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131.
DFT calculations have been carried out for 2-, 3- and 4-methoxybenzyl alcohol radical cations (1+, 3+ and 4+, respectively) and the α-methyl derivatives 2+ and 5+ using the UB3LYP/6-31G(d) method. The theoretical results have been compared with the experimental rate constants for deprotonation of 1+-5+ under acidic and basic conditions. In acidic solution, the decay of 1+-5+ proceeds by cleavage of the C-H bond, while in the presence of −OH all the radical cations undergo deprotonation from the α-OH group. This pH-dependent change in mechanism has been interpreted qualitatively in terms of simple frontier molecular orbital theory. The −OH induced α-O-H deprotonation is consistent with a charge controlled reaction, whereas the C-H deprotonation, observed when the base is H2O, appears to be affected by frontier orbital interactions. 相似文献
132.
Reed M. Izatt Gypzy C. Lindh Ronald L. Bruening Peter Huszthy John D. Lamb Jerald S. Bradshaw James J. Christensen 《Journal of inclusion phenomena and macrocyclic chemistry》1987,5(6):739-745
The macrocycle-mediated fluxes of several alkali metal cations have been determined in a H2O-CH2Cl2-H2O liquid membrane system. Water-insoluble proton-ionizable macrocycles of the pyridono type were used. The proton-ionizable feature allows the coupling of cation transport to reverse H+ transport. This feature offers promise for the effective separation and/or concentration of alkali metal ions with the metal transport being driven by a pH gradient. A counter anion in the source phase is not co-transported. The desired separation of a particular metal ion involves its selective complexation with the macrocycle, subsequent extraction from the aqueous phase to the organic phase, and exchange for H+ at the organic phase-receiving phase interface. Factors affecting transport which were studied include ring size, source phase pH, and receiving phase pH. Lithium was transported at a rate higher than that of the other alkali metals in both single and competitive systems using a 15-crown-5 pyridono carrier. 相似文献
133.
The reaction of gaseous H2S with aqueous ammonium heptamolybdate in the presence of triethylenetetramine (trien) gave a red complex. The complex was recrystallized in hot water and characterized by element analysis and UV, visible, IR, and 1H NMR spectroscopy. PMR has revealed accidental magnetic equivalence, resulting from the proximity of [MoS4]2- species in one complex molecule to the open triethylenetetramine ligand of another molecule. (TrienH2)[MoS4] crystallizes in the orthorhombic crystal system, space group Pca21, a=13.045(2), b=16.461(3), c=13.754(2) , =90, =90, =90°, V=2953.5(9) 3, Z=8, R1=0.0323, wR2=0.0730. The structure consists of the tetrahedral tetrathiomolybdate anions, forming an extended 3D framework in solids due to the interactions with triene cations via Mo-S...H-N hydrogen bonds. 相似文献
134.
钒(Ⅴ)—Ferron—NaBrO3体系极谱吸附催化波的研究 总被引:5,自引:0,他引:5
在pH5.8乙酸盐缓冲溶液中,V(Ⅴ)-7-碘-8-羟基喹啉-5-磺酸-NaBrO3体系产生一灵敏的吸附平行催化波,二次导数峰高与V(Ⅴ)浓度在2.9×10-9~4.7×10-7mol/L范围内呈线性关系,检出限为1×10-9mol/L.研究了电极反应机理,方法应用于水中钒的测定,结果满意. 相似文献
135.
136.
氯酸钾氧化酸性铬深蓝催化光度法测定痕量钒 总被引:6,自引:2,他引:6
基于硫酸介质中,酒石酸作活化剂,钒催化氯酸钾氧化酸性铬深蓝,建立了催化光度法测定痕量钒的新方法并讨论了其动力学条件。灵敏度1.47×10~(11)g/ml,测定范围0~9ng/ml。方法简便快速,用于水及食品中痕量钒的测定,结果满意。 相似文献
137.
阳离子交换柱分离-导数光度法测定原油中钒 总被引:1,自引:0,他引:1
以 5Br PADAP为显色剂 ,用阳离子交换柱分离干扰离子 ,在波长 6 30nm采用一阶导数光度法测定原油中钒 ,方法灵敏度高 ,摩尔吸光系数为 3.0× 10 5L·mol- 1·cm- 1,较其它光度法测定钒的摩尔吸光系数提高 1~ 2个数量级。对实际样品进行分析并做加标回收试验 ,钒的回收率在97.5 %~ 10 4 .0 %。与ICP AES方法进行对照试验 ,结果相吻合。 相似文献
138.
在制备高硬度、高热导、耐磨、耐腐蚀、耐高温的新兴陶瓷材料氧化硼、氮化硅的固相反应中,氮化镁是不可缺少的烧结助剂[‘,’j.同时,氮化镁还可用于制备发泡合金和回收核废料等领域.目前氮化镁的制备方法有:镁粉直接与氮气反应法[‘,‘1、镁在氮等离子流中与氮反应法*‘、在氮气气氛下镁线圈爆炸法‘’‘和低压化学气相沉积法[’j.在上述方法中,有些方法需要复杂和昂贵的设备.有些方法得到氮化镁的产率较低.镁粉直接与氮气反应是具有工业生产价值的方法一然而,这种方法需要SOO”C到gOO”C的高温.我们曾经报道过利用温和… 相似文献
139.
Micrometric BN powders used as catalyst support: influence of the precursor on the properties of the BN ceramic 总被引:1,自引:0,他引:1
Thin powders and foams of boron nitride have been prepared from molecular precursors for use as noble metal supports in the catalytic conversion of methane. Different precursors originating from borazines have been tested. The best results were obtained using a precursor derived from trichloroborazine (TCB) which, after reacting with ammonia at room temperature and then thermolyzing up to 1800°C, led to BN powders with a specific area of more than 300 m2 g−1 and a micrometric spherical texture. Comparable results were obtained using polyborazylene under similar conditions. Aminoborazine-derived precursors did not yield such high specific area ceramics but the BN microstructure resembled a foam with a crystallized skin and amorphous internal part. These differences were related to the chemical mechanism of the conversion of the precursor into BN. Polyhaloborazines and polyborazines yielded BN through gas-solid reactions whereas aminoborazine polymers could be kept waxy up to high temperatures, which favored the glassy foam. Catalysts composed of BN support and platinum have been prepared using two routes: from a mixture of precursor or by impregnation of a BN powder leading to very different catalysts. 相似文献
140.
高效阳离子交换法分离纯化蛋清中的溶菌酶 总被引:3,自引:0,他引:3
建立了用高效阳离子交换分离纯化蛋清中溶菌酶的新方法 ,讨论了纯化的工艺条件。蛋清样品匀浆后 ,用氯化钠初步纯化 ,然后用弱阳离子交换柱XIDACE WCX分离。结果表明 ,被纯化的溶菌酶和杂蛋白得到很好分离。经活性检测 ,溶菌酶过柱后的活性回收率为 10 7% ,蛋白的比活为 15 4 6 7U/mg ,纯化倍数提高了 5 6倍。用尺寸排阻 (SEC)鉴定 ,得到的溶菌酶呈均一性。该法较传统软基质低压离子交换分离速度快 ,纯化效率高。 相似文献