全文获取类型
收费全文 | 24695篇 |
免费 | 3894篇 |
国内免费 | 2044篇 |
专业分类
化学 | 5544篇 |
晶体学 | 64篇 |
力学 | 2935篇 |
综合类 | 624篇 |
数学 | 12067篇 |
物理学 | 9399篇 |
出版年
2024年 | 42篇 |
2023年 | 257篇 |
2022年 | 548篇 |
2021年 | 615篇 |
2020年 | 673篇 |
2019年 | 615篇 |
2018年 | 608篇 |
2017年 | 877篇 |
2016年 | 968篇 |
2015年 | 795篇 |
2014年 | 1307篇 |
2013年 | 1774篇 |
2012年 | 1341篇 |
2011年 | 1501篇 |
2010年 | 1329篇 |
2009年 | 1532篇 |
2008年 | 1699篇 |
2007年 | 1764篇 |
2006年 | 1463篇 |
2005年 | 1314篇 |
2004年 | 1251篇 |
2003年 | 1073篇 |
2002年 | 1028篇 |
2001年 | 838篇 |
2000年 | 738篇 |
1999年 | 704篇 |
1998年 | 612篇 |
1997年 | 547篇 |
1996年 | 447篇 |
1995年 | 424篇 |
1994年 | 280篇 |
1993年 | 258篇 |
1992年 | 183篇 |
1991年 | 221篇 |
1990年 | 149篇 |
1989年 | 95篇 |
1988年 | 126篇 |
1987年 | 92篇 |
1986年 | 72篇 |
1985年 | 85篇 |
1984年 | 66篇 |
1983年 | 42篇 |
1982年 | 44篇 |
1981年 | 50篇 |
1980年 | 40篇 |
1979年 | 38篇 |
1978年 | 24篇 |
1977年 | 20篇 |
1976年 | 16篇 |
1974年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Harald Høiland 《Journal of solution chemistry》1977,6(5):291-297
The isentropic coefficients of compressibility of the homologous series of alcohols and diols R
n
CH2OH (n=2–6), CH3CHOHR
n
(n=1–5), 1,2-propanediol, 1,3- 1,4- and 2,3-butanediol, 1,5-pentanediol, and 1,7-heptanediol dissolved in propylene carbonate have been measured at 25°C. Isentropic partial molal compressibilities and group partial molal compressibilities at infinite dilution have been evaluated. The isentropic partial molal compressibilities of these alcohols and diols have been compared with the corresponding values in water. This comparison shows that the values in propylene carbonate are higher than in water by a factor of 10 due to an increased compressibility of the solvation sheath around nonpolar groups in PC. 相似文献
32.
A model of disordered medium is proposed to describe the monolayer adsorption isotherm on heterogeneous surfaces. The model
is based on the premise that adsorption medium consists of separate regions in each of which there is a permanent local equilibrium
constant, the character of the changes of which is determined by the disorder parameter of the medium.
__________
Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 3, pp. 189–193, May–June, 2006. 相似文献
33.
Nan Zhou 《Mikrochimica acta》1991,105(4-6):159-162
Proposed in this paper is an improved method for removal of tin as the matrix element by volatilization in an anhydrous medium as mixed halides of different composition. Any one of them boils at a lower temperature than SnBr4. This ternary system enhances the eventual recombination of temporarily dissociated species to volatile ones, thus making the process quicker and more efficient. The presence of 2 mg of Pb(II) suffices to prevent Bi(III) from loss due to volatilization. 相似文献
34.
Matthias Schüler Thomas Kovar Hans Lischka Ron Shepard Robert J. Harrison 《Theoretical chemistry accounts》1993,84(6):489-509
Summary In this work a parallel implementation of the COLUMBUS MRSDCI program system is presented. A coarse grain parallelization approach using message passing via the portable toolkit TCGMSG is used. The program is very well portable and runs on shared memory machines like the Cray Y-MP, Alliant FX/2800 or Convex C2 and on distributed memory machines like the iPSC/860. Further implementations on a network of workstations and on the Intel Touchstone Delta are in progress. Overall, results are quite satisfactory considering the complexity and the prodigious requirements, especially the I/O bandwidth, of MRCI programs in general. For our largest test case we obtain a speedup of a factor of 7.2 on an eight processor Cray Y-MP for that section of the program (hamiltonian matrix times trial vector product) which has been parallelized. The speedup for one complete diagonalization iteration amounts to 5.9. An absolute speed close to 1 GFLOPS is found. Results for the iPSC/860 show that ordinary disk I/O is certainly not sufficient in order to guarantee a satisfactory performance. As a solution for that problem, the implementation of a fully asynchronous distributed-memory model for certain data files is in preparation.
On leave from: Bereich Informatik, Universität Leipzig, Augustusplatz 10/11, O-7010 Leipzig, Germany 相似文献
35.
Groshev gave a characterization of the union of domains of partial attraction of all Poisson laws in 1941. His classical condition is expressed by the underlying distribution function and disguises the role of the mean of the attracting distribution. In the present paper we start out from results of the recent probabilistic approach and derive characterizations for any fixed >0 in terms of the underlying quantile function. The approach identifies the portion of the sample that contributes the limiting Poisson behavior of the sum, delineates the effect of extreme values, and leads to necessary and sufficient conditions all involving . It turns out that the limiting Poisson distributions arise in two qualitatively different ways depending upon whether >1 or <1. A concrete construction, illustrating all the results, also shows that in the boundary case when =1 both possibilities may occur. 相似文献
36.
The partial molal volumes of Li+, Na+, K+, Rb+, Cs+, Cl–, Br–, I–, and NO
3
-
in DMSO at 25°C have been determined from ultrasonic vibration potential data and density data for solutions of uni-univalent electrolytes. Hepler's semiemprirical equation has been used to split ionic partial molal volumes into geometric and electrostrictive contributions. The results obtained in this work confirm the conclusion of our previous studies, namely, that the contribution of electrostriction is essentially determined by the properties of that layer of atoms, 0.3 to 0.4 nm thick, in contact with the ion and by the degree of steric hindrance of the poles of the dipole of the solvent molecule. On the other hand, the geometric contribution depends on the size of the solvent molecule and also on the arrangement of the solvent molecules about the ions. It is shown that the geometric contribution to the partial molal volume of ions is largely increased when ions cannot come close enough to the poles of the solvent-molecule dipole, owing to steric hindrance. 相似文献
37.
Aqueous polymerization of acrylonitrile (M) initiated by the Ce(IV)-glucose (R) redox system has been studied under nitrogen in the temperature range of 30–40 °C. The rate of polymerization (Rp) is proportional to [M]2, [R] and inversely proportional to [Ce(IV)]. The rate of ceric ion disappearance is proportional to [R] and [Ce(IV)]. The end group in the polymer is characterised by IR spectra. A suitable kinetic scheme has been proposed and explained in the light of these experimental findings. 相似文献
38.
Solid solutions NaCl—CdCl2 were studied in an interval of CdCl2 concentrations of 0.05—3 mol.% by Raman spectroscopy. The molecular form Na2CdCl4 decomposes: Na2CdCl4 2Na+ + Cd2+ + 2Cl2
– + 2e–; 2Na + 2e– 2Na0. Free sodium atoms form color centers of crystal (F centers) in the region of jumpwise changing the partition coefficient of CdCl2 in NaCl (K jump). 相似文献
39.
C. Marhag H. Said P. Satre C. Favotto J. Rogez 《Journal of Thermal Analysis and Calorimetry》2003,74(1):275-285
Study of solid-liquid phase diagram of LiPO3-Pb(PO3)2 binary system, in certain calcination conditions, shows the existence of several metastable phasis. When heated at a temperature
of 723 K the binary mixtures lead uncompletely to a defined compound Pb2Li(PO3). On heating these ternary solid mixtures, three eutectic reactions have been observed: LiPO3+Pb(PO3)2→Liquid at a temperature of 793 K(1) LiPO3+Pb2Li(PO3)5→Liquid at a temperature of 843 K (2) Pb2Li(PO3)5+Pb(PO3)2→Liquid at a temperature of 891 K (3) The metastable liquid phase appears in the system at temperature of 793 K. DTA experiments
performed on the binary LiPO3-Pb(PO3)2 mixtures, show a superposition of two diagrams. The first one is metastable and the second represents the stable equilibrium
phase diagram. Measurements of liquid enthalpy of binary LiPO3-Pb(PO3)2 system at temperature of 979.65 K were reported. The corresponding values were very small and so the binary system can be
considered as athermal. Assuming an ideal behaviour, the liquidus curves in the metastable diagram were calculated and the
eutectic reaction (LiPO3-Pb(PO3)2→Liquid) was confirmed at 793 K.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
40.