全文获取类型
收费全文 | 5290篇 |
免费 | 201篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 30篇 |
化学工业 | 559篇 |
金属工艺 | 40篇 |
机械仪表 | 66篇 |
建筑科学 | 90篇 |
矿业工程 | 7篇 |
能源动力 | 89篇 |
轻工业 | 270篇 |
水利工程 | 30篇 |
石油天然气 | 7篇 |
无线电 | 293篇 |
一般工业技术 | 615篇 |
冶金工业 | 2984篇 |
原子能技术 | 18篇 |
自动化技术 | 399篇 |
出版年
2023年 | 32篇 |
2022年 | 53篇 |
2021年 | 86篇 |
2020年 | 62篇 |
2019年 | 93篇 |
2018年 | 102篇 |
2017年 | 77篇 |
2016年 | 92篇 |
2015年 | 71篇 |
2014年 | 109篇 |
2013年 | 165篇 |
2012年 | 154篇 |
2011年 | 209篇 |
2010年 | 142篇 |
2009年 | 133篇 |
2008年 | 169篇 |
2007年 | 151篇 |
2006年 | 114篇 |
2005年 | 95篇 |
2004年 | 74篇 |
2003年 | 66篇 |
2002年 | 60篇 |
2001年 | 27篇 |
2000年 | 35篇 |
1999年 | 120篇 |
1998年 | 862篇 |
1997年 | 530篇 |
1996年 | 305篇 |
1995年 | 181篇 |
1994年 | 151篇 |
1993年 | 179篇 |
1992年 | 44篇 |
1991年 | 33篇 |
1990年 | 42篇 |
1989年 | 52篇 |
1988年 | 56篇 |
1987年 | 34篇 |
1986年 | 30篇 |
1985年 | 23篇 |
1984年 | 25篇 |
1983年 | 19篇 |
1982年 | 24篇 |
1981年 | 16篇 |
1980年 | 26篇 |
1979年 | 16篇 |
1978年 | 16篇 |
1977年 | 80篇 |
1976年 | 176篇 |
1975年 | 13篇 |
1971年 | 13篇 |
排序方式: 共有5497条查询结果,搜索用时 15 毫秒
991.
We discuss a procedure for designing high-rate turbo-codes via puncturing, with applications to BPSK/QPSK channels. Rates in the form k/(k+1), 2⩽k⩽16, are considered for constituent encoders with memory sizes m=3 and 4. The algorithm includes the selection of constituent encoder generator polynomials, puncture patterns, and interleavers with the goal of maximizing the minimum codeword weight for weight-two and weight-three inputs. The performance of the proposed codes are found via computer simulation and are observed in each case to be less than 0.9 dB (m=3), and 0.75 dB (m=4), from their respective channel capacity limits at a bit-error rate of 10-5. We consider two applications of punctured turbo-codes 相似文献
992.
Validity and reliability coefficients and standard errors of measurement for 2 7-subtest short forms (SF) of the Wechsler Adult Intelligence Scale-III (WAIS–III; D. Wechsler, 1997) are provided. Data for the study were obtained from the WAIS-III—WMS-III Technical Manual and were based on the 2,450 adolescents and adults in the WAIS–III standardization sample. SF1 consists of Information, Digit Span, Arithmetic. Similarities, Picture Completion, Block Design, and Digit Symbol-Coding. SF2 uses the same subtest combination, except matrix Reasoning is substituted for Block Design. For the 13 age groups in the standardization sample, the 2 short forms have impressively high validity and reliability, and small standard errors of measurement. Whenever a short form IQ is used. it is recommended that the examiner append the abbreviation Est next to the value. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
993.
AI Alayash BA Ryan RF Eich JS Olson RE Cashon 《Canadian Metallurgical Quarterly》1999,274(4):2029-2037
Distal pocket mutants of sperm whale oxymyoglobin (oxy-Mb) were reacted with a 2.5-fold excess of hydrogen peroxide (HOOH) in phosphate buffer at pH 7.0, 37 degreesC. We describe a mechanism composed of three distinct steps: 1) initial oxidation of oxy- to ferryl-Mb, 2) autoreduction of the ferryl intermediate to ferric metmyoglobin (metMb), and 3) reaction of metMb with an additional HOOH molecule to regenerate the ferryl intermediate creating a pseudoperoxidase catalytic cycle. Mutation of Leu-29(B10) to Phe slows the initial oxidation reaction 3-fold but has little effect on the rate of ferryl reduction to ferric met-aquo-myoglobin. In contrast, the Val-68(E11) to Phe mutation causes a small, 60% increase in the initial oxidation reaction and a much larger 2. 5-fold increase in the rate of autoreduction. Double insertion of Phe at both the B10- and E11-positions (L29F/V68F) produces a mutant with oxidation characteristics of both single mutants, slow initial oxidation, and rapid autoreduction, but an extraordinarily high affinity for O2. Replacing His-64(E7) with Gln produces 3-4-fold increases in both processes. Combining the mutation H64Q with L29F results in a myoglobin with enhanced resistance to metMb formation in the absence of antioxidant enzymes (i.e. catalase and superoxide dismutase) due to its own high pseudoperoxidase activity, which rapidly removes any HOOH produced in the initial stages of autoxidation. This double substitution occurs naturally in the myoglobin of Asian elephants, and similar multiple replacements have been used to reduce selectively the rate of nitric oxide (NO)-induced oxidation of both recombinant MbO2 and HbO2 blood substitute prototypes without altering O2 affinity. 相似文献
994.
995.
Lacticin 3147 is a broad-spectrum bacteriocin produced by the food-grade organism Lactococcus lactis. Lacticin 3147 is active at a neutral pH and has been shown to be bactericidal to streptococci and staphylococci in vitro. The effectiveness of an intramammary teat seal formulation, and a teat seal containing lacticin 3147 was evaluated at drying off in 68 uninfected quarters of 18 cows. Following infusion of either teat seal or lacticin 3147 combined with teat seal, a deliberate infection challenge of Streptococcus dysgalactiae (approximately equal to 1.5 x 10(4) cfu per teat) was administered by direct inoculation into the teat sinus. During an 8-d experimental period following inoculation, 61% of control quarters and 6% of the treatment quarters either developed clinical mastitis or were shedding the challenge organism. Randomly amplified polymorphic DNA polymerase chain reaction genetic typing was used to confirm that both the new infections and the bacteria surviving in the teats at the end of the experiment were the challenge strain. The combination of teat seal and lacticin 3147 was well tolerated within the udder and elicited only a temporary increase in somatic cell count to 5.7 x 10(5)/ml (88 h after infusion) in a previously uninfected lactating udder quarter. Therefore, we concluded that this nonantibiotic approach to mastitis prevention may contribute to a reduction in the routine application of antibiotics at drying off in the future. 相似文献
996.
Trina C. Maurice Charles E. Mazzucco Chandra S. Ramanathan Brenda M. Ryan Glenn A. Warr John W. Puziss 《Yeast (Chichester, England)》1998,14(12):1105-1113
A paralog (intraspecies homolog) of the Saccharomyces cerevisiae YEF3 gene, encoding elongation factor-3, has been sequenced in the course of the yeast genome project, and identified by database searching; this gene has been designated HEF3. Bioinformatic and Northern blot analysis indicate that the HEF3 gene is not expressed during vegetative growth. Deletion of the HEF3 gene reveals no growth defects, nor any defects in mating or sporulation. A high copy 2μ clone of HEF3 was constructed, and was shown to be unable to complement a null allele of yef3. Finally, an in vitro assay for ribosome-stimulated ATPase activity was performed with isogenic HEF3 and Δhef3 strains; no difference in biochemical activity could be detected in these strains. From these results, we conclude that the HEF3 gene does not encode a functional homolog of YEF3. © 1998 John Wiley & Sons, Ltd. 相似文献
997.
HelenT.Ryan MichaelReinehr MarkDevlin 《石油商技》2005,23(2):14-15
作为一种可再生能源,风力涡轮机数量增长很快。OEM在过去的几年里提出了应用于风力涡轮机齿轮和轴承的润滑油新标准,这些新标准同时被应用于传统的工业齿轮油中。这不但明显提高了传统工业齿轮的用油水平,也提高了开发新技术的费用。 相似文献
998.
通过绿色基础设施途径,处理美国波士顿北部的马萨诸塞州城市流域的水资源规划问题。从多个尺度为风景园林师提供水资源规划的经验与启发,探究公众对新型绿色基础设施解决方案的态度与偏好,以及公众偏好对于整体规划设计的重要作用。 相似文献
999.
Zhen Wang Junbo Wang Zhenpeng Xu Ryan Hensleigh Haotian Lu Mack Sowers Marcus A. Worsley Yahya Rahmat-Samii Xiaoyu Zheng 《Advanced functional materials》2024,34(18):2313839
Charge-programmed 3D printing enables the fabrication of 3D electronics with lightweight and high precision via selective patterning of metals. This selective metal deposition is catalyzed by Pd nanoparticles that are specifically immobilized onto the charged surface and promises to fabricate a myriad of complex electronic devices with self-sensing, actuation, and structural elements assembled in a designed 3D layout. However, the achievable property space and the material-performance correlation of the charge-programmed printing remain unexplored. Herein, a series of photo-curable resins are designed for unveiling how the charge and crosslink densities synergistically impact the nanocatalyst-guided selective deposition in catalytic efficiency and properties of the 3D printed charge-programmed architectures, leading to high-quality 3D patterning of solid and liquid metals. The findings offer a wide tunability of the structural properties of the printed electronics, ranging from stiff to extreme flexibility. Capitalizing on these results, the printing and successful application of an ultralight-weight and deployable 3D multi-layer antenna system operating at an ultrahigh-frequency of 19 GHz are demonstrated. 相似文献
1000.
Weighted Gene Co‐Expression Network Analysis Identifies Gender Specific Modules and Hub Genes Related to Metabolism and Inflammation in Response to an Acute Lipid Challenge 下载免费PDF全文