全文获取类型
收费全文 | 2664篇 |
免费 | 94篇 |
国内免费 | 14篇 |
专业分类
化学 | 2196篇 |
晶体学 | 17篇 |
力学 | 39篇 |
数学 | 186篇 |
物理学 | 334篇 |
出版年
2023年 | 13篇 |
2022年 | 10篇 |
2021年 | 26篇 |
2020年 | 32篇 |
2019年 | 56篇 |
2018年 | 22篇 |
2017年 | 28篇 |
2016年 | 65篇 |
2015年 | 48篇 |
2014年 | 55篇 |
2013年 | 109篇 |
2012年 | 178篇 |
2011年 | 216篇 |
2010年 | 78篇 |
2009年 | 89篇 |
2008年 | 157篇 |
2007年 | 194篇 |
2006年 | 171篇 |
2005年 | 178篇 |
2004年 | 155篇 |
2003年 | 128篇 |
2002年 | 117篇 |
2001年 | 50篇 |
2000年 | 39篇 |
1999年 | 25篇 |
1998年 | 30篇 |
1997年 | 21篇 |
1996年 | 33篇 |
1995年 | 17篇 |
1994年 | 35篇 |
1993年 | 29篇 |
1992年 | 22篇 |
1991年 | 23篇 |
1989年 | 19篇 |
1988年 | 17篇 |
1987年 | 16篇 |
1986年 | 12篇 |
1985年 | 21篇 |
1984年 | 23篇 |
1983年 | 22篇 |
1982年 | 15篇 |
1981年 | 22篇 |
1980年 | 12篇 |
1978年 | 12篇 |
1977年 | 14篇 |
1976年 | 13篇 |
1975年 | 7篇 |
1974年 | 12篇 |
1973年 | 11篇 |
1971年 | 7篇 |
排序方式: 共有2772条查询结果,搜索用时 0 毫秒
21.
22.
On orthogonal and symplectic matrix ensembles 总被引:1,自引:0,他引:1
The focus of this paper is on the probability,E
(O;J), that a setJ consisting of a finite union of intervals contains no eigenvalues for the finiteN Gaussian Orthogonal (=1) and Gaussian Symplectic (=4) Ensembles and their respective scaling limits both in the bulk and at the edge of the spectrum. We show how these probabilities can be expressed in terms of quantities arising in the corresponding unitary (=2) ensembles. Our most explicit new results concern the distribution of the largest eigenvalue in each of these ensembles. In the edge scaling limit we show that these largest eigenvalue distributions are given in terms of a particular Painlevé II function. 相似文献
23.
Moreno KX Harrison C Sherry AD Malloy CR Merritt ME 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2011,213(1):187-191
Nuclei with long T1s are optimal targets for dynamic nuclear polarization (DNP). Therefore, most of the agents used in metabolic imaging and spectroscopy studies are based on carboxylic acid moieties that lack protons, a strong source of dipolar relaxation. Metabolic flux information encoded into spectra of small molecule metabolites in the form of the 13C isotopomer data cannot be accessed using standard 13C hyperpolarization methods because protonated carbons relax too quickly through T1 dipolar relaxation. It is shown here that the longitudinal mixing sequence FLOPSY-8 can be used to transfer polarization from a long T1 storage nucleus to adjacent protonated carbons so that they may be detected with high sensitivity. We demonstrate that FLOPSY-8 allows a direct readout of isotopomer populations in butyrate and glutamate in vitro. 相似文献
24.
The ultrasonically induced degradations of nickel(II) 2,9,16,23-tetraphenoxy-29H, 31H-phthalocyanine and vanadyl 2,9,16,23-tetraphenoxy-29H, 31H-phthalocyanine in a biphasic system consisting of chloroform and water are investigated. Decolourisation of the organic phase containing the metallo-phthalocyanines is found to occur rapidly (approximately minutes for 8 ml of ca. 5 microM solution). Analysis of the aqueous solute via ICP-OES, reveals significant amounts of the released nickel ultimately transfers into the aqueous phase but at a rate much slower than that of decolourisation, whereas the vanadium remains within the organic phase suggesting only partial degradation despite efficient decolourisation. 相似文献
25.
Ding WX Brower DL Terry SD Craig D Prager SC Sarff JS Wright JC 《Physical review letters》2003,90(3):035002
Magnetic field fluctuations (and the associated current perturbation) have been measured in the core of a high-temperature reversed-field pinch using a newly developed fast-polarimetry system. Radial magnetic field fluctuation levels of approximately 1% are measured in standard-reversed-field pinch discharges which increase to approximately 4% during the sawtooth crash (enhanced dynamo). The fluctuation level is reduced fourfold for high-confinement plasmas where the core-resonant tearing modes are suppressed. 相似文献
26.
Venkatesh Vasudevan David F. Davidson Ronald K. Hanson Craig T. Bowman David M. Golden 《Proceedings of the Combustion Institute》2007,31(1):175-183
The two-channel thermal decomposition of formaldehyde [CH2O], (1a) CH2O + Ar → HCO + H + Ar, and (1b) CH2O + Ar → H2 + CO + Ar, was studied in shock tube experiments in the 2258-2687 K temperature range, at an average total pressure of 1.6 atm. OH radicals, generated on shock heating trioxane-O2-Ar mixtures, were monitored behind the reflected shock front using narrow-linewidth laser absorption. 1,3,5 trioxane [C3H6O3] was used as the CH2O precursor in the current experiments. H-atoms formed upon CH2O and HCO decomposition rapidly react with O2 to produce OH via H + O2 → O + OH. The recorded OH time-histories show dominant sensitivity to the formaldehyde decomposition pathways. The second-order reaction rate coefficients were inferred by matching measured and modeled OH profiles behind the reflected shock. Two-parameter fits for k1a and k1b, applicable in this temperature range, are:
27.
We have studied the effects of controlled ion bombardment on the electronic structure of the Si(0 0 1) surface. The surface was exposed to various doses of Ar+ ions accelerated towards the surface at 500 eV. X-ray photoelectron spectroscopy (XPS) spectra of the irradiated H-terminated Si(0 0 1) surface reveal the appearance of peaks that are associated with the presence of cleaved Si bonds. Ultraviolet photoelectron spectroscopy (UPS) spectra of the irradiated Si(0 0 1)2 × 1 surface show that the dimer dangling-bond surface state decays monotonically with increasing dose. These results, coupled with previous scanning tunneling microscopy (STM) studies, indicate that the breaking of dimers, and possibly the creation of adatom-like defects, during ion irradiation are responsible for the changes in the electronic structure of the valence band for this surface. 相似文献
28.
Craig F Ferris Tara Stolberg Praveen Kulkarni Murali Murugavel Robert Blanchard D Caroline Blanchard Marcelo Febo Mathew Brevard Neal G Simon 《BMC neuroscience》2008,9(1):111
Background
With the advent of functional magnetic resonance imaging (fMRI) in awake animals it is possible to resolve patterns of neuronal activity across the entire brain with high spatial and temporal resolution. Synchronized changes in neuronal activity across multiple brain areas can be viewed as functional neuroanatomical circuits coordinating the thoughts, memories and emotions for particular behaviors. To this end, fMRI in conscious rats combined with 3D computational analysis was used to identifying the putative distributed neural circuit involved in aggressive motivation and how this circuit is affected by drugs that block aggressive behavior. 相似文献29.
30.
In this paper the enhancement of the values of the cubic molecular hyperpolarizability of the nickel benzendithiol system, resulting from the selective addition of acceptor and donor groups to the ligand structure, is presented. The polarization of the molecular electronic structure is calculated by the finite field method. Significant increases in the values of are obtained from bridging two p-nitroaniline molecules with the square planar nickel structure. These results show that structures with significant values of x
(2) that are derived from the inclusion of donor and acceptor groups might also be included into the ligands of the nickel dithiolene complex to give rise to materials with enhanced values of x
(3). 相似文献