全文获取类型
收费全文 | 1429篇 |
免费 | 80篇 |
国内免费 | 4篇 |
学科分类
工业技术 | 1513篇 |
出版年
2023年 | 11篇 |
2022年 | 13篇 |
2021年 | 37篇 |
2020年 | 30篇 |
2019年 | 23篇 |
2018年 | 40篇 |
2017年 | 47篇 |
2016年 | 38篇 |
2015年 | 36篇 |
2014年 | 61篇 |
2013年 | 83篇 |
2012年 | 44篇 |
2011年 | 68篇 |
2010年 | 59篇 |
2009年 | 57篇 |
2008年 | 48篇 |
2007年 | 56篇 |
2006年 | 59篇 |
2005年 | 45篇 |
2004年 | 43篇 |
2003年 | 37篇 |
2002年 | 32篇 |
2001年 | 30篇 |
2000年 | 30篇 |
1999年 | 37篇 |
1998年 | 89篇 |
1997年 | 69篇 |
1996年 | 46篇 |
1995年 | 30篇 |
1994年 | 28篇 |
1993年 | 26篇 |
1992年 | 19篇 |
1991年 | 12篇 |
1990年 | 18篇 |
1989年 | 13篇 |
1988年 | 12篇 |
1987年 | 6篇 |
1986年 | 9篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 6篇 |
1982年 | 4篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 8篇 |
1978年 | 6篇 |
1977年 | 4篇 |
1976年 | 11篇 |
1973年 | 3篇 |
1936年 | 2篇 |
排序方式: 共有1513条查询结果,搜索用时 0 毫秒
81.
Frédéric Rambaud Karine Vallé Simon Thibaud Beatriz Julián‐López Clément Sanchez 《Advanced functional materials》2009,19(18):2896-2905
The one‐pot synthesis and properties of multifunctional hybrid mesoporous organosilica fibers with helical shapes are described. These hybrid mesoporous fibers are prepared without chiral elements and functionalized with a large variety of organic R functions (R = alkylthiols, phenylsulfonates, alkylphosphonates, dansyl, aminopropyl, fluoroalkyl, etc.). The resulting nanomaterials are thoroughly characterized by a variety of techniques. The use of a synergetic combination of achiral molecules as co‐directing structuring agents, a surfactant, and an organofunctional silica precursor R‐Si(OR)3 allows, via carefully tuning of the main synthesis parameters and processing conditions, to control the shape, which is the anisotropic factor, of the hybrid nanofibers. The functionalization of the hybrid materials with fluorescent molecules (dansyl) and gold nanoparticles opens possibilities for sensor and catalytic applications, respectively. Moreover, these hybrid nanofibers can be easily transferred in organic solvents or in a “green” solvent such as water to make stable colloidal dispersions. This tunable functionality of nanofibers also allows their transferability into a variety of polymeric hosts (PVDF, PVBu, and PVP) allowing the formation of functional homogeneous nanocomposite hybrid membranes. 相似文献
82.
The vibrational (IR and Raman) spectrum of Vandenbrandeite, Cu[UO2(OH)4], has been recorded and discussed on the basis of structural considerations through the use of empirical expressions. As the H-bonding in the lattice is poorly known, the characteristics of this bond has been analyzed with the aid of H/D isotope exchange, thermal assays and electron microscopy. Samples are practically amorphous to XRD up to 700°C whereas crystals morphologically different by SEM microscopy and well characterized by XRD technique are observed from 800°C. Vibrational spectroscopy reveals that the atomic arrangement in the structure remains largely unaffected as the dehydration proceeds, suggesting a topochemically controlled process. EPR spectroscopy suggests a disordered distribution of Cu(II) ions as temperature increases. Finally, thermal dehydroxylation and paragenesis of the copper-uranyl oxide hydrate are correlated. 相似文献
83.
Modified Kostiakov Infiltration Function: Accounting for Initial and Boundary Conditions 总被引:1,自引:0,他引:1
A. Furman A. W. Warrick D. Zerihun C. A. Sanchez 《Canadian Metallurgical Quarterly》2006,132(6):587-596
The effect of specific initial and boundary conditions is generally not considered when applying the Kostiakov infiltration functions. A methodology is developed to account for changes in water levels and initial soil moisture. First, Richards’ equation is solved numerically to generate a database of one-dimensional infiltration values, with varying initial (water content or pressure head) and boundary (ponding depth) conditions for three contrasting soils. These are then used to calibrate corresponding coefficients for modified Kostiakov models and, by considering linear regressions, to obtain simple correction factors. Results show that the correction factors are not universally valid, and only the correction to the Kostiakov k parameter shows statistically consistent applicability. However, examples demonstrate potentially significant improvement in the accuracy of irrigation models by correcting the Kostiakov equation to account for initial and boundary conditions. 相似文献
84.
Miguel A. Rodriguez Joan E. Ricart Pablo Sanchez 《Creativity & Innovation Management》2002,11(3):135-146
Does the need for sustainable development hinder businesses’ ability to create value? Is a firm’s competitiveness negatively affected by considering that need? After quickly reviewing the main literature contributions on the relationship between business and society, and drawing from resource‐based view of the firm and sustainable development literature, this paper presents a proposal for a dynamic and sustainable view of the firm. It shows how considering the changes introduced into the competitive landscape by sustainable development influences the way in which companies develop their resources, capabilities and activities, fostering the persistence of competitive advantages based on knowledge and innovation. 相似文献
85.
Luna E. Guzman A. Sdnchez-Rojas J.L. Sanchez J.M. Munoz E. 《IEEE journal of selected topics in quantum electronics》2002,8(5):992-997
Double-barrier quantum-well infrared photodetectors are promising for operation in the midinfrared region. In this paper, we present a series of novel molecular beam epitaxy (MBE)-grown devices based on modulation-doped (MD) AlGaAs-AlAs-GaAs structures that exhibit a remarkable responsivity at zero bias (0.05 A/W) at 4.6 /spl mu/m. Since the photovoltaic properties are strongly dependent on the symmetry of the potential profile, we have systematically varied the position of the dopant in the barriers for a series of single-color detectors. Low-temperature photocurrent spectra and current-voltage (I-V) characteristics (in the dark and under illumination) show that the location of the dopant is a relevant design parameter, due to its role in the photovoltaic behavior (i.e., the presence or absence of zero bias signal). The performance of the MD devices is compared with that of a detector with doping in the center of the well and otherwise the same structure. In particular, the responsivity and detectivity seem to be higher for the MD detectors than for well-doped samples, especially when the dopant is located in the barrier closest to the substrate. Therefore, we have chosen that MD dopant profile when designing and growing, to our knowledge, the first 3-5 /spl mu/m two-color detector, with simultaneous detection at 3.8 and 4.4 /spl mu/m. 相似文献
86.
Angela M. Gyurko Gregory E. Vignoul John K. Tien Juan M. Sanchez 《Metallurgical and Materials Transactions A》1992,23(11):3073-3076
Engineering, University of Texas at Austin, Austin, TX 78712 While much of the high-temperature intermetallics research has
centered around Ni3Al and other aluminum-based systems, the present study focuses on the Engel-Brewer Ll2 intermetallic Ir3Zr, which has a melting temperature approaching that of ceramics (2280 °C). Due to limited material availability, the technique
of microindentation was used to study both the temperature and time dependence of strength. Because of the widely held belief
that certain mechanical properties of intermetallics scale roughly with temperature, Ir3Zr was expected to exhibit high strength. The microhardness was observed to vary from 225 MPa at room temperature to 75 MPa
at 1400 °C, which is significantly lower than the behavior of Ni3Al. The activation energy for creep was determined to be 467 kJ/mole, and the stress exponent was found to be 18.2. The ordering
energy of this system was calculated to be 0.114 eV. If it can be assumed that high ordering energy correlates to a high antiphase
boundary (APB) energy, then the behavior of this system is consistent with a model that predicts highly glissile dislocation
cores. 相似文献
87.
88.
A new simple two-axis magnetometer has been developed. based on the superposition of an amorphous ferromagnetic disc over a disc-shaped piezoelectric support. At low frequencies, this device exhibits a sensitivity of ~1.7 μV/μT when the external magnetic field is orthogonal to one of the pick-up coils 相似文献
89.
Several synthetic interleukin-1 (IL-1) peptides were tested in vivo for pyrogenic activity and in vivo for their ability to stimulate prostaglandin production. Only the IL-1beta fragment (208-240) enhanced body temperature, although both IL-1beta (208-240) and IL-1alpha (223-250) stimulated prostaglandin E2 (PGE2) production in vitro. We report here that the IL-1beta fragment (208-240) did not have the capacity to induce arachidonic acid (AA) mobilization by 3T6 fibroblasts. However, this peptide was able to increase the expression of the inducible prostaglandin H synthase isoform (PGHS-2; EC 1.14.99.1.), which is related to its ability to stimulate prostaglandin E2 synthesis. 相似文献
90.
Tharinger Deborah J.; Lambert Nadine M.; Bricklin Patricia M.; Feshbach Norma; Johnson Neal F.; Oakland Thomas D.; Paster Vera S.; Sanchez William 《Canadian Metallurgical Quarterly》1996,27(1):24
National, state, and local education reform agendas have been on a fast track for more than a decade. Although some psychologists have been active in promoting psychology and psychological services in education reform initiatives, knowledge about their efforts is fragmented. In order to educate psychologists about education reform, this article highlights the impetus for the recent education reform movement, briefly reviews the latest waves of education reform, and discusses the development of the National Education Goals. Then, an argument is made for the integration of education, health, and social reform initiatives; state-level education reform principles and initiatives are highlighted, illustrated by the systemic education reform mandate in Kentucky. Next, progress toward the development and implementation of an APA-sponsored response to the National Education Goals is discussed. Finally, objectives and roles for psychologists in advancing education reform are presented, and guidelines for the education and training of future psychologists are introduced. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献