全文获取类型
收费全文 | 1046篇 |
免费 | 18篇 |
国内免费 | 23篇 |
专业分类
化学 | 670篇 |
晶体学 | 7篇 |
力学 | 13篇 |
数学 | 131篇 |
物理学 | 266篇 |
出版年
2023年 | 6篇 |
2022年 | 7篇 |
2021年 | 6篇 |
2020年 | 8篇 |
2019年 | 12篇 |
2018年 | 20篇 |
2017年 | 14篇 |
2016年 | 32篇 |
2015年 | 22篇 |
2014年 | 37篇 |
2013年 | 57篇 |
2012年 | 80篇 |
2011年 | 74篇 |
2010年 | 49篇 |
2009年 | 51篇 |
2008年 | 46篇 |
2007年 | 59篇 |
2006年 | 72篇 |
2005年 | 52篇 |
2004年 | 38篇 |
2003年 | 28篇 |
2002年 | 25篇 |
2001年 | 16篇 |
2000年 | 15篇 |
1999年 | 14篇 |
1998年 | 15篇 |
1997年 | 14篇 |
1996年 | 9篇 |
1995年 | 13篇 |
1994年 | 6篇 |
1993年 | 9篇 |
1992年 | 12篇 |
1991年 | 13篇 |
1990年 | 9篇 |
1989年 | 5篇 |
1988年 | 8篇 |
1987年 | 8篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 8篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 8篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1977年 | 8篇 |
1975年 | 7篇 |
1972年 | 5篇 |
1971年 | 4篇 |
1968年 | 7篇 |
排序方式: 共有1087条查询结果,搜索用时 31 毫秒
121.
We describe an accurate method for protein quantification based on conventional acid hydrolysis and an isotope dilution-HPLC-mass spectrometry (ID-HPLC-MS) method. Sample purity was confirmed using capillary zone electrophoresis, HPLC and MS. The analyte protein, human growth hormone (hGH), was effectively hydrolyzed by incubation with 8 M hydrochloric acid at 130 °C for 48 h, where at least 1 μM of hGH was treated to avoid possible degradation of released amino acids during hydrolysis. Using a reversed-phase column, the analytes (isoleucine, phenylalanine, proline and valine) were separated within 5 min using an isocratic eluent comprising 10% acetonitrile containing 0.1% trifluoroacetic acid. The detection limit (signal to noise ratio of 3) of amino acids was 5.5-6.2 fmol per injection. The quantification precision (RSD) of amino acids for intra- and inter-day assays was less than 0.98% and 0.39%, respectively. Comparison with other biochemical and instrumental methods revealed substantially higher accuracy and reproducibility of the ID-HPLC-MS/MS method as expected. The optimized hydrolysis and analytical conditions in our study were suitable for accurate quantification of hGH. 相似文献
122.
A gentle, but fast means for low-stress, high-throughput platelet purification is of significant clinical and biotechnological utility. Current implementations to sort platelets, however, require an external physical field, specialized buffer, or the harsh separation condition of high shear stress that tends to cause platelet stimulation. Here we report the use of hydrophoretic size separation in a wider channel and its parallelization to augment its throughput capability, maintaining physiological shear-stress range. We demonstrate a parallelized device comprising 10 stacks of the wide-channel hydrophoresis device, yielding a throughput of 2.9 million cells s(-1) and a platelet purity of 76.8%. The use of the wide channel for hydrophoresis also facilitates clogging-free separation by sorting blood clots and plaques. The wide-channel hydrophoresis offers the potential for gentle, fast, clogging-free sorting of rare blood cells with extreme throughput capabilities. 相似文献
123.
Miloslav Feistauer Václav Kučera Karel Najzar Jaroslava Prokopová 《Numerische Mathematik》2011,117(2):251-288
The paper presents the theory of the discontinuous Galerkin finite element method for the space–time discretization of a nonstationary
convection–diffusion initial-boundary value problem with nonlinear convection and linear diffusion. The problem is not singularly
perturbed with dominating convection. The discontinuous Galerkin method is applied separately in space and time using, in
general, different space grids on different time levels and different polynomial degrees p and q in space and time dicretization. In the space discretization the nonsymmetric, symmetric and incomplete interior and boundary
penalty (NIPG, SIPG, IIPG) approximation of diffusion terms is used. The paper is concerned with the proof of error estimates
in “L
2(L
2)”- and “DG”-norm formed by the “L
2(H
1)”-seminorm and penalty terms. A special technique based on the use of the Gauss–Radau interpolation and numerical integration
has been used for the derivation of an abstract error estimate. In the “DG”-norm the error estimates are optimal with respect
to the size of the space grid. They are optimal with respect to the time step, if the Dirichlet boundary condition has behaviour
in time as a polynomial of degree ≤ q. 相似文献
124.
In this paper we study polynomial Dirac equation p(??)f = 0 including (?? ? λ)f = 0 with complex parameter λ and ??kf = 0(k?1) as special cases over unbounded subdomains of ?n + 1. Using the Clifford calculus, we obtain the integral representation theorems for solutions to the equations satisfying certain decay conditions at infinity over unbounded subdomains of ?n + 1. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
125.
126.
For any integer r > 1, an r-trestle of a graph G is a 2-connected spanning subgraph F with maximum degree Δ(F) ≤ r. A graph G is called K
1,r
-free if G has no K
1,r
as an induced subgraph. Inspired by the work of Ryjáček and Tkáč, we show that every 2-connected K
1,r
-free graph has an r-trestle. The paper concludes with a corollary of this result for the existence of k-walks. 相似文献
127.
Üçüncü M Karakuş E Kuş M Akpınar GE Aksın-Artok Ö Krause N Karaca S Elmacı N Artok L 《The Journal of organic chemistry》2011,76(15):5959-5971
Two methods involving the rhodium-catalyzed reaction of 2-en-4-yne acetates and the palladium-catalyzed reaction of 2-en-4-yne carbonates with organoboronic acids were investigated; both afforded exclusively the (E)-configured vinylallenes. The coordinative interaction of the rhodium with the acetate group promoted the δ-elimination of Rh(I)-OAc from the alkenylrhodium intermediate II in both syn and anti modes, with the syn-elimination being the major path. DFT calculations revealed that a conformer of this intermediate (II), which can lead to the (E)-configured vinylallene product via the syn-elimination mode, is energetically the most favorable conformer. The rhodium-catalyzed procedure is not applicable to reactions involving (E)-configured enyne acetates, because the geometry of the alkenylrhodium intermediate that is derived from the corresponding (E)-enyne acetate would not allow such coordinative interaction to occur. The palladium-catalyzed method, which proceeds through formation of the σ-vinylallenylpalladium intermediate, B, is suitable for both the (E)- and (Z)-configured enyne carbonates and appears to have a wider scope for both organoboronic acids and enyne substrates. The palladium-catalyzed reaction of an enantiomerically enriched enyne carbonate proceeded with racemization. 相似文献
128.
Jonghee Lee Jeong‐Ik Lee Moo‐Jin Park Young Kwan Jung Nam Sung Cho Hoon Je Cho Do‐Hoon Hwang Sang‐Kyu Lee Jong‐Hwa Park Jiwon Hong Hye Yong Chu Hong‐Ku Shim 《Journal of polymer science. Part A, Polymer chemistry》2007,45(7):1236-1246
A novel series of poly(10‐hexyl‐phenothiazine‐S,S‐dioxide‐3,7‐diyl) and poly(9,9′‐dioctyl‐fluorene‐2,7‐diyl‐alt‐10‐hexyl‐3,7‐phenothiazine‐S,S‐dioxide) (PFPTZ‐SS) compounds were synthesized through Ni(0)‐mediated Yamamoto polymerization and Pd(II)‐catalyzed Suzuki polymerization. The synthesized polymers were characterized by 1H NMR spectroscopy and elemental analysis and showed higher glass transition temperatures than that of pristine polyfluorene. In terms of photoluminescence (PL), the PFPTZ‐SS compounds were highly fluorescent with bright blue emissions in the solid state. Light‐emitting devices were fabricated with these polymers in an indium tin oxide/poly(3,4‐ethylene dioxythiophene):poly(styrene sulfonate)/polymer/Ca/Al configuration. The electroluminescence (EL) of the copolymers differed from the PL characteristics: the EL device exhibited a redshifted greenish‐blue emission in contrast to the blue emission observed in the PL. Additionally, this unique phenothiazine‐S,S‐dioxide property, triggered by the introduction of an electron‐deficient SO2 unit into the electron‐rich phenothiazine, gave rise to improvements in the brightness, maximum luminescence intensity, and quantum efficiency of the EL devices fabricated with PFPTZ‐SS. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1236–1246, 2007 相似文献
129.
Joseph R. Lakowicz Henryk Cherek Józef Kuśba Ignacy Gryczynski Michael L. Johnson 《Journal of fluorescence》1993,3(2):103-116
This didactic paper summarizes the mathematical expressions needed for analysis of fluorescence anisotropy decays from polarized frequency-domain fluorescence data. The observed values are the phase angle difference between the polarized components of the emission and the modulated anisotropy, which is the ratio of the polarized and amplitude-modulated components of the emission. This procedure requires a separate measurement of the intensity decay of the total emission. The expressions are suitable for any number of exponential components in both the intensity decay and the anisotropy decay. The formalism is generalized for global analysis of anisotropy decays measured at different excitation wavelengths and for different intensity decay times as the result of quenching. Additionally, we describe the expressions required for associated anisotropy decays, that is, anisotropy decays where each correlation time is associated with a decay time present in the anisotropy decay. And finally, we present expressions appropriate for distributions of correlation times. This article should serve as a reference for researchers using frequency-domain fluorometry. 相似文献
130.
Sang Kyu Lee Byung‐Jun Jung Taek Ahn Young Kwan Jung Jeong‐Ik Lee In‐Nam Kang Jonghee Lee Jong‐Hwa Park Hong Ku Shim 《Journal of polymer science. Part A, Polymer chemistry》2007,45(15):3380-3390
A series of fluorene‐based copolymers composed of blue‐ and orange‐light‐emitting comonomers were synthesized through palladium‐catalyzed Suzuki coupling reactions. 9,9‐Dihexylfluorene and 2‐(2,6‐bis‐{2‐[1‐(9,9‐dihexyl‐9H‐fluoren‐2‐yl)‐1,2,3,4‐tetrahydroquinolin‐6‐yl]‐vinyl}‐pyran‐4‐ylidene)‐malononitrile (DCMF) were used as the blue‐ and orange‐light‐emitting chromophores, respectively. The resulting single polymers exhibited simultaneous blue (423/450 nm) and orange (580–600 nm) emissions from these two chromophores. By adjusting the fluorene and DCMF contents, white light emission could be obtained from a single polymer; a device with an ITO/PEDOT:PSS/polymer/Ca/Al configuration was found to exhibit pure white electroluminescence with Commission Internationale de L'Eclairage (CIE) coordinates of (0.33, 0.31), a maximum brightness of 1180 cd/m2, and a current efficiency of 0.60 cd/A. Furthermore, the white light emission of this device was found to be very stable with respect to variation of the driving voltage. The CIE coordinates of the device were (0.32, 0.29), (0.32, 0.29), and (0.33, 0.31) for driving voltages of 7, 8, and 10 V, respectively. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3380–3390, 2007 相似文献