全文获取类型
收费全文 | 15410篇 |
免费 | 787篇 |
国内免费 | 600篇 |
专业分类
电工技术 | 511篇 |
技术理论 | 1篇 |
综合类 | 1589篇 |
化学工业 | 1967篇 |
金属工艺 | 379篇 |
机械仪表 | 868篇 |
建筑科学 | 2561篇 |
矿业工程 | 525篇 |
能源动力 | 1015篇 |
轻工业 | 864篇 |
水利工程 | 694篇 |
石油天然气 | 1076篇 |
武器工业 | 102篇 |
无线电 | 371篇 |
一般工业技术 | 1550篇 |
冶金工业 | 858篇 |
原子能技术 | 257篇 |
自动化技术 | 1609篇 |
出版年
2024年 | 40篇 |
2023年 | 138篇 |
2022年 | 277篇 |
2021年 | 320篇 |
2020年 | 342篇 |
2019年 | 312篇 |
2018年 | 301篇 |
2017年 | 341篇 |
2016年 | 443篇 |
2015年 | 489篇 |
2014年 | 972篇 |
2013年 | 947篇 |
2012年 | 929篇 |
2011年 | 1266篇 |
2010年 | 887篇 |
2009年 | 880篇 |
2008年 | 891篇 |
2007年 | 1033篇 |
2006年 | 977篇 |
2005年 | 835篇 |
2004年 | 795篇 |
2003年 | 702篇 |
2002年 | 549篇 |
2001年 | 433篇 |
2000年 | 337篇 |
1999年 | 274篇 |
1998年 | 204篇 |
1997年 | 162篇 |
1996年 | 163篇 |
1995年 | 115篇 |
1994年 | 72篇 |
1993年 | 78篇 |
1992年 | 57篇 |
1991年 | 47篇 |
1990年 | 35篇 |
1989年 | 19篇 |
1988年 | 20篇 |
1987年 | 13篇 |
1986年 | 11篇 |
1985年 | 12篇 |
1984年 | 14篇 |
1983年 | 11篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1979年 | 6篇 |
1977年 | 4篇 |
1963年 | 3篇 |
1957年 | 3篇 |
1956年 | 4篇 |
1955年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
A kind of complex additive mainly containing Al, Mg, F, and O was prepared. The synthetical performances of the property-modified prebaked anodes containing additives were tested in laboratory. On the basis of ideal testing results obtained, a large number of industrial prebaked property-modified anodes are prepared in a large-scale aluminum company. Further more, they are all used in 160 kA prebaked anode aluminum electrolysis cells. The statistic result show that, compared with common anodes, the property-modified ones enhance current by 11.6 kg per ton aluminum averagely. 相似文献
12.
13.
提出基于事例学习的目标规划问题,并进一步研究了建模思想的可行性和建模方法的可操作性。利用知识工程、机器学习理论,人工智能技术来存贮和运用专家的经验,实现了在虚拟环境中建筑结构设计、施工,设备的仿真试验,并可对初学者或尚无经验的设计、施工者进行培训学习。该项研究为目标规划问题开辟了基于事例学习的模型生成途径。 相似文献
14.
Takahiro Hoshino 《Computational statistics & data analysis》2008,52(3):1413-1429
The estimation of the differences among groups in observational studies is frequently inaccurate owing to a bias caused by differences in the distributions of covariates. In order to estimate the average treatment effects when the treatment variable is binary, Rosenbaum and Rubin [1983. The central role of the propensity score in observational studies for causal effects. Biometrika 70, 41-55] proposed an adjustment method for pre-treatment variables using propensity scores. Imbens [2000. The role of the propensity score in estimating dose-response functions. Biometrika 87, 706-710] extended the propensity score methodology for estimation of average treatment effects with multivalued treatments.However, these studies focused only on estimating the marginal mean structure. In many substantive sciences such as the biological and social sciences, a general estimation method is required to deal with more complex analyses other than regression, such as testing group differences on latent variables. For latent variable models, the EM algorithm or the traditional Monte Carlo methods are necessary. However, in propensity score adjustment, these methods cannot be used because the full distribution is not specified.In this paper, we propose a quasi-Bayesian estimation method for general parametric models that integrate out the distributions of covariates using propensity scores. Although the proposed Bayes estimates are shown to be consistent, they can be calculated by existing Markov chain Monte Carlo methods such as Gibbs sampler. The proposed method is useful to estimate parameters in latent variable models, while the previous methods were unable to provide valid estimates for complex models such as latent variable models.We also illustrated the procedure using the data obtained from the US National Longitudinal Survey of Children and Youth (NLSY1979-2002) for estimating the effect of maternal smoking during pregnancy on the development of the child's cognitive functioning. 相似文献
15.
16.
17.
A. Benhamida I. Djeran-Maigre H. Dumontet S. Smaoui 《International Journal of Rock Mechanics and Mining Sciences》2005,42(7-8):996-1005
The modelling of hydromechanical behavior of clayey sediments by homogenization theory is described. The rheological model of clays buried in depth requires a three-dimensional approach and laboratory experiments to quantify the model parameters. An iterative process which can be coupled to any homogenization method is used to model the porous media behavior. Hydromechanical compaction results from oedometric experiments are simulated with the proposed model. 相似文献
18.
Hitsman Brian; Borrelli Belinda; McChargue Dennis E.; Spring Bonnie; Niaura Raymond 《Canadian Metallurgical Quarterly》2003,71(4):657
The authors conducted a meta-analysis of published studies to (a) evaluate the premise that a history of major depression is associated with failure to quit smoking and (b) identify factors that moderate the relationship between history of depression and cessation outcome. Fifteen studies met the selection requirements and were coded for various study methodology and treatment characteristics. DSTAT was used to calculate individual study effect sizes, determine the mean effect size across studies. and test for moderator effects. No differences in either short-term (≤ 3 months) or long-term abstinence rates (≥ 6 months) were observed between smokers positive versus negative for history of depression. Lifetime history of major depression does not appear to be an independent risk factor for cessation failure in smoking cessation treatment. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
19.
Using meta-analysis, randomized experiments in education that either clearly did or clearly did not experience student attrition were examined for the baseline comparability of groups. Results from 35 studies suggested that after attrition, the observed measures of baseline comparability of groups did not differ more than would be expected given sampling error. The degree of either overall or differential attrition did not relate to baseline comparability, a finding that held under sensitivity analyses. Also, both overall and differential attrition rates were unrelated to posttest effect sizes. All of these analyses, however, lacked sufficient statistical power to detect small but potentially meaningful effects. Results suggest caution is warranted when applying quality scales and other blanket rules pertaining to attrition that are meant to either serve as inclusion-exclusion criteria or in scoring study quality. Much greater attention is needed to both the reporting of attrition in primary studies and to the development of conceptual and empirical models of the attrition process. These developments would aid further investigation of the relation between attrition and study outcomes. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
20.
M. Mar López-González 《Polymer》2005,46(12):4322-4329
This work reports the experimental isotherms describing the concentration of oxygen and nitrogen in poly(bisphenol A carbonate-co-4,4′-(3,3,5-trimethylcyclohexylidene) diphenol carbonate) vs pressure, at 30 °C. The solubility coefficients are interpreted in terms of the Flory-Huggins theory, obtaining reasonable values for the enthalpic polymer-gas parameter. A new method is outlined to simulate the probabilities of inserting/removing a gas molecule in a host matrix already containing n molecules of gas. The simulated isotherms representing the pressure dependence of the concentration exhibit the same pattern as those experimentally obtained. 相似文献