全文获取类型
收费全文 | 3227篇 |
免费 | 139篇 |
国内免费 | 18篇 |
专业分类
化学 | 2226篇 |
晶体学 | 17篇 |
力学 | 97篇 |
数学 | 508篇 |
物理学 | 536篇 |
出版年
2023年 | 27篇 |
2022年 | 55篇 |
2021年 | 63篇 |
2020年 | 80篇 |
2019年 | 59篇 |
2018年 | 79篇 |
2017年 | 75篇 |
2016年 | 122篇 |
2015年 | 106篇 |
2014年 | 132篇 |
2013年 | 230篇 |
2012年 | 248篇 |
2011年 | 244篇 |
2010年 | 158篇 |
2009年 | 134篇 |
2008年 | 196篇 |
2007年 | 197篇 |
2006年 | 144篇 |
2005年 | 134篇 |
2004年 | 143篇 |
2003年 | 96篇 |
2002年 | 82篇 |
2001年 | 43篇 |
2000年 | 34篇 |
1999年 | 30篇 |
1998年 | 22篇 |
1997年 | 17篇 |
1996年 | 25篇 |
1995年 | 14篇 |
1994年 | 20篇 |
1993年 | 20篇 |
1992年 | 19篇 |
1991年 | 14篇 |
1990年 | 19篇 |
1989年 | 15篇 |
1988年 | 11篇 |
1987年 | 25篇 |
1986年 | 12篇 |
1985年 | 27篇 |
1984年 | 21篇 |
1983年 | 9篇 |
1982年 | 16篇 |
1981年 | 17篇 |
1980年 | 22篇 |
1979年 | 12篇 |
1978年 | 13篇 |
1977年 | 13篇 |
1976年 | 12篇 |
1975年 | 18篇 |
1973年 | 11篇 |
排序方式: 共有3384条查询结果,搜索用时 31 毫秒
131.
Dae Sung You Chang Su Kim Yong Jin KangKyounga Lim Sunghoon JungDo-Geun Kim Jong-Kuk KimSungjin Jo Joo Hyun Kim Jae-Wook Kang 《Current Applied Physics》2012,12(3):908-910
We report on the fabrication of efficient annealing-free organic solar cells using co-solvent solution considered as a promising method for low-cost and time-saving manufacturing. Higher device efficiency could be obtained compared to the pure solvent casted device, resulting from the improved crystallinity, optical absorption and transport properties. The power conversion efficiency of 2.8% was obtained, demonstrating the feasibility of achieving low-cost and high-efficiency organic solar cells without any additional treatment and processing additives. 相似文献
132.
Maria Jo?o Carrilho Plancha Carmen Mireya Rangel César Augusto Correia de Sequeira 《Journal of Solid State Electrochemistry》2012,16(2):665-671
The (PEO)4ZnCl2 electrolyte (PEO, polyethylene oxide) was studied in view of its potential application in a solid-state rechargeable zinc
cell. The electrochemical stability window was established, and decomposition voltage values between 3.19 (20 °C) and 1.44 V
(150 °C) were estimated. Cyclic voltammetry studies using a Pt/(PEO)4ZnCl2/Pt cell indicated reversibility of the Zn2+/Zn couple at the electrode/electrolyte interface. Laboratory cells Zn(−)/(PEO)4ZnCl2/Nb2O5(+) were assembled and studied at 55 °C, under various discharge current densities. Results of cell discharge profiles, capacity
values, charge–discharge cycles and cell stabilities are reported. 相似文献
133.
Christelle Mouveaux Fabienne Hochart Joëlle Levalois-Mitjaville Roger De Jaeger 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1)
Abstract Multisite receptors containing more than two macrocyclic cavities. despite of the fact that their syntheses, most often, require sophisticated pathways, arc of very high interest since they may allow new insights into ion channel transfer, ion conduction.[1] We report here a method which combine simple reactions, high yields (80%), with easily prepared starting reagents[2], of two new polymacrocyclic system, a tri-(r) and an hexamacrocyck(II). They were obtained by a condensation reaction between 4-formylbenzo-15-crown-5 (3 or 6 quiv, respectively) and phosphouihydrazide (1 equiv.) or hexahydrazide (1 equiv.) in tetrahydrofuran. 相似文献
134.
Trajectory planning is a well-known open-loop control strategy to minimize residual vibrations in point-to-point tasks of systems featuring mechanical flexibility. However, the major drawback of open-loop control is its limitation in coping with modeling uncertainty. In this paper a novel approach to trajectory planning based on LQR theory is proposed and applied to a single flexible link robot. To improve performance under parameter uncertainty the strategy is combined with collocated vibration control through piezoelectric actuation of the link. This combination raises the issue of the roles and the contribution of each actuator type to the overall performance of the maneuver. An actuator specialization is proposed where the joint controller is responsible for the gross vibrationless motion of the link, while the link actuators are expected to deal only with residual vibrations that may arise from modeling errors. Simulation and experimental results validate the trajectory planning methodology and the combination of the open-loop strategy with collocated vibration control. 相似文献
135.
Valentin Guillon Daniela Bauer Marc Fleury Marie-Christine Néel 《Transport in Porous Media》2014,101(2):251-267
We present a pore network model combined with a random walk algorithm allowing the simulation of molecular displacement distributions in porous media as measured by NMR. A particular feature of this technique is the ability to probe the time evolution of these distributions. The objective is to predict the displacement behaviour for time intervals larger than the experimental observation time and explore the asymptotic dispersion regime at long times. Starting from 3D micro-CT images, we computed the variance of displacement distributions of water molecules in a Fontainebleau sand and found very good agreement of the time evolution of the variance with experimental data, without fitting parameter. The model confirms a weak superdispersion in the asymptotic regime. In addition, we conclude that, since pore network models do not take into account small scale features of the porous medium (e.g., surface roughness and grain shape), the origin of the observed superdispersion is mainly due to the topology and geometry of the porous medium. 相似文献
136.
Maja Vončina Robert Tisu Jožef Medved 《Journal of Thermal Analysis and Calorimetry》2017,129(1):117-122
Since titanium metal first became a commercial reality in 1950, corrosion resistance has been an important consideration in its selection as an engineering structural material. Titanium has gained acceptance in many media where its corrosion resistance and engineering properties have provided the corrosion and design engineer with a reliable and economic material. Titanium, like any other metal, is subject to corrosion in environments of air, oxygen, moisture, and so on. In this work, high-temperature stability of Ti and various Ti-alloys (by ASTM standard) was investigated. The best results showed that for Ti-Gr.5 alloy, the oxidation at 800 °C was 3.39% and at 900 °C 8.35%. For the comparison, commercial pure Ti-alloys Ti-Gr.2 and Ti-Gr.37 containing Al were used, whereas the oxidation resistance was much worse. 相似文献
137.
Byoung-Kee Jo Hyun-Don Kim Chun-Hag Jang Ki-Won Song Jang-Oo Lee 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(11):2293-2310
Abstract Interpolymer complex formation between basic polypeptides, poly(L- proline) Form I [PLP(I)], Form II [PLP(II)] and poly-4-hydroxy-L-proline (PHLP), and acidic polypeptides, poly(L-glutamic acid) (PLGA), poly(D- glutamic acid) (PDGA) and poly(L-aspartic acid) (PLAA), has been studied in water-methanol (1:2 v/v) mixed-solvent by viscometry, potentiometry, light scattering and circular dichroism (CD) measurements. It has been found that polymer complexes between basic- and acidic- polypeptides are formed via hydrogen bonding with a stoichiometric ratio of basic/acidic polypeptides =1:2 (in unit mole ratio) and that PLP(II) forms polymer complex more favorably with PLGA than with PLAA, and the complex of PLP(II) with PLGA is also more favorable than the complex formation of PHLP with PLGA. In addition, the complex formation is highly dependent on the conformation, especially the optical structure of the component polymers, i.e., the stereoselective complexation is observed. The PLGA having a right-handed helix at pH 3.2 formed the complex favorably and quickly with left-handed helix PLP(II), whereas PDGA having a left-handed helix at pH 3.2 favorably formed the complex with right-handed helix PLP(I). 相似文献
138.
139.
Renata Longhini Traudi Klein Marcos Luciano Bruschi Waldir Veríssimo da Silva Jr Juliana Rodrigues Norberto Peporine Lopes João Carlos Palazzo de Mello 《Journal of separation science》2013,36(7):1247-1254
The phenolic compounds are the main phytochemical constituents of the bark of Trichilia catigua and are commonly used for medicinal purposes. An HPLC method for the simultaneous quantification of phenolic compounds (procyanidin B2 (PB2), epicatechin (EPC), chinchonains Ia, Ib, IIa, IIb, catechin, and chrologenic acid) in T. catigua extract was developed and validated. A suitable chromatographic system was selected, which uses a gradient elution with methanol/ACN (75:25), and water both with 0.05% TFA, as mobile phase, column Luna, 280 nm, and flow 0.4 mL/min. Validation of the analytical method was based on the parameters: linearity, precision, LODs and LOQs, accuracy, robustness, and stability. The method showed linearity for PB2 and EPC, in the range 10–120 μg/mL with good correlation coefficients (>0.996). For precision, the repeatability ranged from 1.89 to 3.23%, and the values for accuracy for PB2 and EPC were 95 and 89%, respectively. The LODs and LOQs for PB2 were 1.36 and 4.12 μg/mL, and for EPC were 2.18 and 6.61 μg/mL, respectively. The method was robust under the conditions employed. The proposed method could be employed for quality assessment of T. catigua, as well as pharmaceutical products. 相似文献
140.
Molecular imprinted polymer is an artificial receptor made by imprinting molecules of a template in a polymer matrix followed by removing the template molecules via thorough washing to give the permanent template grooves. They show favored affinity to the template molecule compared to other molecules, and this property is the basic driving force for such diverse application of this techniques. Such techniques have been increasingly employed in a wide scope of applications such as chromatography, sample pretreatment, purification, catalysts, sensors, and drug delivery, etc., mostly in bioanalytical areas. A major part of them is related to development of new stationary phases and their application in chromatography and sample pretreatment. Embodiments of molecular imprinted polymer materials have been carried out in a variety of forms such as irregularly ground particles, regular spherical particles, nanoparticles, monoliths in a stainless steel or capillary column, open tubular layers in capillaries, surface attached thin layers, membranes, and composites, etc. There have been numerous review articles on molecular imprinted polymer issues. In this special review, the reviews in recent ca. 10 years will be categorized into several subgroups according to specified topics in separation science, and each review in each subgroup will be introduced in the order of date with brief summaries and comments on new developments and different scopes of prospects. Brief summaries of each categories and conclusive future perspectives are also given. 相似文献