全文获取类型
收费全文 | 8009篇 |
免费 | 733篇 |
国内免费 | 966篇 |
专业分类
化学 | 7408篇 |
晶体学 | 70篇 |
力学 | 558篇 |
综合类 | 103篇 |
数学 | 553篇 |
物理学 | 1016篇 |
出版年
2024年 | 14篇 |
2023年 | 105篇 |
2022年 | 253篇 |
2021年 | 239篇 |
2020年 | 329篇 |
2019年 | 306篇 |
2018年 | 306篇 |
2017年 | 482篇 |
2016年 | 519篇 |
2015年 | 435篇 |
2014年 | 463篇 |
2013年 | 519篇 |
2012年 | 575篇 |
2011年 | 547篇 |
2010年 | 480篇 |
2009年 | 454篇 |
2008年 | 369篇 |
2007年 | 454篇 |
2006年 | 401篇 |
2005年 | 334篇 |
2004年 | 298篇 |
2003年 | 239篇 |
2002年 | 237篇 |
2001年 | 182篇 |
2000年 | 187篇 |
1999年 | 155篇 |
1998年 | 134篇 |
1997年 | 136篇 |
1996年 | 134篇 |
1995年 | 104篇 |
1994年 | 87篇 |
1993年 | 31篇 |
1992年 | 22篇 |
1991年 | 22篇 |
1990年 | 31篇 |
1989年 | 17篇 |
1988年 | 17篇 |
1987年 | 10篇 |
1986年 | 9篇 |
1985年 | 12篇 |
1984年 | 11篇 |
1983年 | 8篇 |
1982年 | 11篇 |
1981年 | 8篇 |
1980年 | 5篇 |
1979年 | 6篇 |
1976年 | 3篇 |
1971年 | 1篇 |
1959年 | 4篇 |
1957年 | 1篇 |
排序方式: 共有9708条查询结果,搜索用时 500 毫秒
951.
H.-J. Dietze 《Isotopes in environmental and health studies》2013,49(2-3):46-51
Es wird ein Verfahren zur Isotopenverdünnungsanalyse mit stabilen Isotopen unter Verwendung einer Funkenionenquelle und einem doppelfokussierenden Massenspektrographen beschrieben, welches die gleichzeitige Analyse mehrerer Elemente in pulverförmigen Feststoffen erlaubt. Die Leistungsfähigkeit des Analysenverfahrens wild am Beispiel der Spurenanalyse geologischer Standardproben demonstriert. Das Analysenverfahren erlaubt die Bestimmung von Spurenkonzentrationen bis in den ppb-Bereich mit Standardabweichungen zwischen 2 und 10%. 相似文献
952.
对太阳实际光谱与连续氙灯的光谱进行了测试,结果显示氙灯发光光谱的红外部分占全部光谱的55.6%,与实际太阳光谱的28.4%有较大差别。依据这种差别进行光谱曲线拟合,得到925 nm最低点的透过率曲线。采用滤光片对氙灯发光光谱的红外部分光强进行适当过滤,测得过滤后的光谱达到标准匹配度。通过测试滤光后6个不同位置点的光谱发现,光谱最大偏差仅为12.5%,表明过滤后的氙灯光谱均匀性较好。利用电致发光检测有缺陷的硅电池进行电池的电性能测试,发现经过采用滤光片和未采用滤光片的连续氙灯光照测试的Ⅰ-Ⅴ电性能值不同,功率相差0.22 W,表明氙灯光谱匹配度直接影响电池电性能测试的准确度。 相似文献
953.
954.
955.
为了利用吸附等温线理论模型模拟高真空多层绝热LNG槽车内吸气剂的吸附过程,对在真空技术中常用的等温式进行了分析研究。通过实验获得吸气剂在室温下的吸氢等温线,同时利用实验数据得到考虑分子间作用力的BET模型中的参数值。将模型结果与实验数据进行对比分析,结果表明:考虑分子间作用力的BET模型不能用作高真空多层绝热LNG槽车真空夹层内吸气剂吸附量的计算。利用Temkin和Freundlich等温式分段对实验数据进行拟合,对于1#吸气剂,拟合方程式计算得出的吸附量与实验数据的相对误差仅为2.6%,表明拟合方程能够对吸气剂在室温下的吸氢量进行准确预测。 相似文献
956.
V. L. Cherginets T. P. Rebrova Yu. N. Datsko T. V. Ponomarenko R. P. Yavetsky V. Yu. Pedash 《Crystal Research and Technology》2013,48(1):16-21
CsI single crystals were grown from the melt scavenged by Y3+ (YCl3) addition in 6.7·10−4–6.7·10−3 mol·kg−1 range. The addition of the scavenger amounts comparable with the total concentration of the oxygen‐containing admixtures in molten CsI results in complete destruction of the latter. Because of this, the intensity of the band with a maximum at 2.8 eV in radioluminescence spectra caused by the oxygen‐containing admixtures (anion vacancies) considerably decreases, and the fraction of the slow 2μs‐component corresponding to these admixtures becomes lower than 0.01 (0.007). The addition of larger quantities of YCl3 leads to the appearance of a wide band with a maximum at 2.8 eV caused by cation vacancies, and the intensity of the slow 2μs‐component increases to 0.02. The maximum ratio of two faster components with the decay constants equal to 7 and 30 ns reaches 0.65:0.33 at Y3+ concentration in CsI melt equal to 6.7·10‐3 mol·kg‐1, the effective luminescence time of fastest components is ca 14 ns. The dependence of the ‘Fast/Total ratio’ on Y3+ concentration passes through its maximum (0.81) corresponding to the equivalence of Y3+ and O2− concentrations in the growth CsI melt. 相似文献
957.
Arnaud METSUE Taku TSUCHIYA 《Proceedings of the Japan Academy. Series B, Physical and biological sciences》2013,89(1):51-58
We investigate the shear response of possible slip systems activated in pure and Fe-bearing MgSiO3 post-perovskite (PPv) through ab initio generalized stacking fault (GSF) energy calculations. Here we show that the [100](001) slip system has the easiest response to plastic shear among ten possible slip systems investigated. Incorporation of Fe2+ decreases the strength of all slip systems but does not change the plastic anisotropy style. Therefore, pure and Fe-bearing MgSiO3 PPv should demonstrate similar LPO patterns with a strong signature of the [100](001) slip system. An aggregate with this deformation texture is expected to produce a VSH > VSV type polarization anisotropy, being consistent with seismological observations. 相似文献
958.
《应用光谱学评论》2013,48(1):71-99
Abstract High performance liquid chromatography (HPLC) has often been employed in the separation and speciation of metal containing compounds. One of the most sensitive devices used for detecting those compounds after the separation is the inductively coupled plasma (ICP). The similar flow rates for these two techniques render the coupling of the devices trivial, usually involving only a short length of capillary tubing. Upon entering the plasma, species are typically determined either via atomic emission spectrometry or mass spectrometry. HPLC-ICP devices have been employed less frequently for the determination of non-metals. This review will describe the applications of HPLC-ICP techniques to the determination of compounds containing carbon, sulfur, phosphorus, and the halogens. The instrumentation used for each application will be described, and the performance of the systems will be summarized. 相似文献
959.
A. G. Agwu Nnanna 《实验传热》2013,26(2):157-173
This article presents an experimental study of thermo-hydrodynamic phenomena in a microchannel heat exchanger system. The aim of this investigation is to develop correlations between flow/thermal characteristics in the manifolds and the heat transfer performance of the microchannel. A rectangular microchannel fabricated by a laser-machining technique with channel width and hydraulic diameter of 87 μm and 0.17 mm, respectively, and a trapezoidal-shaped manifold are used in this study. The heat sink is subjected to iso-flux heating condition with liquid convective cooling through the channels. The temporal and spatial evolutions of temperature as well as total pressure drop across the system are monitored using appropriate sensors. Data obtained from this study were used to establish relationships between parameters such as longitudinal wall conduction factor, residence and switching time, and thermal spreading resistance with Reynolds number. Result shows that there exist an optimum Reynolds number and conditions for the microchannel heat exchanger system to result in maximum heat transfer performance. The condition in which the inlet manifold temperature surpasses the exit fluid temperature results in lower junction temperature. It further shows that for a high Reynolds number, the longitudinal wall conduction parameter is greater than unity and that the fluid has sufficient dwelling time to absorb heat from the wall of the manifold, leading to high thermal performance. 相似文献
960.
ABSTRACTPresent study investigates the heat transfer and friction characteristics of heat exchanger tube fitted with perforated twisted tape (PTT) insert having V cuts. A copper tube of 1 m length and 0.032 m inner diameter is used as test section to collect the experimental data by varying the twist ratio of PTT from 2 to 6 for the Reynolds number range of 2,700–23,400. V cuts are introduced in the PTT and the V-cut relative pitch ratio is varied from 1 to 2. The maximum thermo-hydraulic performance parameter is found to be 1.58. 相似文献