全文获取类型
收费全文 | 2362篇 |
免费 | 84篇 |
国内免费 | 23篇 |
专业分类
化学 | 1463篇 |
晶体学 | 7篇 |
力学 | 42篇 |
数学 | 400篇 |
物理学 | 557篇 |
出版年
2023年 | 9篇 |
2022年 | 22篇 |
2021年 | 29篇 |
2020年 | 38篇 |
2019年 | 29篇 |
2018年 | 30篇 |
2017年 | 36篇 |
2016年 | 61篇 |
2015年 | 59篇 |
2014年 | 62篇 |
2013年 | 121篇 |
2012年 | 186篇 |
2011年 | 176篇 |
2010年 | 123篇 |
2009年 | 110篇 |
2008年 | 158篇 |
2007年 | 164篇 |
2006年 | 167篇 |
2005年 | 203篇 |
2004年 | 138篇 |
2003年 | 124篇 |
2002年 | 115篇 |
2001年 | 19篇 |
2000年 | 23篇 |
1999年 | 15篇 |
1998年 | 15篇 |
1997年 | 15篇 |
1996年 | 33篇 |
1995年 | 17篇 |
1994年 | 17篇 |
1993年 | 19篇 |
1992年 | 11篇 |
1991年 | 5篇 |
1990年 | 8篇 |
1989年 | 12篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1986年 | 7篇 |
1985年 | 12篇 |
1984年 | 10篇 |
1983年 | 10篇 |
1982年 | 9篇 |
1981年 | 10篇 |
1980年 | 5篇 |
1979年 | 7篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1973年 | 5篇 |
1972年 | 3篇 |
1970年 | 2篇 |
排序方式: 共有2469条查询结果,搜索用时 328 毫秒
221.
James B Whitney Saied Mirshahidi So-Yon Lim Lauren Goins Chris C Ibegbu Daniel C Anderson Richard B Raybourne Fred R Frankel Judy Lieberman Ruth M Ruprecht 《Journal of immune based therapies and vaccines》2011,9(1):2
Background
We have evaluated an attenuated Listeria monocytogenes (Lm) candidate vaccine vector in nonhuman primates using a delivery regimen relying solely on oral vaccination. We sought to determine the impact of prior Lm vector exposure on the development of new immune responses against HIV antigens. 相似文献222.
Hironari Yamada Dorian Minkov Yuki Shimura Chris Scourtis Okoye Kenneth Ejike Daisuke Hasegawa Mami Yamada Takayasu Hanashima Ken Atkinson 《Journal of synchrotron radiation》2011,18(5):702-707
The only available tabletop electron storage rings are the machines from the MIRRORCLE series. The electrons are accelerated in a microtron and injected into the storage ring. During its circulation, each electron passes through a tiny target many times, emitting a photon beam. Both the spectrum and the angular distribution of the radiation depend on the material, the thickness and the shape of the target. In this paper measured angular distributions of the radiation from several different targets in the magnetic field of the 20 MeV storage ring MIRRORCLE‐20SX are presented. The detector comprises a 3 mm × 3 mm × 8.5 µm plastic scintillator (PS) coupled to a photomultiplier by a bundle of optical fibers. The output of the photomultiplier is digitized by an IF converter. This detector is sensitive mostly to soft X‐ray radiation, and its PS is moved by a mechanical system in a plane perpendicular to the radiation axis. The measured angular distributions for Mo and Sn targets contain an annulus which is attributed to transition radiation. The angular distributions for Al, carbon nanotube and diamond‐like carbon (DLC) targets show some suppression of the radiation along the magnetic field. This is the first evidence of observation of the angular distribution of synchrotron Cherenkov radiation, which represents Cherenkov radiation in a magnetic field. The power radiated from the DLC target is estimated. 相似文献
223.
Correlated stability conjecture (CSC) proposed by Gubser and Mitra (2000, 2001) and linked the thermodynamic and classical (in)stabilities of black branes. The classical instabilities, whenever occurring, were conjectured to arise as Gregory–Laflamme (GL) instabilities of translationally invariant horizons. In Buchel (2005) [3] it was shown that the thermodynamic instabilities, specifically the negative specific heat, indeed result in the instabilities in the hydrodynamic spectrum of holographically dual plasma excitations. A counter-example of CSC was presented in the context of black branes with scalar hair undergoing a second-order phase transition (Friess et al., 2005 [4]). In this Letter we discuss a related counter-example of CSC conjecture, where a thermodynamically stable translationally invariant horizon has a genuine tachyonic instability. We study the spectrum of quasinormal excitations of a black brane undergoing a continuous phase transition, and explicitly identify the instability. We compute the critical exponents of the critical momenta and the frequency of the unstable fluctuations and identify the dynamical critical exponent of the model. 相似文献
224.
Chris Fields 《Acta Analytica》2014,29(2):131-148
The common practice of advancing arguments based on current physics in support of metaphysical conclusions has been criticized on the grounds that current physics may well be wrong. A further criticism is leveled here: current physics itself depends on metaphysical assumptions, so arguing from current physics is in fact arguing from yet more metaphysics. It is shown that the metaphysical assumptions underlying current physics are often deeply embedded in the formalism in which theories are presented, and hence impossible to dismiss as mere motivational or interpretative speculation. It is then shown that such assumptions, when made explicit, can wreck havoc on otherwise-sensible philosophical arguments. It is argued in conclusion that this situation is both unlikely to be reparable just by being more careful, and unlikely to go away as further, presumably more subtle physical theories are developed. 相似文献
225.
In service systems, in order to balance the server’s idle times and the customers’ waiting times, one may fix the arrival times of the customers beforehand in an appointment schedule. We propose a procedure for determining appointment schedules in such a D/G/1-type of system by sequentially minimizing the per-customer expected loss. Our approach provides schedules for any convex loss function; for the practically relevant cases of the quadratic and absolute value loss functions appealing closed-form results are derived. Importantly, our approach does not impose any conditions on the service time distribution; it is even allowed that the customers’ service times have different distributions. 相似文献
226.
In this introductory paper we take partial stock of the current state of field on calculus research, exemplifying both the promise of research advances as well as the limitations. We identify four trends in the calculus research literature, starting with identifying misconceptions to investigations of the processes by which students learn particular concepts, evolving into classroom studies, and, more recently research on teacher knowledge, beliefs, and practices. These trends are related to a model for the cycle of research and development aimed at improving learning and teaching. We then make use of these four trends and the model for the cycle of research and development to highlight the contributions of the papers in this issue. We conclude with some reflections on the gaps in literature and what new areas of calculus research are needed. 相似文献
227.
We show that for any mod 2m characters, χ1, χ2, the complete exponential sum,∑~(2m)_(x=1)χ1(x)χ2(Ax~k+ B) has a simple explicit evaluation. 相似文献
228.
Meiling Lu Xing‐Fang Li X. Chris Le Michael Weinfeld Hailin Wang 《Rapid communications in mass spectrometry : RCM》2010,24(11):1523-1532
We describe a method for probing surface‐exposed cysteines in proteins by selective labeling with p‐hydroxymercuribenzoate (PMB) combined with nano‐electrospray ionization mass spectrometric analysis (nanoESI‐MS). The rapid, stoichiometric, and specific labeling by PMB of surface‐exposed cysteines allows for characterization of the accessibility of the cysteines using a single MS analysis. Moreover, by taking advantage of the large mass shift of 321 Da, unique isotopic pattern, and enhanced MS signal of PMB‐labeled cysteine‐containing peptide fragments, the surface‐exposed cysteines in proteins can be accurately identified by peptide mapping. The number and sites of reactive cysteines on the surface of human and rat hemoglobins (hHb and rHb) were identified as examples. Collision‐induced dissociation tandem mass spectrometric (MS/MS) analysis of specific peptides further confirmed the selective labeling of PMB in hHb. The subtle difference between the different cysteine residues in rHb was also evaluated by multiple PMB titrations. The difference between the two cysteines in their environment may partially explain their reaction specificity. Cysteine 125 in the β unit of rHb is exposed on the surface, explaining its reactivity with glutathione. Cysteine 13 in the α subunit of rHb is much less exposed, and is located in a hydrophobic pocket, a conclusion that is consistent with the previous observation of its selective binding with dimethylarsinous acid, a reactive arsenic metabolite. The method is potentially useful for probing cysteines in other biologically important proteins and for studying proteins that are associated with conformational or structural changes induced by denaturing processes, protein modifications, protein‐protein interactions and protein assemblies. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
229.
Antony Lewis Chris Doran Anthony Lasenby 《International Journal of Theoretical Physics》2001,40(1):363-376
Using the spacetime algebra formulation of the Dirac equation, we demonstrate how to perform cross-section calculations following a method suggested by Hestenes (1982). Instead of an S-matrix, we use an operator that rotates the initial states into the scattered states. By allowing the scattering operator to become a function of the initial spin, we can neatly handle spin-dependent calculations. When the operator is independent of spin, we can provide manifestly spin-independent results. We use neither spin basis nor spin sums, instead handling the spin orientation directly. As examples, we perform spin-dependent calculations in Coulomb scattering to second order, and briefly consider more complicated calculations in QED. 相似文献
230.
Stephanie B. A. De Beer Alice GlÄttli Johannes Hutzler Nico P. E. Vermeulen Chris Oostenbrink 《Journal of computational chemistry》2011,32(10):2160-2169
4‐Hydroxyphenylpyruvate dioxygenase is a relevant target in both pharmaceutical and agricultural research. We report on molecular dynamics simulations and free energy calculations on this enzyme, in complex with 12 inhibitors for which experimental affinities were determined. We applied the thermodynamic integration approach and the more efficient one‐step perturbation. Even though simulations seem well converged and both methods show excellent agreement between them, the correlation with the experimental values remains poor. We investigate the effect of slight modifications on the charge distribution of these highly conjugated systems and find that accurate models can be obtained when using improved force field parameters. This study gives insight into the applicability of free energy methods and current limitations in force field parameterization. © 2011 Wiley Periodicals, Inc. J Comput Chem 2011 相似文献