全文获取类型
收费全文 | 100028篇 |
免费 | 9592篇 |
国内免费 | 9506篇 |
专业分类
化学 | 31700篇 |
晶体学 | 385篇 |
力学 | 9556篇 |
综合类 | 1594篇 |
数学 | 42774篇 |
物理学 | 33117篇 |
出版年
2024年 | 159篇 |
2023年 | 910篇 |
2022年 | 1615篇 |
2021年 | 1842篇 |
2020年 | 2325篇 |
2019年 | 2523篇 |
2018年 | 2139篇 |
2017年 | 2356篇 |
2016年 | 2670篇 |
2015年 | 2489篇 |
2014年 | 3848篇 |
2013年 | 7064篇 |
2012年 | 4217篇 |
2011年 | 5023篇 |
2010年 | 4523篇 |
2009年 | 5776篇 |
2008年 | 6379篇 |
2007年 | 6500篇 |
2006年 | 5939篇 |
2005年 | 5344篇 |
2004年 | 4676篇 |
2003年 | 4701篇 |
2002年 | 4302篇 |
2001年 | 3512篇 |
2000年 | 3426篇 |
1999年 | 3119篇 |
1998年 | 2878篇 |
1997年 | 2366篇 |
1996年 | 2052篇 |
1995年 | 1807篇 |
1994年 | 1654篇 |
1993年 | 1333篇 |
1992年 | 1312篇 |
1991年 | 1051篇 |
1990年 | 861篇 |
1989年 | 713篇 |
1988年 | 650篇 |
1987年 | 532篇 |
1986年 | 469篇 |
1985年 | 542篇 |
1984年 | 520篇 |
1983年 | 257篇 |
1982年 | 431篇 |
1981年 | 465篇 |
1980年 | 353篇 |
1979年 | 348篇 |
1978年 | 253篇 |
1977年 | 233篇 |
1976年 | 178篇 |
1973年 | 125篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
We study the transversal spin–spin correlations in the non-equilibrium steady state of the XY chain constructed by coupling a finite cutout of the chain to the two infinite parts to its left and right acting as thermal reservoirs at different temperatures. We prove that the spatial decay of these correlations is at least exponentially fast. 相似文献
992.
This paper is concerned with the spectral analysis of a one-velocity transport operator with Maxwell boundary condition in
L
1-space. After a detailed spectral analysis it is shown that the associated Cauchy problem is governed by a C
0-semigroup. Next, we discuss the irreducibility of the transport semigroup. In particular, we show that the transport semigroup
is irreducible. Finally, a spectral decomposition of the solutions into an asymptotic term and a transient one which will
be estimated for smooth initial data is given. 相似文献
993.
The constitutive behavior of porous materials (including the yield loci, the void growth rate, the macro stress-strain relation
and the strain to localization instability) is examined based on the lower bound approach proposed by the present authors.
These results are then compared with the experimental and the finite element results as well as those predicted by Gurson's
equations. Emphasis is placed on approaching the real behavior from the upper and the lower bound analysis. Calculation is
also made on the influence of void nucleation on the critical strain to instability and a modified strain-controlled nucleation
criterion is proposed. Finally the instability and fracture of AISI4340 steel in plane strain tension is examined and comparison
is made between theoretical and experimental results. 相似文献
994.
This paper develops a mathematical model of the ring-spinning process that takes into account its non-stationary nature. A complex system of differential equations is obtained, which from a mathematical point of view constitutes a ‘free-boundary’ problem. Its solution involves definition of suitable boundary conditions related to the mechanical characteristics of the process and of the spinning machine itself. The boundary conditions which determine the solution are pointed out. A numerical solution of the system of differential equations can be obtained by the Finite-Segments method, as shown in an example. 相似文献
995.
The problem treated in this paper concerns calculating the evolution of the pressure in a single-phase, slightly compressible fluid in a porous medium consisting of communicating layers. The fluid is produced through a point sink located on the side of an otherwise sealed cylindrical wellbore. This location of the sink causes the flow around the wellbore to be azimuthally asymmetric.The problem is solved through successive application of Laplace, finite Fourier and finite Hankel transforms. Although apparently straightforward, this approach leads to serious numerical difficulties. The published form of the inversion formula for the finite Hankel transform leads to inaccurate computation for the higher azimuthal modes even with 128 bit arithmetic. An alternative form is developed which enables accurate evaluation of the solution with the more practical 64 bit arithmetic. The technique for two-layer solution presented here can be directly extended to a problem with a larger number of communicating layers. This is the first instance of successful application of the finite Hankel transform to an azimuthally asymmetric diffusion problem. 相似文献
996.
997.
T. N. Sokolova V. R. Kartashov I. V. Timofeev Yu. K. Grishin N. S. Zefirov 《Russian Chemical Bulletin》1994,43(3):461-465
The dependence of the regiochemistry of the mercuration of bornylene on the nature of the mercurating reagent and on the solvent has been found. The structures of the intermediate and transition state in these reactions have been proposed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 501–505, March, 1994. 相似文献
998.
Sokolova T. N. Grishin Yu. K. Timofeev I. V. Kartashov V. R. 《Russian Chemical Bulletin》1994,43(6):1044-1047
Regiochemistry and stereochemistry of the addition of mercury salts to benzobarrelene and tetrafluorobenzobarrelene have been studied in acetic acid and methanol. The effect of the substrate structure on the regiochemistry of the reaction is discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1105–1108, June, 1994. 相似文献
999.
The thermal dehydration of copper(II) acetate hydrate has been studied between 353 and 406 K, over a range of humidities.
The dehydration is controlled by nucleation-and-growth kinetics at low temperatures, with an activation energy of 154 kJ·mol−1, which changes to contracting-disc kinetics at higher temperatures with a lower activation energy of 76 kJ·mol−1. Frequency factors have also been derived; the value for the high temperature process is low (107s−1) and that for the low temperature step is high (1017s−1). Optical microscopy has been used to clarify the bulk kinetics; there is evidence for a reactive layer at the surface of
the decomposing solid.
In celebration of the 60th birthday of Dr Andrew K. Galwey 相似文献
1000.
Polypropylenes of differing morphologies were examined by differential thermal analysis. The problems of reordering during
the programmed heating are discussed. Four potential procedures by which the reordering could be inhibited are considered,
and three of these are experimentally assessed. Their advantages and deficiencies are identified. Two pretreatments, an etching
and a crosslinking, are recognised as able to qualitatively characterise the initial morphology, with a preference for the
former. A test to identify the occurrence of reordering is identified.
In celebration of the 60th birthday of Dr. Andrew K. Galwey 相似文献