全文获取类型
收费全文 | 2345篇 |
免费 | 103篇 |
国内免费 | 9篇 |
专业分类
化学 | 1955篇 |
晶体学 | 12篇 |
力学 | 25篇 |
数学 | 235篇 |
物理学 | 230篇 |
出版年
2023年 | 24篇 |
2022年 | 14篇 |
2021年 | 68篇 |
2020年 | 48篇 |
2019年 | 59篇 |
2018年 | 40篇 |
2017年 | 37篇 |
2016年 | 82篇 |
2015年 | 85篇 |
2014年 | 82篇 |
2013年 | 121篇 |
2012年 | 150篇 |
2011年 | 201篇 |
2010年 | 120篇 |
2009年 | 109篇 |
2008年 | 152篇 |
2007年 | 153篇 |
2006年 | 114篇 |
2005年 | 121篇 |
2004年 | 100篇 |
2003年 | 93篇 |
2002年 | 75篇 |
2001年 | 37篇 |
2000年 | 20篇 |
1999年 | 34篇 |
1998年 | 18篇 |
1997年 | 13篇 |
1996年 | 18篇 |
1995年 | 23篇 |
1994年 | 22篇 |
1993年 | 21篇 |
1992年 | 11篇 |
1991年 | 13篇 |
1990年 | 19篇 |
1989年 | 15篇 |
1988年 | 11篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 15篇 |
1984年 | 12篇 |
1983年 | 6篇 |
1982年 | 12篇 |
1980年 | 13篇 |
1979年 | 13篇 |
1978年 | 9篇 |
1975年 | 4篇 |
1974年 | 5篇 |
1973年 | 7篇 |
1967年 | 5篇 |
1966年 | 4篇 |
排序方式: 共有2457条查询结果,搜索用时 15 毫秒
951.
We study boundedness properties of a class ofmultiparameter paraproducts on the dual space of the dyadic Hardy space H d 1 (T N ), the dyadic product BMO space BMO d (T N ). For this, we introduce a notion of logarithmic mean oscillation on the polydisc. We also obtain a result on the boundedness of iterated commutators on BMO [0, 1] N ). 相似文献
952.
Gerwen Lammers Günter Roth Mathias Heck Roland Zengerle G. Sandra Tjabringa Elly M. Versteeg Theo Hafmans Ronnie Wismans Dieter P. Reinhardt Eugene T. P. Verwiel Patrick L. J. M. Zeeuwen Joost Schalkwijk Roland Brock Willeke F. Daamen Toin H. van Kuppevelt 《Macromolecular bioscience》2012,12(5):675-691
A papillary‐structured collagen fibril membrane is created, mimicking the 3D‐architecture of the human papillary dermis. Primary human keratinocytes cultured to confluency on papillar‐structured films are compared to keratinocytes cultured on flat membranes. Microscopical evaluation reveals the presence of morphologically distinct cells at the base of the papillar structures that are not observed on flat membranes. Gene expression microarrays and RT‐qPCR indicate that these cells are in a more proliferative/migrational state, whereas cells on flat membranes have a more differentiated expression profile. Immunohistochemical stainings confirm these results. In conclusion, specific collagen architecture can direct keratinocyte behavior, and this may be used to further improve skin regeneration.
953.
Dreisigacker S Latek D Bockelmann S Huss M Wieczorek H Filipek S Gohlke H Menche D Carlomagno T 《Journal of chemical information and modeling》2012,52(8):2265-2272
Vacuolar ATPases are a potential therapeutic target because of their involvement in a variety of severe diseases such as osteoporosis or cancer. Archazolide A (1) and related analogs have been previously identified as selective inhibitors of V-ATPases with potency down to the subnanomolar range. Herein we report on the determination of the ligand binding mode by a combination of molecular docking, molecular dynamics simulations, and biochemical experiments, resulting in a sound model for the inhibitory mechanism of this class of putative anticancer agents. The binding site of archazolides was confirmed to be located in the equatorial region of the membrane-embedded V(O)-rotor, as recently proposed on the basis of site-directed mutagenesis. Quantification of the bioactivity of a series of archazolide derivatives, together with the docking-derived binding mode of archazolides to the V-ATPase, revealed favorable ligand profiles, which can guide the development of a simplified archazolide analog with potential therapeutic relevance. 相似文献
954.
955.
956.
Eliane M.Z. Michielin Sibele R. Rosso Elton Franceschi Gustavo R. Borges Marcos L. Corazza J. Vladimir Oliveira Sandra R.S. Ferreira 《The Journal of chemical thermodynamics》2009,41(1):130-137
The aim of this work is to report phase equilibrium data for the binary systems (CO2 + α-humulene) and (CO2 + trans-caryophyllene), and for the ternary system (CO2 + α-humulene + trans-caryophyllene). Results from literature show that α-humulene and trans-caryophyllene are the main compounds responsible for the anti-inflammatory and anti-allergic characteristics attributed to the medicinal plant Cordia verbenacea D.C., hence giving importance to the phase behaviour investigation performed in this work. Phase equilibrium experiments were performed in a high-pressure, variable-volume view cell over the temperature range of T = (303 to 343) K and pressures up to 20 MPa. (Liquid + liquid) and (vapour + liquid + liquid) equilibrium were observed at T = 303 K, while (vapour + liquid) phase transitions were verified to occur from T = (313 to 343) K, for all systems studied. Thermodynamic modelling was performed using the Peng–Robinson equation of state and the classical quadratic mixing rules, with a satisfactory agreement between experimental and calculated values. 相似文献
957.
Tatjana Tomić Sandra Babić Nada Uzorinac Nasipak Maja Fabulić Ruszkowski Livijana Škrobonja Marija Kaštelan-Macan 《Journal of chromatography. A》2009,1216(18):3819-3824
Alkene content determinations in fluid catalytic cracking (FCC) liquid products were performed by means of normal-phase high-performance liquid chromatography (NP-HPLC) with diode array detection (UV/DAD). Separation of alkenes from aromatic hydrocarbons was performed on amino-modified silica gel column with n-heptane as mobile phase. The column has a little affinity to alkenes and saturated hydrocarbons and a pronounced affinity to aromatic compounds. The problem of alkenes and saturates co-elution on this column type was overcome with the detection system, UV/DAD, sensitive and selective to alkenes, while saturates are inactive in UV field. Total alkene content was determined as a sum of mono- and dialkene groups quantified by external standard method. Validation and verification of the developed method proved their applicability. The following criteria were used to validate the HPLC–DAD method: selectivity, linearity, precision, limits of detection and quantification. Alkene contents were quantified with the external standard method of wide calibration range, so both low and high alkene contents can be determined by the single calibration. Correlation coefficients were higher than 0.99. Precision was evaluated as repeatability and intermediary precision with relative standard deviations less than 5%. Some structural investigation of alkene groups was performed to confirm the assumption. Proposed method was compared with certified NMR method. Six commercial motor gasoline samples were analyzed by these two methods. Obtained results indicate good agreement between alkene content determined by both methods. The developed method was applied to the determination of alkene content in liquid FCC products in the boiling range from 70 °C to 190 °C. 相似文献
958.
Rino Morent Nathalie De Geyter Sandra Van Vlierberghe Els Vanderleyden Peter Dubruel Christophe Leys Etienne Schacht 《Plasma Chemistry and Plasma Processing》2009,29(2):103-117
The present work describes the plasma polymerisation of acrylic acid at atmospheric pressure. The influence of two operating
parameters (monomer concentration and discharge power) on the properties of the deposited films is investigated. Results show
that at a monomer concentration of 2.5 ppm and a discharge power of 9.5 W, the monomer is only slightly fragmented leading
to a high amount of carboxylic acid groups on the deposited films. In contrast, when monomer concentration is decreased or
discharge power increased, the incidence of monomer fragmentation processes is higher, leading to a lower amount of carboxylic
acid groups on the films. This behaviour can be explained by a higher energy amount available per monomer molecule at low
monomer concentrations and high discharge powers and a higher flux of positive ions attacking the surface at high discharge
powers. Taking into account these results, it can be concluded that the deposition parameters should be carefully selected
in order to preserve the stability of the monomer and thus obtain coatings with high carboxylic acid densities. 相似文献
959.
Sandra Rachmilovich‐Calis Naomi Meyerstein Prof. Dr. Dan Meyerstein Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(31):7717-7723
The reactions of .OH radicals with deoxyribose, DR, form five different DR. radicals, only one of which is transformed into malondialdehyde (MDA)‐like products. The radiolytic yield of the MDA‐like products increases with the increase in the DR concentration indicating that some of the initially formed “unproductive” radicals react with DR to form the “productive” radicals. The yield of the MDA‐like products also increases with the dose rate delivered to the solution suggesting that the formation of the MDA‐like products involves the reaction of the “productive” radicals with a radical. The addition of ascorbate, AH?, to the solution decreases the yield of the MDA‐like products as expected from the relative rates of the reaction of DR and AH? with .OH radicals. On the other hand the addition of the exogenous thiol, N‐acetylcysteine (NAC), to the solutions decreases the yield of the MDA‐like products considerably more than expected from the rate constants of the reaction with .OH radicals. The addition of the endogenous thiol, glutathione (GSH), to the solutions affects the yield of the MDA‐like products at low concentration less than expected and at “high” concentrations more than expected from the rate constant of the reaction. Addition of low concentration of AH? to solutions containing GSH increases considerably its antioxidant activity whereas addition of small concentrations of AH? to solutions containing NAC has no effect on its antioxidant activity. The results point out that the DR. radicals react differently with NAC and GSH and that the GS. and NAC. radicals react differently with DR, the GS. radical being considerably more active than the NAC. radical. Thus it has to be concluded that the relative activity of antioxidants depends also on the rate constants of many secondary reactions and on the concentrations of all the solutes present in the system. 相似文献
960.
The scrambling index of an n×n primitive matrix A is the smallest positive integer k such that Ak(At)k=J, where At denotes the transpose of A and J denotes the n×n all ones matrix. For an m×n Boolean matrix M, its Boolean rank b(M) is the smallest positive integer b such that M=AB for some m×b Boolean matrix A and b×n Boolean matrix B. In this paper, we give an upper bound on the scrambling index of an n×n primitive matrix M in terms of its Boolean rank b(M). Furthermore we characterize all primitive matrices that achieve the upper bound. 相似文献