全文获取类型
收费全文 | 6396篇 |
免费 | 152篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 73篇 |
综合类 | 1篇 |
化学工业 | 1087篇 |
金属工艺 | 116篇 |
机械仪表 | 101篇 |
建筑科学 | 253篇 |
矿业工程 | 32篇 |
能源动力 | 148篇 |
轻工业 | 568篇 |
水利工程 | 41篇 |
石油天然气 | 31篇 |
无线电 | 478篇 |
一般工业技术 | 914篇 |
冶金工业 | 1781篇 |
原子能技术 | 87篇 |
自动化技术 | 843篇 |
出版年
2022年 | 44篇 |
2021年 | 50篇 |
2020年 | 48篇 |
2019年 | 51篇 |
2018年 | 62篇 |
2017年 | 56篇 |
2016年 | 69篇 |
2015年 | 71篇 |
2014年 | 108篇 |
2013年 | 313篇 |
2012年 | 188篇 |
2011年 | 242篇 |
2010年 | 202篇 |
2009年 | 226篇 |
2008年 | 263篇 |
2007年 | 251篇 |
2006年 | 230篇 |
2005年 | 188篇 |
2004年 | 152篇 |
2003年 | 150篇 |
2002年 | 163篇 |
2001年 | 135篇 |
2000年 | 127篇 |
1999年 | 109篇 |
1998年 | 248篇 |
1997年 | 218篇 |
1996年 | 172篇 |
1995年 | 141篇 |
1994年 | 140篇 |
1993年 | 119篇 |
1992年 | 120篇 |
1991年 | 56篇 |
1990年 | 98篇 |
1989年 | 87篇 |
1988年 | 83篇 |
1987年 | 89篇 |
1986年 | 85篇 |
1985年 | 112篇 |
1984年 | 103篇 |
1983年 | 107篇 |
1982年 | 100篇 |
1981年 | 104篇 |
1980年 | 63篇 |
1979年 | 89篇 |
1978年 | 83篇 |
1977年 | 87篇 |
1976年 | 109篇 |
1975年 | 90篇 |
1974年 | 53篇 |
1973年 | 54篇 |
排序方式: 共有6554条查询结果,搜索用时 15 毫秒
1.
Lihua Lou Weijie Yu Ronald J. Kendall Ernest Smith Seshadri S. Ramkumar 《应用聚合物科学杂志》2020,137(30):49213
A tensile properties testing study was conducted to understand the influence of thickness, cross-head speed (speed of testing), gauge length (GL; specimen test length), and sample shape on important tensile properties of polyvinyl alcohol (PVA) nanofiber webs. The effects of each testing parameter on load at break, extension at break, Young's modulus, and tensile stress–strain curve of PVA nanofiber webs are analyzed. The Welch two sample t-tests show the significant difference among tested data. Using interaction plots, two-way analysis of variance, and margin mean plots, the interaction effects among testing parameters have been analyzed. Of all the factors, cross-head speed, the interaction among GL, and sample thickness (GL: Thickness) and the interaction among GL, testing speed and sample thickness (GL: Speed: Thickness) have significant influence on the tensile properties of PVA nanofiber webs. Moreover, the hypothesized model of mechanism of tensile strain–stress curve of PVA nanofiber webs has been proposed. Based on the model, the tensile strain–stress curve can be split into three stages: linear elastic, partial break up, and complete breakage. This study will provide a better understanding of tensile testing parameters' effects and their interaction effects on the tensile properties of nanowebs. 相似文献
2.
3.
Y. Yin C.K. Erdonmez A. Cabot S. Hughes A.P. Alivisatos 《Advanced functional materials》2006,16(11):1389-1399
Formation of cobalt sulfide hollow nanocrystals through a mechanism similar to the Kirkendall Effect has been investigated in detail. It is found that performing the reaction at > 120 °C leads to fast formation of a single void inside each shell, whereas at room temperature multiple voids are formed within each shell, which can be attributed to strongly temperature‐dependent diffusivities for vacancies. The void formation process is dominated by outward diffusion of cobalt cations; still, the occurrence of significant inward transport of sulfur anions can be inferred as the final voids are smaller in diameter than the original cobalt nanocrystals. Comparison of volume distributions for initial and final nanostructures indicates excess apparent volume in shells, implying significant porosity and/or a defective structure. Indirect evidence for fracture of shells during growth at lower temperatures was observed in shell‐size statistics and transmission electron microscopy images of as‐grown shells. An idealized model of the diffusional process imposes two minimal requirements on material parameters for shell growth to be obtainable within a specific synthetic system. 相似文献
4.
5.
Optimal space-time constellations from groups 总被引:10,自引:0,他引:10
Hughes B.L. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2003,49(2):401-410
We consider the design of space-time constellations based on group codes for fading channels with multiple transmit and receive antennas. These codes can be viewed as multiantenna extensions of phase-shift keying (PSK), in the sense that all codewords have equal energy, all are rotations of a fixed codeword, and there is a simple differential transmission rule that allows data to be sent without channel estimates at the transmitter or receiver. For coherent detection, we show that all optimal full-rank space-time group codes are unitary (each code matrix has equal-energy, orthogonal rows). This leads to a simpler code design criterion and suggests that unitary codes may play an important role in coherent as well as noncoherent communication. For any number of transmit antennas t, we then use the design criterion to characterize all full-rank unitary space-time group codes of minimum block length (also t) which have 2/sup p/ codewords. These results allow us to characterize all optimal 2/sup p/-ary unitary group codes with square code matrices. This restricted class of block codes matches the class proposed for differential modulation by Hughes (see IEEE Trans. Inform. Theory, vol.46, p.2567-78, Nov. 2000), and by Hochwald and Sweldens (see IEEE Trans. Commun., vol.48, p.2041-2052, Dec. 2000). 相似文献
6.
JB Kamien WK Bickel BJ Smith GJ Badger JR Hughes 《Canadian Metallurgical Quarterly》1997,58(4):983-991
The percentage of long-term survivors after intensive chemotherapy and the outcome of MDS patients who achieve partial remission (PR) with intensive chemotherapy (IC) are not known. Between 1981 and 1996 we treated 99 patients with de novo MDS who had high-risk MDS or progression to AML, with IC. 41 (41%) achieved CR, 16 (16%) achieved partial remission (PR), 26 (26%) had failure, and 16 (16%) died in aplasia. Eight of the patients who achieved CR were autografted, three were allografted and the remaining cases received moderate consolidation chemotherapy. After IC, the 16 PR patients fulfilled the criteria for RA in 15 cases and CMML in one case. Median PR duration was 17 months, and three PR were > 3 years (39, 50+, 82+ months). Median actuarial survival of patients who achieved PR and CR was 18 months and 20 months from the onset of IC, respectively (difference not significant). Of the 71 patients treated before 1993, with sufficient follow-up, 10 (14%) had survived > 4 years (long-term survivors). Four of them were alive in first CR after 49+ to 110+ months and probably cured, two were alive in PR after 50+ and 82+ months and four had died after 49-78 months. Long-term survivors were characterized by a significantly higher incidence of RAEB-T at diagnosis, and with normal or favourable cytogenetic findings. In patients with RAEB-T at diagnosis included before 1993, 8/23 (35%) cases who had no unfavourable karyotype had survived > 4 years. Our findings suggest that MDS patients who achieve PR with IC, and not only those who achieve CR, can benefit from this type of treatment. The percentage of long-term survivors remains low, however, and is almost restricted to patients with RAEB-T at diagnosis and no unfavourable karyotype. 相似文献
7.
Chris Gibbons Corrine Chaves Ronald B. Wilkes Mark N. Frolick 《Information Systems Management》1994,11(3):51-56
Information-based organizations are structured to function with as small and efficient a staff as possible. To this end, executives at The Promus Companies are using IT to spread decision-making authority and responsibility for customer satisfaction and customer service throughout the organization. 相似文献
8.
9.
Ahn Jaeshin Stromsmoe Keith A. Lawson Ronald P. W. 《Industrial Electronics, IEEE Transactions on》1985,(4):405-409
A microprocessor-based system with 32 A/D, 24 D/A, and 16 ac load controllers, has been designed and built to monitor and control an ion beam thin-film deposition system. The A/D and D/A channels have electrical isolation of 7.5 kV between channels and between input and output. The microprocessor system keeps the ion beam deposition parameters stable for extended periods of operation and it is proposed as a means to greatly simplify switching from one deposition species to another to grow thin multilayer or alloy films. 相似文献
10.
A new and simple method of finite-element grid improvement is presented. The objective is to improve the accuracy of the analysis. The procedure is based on a minimization of the trace of the stiffness matrix. For a broad class of problems this minimization is seen to be equivalent to minimizing the potential energy. The method is illustrated with the classical tapered bar problem examined earlier by Prager and Masur. Identical results are obtained. 相似文献