全文获取类型
收费全文 | 1748篇 |
免费 | 61篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 44篇 |
综合类 | 2篇 |
化学工业 | 435篇 |
金属工艺 | 42篇 |
机械仪表 | 45篇 |
建筑科学 | 83篇 |
矿业工程 | 3篇 |
能源动力 | 91篇 |
轻工业 | 182篇 |
水利工程 | 8篇 |
石油天然气 | 2篇 |
无线电 | 74篇 |
一般工业技术 | 312篇 |
冶金工业 | 170篇 |
原子能技术 | 20篇 |
自动化技术 | 297篇 |
出版年
2023年 | 7篇 |
2022年 | 18篇 |
2021年 | 26篇 |
2020年 | 25篇 |
2019年 | 33篇 |
2018年 | 36篇 |
2017年 | 37篇 |
2016年 | 54篇 |
2015年 | 30篇 |
2014年 | 67篇 |
2013年 | 116篇 |
2012年 | 84篇 |
2011年 | 146篇 |
2010年 | 79篇 |
2009年 | 87篇 |
2008年 | 98篇 |
2007年 | 90篇 |
2006年 | 90篇 |
2005年 | 84篇 |
2004年 | 52篇 |
2003年 | 64篇 |
2002年 | 36篇 |
2001年 | 42篇 |
2000年 | 34篇 |
1999年 | 23篇 |
1998年 | 43篇 |
1997年 | 31篇 |
1996年 | 22篇 |
1995年 | 22篇 |
1994年 | 15篇 |
1993年 | 19篇 |
1992年 | 12篇 |
1991年 | 11篇 |
1990年 | 13篇 |
1989年 | 16篇 |
1988年 | 16篇 |
1987年 | 15篇 |
1986年 | 7篇 |
1985年 | 11篇 |
1984年 | 9篇 |
1983年 | 13篇 |
1982年 | 11篇 |
1981年 | 10篇 |
1980年 | 4篇 |
1979年 | 7篇 |
1978年 | 6篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1975年 | 5篇 |
1967年 | 3篇 |
排序方式: 共有1810条查询结果,搜索用时 15 毫秒
141.
Anders Knudby Ellsworth LeDrew Alexander Brenning 《Remote sensing of environment》2010,114(6):1230-1241
During the last three decades, the large spatial coverage of remote sensing data has been used in coral reef research to map dominant substrate types, geomorphologic zones, and bathymetry. During the same period, field studies have documented statistical relationships between variables quantifying aspects of the reef habitat and its fish community. Although the results of these studies are ambiguous, some habitat variables have frequently been found to correlate with one or more aspects of the fish community. Several of these habitat variables, including depth, the structural complexity of the substrate, and live coral cover, are possible to estimate with remote sensing data. In this study, we combine a set of statistical and machine-learning models with habitat variables derived from IKONOS data to produce spatially explicit predictions of the species richness, biomass, and diversity of the fish community around two reefs in Zanzibar. In the process, we assess the ability of IKONOS imagery to estimate live coral cover, structural complexity and habitat diversity, and we explore the importance of habitat variables, at a range of spatial scales, in the predictive models using a permutation-based technique. Our findings indicate that structural complexity at a fine spatial scale (∼ 5 to 10 m) is the most important habitat variable in predictive models of fish species richness and diversity, whereas other variables such as depth, habitat diversity, and structural complexity at coarser spatial scales contribute to predictions of biomass. In addition, our results demonstrate that complex model types such as tree-based ensemble techniques provide superior predictive performance compared to the more frequently used linear models, achieving a reduction of the cross-validated root-mean-squared prediction error of 3-11%. Although aerial photographs and airborne lidar instruments have recently been used to produce spatially explicit predictions of reef fish community variables, our study illustrates the possibility of doing so with satellite data. The ability to use satellite data may bring the cost of creating such maps within the reach of both spatial ecology researchers and the wide range of organizations involved in marine spatial planning. 相似文献
142.
Simon M. M. Pedersen Caroline Nebel Niels Chr. Nielsen Henrik J. Andersen Johan Olsson Magnus Simrén Lena Öhman Ulla Svensson Hanne C. Bertram Anders Malmendal 《European Food Research and Technology》2011,233(6):1013-1021
In the present study, the use of gas chromatography mass spectrometry (GC–MS)-based metabonomics to characterize blood serum
in an intervention study of patients suffering from the common gastrointestinal disorder irritable bowel syndrome (IBS) was
investigated. The patients included in the study consumed an acidified milk product with (n = 30) or without probiotics (n = 31) (Lactobacillus paracasei F19, Lactobacillus acidophilus LA-5 and Bifidobacterium lactis BB-12) for an 8-week period, and blood serum samples were collected before and after the intervention. Acidified milk is
commonly used as a delivering vector for probiotics in commercial consumer settings. The serum samples were extracted and
derivatized using N-Methyl-N-(trimethylsilyl) trifluoroacetamide (MSTFA), and GC–MS analysis was carried out. Multivariate data analysis including principal
component analysis (PCA), orthogonal partial least squares-discriminant analysis (OPLS-DA), and S-plot was applied on the
obtained GC–MS data, which revealed higher serum lactate, glutamine, proline creatinine/creatine, and aspartic acid levels
and lower serum glucose levels after the intervention period for both treatment groups. Consequently, the present study indicated
an effect of acidified milk consumption on the plasma metabolite profile, which was independent of a concomitant intake of
probiotics. In addition, the present study demonstrates that GC–MS is a useful analytical technique for metabonomics studies
of blood serum. 相似文献
143.
Anders Olsson Jan Oscarsson Erik Serrano Bo Källsner Marie Johansson Bertil Enquist 《Holz als Roh- und Werkstoff》2013,71(3):319-333
Machine strength grading of structural timber is based upon relationships between so called indicating properties (IPs) and bending strength. However, such relationships applied on the market today are rather poor. In this paper, new IPs and a new grading method resulting in more precise strength predictions are presented. The local fibre orientation on face and edge surfaces of wooden boards was identified using high resolution laser scanning. In combination with knowledge regarding basic wood material properties for each investigated board, the grain angle information enabled a calculation of the variation of the local MOE in the longitudinal direction of the boards. By integration over cross-sections along the board, an edgewise bending stiffness profile and a longitudinal stiffness profile, respectively, were calculated. A new IP was defined as the lowest bending stiffness determined along the board. For a sample of 105 boards of Norway spruce of dimension 45 × 145 × 3,600 mm³, a coefficient of determination as high as 0.68–0.71 was achieved between this new IP and bending strength. For the same sample, the coefficient of determination between global MOE, based on the first longitudinal resonance frequency and the board density, and strength was only 0.59. Furthermore, it is shown that improved accuracy when determining the stiffness profiles of boards will lead to even better predictions of bending strength. The results thus motivate both an industrial implementation of the suggested method and further research aiming at more accurately determined board stiffness profiles. 相似文献
144.
145.
The use of supercritical fluids for delivering biocides into wood and wood composites is an attractive technique because of the high penetration capacity of these solvents compared to the liquids used in conventional treatment methods. During the past two decades supercritical wood impregnation has moved from lab scale to commercial scale.This review presents an overview of the main research efforts that has been carried out within the field of supercritical wood impregnation. Results and conclusions of research within four main categories, i.e. (1) effects of impregnation on physical properties of samples, (2) retention and distribution of biocide in impregnated samples, (3) biological performance of impregnated samples, and (4) mathematical modeling of supercritical impregnation are reviewed and discussed. 相似文献
146.
Katarina Stenman Jón B. Hauksson Gerhard Gröbner Pär Stattin Anders Bergh Katrine Riklund 《Magma (New York, N.Y.)》2009,22(6):327-331
Object
Polyunsaturated omega-6 fatty acids (PUFAs) have been shown to promote prostate cancer. Here, we describe the use of HRMAS NMR spectroscopy to detect omega-6 PUFA species in prostate tissues. 相似文献147.
The RCSJ model of resistively and capacitively shunted Josephson junctions is used to describe superconducting point contacts over a wide range of resistances up to the metallic–tunneling transition. Their small dynamic capacitance of order C = 0.1 fF due to the point-contact geometry results in a huge plasma frequency. The critical current is then strongly suppressed and the contact resistance becomes finite because of quantum-mechanical zero-point fluctuations of the Josephson plasma and the rather large escape rate out of the zero-voltage state due to quantum tunneling. We test the predictions of the RCSJ model on the classical superconductors lead, indium, aluminum, and cadmium. 相似文献
148.
Dangerously high interference temperatures can occur at points where cables cross external heat sources even when the crossing occurs at 90°. For perpendicular and oblique crossings, these interference temperatures are usually ignored for distribution circuits, whereas for transmission cables, corrective actions in physical installation condition are sometimes taken. Analytical solutions are almost never used to determine the effect of external heat source on the ampacity of the rated cable. The main reason no computations are performed is an absence of either derating formulas or derating tables (curves) and not the lack of a need. To fill this gap, an analytical solution for the computation of the derating factors has been developed and is presented in this paper. The solution is simple and accurate enough to be suitable for standardization purposes. A numerical example involving the intersection of a pipe-type cable by a distribution circuit is presented to show the effect of perpendicular and oblique crossings on the ampacity of both circuits. In this practical example, the ampacity of the pipe-type cable is significantly affected for a range of crossing angles. A conservative practice, used by many utilities in cases like this, would be to assume that the cables are parallel. However, in our example for a 90° crossing, such an approach would unnecessarily decreases the ampacity of the pipe-type cable by almost 20% 相似文献
149.
Anders Broberg 《工程教育杂志》2001,90(1):63-68
Traditionally, behavioristic models have been used for the design of interactive learning environments. In contrast, this paper proposes a pedagogical model based on social constructionism and phenomenology which we believe is more adequate when, for instance, information seeking and WWW become natural components in the learning situation. In this model, learners are seen as persons who continuously alter their conceptions and ideas by working with data, information, and knowledge, i.e. learners as knowledge workers. The most important point in viewing learners as knowledge workers is exactly that the learners change their understanding by working with the information, and that they do that with the help of cognitive tools. I see it as a necessity that the learning environment consists of tools that support them in their learning processes: tools for constructing, processing and observing information, data, and knowledge. Equally important in this new kind of learning situation are tools to establish and maintain focus, manage information overload, to bridge distances in the learning situation, and to communicate. 相似文献
150.