全文获取类型
收费全文 | 8175篇 |
免费 | 703篇 |
国内免费 | 403篇 |
专业分类
电工技术 | 511篇 |
综合类 | 596篇 |
化学工业 | 1442篇 |
金属工艺 | 347篇 |
机械仪表 | 413篇 |
建筑科学 | 590篇 |
矿业工程 | 220篇 |
能源动力 | 284篇 |
轻工业 | 682篇 |
水利工程 | 130篇 |
石油天然气 | 270篇 |
武器工业 | 39篇 |
无线电 | 896篇 |
一般工业技术 | 985篇 |
冶金工业 | 439篇 |
原子能技术 | 153篇 |
自动化技术 | 1284篇 |
出版年
2024年 | 17篇 |
2023年 | 87篇 |
2022年 | 247篇 |
2021年 | 318篇 |
2020年 | 219篇 |
2019年 | 225篇 |
2018年 | 227篇 |
2017年 | 242篇 |
2016年 | 226篇 |
2015年 | 308篇 |
2014年 | 352篇 |
2013年 | 472篇 |
2012年 | 495篇 |
2011年 | 523篇 |
2010年 | 488篇 |
2009年 | 408篇 |
2008年 | 429篇 |
2007年 | 434篇 |
2006年 | 359篇 |
2005年 | 257篇 |
2004年 | 304篇 |
2003年 | 425篇 |
2002年 | 554篇 |
2001年 | 498篇 |
2000年 | 222篇 |
1999年 | 160篇 |
1998年 | 145篇 |
1997年 | 101篇 |
1996年 | 85篇 |
1995年 | 73篇 |
1994年 | 49篇 |
1993年 | 64篇 |
1992年 | 38篇 |
1991年 | 16篇 |
1990年 | 35篇 |
1989年 | 30篇 |
1988年 | 6篇 |
1987年 | 15篇 |
1986年 | 13篇 |
1985年 | 11篇 |
1984年 | 6篇 |
1983年 | 10篇 |
1982年 | 8篇 |
1981年 | 5篇 |
1980年 | 14篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1977年 | 8篇 |
1976年 | 13篇 |
1975年 | 7篇 |
排序方式: 共有9281条查询结果,搜索用时 0 毫秒
11.
Da SHU Baode SUN Ke LI Jun WANG Yaohe ZHOUState Key Laboratory of Metal Matrix Composites Shanghai Jiao Tong University Shanghai China 《材料科学技术学报》2003,19(3):221-225
The continuous separation of inclusions from aluminum melt flowing in a circular pipe using a high frequency magneticfield was investigated both theoretically and experimentally The separation efficiency was calculated based on thetrajectory method and compared with experimental results. It is found that the separation efficiency is a functilnondimensional parameters t_i·d_p~2B_e~2/μ_fμ_eα~2 and α/δ.The effective way to improve the separation efficiency is to increasethe effective magnetic flux density and decrease the pipe radius. and the value of α/δ should be kept about 2 in orderto obtain the optimum separation efficiency. 相似文献
12.
13.
Jones Enrico E.; Ghannam Jess; Nigg Joel T.; Dyer Jennifer F. 《Canadian Metallurgical Quarterly》1993,61(3):381
Articulates a paradigm for single-case research in psychotherapy. A patient diagnosed as having major depressive disorder was seen in an intensive, twice-weekly psychodynamic psychotherapy for 2.5 years. Each session was videotaped, and assessments of patient change were obtained at regular intervals. A time-series analysis was used to model fluctuations in the therapy process to take into account time and the effect of previous events on subsequent changes, thereby preserving the context-determined meaning for therapist and patient actions. A bidirectional analysis of causal effects shows that the influence processes between therapist and patient are mutual and reciprocal and suggests that the effect of the patient on the therapist and on the process has not been made sufficiently explicit in previous models of process and change. The potential of intensive single-case designs for uncovering causal effects in psychotherapy is demonstrated. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
14.
The axisymmetric Laplace equation is solved numerically to extract contact-angle data for a flat liquid/vapor interface contacting a submerged hemispherical solid. The liquid/vapor interface is treated as a membrane, with a membrane tension equal to the surface energy of the liquid. By measuring the vertical displacement of the membrane and the projected contact area the membrane makes with the hemisphere, the contact angle and correspondingly the driving force for motion of the contact line can be measured. We show that characteristic receding and advancing contact angles can be obtained by measuring the contact radii formed upon initial contact between the interface and hemisphere and final contact just prior to detachment of the interface, respectively. Use of the technique is illustrated with a model experiment involving the contact of an air/water interface with a poly(methyl methacrylate) surface. 相似文献
15.
Giovanni Giambene Enrico Zoli 《International Journal of Satellite Communications and Networking》2003,21(2):199-225
In this paper, we investigate a packet access scheme that is able to support mixed traffics in the presence of high propagation delays. Referring to a Time‐Code Division Multiple Access air interface, we propose a Medium Access Control (MAC) protocol based on a random access scheme. A successful attempt grants the use of a slot‐code resource. This protocol is named Adaptive Time Code‐Packet Reservation Multiple Access (ATC‐PRMA), since the access parameters are changed, depending on the traffic load conditions, so as to fulfil Quality of Service requirements. Numerical examples are carried out for the Low Earth Orbit (LEO)‐Mobile Satellite System (MSS) scenario, but all these considerations could be applied to High‐Altitude Platform Stations (HAPSs) as well. In both cases, high propagation delays prevent an immediate feedback to users. An analytical approach is proposed to study the stability of our MAC scheme. Accordingly, we define a criterion for optimizing system performance. The predicted ATC‐PRMA behaviour is supported by simulation results. Finally, we show the performance improvement of ATC‐PRMA with respect to a MAC protocol not employing adaptive parameters. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
16.
C. N. Elias C. S. Da Costa Viana 《Journal of Materials Engineering and Performance》1992,1(6):751-754
In the present work, the composition of H- 13 tool steel was modified with respect to the vanadium content to include an addition
of niobium to obtain improved austenite grain size control without altering the tempering response of the steel. Optical metallography
and transmission electron microscopy (TEM) observation of extraction replicas showed that the new steel had a smaller austenite
grain size and a finer carbide size distribution than the vanadium steel, which indicates a higher potential toughness. 相似文献
17.
19.
Yang Lüyun 《中国稀土学报(英文版)》2006,24(Z2)
The fabrication of one kind of large core area Nd3 doped silicate glass photonic crystal fiber, and demonstration of the fiber's waveguidence properties were reported. This fiber owns a random air hole distribution in the cladding. The measured minimum loss of this kind of fiber is 10 dB·m-1 at 660 nm. These fibers can sustain only a single mode at least over wavelength ranging from 660 nm to 980 nm. 相似文献
20.
Sodium sulfonate‐terminated dendritic poly(ester‐amine) (SPEA) was synthesized by sulfonation of acrylic double bond‐terminated dendritic poly(ester‐amine) (APEA) with sodium hydrogen sulfite (NaHSO3) in mixture of diglycol and 2‐butanone under normal pressure. The structure of SPEA was characterized by IR, 1H‐NMR, and elemental analysis. SPEA was water‐soluble. 1.0–40.0% (mass) SPEA aqueous solutions appeared as dilatant fluid. When pH value varied from 1.5 to 12.0, the viscosity of 1–5% (mass) SPEA aqueous solutions changed very small, and the electric conductivity almost kept stable within pH 3.0–10.0. The relationship between the viscosity and the concentration of SPEA water solutions was similar to that of NaCl water solutions. The surface tension of SPEA water solutions was lower than that of polyethylene glycol 2000 water solutions with the same concentration. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献