全文获取类型
收费全文 | 2552篇 |
免费 | 147篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 102篇 |
综合类 | 4篇 |
化学工业 | 629篇 |
金属工艺 | 96篇 |
机械仪表 | 50篇 |
建筑科学 | 91篇 |
矿业工程 | 7篇 |
能源动力 | 90篇 |
轻工业 | 197篇 |
水利工程 | 9篇 |
石油天然气 | 5篇 |
无线电 | 211篇 |
一般工业技术 | 434篇 |
冶金工业 | 393篇 |
原子能技术 | 21篇 |
自动化技术 | 362篇 |
出版年
2023年 | 49篇 |
2022年 | 61篇 |
2021年 | 98篇 |
2020年 | 86篇 |
2019年 | 79篇 |
2018年 | 78篇 |
2017年 | 75篇 |
2016年 | 90篇 |
2015年 | 56篇 |
2014年 | 103篇 |
2013年 | 152篇 |
2012年 | 116篇 |
2011年 | 156篇 |
2010年 | 88篇 |
2009年 | 98篇 |
2008年 | 115篇 |
2007年 | 84篇 |
2006年 | 78篇 |
2005年 | 52篇 |
2004年 | 57篇 |
2003年 | 53篇 |
2002年 | 49篇 |
2001年 | 35篇 |
2000年 | 26篇 |
1999年 | 47篇 |
1998年 | 132篇 |
1997年 | 84篇 |
1996年 | 39篇 |
1995年 | 48篇 |
1994年 | 44篇 |
1993年 | 40篇 |
1992年 | 19篇 |
1991年 | 15篇 |
1990年 | 19篇 |
1989年 | 14篇 |
1988年 | 13篇 |
1987年 | 16篇 |
1986年 | 12篇 |
1985年 | 21篇 |
1984年 | 10篇 |
1983年 | 15篇 |
1982年 | 9篇 |
1981年 | 9篇 |
1980年 | 9篇 |
1979年 | 16篇 |
1978年 | 9篇 |
1977年 | 16篇 |
1976年 | 20篇 |
1973年 | 15篇 |
1967年 | 11篇 |
排序方式: 共有2701条查询结果,搜索用时 15 毫秒
11.
12.
AIM: The quality of segmentation and three-dimensional reconstruction of anatomical structures in tomographic slices is often impaired by disturbances due to partial volume effects (PVE). The potential for artefact reduction by use of the morphological image processing operators (MO) erosion and dilation is investigated. DESIGN: The CT examinations of 31 patients with pathological alterations in lung or brain were segmented using automatic region growing and the MO were applied in a different number of iterations. The processed regions were 3D-reconstructed (shaded surface display, MIP, volume rendering) and the occurrence of PVE-related artefacts using the signal-to-background ratio (SBR) prior to and after MO application was compared. RESULTS: For all patients under review, the artefacts caused by PVE were significantly reduced by erosion (lung: mean SBRpre = 1.67, SBRpost = 4.83; brain: SBRpre = 1.06, SBRpost = 1.29) even with only a small number of iterations. Region dilation was applied to integrate further structures (e.g. at tumor borders) into a configurable neighbourhood for segmentation and quantitative analysis. CONCLUSIONS: The MO represent an efficient approach for the reduction of PVE artefacts in 3D-CT reconstructions and allow optimized visualization of individual objects. 相似文献
13.
Generating topological structures for surface models 总被引:4,自引:0,他引:4
Rapid prototyping has imposed new requirements on the processing of CAD models. To manufacture an object directly, the model must correspond to a real object and thus represent a closed volume. Its boundary must be continuous and closed, and no cracks or improper intersections are allowed. CAD models cannot always meet these requirements, especially when they are constructed by a surface modeler. The algorithm discussed analyzes surface models and generates a topological structure for them that meets rapid prototyping requirements for a closed volume with a continuous, closed boundary 相似文献
14.
Lasserre S Hernando J Hill S Schümann F Anasagasti Pde M Jaoudé GA Markram H 《IEEE transactions on visualization and computer graphics》2012,18(2):214-227
We present a process to automatically generate three-dimensional mesh representations of the complex, arborized cell membrane surface of cortical neurons (the principal information processing cells of the brain) from nonuniform morphological measurements. Starting from manually sampled morphological points (3D points and diameters) from neurons in a brain slice preparation, we construct a polygonal mesh representation that realistically represents the continuous membrane surface, closely matching the original experimental data. A mapping between the original morphological points and the newly generated mesh enables simulations of electrophysiolgical activity to be visualized on this new membrane representation. We compare the new mesh representation with the state of the art and present a series of use cases and applications of this technique to visualize simulations of single neurons and networks of multiple neurons. 相似文献
15.
For pseudo-random generators where one or several LFSRs are combined by a memoryless function, it is known that the output sequences are correlated to certain LFSR-sequences whose correlation coefficients c
t
satisfy the equation
i
c
2
i
= 1. In this paper it is proved that a corresponding result also holds for generators whose LFSRs are connected to a combiner with memory.If correlation probabilities are conditioned on side information, e.g., on known output digits, it is shown that new or stronger correlations may occur. This is exemplified for the summation cipher with only two LFSRs where such correlations can be exploited in a known plaintext attack. A cryptanalytic algorithm is given which is shown to be successful for LFSRs of considerable length and with arbitrary feedback connection.A preliminary version of this paper was presented at Eurocrypt '90, May 21–24, Århus, Denmark, and has appeared in the proceedings, pp. 204–213. 相似文献
16.
Felix Baessler 《OR Spectrum》1992,14(1):11-18
Summary In this paper, we present a novel relaxation method for the integer programming problem:Ax=b,A {–1,0,+1}m×N,x {0,1}N, N>m. The report includes experimental results of problems with up tom=100 equations andN=400 variables. 相似文献
17.
Lisa Goedtke Heike Sprenger Ute Hofmann Felix F. Schmidt Helen S. Hammer Ulrich M. Zanger Oliver Poetz Albrecht Seidel Albert Braeuning Stefanie Hessel-Pras 《International journal of molecular sciences》2021,22(1)
Polycyclic aromatic hydrocarbons (PAHs) are environmental pollutants produced by incomplete combustion of organic matter. They induce their own metabolism by upregulating xenobiotic-metabolizing enzymes such as cytochrome P450 monooxygenase 1A1 (CYP1A1) by activating the aryl hydrocarbon receptor (AHR). However, previous studies showed that individual PAHs may also interact with the constitutive androstane receptor (CAR). Here, we studied ten PAHs, different in carcinogenicity classification, for their potential to activate AHR- and CAR-dependent luciferase reporter genes in human liver cells. The majority of investigated PAHs activated AHR, while non-carcinogenic PAHs tended to activate CAR. We further characterized gene expression, protein abundancies and activities of the AHR targets CYP1A1 and 1A2, and the CAR target CYP2B6 in human HepaRG hepatoma cells. Enzyme induction patterns strongly resembled the profiles obtained at the receptor level, with AHR-activating PAHs inducing CYP1A1/1A2 and CAR-activating PAHs inducing CYP2B6. In summary, this study provides evidence that beside well-known activation of AHR, some PAHs also activate CAR, followed by subsequent expression of respective target genes. Furthermore, we found that an increased PAH ring number is associated with AHR activation as well as the induction of DNA double-strand breaks, whereas smaller PAHs activated CAR but showed no DNA-damaging potential. 相似文献
18.
Jan Haas Karen S. Frese Farbod Sedaghat-Hamedani Elham Kayvanpour Rewati Tappu Rouven Nietsch Oguz Firat Tugrul Michael Wisdom Carsten Dietrich Ali Amr Tanja Weis Torsten Niederdrnk Michael P. Murphy Thomas Krieg Marcus Drr Uwe Vlker Jens Fielitz Norbert Frey Stephan B. Felix Andreas Keller Hugo A. Katus Benjamin Meder 《International journal of molecular sciences》2021,22(4)
With more than 25 million people affected, heart failure (HF) is a global threat. As energy production pathways are known to play a pivotal role in HF, we sought here to identify key metabolic changes in ischemic- and non-ischemic HF by using a multi-OMICS approach. Serum metabolites and mRNAseq and epigenetic DNA methylation profiles were analyzed from blood and left ventricular heart biopsy specimens of the same individuals. In total we collected serum from n = 82 patients with Dilated Cardiomyopathy (DCM) and n = 51 controls in the screening stage. We identified several metabolites involved in glycolysis and citric acid cycle to be elevated up to 5.7-fold in DCM (p = 1.7 × 10−6). Interestingly, cardiac mRNA and epigenetic changes of genes encoding rate-limiting enzymes of these pathways could also be found and validated in our second stage of metabolite assessment in n = 52 DCM, n = 39 ischemic HF and n = 57 controls. In conclusion, we identified a new set of metabolomic biomarkers for HF. We were able to identify underlying biological cascades that potentially represent suitable intervention targets. 相似文献
19.
We show that the model checking problem for intuitionistic propositional logic with one variable is complete for logspace-uniform AC 1. For superintuitionistic logics with one variable, we obtain NC 1-completeness for the model checking problem. 相似文献
20.
Summary: The dicationic [(dppp)Pd(NCCH3)2](BF4)2 catalyst (dppp = 1,3‐bis(diphenylphosphino)propane) was applied in a liquid monomer, two phase process for the CO/propene copolymerization reaction. For the first time it was possible to synthesize propene/CO copolymers with an activity up to 7 500 g/(mol · h) and molecular weights of 500 000 g/mol. Activities up to 40 000 g/(mol · h) could be obtained with the use of the unsymmetric catalyst [(CF3‐dppp)Pd(NCCH3)](BF4)2 (CF3‐dppp = 1‐diphenylphosphino‐3‐bis[3,5‐di(trifluormethyl)phenyl]phosphinopropane) in homogeneous liquid propene solution.