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991.
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
992.
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
993.
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
994.
Tao Zhang JunHong Jin DaYong Hu ShengLin Yang Guang Li JianMing Jiang 《中国科学E辑(英文版)》2009,52(4):906-909
The effect of coagulation temperature on the morphology, microstructures and mechanical properties of dihydroxy poly(p-phenylene benzobisoxazole) (DHPBO) fibers was investigated during dry-jet wet-spinning process, in which the coagulation
bath concentration and drawn ratio were kept as 10 wt% of PPA in water and 1.7, respectively. The structures and mechanical
properties of the as-spun DHPBO fibers were characterized by FTIR, XRD, SEM, and single fiber tensile testing. The results
indicated that in PPA/H2O coagulation system, when the coagulation temperature was 25°C, highly crystallized DHPBO as-spun fibers possessing fine
crystallites, circular and smooth morphology, and excellent mechanical properties could be achieved.
Supported by the National Natural Science Foundation of China (Grant No. 50673017), Shanghai Leading Academic Discipline Project
(Grant No. B603) and the Program of Introducing Taleuts of Discipline to University of People’s Republic of China (“111” Program)
(Grant No. 111-2-04) 相似文献
995.
A neural network model with high nonlinear recognition capability was constructed to describe the relationship between the deformation impact factors and the deformation results of vascular stent.Then,using the weighted correction method with the attached momentum term,the network training algorithm was optimized by introducing learning factor η and momentum factor ψ,so the speed of the network training and the system robustness were enhanced.The network was trained by some practi-cal cases,and the statisti... 相似文献
996.
In multistage machining processes(MMPs),the final quality of a part is influenced by a series of machining processes,which are complex correlations.So it is necessary to research the rule of machin-ing error propagation to ensure the machining quality.For this issue,a change management method of quality control nodes(i.e.,QC-nodes) for machining error propagation is proposed.A new framework of QC-nodes is proposed including association analysis of quality attributes,quality closed-loop control,error tracing... 相似文献
997.
Equilibrium equations for nonlinear buckling analysis of drill-strings in 3D curved well-bores 总被引:1,自引:0,他引:1
With the development of drilling technology, the oil/gas well has evolved from its early vertical straight form to the inclined, horizontal, plane curved, or even 3D curved well-bore. Understanding of the buck-ling behavior of a drill-string in a well-bore is crucial for the success of a drilling operation. Therefore, equilibrium equations for analyzing the buckling behavior of a drill-string in a 3D curved well-bore are required. Based on Love’s equilibrium equations for a curved and twisted rod in space, ... 相似文献
998.
The overall behavior of concrete depends on its meso structures such as aggregate shape, interface status, and mortar matrix
property. The two key meso structure characters of concrete, bond status of interface and nonlinear property of matrix, are
considered in focus. The variational structure principle is adopted to establish the macro-meso constitutive law of concrete.
Specially, a linear reference composite material is selected to make its effective behavior approach the nonlinear overall
behavior of concrete. And the overall property of linear reference composite can be estimated by classical estimation method
such as self-consistent estimates method and Mori-Tanaka method. This variational structure method involves an optimum problem
ultimately. Finally, the macro-meso constitutive law of concrete is established by optimizing the shear modulus of matrix
of the linear reference composite. By analyzing the constitutive relation of concrete established, we find that the brittleness
of concrete stems from the imperfect interface and the shear dilation property of concrete comes from the micro holes contained
in concrete.
Supported by the National Natural Science Foundation of China (Grant Nos. 50679022, 90510017, 50539090) and National Basic
Research Program of China (Grant No. 2007CB714104) 相似文献
999.
In order to in situ measure chemical parameters of deep-sea water and hydrothermal fluids at midocean ridge(MOR), it is necessary to use high temperature and high pressure chemical sensors.Developing new sensors is essential to measure in-situ pH and other chemical parameters(dissolved H2, dissolved H2S) of deep-sea water and hydrothermal fluids in a wide temperature range(2℃―400℃) at MOR vents.The YSZ(Yttria Stabilized Zirconia, 9%Y2O3) ceramic-based(HgO/Hg) chemical sensors possess excellent electrochemic... 相似文献
1000.
Thermal activation and radiation quenching characteristics and their application to the pre-dose dating of porcelain 总被引:1,自引:1,他引:0
WeiDa Wang 《中国科学E辑(英文版)》2009,52(2):324-331
The pre-dose technique is important for thermoluminescence (TL) dating of porcelain. The principle of pre-dose dating is based on two characteristics: thermal activation and radiation quenching of the porcelain. Based on these principles, two measurement methods, "the activation method" and "the quenching method", respectively, have been developed for evaluation of the porcelain paleodose. The paleodose values obtained are the same for the ages in the range of 100―1000 a BP for porcelains measured by these two methods. But for dating at lower age limits (less than 100 a BP), the activation method is more accurate; conversely, at higher age limits (greater than 1000 a BP) the quenching method is more accurate. In addition, two specific calculating methods are described for a few porce-lains having anomalous activation and quenching characteristics that make these two methods invalid. 相似文献