全文获取类型
收费全文 | 588496篇 |
免费 | 8021篇 |
国内免费 | 1691篇 |
专业分类
化学 | 315288篇 |
晶体学 | 8709篇 |
力学 | 24899篇 |
综合类 | 17篇 |
数学 | 74099篇 |
物理学 | 175196篇 |
出版年
2021年 | 4943篇 |
2020年 | 5691篇 |
2019年 | 6075篇 |
2018年 | 7899篇 |
2017年 | 7784篇 |
2016年 | 12249篇 |
2015年 | 7983篇 |
2014年 | 11665篇 |
2013年 | 27907篇 |
2012年 | 21670篇 |
2011年 | 25938篇 |
2010年 | 18341篇 |
2009年 | 17918篇 |
2008年 | 23779篇 |
2007年 | 23416篇 |
2006年 | 21812篇 |
2005年 | 19710篇 |
2004年 | 18094篇 |
2003年 | 15970篇 |
2002年 | 15527篇 |
2001年 | 17218篇 |
2000年 | 13175篇 |
1999年 | 10286篇 |
1998年 | 8573篇 |
1997年 | 8271篇 |
1996年 | 8108篇 |
1995年 | 7254篇 |
1994年 | 7244篇 |
1993年 | 6935篇 |
1992年 | 7792篇 |
1991年 | 7681篇 |
1990年 | 7474篇 |
1989年 | 7203篇 |
1988年 | 7179篇 |
1987年 | 7063篇 |
1986年 | 6650篇 |
1985年 | 8727篇 |
1984年 | 8873篇 |
1983年 | 7329篇 |
1982年 | 7441篇 |
1981年 | 7295篇 |
1980年 | 6820篇 |
1979年 | 7377篇 |
1978年 | 7502篇 |
1977年 | 7342篇 |
1976年 | 7296篇 |
1975年 | 6858篇 |
1974年 | 6808篇 |
1973年 | 6984篇 |
1972年 | 4821篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Tomáš Hložek Martin Štícha Miroslava Bursová Ivan Jelínek Petr Tůma Radomír Čabala 《Electrophoresis》2020,41(18-19):1564-1567
Riociguat is novel antihypertensive drug for treatment of pulmonary hypertension. As such, it is still being tested in many clinical and pharmacokinetic trials. Existing methods that determine serum riociguat and desmethylriociguat (DMR) are based solely on liquid chromatography with mass spectrometry. Therefore, we present a novel capillary electrophoresis with mass spectrometry method (CE-MS) for their determination in human serum as alternative method for ongoing trials. Complete resolution of both analytes was achieved by means of pH optimization of ammonium formate background electrolytes that are fully compatible with ESI/MS detection. Simple liquid-liquid extraction was used as sample pretreatment. The calibration dependence of the method was linear (in the range of 10–1000 ng/mL), with adequate accuracy (90.1–114.9%) and precision (13.4%). LOD and LOQ were arbitrarily set at 10 ng/mL for both analytes. Clinical applicability was validated using serum samples from patients treated with riociguat in pharmacokinetic study and the results corresponded with reference HPLC-MS/MS values. Capillary electrophoresis proved to be sensitive and selective tool for the analysis of riociguat and DMR. 相似文献
52.
A liquid dewetting method for the determination of the viscoelastic properties of ultrathin polymer films has been extended to study thickness effects on the properties of ultrathin polycarbonate (PC) films. PC films with film thicknesses ranging from 4 to 299 nm were placed on glycerol at temperatures from below the macroscopic glass transition temperature (Tg) to above it with the dewetting responses being monitored. It is found that the isothermal creep results for films of the same thickness, but dewetted at different temperatures can be superposed into one master curve, which is consistent with the fact of PC being a thermorheologically simple material. Furthermore, the results show that the Tg of PC thin films is thickness dependent, but the dependence is weaker than the results for freely standing films and similar to literature data for PC films supported on rigid substrates. It was also found that the rubbery plateau region for the PC films stiffens dramatically, but still less than what has been observed for freely standing polycarbonate films. The rubbery stiffening is discussed in terms of a recently reported model that relates macroscopic segmental dynamics with the stiffening. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1559–1566 相似文献
53.
54.
Pengjin Qin Li-An Wang Prof. Joseph M. O'Connor Prof. Kim K. Baldridge Yifan Li Burak Tufekci Jiyue Chen Prof. Arnold L. Rheingold 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(41):18114-18121
Triene 6π electrocyclization, wherein a conjugated triene undergoes a concerted stereospecific cycloisomerization to a cyclohexadiene, is a reaction of great historical and practical significance. In order to circumvent limitations imposed by the normally harsh reaction conditions, chemists have long sought to develop catalytic variants based upon the activating power of metal–alkene coordination. Herein, we demonstrate the first successful implementation of such a strategy by utilizing [(C5H5)Ru(NCMe)3]PF6 as a precatalyst for the disrotatory 6π electrocyclization of highly substituted trienes that are resistant to thermal cyclization. Mechanistic and computational studies implicate hexahapto transition-metal coordination as responsible for lowering the energetic barrier to ring closure. This work establishes a foundation for the development of new catalysts for stereoselective electrocyclizations. 相似文献
55.
Attila Kovács 《International journal of quantum chemistry》2020,120(1):e26051
Lanthanide dinitrogen complexes, Ln(N2) x (x = 1-8), were investigated by Density Functional Theory computations using the B3LYP exchange-correlation functional in conjunction with quasirelativistic pseudopotentials for Ln. After a recent study on the lanthanum complexes (A. Kovács, Structural Chemistry 2018 , 29, 1825), the present study aimed to probe the changes upon variously filled 4f subshells of Ln on the structures, stabilities, and bonding properties in related complexes of Nd, Ho, and Lu. The bonding properties were assessed on the basis of natural atomic charges, Ln valence orbital populations, and analysis of bonding molecular orbitals. 相似文献
56.
The influence of different referencing methods on the accuracy of δ13C value measurement of ethanol fuel by gas chromatography/combustion/isotope ratio mass spectrometry
下载免费PDF全文
![点击此处可从《Rapid communications in mass spectrometry : RCM》网站下载免费的PDF全文](/ch/ext_images/free.gif)
57.
ABSTRACTThe Coupled-Cluster (CC) theory is one of the most successful high precision methods used to solve the stationary Schrödinger equation. In this article, we address the mathematical foundation of this theory with focus on the advances made in the past decade. Rather than solely relying on spectral gap assumptions (non-degeneracy of the ground state), we highlight the importance of coercivity assumptions – Gårding type inequalities – for the local uniqueness of the CC solution. Based on local strong monotonicity, different sufficient conditions for a local unique solution are suggested. One of the criteria assumes the relative smallness of the total cluster amplitudes (after possibly removing the single amplitudes) compared to the Gårding constants. In the extended CC theory the Lagrange multipliers are wave function parameters and, by means of the bivariational principle, we here derive a connection between the exact cluster amplitudes and the Lagrange multipliers. This relation might prove useful when determining the quality of a CC solution. Furthermore, the use of an Aubin–Nitsche duality type method in different CC approaches is discussed and contrasted with the bivariational principle. 相似文献
58.
Dr. Yulia Y. Enakieva Dr. Anna A. Sinelshchikova Prof. Mikhail S. Grigoriev Prof. Vladimir V. Chernyshev Dr. Konstantin A. Kovalenko Prof. Irina A. Stenina Prof. Andrey B. Yaroslavtsev Prof. Yulia G. Gorbunova Prof. Aslan Y. Tsivadze 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(45):10552-10556
The design of new solid-state proton-conducting materials is a great challenge for chemistry and materials science. Herein, a new anionic porphyrinylphosphonate-based MOF ( IPCE-1Ni ), which involves dimethylammonium (DMA) cations for charge compensation, is reported. As a result of its unique structure, IPCE-1Ni exhibits one of the highest value of the proton conductivity among reported proton-conducting MOF materials based on porphyrins (1.55×10−3 S cm−1 at 75 °C and 80 % relative humidity). 相似文献
59.
60.