首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   4675篇
  免费   166篇
  国内免费   3篇
电工技术   72篇
综合类   15篇
化学工业   1006篇
金属工艺   95篇
机械仪表   69篇
建筑科学   229篇
矿业工程   25篇
能源动力   113篇
轻工业   375篇
水利工程   27篇
石油天然气   2篇
无线电   470篇
一般工业技术   801篇
冶金工业   907篇
原子能技术   65篇
自动化技术   573篇
  2023年   37篇
  2022年   23篇
  2021年   71篇
  2020年   61篇
  2019年   71篇
  2018年   82篇
  2017年   58篇
  2016年   94篇
  2015年   88篇
  2014年   126篇
  2013年   204篇
  2012年   171篇
  2011年   279篇
  2010年   168篇
  2009年   177篇
  2008年   202篇
  2007年   154篇
  2006年   154篇
  2005年   108篇
  2004年   112篇
  2003年   112篇
  2002年   131篇
  2001年   97篇
  2000年   88篇
  1999年   106篇
  1998年   305篇
  1997年   216篇
  1996年   134篇
  1995年   113篇
  1994年   104篇
  1993年   96篇
  1992年   64篇
  1991年   80篇
  1990年   57篇
  1989年   52篇
  1988年   51篇
  1987年   43篇
  1986年   26篇
  1985年   47篇
  1984年   45篇
  1983年   36篇
  1982年   25篇
  1981年   29篇
  1980年   30篇
  1979年   22篇
  1978年   21篇
  1977年   32篇
  1976年   61篇
  1975年   24篇
  1972年   20篇
排序方式: 共有4844条查询结果,搜索用时 62 毫秒
91.
Multiple sclerosis is characterized by inflammatory demyelination and axonal loss as pathophysiological correlates of relapsing activity and progressive development of clinical disability. The molecular processes involved in this pathogenesis are still unclear as they are quite complex and heterogeneous. In this article we present protein expression analysis of brain and spinal cord tissues from different models of murine experimental autoimmune encephalomyelitis (EAE), the most commonly used animal model for multiple sclerosis. We observed a number of EAE-specific protein expression and PTM differences. Proteome analysis was extended to multiple sclerosis specimens in order to validate the EAE findings. Our findings suggest the regulation of a number of proteins that shed light on the molecular mechanisms of the disease processes taking place in EAE and multiple sclerosis. We found consistent modulation of proteins including serum amyloid P component, sirtuin 2, dihydropyrimidinase-related protein family proteins, stathmin 1, creatine kinase B and chloride intracellular channel protein 1. Functional classification of the proteins by database and the literature mining reveals their association with neuronal development and myelinogenesis, suggesting possible disease processes that mediate neurodegeneration.  相似文献   
92.
We examined the high precision deposition of toner and polymer microparticles with a typical size of approximately 10 microm on electrode arrays with electrodes of 100 microm and below using custom-made microelectronic chips. Selective desorption of redundant particles was employed to obtain a given particle pattern from preadsorbed particle layers. Microparticle desorption was regulated by dielectrophoretic attracting forces generated by individual pixel electrodes, tangential detaching forces of an air flow, and adhesion forces on the microchip surface. A theoretical consideration of the acting forces showed that without pixel voltage, the tangential force applied for particle detachment exceeded the particle adhesion force. When the pixel voltage was switched on, however, the sum of attracting forces was larger than the tangential detaching force, which was crucial for desorption efficiency. In our experiments, appropriately large dielectrophoretic forces were achieved by applying high voltages of up to 100 V on the pixel electrodes. In addition, electrode geometries on the chip's surface as well as particle size influenced the desorption quality. We further demonstrated the compatibility of this procedure to complementary metal oxide semiconductor chip technology, which should allow for an easy technical implementation with respect to high-resolution microparticle deposition.  相似文献   
93.
Estimating the virial coefficients of small polar molecules   总被引:2,自引:0,他引:2  
We adapt existing models for estimating the second and third virial coefficients of small molecules to the halogenated methanes and ethanes. We compare the results with the abundant new, high-qualityPVT data resulting from the search for alternative refrigerants. The present model provides an accurate method for calculating densities, and therefore it should provide reliable thermodynamic properties and fugacity coefficients. We give equations and parameters useful for estimating the properties of pure refrigerants and their mixtures when noPVT data are available.Nomenclature B Second virial coeficient - B 12 Mixture cross second virial - B h Second virial of a hard sphere fluid - i (T) Temperature function, second virial, Eq. (7) - C Third virial coefficient - C 112,C 122 Mixture cross third virials - C h Third virial of a hard sphere fluid - N Avogadro's number Virial Coefficients P c Critical pressure - P c12 Characteristic critical pressure of a binary mixture - T c Critical temperature - T c12 Characteristic critical temperature of a binary mixture - T r Reduced temperature,T/T c - Parameter measuring polar contribution toB, Eq. (3) - b Volume of a hard sphere molecule - f (f) Polynomials determining temperature dependence of the nonpolar part ofB - k 12 Binary interaction parameter for mixtures, Eq. (9a) - c Critical volume - e Molecular polarizability - Dipole moment - R Reduced dipole moment, Eq. (4) - R12 Mixture reduced dipole moment, second virial - R112, R122 Mixture reduced dipole moment, third virial - Pitzer acentric factor - 12 Mixture acentric factor - (r) Intermolecular potential - c Critical density (1/c)  相似文献   
94.
95.
Poly[1-methyl-1-[3-(3-pyridinyl)propyl]-1-sila-cis-pent-3-ene], poly[1-phenyl-1-[3-(3-pyridinyl)propyl)-1-sila-cis-pent-3-ene], and poly[1-phenyl-1-(4-pyridinyl)-1-sila-cis-pent-3-ene] were synthesized by the anionic ring-opening polymerization of 1-methyl-1-[3-(3-pyridinyl)propyl]-1-silacyclopent-3-ene, 1-phenyl-1-[3-(3-pyridinyl)propyl]-1-silacyclopent-3-ene, and 1-phenyl-1-(4-pyridinyl)-1-silacyclopent-3-ene, respectively. These are the first polycarbosilanes which contain heterocyclic pyridine units as side-chain substituents. These polymers were characterized by1H,13C, and29Si NMR as well as by IR and UV spectroscopy. The molecular weight distributions were determined by gel permeation chromatography, glass transition temperatures, by differential seanning calorimetry: (DSC) and thermal behavior, by thermogravimetric analysis. (TGA).  相似文献   
96.
The development of multilayer mirror technology capable of operating in the range of 3-30 nm and the construction of thin membranes with excellent uniformity and strength have made it possible to design and implement a Mach-Zehnder interferometer operating at 15.5 nm. We have tested this interferometer by using a soft x-ray laser as a source, and we show its use in probing high-density plasmas.  相似文献   
97.
Electron–phonon interactions play an essential role in charge transport and transfer processes in semiconductors. For most structures, tailoring electron–phonon interactions for specific functionality remains elusive. Here, it is shown that, in hybrid perovskites, coherent phonon modes can be used to manipulate charge transfer. In the 2D double perovskite, (AE2T)2AgBiI8 (AE2T: 5,5“-diylbis(amino-ethyl)-(2,2”-(2)thiophene)), the valence band maximum derived from the [Ag0.5Bi0.5I4]2– framework lies in close proximity to the AE2T-derived HOMO level, thereby forming a type-II heterostructure. During transient absorption spectroscopy, pulsed excitation creates sustained coherent phonon modes, which periodically modulate the associated electronic levels. Thus, the energy offset at the organic–inorganic interface also oscillates periodically, providing a unique opportunity for modulation of interfacial charge transfer. Density-functional theory corroborates the mechanism and identifies specific phonon modes as likely drivers of the coherent charge transfer. These observations are a striking example of how electron–phonon interactions can be used to manipulate fundamentally important charge and energy transfer processes in hybrid perovskites.  相似文献   
98.
Distributed and Parallel Databases - Massive data transfers in modern data-intensive systems resulting from low data-locality and data-to-code system design hurt their performance and scalability....  相似文献   
99.
100.
Early phase distributed system design can be accomplished using solution spaces that provide an interval of permissible values for each functional parameter. The feasibility property guarantees fulfillment of all design requirements for all possible realizations. Flexibility denotes the size measure of the intervals, with higher flexibility benefiting the design process. Two methods are available for solution space identification. The direct method solves a computationally cheap optimization problem. The indirect method employs a sampling approach that requires a relaxation of the feasibility property through re-formulation as a chance constraint. Even for high probabilities of fulfillment, \(P>0.99\), this results in substantial increases in flexibility, which offsets the risk of infeasibility. This work implements the chance constraint formulation into the direct method for linear constraints by showing that its problem statement can be understood as a linear robust optimization problem. Approximations of chance constraints from the literature are transferred into the context of solution spaces. From this, we derive a theoretical value for the safety parameter \(\varOmega\). A further modification is presented for use cases, where some intervals are already predetermined. A problem from vehicle safety is used to compare the modified direct and indirect methods and discuss suitable choices of \(\varOmega\). We find that the modified direct method is able to identify solution spaces with similar flexibility, while maintaining its cost advantage.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号