全文获取类型
收费全文 | 1477篇 |
免费 | 120篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 7篇 |
综合类 | 4篇 |
化学工业 | 458篇 |
金属工艺 | 15篇 |
机械仪表 | 22篇 |
建筑科学 | 33篇 |
矿业工程 | 2篇 |
能源动力 | 38篇 |
轻工业 | 546篇 |
水利工程 | 11篇 |
石油天然气 | 14篇 |
无线电 | 46篇 |
一般工业技术 | 161篇 |
冶金工业 | 106篇 |
原子能技术 | 6篇 |
自动化技术 | 133篇 |
出版年
2024年 | 4篇 |
2023年 | 10篇 |
2022年 | 31篇 |
2021年 | 63篇 |
2020年 | 35篇 |
2019年 | 39篇 |
2018年 | 55篇 |
2017年 | 54篇 |
2016年 | 51篇 |
2015年 | 54篇 |
2014年 | 72篇 |
2013年 | 96篇 |
2012年 | 95篇 |
2011年 | 114篇 |
2010年 | 76篇 |
2009年 | 69篇 |
2008年 | 77篇 |
2007年 | 63篇 |
2006年 | 64篇 |
2005年 | 62篇 |
2004年 | 48篇 |
2003年 | 43篇 |
2002年 | 35篇 |
2001年 | 28篇 |
2000年 | 14篇 |
1999年 | 26篇 |
1998年 | 47篇 |
1997年 | 26篇 |
1996年 | 36篇 |
1995年 | 16篇 |
1994年 | 18篇 |
1993年 | 12篇 |
1992年 | 10篇 |
1991年 | 6篇 |
1990年 | 15篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1986年 | 2篇 |
1985年 | 12篇 |
1984年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1976年 | 4篇 |
1975年 | 1篇 |
1971年 | 2篇 |
1965年 | 1篇 |
1964年 | 1篇 |
排序方式: 共有1602条查询结果,搜索用时 109 毫秒
81.
Stability of dolphinfish (Coryphaena hippurus) and sardines (Sardina pilchardus) of different fat content (lean and fatty sardines) during frozen storage and its suitability for cold-smoking throughout storage were evaluated in order to overcome seasonal and excess catches of these species. Dolphinfish showed a relative stability regarding protein functionality (protein solubility, apparent viscosity, water and lipid holding capacity), lipid oxidation and total volatile basic nitrogen (TVBN) accumulation, which led to high acceptability ratings of the resulting smoked product throughout frozen storage (340 days). However, both lean and fatty sardines showed a marked loss of protein functionality, which coincided with the accumulation of oxidation products and TVBN. Freezing of raw muscle may become a valuable preservation method for the smoking industry to overcome the short caught period of dolphinfish in the Balearic Islands and to make use of excess catches of both, lean and fatty sardine. High quality smoked products may be obtained from the frozen muscle during approximately twelve, four and two months of frozen storage for Dolphinfish, lean and fatty sardine, respectively. 相似文献
82.
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
83.
Mario Gonzalez-de la Parra Pilar Rodriguez-Loaiza Salvador Namur 《Quality Engineering》2006,18(2):225-235
The impurity profile is one of the most important quality characteristics of a drug substance. Although it is always desirable to determine the chemical structure of all impurities forming the impurity profile, unfortunately this is not always economically and technically feasible because of the extremely low concentrations at which some impurities may be found in the drug substance. Therefore, alternative approaches to the chemical analysis are needed for trying to determine the origin of the unidentified impurities.
In a previous study conducted by our group, based on exploratory (principal component and hierarchical cluster) analysis, we were able to suggest a hypothesis for explaining the origin of the unidentified impurities of a drug substance. However, there was still a concern that alternative hypotheses might explain the same phenomenon equally well. This article explores the application of recent developments in structural equation modeling for the systematic generation and selection of hypotheses (models) worthy of being confirmed by chemical research. 相似文献
In a previous study conducted by our group, based on exploratory (principal component and hierarchical cluster) analysis, we were able to suggest a hypothesis for explaining the origin of the unidentified impurities of a drug substance. However, there was still a concern that alternative hypotheses might explain the same phenomenon equally well. This article explores the application of recent developments in structural equation modeling for the systematic generation and selection of hypotheses (models) worthy of being confirmed by chemical research. 相似文献
84.
We tested the ability of male slow-worms, Anguis fragilis, a limbless anguid lizard with secretive, semifossorial habits, to detect chemical associated with conspecifics by using a T-maze in the laboratory. Male slow-worms discriminated conspecific male and female scent deposits. Males selected the arm with female scent, suggesting that scent deposits may be used to locate potential mates. Also, male slow-worms did not avoid the chemicals of other males, suggesting that they are not territorial. However, males discriminated their own scent from those of other males, and spent more time exploring the arm with other male scent, which suggests that scent marks may bear information that could be used in future intrasexual social contexts. We conclude that discrimination of conspecifics based on scents may be more widespread than previously expected among lizards inhabiting visually restricted environments. 相似文献
85.
A technique that allows one to measure simultaneously the three velocity components in a fluid plane is presented. One obtains the quantitative information from only one holographic recording by combining two different reconstruction processes. As both processes use an interferometric comparison of two waves, we refer to this technique as dual holographic interferometry. The far-field fringe pattern that is obtained when reconstruction is made with an expanded laser beam allows one to determine the in-plane velocity components. The image-field fringe pattern that is obtained when a pointwise laser beam is used for reconstruction contains information about an out-of-plane velocity component. As the two reconstruction processes have different sensitivities, two different ways to combine them are proposed. The system has been demonstrated in a fluidlike solid object and in a convective flow. 相似文献
86.
Althaus R Torres A Peris C Beltran MC Fernandez N Molina MP 《Journal of food protection》2003,66(3):473-478
The presence of drug residues in ewe's milk samples can be determined by microbial assays. The main limitation of these tests is the large number of false-positive results associated with them. False-positive results can be explained by the interaction of certain substances naturally existing in ewe's milk with the growth of the microorganism used in the test. In this study, milk chemical composition (fat, protein, lactose, total solids), somatic cell counts (SCCs), free fatty acid concentrations, and lactoperoxidase system components were determined in order to investigate their influence on the rate of false-positive results for the BRT and Delvotest microbiological inhibitor tests. Milk samples were obtained after morning milking of Manchega ewes at 15, 30, 45, 60, 75, 90, 105, 120, and 135 days after parturition. The animals did not receive any kind of treatment or medicated feed throughout the experiment. The false-positive rates for BRT and Delvotest were 3.75 and 2.4%, respectively. When the logistic regression model was applied, the percentages of total solids for positive samples were significantly different from those for negative samples (16.90 versus 18.42% for BRT, 16.05 versus 18.45% for Delvotest), while the SCC logarithmic transformation was significantly higher for the positive samples than for the negative samples (5.38 versus 5.11 log units for BRT, 5.32 versus 5.11 log units for Delvotest). Moreover, Delvotest-positive samples exhibited thiocyanate concentrations higher than those of Delvotest-negative samples (8.18 mg/liter versus 6.85 mg/liter). Further analyses are needed to confirm the possible presence of antimicrobial residues in this particular type of milk sample. 相似文献
87.
MR imaging of baker cysts—prevalence and relation to internal derangements of the knee 总被引:3,自引:0,他引:3
Rationale and objectives: To evaluate the prevalence of popliteal cysts in patients studied with magnetic resonance (MR) imaging. Cyst presence and
volume will be related to other internal derangement of the knee.Materials and methods: Three hundred and eighty-two consecutive patients with a MR study of the knee were included. Images were obtained in the
three spatial orthogonal planes and evaluated through consensus. Four categories were established for the Baker cyst and synovial
fluid (absence, minimum, moderate and massive), and the presence of meniscal, cruciate ligaments and cartilage lesions were
recorded. Statistical analysis was carried out with bivariate analysis (χ2 of Pearson and Gamma tests).Results: From the 382 patients, 145 had Baker cysts (38.0%). Cyst content was minimum in 99, moderate in 34 and massive in 12. Joint
effusion was observed in 269 patients (70.4%), being minimal in 140 patients, moderate in 119 and massive in ten. Meniscal
lesions were observed in 195 patients (51%), while 58 patients (15%) had a cruciate ligament lesion. Baker cyst has a statistically
significant direct relationship with the presence and quantity of synovial fluid (P=0.002) and with the presence and type of meniscal lesion (P=0.01) but not with cruciate ligaments or cartilage lesions.Conclusions: The prevalence of Baker cysts in MR studies of the knee is high. Its presence and volume are related to the quantity of
synovial fluid, and to the presence and severity of meniscal lesions. 相似文献
88.
This work describes a framework that combines techniques from Adaptive Hypermedia and Natural Language processing in order to create, in a fully automated way, on-line information systems from linear texts in electronic format, such as textbooks. The process is divided into two steps: an off-line processing step, which analyses the source text, and an on-line step, which executes when a user connects to the system with a web browser, moment at which the contents and hyperlinks are generated. The framework has been implemented as the Welkin system, which has been used to build three adaptive on-line information sites in a quick and easy way. Some controlled experiments have been performed with real users aimed to provide positive feedback on the implementation of the system. 相似文献
89.
Pilar García-Soidán 《TEST》2007,16(3):479-503
In this work, the Nadaraya–Watson semivariogram estimation is considered for both the isotropic and the anisotropic settings.
Several properties of these estimators are analyzed and, particularly, their asymptotic normality is established in terms
of unknown characteristics of the random process. The latter provides a theoretical procedure for construction of confidence
intervals for the semivariogram via the normal quantiles, which in practice must be appropriately estimated. A numerical study
is included to illustrate the performance of the Nadaraya–Watson estimation when used to obtain confidence intervals.
相似文献
90.
Leonardo Augusto dos Santos Vieira Sergio Fernando Mayerle Carolina Luisa dos Santos Vieira Mônica Maria Mendes Luna 《Optimization and Engineering》2016,17(4):761-780
Available productive capacity is determinant of a company’s success once it allows meeting the current and future demand. This article proposes a quantitative model for determining long-term productive capacity in competitive oligopolistic markets, based on the Nash Equilibrium formulated as a Variational Inequality problem. Numerical examples enable an analytical evaluation of the economic equilibrium’s sensitivity to marginal costs, investment costs, hurdle rate, and market saturation. Results show that, in order to achieve a greater market share, it is important to adopt strategies that reduce marginal costs. On the other hand, variations in the hurdle rate may or may not reinforce the position of a competitor in the market and his interest in investing in capacity expansion. Additionally, market saturation may be achieved, beyond which investment becomes unattractive. Each of these is a positive outcome for society, triggering diversified investments and competition in economic sectors where competition is low and profits are high. 相似文献