全文获取类型
收费全文 | 11020篇 |
免费 | 714篇 |
国内免费 | 1417篇 |
专业分类
化学 | 6776篇 |
晶体学 | 171篇 |
力学 | 660篇 |
综合类 | 70篇 |
数学 | 955篇 |
物理学 | 4519篇 |
出版年
2024年 | 13篇 |
2023年 | 160篇 |
2022年 | 167篇 |
2021年 | 199篇 |
2020年 | 222篇 |
2019年 | 252篇 |
2018年 | 211篇 |
2017年 | 305篇 |
2016年 | 328篇 |
2015年 | 276篇 |
2014年 | 479篇 |
2013年 | 677篇 |
2012年 | 786篇 |
2011年 | 816篇 |
2010年 | 619篇 |
2009年 | 820篇 |
2008年 | 821篇 |
2007年 | 840篇 |
2006年 | 724篇 |
2005年 | 641篇 |
2004年 | 556篇 |
2003年 | 402篇 |
2002年 | 372篇 |
2001年 | 276篇 |
2000年 | 259篇 |
1999年 | 275篇 |
1998年 | 227篇 |
1997年 | 248篇 |
1996年 | 148篇 |
1995年 | 145篇 |
1994年 | 136篇 |
1993年 | 140篇 |
1992年 | 134篇 |
1991年 | 84篇 |
1990年 | 62篇 |
1989年 | 54篇 |
1988年 | 45篇 |
1987年 | 46篇 |
1986年 | 37篇 |
1985年 | 13篇 |
1984年 | 19篇 |
1983年 | 9篇 |
1982年 | 20篇 |
1981年 | 19篇 |
1980年 | 9篇 |
1979年 | 21篇 |
1978年 | 13篇 |
1977年 | 7篇 |
1976年 | 8篇 |
1973年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 453 毫秒
91.
本文采用氢化物-非色散原子荧光光谱法研究了十几种饲料矿物添加剂中金属离子对砷测定的干扰,采用加入硫脲-抗坏血酸混合溶液、碘化钾分离、加热蒸干等方法消除干扰。同时本文还对测定砷的酸度、硼氢化钾浓度和仪器工作参数进行了研究和优化。方法相对标准偏差(RSD)为0.54%,检出限(D.L)为54.5ng/L,样品国.加标回收率为102.9%。实际样品测定结果与胂斑法相比具有很好的一致性。 相似文献
92.
The constants of binding dye molecules with the micelles of sodium dodecyl sulfate are determined using quenching of delayed fluorescence of acridine dyes by sodium iodide in aqueous–micellar solutions. Kinetic equations have been composed that describe the processes of deactivation of the excited states of dyes. By solving these equations at the concentration of the quencher sodium iodide corresponding to the minimum lifetime of triplet states and at the concentration of micelles corresponding to the least value of the delayed fluorescence quenching rate constants, we obtained the constants of binding dyes with micelles equal to 1.3·107, 2.9·107, and 3.1·107 M–1 for trypaflavine, acridine orange, and acridine yellow, respectively. We calculated the rate constants of quenching of the triplet states of the molecules of dyes by iodide ions (I
–) that decreased in transition from trypaflavine to acridine orange and acridine yellow. 相似文献
93.
We present a new linearized model for the zero-one quadratic programming problem, whose size is linear in terms of the number of variables in the original nonlinear problem. Our derivation yields three alternative reformulations, each varying in model size and tightness. We show that our models are at least as tight as the one recently proposed in [7], and examine the theoretical relationship of our models to a standard linearization of the zero-one quadratic programming problem. Finally, we demonstrate the efficacy of solving each of these models on a set of randomly generated test instances. 相似文献
94.
In this work we display a numerical comparison, under statistical and computational point of view, between semi-analytical Eulerian and Lagrangian dispersion models to simulate the ground-level concentration values of a passive pollutant released from a low height source. The Eulerian approach is based on the solution of the advection–diffusion equation by the Laplace transform technique. The Lagrangian approach is based on solution of the Langevin equation through the Picard’s Iterative Method. Turbulence inputs are calculated according to a parameterization capable of generating continuous values in all stability conditions and in all heights of the Planetary Boundary Layer (PBL). Numerical simulations and comparisons show a good agreement between predicted and observed concentrations values. The comparison reveals the main advantages and disadvantages between the models. 相似文献
95.
96.
毛细管电色谱研究进展 总被引:7,自引:2,他引:7
毛细管电色谱是一种新兴的具有高效,高选择性的微分离技术。本文评述了毛细管电色说的发展状况和相关的技术,并对其发展前景进行了展望,引用文献24篇 。 相似文献
97.
本文拟定的纸色谱法是以苯-乙酸乙酯-甲醇-乙酸(9:2:1:1)作展开剂,将血卟啉衍生物(HPD)分离为五部份,分别测定各部份浸取液的荧光发射光谱,作为一种对血卟啉衍生物组份作对比鉴定的参考方法。采用Ward的高效液相色谱程序对比研究结果表明,国产与美国产HPD的组份近似,均以血卟啉为主要组份,而前者血卟啉的含量较高;二者还均含有羟乙基乙烯基衍生物和羟基乙酸酯,初步研究了血卟啉衍生物在甲醇-水溶剂系统中的高效液相色谱行为,进一步将血卟啉衍生物分离为九部份,有利于单一组份研究。 相似文献
98.
99.
Sonochemistry and its dosimetry 总被引:3,自引:0,他引:3
The effects of ultrasound originate primarily in acoustic cavitation. The cavitation bubbles collapse violently enough to lead to interesting chemical effects, known as sonochemistry. There is a great need to relate the efficiency of sonochemical reaction to the energy of ultrasonic irradiation used to produce them. In this paper, three OH radical dosimeters, Fricke dosimeter, terephthalate dosimeter, and iodide dosimeter, are compared from the analytical point of view. The dosimeters based on photometry, i.e., Fricke and iodide, produced reliable and reproducible results, but the sensitivity is not enough for special applications, such as chemical monitoring of single bubble cavitation. The dosimeter based on fluorometry, terephthalate dosimeter, offered high sensitivity, 1.2×1011 molecules ml−1. The effects of some experimental parameters in sonochemistry, i.e., solution temperature and the dissolved gas species, were evaluated with the dosimeters. 相似文献
100.
The solid diffusion coefficient of lithium-ion in LiCoO2 cathode material has been investigated by the capacity intermittent titration technique (CITT) at different voltages and at different charge/discharge cycles. By SEM, XRD and FTIR techniques, the structure of LiCoO2 was studied before and after charge-discharge cycles, and the relationship between solid diffusion coefficient and crystal structure was further discussed. CITT results show that the value of Li+ solid diffusion coefficient of LiCoO2 is about 10-12 cm2·s-1. During the whole charge-discharge cycles, the Li+ solid diffusion coefficient decreased within the voltage of 4.0~4.3 V, which is attributed to the change of the structure of LiCoO2. 相似文献