全文获取类型
收费全文 | 584篇 |
免费 | 25篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 4篇 |
化学工业 | 71篇 |
金属工艺 | 2篇 |
机械仪表 | 7篇 |
建筑科学 | 18篇 |
能源动力 | 6篇 |
轻工业 | 79篇 |
水利工程 | 6篇 |
石油天然气 | 10篇 |
无线电 | 21篇 |
一般工业技术 | 78篇 |
冶金工业 | 244篇 |
自动化技术 | 64篇 |
出版年
2023年 | 6篇 |
2022年 | 2篇 |
2021年 | 5篇 |
2020年 | 3篇 |
2019年 | 4篇 |
2018年 | 8篇 |
2017年 | 13篇 |
2016年 | 13篇 |
2015年 | 3篇 |
2014年 | 17篇 |
2013年 | 25篇 |
2012年 | 17篇 |
2011年 | 24篇 |
2010年 | 24篇 |
2009年 | 22篇 |
2008年 | 32篇 |
2007年 | 26篇 |
2006年 | 33篇 |
2005年 | 21篇 |
2004年 | 23篇 |
2003年 | 25篇 |
2002年 | 34篇 |
2001年 | 13篇 |
2000年 | 14篇 |
1999年 | 14篇 |
1998年 | 10篇 |
1997年 | 13篇 |
1996年 | 9篇 |
1995年 | 13篇 |
1994年 | 16篇 |
1993年 | 12篇 |
1992年 | 13篇 |
1991年 | 8篇 |
1990年 | 6篇 |
1989年 | 13篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 8篇 |
1985年 | 13篇 |
1984年 | 3篇 |
1983年 | 6篇 |
1982年 | 7篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1954年 | 1篇 |
排序方式: 共有610条查询结果,搜索用时 12 毫秒
1.
William W. Bowerman Amy S. Roe Michael J. Gilbertson David A. Best James G. Sikarskie Rachel S. Mitchell Cheryl L. Summer 《Lakes & Reservoirs: Research and Management》2002,7(3):183-187
The bald eagle (Haliaeetus leucocephalus) is one of the most studied birds of North America, and a great amount of natural life‐history information, including the response of various stressors on the eagles' ability to reproduce, are well known. In Michigan, the eagle has been chosen to track the trends of bioaccumulative compounds of concern across watersheds in the state. The state has been divided into major watersheds, and 20% of these are surveyed each year. A control area in northern Minnesota, Voyageurs National Park, is also sampled annually. We report here on the methods used, the preliminary results of the 1999 field season, and how differences in mercury concentrations varied over a 10‐year period. Mercury in feathers of nestling eagles declined over time only in Lakes Michigan and Huron, but have not decreased among other subpopulations in Michigan. Concentrations of polychlorinated biphenyls (PCBs) and 4,4′‐DDE in blood plasma from nestling eagles have declined over time for most subpopulations; however, they remain greater for breeding areas associated with the Great Lakes' food web. Sea eagles of the genus Haliaeetus are a good sentinel species to track trends in bioaccumulative compounds in aquatic systems. 相似文献
2.
Blotcky Alan D.; Cohen Debra G.; Conatser Cheryl; Klopovich Patricia 《Canadian Metallurgical Quarterly》1985,53(5):729
Examined psychosocial variables by comparing 10 13–17 yr old adolescents (and their mothers) who had refused cancer treatment with a group of 10 consenting adolescents who were matched on age and demographic and illness variables. Adolescents completed the State-Trait Anxiety Inventory for Children and measures of family characteristics, locus of control, religion, hopelessness, impact of event, and satisfaction with physician. Mothers completed the State-Trait Anxiety Inventory and measures of coping and religion. Adolescent refusers scored lower on state anxiety and subjective distress but scored higher on trait anxiety, religiosity, and external locus of control. Their mothers also scored higher than did the consenting-group mothers on religiosity and trait anxiety. It is suggested that refusers are prone to anxiety and cope with their present distress by maintaining the belief that their lives are determined by fate or religious convictions. An intervention approach that fosters mastery over the cancer experience is advocated. (8 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
3.
Mathematical models for liquid-liquid extraction processes are not widely available. The correlation of liquid-liquid equilibrium for such a model is often difficult. One correlation, based upon the Redlich-Kister expansion for the molar excess Gibb's free energy, has been shown to accurately represent ternary liquid-liquid equilibrium systems used in liquid-liquid extraction operations.
The use of this correlation in an extraction model was investigated and found to be suitable for a ternary liquid-liquid extraction model with only minor limitations. A successful ternary liquid-liquid extraction model was developed using this equilibrium correlation. 相似文献
The use of this correlation in an extraction model was investigated and found to be suitable for a ternary liquid-liquid extraction model with only minor limitations. A successful ternary liquid-liquid extraction model was developed using this equilibrium correlation. 相似文献
4.
LONG TERM STORAGE STABILITY OF MIDDLE DISTILLATE FUELS FROM A CHEMICAL MECHANISTIC POINT OF VIEW. PART 2. 总被引:1,自引:0,他引:1
Bruce Beaver 《Petroleum Science and Technology》1992,10(1):1-37
The objective of this review is to (i) articulate the current level of understanding of the types of “reactive molecules” intimately involved in the long term oxidative storage instability of middle distillates, (11) review the types of chemical reaction mechanisms most likely involved in the “oxidative phase” of insoluble formation, (iii) review the postulated chemical mechanisms of stabilizer (additive) operation, and (iv) discuss future research areas that must be explored if a greater understanding and control of middle distillate instability is to be realized. 相似文献
5.
A (t, n)-locally random reduction maps a problem instancex into a set of problem instancesy
1,...,y
n in such a way that it is easy to construct the answer tox from the answers toy
1,...,y
n, and yet the distribution ont-element subsets ofy
1,...,y
n depends only on |x|. In this paper we formalize such reductions and give improved methods for achieving them. Then we give a cryptographic application,
showing a new way to prove in perfect zero knowledge that committed bitsx
1,...,x
m satisfy some predicateQ. Unlike previous techniques for such perfect zero-knowledge proofs, ours uses an amount of communication that is bounded
by a fixed polynomial inm, regardless of the computational complexity ofQ.
These results were presented in preliminary form at the 10th Annual Crypto Conference, Santa Barbara, CA, August 1990. The
work of D. Beaver was done at Harvard University, supported in part by NSF Grant CCR-870-4513. The work of J. Kilian was done
at MIT and Harvard University, supported by an NSF postdoctoral fellowship. 相似文献
6.
Cheryl M. M. Carey Gene H. Golub Kincho H. Law 《International journal for numerical methods in engineering》1994,37(16):2857-2883
In this paper, a new solution method for the modified eigenvalue problem with specific application to structural dynamic reanalysis is presented. The method, which is based on the block Lanczos algorithm, is developed for multiple low rank modifications to a system and calculates a few selected eigenpairs. Given the solution to the original system Ax = λx, procedures are developed for the modified standard eigenvalue Problem (A + ΔA)x? = λ x?, where
- 1 ΔA = ΣjBSjBT, where Sj = S ∈ ?p × p, p ? n and B ∈ ?n × p is constant for all the perturbations Sj.
- 2 ΔA = ΣiΣj BiSjBiT, where Bi ∈ ?n × p may vary with the pertubations Sj.
7.
MacKenzie Scott B.; Podsakoff Philip M.; Jarvis Cheryl Burke 《Canadian Metallurgical Quarterly》2005,90(4):710
The purpose of this study was to review the distinction between formative- and reflective-indicator measurement models, articulate a set of criteria for deciding whether measures are formative or reflective, illustrate some commonly researched constructs that have formative indicators, empirically test the effects of measurement model misspecification using a Monte Carlo simulation, and recommend new scale development procedures for latent constructs with formative indicators. Results of the Monte Carlo simulation indicated that measurement model misspecification can inflate unstandardized structural parameter estimates by as much as 400% or deflate them by as much as 80% and lead to Type I or Type II errors of inference, depending on whether the exogenous or the endogenous latent construct is misspecified. Implications of this research are discussed. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献
8.
Birch Cheryl D.; Stewart Sherry H.; Wall Anne-Marie; McKee Sherry A.; Eisnor Shondalee J.; Theakston Jennifer A. 《Canadian Metallurgical Quarterly》2004,18(3):231
This study investigated whether exposure to musical mood induction procedures (MMIP) differentially increases the strength of specific alcohol expectancies for coping motivated (CM) versus enhancement motivated (EM) drinkers. Participants were 86 undergraduates who had elevated scores on either the CM or EM subscale of the Drinking Motives Questionnaire (M. L. Cooper, 1994). Participants were randomly assigned to either a positive or negative mood condition. The Alcohol Craving Questionnaire (E. G. Singleton, S. T. Tiffany, & J. E. Henningfield, 1994) was administered at baseline and after MMIP to assess phasic changes in alcohol expectancy strength. Consistent with hypotheses, only CM drinkers in the negative mood condition reported increased relief expectancies, and only EM drinkers in the positive mood condition reported increased reward expectancies. Theoretical and clinical implications are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
9.
Jon J. Camp Cheryl R. Hann Douglas H. Johnson James E. Tarara Richard A. Robb 《Scanning》1997,19(4):258-263
Conventional two-dimensional imaging of the trabecular meshwork (TM) provides limited information about the size, shape, and interconnection of the aqueous channels within the meshwork. Understanding the three-dimensional (3-D) relationships of the channels within this tissue may give insight into its normal function and possible changes present in the eye disease glaucoma. The purpose of our study was to compare laser scanning confocal microscopy with standard 1 μm Araldite-embeddedhistologic sections for 3-D analysis of the trabecular meshwork. In addition, the study was done to determine whether computerized 3-D reconstruction could isolate the fluid spaces of the trabecular meshwork and determine the size of interconnections between the fluid spaces. Confocal microscopy appears comparable to 1 μm Araldite-embedded tissue sections and has the advantage of inherent registration of the serial tissue sections. Three-dimensional reconstruction allowed the isolation of the fluid spaces within the trabecular meshwork and revealed the presence of numerous interconnections between larger fluid spaces. The distribution of these interconnections was randomly arranged, with no predilection for specific regions within the trabecular meshwork. This distribution of constrictions and “expansion chambers” may provide a clue to the mechanism by which subtle histologic changes are associated with increased ocular pressure in glaucoma. 相似文献
10.
Michael Yvonne L.; Carlson Nichole E.; Bowen Deborah J.; Ritenbaugh Cheryl 《Canadian Metallurgical Quarterly》2011,30(3):375
[Correction Notice: An erratum for this article was reported in Vol 30(4) of Health Psychology (see record 2011-13978-001). The letter was missing the doi. The correct doi is 10.1037/a0022737. The online version of this article has been corrected.] Responds to the comments by J. C. Coyne and C. Johansen (see record 2011-09497-016) on the current author's original article, "Influence of stressors on breast cancer incidence in the Women's Health Initiative" (see record 2009-03297-001). Coyne and Johansen (2011) took issue with the study conducted by the current authors' group (Michael et al., 2009), which analyzed the interaction between stressful life events and social support on breast cancer risk among 83,334 postmenopausal women enrolled in the Women’s Health Initiative (WHI). While the current authors agree with the Coyne and Johansen that too often null results are difficult to publish due to confirmatory bias that privileges results that support an alternative hypothesis, they strongly disagree with the assertion that their group selectively reported findings, inaccurately reported findings, or provided selective and uncritical reference to the existing literature. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献