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   23143篇
  免费   3654篇
  国内免费   1930篇
化学   14385篇
晶体学   529篇
力学   914篇
综合类   188篇
数学   666篇
物理学   12045篇
  2024年   38篇
  2023年   141篇
  2022年   417篇
  2021年   436篇
  2020年   605篇
  2019年   595篇
  2018年   611篇
  2017年   780篇
  2016年   1007篇
  2015年   936篇
  2014年   1075篇
  2013年   2349篇
  2012年   1368篇
  2011年   1434篇
  2010年   1163篇
  2009年   1251篇
  2008年   1368篇
  2007年   1380篇
  2006年   1301篇
  2005年   1150篇
  2004年   1165篇
  2003年   1018篇
  2002年   1116篇
  2001年   771篇
  2000年   782篇
  1999年   645篇
  1998年   559篇
  1997年   432篇
  1996年   402篇
  1995年   400篇
  1994年   311篇
  1993年   266篇
  1992年   248篇
  1991年   185篇
  1990年   165篇
  1989年   113篇
  1988年   128篇
  1987年   109篇
  1986年   98篇
  1985年   80篇
  1984年   79篇
  1983年   36篇
  1982年   54篇
  1981年   29篇
  1980年   32篇
  1979年   38篇
  1978年   12篇
  1977年   7篇
  1976年   7篇
  1973年   16篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
102.
Aspects of the mechanism of the overall reaction between CaCO3/CaO and SO2/SO3 under oxidizing conditions are discussed. The limestone and lime sulphation processes were carried out in a thermobalance under conditions relevant to atmospheric fluidized bed combustion. Sulphated samples, prepared in the form of cross-section particles, were examined in a scanning electron microscope by energy-dispersive X-ray and back-scattered electron imaging. Photomicrographs are presented. The reaction proceeded from the outer surface of the particles and along the pores. Surface textural changes during the reaction were considered. The layer of products was identified as controlling both the rate and extent of limestone/lime sulphation. In the products, two sulphur-bearing solids (CaSO4 and CaS) were identified. The presence of CaS, which may cause difficulties in practice, is attributed to CaSO3 disproportionation. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   
103.
Nanocrystalline ZnFe2O4 spinel powders are synthesized by high-energy ball milling, starting from a powder mixture of hematite (α-Fe2O3) and zincite (ZnO). The millings are performed under air using hardened steel vials and balls. X-ray diffraction and Mössbauer spectrometry are used to characterize the powders. A spinel phase begins to appear after 3 h of milling and the synthesis is achieved after 9 h. Phase transformation is accompanied by a contamination due to iron coming from the milling tools. A redox reaction is also observed between Fe(III) and metallic iron during milling, leading to a spinel phase containing some Fe(II). The mechanism for the appearance of this phase is studied: ZnO seems to have a non-negligeable influence on the synthesis, by creating an intermediate wüstite-type phase solid solution with FeO.  相似文献   
104.
Crystallization of poly(ethylene terephthalate) from the amorphous state has been studied in the temperature range 90°–120°C to characterize the amorphous phase when crystalline microstructure is developing. Small-angle x-ray scattering, scanning electron microscopy, and density measurements were used to investigate the morphology of semi-crystalline materials. Differential scanning calorimetry and dynamical mechanical spectroscopy experiments were carried out on amorphous, partially crystallized and crystallized specimens and, when structural relaxation is allowed (thermal treatments close to but below glass transition temperature), strong evidence is obtained for the existence of two different amorphous phases with different mobilities.  相似文献   
105.
The crystalline structure of a new compound Rh(III) of (NH4)2[Rh(NO2)3(NH3)(μ-OH)]2 composition has been determined. The crystallographic characteristics are H16N10O14Rh2: a = 6.3963(2) Å, b = 9.3701(4) Å, c = 13.6646(5) Å, β = 102.266(1)°, V = 800.28(5) Å3, Z = 2, d calc = 2.432 g/cm3. The distance Rh...Rh in the dimer is 3.200 Å. Original Russian Text Copyright ? 2006 by S. P. Khranenko, I. A. Baidina, and S. A. Gromilov __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 47, No. 2, pp. 380–384, March–April, 2006.  相似文献   
106.
Coexistence Relations, Preparation and Properties of Ternary Compounds in the System Cu/Mo/O The phase diagram of the ternary system Cu/Mo/O is presented at 773 K. The compounds CuMoO4, Cu3Mo2O9, Cu4Mo5O17, Cu6Mo5O18, Cu4–xMo3O12, and CuxMoO3 are found to be thermodynamical stable. The homogeneity range of Cu4–xMo3O12 runs to x = 0.1–0.2. Single crystals of CuMoO4 and Cu3Mo2O9 were grown by chemical transport reactions with TeCl4, Cl2, HCl, and Br2 as transport agent. The results were compared with thermochemical calculations. The decomposition of CuMoO4 and Cu3Mo2O9 was investigated with thermal analysis and decompositon pressure measurements.  相似文献   
107.
《Electroanalysis》2004,16(16):1305-1310
A novel amperometric biosensor was constructed for the determination of phenols in pure organic phase. This biosensor was fabricated by immobilizing tyrosinase in a titania sol‐gel membrane which was obtained with a vapor deposition method. This method was facile and avoided the calcination step needed in conventional titania sol‐gel process. The titania sol‐gel membrane could effectively retain the essential water layer around the enzyme molecule needed for maintaining its activity in organic phase. The experimental parameters such as solvent and operating potential were optimized. At ?100 mV this biosensor showed a good amperometric response to phenols in pure chloroform without any mediator and rehydration of the enzyme. For catechol determination the sensor exhibited a fast response of less than 5 seconds. The sensitivity of different phenols was as follows: catechol > phenol > p‐cresol. Additionally, the apparent Michaelis‐Menten constants of the encapsulated tyrosinase to catechol, phenol and p‐cresol were found to be 0.15±0.003, 0.17±0.008 and 0.21±0.004 mM, respectively. The biosensor had also good reproducibility and stability. This work provided a promising platform for the construction of pure organic phase biosensors and the determination of substrates with poor water solubility.  相似文献   
108.
The spreading of a globally distributed damage, created in the stationary regime, is studied in a single-component irreversible reaction process, i.e., the BK model [Browne and Kleban,Phys. Rev. A 40, 1615 (1989)]. The BK model describes one variant of the A+AA2 reaction process on a lattice in contact with a reservoir of A species. The BK model has a single parameter, namely the rate of arrival of A species to the lattice (Y). The model, exhibits an irreversible phase transition between a stationary reactive state with production of A2 species and a poisoned state with the lattice fully covered by A species. The transition takes place at critical points (Y C ) which solely depend on the Euclidean dimensiond. It is found that the system is immune ford=1 andd=2, in the sense that even 100% of initial damage is healed within a finite healing period (T H ). Within the reactive regime,T H diverges when approachingY C according toT H (Y C Y), with 1.62 and 1.08 ford=1 andd=2, respectively. Ford=3 a frozen-chaotic transition is found close toY s 0.4125, i.e., well inside the reactive regime 0YY C 0.4985. Just atY S the damageD(t) heals according toD(t) t , with 0.71. For the frozen-chaotic transition atd=3 the order parameter critical exponent 0.997 is determined.  相似文献   
109.
Recent experimental investigations of criticality and phase separation in ionic fluids have revealed behavior of great theoretical interest. In seeking to understand the experiments, some of which appear to exhibit argonlike criticality and some of which exhibit classical (mean-field) criticality, a convenient starting point is the restricted primitive model (RPM) of symmetrically charged hard spheres, all of equal diameter , each sphere bearing a positive or negative charge of magnitudeq. There is overall charge neutrality, so that the expected number densities of the anions and cations are equal, += -. Studies of RPM charge-charge and density-density correlation functions indicate that the fluctuation-suppressing mechanism that yields mean-field critical behavior in nonionic systems with long-range interparticle potentials is not operative in the RPM. On the basis of plausible assumptions, Ising-like behavior is instead expected. The above work is summarized. New work of Zhang and the author is outlined, showing that when one loses the RPM symmetry (through, e.g., different valence, diameter, or dipole moment of anions and cations) a strong coupling between charge-charge and density-density correlation ensues. The way in which this can be expected to give rise to mean-field or mean-field-like behavior is noted. Other new observations concern the mean-field analogy found by Høye and the author between the parameter 2/(d–2) (d is the dimensionality) in that model and the monomer number in high polymers, with respect to the coexistence-curve shape dependence on those parameters.  相似文献   
110.
A particular case of a cellular automata-based model of two-state opinion formation in social groups with a strong leader is studied. We consider a 2D Euclidian geometry of social space and mutual interactions 1/r n . The model shows an interesting dynamics which can be analytically calculated. There are two stable states of the system: a cluster around the leader and unification. Unstable clusters may also appear. A variation in parameters such as the leader's strength or the social temperature can change the size of a cluster or, when they reach some critical values, make the system jump into another state. For a certain range of parameters the system exhibits bistability and hysteresis phenomena. We obtained explicit formulas for the cluster size, critical leader's strength, and critical social temperature. These analytical results are verified by computer simulations.  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