全文获取类型
收费全文 | 601919篇 |
免费 | 6986篇 |
国内免费 | 1889篇 |
专业分类
电工技术 | 10092篇 |
综合类 | 2714篇 |
化学工业 | 89458篇 |
金属工艺 | 27564篇 |
机械仪表 | 20049篇 |
建筑科学 | 12849篇 |
矿业工程 | 4191篇 |
能源动力 | 14600篇 |
轻工业 | 38272篇 |
水利工程 | 7440篇 |
石油天然气 | 14186篇 |
武器工业 | 26篇 |
无线电 | 67699篇 |
一般工业技术 | 124580篇 |
冶金工业 | 97811篇 |
原子能技术 | 13752篇 |
自动化技术 | 65511篇 |
出版年
2021年 | 4804篇 |
2020年 | 3698篇 |
2019年 | 4756篇 |
2018年 | 21925篇 |
2017年 | 20961篇 |
2016年 | 18371篇 |
2015年 | 5979篇 |
2014年 | 9244篇 |
2013年 | 24654篇 |
2012年 | 17171篇 |
2011年 | 27726篇 |
2010年 | 22929篇 |
2009年 | 22319篇 |
2008年 | 23841篇 |
2007年 | 24497篇 |
2006年 | 15417篇 |
2005年 | 14797篇 |
2004年 | 14052篇 |
2003年 | 13975篇 |
2002年 | 12730篇 |
2001年 | 12314篇 |
2000年 | 11668篇 |
1999年 | 11870篇 |
1998年 | 29521篇 |
1997年 | 20607篇 |
1996年 | 15794篇 |
1995年 | 11745篇 |
1994年 | 10343篇 |
1993年 | 10434篇 |
1992年 | 7677篇 |
1991年 | 7413篇 |
1990年 | 7392篇 |
1989年 | 6998篇 |
1988年 | 6720篇 |
1987年 | 6039篇 |
1986年 | 5961篇 |
1985年 | 6530篇 |
1984年 | 6013篇 |
1983年 | 5561篇 |
1982年 | 5121篇 |
1981年 | 5378篇 |
1980年 | 4968篇 |
1979年 | 5031篇 |
1978年 | 5172篇 |
1977年 | 5558篇 |
1976年 | 7227篇 |
1975年 | 4512篇 |
1974年 | 4389篇 |
1973年 | 4475篇 |
1972年 | 3922篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
M. I. Mazurkov V. S. Dmitrenko S. N. Kropachev 《Radioelectronics and Communications Systems》2008,51(2):106-111
It is proposed a rule of total classes of composition systems of discrete frequency signals (CDF-signals) construction in extended Galois fields. It is carried out modeling and research a correlation properties of CDF-signals, and determined their practical attraction. 相似文献
992.
Jatuporn Wittayakun Pongtanawat Khemthong Sanchai Prayoonpokarach 《Korean Journal of Chemical Engineering》2008,25(4):861-864
Rice husk silica (RHS) in amorphous phase with 98% purity was prepared from a waste rice husk from rice milling by leaching
with hydrochloric acid and calcination. The RHS was used effectively as a silica source for the synthesis of zeolite Y in
sodium form (NaY). The zeolite in pure phase was obtained from a two-step synthetic route in which the starting gels were
mixed, aged for 24 h at room temperature and crystallized for 24 h at 90 °C. The diameter of single crystal particles from
a scanning electron microscope was approximately 1.0 μm, whereas the average particle diameter from laser diffraction particle
size analyzer was approximately 10 μm because of the agglomeration of small crystals. Longer crystallization time in this
route resulted in a mixed phase containing NaY and zeolite P in sodium form (NaP). In addition, a one-step synthetic route
(no aging) was studied and the product was also a mixed phase zeolite. 相似文献
993.
A novel method for the fabrication of highly ordered nanopore arrays with very small diameter of 14 nm was demonstrated by
using low-temperature anodization. Two-step anodization was carried out at 25 V, sulfuric acid concentration of 0.3 M, and
electrolyte temperature of −15 °C. After anodization, a regular pore array with mean diameter of 14 nm and interpore distance
of 65 nm was formed. The pore diameter and regular arrangement were confirmed by scanning electron microscopy (SEM) and fast
Fourier transformation (FFT), respectively. The present results strongly suggest that the diameter of pores in a highly ordered
alumina template can be reduced by lowering the anodization temperature. 相似文献
994.
In this work, the kinetics and mechanism of free-radical polymerisation of glycidyl methacrylate (GMA) using potassium peroxydisulphate
(PDS) as water soluble initiator in the presence of synthesized 1, 4-Bis (tributyl methyl ammonium) benzene dichloride (TBMABDC)
as multi-site phase transfer catalyst (MPTC) was studied. The polymerisation reactions were carried out under inert and unstirred
conditions at constant temperature of 60 ± 1°C in cyclohexane/water biphase media. The role of concentrations of monomer,
initiator, catalyst and volume fraction of aqueous phase, solvent polarity and temperature on the rate of polymerisation (Rp)
was ascertained. The order with respect to monomer and initiator was found to be unity. The order with respect to catalyst
was found to be 0.51. The rate of polymerisation is independent of ionic strength and pH of the medium. However, an increase
in the polarity of solvent has slightly increased the Rp value. Based on the results obtained, a suitable kinetic scheme has
been proposed to account for the experimental observations and its significance discussed. 相似文献
995.
Transglutaminase (TGase) was separated from the culture broth of an isolated strain of Streptoverticillium mobaraense. The crude enzyme was prepared by centrifugation, ultrafiltration, precipitation by alcohol, centrifugation and freeze‐drying. The yield after these processes was 65–70%. Then the enzyme was purified to homogeneity by chromatography on CM‐cellulose and Sephadex G‐75 on which the yields were about 70% and 80%, respectively; the purified folds reached 2.5–4.7 and 1.08–2.06, respectively. The molecular weight of this TGase was 39,500–40,100 Da by gel filtration chromatography. Optimum enzyme activity was observed in the pH range of 5.0–7.0, and it was maintained stable at 20–40C. The optimal temperature and pH was 52C and 6.0, respectively. At 1 mM and 5 mM metal ion or inhibitors concentration, TGase activity was strongly inhibited by Zn2+ and NEM, and not affected obviously by Ba2+, Ca2+, Co2+, Cu2+, Fe2+, Fe3+, Mg2+, Mn2+, Na+ as well as PMSF and EDTA. The effects of these additions on this TGase were compared with those of other microbial TGases. 相似文献
996.
An analogy is established between the solutions of the problems of singularities of stresses in linear and bilinear elastic isotropic media. It is shown that the distributions of stresses and displacements in the vicinity of singular points on the boundary of the body (characterized by the singularities of stresses) are described, in both cases, by the same functional dependences on the space coordinates but with different characteristics of the material. We deduce expressions for the effective moduli of elasticity and Poisson's ratio of the bielastic medium including the parameter of hardening of the material. The solution of the problem of singularities of stresses in bilinear materials is obtained from the solution of the corresponding problem for the linear elastic medium by replacing the elastic constants with the corresponding effective values depending on the parameter of hardening of the material. The cases of wedge-shaped notches (for various boundary conditions imposed on their edges), two-component wedges, plane wedge-shaped cracks, and circular conic notches or rigid inclusions in the bielastic space are studied in detail. 相似文献
997.
Alia-Klein Nelly; Goldstein Rita Z.; Tomasi Dardo; Zhang Lei; Fagin-Jones Stephanie; Telang Frank; Wang Gene-Jack; Fowler Joanna S.; Volkow Nora D. 《Canadian Metallurgical Quarterly》2007,7(4):735
Reports an error in "What is in a word? No versus Yes differentially engage the lateral orbitofrontal cortex" by Nelly Alia-Klein, Rita Z. Goldstein, Dardo Tomasi, Lei Zhang, Stephanie Fagin-Jones, Frank Telang, Gene-Jack Wang, Joanna S. Fowler and Nora D. Volkow (Emotion, 2007[Aug], Vol 7[3], 649-659). The supplemental materials link should appear as follows: http://dx.doi.org/10.1037/1528-3542.7.3.649.supp. (The following abstract of the original article appeared in record 2007-11660-018.) The words "No" and "Yes" are involved in conditioning to prohibit or encourage behavior, respectively. The authors, therefore, hypothesized that these words would be attributed to endogenous valence, activating neuronal circuits involved with valence and emotional control. Functional MRI (fMRI) at 4 Tesla was used to record regional brain activity while participants were exposed to emphatic vocalizations of the words. Results showed that No and Yes were associated with opposite brain-behavior responses; while No was negatively valenced, produced slower response times, and evoked a negative signal in the right lateral orbitofrontal cortex (OFC), Yes was positively valenced, produced faster response times, and evoked a positive signal in a contiguous region of the OFC. Attribution of negative valence to No and trait anger control were associated with increased responsivity of the OFC to No. Inasmuch as sensitivity to the prohibitive command No develops during childhood through interaction with primary caregivers as the first social objects, our findings may implicate the lateral OFC in the neurobiology of emotion regulation and subsequent social development. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
998.
S. C. Hogg H. V. Atkinson P. Kapranos 《Metallurgical and Materials Transactions A》2004,35(3):899-910
The rheology of Al-30Si-5Cu and Al-30Si-5Cu-2Mg spray-formed alloys has been characterized after holding at various times
and temperatures, using semisolid rapid compression to obtain load-displacement curves. Microstructures were examined after
partial remelting and compression in an attempt to understand the flow behavior. The initial resistance to flow generally
increased with holding time at temperature. This increase was attributed to the increased strength of a three-dimensional
(3-D) solid silicon network present in these alloys in the semisolid state, with the initial resistance to flow smaller in
the magnesium-containing alloys. With increased temperature, the initial resistance decreased due to increased liquid content
and grain spheroidization. The viscosity vs shear rate response was studied using the approach of Laxmanan and Flemings. The materials shear thinned rapidly during the
test conditions, in which the shear rate rapidly increased from approximately 2.5 to 92 s−1. The results were fitted to a power-law model, and the viscosities showed a drop of approximately two to four orders of magnitude
when extrapolated to a shear rate of 1000 s−1 (a typical value in actual component manufacture). The rapid compression test, which is close to conditions present in component
manufacture, was shown to have more in common with a shear rate jump experiment, rather than steady-state viscometry. 相似文献
999.
Finite sample properties of estimators of spatial autoregressive models with autoregressive disturbances 总被引:1,自引:0,他引:1
The article investigates the finite sample properties of estimators for spatial autoregressive models where the disturbance
terms may follow a spatial autoregressive process. In particular we investigate the finite sample behavior of the feasible
generalized spatial two-stage least squares (FGS2SLS) estimator introduced by Kelejian and Prucha (1998), the maximum likelihood
(ML) estimator, as well as that of several other estimators. We find that the FGS2SLS estimator is virtually as efficient
as the ML estimator. This is important because the ML estimator is computationally burdensome, and may even be forbidding
in large samples, while the FGS2SLS estimator remains computationally feasible in large samples.
Received: 20 January 2001 / Accepted: 31 August 2001 相似文献
1000.