全文获取类型
收费全文 | 120814篇 |
免费 | 778篇 |
国内免费 | 840篇 |
专业分类
电工技术 | 2527篇 |
综合类 | 139篇 |
化学工业 | 16287篇 |
金属工艺 | 10114篇 |
机械仪表 | 7381篇 |
建筑科学 | 2265篇 |
矿业工程 | 955篇 |
能源动力 | 2102篇 |
轻工业 | 3478篇 |
水利工程 | 1498篇 |
石油天然气 | 2851篇 |
无线电 | 11459篇 |
一般工业技术 | 31253篇 |
冶金工业 | 13437篇 |
原子能技术 | 1908篇 |
自动化技术 | 14778篇 |
出版年
2021年 | 340篇 |
2019年 | 374篇 |
2018年 | 9725篇 |
2017年 | 10397篇 |
2016年 | 5804篇 |
2015年 | 1111篇 |
2014年 | 898篇 |
2013年 | 2442篇 |
2012年 | 4214篇 |
2011年 | 10755篇 |
2010年 | 10064篇 |
2009年 | 9034篇 |
2008年 | 8629篇 |
2007年 | 10945篇 |
2006年 | 1479篇 |
2005年 | 5143篇 |
2004年 | 3358篇 |
2003年 | 2846篇 |
2002年 | 1779篇 |
2001年 | 1185篇 |
2000年 | 1107篇 |
1999年 | 1021篇 |
1998年 | 2120篇 |
1997年 | 1659篇 |
1996年 | 1454篇 |
1995年 | 994篇 |
1994年 | 788篇 |
1993年 | 801篇 |
1992年 | 614篇 |
1991年 | 596篇 |
1990年 | 524篇 |
1989年 | 485篇 |
1988年 | 376篇 |
1987年 | 402篇 |
1986年 | 363篇 |
1985年 | 381篇 |
1984年 | 305篇 |
1983年 | 300篇 |
1982年 | 301篇 |
1981年 | 296篇 |
1980年 | 349篇 |
1979年 | 341篇 |
1978年 | 294篇 |
1977年 | 415篇 |
1976年 | 629篇 |
1975年 | 308篇 |
1974年 | 292篇 |
1973年 | 311篇 |
1968年 | 318篇 |
1966年 | 277篇 |
排序方式: 共有10000条查询结果,搜索用时 687 毫秒
81.
82.
H. L. Du S. R. Rose Z. D. Xiang P. K. Datta X. Y. Li 《Materialwissenschaft und Werkstofftechnik》2003,34(4):421-426
The oxidation/sulphidation behaviour of a Ti‐46.7Al‐1.9W‐0.5Si alloy with a TiAl3 diffusion coating was studied in an environment of H2/H2S/H2O at 850oC. The kinetic results demonstrate that the TiAl3 coating significantly increased the high temperature corrosion resistance of Ti‐46.7Al‐1.9W‐0.5Si. The SEM, EDX, XRD and TEM analysis reveals that the formation of an Al2O3 scale on the surface of the TiAl3‐coated sample was responsible for the enhancement of the corroison resistance. The Ti‐46.7Al‐1.9W‐0.5Si alloy was also modified by Nb ion implantation. The Nb ion implanted and as received sampels were subjected to cyclic oxidation in an open air at 800oC. The Nb ion implantation not only increased the oxidation resistance but also substantially improved the adhesion of scale to the substrate. 相似文献
83.
V. N. Petrov V. V. Grebenshikov B. D. Grachev A. S. Kamochkin M. K. Yarmarkin 《Technical Physics Letters》2004,30(2):157-160
A compact electron polarimeter employing the classical Mott scheme has been developed and tested. The device has an efficiency
of about 5.6×10−4, a maximum count rate of 5×105 cps, dimensions 15 cm (diameter) × 25 cm (length), and a working voltage of 40 kV. The polarimeter can operate for a long
time under arbitrary vacuum conditions without maintenance, exhibiting no changes in the main working characteristics, and
obeys all requirements to the electron spin polarization studies on the modern level. 相似文献
84.
85.
F. M. Xu S. J. Zhu J. Zhao M. Qi F. G. Wang S. X. Li Z. G. Wang 《Materials Science and Engineering: A》2003,360(1-2):191-196
The SiC/Al graded composite was fabricated by powder metallurgy processing and its fatigue crack growth behavior was studied. The volume percentage of SiC particulates was distributed from 5 to 30% layer by layer on the cross section. Since the aluminium was dissolved together, there was no evident interface between the two layers with different volume fraction of SiC particulates. Fatigue crack growth was in direction of from 5 to 30% SiC layers under sinusoidal wave-form. The retardation of fatigue crack growth was found when crack propagated from low volume fraction of SiC to high volume fraction of SiC. The crack deflection and branching between two layers were observed, which decreased crack growth rates. In view of crack tip driving force, the plasticity mismatch between the layers shielded crack tip driving force, i.e. decreased the effective J-integral at the tip of the crack as the plastic zone of the crack tip spread from the weaker material into the stronger material. 相似文献
86.
R. K. Melekhov A. V. Vasylyk E. I. Palashchuk H. M. Krutsan Ya. D. Onyshchak 《Materials Science》2004,40(5):668-675
We study the process of degradation and damage for superheater tubes of the pressure boilers of power plants made of austenitic chromium-nickel steel. The role of sensitization and partial sigmatization of austenitic steel in the embrittlement of the tubes is analyzed.__________Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 40, No. 4, pp. 81–86, July–August, 2004. 相似文献
87.
A coupled finite-element model, CON2D, has been developed to simulate temperature, stress, and shape development during the
continuous casting of steel, both in and below the mold. The model simulates a transverse section of the strand in generalized
plane strain as it moves down at the casting speed. It includes the effects of heat conduction, solidification, nonuniform
superheat dissipation due to turbulent fluid flow, mutual dependence of the heat transfer and shrinkage on the size of the
interfacial gap, the taper of the mold wall, and the thermal distortion of the mold. The stress model features an elastic-viscoplastic
creep constitutive equation that accounts for the different responses of the liquid, semisolid, delta-ferrite, and austenite
phases. Functions depending on temperature and composition are employed for properties such as thermal linear expansion. A
contact algorithm is used to prevent penetration of the shell into the mold wall due to the internal liquid pressure. An efficient
two-step algorithm is used to integrate these highly nonlinear equations. The model is validated with an analytical solution
for both temperature and stress in a solidifying slab. It is applied to simulate continuous casting of a 120 mm billet and
compares favorably with plant measurements of mold wall temperature, total heat removal, and shell thickness, including thinning
of the corner. The model is ready to investigate issues in continuous casting such as mold taper optimization, minimum shell
thickness to avoid breakouts, and maximum casting speed to avoid hot-tear crack formation due to submold bulging. 相似文献
88.
89.
New information systems and recent applications (grid computing, Web Services, and so on) are often distributed, large-scale, open, heterogeneous, and characterized by a dynamic environment. To model these complex systems, researchers have spent much effort during the last few years on multiagent systems. The aim is to model complex distributed systems as a set of (possibly organized) software agents that interact in a common environment. The decomposition of a system into a number of agents lets the system react and adapt better in a changing environment. Moreover, organized structures ("social" structures) can emerge from interactions between agents, which in turn constrain and coordinate the agents' behavior. A multiagent system takes its metaphors of interaction from social systems rather than using the metaphor of the isolated thinker that early artificial intelligence researchers preferred. An important issue when dealing with this increasing complexity is to build adaptive agents and multiagent systems. Agents and multiagent systems must be aware of their own capabilities and of changes to other agents and their environment. To remain effective, agents must be able to adapt their structures and knowledge while they execute. 相似文献
90.
A. I. D’Souza M. G. Stapelbroek P. N. Dolan P. S. Wijewarnasuriya R. E. DeWames D. S. Smith J. C. Ehlert 《Journal of Electronic Materials》2003,32(7):633-638
The 1/f noise in photovoltaic (PV) molecular-beam epitaxy (MBE)-grown Hg1−xCdxTe double-layer planar heterostructure (DLPH) large-area detectors is a critical noise component with the potential to limit
sensitivity of the cross-track infrared sounder (CrIS) instrument. Therefore, an understanding of the origins and mechanisms
of noise currents in these PV detectors is of great importance. Excess low-frequency noise has been measured on a number of
1000-μm-diameter active-area detectors of varying “quality” (i.e., having a wide range of I-V characteristics at 78 K). The
1/f noise was measured as a function of cut-off wavelength under illuminated conditions. For short-wave infrared (SWIR) detectors
at 98 K, minimal 1/f noise was measured when the total current was dominated by diffusion with white noise spectral density
in the mid-10−15A/Hz1/2 range. For SWIR detectors dominated by other than diffusion current, the ratio, α, of the noise current in unit bandwidth
in(f = 1 Hz, Vd = −60 mV, and Δf = 1 Hz) to dark current Id(Vd = −60 mV) was αSW-d = in/Id ∼ 1 × 10−3. The SWIR detectors measured at 0 mV under illuminated conditions had median αSW-P = in/Iph ∼ 7 × 10−6. For mid-wave infrared (MWIR) detectors, αMW-d = in/Id ∼ 2 × 10−4, due to tunneling current contributions to the 1/f noise. Measurements on forty-nine 1000-μm-diameter MWIR detectors under
illuminated conditions at 98 K and −60 mV bias resulted in αMW-P = in/Iph = 4.16 ± 1.69 × 10−6. A significant point to note is that the photo-induced noise spectra are nearly identical at 0 mV and 100 mV reverse bias,
with a noise-current-to-photocurrent ratio, αMW-P, in the mid 10−6 range. For long-wave infrared (LWIR) detectors measured at 78 K, the ratio, αLW-d = in/Id ∼ 6 × 10−6, for the best performers. The majority of the LWIR detectors exhibited αLW-d on the order of 2 × 10−5. The photo-induced 1/f noise had αLW-P = in/Iph ∼ 5 × 10−6. The value of the noise-current-to-dark-current ratio, α appears to increase with increasing bandgap. It is not clear if
this is due to different current mechanisms impacting 1/f noise performance. Measurements on detectors of different bandgaps
are needed at temperatures where diffusion current is the dominant current. Excess low-frequency noise measurements made as
a function of detector reverse bias indicate 1/f noise may result primarily from the dominant current mechanism at each particular
bias. The 1/f noise was not a direct function of the applied bias. 相似文献