全文获取类型
收费全文 | 741438篇 |
免费 | 92392篇 |
国内免费 | 55533篇 |
专业分类
电工技术 | 49010篇 |
技术理论 | 56篇 |
综合类 | 39564篇 |
化学工业 | 112832篇 |
金属工艺 | 50095篇 |
机械仪表 | 34207篇 |
建筑科学 | 44113篇 |
矿业工程 | 23311篇 |
能源动力 | 23912篇 |
轻工业 | 62581篇 |
水利工程 | 14270篇 |
石油天然气 | 34427篇 |
武器工业 | 6189篇 |
无线电 | 94361篇 |
一般工业技术 | 110059篇 |
冶金工业 | 74409篇 |
原子能技术 | 8220篇 |
自动化技术 | 107747篇 |
出版年
2024年 | 3325篇 |
2023年 | 9202篇 |
2022年 | 13134篇 |
2021年 | 18685篇 |
2020年 | 18453篇 |
2019年 | 26159篇 |
2018年 | 29680篇 |
2017年 | 31675篇 |
2016年 | 30836篇 |
2015年 | 32292篇 |
2014年 | 35921篇 |
2013年 | 45967篇 |
2012年 | 40915篇 |
2011年 | 42022篇 |
2010年 | 36156篇 |
2009年 | 33043篇 |
2008年 | 31672篇 |
2007年 | 30577篇 |
2006年 | 30061篇 |
2005年 | 27212篇 |
2004年 | 23584篇 |
2003年 | 21153篇 |
2002年 | 19904篇 |
2001年 | 18613篇 |
2000年 | 18212篇 |
1999年 | 20026篇 |
1998年 | 28485篇 |
1997年 | 21670篇 |
1996年 | 18469篇 |
1995年 | 15161篇 |
1994年 | 12873篇 |
1993年 | 11298篇 |
1992年 | 8841篇 |
1991年 | 7591篇 |
1990年 | 6421篇 |
1989年 | 5948篇 |
1988年 | 5392篇 |
1987年 | 3876篇 |
1986年 | 3613篇 |
1985年 | 3941篇 |
1984年 | 3405篇 |
1983年 | 3016篇 |
1982年 | 2872篇 |
1981年 | 2831篇 |
1980年 | 2644篇 |
1979年 | 2387篇 |
1978年 | 2348篇 |
1977年 | 2890篇 |
1976年 | 4464篇 |
1975年 | 2094篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Russel B. Miller Isaac M. Horowitz Constantine H. Houpis A. Finley Barfield 《国际强度与非线性控制杂志
》1994,4(1):211-230
》1994,4(1):211-230
Nonlinear quantitative feedback theory (QFT) and pilot compensation techniques are used to design a 2 × 2 flight control system for the YF-16 aircraft over a large range of plant uncertainty. The design is based on numerical input-output time histories generated with a FORTRAN implemented nonlinear simulation of the YF-16. The first step of the design process is the generation of a set of equivalent linear time-invariant (LTI) plant models to represent the actual nonlinear plant. It has been proven that the solution to the equivalent plant problem is guaranteed to solve the original nonlinear problem. Standard QFT techniques are then used in the design synthesis based on the equivalent plant models. A detailed mathematical development of the method used to develop these equivalent LTI plant models is provided. After this inner-loop design, pilot compensation is developed to reduce the pilot's workload. This outer-loop design is also based on a set of equivalent LTI plant models. This is accomplished by modelling the pilot with parameters that result in good handling qualities ratings, and developing the necessary compensation to force the desired system responses. 相似文献
992.
A failed effort to implement new technology is always a failure to understand and adequately manage the change process. IS professionals are now in the change business and must become experts in managing organizational and human change. 相似文献
993.
Shouhong Wang 《Information Systems Management》1994,11(2):36-43
Business reengineering requires new systems analysis tools for process modeling. An object-oriented (OO) approach may be better than the traditional data flow diagram method in modeling business processes. This article explains the development of an OO tool that may potentially benefit IS in reengineering business processes. 相似文献
994.
What is the implication for business when information technology (IT) changes in the workplace without a commensurate change in the composition of business programs educating tomorrow's employees? A survey of MBA graduates forms the basis of this article on the IT skills needed in the marketplace. 相似文献
995.
This paper is a reply to Laviolette and Seaman's critical discussion of fuzzy set theory. Rather than questioning the interest of the Bayesian approach to uncertainty, some reasons why Bayesian find the idea of a fuzzy set not palatable are laid bare. Some links between fuzzy sets and probability that Laviolette and Seaman seem not to be aware of are pointed out. These links suggest that, contrary to the claim sometimes found in the literature, probability theory is not a special case of fuzzy set theory. The major objection to Laviolette and Seaman is that they found their critique on as very limited view of fuzzy sets, including debatable papers, while they fail to account for significant works pertaining to axiomatic derivation of fuzzy set connectives, possibility theory, fuzzy random variables, among others 相似文献
996.
In the editorial by J.C. Bezdek (ibid., p.1), an example is presented to demonstrate differences between fuzzy membership and probability. The authors argue that probability can be used in a way much more closely analogous to this use of fuzzy membership, weakening the argument for the latter 相似文献
997.
PS,LS和煤油体系的界面张力 总被引:3,自引:0,他引:3
本文以石油磺酸盐(PS)、木质素磺酸盐(LS)和煤油体系为对象,研究了PS/LS比、盐度、醇、Na_2SiO_3及聚合物对体系界面张力(IFT)的影响,探讨了PS与各组分间的相互作用,结果发现,在一定盐度和混合醇(正丁醇+异丙醇)浓度下,PS/LS>0.3/0.7时,体系可形成中相微乳液,IFT值达1×10~(-3)mN/m左右;LS和聚合物的存在使IFT升高;在表面活性剂驱油体系中,可用廉价的LS部分代替PS。 相似文献
998.
TW Mittag A Tormay C Severin T Taniguchi PY Lee RF Wang SM Podos 《Canadian Metallurgical Quarterly》1993,34(3):606-612
PURPOSE: The activity of Al3+, Ga3+, and Be2+ ions in the presence of NaF to directly activate G-proteins was investigated by their potentiative effect on forskolin (FSK)-activated adenylyl cyclase in rabbit ciliary process membranes and their effects on aqueous humor dynamics in vivo. METHODS: Adenylyl cyclase (AC) was determined by radiometric conversion of ATP to cAMP by the particulate fraction of rabbit ciliary processes. Intravitreal injections of sterile solutions of analytical grade salts were made into the center of the vitreous in a volume of 20 microliters. Intraocular pressure, aqueous humor flow, and uveoscleral outflow measurements were made by pneumatonometry, fluorophotometry, and fluorescein-dextran method, respectively. Outflow facility was determined by tonography in the intact eyes and by two-level constant pressure perfusion in cannulated eyes. RESULTS: Both Al3+ (EC50, 40 mumol/l) and Be2+ (EC50, 11 mumol/l) in the presence of 0.5-2 mM NaF activated the stimulatory G-protein Gs. Ga3+ was ineffective and did not antagonize the activation by Al3+. Intravitreal injections of Al3+ (1 mumol/eye) or Be2+ (0.5 or 1 mumol/eye) had no significant intraocular pressure (IOP) effect, nor did 1.5 or 3 mumol/eye of NaF, but when either cation was injected together with NaF, IOP decreased by up to 40% for up to 140 hr. At the time of maximum IOP effect (72 hr) aqueous humor flow determined by fluorophotometry was decreased in BeCl2+ NaF-treated eyes by 40% relative to BeCl2-treated eyes; however, tonographic facility of outflow was unaffected. Uveoscleral flow was also decreased by 38% in BeCl2+ NaF treated eyes. CONCLUSIONS: These findings support the hypothesis that Gs activation of ciliary process adenylyl cyclase decreases aqueous humor formation rate in rabbit eyes, and that activation of G-proteins mediates contraction of ciliary muscles causing a decrease of aqueous humor outflow via the uveoscleral route. The results suggest that G-proteins putatively involved in trabecular facility changes are less sensitive to activation by BeF3- than are other parameters of aqueous humor dynamics. 相似文献
999.
1000.
K Underwood K Sj?str?m R Darveau R Lamont H Schenkein J Gunsolley R Page D Engel 《Canadian Metallurgical Quarterly》1993,168(6):1436-1443
Actinobacillus actinomycetemcomitans is frequently associated with severe periodontitis. Many periodontitis patients have elevated levels of serum IgG antibodies to A. actinomycetemcomitans, but the role of these antibodies is unknown. This study evaluated the functional capacity of anti-A. actinomycetemcomitans IgG antibody to enhance phagocytosis of A. actinomycetemcomitans by polymorphonuclear leukocytes. Chemoluminescence assays were done using sera from 64 subjects, 61 of whom had severe periodontitis; results were compared with the subject's anti-A. actinomycetemcomitans IgG titer and avidity. There was a strong correlation between chemoluminescence and antibody log titer (P < .00001) and a weak correlation between chemoluminescence and antibody avidity (P < .05). The results support the hypothesis that anti-A. actinomycetemcomitans IgG antibodies are important in promoting phagocytosis and killing of A. actinomycetemcomitans. Subjects who develop high levels of highly avid antibodies against A. actinomycetemcomitans may have greater resistance to continued or repeated infection by this pathogen. 相似文献