全文获取类型
收费全文 | 2777篇 |
免费 | 76篇 |
国内免费 | 28篇 |
专业分类
化学 | 1614篇 |
晶体学 | 11篇 |
力学 | 48篇 |
数学 | 546篇 |
物理学 | 662篇 |
出版年
2023年 | 17篇 |
2022年 | 56篇 |
2021年 | 77篇 |
2020年 | 51篇 |
2019年 | 63篇 |
2018年 | 67篇 |
2017年 | 58篇 |
2016年 | 86篇 |
2015年 | 79篇 |
2014年 | 88篇 |
2013年 | 138篇 |
2012年 | 196篇 |
2011年 | 171篇 |
2010年 | 129篇 |
2009年 | 124篇 |
2008年 | 190篇 |
2007年 | 173篇 |
2006年 | 167篇 |
2005年 | 172篇 |
2004年 | 152篇 |
2003年 | 94篇 |
2002年 | 96篇 |
2001年 | 57篇 |
2000年 | 38篇 |
1999年 | 40篇 |
1998年 | 46篇 |
1997年 | 31篇 |
1996年 | 22篇 |
1995年 | 28篇 |
1994年 | 26篇 |
1993年 | 13篇 |
1992年 | 10篇 |
1991年 | 11篇 |
1990年 | 12篇 |
1989年 | 8篇 |
1988年 | 5篇 |
1986年 | 5篇 |
1985年 | 11篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 8篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1974年 | 6篇 |
1969年 | 3篇 |
排序方式: 共有2881条查询结果,搜索用时 15 毫秒
1.
Cover Picture: Coordination Chemistry of N‐Heterocyclic Nitrenium‐Based Ligands (Chem. Eur. J. 19/2015) 下载免费PDF全文
2.
Ozonolysis of a Series of Methylated Alkenes: Reaction Rate Coefficients and Gas‐Phase Products 下载免费PDF全文
Tristan Braure Véronique Riffault Alexandre Tomas Romeo Iulian Olariu Cecilia Arsene Yuri Bedjanian Patrice Coddeville 《国际化学动力学杂志》2015,47(9):596-605
The gas‐phase ozonolysis of three methylated alkenes, i.e., trans‐2,2‐dimethyl‐3‐hexene (22dM3H), trans‐2,5‐dimethyl‐3‐hexene (25dM3H), and 4‐methyl‐1‐pentene (4M1P), has been investigated in the presence of sufficient hydroxyl radical scavenger in a laminar flow reactor at ambient temperature (296 ± 2 K) and P = 1 atm of dry air (RH ≤ 5%). Ozone levels in the reactor were monitored by an automatic analyzer. Alkene and gas‐phase product concentrations were determined via online sampling either on three‐bed adsorbent cartridges followed by thermodesorption and GC/FID‐MS analysis or on 2,4‐dinitrophenylhydrazine (DNPH) cartridges for subsequent HPLC/UV analysis. Reaction rate coefficients of (3.38 ± 0.12) × 10?17 for 22dM3H and (2.71 ± 0.26) × 10?17 for 25dM3H, both in cm3 molecule?1 s?1 units, have been obtained under pseudo–first‐order conditions. Primary carbonyl products have been identified for the three investigated alkenes, and branching ratios are reported. In the case of 4M1P ozonolysis, the yield of a Criegee intermediate was indirectly determined. Kinetics and product study results are compared to those of literature when available. This work represents the first investigation of reaction products in the ozonolysis of 22dM3H, 25dM3H, and 4M1P in a flow reactor. 相似文献
3.
A mixed problem is considered for a system of partial differential equations modeling the process of adsorption dynamics. An existence and uniqueness theorem is proved for this problem, and the solution properties are investigated. The inverse problem is posed, involving the determination of the system coefficient given additional information about the solution. A uniqueness theorem is proved for the solution of the inverse problem.__________Translated from Prikladnaya Matematika i Informatika, No. 16, pp. 5 – 14, 2004. 相似文献
4.
In this paper we relate the operators in the operator representations of a generalized Nevanlinna function N(z) and of the function −N(z)−1 under the assumption that z=∞ is the only (generalized) pole of nonpositive type. The results are applied to the Q-function for S and H and the Q-function for S and H∞, where H is a self-adjoint operator in a Pontryagin space with a cyclic element w, H∞ is the self-adjoint relation obtained from H and w via a rank one perturbation at infinite coupling, and S is the symmetric operator given by S=H∩H∞. 相似文献
5.
K.B. Welter Q. Wu Y. You K. Abel D. McCreary S.M. Bajorek J.N. Reyes Jr 《International Journal of Multiphase Flow》2004,30(12):407-1484
This article describes a comprehensive literature review of liquid entrainment in horizontal pipes with vertical-up branches. Deficiencies in the available data and correlations were identified. The Air–water Test Loop for Advanced Thermal–hydraulic Studies (ATLATS) was constructed and entrainment onset and steady-state data were collected for a wide range of flow conditions. Using new insights gained from experimental testing, the authors developed a model for predicting the onset of entrainment and steady-state entrainment rate. Previously published correlations, along with the new model, are compared against all available data. The new model shows very good agreement with the onset data, but is not very good at predicting branch quality at high liquid flow rates. 相似文献
6.
Yuri M. Boiko Anders Bach Jørgen Lyngaae-Jørgensen 《Journal of Polymer Science.Polymer Physics》2004,42(10):1861-1867
Films of amorphous polystyrene (PS) with a weight-average molecular weight (Mw) of 225 × 103 g/mol were bonded in a T-peel test geometry, and the fracture energy (G) of a PS/PS interface was measured at the ambient temperature as a function of the healing time (th) and healing temperature (Th). G was found to develop with (th)1/2 at Th = Tg-bulk − 33 °C (where Tg-bulk is the glass-transition temperature of the bulk sample), and log G was found to develop with 1/Th at Tg-bulk − 43 °C ≤ Th ≤ Tg-bulk − 23 °C. The smallest measured value of G = 1.4 J/m2 was at least one order of magnitude larger than the work of adhesion required to reversibly separate the PS surfaces. These three observations indicated that the development of G at the PS/PS interface in the temperature range investigated (<Tg-bulk) was controlled by the diffusion of chain segments feasible above the glass-transition temperature of the interfacial layer, in agreement with our previous findings for fracture stress development at several polymer/polymer interfaces well below Tg-bulk. Close values of G = 8–9 J/m2 were measured for the symmetric interfaces of polydisperse PS [Mw = 225 × 103, weight-average molecular weight/number-average molecular weight (Mw/Mn) = 3] and monodisperse PS (Mw = 200 × 103, Mw/Mn = 1.04) after healing at Th = Tg-bulk − 33 °C for 24 h. This implies that the self-bonding of high-molecular-weight PS at such relatively low temperatures is not governed by polydispersity. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1861–1867, 2004 相似文献
7.
8.
An assignment of the near-infrared bands in the 600–800 nm spectral region observed in magnetic circular dichroism (MCD)
spectra of high-spin ferrous haemoproteins is presented. The assignment is based on a relative energy level scheme for iron
d-electrons, a comparison of predicted and measured temperature dependences of MCD intensity, a sign of MCD bands and a group
theoretical analysis of allowed transitions. The proposed assignment is consistent with the ∼15-nm red shift of the ∼760 nm
band on breakage of the Fe-His bond in deoxy-myoglobin at low pH, with low-temperature photolysis experiments available for
CO complexes of several haemoproteins. In accordance with the observations, the intensity of the MCD bands for proteins with
a sulphur anion of cysteine as proximal haemligand (cytochrome P450 and chloroperoxidase) is predicted to be diminished by
at least one order of magnitude compared to that for proteins with an imidazole of a histidine as a protein-derived haemligand
(i.e. myoglobin, haemoglobin and horseradish peroxidase).
Received: 4 February 1997 / Accepted: 1 May 1997 相似文献
9.
Optical properties of polarization-dependent geometric phase elements with partially polarized light
Yuri Gorodetski 《Optics Communications》2006,266(2):365-375
The behavior of geometric phase elements illuminated with partially polarized monochromatic beams is investigated both theoretically and experimentally. The element discussed in this paper is composed of wave plates with π-retardation and a space-variant orientation angle. We found that a beam emerging from such an element comprises two polarization orders; right-and left-handed circularly polarized states with conjugate geometric phase modification. This phase equals twice the orientation angle of the space-variant wave plate comprising the element. Apart from the two polarization orders, the emerging beam coherence polarization matrix includes a “vectorial interference matrix” which contains information concerning the correlation between the two orthogonal, circularly polarized portions of the incident beam. In this paper we measure this correlation by a simple interference experiment. In addition, we found that the equivalent mutual intensity of the emerging beam is modulated according to the geometric phase induced by the element. Other interesting phenomena concerning propagation will be discussed theoretically and demonstrated experimentally. The experiment made use of a spherical geometric phase element that was realized by use of a space-variant subwavelength grating illuminated with CO2 laser radiation of 10.6 μm wavelength. 相似文献
10.
Yuri L. Sachkov 《Transactions of the American Mathematical Society》2004,356(2):457-494
Flat sub-Riemannian structures are local approximations -- nilpotentizations -- of sub-Riemannian structures at regular points. Lie algebras of symmetries of flat maximal growth distributions and sub-Riemannian structures of rank two are computed in dimensions 3, 4, and 5.