全文获取类型
收费全文 | 10389篇 |
免费 | 1108篇 |
国内免费 | 205篇 |
专业分类
化学 | 8880篇 |
晶体学 | 12篇 |
力学 | 30篇 |
综合类 | 5篇 |
数学 | 27篇 |
物理学 | 2748篇 |
出版年
2023年 | 75篇 |
2022年 | 146篇 |
2021年 | 209篇 |
2020年 | 361篇 |
2019年 | 271篇 |
2018年 | 242篇 |
2017年 | 181篇 |
2016年 | 373篇 |
2015年 | 359篇 |
2014年 | 455篇 |
2013年 | 682篇 |
2012年 | 416篇 |
2011年 | 485篇 |
2010年 | 387篇 |
2009年 | 453篇 |
2008年 | 435篇 |
2007年 | 492篇 |
2006年 | 435篇 |
2005年 | 370篇 |
2004年 | 324篇 |
2003年 | 342篇 |
2002年 | 1213篇 |
2001年 | 199篇 |
2000年 | 150篇 |
1999年 | 164篇 |
1998年 | 160篇 |
1997年 | 93篇 |
1996年 | 103篇 |
1995年 | 116篇 |
1994年 | 56篇 |
1993年 | 54篇 |
1992年 | 42篇 |
1991年 | 41篇 |
1990年 | 29篇 |
1988年 | 24篇 |
1987年 | 24篇 |
1985年 | 92篇 |
1984年 | 117篇 |
1983年 | 106篇 |
1982年 | 149篇 |
1981年 | 113篇 |
1980年 | 97篇 |
1979年 | 100篇 |
1978年 | 106篇 |
1977年 | 144篇 |
1976年 | 118篇 |
1975年 | 129篇 |
1974年 | 165篇 |
1973年 | 133篇 |
1972年 | 82篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
Anita Sargent Thomas Loi Susannah Gal Omowunmi A. Sadik 《Journal of Electroanalytical Chemistry》1999,470(2):122
The modification of conducting polymer electrodes with antibodies (i.e. proteins) by means of electrochemical polymerization is a simple step that can be used to develop an immunological sensor. However, the electrochemical processes involved leading to the generation of analytical signals by the sensor have not been fully investigated. In this work, we report on the characterization of the interaction between an antigen, human serum albumin (HSA) and an antibody-immobilized polypyrrole electrode (such as anti-HSA) using cyclic voltammetry (CV) and impedance spectroscopy. This interaction was monitored using electrochemical impedance spectroscopy at three different potentials. The potentials correspond to the three redox states of the electroconducting polymer (i.e. reduced, doped and overoxidized states). Evidence from the CV experiments confirmed that there was a shift in the potential, which was found to be proportional to the concentration. Both the CV and the impedance experiments indicated that this potential-dependent shift could be attributed to antibody–antigen (Ab–Ag) binding. 相似文献
952.
Vladimir P. Zhdanov 《Surface science》2005,575(3):313-320
Heterogeneous catalytic reactions usually contain steps, e.g., adsorption, generating energy-rich (“hot”) precursors for other steps. With increasing the rate of energy relaxation one can observe a transition from the reaction regime dominated by “hot” precursors to conventional thermal activation. To illustrate this transition in detail and to show what may happen in various situations, I present an analytical model based on the Fokker-Planck equation for energy relaxation. 相似文献
953.
This presentation reports some novel examples of organic ring amination reactions via metal mediation. The organic transformations
are highly regioselective and can be controlled by the proper selection of the mediator complex. The two isomeric organic
ligands viz. HL1 and HL2 were isolated in their pure states by the removal of the metal ions. These were fully characterized. The ligand HL1 has lowpKa, 8.5. Upon deprotonation, it behaves as a potentialbis chelating N,N,N-donors. The coordination chemistry of the HL1 ligand involving some 3d-metal ions is described. Two unusual low-spin complexes of manganese(II) and iron(III) are reported. The ferric complex displayed a rhombic EPR while, the corresponding manganese compound showed a complex pattern
due to hyperfine coupling. All the complexes displayed large number of redox responses. A brief mention about the future projection
of this work is noted. 相似文献
954.
Luigi Anastasia 《Tetrahedron letters》2005,46(35):5803-5806
TiF4 has proven to be the Lewis acid of choice for promoting the biomimetic addition of 2-trimethylsilylmethyl-1,5-dienes to aliphatic aldehydes with concomitant cyclization. 1,3-cis-Disubstituted methylenecyclohexanes are thus produced in good yields and high diastereoselectivity. The reaction appears to proceed via a highly concerted mechanism involving a chair-like transition state. 相似文献
955.
S.P. Avdeyev V.A. Karnaukhov W.D. Kuznetsov L.A. Petrov V.K. Rodionov A.S. Zubkevich H. Oeschler O.V. Bochkarev L.V. Chulkov E.A. Kuzmin A. Budzanovski W. Karcz M. Janicki E. Norbeck A.S. Botvina W.A. Friedman W. Nörenberg G. Papp 《The European Physical Journal A - Hadrons and Nuclei》1998,3(1):75-83
Multiple emission of intermediate-mass fragments has been studied for the collisions p + Au at 2.16, 3.6 and 8.1 GeV with
the FASA setup. The mean IMF multiplicities for events with at least one IMF are equal to 1.7, 1.9 and 2.1 (±0.2) respectively.
The multiplicity, charge distributions and kinetic energy spectra of IMF are described in the framework of a intranuclear
cascade model followed by the statistical multifragmentation model. However, between the two parts of the calculation the
excitation energies and the residual masses and charges are modified to take into account the losses during expansion. The
results support a scenario of true thermal multifragmentation of a hot and expanded target spectator.
Received: 15 December 1997 / Revised version: 24 April 1998 相似文献
956.
957.
958.
A transient TGA study on oxygen permeation properties of perovskite-type ceramic membrane 总被引:4,自引:0,他引:4
This paper reports transient weight curves of La0.2Sr0.8CoO3−δ (LSC) membrane (crashed in small grains) subject to an instantaneous change of oxygen activity in the gas phase. When the surrounding gas changes between pure oxygen and helium, the LSC sample experiences a slow weight loss in the oxygen desorption period and a rapid weight gain in the oxygen absorption period due mainly to the difference in the driving force. The LSC sample undergoes phase transformation/chemical reaction with the surrounding gas changing between the pure oxygen and methane. A mathematical model considering surface reaction as the rate-limiting step is presented to describe the oxygen transport through the membrane material, and employed to obtain the surface reaction rate constants. A simple correlation between the oxygen permeation flux and rate constants measured by the transient thermogravimetric analysis (TGA) method is given. The oxygen permeation fluxes calculated from the data measured by the present TGA method are consistent with the data measured by the permeation method. The TGA method is found particularly useful for studying the surface reaction rates of oxygen permeation through thin mixed-conducting ceramic membranes. 相似文献
959.
A temperature-dependent integrated kinetics for the overall process of photosynthesis in green plants is discussed. The C4 plants are chosen and in these plants, the rate of photosynthesis does not depend on the partial pressure of O2. Using some basic concepts like chemical equilibrium or steady state approximation, a simplified scheme is developed for
both light and dark reactions. The light reaction rate per reaction center (R′
1) in thylakoid membrane is related to the rate of exciton transfer between chlorophyll neighbours and an expression is formulated
for the light reaction rate R′
1. A relation between R′
1 and the NADPH formation rate is established. The relation takes care of the survival probability of the membrane. The CO2 saturation probability in bundle sheath is also taken into consideration. The photochemical efficiency (ϕ) is expressed in terms of these probabilities. The rate of glucose production is given by R
glucose = (8/3)(R′
1
v
L
)ϕ(T)
g
(T) ([G3P]/[P
i]2
leaf)SS
Q
G3P→glucose where g is the activity quotient of the involved enzymes, and G3P represent glycealdehyde-3-phosphate in steady state. A Gaussian
distribution for temperature-dependence and a sigmoid function for de-activation are incorporated through the quotient g. In general, the probabilities are given by sigmoid curves. The corresponding parameters can be easily determined. The theoretically
determined temperature-dependence of photochemical efficiency and glucose production rate agree well with the experimental
ones, thereby validating the formalism. 相似文献
960.
The adsorption and decomposition of NO on Pd(110) 总被引:1,自引:0,他引:1
The sticking probability of nitric oxide (NO) on Pd(110) and the relative selectivity of the surface to nitrogen (N2) and nitrous oxide (N2O) production has been measured as a function of coverage and as a function of surface and gas temperatures using a molecular beam. It is found that, at low temperatures (<440 K), molecular adsorption occurs with an initial sticking probability of 0.40 ± 0.02, rising quickly to a maximum of about 0.48 ± 0.02 as coverage increases before falling towards saturation. Following adsorption at 170 K four distinct adsorption sites can be identified by subsequent TPD. Hence, if beaming occurs at a temperature above the TPD peak due to a given site, then that site cannot be populated and the saturation coverage is found to be reduced. At higher temperatures (440–650 K) the sticking probability is seen to decrease continuously as a function of coverage. At a given NO uptake, the sticking probability falls with temperature indicating that the rate of NO desorption is significant in this temperature range. In addition, dissociation occurs leading to the desorption of nitrogen and nitrous oxide leaving only oxygen adatoms on the surface. The oxygen adatoms poison further reaction but can be cleaned off, even at the lowest temperature at which dissociation occurs, by hydrogen or carbon monoxide. At the low temperature end of this range more nitrous oxide is produced than nitrogen but this ratio falls with temperature until, above 600 K, there is 100% selectivity to the production of nitrogen which we propose is due to the low lifetime of molecular NO on the surface. However, at such high temperatures, reaction only occurs on a few sites probably located at the few step edges present on the crystal. 相似文献