全文获取类型
收费全文 | 486558篇 |
免费 | 7985篇 |
国内免费 | 1700篇 |
专业分类
电工技术 | 8139篇 |
综合类 | 414篇 |
化学工业 | 75796篇 |
金属工艺 | 19568篇 |
机械仪表 | 16446篇 |
建筑科学 | 11321篇 |
矿业工程 | 2723篇 |
能源动力 | 13227篇 |
轻工业 | 42546篇 |
水利工程 | 5015篇 |
石油天然气 | 9673篇 |
武器工业 | 28篇 |
无线电 | 59985篇 |
一般工业技术 | 96510篇 |
冶金工业 | 82745篇 |
原子能技术 | 10123篇 |
自动化技术 | 41984篇 |
出版年
2022年 | 3112篇 |
2021年 | 5040篇 |
2020年 | 3724篇 |
2019年 | 4446篇 |
2018年 | 7260篇 |
2017年 | 7308篇 |
2016年 | 8168篇 |
2015年 | 5410篇 |
2014年 | 8965篇 |
2013年 | 22903篇 |
2012年 | 14696篇 |
2011年 | 19497篇 |
2010年 | 15318篇 |
2009年 | 16958篇 |
2008年 | 17233篇 |
2007年 | 16654篇 |
2006年 | 14951篇 |
2005年 | 13521篇 |
2004年 | 12741篇 |
2003年 | 12389篇 |
2002年 | 11788篇 |
2001年 | 11890篇 |
2000年 | 10890篇 |
1999年 | 11395篇 |
1998年 | 27018篇 |
1997年 | 18844篇 |
1996年 | 14391篇 |
1995年 | 10968篇 |
1994年 | 9466篇 |
1993年 | 9546篇 |
1992年 | 7012篇 |
1991年 | 6758篇 |
1990年 | 6457篇 |
1989年 | 6289篇 |
1988年 | 6123篇 |
1987年 | 5114篇 |
1986年 | 5077篇 |
1985年 | 5945篇 |
1984年 | 5428篇 |
1983年 | 5020篇 |
1982年 | 4608篇 |
1981年 | 4598篇 |
1980年 | 4478篇 |
1979年 | 4340篇 |
1978年 | 4206篇 |
1977年 | 4630篇 |
1976年 | 5624篇 |
1975年 | 3742篇 |
1974年 | 3510篇 |
1973年 | 3671篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
C Perka K Lindenhayn HH Heilmann M Sittinger M Muschik 《Canadian Metallurgical Quarterly》1996,134(6):562-572
Full thickness defects (diameter 1,7 mm; depth 2,5 mm) were created mechanically in articular cartilage and subchondral bone of the condyles of tibiotarsal joints of 9-month old chickens. This full-thickness defects were repaired with cultured allogenic embryonic chick epiphyseal chondrocytes from the tibiae and femura of 10-days-old chicken embryos. The cells were embedded in a collagen-fibrinogen-matrix. Controls were similarly operated, but received either no treatment or implants the delivery substance only. Healing of the defects was observed macroscopically, histologically, histochemically and histomorphometrically after 3, 12 and 24 weeks. This graft was successfully transplanted in mechanically induced defects in 80%. The resulting hyaline cartilage was structurally reorganized according to the host pattern and under the influence of environmental conditions. The articular zone preserved it's cartilaginous phenotype, whereas the subchondral regions were transformed into bone. 12 weeks after the operation the defects in the experimental group were completely filled. In all instances in this group, there was an initial extreme increase of mitotic rate and cell number. After 24 weeks normal and subnormal values were founded. The defects in the control groups healed with fibrocartilage. Our results showed, that only the defects in the experimental group were completely filled with reparative hyaline cartilage tissue. In the present study the mixture of cultured allogenic embryonic chondrocytes and a collagen-fibrinogen-matrix was used successfully as a transplant for repairing defects in articular cartilage of chickens. Thus allogenic transplantation of cultured embryonal chondrocytes appears to be one of the most promising methods for the restoration of articular cartilage. 相似文献
993.
Summary The potential of the micro-Fourier Transform Raman tool in examining specific localized regions in polymeric materials with some degree of fluorescence when analyzed by conventional Raman spectroscopy is examined. Analysis of characteristic bands of the vibrational spectra obtained in a small area damaged by a visible and NIR laser beam in commercial Polyethylene Terephthalate (PET) shows a different conformer ratio than that observed in a non irradiated zone. 相似文献
994.
995.
N Kayansayan 《International Journal of Refrigeration》1996,19(3):197-207
The paper describes an effectiveness-NTU design method of bayonet-tube evaporators and condensers. Including the effect of the wall superheat on the shell-side film coefficient, and using an energy balance on the tube, differential equations for the steady-state fluid temperatures are formulated. Because of the nonlinear nature of the governing equations, the fourth-order Runge-Kutta method is employed to the solution of the finite difference equations. The results are iterated with the combination of integration techniques. An upper bound to the numerical error being ±5% the fluid temperature distribution as well as the exchanger effectiveness are determined, and presented as a function of the Hurd number, the number of heat transfer units and the flow arrangement. For flow entering through the inner tube, the temperature distribution displays the occurrence of a minimum at a point other than the tube-tip of the exchanger. In an extension of the analysis, an effort is made to illustrate the deviation of the results obtained by uniform film coefficient from the present study, and the differences are outlined. 相似文献
996.
997.
When a heterogeneous elastic material is represented by an effective homogeneous elastic solid, average stress and strain fields are used. The meaning of the J-integral in the effective homogeneous solid is investigated. A periodically layered medium is considered. The relation between the J-integrals in the original layered medium and the effective medium is derived. 相似文献
998.
Comparison of Markov model and fault tree approach in determining initiating event frequency for systems with two train configurations 总被引:1,自引:0,他引:1
This study explores the use of Markov models in some areas of systems analysis in which time evolution of the system may be a significant factor in influencing the system reliability or availability. Comparisons are made between the Markov models and the time-averaged fault tree models for determining support system failure initiating event frequency in a nuclear power plant, for both power and shutdown conditions. Factors affecting consistency between the fault tree approach and the Markov model approach are studied for systems with common two train configurations. A correlation is developed to estimate the ratio between initiator frequencies through both approaches for a two parallel component system. Insights are developed as to when time averaged and simplified fault tree models support a good approximation to the more rigorous time-dependent Markov models. 相似文献
999.
C Serveau L Juliano P Bernard T Moreau R Mayer F Gauthier 《Canadian Metallurgical Quarterly》1994,76(2):153-158
A discontinuous borate/formate buffer system is presented for horizontal polyacrylamide gel electrophoresis of DNA fragments. The resolution potential of the system could be altered by changing the total monomer concentration (5-9%T), the concentration of the crosslinker piperazine diacrylamide (2-5%CPDA), as well as the concentration of formate in the gel (40-120 mM), the leading ion of the buffer system. The separation of DNA fragments would be improved by increasing the migration distance from 22 to 28 cm. This discontinuous polyacrylamide gel electrophoresis system proved highly reproducible. 相似文献
1000.
N. R. Bohidar Norman R. Bohidar Nicholas R. Bohidar 《Drug development and industrial pharmacy》1994,20(5):815-839
A discordant observation is a data point whose value is drastically different from that of the rest of the members in the data set. In the context of content uniformity experiments, however, a discordant observation arises in two ways: (i) when the value of an observation is markedly distant from that of the other data points even though it is within the required compendial range, and (ii) when the value of an observation is outside the permissible compendial range. Several statistical tests for detecting one or more discordant observations are presented. Since discordancy distorts the symmetricity of the data, several tests of symmetricity are provided. Tests for detection of group discordancy induced by discordant samples are also included. The compendial requirements are explained in statistical terms. The impact of discordant observations on compendial compliance requirements is assessed. The statistical basis of the construction of compendial limits as well as the assumptions implicit in the construction is elaborated. The results of the statistical analysis of three content uniformity studies are appropriately interpreted. 相似文献