全文获取类型
收费全文 | 13969篇 |
免费 | 2244篇 |
国内免费 | 1848篇 |
专业分类
化学 | 8824篇 |
晶体学 | 232篇 |
力学 | 592篇 |
综合类 | 96篇 |
数学 | 517篇 |
物理学 | 6223篇 |
无线电 | 1577篇 |
出版年
2024年 | 39篇 |
2023年 | 164篇 |
2022年 | 321篇 |
2021年 | 468篇 |
2020年 | 522篇 |
2019年 | 509篇 |
2018年 | 465篇 |
2017年 | 513篇 |
2016年 | 608篇 |
2015年 | 565篇 |
2014年 | 642篇 |
2013年 | 1486篇 |
2012年 | 775篇 |
2011年 | 895篇 |
2010年 | 736篇 |
2009年 | 870篇 |
2008年 | 852篇 |
2007年 | 819篇 |
2006年 | 839篇 |
2005年 | 739篇 |
2004年 | 669篇 |
2003年 | 629篇 |
2002年 | 511篇 |
2001年 | 398篇 |
2000年 | 482篇 |
1999年 | 354篇 |
1998年 | 262篇 |
1997年 | 268篇 |
1996年 | 256篇 |
1995年 | 171篇 |
1994年 | 199篇 |
1993年 | 167篇 |
1992年 | 150篇 |
1991年 | 124篇 |
1990年 | 91篇 |
1989年 | 77篇 |
1988年 | 73篇 |
1987年 | 39篇 |
1986年 | 51篇 |
1985年 | 47篇 |
1984年 | 47篇 |
1983年 | 13篇 |
1982年 | 27篇 |
1981年 | 22篇 |
1980年 | 14篇 |
1979年 | 16篇 |
1978年 | 10篇 |
1977年 | 10篇 |
1976年 | 7篇 |
1973年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
191.
192.
Vinyl siding is typically
produced by co-extruding a capstock (surface layer) over a PVC substrate formulation.
The capstock is often non-PVC, these systems can result in warpage during
or after production. In our study we will show that this warpage can result
from an interfacial induced stress related to the mismatch between the glass
transition of the substrate and the capstock. Additionally, both TMA and TMDSC
were used to probe the stress release. Capstock formulations which better
match the glass transition of the PVC substrate result in superior performance. 相似文献
193.
J. Hatta M. Okada S. Matuoka H. Yao 《Journal of Thermal Analysis and Calorimetry》1992,38(8):1775-1783
Using an ac calorimetric method, detailed behaviour of the heat capacity in dipalmitoyl-phosphatidylcholine-cholesterol system was studied in the cholesterol concentration less than 5 mol%. It was revealed that the heat capacity near the main transition was composed of at least four anomalies, i.e., multipeak took place in the heat capacity. This fact indicates that a simple theory explaining coexistence of two phases in two component systems does not work in the multipeak region. Then, relation between the multipeak heat capacity and the change of the ripple structure with the cholesterol concentration should be taken into account, when we consider thermodynamical behaviour of the systems.
Zusammenfassung Mittels AC-Kalorimetrie wurde bei Cholesterol-Konzentrationen von weniger als 5 mol% das Verhalten der Wärmekapazität im System Dipalmitoylphosphatidylcholin-Cholesterol untersucht. Es wurde gezeigt, daß sich die Wärmekapazität in der Nähe der Hauptumwandlung aus mindestens vier Anomalien zusammensetzt, d.h. bei der Wärmekapazität kann ein Multipeak beobachtet werden. Diese Tatsache zeigt, daß eine einfache Theorie, welche die Koexistenz zweier Phasen in einem Zweikomponenten-System erklärt, für die Multipeakregion nicht geeignet ist. Weiterhin sollte bei Überlegungen zum thermodynamischen Verhalten von Systemen eine Beziehung zwischen der Multipeak-Wärmekapazität bzw. der Welligkeitsstruktur und der Cholesterol-Konzentration berücksichtigt werden.相似文献
194.
195.
In this paper, the spectral behavior of protein and Poniacyl Carmine 2B (PC 2B) has been studied by spectrophotometric method. The conditional constants, apparent combination constant K and maximum binding number n, were used to express the combination ability of the reactions between PC 2B and protein under a set of given conditions. The Sandell index s was used to express the sensitivity of the determination of protein. The factors, acidity, PC 2B concentration and the ionic strength, were discussed by the change of apparent combination constant and maximum binding number. It was found that acidity of the solution, PC 2B concentration and ionic strength had a significant effect on the sensitivity of the assay of protein. Under the optimal conditions, the apparent combination constant K and the maximum binding number n were 2.36 × 106 L mol?1 and 95, respectively. With further investigation, it was found that the Scatchard model was suitable in treating the data obtained in the experiments. In the buffer medium of HCl‐KCl at 1.87, the addition of protein made the maximum absorption of the system move from 527 nm to 513 nm. Its apparent molar absorptivity is 4.46 × 105 Lmol?1 cm?1 at 513 nm. Beer's law is obeyed in the range of 0 ? 55 μg mL?1. The system developed in this paper has been used for the determination of protein in milk powder successfully. 相似文献
196.
ADSORPTION OF 2,4-DICHLOROBENZOXYACETIC ACID ONTO HYPERCROSSLINKED RESIN MODIFIED BY PHENOLIC HYDROXYL GROUP (AM-1) 总被引:2,自引:0,他引:2
INTRODUCTIONAdsorption has been considered to be the best available technology for removing organics from water in the USSafe Drinking Water Act[1]. Due to many drawbacks of activated carbon[2-7], the most widely used adsorbent,hypercrosslinked polymeric adsorbents developed by Tsyurupa and Davankov[8] have been increasingly viewedas an alternative to activated carbon for selective removal of specific organic substances from contaminatedwater[9-12], and series of researches have been do… 相似文献
197.
Prochiral alkenes, aldehydes, and ketones constitute the most frequently used starting materials for enantioselective organic syntheses. Protocols often involve chiral binding agents or Lewis acids that can give two diastereomeric adducts, the ratios of which are measures of chiral recognition. With π adducts, the diastereomers differ in the enantioface of the C?C or O?C group bound to the Lewis acid. This review provides the first comprehensive analysis of such equilibria and related binding phenomena with chiral transition metal Lewis acids. An extensive body of data from the authors' laboratory for complexes of the pyramidal rhenium fragment [(η5?C5H5)Re(No)(PPh3)]+ ( I ) affords particular insight. Literature data for other complexes are also summarized. A general model for chiral recognition based upon the relative steric properties of four quadrants is presented. This enables binding selectivities to be individually and rationally optimized for different classes of ligands. Electronic effects are also identified and correlated with specific structural properties. Relationships between binding equilibria, reactivity, and product configurations are discussed. 相似文献
198.
The density of neutral oxygen atoms in the MESOX set-up, one device of the PROMES-CNRS solar facilities, was determined by a fiber-optics catalytic probe (FOCP). Plasma was created in a flowing air within a quartz tube with the outer diameter of 5 cm by a 2.45 GHz microwave generator with the output power up to 1000 W. The flow of air was varied between 4 and 20 l/h. The O-atom density was found to increase monotonously with the increasing discharge power, and it decreased with the increasing flow rate. The degree of dissociation of oxygen molecules in the plasma column depended largely on the flow rate. At the air flow of 4 l/h it was about 80% but it decreased to about 20% at the flow of 20 l/h. 相似文献
199.
Interatomic distances in the transition state were estimated for the reactions of radical abstraction: H· + H2, H· + HCl, H· + CH4, N·H2 + NH3, HO· + H2O, HO2
· + HOOH, and C·H3 + SiH4. The calculation was performed by the quantum-chemical density functional method or coupled clusters method (QCH), as well as by the methods of intersecting parabolas (IPM) and Morse curves (IMM), using experimental data (activation energies and reaction enthalpies). The results of the latter two methods are close to the quantum-chemical calculation and differ only by the increment a: r(IPM or IMM) = a + r(QCH), where a = –4.5·10–12 m for IPM and a = +1.9·10–12 m for IMM. 相似文献
200.