全文获取类型
收费全文 | 5620篇 |
免费 | 339篇 |
国内免费 | 11篇 |
专业分类
电工技术 | 109篇 |
综合类 | 9篇 |
化学工业 | 1596篇 |
金属工艺 | 79篇 |
机械仪表 | 167篇 |
建筑科学 | 215篇 |
矿业工程 | 5篇 |
能源动力 | 187篇 |
轻工业 | 550篇 |
水利工程 | 41篇 |
石油天然气 | 23篇 |
无线电 | 447篇 |
一般工业技术 | 927篇 |
冶金工业 | 263篇 |
原子能技术 | 30篇 |
自动化技术 | 1322篇 |
出版年
2024年 | 6篇 |
2023年 | 85篇 |
2022年 | 248篇 |
2021年 | 322篇 |
2020年 | 174篇 |
2019年 | 200篇 |
2018年 | 207篇 |
2017年 | 207篇 |
2016年 | 250篇 |
2015年 | 212篇 |
2014年 | 270篇 |
2013年 | 447篇 |
2012年 | 393篇 |
2011年 | 449篇 |
2010年 | 333篇 |
2009年 | 330篇 |
2008年 | 292篇 |
2007年 | 253篇 |
2006年 | 214篇 |
2005年 | 151篇 |
2004年 | 123篇 |
2003年 | 94篇 |
2002年 | 86篇 |
2001年 | 63篇 |
2000年 | 56篇 |
1999年 | 57篇 |
1998年 | 79篇 |
1997年 | 64篇 |
1996年 | 52篇 |
1995年 | 26篇 |
1994年 | 36篇 |
1993年 | 29篇 |
1992年 | 12篇 |
1991年 | 11篇 |
1990年 | 12篇 |
1989年 | 10篇 |
1988年 | 6篇 |
1987年 | 11篇 |
1985年 | 12篇 |
1984年 | 8篇 |
1983年 | 16篇 |
1982年 | 8篇 |
1981年 | 4篇 |
1980年 | 8篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1977年 | 11篇 |
1974年 | 2篇 |
1973年 | 4篇 |
1971年 | 3篇 |
排序方式: 共有5970条查询结果,搜索用时 15 毫秒
1.
Giampiero Sacchetti Paola Pittia Manuela Biserni Gian G. Pinnavaia & Marco D. Rosa 《International Journal of Food Science & Technology》2003,38(2):135-143
Summary Ready‐to‐eat breakfast cereals immersed in milk undergo undesirable changes in texture because of sudden moisture uptake. The textural changes are ascribable to a plasticizing effect of water, which modifies the mechanical strength of products by softening the starch/protein matrix. In this work, some textural parameters of different cereal flakes were derived from the force–displacement curves monitored during 300 s of immersion in milk. Hardness loss, deformability increment and changes in the force–displacement curve profile were calculated and plotted against soaking time. The application of a sugar coating process to a model cereal flake increased the initial product hardness and improved the preservation of the textural parameters during immersion. The Peleg model closely fitted the experimental data, with regression coefficients from 0.967 to 0.999. 相似文献
2.
Fabrice Martin Marc-Etienne Jan Samuel Rey-Mermet Brahim Belgacem Dong Su Marco Cantoni Paul Muralt 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2006,53(7):1339-1343
Polycrystalline A1N thin films were deposited by RF reactive magnetron sputtering on Pt(111)/Ti electrode films. The substrates were tilted by an angle ranging from 40 degrees to 70 degrees with respect to the target normal. A low deposition temperature and a high sputter gas pressure were found ideal for tilted growth. The resulting grain tilt angle amounts to about half the substrate tilt angle. For coupling evaluation, 5 GHz solidly mounted resonator structures have been realized. The tilted grain A1N films exhibited a permittivity in the 9.5-10.5 range and loss tangent of 0.3%. Two shear modes as well as the longitudinal mode could be clearly identified. The coupling coefficient k2(eff) of the fundamental thickness shear mode (TS0) was found to be about 0.5%, which is compatible with a c-axis tilt of about 6 degrees. 相似文献
3.
Marco Paluszny 《Computer aided design》2008,40(1):56-61
We consider patches that contain any given 3D polynomial curve as a pregeodesic (i.e. geodesic up to reparametrization). A curve is a pregeodesic if and only if its rectifying plane coincides with the tangent plane to the surface, we use this fact to construct ruled cubic patches through pregeodesics and bicubic patches through pairs of pregeodesics. We also discuss the G1 connection of (1,k) patches with abutting pregeodesics. 相似文献
4.
Marco Franchini 《Water Resources Management》1994,8(3):225-238
With reference to the kinematic wave theory coupled with the hypothesis of constant linear velocity for the rating curve, rising limb analytical solutions have been calculated for overland flow, over an Hortonian-infiltrating surface, and sediment discharge. These analytical solutions are certainly easier to use than the numerical integration of the basic equations and they may be used to obtain an initial evaluation of the parameters of more complex models generally devised for complicated cases.Notation
a
exponent of the Horton law [T–1]
-
b
exponent of the rill erosion equation
-
B
inter-rill erosion coefficient [ML–m–2T
m–1]
-
c
sediment concentration [ML–3]
-
c
o
reference sediment concentration [ML–3]
-
E
I
inter-rill erosion [ML–2T–1]
-
E
R
rill erosion [ML–2T–1]
-
f
c
final infiltration rate of the soil [LT–1]
-
f
o
initial infiltration rate of the soil [LT–1]
-
h
flow depth [L]
-
h
o
reference flow depth [L]
-
i
infiltration rate [LT–1]
-
k
rill erosion coefficient [ML–1–b
T–1]
-
K
integration constant
-
L()
Laplace transformation
-
m
exponent of the inter-rill erosion equation
-
n
Manning's coefficient [L–1/3T]
-
p
rainfall intensity [LT–1]
-
q
water discharge per unit width [L2T–1]
-
q
s
sediment discharge per unit width [ML–1T–1]
-
t
time [T]
-
t
p
ponding time [T]
-
x
distance along the flow direction [L]
Greek Letters
coefficient of the stage-discharge equation [L2–T–1]
-
exponent of the stage-discharge equation
-
rill erosion coefficient [L–1] 相似文献
5.
Roberto Confalonieri Gianni Bellocchi Stefano Tarantola Marco Acutis Marcello Donatelli Giampiero Genovese 《Environmental Modelling & Software》2010,25(4):479-488
Sensitivity analysis studies how the variation in model outputs can be due to different sources of variation. This issue is addressed, in this study, as an application of sensitivity analysis techniques to a crop model in the Mediterranean region. In particular, an application of Morris and Sobol' sensitivity analysis methods to the rice model WARM is presented. The output considered is aboveground biomass at maturity, simulated at five rice districts of different countries (France, Greece, Italy, Portugal, and Spain) for years characterized by low, intermediate, and high continentality. The total effect index of Sobol' (that accounts for the total contribution to the output variation due a given parameter) and two Morris indices (mean μ and standard deviation σ of the ratios output changes/parameter variations) were used as sensitivity metrics. Radiation use efficiency (RUE), optimum temperature (Topt), and leaf area index at emergence (LAIini) ranked in most of the combinations site × year as first, second and third most relevant parameters. Exceptions were observed, depending on the sensitivity method (e.g. LAIini resulted not relevant by the Morris method), or site-continentality pattern (e.g. with intermediate continentality in Spain, LAIini and Topt were second and third ranked; with low continentality in Portugal, RUE was outranked by Topt). Low σ values associated with the most relevant parameters indicated limited parameter interactions. The importance of sensitivity analyses by exploring site × climate combinations is discussed as pre-requisite to evaluate either novel crop-modelling approaches or the application of known modelling solutions to conditions not explored previously. The need of developing tools for sensitivity analysis within the modelling environment is also emphasized. 相似文献
6.
In this paper we propose a heuristic approach for the problem of packing equal rectangles within a convex region. The approach is based on an Iterated Local Search scheme, in which the key step is the perturbation move. Different perturbation moves, both combinatorial and continuous ones, are proposed and compared through extensive computational experiments on a set of test instances. The overall results are quite encouraging. 相似文献
7.
Hendriks Martijn Verriet Jacques Basten Twan Theelen Bart Brassé Marco Somers Lou 《International Journal on Software Tools for Technology Transfer (STTT)》2017,19(4):487-510
International Journal on Software Tools for Technology Transfer - System designers make trade-offs between metrics of interest such as execution time, functional quality and cost to create a... 相似文献
8.
Dario Natali Mario Caironi Marco Sampietro Andrew P. Meacham Steven J. Vickers Michael D. Ward 《Optical Materials》2006,28(12):1362-1365
We report on the electrochromic behavior of a dinuclear ruthenium complex, which provides high environmental stability together with an intense absorption maximum at 1237 nm in solution in its +3 oxidation state. To verify its optoelectronic properties, we used this complex as the photoactive material in a planar photodetector prototype for near-infrared light pulses, succeeding in the detection of a train of light pulses at a wavelength of 1280 nm. 相似文献
9.
Veronica Conti Claudio Cantini Marco Romi Maria Michela Cesare Luigi Parrotta Stefano Del Duca Giampiero Cai 《International journal of molecular sciences》2022,23(10)
Future climate scenarios suggest that crop plants will experience environmental changes capable of affecting their productivity. Among the most harmful environmental stresses is drought, defined as a total or partial lack of water availability. It is essential to study and understand both the damage caused by drought on crop plants and the mechanisms implemented to tolerate the stress. In this study, we focused on four cultivars of tomato, an economically important crop in the Mediterranean basin. We investigated the biochemical mechanisms of plant defense against drought by focusing on proteins specifically involved in this stress, such as osmotin, dehydrin, and aquaporin, and on proteins involved in the general stress response, such as HSP70 and cyclophilins. Since sugars are also known to act as osmoprotectants in plant cells, proteins involved in sugar metabolism (such as RuBisCO and sucrose synthase) were also analyzed. The results show crucial differences in biochemical behavior among the selected cultivars and highlight that the most tolerant tomato cultivars adopt quite specific biochemical strategies such as different accumulations of aquaporins and osmotins. The data set also suggests that RuBisCO isoforms and aquaporins can be used as markers of tolerance/susceptibility to drought stress and be used to select tomato cultivars within breeding programs. 相似文献
10.
Binding Properties of RNA Quadruplex of SARS-CoV-2 to Berberine Compared to Telomeric DNA Quadruplex
Rosario Oliva Sanjib Mukherjee Magiliny Manisegaran Marco Campanile Pompea Del Vecchio Luigi Petraccone Roland Winter 《International journal of molecular sciences》2022,23(10)
Previous studies suggest that berberine, an isoquinoline alkaloid, has antiviral potential and is a possible therapeutic candidate against SARS-CoV-2. The molecular underpinnings of its action are still unknown. Potential targets include quadruplexes (G4Q) in the viral genome as they play a key role in modulating the biological activity of viruses. While several DNA-G4Q structures and their binding properties have been elucidated, RNA-G4Qs such as RG-1 of the N-gene of SARS-CoV-2 are less explored. Using biophysical techniques, the berberine binding thermodynamics and the associated conformational and hydration changes of RG-1 could be characterized and compared with human telomeric DNA-G4Q 22AG. Berberine can interact with both quadruplexes. Substantial changes were observed in the interaction of berberine with 22AG and RG-1, which adopt different topologies that can also change upon ligand binding. The strength of interaction and the thermodynamic signatures were found to dependent not only on the initial conformation of the quadruplex, but also on the type of salt present in solution. Since berberine has shown promise as a G-quadruplex stabilizer that can modulate viral gene expression, this study may also contribute to the development of optimized ligands that can discriminate between binding to DNA and RNA G-quadruplexes. 相似文献