全文获取类型
收费全文 | 641911篇 |
免费 | 8113篇 |
国内免费 | 2044篇 |
专业分类
电工技术 | 11768篇 |
综合类 | 690篇 |
化学工业 | 97660篇 |
金属工艺 | 25601篇 |
机械仪表 | 20009篇 |
建筑科学 | 14555篇 |
矿业工程 | 3688篇 |
能源动力 | 17033篇 |
轻工业 | 51852篇 |
水利工程 | 6793篇 |
石油天然气 | 12959篇 |
武器工业 | 38篇 |
无线电 | 73395篇 |
一般工业技术 | 128244篇 |
冶金工业 | 120140篇 |
原子能技术 | 14314篇 |
自动化技术 | 53329篇 |
出版年
2021年 | 5798篇 |
2020年 | 4468篇 |
2019年 | 5478篇 |
2018年 | 9581篇 |
2017年 | 9395篇 |
2016年 | 10201篇 |
2015年 | 6659篇 |
2014年 | 10749篇 |
2013年 | 30199篇 |
2012年 | 17113篇 |
2011年 | 22904篇 |
2010年 | 18403篇 |
2009年 | 20823篇 |
2008年 | 21410篇 |
2007年 | 21019篇 |
2006年 | 18628篇 |
2005年 | 16873篇 |
2004年 | 15785篇 |
2003年 | 15616篇 |
2002年 | 15017篇 |
2001年 | 14772篇 |
2000年 | 13930篇 |
1999年 | 14446篇 |
1998年 | 36959篇 |
1997年 | 26100篇 |
1996年 | 20078篇 |
1995年 | 14994篇 |
1994年 | 13315篇 |
1993年 | 13188篇 |
1992年 | 9609篇 |
1991年 | 9167篇 |
1990年 | 9065篇 |
1989年 | 8796篇 |
1988年 | 8521篇 |
1987年 | 7301篇 |
1986年 | 7268篇 |
1985年 | 8278篇 |
1984年 | 7702篇 |
1983年 | 7019篇 |
1982年 | 6541篇 |
1981年 | 6689篇 |
1980年 | 6298篇 |
1979年 | 6121篇 |
1978年 | 6223篇 |
1977年 | 7170篇 |
1976年 | 9378篇 |
1975年 | 5456篇 |
1974年 | 5124篇 |
1973年 | 5278篇 |
1972年 | 4452篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
941.
942.
943.
G. MENEGHETTI P. LAZZARIN 《Fatigue & Fracture of Engineering Materials & Structures》2007,30(2):95-106
The paper presents an expression useful to estimate the notch stress intensity factor (NSIF) from finite element analyses carried out by using a mesh pattern with a constant element size. The evaluation of the NSIF from a numerical analysis of the local stress field usually requires very refined meshes and then large computational effort. The usefulness of the presented expression is that (i) only the elastic peak stress numerically evaluated at the V‐notch tip is needed and no longer the whole stress–distance set of data; (ii) the adopted meshes are rather coarse if compared to those necessary for the evaluation of the whole local stress field. The proposed expression needs the evaluation of a virtual V‐notch tip radius, i.e. the radius which would produce the same elastic peak stress than that calculated by FEM at the sharp V‐notch tip by means of a given mesh pattern. Once such a radius has been theoretically determined for a given geometry, the expression can be applied in a wide range of notch depths and opening angles. 相似文献
944.
L. T. MO M. HUURMAN S. P. WU A. A. A. MOLENAAR 《Fatigue & Fracture of Engineering Materials & Structures》2007,30(9):823-831
Tensile fatigue behaviours of bitumen–stone adhesion were investigated using a dynamic mechanics analyser under stress‐controlled mode at two temperatures of 5 and 25°C and various controlled‐stress levels. Failure characteristics including interfacial failure and cohesive failure were examined using image analysis of fracture surfaces. Finite‐element analysis on stress distributions was conducted under different temperatures, film thickness and interfacial bonding conditions. A Coulomb–Mohr like criterion in combination with shear and normal stresses is proposed to deal with the extreme thin adhesive layer, which can be further simplified into an adhesive zone without significant loss of accuracy for stress analysis. 相似文献
945.
Nicolas Clauvelin Basile Audoly Sébastien Neukirch 《Scientific Modeling and Simulation》2007,14(1):95-101
The DNA molecule is modeled as an elastic rod with bending and twisting rigidities, subjected to external tension and twist applied at one end, the other end being clamped. We study the plectonemic equilibrium of such a rod, taking into account the impenetrability constraint. Numerical solutions of this boundary value problem have previously shown that purely elastic models can reproduce the supercoiling response of the DNA molecule. Using a variational approach, we derive analytical formulae for the elastic response of the filament, and extend former numerical results. 相似文献
946.
The Modified Embedded Atom Method model for Pu metal is revised so that it more accurately captures the behavior of the Ziegler-Biersack-Littmark
model of ion-ion interactions. Two revision are tested with somewhat different stiffnesses in the 2-1000 eV range. The revised
models show higher damage levels at 20 KeV than an earlier model, suggesting that the behavior of the models above 100 eV
is dominating damage production, at least in the earlier stages of the cascade.
Work was performed at Los Alamos National Laboratory under the auspices of the US Department of Energy, under contract DE-AC52-06NA25396. 相似文献
947.
948.
This paper investigates the effect of chelating agents on the bioavailability of Fe and Cu during anaerobic digestion. The results on metal speciation and methane production in anaerobic serum bottles showed that biomass was able to grow in the presence of citrate 1?mM and nitrilotriacetic acid (NTA) 1?mM, suggesting that the binding sites at the cell surface competed efficiently for the metals with the chelating agents added. The presence of free ethylenediaminetetraacetic acid 1?mM inhibited methanogenesis, and this seemed to be related to a loss in metal uptake capacity. Although the addition of soluble microbial products (SMP) did not change metal distribution in anaerobic systems, it caused an increase in the rate of methane production, and it is believed that direct uptake of Cu-SMP complexes was responsible for this increase. The best protection against Cu toxicity occurred when stoichiometric amounts of NTA, which should complex and solubilize most of the Cu, was added, and it is likely that NTA prevented lethal concentrations of Cu from being adsorbed onto the cell and hence internalized. 相似文献
949.
950.