全文获取类型
收费全文 | 58558篇 |
免费 | 13588篇 |
国内免费 | 80篇 |
专业分类
电工技术 | 1006篇 |
综合类 | 28篇 |
化学工业 | 21208篇 |
金属工艺 | 1020篇 |
机械仪表 | 2011篇 |
建筑科学 | 2083篇 |
矿业工程 | 7篇 |
能源动力 | 1640篇 |
轻工业 | 8539篇 |
水利工程 | 394篇 |
石油天然气 | 60篇 |
无线电 | 10062篇 |
一般工业技术 | 15125篇 |
冶金工业 | 2058篇 |
原子能技术 | 314篇 |
自动化技术 | 6671篇 |
出版年
2024年 | 27篇 |
2023年 | 271篇 |
2022年 | 414篇 |
2021年 | 871篇 |
2020年 | 1788篇 |
2019年 | 3492篇 |
2018年 | 3535篇 |
2017年 | 3821篇 |
2016年 | 4421篇 |
2015年 | 4351篇 |
2014年 | 4579篇 |
2013年 | 6201篇 |
2012年 | 3864篇 |
2011年 | 3855篇 |
2010年 | 3707篇 |
2009年 | 3652篇 |
2008年 | 3176篇 |
2007年 | 2765篇 |
2006年 | 2434篇 |
2005年 | 2071篇 |
2004年 | 1968篇 |
2003年 | 1876篇 |
2002年 | 1808篇 |
2001年 | 1556篇 |
2000年 | 1464篇 |
1999年 | 864篇 |
1998年 | 726篇 |
1997年 | 512篇 |
1996年 | 376篇 |
1995年 | 270篇 |
1994年 | 239篇 |
1993年 | 189篇 |
1992年 | 131篇 |
1991年 | 132篇 |
1990年 | 116篇 |
1989年 | 121篇 |
1988年 | 70篇 |
1987年 | 88篇 |
1986年 | 74篇 |
1985年 | 66篇 |
1984年 | 45篇 |
1983年 | 38篇 |
1982年 | 17篇 |
1981年 | 31篇 |
1980年 | 24篇 |
1979年 | 13篇 |
1978年 | 18篇 |
1977年 | 22篇 |
1976年 | 30篇 |
1975年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
Poly[2‐methoxy‐5‐(2′‐ethyl‐hexyloxy)‐para‐phenylene vinylene] (MEH‐PPV)/silica nanoparticle hybrid films were prepared and characterised. Three kinds of materials were compared: parent MEH‐PPV, MEH‐PPV/silica (hybrid A films), and MEH‐PPV/coupling agent MSMA/silica (hybrid B films), in which MSMA is 3‐(trimethoxysilyl) propyl methacrylate. It was found that the hybrid B films could significantly prevent macrophase separation, as evidenced by scanning electron and fluorescence microscopy. Furthermore, the thermal characteristics of the hybrid films were largely improved in comparison with the parent MEH‐PPV. The UV‐visible absorption spectra suggested that the incorporation of MSMA‐modified silica into MEH‐PPV could confine the polymer chain between nanoparticles and thus increase the conjugation length. The photoluminescence (PL) studies also indicated enhancement of the PL intensity and quantum efficiency by incorporating just 2 wt% of MSMA‐modified silica into MEH‐PPV. However, hybrid A films did not show such enhancement of optoelectronic properties as the hybrid B films. The present study suggests the importance of the interface between the luminescent organic polymers and the inorganic silica on morphology and optoelectronic properties. Copyright © 2004 Society of Chemical Industry 相似文献
72.
Low dielectric poly[methylsilsesquioxane‐ran‐trifluoropropylsilsesquioxane‐ran‐(2,4,6,8‐tetramethyl‐2,4,6,8‐tetraethylenecyclotetrasiloxane)silsesquioxane]s {P[M‐ran‐TFP‐ran‐(TCS)]SSQs} having various compositions were synthesized using trifluoropropyl trimethoxysilane, methyl trimethoxysilane and 2,4,6,8‐tetramethyl‐2,4,6,8‐tetra(trimethoxysilylethyl)cyclotetrasiloxane. The chemical composition of the polymers and the content of SiOH end‐groups were controlled by adjusting the reaction conditions, and they were characterized by 1H‐NMR. The thermally decomposable trifluoropropyl groups on the P[M‐ran‐TFP‐ran‐(TCS)]SSQ backbone and heptakis(2,3,6‐tri‐O‐methyl)‐β‐cyclodextrin (CD) were employed as pore generators. The dielectric constants of the porous CD/P[M‐ran‐TFP‐ran‐(TCS)]SSQ films were in the range 2.0–2.7 (at 100 kHz) depending on the concentration of the porogens, and showed no change over 4 days under aqueous conditions. The pore size of the films showed a bimodal distribution, with diameters of ca 0.5–1.0 nm for those originating from the trifluoropropyl groups and 1.7 nm from the CD. The elastic modulus and hardness of the 30 vol% CD‐blended film with a dielectric constant of 2.26 were 2.40 and 0.38 GPa, respectively, as determined by a nanoindenter. Copyright © 2005 Society of Chemical Industry 相似文献
73.
74.
Due to their small size, mammalian oocytes and embryos pose unique problems during preparation for transmission electron microscopy. This paper outlines a method which combines protein embedding with centrifugation to locate the specimens on the face of a Beem capsule mould. This method facilitates both the processing of oocytes with minimal loss and rapid location of the specimens within the block for simultaneous sectioning, staining and examination. 相似文献
75.
Jong-Hwan Kim Yeon-Chan Hong Sung-Jun Lee Keh-Kun Choi 《Industrial Electronics, IEEE Transactions on》1989,36(3):361-364
A direct adaptive control scheme is proposed for nonminimum-phase systems in which controller parameters are estimated from the recursive least-squares algorithm and additional auxiliary parameters are obtained from the proposed polynomial identity. A local convergence is guaranteed without any extra condition. Integral action is incorporated into the adaptive controller to eliminate the steady-state error and to satisfy a condition of the unique solution for the polynomial identity. The control law used in this scheme is based on the set-point-on-I-only proportional-integral-derivative (PID) structure 相似文献
76.
The effects of gallia additions on the sintering behavior of gadolinia-doped ceria were systematically investigated from the following aspects: the variation in sintered density, the variation in grain size, and the existing forms of Ga2O3 in CeO2.Sintered density increased with increasing Ga2O3 content up to 5 mol.% and then it decreased with further addition of Ga2O3. Grain size also increased with increasing Ga2O3 content up to 5 mol.% and then decreased with further addition of Ga2O3. Decrease in grain size was caused by a pinning effect of Ga2O3 precipitation at grain boundaries. Lattice constant decreased with increasing Ga2O3 content up to 5 mol.%. This decrease will be due to the substitution of smaller Ga3+ ions for Ce4+ ions in the CeO2 structure. According to the results obtained from scanning electron microscope (SEM) and X-ray diffraction (XRD) analyses, the solubility limit of Ga2O3 in Ce0.8Gd0.2O1.9 ceramics can be estimated to be nearly 5 mol.%. The addition of Ga2O3 up to the solubility limit was found to promote the sintering properties of Gd2O3-doped CeO2. 相似文献
77.
Hsing-Chung Liang Wen-Chin Ho Ming-Chieh Cheng 《Reliability, IEEE Transactions on》2005,54(2):358-365
In this paper, we discuss some strategies for identifying unrepairable memories, and from that to introduce a novel theorem that can make more precise identification. A new algorithm for searching repair solutions is also proposed, which characterizes the rows, and columns of defective memory cells with revised effective coefficients. We have simulated it on many generated example maps, and compared it with the previous algorithms to verify its efficiency. It's combined with those arranged strategies of judging unrepairability to generate a complete flow. The complete algorithm has also been run on many examples with various memory sizes, defect numbers, and distribution types. The simulation results further show that identifying unrepairability in advance can help the reconfiguration procedure run much faster than searching solutions directly. 相似文献
78.
Jeongsoo Choi 《Polymer》2005,46(23):9725-9735
A series of star-branched poly(ε-caprolactone)s (SPCLs) was synthesized with structural variation of the arm numbers and lengths through ring-opening polymerization under bulk condition. Arm numbers were varied to be 3, 4, and 6 by using multifunctional initiating cores such as trimethylol propane, pentaerythritol, and dipentaerythritol, respectively. The lengths of the poly(ε-caprolactone) arms were varied by controlling the molar ratio of monomer-to-initiating hydroxyl group molar ratio ([CL]0/[-OH]0=5, 10, 15). Molecular weights were determined by both 1H NMR end-group analysis and MALDI-TOF mass spectrometry, which gave reasonably consistent values. On the contrary, the GPC method failed to give accurate values of molecular weight of SPCLs due to the discrepancy with the linear standard. The branching architecture of SPCLs was evaluated by the branching ratio, g, which is the ratio of the mean-square radius of SPCL to that of liner counterpart, linear poly(ε-caprolactone) (LPCL), which is of the same chemistry and having the same molecular weight. The radii of gyration of SPCLs and LPCLs were determined using small-angle X-ray scattering (SAXS) from the initial slopes of Zimm plots, represented as 1/I(q) vs q2 with I(q) and q being the scattered intensity and scattering vector, respectively. The g values were observed to decrease with increasing arm numbers, indicating more compact molecular structure for SPCLs with higher arm numbers, while no such effect was observed for arm length variation. Thermal properties as well as the degree of crystallinity of SPCLs were found to be also dependent on structural variations. The melting points and the degradation temperatures were observed to increase with increasing arm lengths but with constant arm number. On the other hand, arm number variation with constant arm length gave no such changes to the thermal transitions of SPCLs. However, for the SPCLs with equivalent molecular weights, the degree of crystallinity was found to decrease with increasing arm numbers. 相似文献
79.
Du Young Choi Long Mei Jin Dexian Wang Kyung Ho Row 《Korean Journal of Chemical Engineering》2005,22(3):465-469
High-performance frontal analysis (HPFA) was used for a protein binding study of isoflavones (daidzein, genistin, and genistein),
enantiomers of perillyl alcohol and S-ibuprofen to human serum albumin (HSA). The analyses were performed on a Develosil and
Inertsil 100-Diol-5 column (10 cm×4.6mm). Sodium phosphate solution (pH 7.4, ionic strength 0.17) was used as the mobile phase
at a flow rate of 1 ml/min. To ensure the drug to be eluted as a trapezoidal peak with a plateau, injection volumes were each
fixed up the zonal profile with an evident plateau appears. The unbound drug concentration was determined from a plateau height
of the plateau region after that experimental data were fitted by Scatchard equation. The binding constants (K) and total
binding affinities (nK) of drugs to HSA were calculated, respectively. 相似文献
80.
Gonzalo Martínez‐Barrera Enrique Vigueras‐Santiago Susana Hernndez‐Lpez Gonzalo Martínez‐Barrera Witold Brostow Carmina Menchaca‐Campos 《Polymer Engineering and Science》2005,45(10):1426-1431
Fiber reinforced concrete (FRC) contains fibers physically mixed with gravel, sand, cement, and water. So far, adequate mechanical performance of FRC has been obtained at high cost and using complex technologies; important here is the geometry and surface characteristics of the polymers. We have modified polymeric‐fiber surfaces by using gamma radiation. Irradiated polypropylene (PP) fibers were submitted to 0, 5, 10, 50, and 100 kGy of gamma irradiation dosages. First, tensile strength of PP fibers was evaluated, and then fibers blended at 0, 1.0, 1.5, and 2.0% in volume with Portland cement, gravel, sand, and water. The highest values of compressive strength were obtained with irradiated‐fibers at 10 kGy and 1.5% in volume of fiber. The result is 101 MPa, as compared to 35 MPa for simple concrete without fibers. POLYM. ENG. SCI., 45:1426–1431, 2005. © 2005 Society of Plastics Engineers 相似文献