全文获取类型
收费全文 | 421392篇 |
免费 | 5600篇 |
国内免费 | 1560篇 |
专业分类
电工技术 | 7765篇 |
综合类 | 314篇 |
化学工业 | 60183篇 |
金属工艺 | 14676篇 |
机械仪表 | 11770篇 |
建筑科学 | 10156篇 |
矿业工程 | 1237篇 |
能源动力 | 11138篇 |
轻工业 | 39739篇 |
水利工程 | 3538篇 |
石油天然气 | 4613篇 |
武器工业 | 12篇 |
无线电 | 55938篇 |
一般工业技术 | 77643篇 |
冶金工业 | 87552篇 |
原子能技术 | 6463篇 |
自动化技术 | 35815篇 |
出版年
2021年 | 2878篇 |
2020年 | 2151篇 |
2019年 | 2791篇 |
2018年 | 4407篇 |
2017年 | 4428篇 |
2016年 | 4794篇 |
2015年 | 3488篇 |
2014年 | 5894篇 |
2013年 | 18620篇 |
2012年 | 10407篇 |
2011年 | 14694篇 |
2010年 | 11503篇 |
2009年 | 13242篇 |
2008年 | 13964篇 |
2007年 | 14012篇 |
2006年 | 12858篇 |
2005年 | 11868篇 |
2004年 | 11490篇 |
2003年 | 11332篇 |
2002年 | 10635篇 |
2001年 | 11415篇 |
2000年 | 10388篇 |
1999年 | 11375篇 |
1998年 | 30157篇 |
1997年 | 20407篇 |
1996年 | 15531篇 |
1995年 | 11565篇 |
1994年 | 10059篇 |
1993年 | 9942篇 |
1992年 | 6861篇 |
1991年 | 6549篇 |
1990年 | 6288篇 |
1989年 | 6010篇 |
1988年 | 5710篇 |
1987年 | 4574篇 |
1986年 | 4553篇 |
1985年 | 5436篇 |
1984年 | 4837篇 |
1983年 | 4367篇 |
1982年 | 4019篇 |
1981年 | 4193篇 |
1980年 | 3799篇 |
1979年 | 3521篇 |
1978年 | 3353篇 |
1977年 | 4025篇 |
1976年 | 5226篇 |
1975年 | 2843篇 |
1974年 | 2700篇 |
1973年 | 2735篇 |
1972年 | 2148篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Starting from a microscopic Hamiltonian defined on a semi-infinite cubic lattice, and employing a mean-field approximation, the surface parameters relevant for wetting in confined ternary mixtures are derived. These are found in terms of the microscopic coupling constants, and yield a physical interpretation of their origins. In comparison with the standard expression for the surface free-energy density, several new terms arising from the derivation are identified. The influence of the surface parameters on a predicted unbinding transition in a mixture of oil, water, and amphiphile demonstrate that existing results are robust to the addition of the extra surface terms. 相似文献
82.
Takauchi H. Tamura H. Matsubara S. Kibune M. Doi Y. Chiba T. Anbutsu H. Yamaguchi H. Mori T. Takatsu M. Gotoh K. Sakai T. Yamamura T. 《Solid-State Circuits, IEEE Journal of》2003,38(12):2094-2100
We describe a CMOS multichannel transceiver that transmits and receives 10 Gb/s per channel over balanced copper media. The transceiver consists of two identical 10-Gb/s modules. Each module operates off a single 1.2-V supply and has a single 5-GHz phase-locked loop to supply a reference clock to two transmitter (Tx) channels and two receiver (Rx) channels. To track the input-signal phase, the Rx channel has a clock recovery unit (CRU), which uses a phase-interpolator-based timing generator and digital loop filter. The CRU can adjust the recovered clock phase with a resolution of 1.56 ps. Two sets of two-channel transceiver units were fabricated in 0.11-/spl mu/m CMOS on a single test chip. The transceiver unit size was 1.6 mm /spl times/ 2.6 mm. The Rx sensitivity was 120-mVp-p differential with a 70-ps phase margin for a common-mode voltage ranging from 0.6 to 1.0 V. The evaluated jitter tolerance curve met the OC-192 specification. 相似文献
83.
Lorenzetto G. Galtarossa A. Palmieri L. Santagiustina M. Someda C.G. Fiorone R. 《Lightwave Technology, Journal of》2003,21(2):424-431
First-order polarization-mode dispersion (PMD) compensation by means of a polarization controller and a differential delay line is not sufficient to guarantee error-free transmission for 40-Gb/s channels when higher order effects severely increase signal distortion. Higher order mitigation is possible by cascading more than one first-order block. However, only two-stage or three-stage devices remain simple enough to be actually controlled. The performance of such higher order PMD compensators is evaluated by means of numerical simulations. Two different feedback signals have been used, demonstrating that first-order and higher order PMD distortion of nonreturn-to-zero (NRZ) pulses at 40 Gb/s can be strongly mitigated for instantaneous values of the differential group delay (DGD) up to the bit slot, when the compensator is properly controlled. 相似文献
84.
Thomas S. Lowry John C. Bright Murray E. Close Christina A. Robb Paul A. White Stewart G. Cameron 《国际水资源开发杂志》2003,19(4):579-592
The primary objective of this project is to identify gaps, whether real or perceived, that hinder effective groundwater management in New Zealand. These gaps show as gaps in information, gaps in implementation, gaps in technological and management tools, and gaps in understanding of fundamental processes. The secondary objective is to propose a management strategy to close the identified gaps. Several methods are used to meet these objectives: surveys distributed to selected staff in each regional council; the review of various written reports; the analysis of land-use databases; and private consultation within each regional council. Results show that groundwater management in New Zealand is generally reactionary with the main gaps being in strategic planning and national guidelines. Most gaps appear to be predominantly information and implementation issues. In some cases there are gaps in the understanding of fundamental processes within an aquifer system, including the long-term effects of land-use on groundwater quality. An adaptive management approach is suggested as a means of closing these gaps. 相似文献
85.
On the capacities of bipartite Hamiltonians and unitary gates 总被引:2,自引:0,他引:2
Bennett C.H. Harrow A.W. Leung D.W. Smolin J.A. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2003,49(8):1895-1911
We consider interactions as bidirectional channels. We investigate the capacities for interaction Hamiltonians and nonlocal unitary gates to generate entanglement and transmit classical information. We give analytic expressions for the entanglement generating capacity and entanglement-assisted one-way classical communication capacity of interactions, and show that these quantities are additive, so that the asymptotic capacities equal the corresponding 1-shot capacities. We give general bounds on other capacities, discuss some examples, and conclude with some open questions. 相似文献
86.
A.L. Pan H.G. ZhengZ.P. Yang F.X. Liu Z.J. Ding Y.T. Qian 《Materials Research Bulletin》2003,38(5):789-796
Small Ag particles or clusters dispersed mesoporous SiO2 composite films were prepared by a new method: First the matrix SiO2 films were prepared by sol-gel process combined with the dip-coating technique, then they were soaked in AgNO3 solutions followed by irradiation of γ-ray at room temperature and in ambient pressure. The structures of these films were examined by X-ray diffraction (XRD), high-resolution transmission electron microscope (HRTEM), and optical absorption spectroscopy. It has been shown that the Ag particles grown within the porous SiO2 films are very small, and they are isolated and dispersed from each other with very narrow size distributions. With increasing the soaking concentration and an additional annealing, an opposite peakshift effect of the surface plasmon resonance (SPR) was observed in the optical absorption measurements. 相似文献
87.
P. CRISP T.J. WICKS D. BRUER E.S. SCOTT 《Australian Journal of Grape and Wine Research》2006,12(3):203-211
Grapevine powdery mildew ( Erysiphe necator) affects grape yield and fruit quality worldwide. Managers of conventional vineyards rely mainly on synthetic fungicides and sulfur to control powdery mildew, while in organic vineyards sulfur is the main control agent, often in rotation with canola-based oils, bicarbonates and biological control agents. The efficacy of those materials has not been evaluated critically under field conditions in Australia. Accordingly, a range of materials showing most promise in previous greenhouse trials (Crisp et al. 2006 Australian Journal of Grape and Wine Research 12 , pp. 192–202) were assessed via field trials in commercial vineyards. Applications of either milk or whey (alone, or mixed with a canola oil-based product), as well as applications of potassium bicarbonate (commercial formulation), all reduced the severity of powdery mildew compared with untreated vines. Eight applications of a 1:10 dilution of milk, 45 g/L whey powder or programs comprising rotations of potassium bicarbonate plus oil and whey, applied at 10–14 day intervals, reduced the severity of powdery mildew to levels not significantly different from that on vines sprayed with sulfur (wettable powder, 3–6 g/L). However, the relative control of powdery mildew by the test materials in field trials was dependent on the susceptibility of the grapevine cultivar and the extent of spray coverage achieved. In vineyards where highly susceptible cultivars were planted, and spray coverage was compromised, the resultant control of powdery mildew was reduced; and sometimes to commercially unacceptable levels. 相似文献
88.
Ysebaert G. Vanbleu K. Cuypers G. Moonen M. Pollet T. 《Signal Processing, IEEE Transactions on》2003,51(7):1916-1927
In discrete multitone receivers, the classical equalizer structure consists of a (real) time domain equalizer (TEQ) combined with complex one-tap frequency domain equalizers. An alternative receiver is based on a per tone equalization (PTEQ), which optimizes the signal-to-noise ratio (SNR) on each tone separately and, hence, the total bitrate. In this paper, a new initialization scheme for the PTEQ is introduced, based on a combination of least mean squares (LMS) and recursive least squares (RLS) adaptive filtering. It is shown that the proposed method has only slightly slower convergence than full square-root RLS (SR-RLS) while complexity as well as memory cost are reduced considerably. Hence, in terms of complexity and convergence speed, the proposed algorithm is in between LMS and RLS. 相似文献
89.
D. Vignolles D. Smirnov G. Rikken B. Raquet H. Rakoto C. Proust M. Nardone J. Léotin F. Lecouturier M. Goiran O. Drachenko J. M. Broto L. Brossard A. Audouard 《Journal of Low Temperature Physics》2003,133(1-2):97-120
An overview over past and present activities and future developments at the Toulouse pulsed magnetic field facility is given, both as far as technical developments of the infrastructure, as well as low temperature physics performed at the LNCMP are concerned. 相似文献
90.
H. Yamamoto N. Heyamoto T. Matsui N. Murayama J. Shibata 《International Journal of Thermophysics》2003,24(5):1385-1394
Polyvinylalcohol (PVA) polymer gel is a temperature sensitive polymeric gel, with a critical transition temperature (with H2O) of 310 K. At higher than 310 K, this temperature sensitive polymer gel shrinks because of discharging water, whereas at lower temperatures, the gel swelled because of absorbing water. The reversibility of the gel's volume change was confirmed by temperature swing. The adsorption behavior of an organic compound onto the PVA polymer gel in water was tested at various temperatures. The amount of adsorbed organic compound increased remarkably at temperatures higher than about 310 K. Then, it was confirmed that the organic compound in PVA polymer gel could be reversibly adsorbed and desorbed by a temperature change between 293 and 323 K. The mechanism of adsorption of the organic compound onto the PVA polymer gel could be explained by hydration and dehydration of polymer gel. 相似文献