全文获取类型
收费全文 | 3460篇 |
免费 | 125篇 |
专业分类
电工技术 | 27篇 |
综合类 | 1篇 |
化学工业 | 684篇 |
金属工艺 | 34篇 |
机械仪表 | 28篇 |
建筑科学 | 169篇 |
矿业工程 | 4篇 |
能源动力 | 48篇 |
轻工业 | 516篇 |
水利工程 | 43篇 |
石油天然气 | 12篇 |
无线电 | 129篇 |
一般工业技术 | 421篇 |
冶金工业 | 1152篇 |
原子能技术 | 8篇 |
自动化技术 | 309篇 |
出版年
2023年 | 26篇 |
2022年 | 67篇 |
2021年 | 112篇 |
2020年 | 57篇 |
2019年 | 69篇 |
2018年 | 88篇 |
2017年 | 73篇 |
2016年 | 97篇 |
2015年 | 53篇 |
2014年 | 96篇 |
2013年 | 210篇 |
2012年 | 159篇 |
2011年 | 224篇 |
2010年 | 168篇 |
2009年 | 167篇 |
2008年 | 177篇 |
2007年 | 176篇 |
2006年 | 148篇 |
2005年 | 142篇 |
2004年 | 94篇 |
2003年 | 91篇 |
2002年 | 101篇 |
2001年 | 69篇 |
2000年 | 59篇 |
1999年 | 66篇 |
1998年 | 57篇 |
1997年 | 43篇 |
1996年 | 58篇 |
1995年 | 46篇 |
1994年 | 49篇 |
1993年 | 50篇 |
1992年 | 40篇 |
1991年 | 17篇 |
1990年 | 35篇 |
1989年 | 38篇 |
1988年 | 36篇 |
1987年 | 25篇 |
1986年 | 31篇 |
1985年 | 27篇 |
1984年 | 26篇 |
1983年 | 20篇 |
1982年 | 19篇 |
1981年 | 22篇 |
1980年 | 12篇 |
1979年 | 17篇 |
1978年 | 16篇 |
1976年 | 16篇 |
1975年 | 14篇 |
1974年 | 10篇 |
1969年 | 9篇 |
排序方式: 共有3585条查询结果,搜索用时 0 毫秒
31.
32.
Elizabeth Carvalho Adérito Marcos Maribel Yasmina Santos Jo?o Espregueira-Mendes 《Computer Graphics and Applications, IEEE》2008,28(5):16-21
A cartographic-oriented model uses algebraic map operations to perform spatial analysis of medical data relative to the human body. A prototype system uses 3D visualization techniques to deliver analysis results. A prototype implementation suggests the model might provide the basis for a medical application tool that introduces new information insight. 相似文献
33.
Morphology and structure of the pollen cone and pollen grain of the Araucaria species from Argentina
The pollen cone and the pollen grain of the two Argentinean species of Araucaria are described with LM, SEM and TEM. Primordia of pollen cones are formed in April and May and reach maturity by mid-October in A. angustifolia (Bert.) O. Kuntze and by mid-November in A. araucana. (Mol.) K. Koch. Characters of the mature pollen cones and microsporophylls between both taxa are clearly differentiated. Pollen grains are spheroidal-subspheroidal, inaperturate, and asaccate with granulate exine and a subequatorial annular area that corresponds to the sexine thickness. Sculpturing consists of irregularly dispersed granules that are sometimes fused to each other (A. angustifolia) or forming microrugulae (A. araucana). Microgranules and microspinules are also present. The pollen wall ultrastructure is formed by a granular ectexine and lamellated endexine. Granular elements in A. angustifolia are more loosely disposed, form more interstices, and are gradually smaller towards the endexine than in A. araucana. To asses the probable relationships within the family, we compared the pollen grains of the two Araucaria species with those of other extant genera (Agathis, Wollemia) and also with fossil pollen (Araucariacites, Balmeiopsis, Cyclusphaera, Dilwynites) attributed to Araucariaceae. 相似文献
34.
Psychotherapy studies published in the Journal of Counseling Psychology (JCP) and the Journal of Consulting and Clinical Psychology (JCCP) between 1978 and 1992 were examined. Differences were found between the 2 journals. JCP published mostly process, outcome, and analog research, whereas JCCP published mostly outcome research. Most process and process-outcome studies across journals were of individual, brief therapy. Across the years, more diversity was evident in samples used in process research in terms of student status, gender, and race of clients and therapists. Three content areas were prominent in the process measures and classic studies: therapist techniques, therapist influence, and facilitative conditions. Lists are provided of the frequently used measures, most productive authors, and classic studies in process research. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
35.
The Formation of Calcified Nanospherites during Micropetrosis Represents a Unique Mineralization Mechanism in Aged Human Bone 下载免费PDF全文
Petar Milovanovic Elizabeth A. Zimmermann Annika vom Scheidt Björn Hoffmann George Sarau Timur Yorgan Michaela Schweizer Michael Amling Silke Christiansen Björn Busse 《Small (Weinheim an der Bergstrasse, Germany)》2017,13(3)
Osteocytes—the central regulators of bone remodeling—are enclosed in a network of microcavities (lacunae) and nanocanals (canaliculi) pervading the mineralized bone. In a hitherto obscure process related to aging and disease, local plugs in the lacuno‐canalicular network disrupt cellular communication and impede bone homeostasis. By utilizing a suite of high‐resolution imaging and physics‐based techniques, it is shown here that the local plugs develop by accumulation and fusion of calcified nanospherites in lacunae and canaliculi (micropetrosis). Two distinctive nanospherites phenotypes are found to originate from different osteocytic elements. A substantial deviation in the spherites' composition in comparison to mineralized bone further suggests a mineralization process unlike regular bone mineralization. Clearly, mineralization of osteocyte lacunae qualifies as a strong marker for degrading bone material quality in skeletal aging. The understanding of micropetrosis may guide future therapeutics toward preserving osteocyte viability to maintain mechanical competence and fracture resistance of bone in elderly individuals. 相似文献
36.
Moritz Tebbe Elizabeth Galati Gilbert C. Walker Eugenia Kumacheva 《Small (Weinheim an der Bergstrasse, Germany)》2017,13(37)
Future progress in nanoscience and nanotechnology necessitates further development of versatile, labor‐, and cost‐efficient surface patterning strategies. A new approach to nanopatterning is reported, which utilizes surface segregation of a smooth layer of an end‐grafted homopolymer in a poor solvent. The variation in polymer grafting density yields a range of surface nanostructures, including randomly organized pinned spherical micelles, worm‐like structures, networks, and porous films. The capability to use the polymer patterns for site‐specific deposition of small molecules, polymers, or nanoparticles is shown. This versatile strategy enables patterning of curved surfaces with direct access to the substrate and no need in changing polymer composition to realize different surface patterns. 相似文献
37.
Can an electronic portfolio that is both a multimedia container for student work and a tool to support key learning processes have a positive impact on the literacy practices and self-regulated learning skills of students? This article presents the findings of a yearlong study conducted in three Canadian provinces during the 2007–2008 school year initially involving 32 teachers and 388 students. Due to varying levels of implementation our final data set included 14 teachers and 296 students. Using a non-equivalent pre-test/post-test design, we found that grade 4–6 students who were in classrooms where the teacher provided regular and appropriate use of the electronic portfolio tool ePEARL (i.e., medium–high implementation condition, n = 7 classrooms and 121 students), compared to control students (n = 7 classrooms and 175 students) who did not use ePEARL, showed significant improvements (p < .05) in their writing skills on a standardized literacy measure (i.e., the constructed response subtest of the Canadian Achievement Test-4th ed.) and certain metacognitive skills measured via student self-report. The results of this study indicate that teaching with ePEARL has positive impacts on students’ literacy and self-regulated learning skills when the tool is used regularly and integrated into classroom instruction. 相似文献
38.
39.
Elizabeth J. Malloy Donna Spiegelman Ellen A. Eisen 《Computational statistics & data analysis》2009,53(7):2605-2616
This article presents an application and a simulation study of model fit criteria for selecting the optimal degree of smoothness for penalized splines in Cox models. The criteria considered were the Akaike information criterion, the corrected AIC, two formulations of the Bayesian information criterion, and a generalized cross-validation method. The estimated curves selected by the five methods were compared to each other in a study of rectal cancer mortality in autoworkers. In the stimulation study, we estimated the fit of the penalized spline models in six exposure-response scenarios, using the five model fit criteria. The methods were compared on the basis of a mean squared error score and the power and size of hypothesis tests for any effect and for detecting nonlinearity. All comparisons were made across a range in the total sample size and number of cases. 相似文献
40.
Jos A. Villaseor-Alva Elizabeth Gonzlez-Estrada 《Computational statistics & data analysis》2009,53(11):3835-3841
This paper proposes a bootstrap goodness of fit test for the Generalized Pareto distribution (GPd) with shape parameter γ. The proposed test is an intersection–union test which tests separately the cases of γ≥0 and γ<0 and rejects if both cases are rejected. If the test does not reject, then it is known whether the shape parameter γ is either positive or negative. A Monte Carlo simulation experiment was conducted to assess the power of performance of the intersection–union test. The GPd hypothesis was tested on a data set containing Mexico City’s ozone levels. 1 相似文献