全文获取类型
收费全文 | 962篇 |
免费 | 55篇 |
学科分类
工业技术 | 1017篇 |
出版年
2023年 | 14篇 |
2022年 | 13篇 |
2021年 | 75篇 |
2020年 | 26篇 |
2019年 | 28篇 |
2018年 | 30篇 |
2017年 | 37篇 |
2016年 | 35篇 |
2015年 | 18篇 |
2014年 | 30篇 |
2013年 | 58篇 |
2012年 | 55篇 |
2011年 | 54篇 |
2010年 | 53篇 |
2009年 | 50篇 |
2008年 | 60篇 |
2007年 | 35篇 |
2006年 | 23篇 |
2005年 | 23篇 |
2004年 | 22篇 |
2003年 | 24篇 |
2002年 | 26篇 |
2001年 | 12篇 |
2000年 | 7篇 |
1999年 | 12篇 |
1998年 | 12篇 |
1997年 | 8篇 |
1996年 | 16篇 |
1995年 | 13篇 |
1994年 | 12篇 |
1993年 | 8篇 |
1992年 | 13篇 |
1991年 | 5篇 |
1990年 | 10篇 |
1989年 | 8篇 |
1988年 | 7篇 |
1987年 | 9篇 |
1986年 | 7篇 |
1985年 | 8篇 |
1984年 | 8篇 |
1983年 | 7篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1979年 | 3篇 |
1978年 | 6篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1974年 | 3篇 |
1970年 | 3篇 |
1964年 | 2篇 |
排序方式: 共有1017条查询结果,搜索用时 145 毫秒
61.
Beyond the pages of a book: Interactive book reading and language development in preschool classrooms. 总被引:2,自引:0,他引:2
The effects of a book reading technique called interactive book reading on the language and literacy development of 4 yr olds from low-income families were evaluated. Teachers read books to children and reinforced the vocabulary in the books by presenting concrete objects that represented the words and by providing children with multiple opportunities to use the book-related words. The teachers also were trained to ask open-ended questions and to engage children in conversations about the book and activities. This provided children with opportunities to use language and learn vocabulary in a meaningful context. Children who were in the interactive book reading intervention group scored significantly better than children in the comparison group on Peabody Picture Vocabulary Test—III and other measures of receptive and expressive language. Book reading and related activities can promote the development of language and literacy skills in young children. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
62.
63.
Refutes R. F. Baumeister's (see record 1989-14054-001) argument that the inclusion of sex-difference findings in research reports is undesirable from both political and scientific standpoints. A number of advantages stem from the study of sex differences. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
64.
David Ghezel-Ahmadi Alice Engel Lygia Therese Budnik Ulrich Frick Simone Hauser 《The Science of the total environment》2010,408(4):774-778
Background
Risks from electromagnetic devices are of considerable concern. Electrohypersensitive (EHS) persons attribute a variety of rather unspecific symptoms to the exposure to electromagnetic fields. The pathophysiology of EHS is unknown and therapy remains a challenge.Objectives
Heavy metal load has been discussed as a potential factor in the symptomatology of EHS patients. The main objective of the study was to test the hypothesis of a link between EHS and heavy metal exposure.Methods
We measured lead, mercury and cadmium concentrations in the blood of 132 patients (n = 42 males and n = 90 females) and 101 controls (n = 34 males and n = 67 females).Results
Our results show that heavy metal load is of no concern in most cases of EHS but might play a role in exceptional cases.Conclusions
The data do not support the general advice to heavy metal detoxification in EHS. 相似文献65.
Protected Working Capacity Envelope (PWCE) has been proposed to simplify resource management and traffic control for survivable
WDM networks. In a PWCE-based network, part of the link capacity is reserved for accommodating working routes, and the remaining
capacity is reserved for backup routes. The shortest path routing is applied in PWCE-based networks. An arrival call is accepted
only when each link along the shortest path has a free working channel. Such a working path routing scheme greatly simplifies
the call admission control process for dynamic traffic, and it is especially suitable for implementation in a distributed
manner among network nodes. In this article, we investigate two protection strategies: Bundle Protection (BP) and Individual
Protection (IDP). In BP, only one backup path can be used to protect a failure component, whereas multiple backup paths can
be used in IDP. We formulate four mixed integer non-linear programming (MINLP) problems using BP and IDP strategies for single
link and single node failure protection. Each model is designed to determine link metrics for shortest working path routing,
working and backup channel assignments, and backup path planning. Our objective is to minimize call-blocking probability on
the bottleneck link. Since these models are highly non-linear and non-convex, it is difficult to obtain exact global optimal
solutions. We propose a Simulated Annealing-based Heuristic (SAH) algorithm to obtain near optimal solutions. This SAH adopts
the concepts of simulated annealing as well as the bi-section technique to minimize call-blocking probabilities. To evaluate
the performance, we made simulation comparisons between SAH and the unity link weight assignment scheme. The results indicate
that SAH can greatly reduce call-blocking probabilities on benchmark and the randomly generated networks. 相似文献
66.
Acton PM Fox JF Campbell JE Jones AL Rowe H Martin D Bryson S 《Environmental science & technology》2011,45(23):10265-10272
Mountaintop coal mining (MCM) in the Southern Appalachian forest region greatly impacts both soil and aquatic ecosystems. Policy and practice currently in place emphasize water quality and soil stability but do not consider upland soil health. Here we report soil organic carbon (SOC) measurements and other soil quality indicators for reclaimed soils in the Southern Appalachian forest region to quantify the health of the soil ecosystem. The SOC sequestration rate of the MCM soils was 1.3 MgC ha(-1) yr(-1) and stocks ranged from 1.3 ± 0.9 to 20.9 ± 5.9 Mg ha(-1) and contained only 11% of the SOC of surrounding forest soils. Comparable reclaimed mining soils reported in the literature that are supportive of soil ecosystem health had SOC stocks 2.5-5 times greater than the MCM soils and sequestration rates were also 1.6-3 times greater. The high compaction associated with reclamation in this region greatly reduces both the vegetative rooting depth and infiltration of the soil and increases surface runoff, thus bypassing the ability of soil to naturally filter groundwater. In the context of environmental sustainability of MCM, it is proposed that the entire watershed ecosystem be assessed and that a revision of current policy be conducted to reflect the health of both water and soil. 相似文献
67.
Estrogen content of dairy and swine wastes 总被引:3,自引:0,他引:3
Raman DR Williams EL Layton AC Burns RT Easter JP Daugherty AS Mullen MD Sayler GS 《Environmental science & technology》2004,38(13):3567-3573
Naturally occurring estrogens in animal wastes may cause negative environmental impacts, yet their abundance in animal waste treatment and storage structures is poorly documented. To better quantify estrogen concentrations in animal wastes, multiple waste samples were collected from treatment and storage structures at dairy and swine facilities and analyzed for concentrations of 17beta-estradiol (E2), estrone (E1), and 17alpha-estradiol by gas chromatography-mass spectroscopy and by enzyme linked immunosorbent assay (E2 only). Mass ratios of each estrogen to the macronutrients nitrogen, phosphorus, and potassium were also determined. Because manure application rates are typically macronutrient-based, estrogen to macronutrient ratios are proportional to areal mass application rates of estrogen to fields. Swine farrowing waste (from farrowing sows and piglets) had the highest ratios of E2 to macronutrients. Mean ratios in swine farrowing waste were roughly twice those in swine finishing waste (from growing male and nonpregnant female animals) and more than four times higher than those in dairy waste (from lactating cows in various stages of their reproductive cycles); these differences were statistically significant (alpha = 0.05). Estrone followed a similar trend. In contrast, ratios of 17alpha-estradiol to macronutrients were highest in dairy operations. These results can be used to better predict estrogen loading rates on fields receiving swine and dairy wastes. 相似文献
68.
Sarah Kate Walsh Alice Lucey Jens Walter Emanuele Zannini Elke K. Arendt 《Comprehensive Reviews in Food Science and Food Safety》2022,21(3):2930-2955
Dietary fiber intakes in Western societies are concerningly low and do not reflect global recommended dietary fiber intakes for chronic disease prevention. Resistant starch (RS) is a fermentable dietary fiber that has attracted research interest. As an isolated ingredient, its fine particle size, relatively bland flavor, and white appearance may offer an appealing fiber source to the Western palate, accustomed to highly refined, processed grains. This review aims to provide a comprehensive insight into the current knowledge (classification, production methods, and characterization methods), health benefits, applications, and acceptability of RS. It further discusses the present market for commercially available RS ingredients and products containing ingredients high in RS. The literature currently highlights beneficial effects for dietary RS supplementation with respect to glucose metabolism, satiety, blood lipid profiles, and colonic health. An exploration of the market for commercial RS ingredients indicates a diverse range of products (from isolated RS2, RS3, and RS4) with numerous potential applications as partial or whole substitutes for traditional flour sources. They may increase the nutritional profile of a food product (e.g., by increasing the fiber content and lowering energy values) without significantly compromising its sensory and functional properties. Incorporating RS ingredients into staple food products (such as bread, pasta, and sweet baked goods) may thus offer an array of nutritional benefits to the consumer and a highly accessible functional ingredient to be greater exploited by the food industry. 相似文献
69.
Sergio Neves Monteiro Felipe Perissé Duarte Lopes Anderson Paula Barbosa Alice Barreto Bevitori Isabela Leão Amaral Da Silva Lucas Lopes Da Costa 《Metallurgical and Materials Transactions A》2011,42(10):2963-2974
Recent investigations on the tensile properties of natural cellulose-based fibers revealed an increasing potential as engineering
materials. This is particularly the case of very thin fibers of some species such as sisal, ramie, and curaua. However, several
other commonly used fibers such as flax, jute, hemp, coir, cotton, and bamboo as well as less known bagasse, piassava, sponge
gourde, and buriti display tensile properties that could qualify them as engineering materials. An overview of the strength
limits attained by these fibers is presented. Based on a tensile strength vs density chart, it is shown that natural fibers stand out as a relevant class of engineering materials. 相似文献
70.
Eastwick Paul W.; Eagly Alice H.; Finkel Eli J.; Johnson Sarah E. 《Canadian Metallurgical Quarterly》2011,101(5):993
Five studies develop and examine the predictive validity of an implicit measure of the preference for physical attractiveness in a romantic partner. Three hypotheses were generally supported. First, 2 variants of the go/no-go association task revealed that participants, on average, demonstrate an implicit preference (i.e., a positive spontaneous affective reaction) for physical attractiveness in a romantic partner. Second, these implicit measures were not redundant with a traditional explicit measure: The correlation between these constructs was .00 on average, and the implicit measures revealed no reliable sex differences, unlike the explicit measure. Third, explicit and implicit measures exhibited a double dissociation in predictive validity. Specifically, explicit preferences predicted the extent to which attractiveness was associated with participants' romantic interest in opposite-sex photographs but not their romantic interest in real-life opposite-sex speed-daters or confederates. Implicit preferences showed the opposite pattern. This research extends prior work on implicit processes in romantic relationships and offers the first demonstration that any measure of a preference for a particular characteristic in a romantic partner (an implicit measure of physical attractiveness, in this case) predicts individuals' evaluation of live potential romantic partners. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献