全文获取类型
收费全文 | 23481篇 |
免费 | 2210篇 |
国内免费 | 957篇 |
专业分类
电工技术 | 354篇 |
综合类 | 764篇 |
化学工业 | 5884篇 |
金属工艺 | 1726篇 |
机械仪表 | 5059篇 |
建筑科学 | 446篇 |
矿业工程 | 253篇 |
能源动力 | 362篇 |
轻工业 | 1368篇 |
水利工程 | 125篇 |
石油天然气 | 369篇 |
武器工业 | 132篇 |
无线电 | 2685篇 |
一般工业技术 | 5337篇 |
冶金工业 | 365篇 |
原子能技术 | 371篇 |
自动化技术 | 1048篇 |
出版年
2024年 | 47篇 |
2023年 | 289篇 |
2022年 | 556篇 |
2021年 | 706篇 |
2020年 | 667篇 |
2019年 | 680篇 |
2018年 | 611篇 |
2017年 | 839篇 |
2016年 | 876篇 |
2015年 | 910篇 |
2014年 | 1182篇 |
2013年 | 1442篇 |
2012年 | 1426篇 |
2011年 | 1877篇 |
2010年 | 1324篇 |
2009年 | 1350篇 |
2008年 | 1252篇 |
2007年 | 1154篇 |
2006年 | 1244篇 |
2005年 | 1024篇 |
2004年 | 941篇 |
2003年 | 947篇 |
2002年 | 779篇 |
2001年 | 559篇 |
2000年 | 482篇 |
1999年 | 473篇 |
1998年 | 414篇 |
1997年 | 400篇 |
1996年 | 298篇 |
1995年 | 245篇 |
1994年 | 226篇 |
1993年 | 204篇 |
1992年 | 167篇 |
1991年 | 167篇 |
1990年 | 145篇 |
1989年 | 111篇 |
1988年 | 122篇 |
1987年 | 77篇 |
1986年 | 88篇 |
1985年 | 107篇 |
1984年 | 86篇 |
1983年 | 70篇 |
1982年 | 52篇 |
1981年 | 10篇 |
1980年 | 4篇 |
1979年 | 9篇 |
1977年 | 2篇 |
1975年 | 2篇 |
1973年 | 2篇 |
1959年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
D. Knig S. Carvajal-Gonzalez A. M. Downs J. Vassy P. Rigaut 《Journal of microscopy》1991,161(3):405-433
Within the concept of point processes, a review is presented of quantities which can be used in studies of three-dimensional (3-D) aggregates of particles. Suitable characteristics and estimators are given for both unmarked and marked point processes. To demonstrate the feasibility of such quantitative approaches, an application in histology, dealing with 3-D arrangements of cell nuclei in rat liver, is described. Using a confocal scanning light microscope, 3-D images are recorded and image analysis used to obtain the coordinates of the centroid, together with the volume and DNA content, of each cell nucleus. Examples of results are given, using both unmarked and marked point processes. In the latter case, cell type, nuclear volume and ploidy group are suitable marks. 相似文献
72.
A vibrating Kelvin probe in form of a platinum wire loop is used to measure the surface potential Us on electron-irradiated free-floating metal and insulator specimens as a function of electron energy E. This allows an accurate measurement of the critical electron energy E2 for no charging. At energies below E2, the positive charging increases with decreasing energy to Us=2–5 eV at E=0.5 keV and switching off the collector bias of the Everhart-Thornley detector. A two-to threefold increase of Us is observed when the bias is switched on. For E > E2, the strong increase of a negative surface potential can be measured. Insulating films free-supported on a conductive substrate show a steep decrease to small positive and negative Us when the film thickness becomes lower than the electron range at a critical energy E3 > E2. At insulating specimen the temporal decrease of charging can be measured when the electron beam is switched off. 相似文献
73.
A cryo-specimen storage system for low-temperature scanning electron microscopy (LTSEM) specimens is described, which: liberates multi-specimen experiments from sampling restrictions imposed by the rate at which LTSEM specimens can be examined in the SEM; provides security against experiment loss resulting from breakdown of the SEM or cryo-system; enables collection of specimens in the field or in laboratories remote from the SEM laboratory; and facilitates international air transport of LTSEM specimens. The components of the system, which has a capacity of 98 stub-mounted specimens, are readily made in a laboratory workshop. The details of the design may be altered to suit particular specimen types or experimental approaches. 相似文献
74.
Preparation of polyimide-epoxy composites 总被引:2,自引:0,他引:2
Kevin Gaw Mitsutoshi Kikei Masa-aki Kakimoto Yoshio Imai 《Reactive and Functional Polymers》1996,30(1-3):85-91
The formation of a three dimensional network of crosslinked epoxy leads all unmodified epoxies to have inherent brittleness and relatively low degradation temperatures. Polyimides, on the other hand, are widely used for applications that require high degrees of flexibility and thermal resistance. Here, we have focused on the preparation of epoxy systems cured with polyamic acids instead of traditional amino-group-containing hardening agents. The cure behavior and potential reaction mechanisms of EPON 828 resin and polyamic acid mixtures were evaluated by DSC and TGA. Thermal analysis showed a complex reaction sequence taking place in the mixture and also determined the extent of reaction of the polyamic acid with itself and the competitive reaction of the polyamic acid with the epoxy. The compositions of the mixtures were varied to see the dependence of the cure behavior on component concentrations. Solutions of the two components did not phase separate and also phase separation was not apparent either optically or microscopically in the cured samples. This phase behavior was attributed to a unique in situ reaction. A novel solvent system for the polyamic acid precursor was also used. 相似文献
75.
Alena Orlov 《Materials Science and Engineering: A》1996,220(1-2):117-122
The present work studies the collection of experimental data from which Raj and Pharr (Mater. Sci. Eng., 81 (1986) 217) deduced a universal empirical dependence of the subgrain size on the applied stress. In accord with their result and some theoretical predictions the normalized subgrain size ds/b was ssumed to be proportional to G/σ (G is the shear modulus, b the Burgers vector length, σ the applied stress). The evaluated factor of proportionality K1, having the value within the interval from 0.76 to 180 in the inspected data sets, was discussed from the point of view of various factors which can influence the experimental data. 相似文献
76.
P. WEBSTER 《Journal of microscopy》1993,169(1):85-88
A novel method of using the LKB 7800 series Knifemaker to produce glass knives using a balanced break is described. The method produces knives of sufficient quality to section aldehyde-fixed, sucrose-cryoprotected, frozen biological material in a cooled cryochamber of an ultramicrotome. The modifications to the Knifemaker are minimal and, if required, the machine can be returned easily to its normal state after use. 相似文献
77.
The effect of particle distribution on damage formation in particulate reinforced metal matrix composites deformed in compression 总被引:1,自引:0,他引:1
P.B. Prangnell S.J. Barnes S.M. Roberts P.J. Withers 《Materials Science and Engineering: A》1996,220(1-2):41-56
Image analysis results are reported on the generation of damage in particulate reinforced metal matrix composites during compressive deformation. The technique allows the automated collection of data on the incidence of particle fracture and void formation in the matrix as a function of important microstructural parameters such as local particle volume fraction and particle size. There is a strong relationship between damage and the local volume fraction of the reinforcement proving that damage formation is accentuated in regions of particle clustering. With the SiC reinforced materials examined, there was observed to be a change in dominance of damage mechanism from particle fracture at low local volume fractions to void formation in the matrix within strongly clustered regions. The results are compared with finite element (FE) modelling of the compressive deformation of clustered particles using a simple cluster of equi-spaced particles. The FE results suggest that plastic flow is generally inhibited in clustered regions. In certain highly clustered configurations shielding is such that flow does not occur in the heart of the cluster even at high levels of average plastic strain. The modelling suggests that the change in dominance of damage mechanism is related to the dramatic increase in tensile hydrostatic stresses in the matrix with higher levels of particle clustering. 相似文献
78.
79.
The ElectroScan environmental scanning electron microscope (ESEM) enables wet samples to be observed by eliminating air but allowing water vapour into the sample chamber. However, evaporation from, and condensation on, the sample may occur during the pumpdown sequence used to reach this state, which means that the sample may not be in its natural state when viewed if due care is not taken. In this paper, the pumping system of the ESEM is described mathematically and expressions are derived for the evaporation and condensation. This treatment is then used to calculate the optimum pumpdown sequence. The importance of using the optimized procedure is illustrated by micrographs of fat emulsions. 相似文献
80.
介绍了用有限元方法计算半导体方块电阻四探针测试中二维点电流势场的模型并且证明了其正确性。由于有限元方法对边界没有限制,该方法为方块电阻测试中精确确定边界修正系数,更重要的是为微样品测试结构确定提供直接明了的理论依据。 相似文献