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991.
密闭系统中微波辅助萃取机制探讨 总被引:9,自引:2,他引:9
通过与普通加热萃取虎杖中白藜芦醇的产率进行对比 ,对密闭系统中微波辅助萃取的机理进行了探讨。结果表明 ,微波辅助萃取与普通加热萃取二者的活化能相差不大 ,分别为30.06和30.32kJ·mol-1。但微波辅助萃取的表观速率常数约是普通加热萃取的20倍。并且还利用电子扫描显微镜对样品微结构进行了观察 ,研究表明 ,细胞内极性成分如水吸收了微波能后压力迅速增加导致细胞结构的破坏是MAE快速高效的关键 ,由于细胞的破坏 ,萃取剂和萃取目标化合物更容易通过细胞壁 ,加速了扩散速度 ,进而加速了萃取速度。 相似文献
992.
993.
994.
液相色谱紫外法测定鸡肉中三种硝基咪唑残留量 总被引:3,自引:0,他引:3
建立了测定鸡肉中二甲硝咪唑、罗硝唑、甲硝唑残留量的方法。以二氯甲烷提取,硅胶固相萃取净化,液相色谱紫外法检测。样品添加10μg/kg,50μg/kg,平均回收率为78%~91%,相对标准偏差为6.4%~10.1%。 相似文献
995.
The binding equilibrium between l? and human serum albumin (HSA) or bovine serum albumin (BSA) has been studied by means of the resonance Rayleigh scattering (RRS) and equilibrium dialysis. It has been found for the first time that RRS and multiple frequency scattering (MFS) are enhanced as the l? binding to the HSA and BSA, but fluorescence quenches. The equilibrium dialysis results suggest that the binding of l? to HSA and BSA fits a phase-distribution model other than Scatchard model, and that the order of magnitude of its phase-distribution constant was found to be 104. It is most probable that Cl? or other anion ions influence the binding of l? by changing the ionic strength in the solution. The dialysis at different pH indicates that the binding mechanism is due to the electrostatic forces between the l? and protonated basic amino-acid residues. 相似文献
996.
通过苯乙炔和羟基(+)-10-樟脑磺酰氧基碘苯在氯仿溶剂中反应, 合成出一个新的手性炔基芳基碘盐[苯基(苯乙炔基)(10)-樟脑磺酸碘盐]. 该手性碘盐与β-二羰基化合物的烯醇式负离子在温和条件下易于反应, 产物具有中等e.e.值, 为β-二羰基化合物在α位不对称引进苯乙炔基提供了一个简单方便的方法. 相似文献
997.
Can-hua Zhou Shi-bo Cheng Hong-ming Yin Guo-zhong He 《化学物理学报(中文版)》2009,22(6):681-685
Photodissociation of p-aminobenzoic acid at 266 nm was investigated by probing the nascent OH photoproduct employing the laser-induced fluorescence technique. It was found that the nascent OH radical was vibrationally cold and its rotational state distribution conformed to be a Boltzmann behavior, characterized by a rotational temperature of 1040±110 K. The rotational energy of OH was determined to be 8.78±0.84 kJ/mol. Between the two spinorbit states of OH, ^2Ⅱ3/2 and ^2Ⅱ1/2, the former was found to be preferentially populated. The distribution of the II(A') state for the A-doublet was dominant. Finally, a probable mechanism for the formation of OH produced from the photodissociation of p-aminobenzoic acid is discussed. 相似文献
998.
Ruoyu Du Rongxin Su Xuan Li Xiaowei Tantai Zhaohui Liu Jifeng Yang Wei Qi Zhimin He 《Cellulose (London, England)》2012,19(2):371-380
The effective recycling of cellulase requires an in-depth understanding of cellulase adsorption and desorption. In the present
study, we examined the adsorption behaviors and stabilities of cellulase at different pH values. Acidic pH (<4.8) was found
to favor adsorption, whereas neutral and alkaline pH (especially pH 7 and 10) favored desorption. The influence of pH on cellulase
activity was temperature dependent. Under mild conditions (e.g., pH 7 and 25 °C), the effect of pH on cellulase activity was
reversible, and the cellulase activity can return to almost 100% by adjusting the pH value to 4.8. However, under severe conditions
(e.g. pH 10 and 50 °C), irreversible inactivation may take place. We also explored the roles of pH and temperature in cellulase
adsorption kinetics and isotherms. At pH 4.8, temperature had no remarkable effect on the adsorption capacity of the cellulases
onto substrate. However, at pH 7 and 10, high temperatures lead to more cellulase desorption. Only at pH 4.8 does cellulase
adsorption well fit (R
2 > 0.96) the pseudo-first-order kinetic and Langmuir adsorption isotherm (R
2 > 0.99) models. 相似文献
999.
Dong LiuPeng Yuan Daoyong Tan Hongmei Liu Tong WangMingde Fan Jianxi ZhuHongping He 《Journal of colloid and interface science》2012,388(1):176-184
Hierarchically porous carbons were prepared using a facile preparation method in which diatomite was utilized as both template and catalyst. The porous structures of the carbon products and their formation mechanisms were investigated. The macroporosity and microporosity of the diatomite-templated carbons were derived from replication of diatom shell and structure-reconfiguration of the carbon film, respectively. The macroporosity of carbons was strongly dependent on the original morphology of the diatomite template. The macroporous structure composed of carbon plates connected by the pillar- and tube-like macropores resulted from the replication of the central and edge pores of the diatom shells with disk-shaped morphology, respectively. And another macroporous carbon tubes were also replicated from canoe-shaped diatom shells. The acidity of diatomite dramatically affected the porosity of the carbons, more acid sites of diatomite template resulted in higher surface area and pore volume of the carbon products. The diatomite-templated carbons exhibited higher adsorption capacity for methylene blue than the commercial activated carbon (CAC), although the specific surface area was much smaller than that of CAC, due to the hierarchical porosity of diatomite-templated carbons. And the carbons were readily reclaimed and regenerated. 相似文献
1000.
建立了在不同时间段内转换使用不同波长同时测定忍冬花和叶中7种化学成分(绿原酸、咖啡酸、芦丁、木犀草苷、异绿原酸A、异绿原酸B、异绿原酸C)的高效液相色谱分析方法,同时应用该方法分析了忍冬花、忍冬老叶和新叶中成分含量的差异。色谱柱为Agilent Eclipse Plus C18(250 mm×4.6 mm, 5 μm);流动相为0.3%甲酸水溶液(A)和乙腈(B),梯度洗脱,流速1 mL/min;采用VWD紫外检测器转换波长(330 nm、350 nm)检测。应用所建立的方法测定忍冬新叶中绿原酸、木犀草苷含量分别为2.572%、1.498‰,均比药典中规定的含量高,有必要进一步的研究和开发利用。该方法准确、简便、灵敏度高,适用于忍冬中7种化学成分含量的同时测定和忍冬的质量控制及综合评价。 相似文献