全文获取类型
收费全文 | 380182篇 |
免费 | 4350篇 |
国内免费 | 1650篇 |
专业分类
电工技术 | 7094篇 |
综合类 | 2584篇 |
化学工业 | 52546篇 |
金属工艺 | 20296篇 |
机械仪表 | 15498篇 |
建筑科学 | 9282篇 |
矿业工程 | 1736篇 |
能源动力 | 7868篇 |
轻工业 | 27868篇 |
水利工程 | 3803篇 |
石油天然气 | 3154篇 |
武器工业 | 3篇 |
无线电 | 45075篇 |
一般工业技术 | 75631篇 |
冶金工业 | 57989篇 |
原子能技术 | 5099篇 |
自动化技术 | 50656篇 |
出版年
2021年 | 1589篇 |
2019年 | 1446篇 |
2018年 | 22279篇 |
2017年 | 21910篇 |
2016年 | 15074篇 |
2015年 | 2938篇 |
2014年 | 3479篇 |
2013年 | 11105篇 |
2012年 | 10379篇 |
2011年 | 23237篇 |
2010年 | 20350篇 |
2009年 | 18016篇 |
2008年 | 19030篇 |
2007年 | 21742篇 |
2006年 | 7265篇 |
2005年 | 11033篇 |
2004年 | 8988篇 |
2003年 | 8694篇 |
2002年 | 7285篇 |
2001年 | 6540篇 |
2000年 | 6083篇 |
1999年 | 6527篇 |
1998年 | 16693篇 |
1997年 | 11704篇 |
1996年 | 9050篇 |
1995年 | 6747篇 |
1994年 | 5977篇 |
1993年 | 5794篇 |
1992年 | 4091篇 |
1991年 | 4055篇 |
1990年 | 3603篇 |
1989年 | 3524篇 |
1988年 | 3462篇 |
1987年 | 2916篇 |
1986年 | 2860篇 |
1985年 | 3432篇 |
1984年 | 3063篇 |
1983年 | 2757篇 |
1982年 | 2566篇 |
1981年 | 2584篇 |
1980年 | 2439篇 |
1979年 | 2284篇 |
1978年 | 2244篇 |
1977年 | 2816篇 |
1976年 | 4191篇 |
1975年 | 1861篇 |
1974年 | 1744篇 |
1973年 | 1740篇 |
1972年 | 1440篇 |
1971年 | 1277篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
A system comprising two metal diaphragms with holes and a thin dielectric interlayer exhibits magnetic-field-controlled optical transmission. This phenomenon can be used, in particular, for the creation of light modulators. 相似文献
162.
Gert Schubring 《NTM》2003,11(2):90-99
Enno Heeren Dirksen (1788–1850) was one of several mathematicians originating from Eastern Frisia at the end of the eighteenth
century to acquire prominence in neohumanist reformed Prussia. While striving—like so many of his contemporaries—for more
rigour in the foundations of calculus, his work is significant due to his unusual emphasis on the semiotic aspects of the
basic concepts. As a clear-sighted propagator of Cauchy's conceptual innovations in Germany, his achievements in improving
sign expressions of such concepts enabled him to clarify hitherto not differentiated multiple limit processes—although less
successfully in constructive concept formation itself.
The contribution is based on the analysis of Dirksen's published texts and on the numerous texts which remained drafts for
his projected voluminousOrganon der gesamten Analysis.
Menso Folkerts zum 60. Geburtstag gewidmet 相似文献
Menso Folkerts zum 60. Geburtstag gewidmet 相似文献
163.
The influence of network density on the strain hardening behaviour of amorphous polymers is studied. The network density of polystyrene is altered by blending with poly(2,6-dimethyl-1,4-phenylene-oxide) and by cross-linking during polymerisation. The network density is derived from the rubber-plateau modulus determined by dynamic mechanical thermal analysis. Subsequently uniaxial compression tests are performed to obtain the intrinsic deformation behaviour and, in particular, the strain hardening modulus. At room temperature, the strain hardening modulus proves to be proportional to the network density, irrespective of the nature of the network, i.e. physical entanglements or chemical cross-links. With increasing temperature, the strain hardening modulus is observed to decrease. This decrease appears to be related to the influence of thermal mobility of the chains, determined by the distance to the glass-transition temperature (T−Tg). 相似文献
164.
Performance study of iSCSI-based storage subsystems 总被引:9,自引:0,他引:9
iISCSI is emerging as an end-to-end protocol for transporting storage I/O block data over IP networks. By exploiting the ubiquitous Internet infrastructure, iSCSI greatly facilitates remote storage, remote backup, and data mirroring. This article evaluates the performance of two typical iSCSI storage subsystems by measuring and analyzing block-level I/O access performance and file-level access performance. In the file-level performance study, we compare file access performance in an NAS scheme with that in an iSCSI-based SAN scheme. Our test results show that Gigabit Ethernet-based iSCSI can reach very high bandwidth, close to that of a direct FC disk access in block I/O access. However, when the iSCSI traverses through longer distance, throughput relies heavily on the available bandwidth between the initiator and the target. On the other hand, the file-level performance shows that iSCSI-based file access (SAN scheme) provides higher performance than using NFS protocol in Linux and SMB protocol in Windows (NAS scheme). However, the advantage of using iSCSI-based file accesses decreases as the file size increases. The obtained experimental results shed some light on the performance of applications based on iSCSI storage. 相似文献
165.
The annealing effects on the structural and electrical properties of fluorinated amorphous carbon (a-C:F) thin films prepared from C6F6 and Ar plasma are investigated in a N2 environment at 200 mTorr. The a-C:F films deposited at room temperature are thermally stable up to 250 °C, but as the annealing temperature is increased beyond 300 °C, the fluorine incorporation in the film is reduced, and the degree of crosslinking and graphitization in the film appears to be enhanced. At the annealing temperature of 250 °C, the chemical bond structures of the film are unchanged noticeably, but the interface trapped charges between the film and the silicon substrate are reduced significantly. The increased annealing temperature contributes the decrease of both the interface charges and the effective charge density in the a-C:F film. Higher self-bias voltage is shown to reduce the charge density in the film. 相似文献
166.
This study was undertaken to develop a modified atmosphere package to control microbial growth in ready‐to‐eat (RTE) products stored at ambient temperature. Ethanol and/or limonene associated with modified atmosphere (CO2 : O2 : N2 = 30% : 5% : 65%) was used to inhibit the growth of total air‐borne microorganisms and Escherichia coli in RTE products stored at 25°C. The results indicated that 0.05% ethanol vapour in the headspace was effective to inhibit the growth of air‐borne microorganisms and E. coli at 25°C for 72 h in a model study, and the effectiveness was related to ethanol content. Both 73 ppm limonene and 0.05% ethanol vapour enhanced the bacteriostatic effect of modified atmosphere in RTE sushi roll products, and no off‐flavour was detected using this formulated gas; however, no significant inhibitory effect was observed for RTE cold noodle products. This study concludes that combinations of carbon dioxide, ethanol or limonene vapours are effective to inhibit microbial growth in RTE food at ambient temperature, and the outcome may be due to the hurdle effect. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
167.
Rheological properties of MR fluids under large step strain shear are presented in this paper. The experiments were carried out using a rheometer with parallel-plate geometry. Under the large step strain shear, MR fluids behave as nonlinear viscoelastic properties, where the stress relaxation modulus, G(t, γ), shows a decreasing trend with step strain. The experimental results indicate that G(t, γ) obeys time-strain separability. Thus, a mathematical form based on finite exponential serials is proposed to predict MR behavior. In this model, G(t, γ) is represented as the product of a linear stress relaxation, G(t), and the damping function, h(γ), i.e. G(t, γ)=G(t) h(γ). G(t) is simply represented as a three-parameter exponential serial and h(γ) has a sigmoidal form with two parameters. The parameters are identified by adopting an efficient optimization method proposed by Stango et al. The comparison between the experimental results and the model-predicted values indicates that this mathematical model can accurately predict MR behavior. 相似文献
168.
Yang Aiying Wang Ziyu Zhang Zhaoyi Chen Zhangyuan Wu Deming 《电子科学学刊(英文版)》2003,20(6):461-466
A 10Gbit/s recirculating system is configured with Chirped Fiber Bragg Grating (CFBG) for the dispersion compensation. For the first time, the transmission distance in the loop reaches 1000km with bit error rate of 10-9. The effect of the group delay ripple of the fiber grating is also investigated in the recirculating systems, and it is shown that the transmission distance is limited to 4 cycles (4×167.1km ) in the loop with the power penalty fluctuation below 1.0dB. Thus the group delay ripple should be reduced to allow for the wavelength drift of±5GHz. At the end of this letter, the principles are given for designing long haul recirculating systems with dispersion compensation CFBG. 相似文献
169.
An efficient algorithm is presented for numerically evaluating a self-consistent field theoretic (SCFT) model of block copolymer structure. This algorithm is implemented on a distributed memory parallel cluster in order to solve the SCFT equations on large computational grids. Simulation results are presented for a two-component molten mixture of a symmetric ABA triblock copolymer with an A homopolymer. These results illustrate a case in which simulating a large system is required to resolve features with a wide range of length scales. 相似文献
170.
Yu. I. Golovin D. V. Lopatin R. K. Nikolaev A. V. Umrikhin 《Technical Physics Letters》2004,30(5):426-428
The effect of crystal orientation on the photogeneration of free charge carriers was studied for C60 single crystals in a weak magnetic field. The photoconductivity sharply depends on the orientation of magnetic field with
respect to the crystallographic directions, showing a 5–8% increase for seven axes of the C60 crystal. 相似文献