全文获取类型
收费全文 | 85007篇 |
免费 | 615篇 |
国内免费 | 435篇 |
专业分类
化学 | 28883篇 |
晶体学 | 822篇 |
力学 | 6955篇 |
数学 | 33375篇 |
物理学 | 16022篇 |
出版年
2023年 | 47篇 |
2022年 | 52篇 |
2021年 | 169篇 |
2020年 | 157篇 |
2019年 | 168篇 |
2018年 | 10512篇 |
2017年 | 10318篇 |
2016年 | 6302篇 |
2015年 | 1073篇 |
2014年 | 525篇 |
2013年 | 757篇 |
2012年 | 4260篇 |
2011年 | 10993篇 |
2010年 | 5953篇 |
2009年 | 6355篇 |
2008年 | 7056篇 |
2007年 | 9172篇 |
2006年 | 700篇 |
2005年 | 1697篇 |
2004年 | 1857篇 |
2003年 | 2222篇 |
2002年 | 1239篇 |
2001年 | 323篇 |
2000年 | 343篇 |
1999年 | 195篇 |
1998年 | 250篇 |
1997年 | 216篇 |
1996年 | 288篇 |
1995年 | 169篇 |
1994年 | 149篇 |
1993年 | 147篇 |
1992年 | 105篇 |
1991年 | 106篇 |
1990年 | 103篇 |
1989年 | 105篇 |
1988年 | 97篇 |
1987年 | 97篇 |
1986年 | 86篇 |
1985年 | 90篇 |
1984年 | 104篇 |
1983年 | 75篇 |
1982年 | 86篇 |
1981年 | 69篇 |
1980年 | 86篇 |
1979年 | 73篇 |
1978年 | 64篇 |
1977年 | 46篇 |
1914年 | 46篇 |
1909年 | 41篇 |
1908年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
72.
S. V. Panin I. V. Vlasov V. P. Sergeev B. B. Ovechkin P. O. Marushchak Sunder Ramasubbu P. S. Lyubutin V. V. Titkov 《Physical Mesomechanics》2015,18(3):261-272
The structure and properties of 12Cr1MoV steel irradiated with a zirconium ion beam were studied by optical microscopy, scanning electron microscopy, and micro- and nanoindentation. It is shown that the modification covers the entire cross-section of the irradiated specimens to a depth of 1 mm. The data on irradiation-induced structural changes are used to interpret the changes in mechanical properties of the irradiated specimens under static and cyclic loading. Particular attention is given to analysis of strain estimation by the digital image correlation method. 相似文献
73.
74.
Mihaly Mezei 《Journal of mathematical chemistry》2015,53(10):2184-2190
It is shown that the extent of deviation of a molecular shape from spherical can be characterized by comparing the distribution of the circular variances, a measure originally proposed to quantify angular spread, of the vectors from each atom to the rest of the molecule to the circular variance of a collection of atoms filling the unit sphere. Different measures for quantifying the difference between distribution are proposed and compared. 相似文献
75.
Trehalose is a naturally occurring disaccharide noted for its ability to preserve the biological function of proteins and cell membranes during periods of stress—such as water deprivation or extreme temperature—by stabilizing the conformations of the macromolecules within a glassy matrix. This phenomenon makes use of the propensity for trehalose to interact strongly with protein functional groups and solvent water molecules via hydrogen bonding. Previously, it has been shown that trehalose sugar glasses also support long-range charge transport in oxidation-reduction reactions occurring between spatially separated donors and acceptors. Here, through the use of bulk Arrhenius DC-conductivity measurements, we infer that this anomalously high carrier mobility is due to proton hopping along a hydrogen bonding network formed by sorbed “water wires,” a process known as the Grotthuss mechanism. Additionally, we find that the apparent activation energy of the conductivity depends non-monotonically on the bias voltage. The possibility is raised for novel photovoltaic devices based on the entrapment of photosynthetic proteins within these glasses. 相似文献
76.
Connecting free volume with shape memory properties in noncytotoxic gamma‐irradiated polycyclooctene 下载免费PDF全文
José María Cuevas Clarisse Ribeiro David Mérida José Manuel Laza José Ángel García José Luis Vilas Senentxu Lanceros‐Méndez Fernando Plazaola Luis Manuel León 《Journal of Polymer Science.Polymer Physics》2015,53(15):1080-1088
The free volume holes of a shape memory polymer have been analyzed considering that the empty space between molecules is necessary for the molecular motion, and the shape memory response is based on polymer segments acting as molecular switches through variable flexibility with temperature or other stimuli. Therefore, thermomechanical analysis (TMA) and positron annihilation lifetime spectroscopy (PALS) have been applied to analyze shape recovery and free volume hole sizes in gamma‐irradiated polycyclooctene (PCO) samples, as a noncytotoxic alternative to more conventional PCO crosslinked via peroxide for future applications in medicine. Thus, a first approach relating structure, free volume holes and shape memory properties in gamma‐irradiated PCO is presented. The results suggest that free volume holes caused by gamma irradiation in PCO samples facilitate the recovery process by improving movement of polymer chains and open possibilities for the design and control of the macroscopic response. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1080–1088 相似文献
77.
Edgardo Becerra Giovanny Aguilera-Durn Laura Berumen Antonio Romo-Mancillas Guadalupe García-Alcocer 《Molecules (Basel, Switzerland)》2021,26(4)
Multidrug resistance protein-4 (MRP4) belongs to the ABC transporter superfamily and promotes the transport of xenobiotics including drugs. A non-synonymous single nucleotide polymorphisms (nsSNPs) in the ABCC4 gene can promote changes in the structure and function of MRP4. In this work, the interaction of certain endogen substrates, drug substrates, and inhibitors with wild type-MRP4 (WT-MRP4) and its variants G187W and Y556C were studied to determine differences in the intermolecular interactions and affinity related to SNPs using protein threading modeling, molecular docking, all-atom, coarse grained, and umbrella sampling molecular dynamics simulations (AA-MDS and CG-MDS, respectively). The results showed that the three MRP4 structures had significantly different conformations at given sites, leading to differences in the docking scores (DS) and binding sites of three different groups of molecules. Folic acid (FA) had the highest variation in DS on G187W concerning WT-MRP4. WT-MRP4, G187W, Y556C, and FA had different conformations through 25 ns AA-MD. Umbrella sampling simulations indicated that the Y556C-FA complex was the most stable one with or without ATP. In Y556C, the cyclic adenosine monophosphate (cAMP) and ceefourin-1 binding sites are located out of the entrance of the inner cavity, which suggests that both cAMP and ceefourin-1 may not be transported. The binding site for cAMP and ceefourin-1 is quite similar and the affinity (binding energy) of ceefourin-1 to WT-MRP4, G187W, and Y556C is greater than the affinity of cAMP, which may suggest that ceefourin-1 works as a competitive inhibitor. In conclusion, the nsSNPs G187W and Y556C lead to changes in protein conformation, which modifies the ligand binding site, DS, and binding energy. 相似文献
78.
Fernando Bento Cunha Karina Torres Pomini Ana Maria de Guzzi Plepis Virgínia da Conceio Amaro Martins Eduardo Gomes Machado Renato de Moraes Marcelo de Azevedo e Souza Munhoz Michela Vanessa Ribeiro Machado Marco Antonio Hungaro Duarte Murilo Priori Alcalde Daniela Vieira Buchaim Rogrio Leone Buchaim Victor Augusto Ramos Fernandes Eliana de Souza Bastos Mazuqueli Pereira Andr Antonio Pelegrine Marcelo Rodrigues da Cunha 《Molecules (Basel, Switzerland)》2021,26(6)
Autologous bone grafts, used mainly in extensive bone loss, are considered the gold standard treatment in regenerative medicine, but still have limitations mainly in relation to the amount of bone available, donor area, morbidity and creation of additional surgical area. This fact encourages tissue engineering in relation to the need to develop new biomaterials, from sources other than the individual himself. Therefore, the present study aimed to investigate the effects of an elastin and collagen matrix on the bone repair process in critical size defects in rat calvaria. The animals (Wistar rats, n = 30) were submitted to a surgical procedure to create the bone defect and were divided into three groups: Control Group (CG, n = 10), defects filled with blood clot; E24/37 Group (E24/37, n = 10), defects filled with bovine elastin matrix hydrolyzed for 24 h at 37 °C and C24/25 Group (C24/25, n = 10), defects filled with porcine collagen matrix hydrolyzed for 24 h at 25 °C. Macroscopic and radiographic analyses demonstrated the absence of inflammatory signs and infection. Microtomographical 2D and 3D images showed centripetal bone growth and restricted margins of the bone defect. Histologically, the images confirmed the pattern of bone deposition at the margins of the remaining bone and without complete closure by bone tissue. In the morphometric analysis, the groups E24/37 and C24/25 (13.68 ± 1.44; 53.20 ± 4.47, respectively) showed statistically significant differences in relation to the CG (5.86 ± 2.87). It was concluded that the matrices used as scaffolds are biocompatible and increase the formation of new bone in a critical size defect, with greater formation in the polymer derived from the intestinal serous layer of porcine origin (C24/25). 相似文献
79.
正As one of the most important organic electronic building block, organic field-effect transistors(OFETs) have broad application prospects in the fields of flexible displays, electronic skins, and wearable devices. After more than 30 years of development, the performance(e.g., the carrier mobility)and processing technology of OFETs have made considerable progress [1,2]. However, 相似文献
80.
Guizellini Filipe Corrêa Franzin Bruno Trevizan da Silva Matheus Antonio Abra Luciana Mazotti Hojo Ossamu Pastre Iêda Aparecida Ribeiro Clóvis Augusto Paiva-Santos Carlos de Oliveira Fertonani Fernando Luis 《Journal of Thermal Analysis and Calorimetry》2021,143(1):47-60
Journal of Thermal Analysis and Calorimetry - The aim of this work is to synthesize and characterize a new structured silver–clay dried, calcined or sintered at different temperatures... 相似文献