全文获取类型
收费全文 | 9334篇 |
免费 | 92篇 |
国内免费 | 28篇 |
专业分类
化学 | 7047篇 |
晶体学 | 177篇 |
力学 | 114篇 |
数学 | 957篇 |
物理学 | 1159篇 |
出版年
2024年 | 37篇 |
2023年 | 110篇 |
2022年 | 433篇 |
2021年 | 495篇 |
2020年 | 313篇 |
2019年 | 332篇 |
2018年 | 240篇 |
2017年 | 201篇 |
2016年 | 364篇 |
2015年 | 256篇 |
2014年 | 359篇 |
2013年 | 528篇 |
2012年 | 565篇 |
2011年 | 640篇 |
2010年 | 433篇 |
2009年 | 352篇 |
2008年 | 511篇 |
2007年 | 480篇 |
2006年 | 448篇 |
2005年 | 345篇 |
2004年 | 309篇 |
2003年 | 228篇 |
2002年 | 207篇 |
2001年 | 120篇 |
2000年 | 89篇 |
1999年 | 62篇 |
1998年 | 74篇 |
1997年 | 58篇 |
1996年 | 75篇 |
1995年 | 50篇 |
1994年 | 52篇 |
1993年 | 45篇 |
1992年 | 37篇 |
1991年 | 39篇 |
1990年 | 34篇 |
1989年 | 40篇 |
1988年 | 28篇 |
1987年 | 30篇 |
1986年 | 34篇 |
1985年 | 50篇 |
1984年 | 28篇 |
1983年 | 23篇 |
1982年 | 32篇 |
1981年 | 23篇 |
1980年 | 24篇 |
1979年 | 21篇 |
1977年 | 14篇 |
1976年 | 17篇 |
1974年 | 13篇 |
1968年 | 12篇 |
排序方式: 共有9454条查询结果,搜索用时 0 毫秒
11.
Hoffmann Maria Kaminska Anna Nicolaidou Rosy Paganis Stathes 《The European Physical Journal C - Particles and Fields》2014,74(11):1-7
We study how massive ghost-free gravity \(f(R)\) -modified theories, MGFTs, can be encoded into generic off-diagonal Einstein spaces. Using “auxiliary” connections completely defined by the metric fields and adapted to nonholonomic frames with associated nonlinear connection structure, we decouple and integrate in certain general forms the field equations in MGFT. Imposing additional nonholonomic constraints, we can generate Levi-Civita, LC, configurations and mimic MGFT effects via off-diagonal interactions of effective Einstein and/or Einstein–Cartan gravity with nonholonomically induced torsion. We show that imposing nonholonomic constraints it is possible reproduce very specific models of massive \(f(R)\) gravity studied in Cai et al. (arXiv:1307.7150, 2013), Klusoňet al. (Phys Lett B 726:918, 2013), Nojiri and Odintov (Phys Lett B 716:377, 2012) and Nojiri et al. (JCAP 1305:020, 2013). The cosmological evolution of ghost-free off-diagonal Einstein spaces is investigated. Certain compatibility of MGFT cosmology to small off-diagonal deformations of \(\Lambda \) CDM models is established. 相似文献
12.
Here, we describe the reliable method for the detection and quantitation of a pheomelanin component in melanin pigments. Synthetic melanins with various contents of pheomelanin-type structural units were thermally degraded, and the multiple reaction monitoring mode was applied to detect the pheomelanin markers in the pyrolysates by GC/MS/MS. The method allowed the specific detection and quantitation of a pheomelanin component in melanin with the incorporation of pheomelanin-type units as low as 0.05%. Considering highly universal character of the pheomelanin markers, the method could be applied for structural studies of natural melanin pigments being mixtures of eumelanin and pheomelanin. 相似文献
13.
F Mazzotti H Benabdelkamel L Di Donna CM Athanassopoulos A Napoli G Sindona 《Journal of mass spectrometry : JMS》2012,47(7):932-939
5-Dimethylamino-1-sulfonyl naphthalene (DNS, commonly referred as dansyl) is a functionality, bearing well-established properties in directing the fragmentation, by mass spectrometry (MS), of the corresponding ionized sulfonylated derivatives. This property is shared also by its labeled analogs. The use of d(0)/d(6) DNS derivatives is now exploited in the application of the well-established isotope dilution mass spectrometric approach in the assay of complex mixtures. A new method for the quantitation of amino acids (AAs) in beverages is therefore presented, which relies on liquid chromatographic separation of their N-dansylated derivatives followed by comparative electrospray tandem MS/MS of the d(0)/d(6) isobaric mixtures. Labeled and unlabeled DNS derivatives of the selected AAs are readily available by microwave-assisted synthetic protocols. The novelty of the method is represented by the use of heavy and light DNS-isotopologue providing suitable reporter groups. Multiple-reaction monitoring has been applied in the assay of AAs in wine, pineapple juice and bergamot juice with good-to-excellent results as proved by both relative standard deviation, lower than 15%, and by the accuracy values in the range 90-110%. 相似文献
14.
B. K. Kardashev T. S. Orlova B. I. Smirnov A. R. de Arellano-Lopez J. Martinez-Fernandez 《Physics of the Solid State》2009,51(4):750-753
The effect of the vibrational strain amplitude on the Young’s modulus and ultrasound absorption (internal friction) of a SiC/Si biomorphic composite prepared by pyrolysis of sapele wood followed by infiltration of silicon were investigated. The studies were conducted in air and in vacuum by the acoustic resonance method with the use of a composite vibrator in longitudinal vibrations at frequencies of about 100 kHz. Measurements performed on sapele wood-based bio-SiC/Si samples revealed a substantial effect of adsorption-desorption of molecules contained in air on the effective elasticity modulus and elastic vibration decrement. Microplastic characteristics of the SiC/Si composites prepared from wood of different tree species were compared. 相似文献
15.
16.
The basis set superposition error is investigated in terms of the first-order symmetry adapted perturbation theory (SAPT). The analysis of the first-order SAPT contribution to the interaction energy reveals the origin of the basis set truncation effects at both the one-electron and many-electron levels of approximation. This helps to formulate the necessary conditions which ensure that the calculated interaction energy is free of the basis set superposition contributions. At the level of the one-electron approximation used for both the interacting system and its subsystems a part of the basis set truncation errors can be eliminated by using what is called the dimer-centred basis set. In order to remove all contributions which arise from the symmetrization of the product of wave functions of the subsystems one needs to redefine their reference states. This means that for the interacting system represented by a single HF determinant, the subsystems must be considered at the level of full CI in the orbital space spanned by all occupied orbitals used to describe the dimer. Then, the interaction energy becomes completely free of the basis set superposition contributions. These general considerations are exemplified by calculations of the first-order SAPT interaction energy in helium and H2 dimers at different levels of approximation for monomers. Also the convergence of the calculated energies to the complete basis set limit is investigated. 相似文献
17.
D. O. Krivenkov D. A. Artemenkov V. Bradnova S. Vokál P. I. Zarubin I. G. Zarubina N. V. Kondratieva A. I. Malakhov A. A. Moiseenko G. I. Orlova N. G. Peresadko N. G. Polukhina P. A. Rukoyatkin V. V. Rusakova V. R. Sarkisyan R. Stanoeva M. Haiduc S. P. Kharlamov 《Physics of Atomic Nuclei》2010,73(12):2103-2109
Results on the coherent dissociation of relativistic 9C nuclei in a nuclear track emulsion are described. These results include the charge topology and kinematical features of final states. Events of 9C → 33He coherent dissociation are identified. 相似文献
18.
Zusammenfassung Tabakmosaikvirus hoher spezifischer Aktivität, das am Phosphor und/oder Kohlenstoff markiert war, wurde biosynthetisch hergestellt. Damit wurde jeweils ein Blatt einer Pflanze von Nicotiana tabacum infiziert und der etwaige Transport von intaktem Virus durch das Leitungssystem der Pflanzen dadurch weitgehend unterbunden, daß die Leitgefäße des behandelten Blattes durchtrennt wurden.Das aus den unbehandelten Blättern der Pflanze nach 17 1/2, 48 und 72 Stdn. isolierte Virus wies im Vergleich zum eingesetzten TMV einen viel geringeren Anteil an Gesamtradiokohlenstoff im Protein auf. Dies deutet darauf hin, daß das Virus der unbehandelten Blätter höchstens zu einem sehr geringen Teil aus intakt transportiertem TMV bestehen könnte.Die nicht im TMV enthaltenen Polynukleotide der unbehandelten Blätter enthalten 7 Stdn. nach der Infektion verhältnismäßig viel32P, doch tritt derselbe innerhalb 70 Stdn. zum allergrößten Teil in niedermolekulare Verbindungen über.Die in Puffer unlöslichen Polynukleotide der unbehandelten Blätter (Blattnukleinsäure) weisen ein mit der Zeit abnehmendes Verhältnis von32P/14C auf. Auch innerhalb der Nukleinsäure (NS) des TMV dieser Blätter nimmt dieses Verhältnis zunächst ab, steigt aber später wieder an.Die angeführten Ergebnisse stehen mit der Vorstellung im Einklang, daß das Virus NS abspaltet und sowohl die systemische Infektion der Pflanze wie auch die Virusvermehrung mindestens zum Teil durch diese freie NS bewirkt wird. Die aus dem Virus stammende freie NS unterliegt zum großen Teil lebhaftem Abbau, wobei ihre Komponenten wahrscheinlich dem Aufbau normaler Blattbestandteile dienen.Mit 3 Abbildungen 相似文献
19.
Anna Canale 《Journal of Mathematical Analysis and Applications》2003,287(1):101-117
In unbounded domains we state some a priori bounds for solutions of the Dirichlet problem for linear second order elliptic differential equations in nondivergence form with discontinuous coefficients in weighted spaces. The weight function is related to the distance function from a fixed subset S of ∂Ω. 相似文献
20.
Kathryn A. Downsland Anna M. Greaves 《The Journal of the Operational Research Society》1994,45(7):817-826
The use of a bi-directional, as opposed to a one-way, transportation system, can increase the operational efficiency of automated guided vehicles in both manufacturing and warehousing environments. However, the full potential will only be realized if the routeing algorithms pay particular attention to the problem of collision avoidance. This paper is concerned with the development of such an algorithm. The method is based on the use of delays and deviations to avoid collisions that could arise when using the shortest routes for each vehicle, and is applicable to any transportation system which can be represented as a network with known travel times. 相似文献