全文获取类型
收费全文 | 2814篇 |
免费 | 93篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 45篇 |
综合类 | 6篇 |
化学工业 | 548篇 |
金属工艺 | 43篇 |
机械仪表 | 78篇 |
建筑科学 | 56篇 |
矿业工程 | 1篇 |
能源动力 | 88篇 |
轻工业 | 120篇 |
水利工程 | 8篇 |
石油天然气 | 4篇 |
无线电 | 466篇 |
一般工业技术 | 449篇 |
冶金工业 | 614篇 |
原子能技术 | 8篇 |
自动化技术 | 378篇 |
出版年
2023年 | 13篇 |
2022年 | 41篇 |
2021年 | 52篇 |
2020年 | 29篇 |
2019年 | 33篇 |
2018年 | 54篇 |
2017年 | 44篇 |
2016年 | 52篇 |
2015年 | 42篇 |
2014年 | 90篇 |
2013年 | 189篇 |
2012年 | 141篇 |
2011年 | 157篇 |
2010年 | 118篇 |
2009年 | 150篇 |
2008年 | 153篇 |
2007年 | 137篇 |
2006年 | 98篇 |
2005年 | 82篇 |
2004年 | 76篇 |
2003年 | 70篇 |
2002年 | 65篇 |
2001年 | 49篇 |
2000年 | 44篇 |
1999年 | 52篇 |
1998年 | 232篇 |
1997年 | 165篇 |
1996年 | 78篇 |
1995年 | 63篇 |
1994年 | 56篇 |
1993年 | 44篇 |
1992年 | 34篇 |
1991年 | 32篇 |
1990年 | 14篇 |
1989年 | 9篇 |
1988年 | 16篇 |
1987年 | 12篇 |
1986年 | 11篇 |
1985年 | 12篇 |
1984年 | 14篇 |
1983年 | 5篇 |
1982年 | 9篇 |
1981年 | 11篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1977年 | 12篇 |
1976年 | 20篇 |
1975年 | 5篇 |
1973年 | 6篇 |
1967年 | 3篇 |
排序方式: 共有2912条查询结果,搜索用时 14 毫秒
991.
Tao Ju Joe Warren James Carson Gregor Eichele Christina Thaller Wah Chiu Musodiq Bello Ioannis Kakadiaris 《The Visual computer》2005,21(8-10):764-773
Constructing 3D surfaces that interpolate 2D curves defined on parallel planes is a fundamental problem in computer graphics with wide applications including modeling anatomical structures. Typically the problem is simplified so that the 2D curves partition each plane into only two materials (e.g., air versus tissue). Here we consider the general problem where each plane is partitioned by a curve network into multiple materials (e.g., air, cortex, cerebellum, etc.). We present a novel method that automatically constructs a surface network from curve networks with arbitrary topology and partitions an arbitrary number of materials. The surface network exactly interpolates the curve network on each plane and is guaranteed to be free of gaps or self-intersections. In addition, our method provides a flexible framework for user interaction so that the surface topology can be modified conveniently when necessary. As an application, we applied the method to build a high-resolution 3D model of the mouse brain from 2D anatomical boundaries defined on 350 tissue sections. The surface network accurately models the partitioning of the brain into 17 abutting anatomical regions with complex topology. 相似文献
992.
The channel capacity of indoor multiple‐input multiple‐output ultra‐wide band (MIMO‐UWB) transmission for smart antenna is presented. The genetic algorithm (GA) is used to synthesize the radiation pattern of the directional antenna array to maximize the capacity performance in indoor MIMO‐UWB communication system. Three types of antenna arrays such as circular shape, L shape and Y shape arrays are used in the transmitter and their corresponding capacity on several paths in the indoor environment are calculated. The UWB impulse responses of the indoor channel for any transmitter‐receiver location are computed by applying shooting and bouncing ray/image (SBR/image) techniques, inverse fast Fourier transform and Hermitian processing. By using the calculated frequency response, the capacity performance of the synthesized antenna pattern on MIMO‐UWB system can be computed. Based on the topography of the antenna array and the capacity formula, the array pattern synthesis problem can be reformulated into an optimization problem and solved by the GA algorithm. The GA algorithm optimization is applied to a high order nonlinear optimization problem. The novelties of our approach is not only choosing capacity as the cost function instead of sidelobe level of the antenna pattern, but also considering the antenna feed length effect of each array element. The cost function for the problem is nonsmooth and discontinuous with respect to the antenna pattern. It is difficult to solve by gradient methods, since the derivative is hard to derive. The GA algorithm is employed to optimize the excitation voltages and feed lengths for these antenna arrays to increase the capacity. The strong point of the GA is that it can find out the solution even if the performance index cannot be formulated by simple equations. Numerical results show that the synthesized antenna array pattern is effective to focus maximum gain to the LOS path for these antenna arrays. In other words, the receiver can increase the received signal energy to noise ratio. The synthesized array pattern also can mitigate severe multipath fading in complex propagation environment. As a result, the capacity can be increased substantially in indoor MIMO‐UWB communication system. The investigated results can help communication engineers improve their planning and design of indoor wireless communication. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013. 相似文献
993.
Skeletal muscle tissue was obtained from the vastus lateralis or peroneus brevis muscles of 34 healthy volunteers. Focal and extensive areas of Z band streaming and disruption of myofibrillar architecture without Z band streaming were quantified in Araldite-embedded specimens examined in the phase microscope. Extensive areas of Z band streaming in more than 2.0 percent of fibers was present in only two of the 34 volunteers. Myofibrillar disruptions without Z band streaming was much less common than Z band streaming. The size of extensive areas of Z band streaming or myofibrillar disruptions was quantified by counting the number of adjacent fibrils and contiguous sarcomeres occupied by either type of lesion. These data should be of use in determining if such lesions are present in excessive amounts in suspected pathologic material. 相似文献
994.
Follow-up examinations, ranging from four to more than 20 years, were performed on 100 patients with chronic cyclitis whose ages at onset were from 4 to 58 years. Cataracts were found in 42% of eyes and macular disease secondary to macular edema in 28% of eyes. Band keratopathy, glaucoma, retinal detachment, retinoschisis, vitreous hemorrhage, retinal hemorrhage, and vessels leaving the disk margin were also noted. The complications resulting in decreased vision in chronic cyclitis were macular edema in active cases and macular degenerative changes in the late inactive stages. Of all eyes with final visual acuity of 6/12 (20/40) or less, 74% had permanent, late macular changes secondary to earlier cystoid macular edema. Vitreous opacities or cells, or both, caused decreased visual acuity in the early active stages of chronic cyclitis but were not major factors in the ultimate visual prognosis in the late inactive stages. At the final examination, vitreous opacities caused a visual loss in only 9% of the eyes that had visual acuity of 6/12 (20/40) or less. It was difficult to determine whether corticosteroids caused cataract formation and glaucoma. 相似文献
995.
Dev-Aur Chou Yueh-Hsiung Kuo Ming-Shiou JanYuan-Yen Chang Yi-Chen ChenHis-Lin Chiu Wei-Tang ChangChin-Lin Hsu 《Food chemistry》2012,131(4):1460-1465
The objective of this study was to investigate the anticancer activity of caffeate derivatives in human cancer cells. Our results demonstrate that caffeate derivatives decreased the population growth of COLO 205, assessed using the MTT assay. However, caffeate derivatives, at the concentrations used in this study (0-250 μM) did not affect the viability of HepG2, Huh7, PLC5, and SK-Hep-1 cells. Flow cytometric analysis of COLO 205 cells exposed to decyl caffeate showed that the number of apoptotic cells increased in a time- and dose-dependent manner. Western blot analysis revealed that decyl caffeate stimulated an increase in protein expression levels of p53, Fas, FasL, AIF, and Apaf-1. Additionally, treatment with decyl caffeate changed the expression levels of Bcl-2 family members and subsequently induced the activation of caspase-12, caspase-9, and caspase-3, which was followed by cleavage of PARP. Our findings highlight the chemopreventive potential of decyl caffeate. 相似文献
996.
Kun-Nan Chen Ming-Ju Chen Je-Ruel Liu Chin-Wen Lin Hsin-Yi Chiu 《Journal of food science》2005,70(5):M260-M266
ABSTRACT: The purpose of this research was to improve probiotic microencapsulation using prebiotics and modern optimization techniques to determine optimal processing conditions, performance, and survival rates. Prebiotics (fructooligosaccharides or isomaltooligosaccharides), growth promoter (peptide), and sodium algi-nate were incorporated as coating materials to microencapsulate 4 probiotics ( Lactobacillus acidophilus, Lacto-bacillus casei, Bifidobacterium bifidum , and Bifidobacterium longum ). The proportion of the prebiotics, peptide, and sodium alginate was optimized using response surface methodology (RSM) to 1st construct a surface model, with sequential quadratic programming (SQP) subsequently adopted to optimize the model and evaluate the survival of microencapsulated probiotics under simulated gastric fluid test. Optimization results indicated that 1% sodium alginate mixed with 1% peptide and 3% fructooligosaccharides as coating materials would produce the highest survival in terms of probiotic count. The verification experiment yielded a result close to the predicted values, with no significant difference ( P > 0.05). The storage results also demonstrated that addition of prebiotics in the walls of probiotic microcapsules provided improved protection for the active organisms. These probiotic counts remained at 106 to 107 colony-forming units (CFU)/g for microcapsules stored for 1 mo and then treated in simulated gastric fluid test and bile salt test. 相似文献
997.
Salmonella enterica serovar Choleraesuis may cause swine salmonellosis and human infection. Because the conventional method for detection of this Salmonella serovar may take 3 to 5 days, a PCR method for detection was evaluated. By comparing the sequence of the phase 1 flagellin (fliC) gene of Salmonella Choleraesuis with that of other Salmonella serovars and of other bacteria species available in GenBank, two PCR primers (flinC-F and flinC-R) were designed. Using these primers, all 97 Salmonella Choleraesuis strains assayed generated the expected PCR product, with a molecular mass of 963 bp. Except for S. enterica Paratyphi C, Salmonella isolates other than Salmonella Choleraesuis and non-Salmonella isolates, including strains of Enterobacteriaceae, all generated negative PCR results. Salmonella Paratyphi C could be differentiated from Salmonella Choleraesuis through the use of primers designed from the viaB gene. When Salmonella Choleraesuis isolates from swine stool, pork, liver, feed, and human whole blood samples were assayed with a preenrichment step, as low as 1 CFU/g or ml of the original sample could be detected. 相似文献
998.
Effect of coagulation on the size of MF and UF membrane foulants 总被引:3,自引:0,他引:3
Microfiltration (MF) and ultrafiltration (UF) have become common water treatment technologies for the removal of particles from natural waters. Many water utilities are now integrating MF/UF with other treatment processes to provide treatment for nonparticulate contaminants. Research is needed to understand the impact that other processes have on MF/UF performance. This study was conducted to investigate the interactions between water quality, coagulation, and membrane fouling. The study examined the fouling of MF/UF membranes by natural waters with and without coagulation by specific fractions of constituents in natural water, separated by size. This research found thatthe component of natural organic matter (NOM) smaller than 100 kDa contributes relatively little to fouling during filtration of either raw or coagulated water. The fraction between 1 microm and 100 kDa contributes a significant portion of the fouling. After coagulation pretreatment, fouling due to various size fractions in the feedwater can change. 相似文献
999.
1000.
In this study, individual selected lactic acid bacteria strains Lactobacillus acidophilus (LA), L. delbrueckii subsp. lactis (LDL), and L. gasseri (LGA) were grown in Chingshey purple sweet potato (CPSP) substrate/media. CPSP is rich in anthocyanin, which possesses antioxidant activity and in vitro cell assay. The antioxidant ability and functional properties of the fermented milk were examined. High-performance liquid chromatographic (HPLC) method was used to analyze the free amino acid, organic acids, and anthocyanin content. Total phenolic compounds, scavenging effects of 1,1-diphenyl-2-picyl-hydrazyl (DPPH) radicals, and scavenging effects of superoxide anion radicals were determined to evaluate the antioxidant ability of the samples. The cell proliferation of the fermented PSP milk was evaluated by 3-(4,5-dimethyldiazol-2-yl)-2,5 diphenyl Tetrazolium Bromide (MTT) assay. The result indicated that the antioxidant ability of the fermented CPSP milk through LA, LDL, and LGA strains was significantly higher than CPSP. The main anthocyanins present in the samples are cyanidin and delphinidin. MTT assay has revealed that incubation with both PSP and fermented CPSP milk prevented the cell death of macrophage-like RAW264.7 cells. The potential health benefit of fermented PSP milk through LA, LDL, and LGA strains makes the further application of CPSP in health food highly worthwhile. PRACTICAL APPLICATION: (1) In our study, we have employed the γ-aminobutyric acid (GABA), organic acid contents, total phenol content, anthocyanins content, DPPH, oxygen radical absorbance capacity, superoxide dismutase activity assay, and cytotoxicity assay to assess the functional properties of fermented CPSP milk by different lactic acid bacteria. (2) Our results have revealed that the fermented CPSP milk samples possess high GABA concentrations, organic acid contents, anthocyanins contents, and antioxidant activity. This will provide potential opportunity to develop different functional food products from fermented CPSP milk. (3) The potential health benefit of fermented CPSP milk makes the further application of CPSP in health food highly worthwhile. 相似文献