全文获取类型
收费全文 | 21709篇 |
免费 | 180篇 |
国内免费 | 707篇 |
专业分类
电工技术 | 255篇 |
综合类 | 177篇 |
化学工业 | 2392篇 |
金属工艺 | 785篇 |
机械仪表 | 1018篇 |
建筑科学 | 1322篇 |
矿业工程 | 419篇 |
能源动力 | 99篇 |
轻工业 | 4517篇 |
水利工程 | 395篇 |
石油天然气 | 478篇 |
武器工业 | 80篇 |
无线电 | 1111篇 |
一般工业技术 | 7866篇 |
冶金工业 | 295篇 |
原子能技术 | 227篇 |
自动化技术 | 1160篇 |
出版年
2023年 | 34篇 |
2022年 | 47篇 |
2021年 | 61篇 |
2020年 | 33篇 |
2019年 | 48篇 |
2018年 | 58篇 |
2015年 | 62篇 |
2014年 | 110篇 |
2013年 | 89篇 |
2012年 | 2526篇 |
2011年 | 3309篇 |
2010年 | 641篇 |
2009年 | 292篇 |
2008年 | 2045篇 |
2007年 | 1857篇 |
2006年 | 1571篇 |
2005年 | 1290篇 |
2004年 | 1118篇 |
2003年 | 874篇 |
2002年 | 846篇 |
2001年 | 662篇 |
2000年 | 658篇 |
1999年 | 456篇 |
1998年 | 244篇 |
1997年 | 271篇 |
1996年 | 229篇 |
1995年 | 220篇 |
1994年 | 167篇 |
1993年 | 146篇 |
1992年 | 165篇 |
1991年 | 139篇 |
1990年 | 159篇 |
1989年 | 156篇 |
1988年 | 161篇 |
1987年 | 176篇 |
1986年 | 137篇 |
1985年 | 177篇 |
1984年 | 191篇 |
1983年 | 151篇 |
1982年 | 182篇 |
1981年 | 156篇 |
1980年 | 143篇 |
1979年 | 88篇 |
1978年 | 62篇 |
1975年 | 30篇 |
1974年 | 35篇 |
1973年 | 31篇 |
1965年 | 36篇 |
1964年 | 27篇 |
1958年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
93.
Waveguide grating couplers that have surface corrugation on both boundaries of the waveguide were fabricated by the deposition of waveguide material at high-vacuum pressures onto a surface-relief grating etched into the substrate. A lateral shift between the two gratings along the direction of the common grating vector was created during the waveguide deposition when the substrate normal was tilted with respect to the direction of material deposition. A series of waveguide thicknesses having an identical angle of deposition were examined to observe the effect of the waveguide thickness, and corresponding lateral shift, on the branching ratio and input-coupling efficiency. Branching ratios of above 98% and input-coupling efficiencies near the theoretical limit for an incident Gaussian beam were obtained. 相似文献
94.
One main problem of an interferometric measurement is to evaluate the object distance from the interference function. One of the known methods that delivers the object phase is the phase step method. Here we introduce computer-generated holograms to realize parallel phase steps without phase modulation of the reference path. 相似文献
95.
Improved ray-optics theory and Mie theory for single scattering and an adding-doubling method for multiple scattering have been used to study the interaction of radiation in NASA's Visible and Infrared Spin-Scan Radiometer Atmospheric Sounder Satellite (VAS) IR channels and the microphysics of inhomogeneous cirrus clouds. The simulation study shows that crystal shape has remarkable effects on scattering and on the radiative-transfer properties of cirrus clouds in IR spectra. The sensitivity of the brightness temperature, as observed with VAS-IR channels, to the hexagonal columns and plates in cirrus clouds is noticeable. A method that permits one to infer the optical thickness, crystal shape, ice-water content,and emittance of cirrus clouds by using a multi-IR window channel with a scanning observation technique is developed. Detailed error analyses are carried out, and the characteristics of VAS-IR window channels are investigated through the examination of the effects of sea-surface reflection and variations in the temperature and water-vapor profiles on the VAS measurements. It is shown that these effects are large and need to be considered. Some uncertainties that have risen from the theoretical model are studied; they demonstrate that the Mie-scattering theory should not be used to retrieve the microphysical and optical properties of cirrus clouds. A suitable cloud-microphysics model and a suitable scattering model are needed instead. 相似文献
96.
Image formation with partially coherent radiation is evaluated with the Hopkins formula and then applied to x-ray microscopy. Image characteristics expected from instruments with circular and annular pupils in partially coherent conditions are considered for two-point objects and a knife-edge object. The theoretically expected values for image characteristics that are easy accessible by an experiment, such as the width of a knife edge, are given for various x-ray microscopes. 相似文献
97.
Monodispersed, biocompatible, and readily-functionalized hybrid reporter-embedded core-shell nanopartilces (NPs) have been prepared in a simple route. This composite offers a potential platform for immunochemical detection using surface-enhanced Raman scattering (SERS) due to their high sensitivity, good stability and biocompatiblity. This also provides a new platform for insight into SERS enhancement mechanism. 相似文献
98.
Defense frontier analysis of quantum cryptographic systems 总被引:1,自引:0,他引:1
When a quantum cryptographic system operates in the presence of background noise, security of the key can be recovered by a procedure called key distillation. A key-distillation scheme effective against so-called individual (bitwise-independent) eavesdropping attacks involves sacrifice of some of the data through privacy amplification. We derive the amount of data sacrifice sufficient to defend against individual eavesdropping attacks in both BB84 and B92 protocols and show in what sense the communication becomes secure as a result. We also compare the secrecy capacity of various quantum cryptosystems, taking into account data sacrifice during key distillation, and conclude that the BB84 protocol may offer better performance characteristics than the B92. 相似文献
99.
The paper reports the screening results of two metal-based antineoplastic drugs with mutagenic potential, such as Romcis (trademark of Cisplatinum, produced in Romania) and diphenylantimony(III) diisopropyldithiophosphate (PADTF). Their effects were compared with those induced by Cyclophosphamide. Two mutagenicity tests, the SOS Chromotest and cytogenetic analysis were applied. The tests were carried out with or without metabolic activation (addition of S(9)-mix), either in E. coli PQ 37 cultures, using four doses (0.3, 3, 30 and 300 pmol compound/assay) for the SOS Chromotest or in leukocyte cultures using 0.3 mM from each compound, for cytogenetics. The dose- response relationships and SOSIP values revealed an indirect mutagenic potential for Cyclophosphamide, amplified by S(9) mix in bacterial cultures and an antiproliferative, clastogenic effect on lymphocytes. For Romcis and diphenylantimony(III) diisopropyldithiophosphate, a significant positive response by SOS Chromotest was recorded, which correlated with increased frequencies of chromosomal aberrations. 相似文献
100.