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101.
The aim of this work was to investigate, for the first time, the potential of the enzyme glutathione S-transferase I (isoenzyme GST-I) for uses in analytical chemistry. A novel fiber-optic biosensor for the detection and determination of the triazine herbicide atrazine was developed based on maize GST-I expressed in E. coli. The sensing bioactive material was a three-layer mini-sandwich. The enzyme was immobilized on the outer layer that consisted of a hydrophilic polyvinylidenefluoride membrane. This membrane was supported on an inner glass disk by means of an intermediate binder sol–gel layer that incorporated bromcresol green (BCG). The biosensor operated in a static mode at 25 °C and the rate of the enzymatic reaction, using atrazine as a substrate, served as an analytical signal. A calibration curve was obtained for atrazine, with analytically useful concentration range 2.52–125 μM. The sensor detection limit was 0.84 μM. The reproducibility of atrazine sensing was in the order of ±3–5%. The method was successfully applied to the determination of this herbicide in real water samples, without sample preparation steps. Atrazine recovery ranged between 85 and 110%. No interference from other pesticides, such as alachlor and carbaryl was observed in the absence of atrazine. The immobilized enzyme retained about 75% of its original activity after 1 month use. Simply unscrewing the terminal holding ring of the probe and placing a new bioactive sandwich could easily replace a deteriorated mini-sandwich.  相似文献   
102.
Quadrupolar-type substitution of pi-conjugated chromophores with donor and acceptor groups has been shown to increase their two-photon absorption (TPA) response by up to two orders of magnitude. Here, we apply highly correlated quantum-chemical calculations to evaluate the impact of the nature of conjugated bridge and the charge-transfer distance on that enhancement. We compare chromophores with phenylenevinylene-, thienylenevinylene-, polyene-, and indenofluorene-type backbones substituted by dimethylamino and cyano groups. In all compounds, we find a strongly TPA-active A(g) state (either 2A(g) or 3A(g)) in the low-energy region, as well as a higher lying TPA-active state (mA(g)) at close to twice the energy of the lowest lying one-photon allowed state; the smaller energy detuning in the mA(g) states results in very large TPA cross sections delta. We also investigate the influence of the degree of ground-state polarization on TPA. Independent of the nature of the backbone and the donor-acceptor separation, delta displays the same qualitative evolution with a maximum before the cyanine-like limit; the highest TPA cross sections are calculated for distirylbenzene- and polyene-based systems.  相似文献   
103.
The hydrothermal reaction of CuBr2 and CuBr with phen·H2O (phen= 1,10-phenanthroline) in a molar ratio of 1:1:1.5 gave birth to the first copper-halo cationic cluster [Cu2^Ⅱ Cu2^Br4 (phen)4 ] ^2+(1) with tetranuclear anionic cluster [Cu4Br6]^2-. Changing the precursors or their molar ratios, two mononuclear complexes [Cu(phen)2Br]Br·H2O (2) and [Ni(phen)3][CuCl2]2 (3) as well as two unusual copper-halo chains found in polymers [Cu2Br2(phen)]∞ (4) and [Cu^ⅡCu3^ⅠBr2Ⅰ3 (phen)2 ]∞ (5) were obtained. The (Cu2Br2)∞ chain of 4 looks like a linearar ray of hexagons based on fused Cu3Br3 units, and the linear (Cu3Ⅰ3Br^-)∞ chain of 5 is an alternate combination of the rhombic Cu2I2 cores and the Cu4I4Br2^2- units. In addition, the hydrothermal reaction of CuBr2 with NA(NA=nicotinic acid) or INA (INA =isonicotinic acid) resulted in the syntheses of two compounds [CuBr(NA)] (6) and [CuBr(INA)]∞(7) containing staircase chain. Among them the third-order non-linear optical properties of 2, 5, 6 and 7 were investigated and all exhibit the reverse saturable absorption (α2〉0) and self-defocusing performance (n2〈0).  相似文献   
104.
 4-Dimethylamino-3-cyanobiphenyl (4-DMA-3-CB) was characterized with respect to linear and nonlinear optical properties in a crystal as well as in solution. The crystal structure was studied dependent on the crystallization conditions. It is shown that the crystal structure exhibiting NLO-activity can completely be solved by a combination of electron diffraction and computer modeling. There are four molecules per unit cell in the space group Pna21 with dimensions a=10.28 Å, b=22.64 Å, c=5.27 Å. From this model structure the values and orientation of the dipole μ and static second order polarizability β can be calculated. Their relevance to the values obtained by a combination of polarization dependent measurements of Electric Field Induced Second Harmonic Generation (EFISH) and Hyper-Rayleigh-Scattering (HRS) in solution are discussed. The molecular second order polarizability tensor was found to be dominated by one single component. The orientations of the dipole and the vectorial parts of the second order polarizability delivered by the semiempirical calculations are in good agreement with the results of the EFISH and HRS-measurements and allow a deeper insight into the nonlinear optical properties of the crystal. Received: 15 April 1996 Accepted: 21 June 1996  相似文献   
105.
Protein crystals are usually grown in multi-component aqueous solutions containing salts, buffers and other additives. To measure the X-ray diffraction data of the crystal, crystals are rapidly lowered to cryogenic temperatures. On flash cooling, ice frequently forms affecting the integrity of the sample. In order to eliminate this effect, substances called cryoprotectants are added to produce a glassy (vitrified) state rather than ice. Heretofore, the quantity of cryoprotectant needed to vitrify the sample has largely been established by trial and error. In this study, differential scanning calorimetry (DSC) was used to measure the melting (Tm), devitrification (Td) and glass transition (Tg) temperatures of solutions with a range of compositions typical of those used for growing protein crystals, with the addition of glycerol as cryoprotectant. The addition of cryoprotectant raises the Tg and lowers the Tm of bulk solution thereby decreasing the cooling rates required for vitrification of protein crystals. The theoretical Tg value was calculated using the apparent volume fraction using the Miller/Fox equation extended for multi-component systems. The experimental values of Tg were within approximately ±4% of that predicted by the model. Thus, the use of the model holds the promise of a rational method for the theoretical determination of the composition of cryoprotectant requirement of protein crystallization solutions.  相似文献   
106.
Coherent anti-Stokes Raman scattering (CARS) microscopy is presented as a new nonlinear optical technique. The combination of vibrational spectroscopy and microscopy allows highly sensitive investigations of unlabelled samples. CARS is an ideal tool for studying a broad variety of samples. The main drawback of the technique is its non-zero-background nature, which implies that the signal has to be detected against a nonresonant background. The need to solve this problem is reflected in the rapid technological developments that have been observed during the last decade. Recent results show that CARS microscopy has the potential to become an important complementary technique that can be used with other well-established microscopic methods. Although it has some limitations, it offers unique access to many problems that cannot be tackled with conventional techniques. For this reason, it can be expected that the impressive growth of the field will continue.  相似文献   
107.
稀土掺杂的(K, Sr)Cl·SiO2复合凝胶的荧光性能   总被引:1,自引:0,他引:1  
采用sol gel法制备了单掺铕及共掺铕、铈的(K,Sr)Cl·SiO2复合凝胶,研究了复合凝胶的荧光性能。根据荧光测试结果,复合凝胶中,Eu3+在没有还原剂的作用下,可以与基质作用形成还原态的Eu2+,复合凝胶表现出相应的Eu2+荧光性能;研究认为,Ce3+,Eu3+共掺杂时,复合凝胶激发光谱与发射光谱峰位基本不变,但强度有所不同。330nm处的激发光谱明显增强,且发射光谱随Ce3+的掺杂量增加而增强。当Ce3+掺杂浓度为3.0%(原子分数)时,复合凝胶具有最大的荧光发射强度,表明Ce3+具有很好的敏化作用。在Ce3+,Eu3+共掺杂复合凝胶体系中,复合凝胶荧光强度增大的原因既可能是电子转移过程,也可能是Ce3+→Eu2+的能量传递过程所致。  相似文献   
108.
Many advances have been made in chemical structure research over the past three decades using synchrotron radiation. Synchrotron radiation has a number of unique properties. They include high brightness, high collimation, broad energy spectrum, variable polarization, coherent power, and subnanosecond pulse width. The third-generation storage rings with wiggler and undulator sources and lower electron beam dimensions are delivering over 1012 times higher brightness than laboratory-based sources. The future of synchrotron sources looks very promising with the development of energy recovery linac sources and free-electron laser sources. These will permit dynamic studies of chemical structure with subpicosecond time resolution. Commensurate with the development of X-ray sources, major progress has occurred in optical schemes to meet the challenging needs of chemical structure research. High-resolution monochromatization and submicron focusing of X rays present new avenues for the future.  相似文献   
109.
A series of polyesters with π‐conjugated donor–acceptor segments was synthesized by the condensation of azobenzene‐4,4′‐dicarbonylchloride with 1,4:3,6‐dianhydro‐D‐sorbitol ([α] = + 42.5°) and biphenolic chromophores, bis(4‐hydroxyphenylazo)‐2,2′‐dinitrodiphenylmethane and bis(4‐hydroxyphenylazo)‐2,2′‐dinitrodiphenylsulfone. The polymers were characterized by spectral methods (IR, ultraviolet–visible, and NMR), thermal methods (thermogravimetry and differential scanning calorimetry), wide‐angle X‐ray scattering, and polarimetry. The polymers containing isosorbide units were optically active and crystalline. They exhibited glass‐transition temperature values between 100 and 160 °C and were stable up to 400 °C. The second‐harmonic generation (SHG) efficiency of the polymers was experimentally verified by a powder‐reflection technique with 2‐methyl‐4‐nitroaniline as a reference. The SHG efficiencies of the polymers were compared to those of the chromophores and explained as a function of the percentage of chiral composition. The hyperpolarizability β values were also determined by a two‐level model solvatochromic method and computational methods. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2868–2877, 2002  相似文献   
110.
We discuss electron-transfer processes that govern the physics of several materials or systems of interest for advanced applications. The discussion touches upon several topics, ranging from solvatochromism to solvent-induced symmetry breaking, from excitonic to cooperative effects in molecular crystals, from phase transitions to vibrational contributions to the dielectric constant in organic materials, from spectroscopy to molecular transport. In all these diverse systems electron transfer (ET) plays a major role and is discussed with reference to simple models for delocalized charges.  相似文献   
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