全文获取类型
收费全文 | 1409篇 |
免费 | 20篇 |
国内免费 | 7篇 |
专业分类
化学 | 718篇 |
晶体学 | 13篇 |
力学 | 46篇 |
数学 | 296篇 |
物理学 | 363篇 |
出版年
2021年 | 10篇 |
2020年 | 11篇 |
2019年 | 9篇 |
2017年 | 11篇 |
2016年 | 26篇 |
2015年 | 17篇 |
2014年 | 17篇 |
2013年 | 72篇 |
2012年 | 58篇 |
2011年 | 73篇 |
2010年 | 36篇 |
2009年 | 36篇 |
2008年 | 53篇 |
2007年 | 64篇 |
2006年 | 65篇 |
2005年 | 55篇 |
2004年 | 62篇 |
2003年 | 31篇 |
2002年 | 34篇 |
2001年 | 30篇 |
2000年 | 25篇 |
1999年 | 22篇 |
1998年 | 20篇 |
1997年 | 19篇 |
1996年 | 29篇 |
1995年 | 19篇 |
1994年 | 35篇 |
1993年 | 31篇 |
1992年 | 19篇 |
1991年 | 25篇 |
1990年 | 33篇 |
1989年 | 18篇 |
1988年 | 28篇 |
1987年 | 17篇 |
1986年 | 19篇 |
1985年 | 32篇 |
1984年 | 25篇 |
1983年 | 14篇 |
1982年 | 20篇 |
1981年 | 25篇 |
1980年 | 13篇 |
1979年 | 18篇 |
1978年 | 16篇 |
1977年 | 10篇 |
1976年 | 19篇 |
1975年 | 9篇 |
1974年 | 17篇 |
1973年 | 14篇 |
1972年 | 9篇 |
1969年 | 8篇 |
排序方式: 共有1436条查询结果,搜索用时 15 毫秒
71.
F. Dowell G. H. Stewart 《Phosphorus, sulfur, and silicon and the related elements》2013,188(2-3):135-142
Abstract The activity coefficient of 50 solutes in liquid sulfur have been measured at infinite dilution by gas chromatography. The solvent-solute interactions have been examined in terms of chromatographic models, activity coefficients, and solubility parameter theory. The classification of sulfur with polar chromatographic solvents is examined and attributed to enhanced dispersion of sulfur with compounds which have, relative to alkanes, loosely held electron clouds. Solubility parameter theory is found to provide a basis for the correlation of the behavior of n-alkanes in liquid sulfur. 相似文献
72.
John Morrow Stewart 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(1-2):259-288
The last two decades have been an era of rapid progress in peptide research. This era was begun by the work of Sanger on the amino acid sequence determination of insulin and by du Vigneaud on the structure determination and synthesis of oxytocin. This period has seen impressive progress in the structure elucidation and synthesis of many peptides of natural origin and of great biological significance, as well as in methods for sequence determination and chemical synthesis of peptides [1–4]. Perfection of techniques and instruments for automatic determination of the amino acid sequence of peptides and proteins has made possible a greatly broadened understanding of genetics and evolution as well as the more chemical areas of mechanism of action of enzymes and hormones, and physical chemistry of peptides and proteins. Effective methods of peptide synthesis are crucial to progress in this area, because only by synthesis can adequate amounts of important peptides be made available for chemical, biological, and physical studies, as well as for exploration of the structure-function aspects of biological molecules. In general, progress in peptide synthesis has lagged far behind that in amino acid sequence determination. This is not surprising since effective peptide synthesis requires a very sophisticated system of selectively removable protecting groups for functions of the amino acids involved, and the synthesis of a large heteropolytner of defined sequence requires near perfection of each one of the many steps of the assembly. The classical approach to peptide synthesis, using standard organic chemical methods of synthesis and purification of intermediates, has yielded impressive results during these two decades. However, the special problems associated with the assembly of large molecules make staggering investments in time and materials necessary for the synthesis of large peptides or proteins by classical methods. 相似文献
73.
74.
The Claisen rearrangement of α-(thioalkoxy)-esters provided access to substituted trans-1, 6-dimethylbicyclo[4.3.0]non-2-enes characteristic of the CD rings of the cucurbitanes. 相似文献
75.
Abstract A general deformation of a smectic C liquid crystal is composed of five different distortions, each of which can be made independently. Here we show that to each of these distortions we can assign a simple vector operator. Use of these five basis operators enables us to write down the elastic free energy density as a quadratic form consisting of nine terms. We also discuss how the nine elastic constants defined by the elastic energy expansion must fulfil certain restrictions in terms of inequalities and a specific tilt angle dependence. Assuming the smectic layers to be incompressible, we examine how certain arrangements of the smectic layers can be stable due to an interplay between the incompressibility condition and the boundary conditions which we impose on the director. One such stable configuration is the wedge, where the smectic layers form parts of concentric cylinders with the common axis coinciding with the centre of the wedge. For such a system we discuss the different director configurations which can be achieved and their stability. We also discuss the possibility of inducing Frederiks transitions for some of these configurations and calculate the corresponding thresholds, thereby demonstrating the design of an experiment which would make it possible to measure those elastic constants which are related to the deformations of the smectic layers, constants which are normally difficult to determine experimentally. 相似文献
76.
Dr. Neil J. Stewart Hitomi Nakano Shuto Sugai Mitsushi Tomohiro Yuki Kase Yoshiki Uchio Dr. Toru Yamaguchi Yujirou Matsuo Dr. Tatsuya Naganuma Dr. Norihiko Takeda Dr. Ikuya Nishimura Dr. Hiroshi Hirata Dr. Takuya Hashimoto Dr. Shingo Matsumoto 《Chemphyschem》2021,22(10):915-923
Hyperpolarized [1-13C]fumarate is a promising magnetic resonance imaging (MRI) biomarker for cellular necrosis, which plays an important role in various disease and cancerous pathological processes. To demonstrate the feasibility of MRI of [1-13C]fumarate metabolism using parahydrogen-induced polarization (PHIP), a low-cost alternative to dissolution dynamic nuclear polarization (dDNP), a cost-effective and high-yield synthetic pathway of hydrogenation precursor [1-13C]acetylenedicarboxylate (ADC) was developed. The trans-selectivity of the hydrogenation reaction of ADC using a ruthenium-based catalyst was elucidated employing density functional theory (DFT) simulations. A simple PHIP set-up was used to generate hyperpolarized [1-13C]fumarate at sufficient 13C polarization for ex vivo detection of hyperpolarized 13C malate metabolized from fumarate in murine liver tissue homogenates, and in vivo 13C MR spectroscopy and imaging in a murine model of acetaminophen-induced hepatitis. 相似文献
77.
We have produced and detected molecules using a p-wave Feshbach resonance between 40K atoms. We have measured the binding energy and lifetime for these molecules and we find that the binding energy scales approximately linearly with the magnetic field near the resonance. The lifetime of bound p-wave molecules is measured to be 1.0+/-0.1 ms and 2.3+/-0.2 ms for the ml=+/-1 and ml=0 angular momentum projections, respectively. At magnetic fields above the resonance, we detect quasibound molecules whose lifetime is set by the tunneling rate through the centrifugal barrier. 相似文献
78.
James J. P. Stewart 《International journal of quantum chemistry》1996,58(2):133-146
When conventional matrix algebra is used to solve the semiempirical self-consistent field equations for large systems, the time required rises as the third power of the size of the system. A consequence of this is that self-consistent calculations of large systems such as enzymes are impractical. By using localized molecular orbitals instead of matrix methods, the time required for these systems can be made almost proportional to the size of the system. In partial geometry optimizations, the time required depends only upon the size of the fragment being optimized and is almost independent of the size of the whole system. © 1996 John Wiley & Sons, Inc. 相似文献
79.
Stephen Brown Ronald Grigg Joanne Hinsley Stewart Korn Visuvanathar Sridharan Michael D. Uttley 《Tetrahedron》2001,57(52):809-10355
A wide variety of aryl/heteroaryl iodides undergo an intermolecular Heck reaction with alkylallenes to furnish 1,3-dienes. These subsequently react in situ with various dienophiles to give Diels–Alder adducts. The chemistry has been extended to incorporate cyclisation-anion capture methodology and the stereochemistry of the products has been determined. 相似文献
80.