全文获取类型
收费全文 | 98533篇 |
免费 | 3643篇 |
国内免费 | 376篇 |
专业分类
电工技术 | 1384篇 |
综合类 | 720篇 |
化学工业 | 15182篇 |
金属工艺 | 2610篇 |
机械仪表 | 3808篇 |
建筑科学 | 2051篇 |
矿业工程 | 442篇 |
能源动力 | 2548篇 |
轻工业 | 6081篇 |
水利工程 | 860篇 |
石油天然气 | 258篇 |
武器工业 | 5篇 |
无线电 | 11812篇 |
一般工业技术 | 14504篇 |
冶金工业 | 27155篇 |
原子能技术 | 813篇 |
自动化技术 | 12319篇 |
出版年
2023年 | 718篇 |
2022年 | 943篇 |
2021年 | 1501篇 |
2020年 | 1001篇 |
2019年 | 1053篇 |
2018年 | 1774篇 |
2017年 | 1981篇 |
2016年 | 2664篇 |
2015年 | 2061篇 |
2014年 | 2433篇 |
2013年 | 3875篇 |
2012年 | 5304篇 |
2011年 | 6300篇 |
2010年 | 3621篇 |
2009年 | 3901篇 |
2008年 | 3504篇 |
2007年 | 3075篇 |
2006年 | 2786篇 |
2005年 | 5211篇 |
2004年 | 4257篇 |
2003年 | 3632篇 |
2002年 | 2455篇 |
2001年 | 2018篇 |
2000年 | 1475篇 |
1999年 | 1794篇 |
1998年 | 8328篇 |
1997年 | 5228篇 |
1996年 | 3693篇 |
1995年 | 2406篇 |
1994年 | 1786篇 |
1993年 | 1773篇 |
1992年 | 730篇 |
1991年 | 795篇 |
1990年 | 717篇 |
1989年 | 677篇 |
1988年 | 611篇 |
1987年 | 494篇 |
1986年 | 449篇 |
1985年 | 397篇 |
1984年 | 267篇 |
1983年 | 231篇 |
1982年 | 279篇 |
1981年 | 305篇 |
1980年 | 319篇 |
1979年 | 161篇 |
1978年 | 191篇 |
1977年 | 731篇 |
1976年 | 1475篇 |
1975年 | 178篇 |
1974年 | 113篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
This paper explains the manufacturing process of a composite train carbody with a sandwich composite structure for bodyshell and a stainless steel structure for the under frame. In addition, the structural behavior and safety of the composite carbody of the Korean tilting train was investigated by the static load tests. From the test results, the stiffness of the composite carbody met the specified design. In the aspect of strength, the maximum stress of the composite bodyshell was of 12.2% of strength of CF1263 carbon/epoxy. 相似文献
992.
Hierarchically ordered structures facilitate the incorporation of diverse functions simultaneously. The present report introduces a simple and novel strategy for producing hierarchically ordered polymeric films. Hierarchical ordering of aqueous droplets on a polymer solution is realized by the imposition of physical confinement via various shaped gratings. After drying of the solution, well‐ordered hierarchical structures were fabricated in the remaining polymer film. The size of the grating structure and the lattice size of spontaneous hexagonally packed aqueous pores comprise two different length scales, thereby offering multiscale ordering. Interfacial wetting of the polymer solution to the grating surface was crucial in terms of obtaining a highly ordered structure that can be tuned by dissolving a small amount of surfactant in the polymer solution. The present novel approach provides a new opportunity for lithography‐free fabrication of complex hierarchical structures. 相似文献
993.
994.
Sangho Kim Young-Roc Im Sunghak Lee Hu-Chul Lee Sung-Joon Kim Jun Hwa Hong 《Metallurgical and Materials Transactions A》2004,35(7):2027-2037
This study is concerned with the effects of alloying elements on fracture toughness in the transition temperature region of
base metals and heat-affected zones (HAZs) of Mn-Mo-Ni low-alloy steels. Three kinds of steels whose compositions were varied
from the composition specification of SA 508 steel (grade 3) were fabricated by vacuum-induction melting and heat treatment,
and their fracture toughness was examined using an ASTM E1921 standard test method. In the steels that have decreased C and
increased Mo and Ni content, the number of fine M2C carbides was greatly increased and the number of coarse M3C carbides was decreased, thereby leading to the simultaneous improvement of tensile properties and fracture toughness. Brittle
martensite-austenite (M-A) constituents were also formed in these steels during cooling, but did not deteriorate fracture
toughness because they were decomposed to ferrite and fine carbides after tempering. Their simulated HAZs also had sufficient
impact toughness after postweld heat treatment. These findings indicated that the reduction in C content to inhibit the formation
of coarse cementite and to improve toughness and the increase in Mo and Ni to prevent the reduction in hardenability and to
precipitate fine M2C carbides were useful ways to improve simultaneously the tensile and fracture properties of the HAZs as well as the base
metals. 相似文献
995.
Decentralized control design for large-scale systems with strong interconnections using neural networks 总被引:2,自引:0,他引:2
We propose a decentralized neural network (NN) controller for a class of large-scale nonlinear systems with the strong interconnections. The NNs are used to approximate the unknown subsystems and interconnections. Due to the functional approximation capabilities of NNs, the additional precautions are not required to be made for avoiding the possible control singularity problems. Semiglobal asymptotic stability results are obtained and the tracking error converges to zero. Furthermore, the issue of transient performance of the subsystems is also addressed under an analytical framework. 相似文献
996.
997.
Matrix metalloproteinases are thought to be key players in the remodelling activity of cells associated with both physiological and pathological processes. They share a relatively conserved structure with a number of identifiable modules linked to their specific functions. The structure of the individual domains of a number of matrix metalloproteinases have now been elucidated. Here we review these data in the light of complementary studies on the behaviour of these enzymes in biological systems. In particular we focus on the C-terminal hemopexin-like domain which has intriguingly specific roles in individual matrix metalloproteinases. 相似文献
998.
M Zawadzka B Barański J Wi?niewska-Knypl T Wrońska-Nofer 《Canadian Metallurgical Quarterly》1993,6(4):391-397
Genotoxic effect and hepatic microsomal monooxygenase activities were assessed in mice treated with Acid Green 16 (single i.p. injection at dose 75 mg/kg) superimposed on prolonged ethanol consumption (10% solution in drinking water for 2-4 months). Treatment of mice with Acid Green 16 led to an increased frequency of micronucleated erythrocytes in bone marrow. In animals pretreated with ethanol the frequency of micronucleated erythrocytes, produced by Acid Green 16, was significantly higher. The changes in frequency of micronucleated erythrocytes were accompanied by the enhanced activity of microsomal monooxygenases manifested by higher activity of 7-ethoxycoumarin o-deethylase (the level of cytochrome P-450 was not altered). The obtained results showed that ethanol tended to increase the genotoxic effect of Acid Green 16. However, the slight inductive effect of ethanol on microsomal monooxygenases did not provide clear evidence that the genotoxic effect of Acid Green 16 was associated with ethanol stimulation of the metabolic activation of the dye in the liver. 相似文献
999.
The authors tried to find the correlation between the occurrence of genital tract candidiasis in adolescents and some subjective and objective examination parameters. The highest correlation rates were found for pudendal pruritus, lower abdominal pains and early applied antibiotic therapy material: 188 adolescent girls. 相似文献
1000.
Reports an error in "Current issues relating to psychosocial job strain and cardiovascular disease research" by T?res Theorell and Robert A. Karasek (Journal of Occupational Health Psychology, 1996[Jan], Vol 1[1], 9-26). On p. 12, in the caption to Figure 2, the copyright statement is missing. The caption should have read "The environment, the worker, and illness: Dynamic associations linking environmental strain and learning to evolution of personality. From Healthy Work: Stress, Productivity, and the Reconstruction of Working Life (p. 99), by R. A. Karasek and T. Theorell, 1990, New York: Basic Books. Copyright 1990 by Basic Books. Used with permission." (The following abstract of the original article appeared in record 1996-04477-002.) Examines recent reviews of cardiovascular (CV) job strain (JS) research by P. L. Schnall and P. A. Landsbergis (1994) and T. S. Kristensen (see record 1995-39109-001), which conclude that JS as defined by the demand-control model (the combination of contributions of low job decision latitudes and high psychological job demands) is confirmed as a risk factor for CV mortality in a large majority of studies. Lack of social support at work appears to increase this risk. Several still-unresolved issues are discussed in light of recent research. Methodological issues related to the use of occupational & career aggregate estimates, use of standard scales for job analysis, and recall bias in issues of self-reporting are examined. Confounding factors and differential strengths of associations by subgroups in JS-CV disease analyses with respect to social class, gender, and working hours are addressed. A review of results of monitoring JS-blood pressure associations and associated methodological issues is provided. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献