全文获取类型
收费全文 | 714篇 |
免费 | 19篇 |
国内免费 | 14篇 |
专业分类
化学 | 351篇 |
晶体学 | 20篇 |
力学 | 29篇 |
数学 | 167篇 |
物理学 | 180篇 |
出版年
2023年 | 7篇 |
2022年 | 20篇 |
2021年 | 17篇 |
2020年 | 17篇 |
2019年 | 26篇 |
2018年 | 12篇 |
2017年 | 14篇 |
2016年 | 25篇 |
2015年 | 25篇 |
2014年 | 23篇 |
2013年 | 114篇 |
2012年 | 32篇 |
2011年 | 30篇 |
2010年 | 35篇 |
2009年 | 26篇 |
2008年 | 26篇 |
2007年 | 14篇 |
2006年 | 21篇 |
2005年 | 20篇 |
2004年 | 23篇 |
2003年 | 18篇 |
2002年 | 9篇 |
2001年 | 11篇 |
2000年 | 7篇 |
1999年 | 6篇 |
1998年 | 10篇 |
1997年 | 14篇 |
1996年 | 8篇 |
1995年 | 8篇 |
1994年 | 11篇 |
1993年 | 7篇 |
1991年 | 3篇 |
1987年 | 3篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1973年 | 4篇 |
1969年 | 3篇 |
1967年 | 6篇 |
1966年 | 5篇 |
1965年 | 7篇 |
1964年 | 4篇 |
1962年 | 9篇 |
1960年 | 4篇 |
1959年 | 3篇 |
1956年 | 3篇 |
1955年 | 4篇 |
1934年 | 2篇 |
1933年 | 4篇 |
1927年 | 2篇 |
1923年 | 2篇 |
排序方式: 共有747条查询结果,搜索用时 31 毫秒
51.
Phosphonic acid functional polymers are currently of interest because of their high proton conductivity in humidified and anhydrous systems. In addition, heterocyclic compounds are used in anhydrous proton conducting polymer membranes. In that study, a new copolymer based on 1‐vinyl‐1,2,4‐triazole (VTri) and diisopropyl‐p‐vinylbenzyl phosphonate (VBP) was synthesized, and their thermal, chemical, and proton conducting properties were investigated. The copolymers were synthesized by free radical copolymerization of the corresponding monomers at several monomer feed ratios to obtain P(VTri‐co‐VBP) copolymers. The copolymer samples were then hydrolyzed to produce poly(vinyl triazole‐co‐vinyl phosphonic acid) copolymers. The composition of the copolymers was determined by elemental analysis. The copolymerization and hydrolysis reactions were verified by Fourier transform infrared spectroscopy and ion exchange capacity measurements. Thermogravimetry analysis indicates that the copolymers are thermally stable up to 300°C. In order to increase the proton conductivity, the copolymers were doped with H3PO4 at several stoichometric ratios. The proton conductivity increases with triazole and phosphoric acid content. In the absence of humidity, the copolymer electrolyte, P(VTri‐co‐VBPA)1:0.5 X = 2, showed a proton conductivity of 0.005 S/cm at 150°C. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
52.
Nonmetal cation (NMC) pentaborate structures were synthesized using the amino acid molecules as cations precursors. Chemical composition analysis, infrared spectroscopy, mass analysis, boron nuclear magnetic resonance, and thermal gravimetric analysis (TGA/DTA) methods were used for structural characterization. The hydrogen storage efficiency of molecules was also determined experimentally. The recorded infrared spectra support the structural similarities of the molecules. Stretchings of pentaborate rings and characteristic peaks of amino acids were detected in infrared spectra. When the thermal analysis curves were recorded, it was found that the structures showed similar decomposition steps. Due to the result of thermal decay, glassy boron oxide (B2O3) formation was observed as the final decomposition products of all molecules. Peaks associated with boric acid, triborate, and pentaborate were observed in the 11B spectra of these salts. Powder X-ray diffraction spectroscopy supports the presence of BO3 and BO4− groups regarding the presence of pentaborate rings. It also indicates the high crystallinity of the structures. The molecular cavities detected by brunauer–emmett–teller analysis were found to be 3.586, 1.922, 1.673, and 1.923 g/cm3. Low-molecular cavities can be attributed to the high hydrogen-bonding capacity of the structures. The hydrogen capture efficiency of the pentaborate salts was found to be in the range of 0.039-0. 相似文献
53.
利用化学计量学二阶校正方法结合高效液相色谱对枣花蜜中10种酚酸类物质的快速定量分析进行了研究。首先通过验证样本研究了所建立模型的准确性。结果显示:10种酚酸类物质的线性相关系数(R)为0.9982~0.9999,平均回收率为97.6%~101.1%,说明所建立的模型稳定可靠。其次,通过模拟蜂蜜试验,确定了固相萃取柱的种类及操作条件(HLB柱,酸化水淋洗,甲醇洗脱)。最后,利用模拟蜂蜜得到的最优条件结合化学计量学二阶校正方法,测定了枣花蜜中10种酚酸类物质的含量,并测得其加标回收率为62.1%~93.8%,考虑到目标分析物的种类较多,且蜂蜜基质极为复杂,该结果基本满足要求。另外,还利用统计与品质因子验证了试验方法的可靠性,结果令人满意。该方法具有简单、快速等优点,可用于复杂基质中多种目标分析物的同时定量分析。 相似文献
54.
A comprehensive set of spectra for the benzene cation and the perdeuterated benzene cation has been recorded with full rotational resolution using zero kinetic energy photoelectron spectroscopy (ZEKE) at high resolution (up to 0.2 cm?1), using a slow-rising extraction pulse. With different rovibronic levels in the S1 6l state as intermediate resonance, the rotational transitions to the vibronic ground state of the cation have been recorded using two-colour, two-photon resonance enhanced multiphoton ionization. A simple spectator model has been employed to simulate the intensities of the ZEKE transitions. By fitting the simulations to the recorded spectra, improved values for the rotational constants and the Coriolis coupling parameters of benzene and perdeuterated benzene have been obtained. The CC and CH bond lengths of the cation have been deduced. The spectator model is shown to be reliable despite the fact that no specific allowance is made for the effect of final state interactions on the signal intensity. 相似文献
55.
In this Letter, the dynamic plane elasticity problems of 2D quasicrystals is considered. By use of the Fourier transform and matrix transformations the system is reduced to uncoupled ordinary differential equations. Fourier images of Green's functions for dynamic plane elasticity problems of 2D dodecagonal, pentagonal and decagonal quasicrystals are obtained explicitly by the suggested method. 相似文献
56.
Turkish accelerator complex (TAC) project was approved by State Planning Organization (DPT) of Turkey in 2006. The complex will contain a linac-ring type electron–positron collider as a particle factory and different accelerator based light sources. As a first step to the national center, the construction of an IR FEL facility is planned until 2011. It is also planned that the technical design report for TAC will be completed in 2010. The TAC IR FEL facility will consist of an electron linac in the range of 15–40 MeV energy to obtain FEL in 2–185 microns range. In this study, the preliminary parameters of TAC IR FEL facility were presented. The possible using of the obtained FEL in material science, nonlinear optics, semiconductors, biotechnology, medicine and photochemical processes were discussed. 相似文献
57.
Dr. Joachim RosenmÜller 《Probability Theory and Related Fields》1971,17(4):259-308
Ohne ZusammenfassungBesonders bedanken möchte ich mich bei Herrn Prof. K.Jacobs fÜr sein dauerndes Interesse an meinen BemÜhungen. 相似文献
58.
59.
Summary. We present a new O(n3) algorithm which computes the SVD of a weakly diagonally dominant M-matrix to high relative accuracy. The algorithm takes as an input the offdiagonal entries of the matrix and its row sums.Mathematics Subject Classification (1991): 65F15Revised version received September 19, 2003This material is based in part upon work supported by the LLNL Memorandum Agreement No. B504962 under DOE Contract No. W-7405-ENG-48, DOE Grants No. DE-FG03-94ER25219, DE-FC03-98ER25351 and DE-FC02-01ER25478, NSF Grant No. ASC-9813362, and Cooperative Agreement No. ACI-9619020. 相似文献
60.
Let (W,H,μ) be an abstract Wiener space, assume that is a second probability measures on such that , with lower bounded and H-convex. Let , be the solution of the Monge problem transporting μ to ν and realizing the H-Wasserstein distance between μ and ν. We prove that hence the Gaussian Jacobian is well-defined and T is the strong solution of the Monge–Ampère equation ΛL°T=1 a.s. on W. To cite this article: D. Feyel, A.S. Üstünel, C. R. Acad. Sci. Paris, Ser. I 339 (2004). 相似文献