vectorfield these functionals measure the part of the manifold foliated by ergodic invariant tori of fixed isotopy types. We use the KAM theory to establish some continuity properties of these functionals in the Ck-topology. This allows one to get a lower bound for the Ck-distance between a divergence-free vectorfield (in particular, a steady solution) and a trajectory of the Euler flow. 相似文献
109.
Boris?ShapiroEmail author Kouichi?Takemura Milo??Tater 《Communications in Mathematical Physics》2012,311(2):277-300
The well-known Heun equation has the form
ll{Q(z)\frac d2dz2+P(z)\fracddz+V(z)}S(z)=0,\begin{array}{ll}\left\{Q(z)\frac {d^2}{dz^2}+P(z)\frac{d}{dz}+V(z)\right\}S(z)=0,\end{array} 相似文献
110.
Capillary zone electrophoresis (CZE) has been applied for fractionation and characterization of soil-derived humic acids (HAs). Humic acids from soddy-podzolic (HA(s)) and chernozem (HA(ch)) soils were studied as well as hydrophobic high-molecular-weight (HMW) and hydrophilic low-molecular-weight (LMW) HA(s) fractions obtained by salting-out with ammonium sulfate at a saturation of 0-40% and >70%, respectively. The possibility of CZE partial fractionation of HAs has been demonstrated. The shape of "humic hump" was shown to depend on the pH of running electrolyte. Almost the whole peak overlapping occurred if alkaline solutions were used for fractionation, but the peak resolution was improved at pH 5-7. Under appropriate fractionation conditions (pH 7), at least three humic acid subfractions with different electrophoretic mobilities were distinguished in the electropherograms of initial HA and HA(s) fractions. Such a high peak resolution has never been achieved for humic acids before. The presence of three subfractions in the HA is in agreement with gel-filtration analysis and was confirmed by comparison of the electrophoretic behavior of HA(s) with those of its HMW (hydrophobic) and the LMW (hydrophilic) fractions. The potentiometric titration of HA and its fractions was performed and the pK(a) of the functional groups were calculated. An attempt was made for the first time to relate the variation of electrophoretic mobility values with acid-base properties of humic acids. It was shown that changes in the humate charge resulting from the variation of the ionization degree of its functional groups as a function of pH can be estimated on the basis of electrophoretic mobility values. Potential of CZE in estimation of HA isoelectric point was demonstrated. The pH value corresponding to the lowest absolute electrophoretic mobility value of about 20 x 10(-5) cm(2) V(-1) s(-1) can be used for approximate estimation of HA isoelectric point. The data were discussed and agreement with the random coil structural model has been shown. 相似文献
|