全文获取类型
收费全文 | 6240篇 |
免费 | 230篇 |
国内免费 | 37篇 |
专业分类
化学 | 3662篇 |
晶体学 | 57篇 |
力学 | 239篇 |
数学 | 1452篇 |
物理学 | 1097篇 |
出版年
2023年 | 53篇 |
2022年 | 124篇 |
2021年 | 162篇 |
2020年 | 147篇 |
2019年 | 183篇 |
2018年 | 187篇 |
2017年 | 174篇 |
2016年 | 248篇 |
2015年 | 198篇 |
2014年 | 262篇 |
2013年 | 429篇 |
2012年 | 394篇 |
2011年 | 410篇 |
2010年 | 224篇 |
2009年 | 247篇 |
2008年 | 303篇 |
2007年 | 266篇 |
2006年 | 211篇 |
2005年 | 180篇 |
2004年 | 176篇 |
2003年 | 140篇 |
2002年 | 145篇 |
2001年 | 95篇 |
2000年 | 76篇 |
1999年 | 57篇 |
1998年 | 47篇 |
1997年 | 52篇 |
1996年 | 67篇 |
1995年 | 57篇 |
1994年 | 48篇 |
1993年 | 59篇 |
1992年 | 57篇 |
1991年 | 50篇 |
1990年 | 55篇 |
1989年 | 33篇 |
1988年 | 51篇 |
1987年 | 50篇 |
1986年 | 52篇 |
1985年 | 65篇 |
1984年 | 53篇 |
1983年 | 54篇 |
1982年 | 56篇 |
1981年 | 49篇 |
1980年 | 55篇 |
1979年 | 60篇 |
1978年 | 53篇 |
1977年 | 43篇 |
1976年 | 57篇 |
1975年 | 34篇 |
1974年 | 27篇 |
排序方式: 共有6507条查询结果,搜索用时 109 毫秒
31.
32.
33.
Arielle Milliet Georges Sozzi Henri E. Audier 《Journal of mass spectrometry : JMS》1992,27(7):787-794
Radical cations derived from the ethers ROCH2CH2OR′ (R, R′ = H, CH3, C25) were studied, since β-distonic oxonium ions are often prepared from ionized ethers of glycol. The first step in the fragmentation is a 1,5-transfer of an α-hydrogen to oxygen of a terminal alkoxy group leading to a δ-distonic oxonium ion. This step is thermo-neutral and reversible in the ROCH2CH2OH radical cations and exothermic and irreversible in the dialkyl ether radical cations. Depending on R and R,′ these δ-distonic oxonium ions fragment by three reactions: the loss of an alcohol or a water molecule, the formation of a β-distonic oxonium ion ˙CH2CH2O(H)+R and a 1,4-H migration between carbon atoms. Competition between these processes is discussed. 相似文献
34.
35.
The passive control of bluff body flows using porous media is investigated by means of the penalization method. This method is used to create intermediate porous media between solid obstacles and the fluid in order to modify the boundary layer behaviour. The study covers a wide range of two‐dimensional flows from low transitional flow to fully established turbulence by direct numerical simulation of incompressible Navier–Stokes equations. A parametric study is performed to illustrate the effect of the porous layer permeability and thickness on the passive control. The numerical results reveal the ability of porous media to both regularize the flow and to reduce the drag forces up to 30%. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
36.
Thi Thi Nge Naruhito Hori Akio Takemura Hirokuni Ono Tsunehisa Kimura 《Journal of Polymer Science.Polymer Physics》2003,41(7):711-714
A high magnetic field of 5 T was used to fabricate a magnetically aligned, optically anisotropic, liquid‐crystalline chitin/poly(acrylic acid) composite. The aligned mesophase was fixed by photoinitiated free‐radical polymerization. From an examination of polarized optical micrographs and an X‐ray diffraction study, a high degree of orientation of 0.70 was observed for the composite with a higher liquid‐crystalline chitin concentration (10.70 wt %); the orientation was reduced with a decreased chitin concentration at a given acrylic acid concentration. The X‐ray data for the developed composite showed a uniplanar orientation for the chitin crystallites, with its molecular long axes perpendicular to the direction of the magnetic field. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 711–714, 2003 相似文献
37.
We consider the first initial boundary-value problem for strongly parabolic systems in an infinite cylinder with nonsmooth boundary. We establish conditions for the existence of generalized solutions, an estimate for this solutions, and an estimate for the derivative of the solution. 相似文献
38.
In this paper experimental study and mathematical modelling of newly designed vibro-impact moling rig are presented. The design is based on electro-mechanical interactions of a conductor with an oscillating magnetic field. The rig consists of a metal bar placed within a solenoid which is connected to an RLC circuit, and an obstacle block positioned nearby. Both the solenoid and the block are attached to a base board. Externally supplied alternating voltage causes the bar to oscillate and hit the block resulting in the forward motion of the base board mimicking a mole penetration through the soil. By varying the excitation voltage and the capacitance in the circuit, a variety of system responses can be obtained.In the paper the rig design and experimental procedure are explained in detail, and the mathematical modelling of the rig is described. Then the obtained coupled electro-mechanical equations of motion are integrated numerically, and a comparison between experimental results and numerical predictions is presented. 相似文献
39.
40.
I. M. Lavit Nguyen Viet Trung 《Journal of Applied Mechanics and Technical Physics》2008,49(3):491-499
The thermoelastoplastic fracture mechanics problem of a thick-walled cylinder subjected to internal pressure and a nonuniform
temperature field is solved by the method of elastic solutions combined with the finite-element method. The correctness of
the solution is provided by using the Barenblatt crack model, in which the stress and strain fields are regular. The elastoplastic
problem of a cracked cylinder subjected to internal pressure and a nonuniform temperature field are solved. The calculation
results are compared with available data.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 3, pp. 173–183, May–June, 2008. 相似文献