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排序方式: 共有458条查询结果,搜索用时 10 毫秒
91.
92.
We investigated the variations of acute toxicity of mercury (Hg) in Daphnia magna under different temperatures, population origins, body sizes, and Hg pre-exposures. We measured Hg concentrations in the water and in the surviving daphnids, and used the subcellular fractionation approach to determine Hg in the metal-sensitive fraction (MSF) to predict Hg toxicity. The 24-h median lethal concentrations and 24-h lethal body burden were 12-55 microg L(-1) and 10-26 mg kg(-1) wet wt, respectively. High Hg tolerance accompanied by reduced Hg uptake occurred in the daphnids under extreme conditions (low temperature and high pre-exposure to Hg). Correlating Hg levels in different compartments and daphnid survival resulted in the following order of sequence: aqueous Hg > whole body Hg > Hg in the MSF. However, the threshold lethal concentration of Hg (concentration causing 1% mortality) based on the concentration of Hg in the MSF was the best indicator of Hg toxicity. Therefore, the subcellular fractionation approach is less useful in explaining acute toxicity than is sub-lethal Hg toxicity. The number of Hg binding sites in the animals varied under different conditions but the affinity of the transporter to Hg generally decreased as the animals' tolerance increased. Mercury tolerance under different conditions could be enhanced by reducing the Hg uptake, enhancing the intrinsic tolerance, and/or increasing the detoxification activity. 相似文献
93.
Forzani ES Li X Zhang P Tao N Zhang R Amlani I Tsui R Nagahara LA 《Small (Weinheim an der Bergstrasse, Germany)》2006,2(11):1283-1291
A method to functionalize single-walled carbon nanotubes (SWNTs) in a field-effect transistor (FET) device for the selective detection of heavy-metal ions is presented. In this method, peptide-modified polymers were electrochemically deposited onto SWNTs and the selective detection of metal ions was demonstrated by choosing appropriate peptide sequences. The signal transduction mechanism of the peptide-modified SWNT-FETs has also been studied. 相似文献
94.
– | This paper employs multiple theoretical perspectives — resource-and knowledge-based views as well as social network theory — to explore the dynamics of guanxi in the context of Chinese entrepreneurial firms. |
– | We propose a dynamic model and offer multiple propositions for researchers to examine the role of guanxi for knowledge management and decision-making at various developmental stages of such firms. |
95.
Using a heart motion observer, we compared the performance of two image reconstruction techniques, a 3D OS-EM algorithm with post Butterworth spatial filtering and a 4D MAP-RBI-EM algorithm. The task was to classify gated myocardial perfusion (GMP) SPECT images of beating hearts with or without regional motion abnormalities. Noise-free simulated GMP SPECT projection data was generated from two 4D NCAT beating heart phantom models, one with normal motion and the other with a 50% motion defect in a pie-shaped wedge region-of-interest (ROI) in the anterior-lateral left ventricular wall. The projection data were scaled to clinical GMP SPECT count level before Poisson noise was simulated to generate 40 noise realizations. The noise-free and noisy projection data were reconstructed using the two reconstruction algorithms, parameters chosen to optimize the tradeoff between image bias and noise. As a motion observer, a 3D motion estimation method previously developed was applied to estimate the radial motion on the ROI from two adjacent gates. The receiver operating characteristic (ROC) curves were computed for radial motion magnitudes corresponding to each reconstruction technique. The area under the ROC curve (AUC) was calculated as an index for classification of regional motion. The reconstructed images with better bias and noise tradeoff were found to offer better classification for hearts with or without regional motion defects. The 3D cardiac motion estimation algorithm, serving as a heart motion observer, was better able to distinguish the abnormal from the normal regional motion in GMP SPECT images obtained from the 4D MAP-RBI-EM algorithm than from the 3D OS-EM algorithm with post Butterworth spatial filtering. 相似文献
96.
Yeng-Yung Tsui Yi-Cheng Huang Chun-Lung Huang Shi-Wen Lin 《Numerical Heat Transfer, Part B: Fundamentals》2013,63(4):326-349
It is common to adopt finite-element methods to solve solid mechanics problems and finite-volume methods for fluid dynamics computations. The use of different methods causes complication of the solution procedure for problems involving both fluids and solids. In this study, a partitioned approach based on the finite-volume method for dynamic fluid–structure interaction is presented. The method is formulated in a way suitable for an unstructured mesh with arbitrary grid geometry. The variables for the fluid are stored at the centroids of grid cells, whereas those for the solid at the grid nodes. The latter arrangement makes it more suitable for large structure deformation. After spatial discretization for the solid using the finite-volume approach, the resulting system of ordinary differential equations is solved implicitly using the dual-time-stepping scheme. As for the fluid calculation, a pressure-based algorithm is employed and the time step is advanced in a prediction-correction manner. The finite-volume method for the solid is assessed by calculating the deformation and dynamics of a cantilever under various loads. Good agreement with analytical solutions is obtained. Then, the solution procedure is applied to two cases with coupled fluid flow and structure dynamics. One is the flow over a vertical plate with one end fixed on the floor in a channel. The other is the flow over a cylinder with a plate attached to it on the lee side. 相似文献
97.
Detection of lead in water using laser-induced breakdown spectroscopy and laser-induced fluorescence
Laser-induced breakdown spectroscopy (LIBS) is a well-known technique for fast, stand-off, and nondestructive analysis of the elemental composition of a sample. We have been investigating micro-LIBS for the past few years and demonstrating its application to microanalysis of surfaces. Recently, we have integrated micro-LIBS with laser-induced fluorescence (LIF), and this combination, laser ablation laser-induced fluorescence (LA-LIF), allows one to achieve much higher sensitivity than traditional LIBS. In this study, we use a 170 microJ laser pulse to ablate a liquid sample in order to measure the lead content. The plasma created was re-excited by a 10 microJ laser pulse tuned to one of the lead resonant lines. Upon optimization, the 3sigma limit of detection was found to be 35 +/- 7 ppb, which is close to the EPA standard for the level of lead allowed in drinking water. 相似文献
98.
It is well known that seven parameters completely describe a circular cone-beam geometry in either flat-panel X-ray computed tomography (CT) or single pinhole SPECT imaging. This paper considers the problem of determining one of the seven parameters only, the detector in-plane rotation or twist angle η. We describe a graphical procedure that can determine η independently of all other six parameters from a geometric calibration scan of point objects. Our method is exact in the ideal noise-free case and is general in that the other two out-of-plane detector rotation angles θ and φ can be nonzero. The calibration scan typically needs at least two point objects and an even number of projection views over a full 360° data acquisition. Under certain conditions, projection data truncation or a short scan acquisition of 180° + fan angle can be accommodated without affecting the accuracy of the calibration result. The graphical method is equally applicable to rotational multipinhole SPECT geometry. In this case, the final result is averaged from the individual estimates considering each pinhole separately. We use computer simulations and a multipinhole SPECT experiment to demonstrate the accuracy and precision of the proposed method. 相似文献
99.
Derivation of Varying Specific Heat Gasdynamic Functions,Normal Shock Analytical Solution and its Improvements 总被引:1,自引:0,他引:1
TsuiChih-Ya 《热科学学报(英文版)》1992,1(4):235-240
A set of new gasdynamic functions with varying specific heat are derived for the first time.An original analyticalsolution of normal shock waves is worked out therewith.This solution is thereafter further improved by notinvolving total temperature.Illustrative examples of comparison are given,including also some approximatesolutions to show the orders of their errors. 相似文献
100.
Shu-Yu Cheng Nan-Fu Chen Zhi-Hong Wen Zhi-Kang Yao Kuan-Hao Tsui Hsiao-Mei Kuo Wu-Fu Chen 《International journal of molecular sciences》2021,22(13)
Glioblastoma multiforme (GBM) is a malignant primary brain tumor. The 5-year relative survival rate of patients with GBM remains <30% on average despite aggressive treatments, and secondary therapy fails in 90% of patients. In chemotherapeutic failure, detoxification proteins are crucial to the activity of chemotherapy drugs. Usually, glutathione S-transferase (GST) superfamily members act as detoxification enzymes by activating xenobiotic metabolites through conjugation with glutathione in healthy cells. However, some overexpressed GSTs not only increase GST activity but also trigger chemotherapy resistance and tumorigenesis-related signaling transductions. Whether GSTM3 is involved in GBM chemoresistance remains unclear. In the current study, we found that T98G, a GBM cell line with pre-existing temozolomide (TMZ) resistance, has high glycolysis and GSTM3 expression. GSTM3 knockdown in T98G decreased glycolysis ability through lactate dehydrogenase A activity reduction. Moreover, it increased TMZ toxicity and decreased invasion ability. Furthermore, we provide next-generation sequencing–based identification of significantly changed messenger RNAs of T98G cells with GSTM3 knockdown for further research. GSTM3 was downregulated in intrinsic TMZ-resistant T98G with a change in the expression levels of some essential glycolysis-related genes. Thus, GSTM3 was associated with glycolysis in chemotherapeutic resistance in T98G cells. Our findings provide new insight into the GSTM3 mechanism in recurring GBM. 相似文献