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991.
Asymptotic state behaviour and its modeling for saturated sand 总被引:3,自引:0,他引:3
A new double hardening elasto-plastic model is proposed in this paper based on the existing unified hardening model (UH model).
By assuming that there is part coupling effect between the plastic volumetric strain and plastic shear strain, hardening parameters
consisting of a coupled and an uncoupled components are adopted in this model. A unique feature of this model is that it can
describe not only the conventional drained and undrained behaviors of soil, but also the stress-strain relationships of soil
under partially drained conditions which can be volumetric compression or dilation. Adopting the asymptotic state concept,
simple equations for estimating the limiting stress ratio under undrained or earth pressure at rest (i.e. K
0) conditions are derived. The new model is relatively simple to be adopted in practice for two reasons. First, the same soil
parameters as in Cam-clay model are used except the addition of one extra parameter, the stress ratio at the characteristic
state. Second, all the parameters can be determined using conventional triaxial compression tests.
Supported by the National Natural Science Foundation of China (Grant Nos. 10672010 and 50479001) and the National Earthquake
Science Item (Grant No. 200808076) 相似文献
992.
Methane absorption and application of mixed organic aggregate prepared from Span80 and alkaline salt
The water-based materials for mine gas absorption and explosion suppression were prepared, in which the mixed organic aggregate
of Span80 and alkaline salt can be used as methane absorbent. Methane was used as a model of mine gas, and the absorptions
of methane with different complex materials were studied using head space gas chromatography. Then the state of aqueous material
was characterized with laser light scattering instrument and the effects of different complex materials on explosion suppression
were preliminarily studied in explosion chamber which can simulate mine gas explosion. The research results showed that complex
material could absorb methane and there was some correlation between the mean diameter of organic aggregate in aqueous material
and the absorption effect. Additionally, the aqueous material could suppress the methane explosion to some degree. The material
can absorb mine gas in atomization condition, therefore, degrease mine gas concentration and influence the distribution of
mine gas in the space, and then suppress the mine gas explosion to some extent. 相似文献
993.
HaiLing Zhu JunYing Zhang TianMin Wang LiuGang Wang Xiang Lan BaiBiao Huang 《中国科学E辑(英文版)》2009,52(8):2175-2179
Aiming at reducing the recombination of photo-induced carriers in semiconductor photocatalytic process, we prepared TiO2 thin film with its surface modified by a connected Cu micro-grid via a microsphere lithography strategy, which showed higher
photocatalytic activity than the pure TiO2 film. The improvement of photocatalytic activity of Cu micro-grid to the TiO2 film is due to the charge carrier separation and electron transfer by the conducting metal grid. The photocatalytic activity
was improved as metal loading increased, which obtained the best performance at a certain loading amount, and then decreased
at higher loading amount. This phenomenon was attributed to the metal’s bulk effect which could be explained by the relationship
between the energetic positions and the metal cluster size.
Supported by the National Natural Science Foundation of China (Grant Nos. 50672003, 50872005) and the National Basic Research
Program of China (“973” Project) (Grant No. 2007CB613302) and the Fok Ying Tong Education Foundation (Grant No. 111050) 相似文献
994.
Field measurement on wind characteristic and buffeting response of existing bridge is of great value to the development of
bridge wind engineering, and the structural health monitoring system (SHMS) employed in many long-span bridges provide a research
basis for the field measurement. In order to provide reliable basis for wind resistant evaluation of Runyang Suspension Bridge
(RSB), two anemometers and 85 accelerometers were installed in the SHMS of RSB. In August 2005, Typhoon Matsa crossed over
Jiangsu, the SHMS timely recorded the typhoon and structural vibration responses. In this paper by using the time-frequency
technique and statistical theory, the recorded data were analyzed to obtain the strong wind characteristics, the buffeting
response characteristics of the cable and deck, and the variation of buffeting response RMS versus wind speed. Results obtained
in this study can be employed to validate the credibility of current buffeting response analysis theory techniques, and provide
reference values for wind resistant evaluation of other long-span bridges.
Supported by the National Hi-Tech Research and Development Program of China (“863” Project) (Grant No. 2006AA04Z416), the
Key Project of the National Natural Science Foundation of China (Grant No. 50538020) and the Outstanding Youth Fund of the
National Natural Science Foundation of China (Grant No. 50725828) 相似文献
995.
JunHu Ma HeQing Yang YuZhe Song Li Li XiaoLi Xie RuiNi Liu LinFang Wang 《中国科学E辑(英文版)》2009,52(5):1264-1272
Large-scale oriented ZnO nanocone arrays were directly grown on zinc substrate through a hydro-thermal reaction of Zn foil with aqueous butylamine solution(3 mol/L) at 100—180 ℃ for 12 h.The syn-thesized products were characterized with X-ray diffraction,Raman spectrum,scanning electron mi-croscopy and transmission electron microscopy.The results showed that the ZnO nanocones were single crystalline with the wurtzite structure and grown along the [0001] direction.The diameter of nanocones is decreased with ... 相似文献
996.
Poly(vinyl alcohol)/Hydroxylapatite (PVA/HA) composite hydrogel was prepared with poly(vinyl alcohol) and hydroxylapatite
as raw materials, using the method of repeated freezing and thawing. The morphologies of PVA/HA composite hydrogel were observed
by means of high-accuracy 3D profiler and scanning electron microscope (SEM). The compressive elastic modulus and the stress
relaxation characteristics of PVA/HA composite hydrogel were measured using the flat-head cylinder indenter. The friction
and wear tests between PVA/HA composite hydrogel and bovine knee articular cartilage were performed on the micro-tribometer.
The worn morphologies of PVA/HA composite hydrogel were observed with environmental scanning electron microscope (ESEM). The
results showed that PVA/HA composite hydrogel has the cross-link network microstructure which is similar to that of the natural
bovine knee articular cartilages. With the increase of freezing-thawing cycles and the HA content, the degree of cross-link
and the crystallization of PVA/HA composite hydrogel both increase, the elastic modulus increases evidently, the rate of stress
relaxation is improved and the value of balance stress decreases. The friction coefficient decreases with the increase of
the freezing-thawing cycles and the HA content. The more the freezing-thawing cycles are, the earlier the friction coefficient
reaches the stable balance value. The friction deformation depth between PVA/HA composite hydrogel and bovine knee articular
cartilage is inversely proportional to freezing-thawing cycles and the HA content. The main wear mechanisms of PVA/HA composite
hydrogel are plastic flowing and adhesive flaking. The wear severity degree decreases with the increase of freezing-thawing
cycles and the HA content.
Supported by Key Program of the National Natural Science Foundation of China (Grant No. 50535050), Program for New Century
Excellent Talents in University (Grant No. NCET-06-0479) and Natural Science Foundation of Jiangsu Province (Grant No. BK2005403) 相似文献
997.
Electroosmotic flow (EOF) is a promising way for driving and mixing fluids in microfluidics. For the parallel-plate microchannel
with the hydrophobic surface, this paper solved the governing equations using the finite element method (FEM), and the effects
of microchannel height, electric strength and ionic concentration on EOF were thus investigated. The simulation indicates
that the transient characteristics of EOF are similar in hydrophobic and hydrophilic microchannels, the steady time of EOF
is proportional to the square of microchannel height, and the scale is microsecond. EOF velocity is proportional to the electric
strength and independent of the channel height, and decreases slowly with the ionic concentration, which is lower than that
in hydrophilic microchannel due to the presence of slip length in hydrophobic microchannel. The results can provide valuable
insights into the optimal design of microchannel surfaces to achieve accurate EOF control in hydrophobic microchannel.
Supported by the National Natural Science Foundation of China (Grant No. 50730007) 相似文献
998.
Copolymers of 9,9-dioctylfluorene (DOF) and 2-thienyl-benzothiadiazole (DBT) were synthesized by Suzuki reaction and end-capped
by N-hexyl-carbazole and benzene, which were abbreviated as PDOF-DBT-Cz and PDOF-DBT-B, respectively. The photophysical, electrochemical
and thermal properties of the copolymers were studied. The results indicated that replacement of N-hexyl-carbazole as end-capping
group of PDOF-DBT can vary light color and improve luminescence efficiency.
Supported by the Major Project of Science Foundation Ministry of Education of China (Grant No. 207015) and the National Natural
Science Foundation of China (Grant No. 20671068) 相似文献
999.
Hydrogen atom adsorption and diffusion properties on clean and vacancy defective Mg (0001) surface have been investigated
systematically by using a first-principles calculations method based on the density functional theory. The calculation results
of adsorption energy and diffusion energy barrier show that hydrogen atom is apt to be adsorbed at fcc and hcp sites on clean
Mg (0001) surface, and fcc adsorption site is found to be more preferred. The highest diffusion energy barrier is estimated
as 0.6784 eV for the diffusion of hydrogen from clean Mg (0001) surface into its bulk. Surface effects, which affect hydrogen
diffusion obviously, results in a slow diffusion velocity of hydrogen from surface to subsurface, while a fast one from subsurface
to bulk, indicating the range of surface effects is only restricted within two topmost layers of Mg (0001) surface. Comparatively,
Mg atom vacancy on Mg (0001) surface not only enhances the chemisorption interaction between H and Mg surface, but also benefits
H atom diffusion in Mg bulk with relatively more diffusion paths compared with that of clean surface. Besides, hydrogen atom
is found to occupy mostly the tetrahedral interstice when it diffuses into the Mg bulk. Further analysis of the density of
states (DOS) shows that the system for hydrogen atom to be adsorbed at fcc site has a lower DOS value (N (E
F)) at Fermi level and more bonding electrons at the energy range blow the Fermi level of H/Mg (0001) system as compared with
that at hcp site. On the other hand, the enhanced chemisorption interaction between hydrogen and defective surface should
be attributed to the fact that the electronic structures of Mg (0001) surface are modified by an Mg vacancy, and the bonding
electrons of the topmost layer Mg atoms are transferred from low energy range to Fermi level, which is in favor of improving
the surface activity of Mg (0001) surface.
Supported by the PhD Programs Foundation of Ministry of Education of China (Grant No. 200805321032), the Science and Technology
Program Project of Hunan Province (Grant No. 2008GK3083) and the Program for Changjiang Scholars and the Innovative Research
Team in university (Grant No. 531105050037) 相似文献
1000.
Separation of nanocolloids driven by dielectrophoresis: A molecular dynamics simulation 总被引:1,自引:0,他引:1
The nonequilibrium molecular dynamics (MD) method was used to model the nanocolloids and the solvent particles. By introducing
a non-uniform electric field, colloids were polarized to have opposite polarities. Separation of colloids driven by dielectrophoresis
(DEP) could be seen clearly under a strong electric field at low temperatures. Analyzing the ratio of DEP velocities of colloids
to thermal velocities of neutral solvent particles showed that when the ratio was correspondingly big, collision between colloids
and solvent particles would be intense, making the DEP velocity of colloids fluctuate frequently. By changing the electric
field strength, it was found that the enhancement of electric field strength would quicken the separation of colloids. But
when the electric field strength increased to a certain degree, the separation motion would be slow because of the strong
friction resistance of the solvent particles to the colloids. Moreover, studying the separation reason of colloids based on
the potential energy showed that after colloids were polarized, the attractive potential energy among the colloids would be
weaker than before, while the increase of temperature would reduce the attractive potential energy and increase the repulsive
potential energy, which accorded with the DLVO theory.
Supported by the National Hi-Tech Research and Derelopment Program of China (“863” Project) (Grant No. 2006AA04Z351) and the
National Natural Science Foundation of China (Grant Nos. 50675033, 30770553) 相似文献