全文获取类型
收费全文 | 31933篇 |
免费 | 2913篇 |
国内免费 | 1313篇 |
专业分类
电工技术 | 1761篇 |
技术理论 | 1篇 |
综合类 | 1912篇 |
化学工业 | 5522篇 |
金属工艺 | 1867篇 |
机械仪表 | 1909篇 |
建筑科学 | 2556篇 |
矿业工程 | 937篇 |
能源动力 | 964篇 |
轻工业 | 2255篇 |
水利工程 | 585篇 |
石油天然气 | 1515篇 |
武器工业 | 280篇 |
无线电 | 3623篇 |
一般工业技术 | 4069篇 |
冶金工业 | 1570篇 |
原子能技术 | 431篇 |
自动化技术 | 4402篇 |
出版年
2024年 | 181篇 |
2023年 | 648篇 |
2022年 | 1111篇 |
2021年 | 1579篇 |
2020年 | 1206篇 |
2019年 | 929篇 |
2018年 | 1029篇 |
2017年 | 1210篇 |
2016年 | 1074篇 |
2015年 | 1352篇 |
2014年 | 1642篇 |
2013年 | 1938篇 |
2012年 | 2059篇 |
2011年 | 2193篇 |
2010年 | 1860篇 |
2009年 | 1716篇 |
2008年 | 1593篇 |
2007年 | 1480篇 |
2006年 | 1463篇 |
2005年 | 1387篇 |
2004年 | 918篇 |
2003年 | 792篇 |
2002年 | 713篇 |
2001年 | 602篇 |
2000年 | 633篇 |
1999年 | 744篇 |
1998年 | 684篇 |
1997年 | 556篇 |
1996年 | 569篇 |
1995年 | 471篇 |
1994年 | 402篇 |
1993年 | 301篇 |
1992年 | 236篇 |
1991年 | 192篇 |
1990年 | 144篇 |
1989年 | 119篇 |
1988年 | 113篇 |
1987年 | 72篇 |
1986年 | 52篇 |
1985年 | 37篇 |
1984年 | 36篇 |
1983年 | 16篇 |
1982年 | 19篇 |
1981年 | 17篇 |
1980年 | 15篇 |
1979年 | 13篇 |
1978年 | 6篇 |
1976年 | 10篇 |
1975年 | 4篇 |
1959年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Combined-Stage Sintering Model 总被引:8,自引:0,他引:8
James D. Hansen Richard P. Rusin Mao-Hua Teng D. Lynn Johnson 《Journal of the American Ceramic Society》1992,75(5):1129-1135
By focusing on the similarities between the three stages of sintering, a single equation is derived that quantifies sintering as a continuous process from beginning to end. The microstructure is characterized by two separate parameters representing geometry and scale. The dimensionless geometry parameter, denoted T, comprises five scaling factors that relate specific microstructural featuers (e.g., surface curvature) to the scale (grain diameter). Calculations of T from experimental data show (a) agreement with computer simulations of initial-stage sintering, (b) the effect of surface diffusion on T, and (c) changes in T with microstructural evolution during sintering. Application of the model to the design of firing schedules and the study of microstructural geometry effects on sintering is discussed. 相似文献
92.
The authors present a new traveling wave method for calculating the linewidth, the frequency tuning efficiency, and a mode stability parameter for a general class of laser-diode structures. The method leads to simple semianalytic expressions which allow an easy numerical determination of the three parameters 相似文献
93.
双噁唑啉化合物对PBT的增粘作用 总被引:1,自引:0,他引:1
以2.2'-双(2-唑啉)和双(2-唑啉基)苯作扩链剂,用焙融挤出的方法,对聚对苯二甲酸丁二酯(PBT)进行扩链,考察扩链剂的用量、反应时间和反应温度对PBT的特性粘度及端羧基含量(CV)的影响。结果表明,当用2,2'-双(2-唑啉)作扩链剂时,PBT的特性粘度[η]从0.799提高到0.926dL/g,CV降至5eq/10 ̄6g以下;当用双(2- 唑啉基)苯作扩链剂,[η]从0.763增至0.925dL/g,CV降至10eq/10 ̄6g以下,达到了较满意的扩链效果。 相似文献
94.
95.
潘勇琨 《石油化工设备技术》2007,28(5):16-18
欧盟、美国和我国压力容器标准对不等厚板材对接时均有削薄要求,通过有限元方法计算不同条件下连接时的应力分布,认为不等厚板材对接连接时,按照EN13445(2002)要求增加直边段,对减小局部应力有一定好处,对提高射线检测灵敏度有利. 相似文献
96.
The honeycomb rectangular torus is an attractive alternative to existing networks such as mesh-connected networks in parallel and distributed applications because of its low network cost and well-structured connectivity. Assume that m and n are positive even integers with n ? 4. It is known that every honeycomb rectangular torus HReT(m,n) is a 3-regular bipartite graph. We prove that in any HReT(m,n), there exist three internally-disjoint spanning paths joining x and y whenever x and y belong to different partite sets. Moreover, for any pair of vertices x and y in the same partite set, there exists a vertex z in the partite set not containing x and y, such that there exist three internally-disjoint spanning paths of G-{z} joining x and y. Furthermore, for any three vertices x, y, and z of the same partite set there exist three internally-disjoint spanning paths of G-{z} joining x and y if and only if n ? 6 or m = 2. 相似文献
97.
通过对活性炭载体进行不同条件的超声波处理获得了具有不同表面化学性质的载体,使用比表面积(BET)、酸碱滴定等技术手段对载体的物理化学性质进行了表征。将经过超声波处理的活性炭载体制备成Pt/C催化剂,并将催化剂直接用于催化反应,考察了活性炭载体的不同超声波处理条件对Pt/C催化剂性能的影响。实验发现,活性炭载体经过超声波处理后,表面灰分含量、pH值和中孔孔容有较大的变化;使用经过60min超声波处理后中孔孔容较大的活性炭作为载体制备的Pt/C催化剂,在催化加氢反应性能测试中显示了最高的催化活性。在此基础上,就活性炭载体的超声波处理对Pt/C催化剂活性的影响进行了讨论。 相似文献
98.
99.
T. Luo C. Yu L.-S. Yan S. Kumar Z. Pan A.E. Willner 《Photonics Technology Letters, IEEE》2006,18(15):1606-1608
We demonstrate a simple optical-fiber-based autocorrelator for picosecond short pulses based on degree-of-polarization measurement while tuning the relative delay of the two orthogonal polarization states of the pulse. The pulsewidths of 20-, 40-, and 80-GHz pulse trains and 2-ps pulses generated by a mode-locked laser are measured. The <-10-dBm optical powers are used in the experiment. The measurement results agree well with the measurements using conventional techniques. Compared with conventional autocorrelators, this technique has the advantages of 1) wavelength independent, 2) significant less alignment, and 3) no high power required. 相似文献
100.
We provide a unified framework for the investigation of convergence properties of the iterative algorithms for photon attenuation correction in SPECT, including the iterative Chang method--a commonly used approach in which an average attenuation factor calculated over all projection angles is employed in a pointwise correction scheme. A new average attenuation factor calculated along the projection line is introduced, which can compensate exactly for the attenuation effect in the case of a uniform activity distribution. We propose a new hybrid approach in which we use this new average attenuation factor initially and then shift to the iterative Chang method in later iterations. This hybrid approach was evaluated in a simulation study by use of a computer-generated phantom with both non-uniform activity and non-uniform attenuation distributions. The results demonstrate that this hybrid approach improves the convergence speed of the iterative Chang method and produces reconstructed images of high quality. 相似文献