全文获取类型
收费全文 | 3206篇 |
免费 | 138篇 |
国内免费 | 7篇 |
专业分类
化学 | 2377篇 |
晶体学 | 37篇 |
力学 | 36篇 |
数学 | 427篇 |
物理学 | 474篇 |
出版年
2023年 | 16篇 |
2022年 | 25篇 |
2021年 | 40篇 |
2020年 | 58篇 |
2019年 | 60篇 |
2018年 | 27篇 |
2017年 | 39篇 |
2016年 | 92篇 |
2015年 | 96篇 |
2014年 | 117篇 |
2013年 | 156篇 |
2012年 | 164篇 |
2011年 | 211篇 |
2010年 | 140篇 |
2009年 | 108篇 |
2008年 | 169篇 |
2007年 | 182篇 |
2006年 | 150篇 |
2005年 | 147篇 |
2004年 | 130篇 |
2003年 | 103篇 |
2002年 | 108篇 |
2001年 | 65篇 |
2000年 | 60篇 |
1999年 | 46篇 |
1998年 | 66篇 |
1997年 | 46篇 |
1996年 | 48篇 |
1995年 | 70篇 |
1994年 | 59篇 |
1993年 | 56篇 |
1992年 | 39篇 |
1991年 | 45篇 |
1990年 | 35篇 |
1989年 | 30篇 |
1988年 | 22篇 |
1987年 | 20篇 |
1986年 | 22篇 |
1985年 | 34篇 |
1984年 | 31篇 |
1983年 | 20篇 |
1982年 | 19篇 |
1981年 | 16篇 |
1980年 | 20篇 |
1979年 | 20篇 |
1978年 | 13篇 |
1977年 | 16篇 |
1975年 | 10篇 |
1973年 | 16篇 |
1972年 | 8篇 |
排序方式: 共有3351条查询结果,搜索用时 31 毫秒
121.
Tao Zhou Silke Richter Ralf Matschat Heinrich Kipphardt 《Accreditation and quality assurance》2013,18(4):341-349
A candidate material for the use as primary standard for silver determination was characterized with respect to total purity. Except the radioactive elements and He, all possible impurities were considered. Based on glow discharge mass spectrometry, inductively coupled plasma-mass spectrometry and carrier gas hot extraction measurements, the demonstrated total purity and its standard uncertainty is w(Ag) = (99.999 52 ± 0.000 11) %. The purity value and its uncertainty is dominated by the contributions from the measurements of the nonmetallic impurities, namely S, N, C and O. 相似文献
122.
Rüdiger W. Seidel Richard Goddard Jürgen Breidung Ernst‐G. Jäger 《无机化学与普通化学杂志》2014,640(10):1946-1952
A combined synchrotron X‐ray and density functional theory (DFT) study on the structure of a Jäger‐type N2O2 chelate complex was carried out. The ethoxy‐substituted bis(3‐oxo‐enaminato)cobalt(II) complex ( 1 ) was an original sample from the laboratory of the late Professor Ernst‐G. Jäger (University of Jena, Germany). Single‐crystal X‐ray analysis revealed essentially flat molecules of 1 , which are unsolvated and coordinatively unsaturated. The DFT calculations on the isolated molecule predict a planar structure for the non‐hydrogen atoms, which is a local minimum on the energy surface. The crystal packing is achieved through off‐set stacking (staircase arrangement), resulting in a herringbone pattern in the space group P212121. The structure of 1 is compared to known structures of related bis(3‐oxo‐enaminato)cobalt(II) complexes ( 2 – 4 ). Original bulk material of 1 was investigated by scanning electron microscopy (SEM), powder X‐ray diffraction (PXRD), melting point determination, and infrared (IR) spectroscopy. 相似文献
123.
Andrej Frolov Matthias Blüher Ralf Hoffmann 《Analytical and bioanalytical chemistry》2014,406(24):5755-5763
Glucose can modify proteins in human blood, forming early glycation products (e.g., Amadori compounds), which can slowly degrade to advanced glycation endproducts (AGEs). AGEs contribute significantly to complications of diabetes mellitus and, thus, represent markers of advanced disease stages. They are, however, currently unsuitable for early diagnosis and therapeutic monitoring. Here, we report sensitive strategies to identify and relatively quantify protein glycation sites in human plasma samples obtained from type 2 diabetes mellitus (T2DM) patients and age-matched nondiabetic individuals using a bottom-up approach. Specifically, Amadori peptides were enriched from tryptic digests by boronic acid affinity chromatography, separated by reversed-phase chromatography, and analyzed on-line by high-resolution mass spectrometry. Among the 52 Amadori peptides studied here were 20 peptides resembling 19 glycation sites in six human proteins detected at statistically significantly higher levels in T2DM than in the normoglycemic controls. Four positions appeared to be unique for T2DM within the detection limit. All 19 glycation sites represent promising new biomarker candidates for early diagnosis of T2DM and adequate therapeutic control, as they may indicate early metabolic changes preceding T2DM. Graphical Abstract
? 相似文献
124.
Multi-analyte immunoassays on microarrays and on multiplex DNA microarrays have been described for quantitative analysis of small organic molecules (e.g., antibiotics, drugs of abuse, small molecule toxins), proteins (e.g., antibodies or protein toxins), and microorganisms, viruses, and eukaryotic cells. In analytical chemistry, multi-analyte detection by use of analytical microarrays has become an innovative research topic because of the possibility of generating several sets of quantitative data for different analyte classes in a short time. Chemiluminescence (CL) microarrays are powerful tools for rapid multiplex analysis of complex matrices. A wide range of applications for CL microarrays is described in the literature dealing with analytical microarrays. The motivation for this review is to summarize the current state of CL-based analytical microarrays. Combining analysis of different compound classes on CL microarrays reduces analysis time, cost of reagents, and use of laboratory space. Applications are discussed, with examples from food safety, water safety, environmental monitoring, diagnostics, forensics, toxicology, and biosecurity. The potential and limitations of research on multiplex analysis by use of CL microarrays are discussed in this review. Figure
Achievements in the development of CL microarray analysis platforms 相似文献
125.
126.
In this contribution main aspects of material characterization and modelling of a curing adhesive are denoted. It is pointed out how to deal with the exothermic heat generation during curing, both, how to obtain it experimentally as well as how to account for it in the continuum mechanical an FE-modelling framework. Furthermore, a strategy to simulate spatially graded gelation processes in ANSYS® is presented. An academic simulation example completes this work. By the help of this simulation tool a better understanding of a novel manufacturing process of smart semi-finished light weight structures is ensured. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
127.
Metal sheet forming processes like deep drawing are applied in order to produce carriage parts in mass production. Therefore, forming tools are required that are well protected against wear. For such forming tools, wear resistant surfaces are, e.g., produced by thermal spraying of hard material coatings. The thermal spraying process itself is a highly transient thermo-mechanical process. In order to gain a better understanding of the heat input and transfer during thermal spraying, a simulation framework for thermal spraying processes is presented. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
128.
In Shutov et al. (Comput Methods Appl Mech Eng 265:213–225, 2013), the numerical time integration of a famous large strain model of Maxwell fluid type has been considered. The underlying model is based on the multiplicative decomposition of the deformation gradient and includes a Neo-Hookean hyperelasticity relation as well as an incompressible viscous flow rule. Shutov et al. presented a time stepping algorithm for implicit time integration of the inelastic flow rule, which is based on Euler backward time discretisation, prevents error accumulation and is iteration free. In this contribution, the basic idea of the this approach is applied to more general models of multiplicative viscoelasticity. Here, extended hyperelastic relations including general functions of the first principal invariant of deformation tensors are regarded. An efficient time stepping algorithm is derived, where only one scalar equation for one scalar unknown has to be solved within every time step. The approach is applied to a specific viscoelastic model. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
129.
Jiawang Liu Carolin Schneider Ji Yang Zhihong Wei Haijun Jiao Robert Franke Ralf Jackstell Matthias Beller 《Angewandte Chemie (International ed. in English)》2021,60(1):371-379
A chemo‐, regio‐, and stereoselective mono‐hydroamidation of (un)symmetrical 1,3‐diynes is described. Key for the success of this novel transformation is the utilization of an advanced palladium catalyst system with the specific ligand Neolephos. The synthetic value of this general approach to synthetically useful α‐alkynyl‐α, β‐unsaturated amides is showcased by diversification of several structurally complex molecules and marketed drugs. Control experiments and density‐functional theory (M06L‐SMD) computations also suggest the crucial role of the substrate in controlling the regioselectivity of unsymmetrical 1,3‐diynes. 相似文献
130.
Vladislav S. Krasnoukhov Prof. Dr. Valeriy N. Azyazov Prof. Dr. Alexander M. Mebel Dr. Srinivas Doddipatla Dr. Zhenghai Yang Shane Goettl Prof. Dr. Ralf I. Kaiser 《Chemphyschem》2021,22(14):1497-1504
The chemical dynamics of the elementary reaction of ground state atomic silicon (Si; 3P) with germane (GeH4; X1A1) were unraveled in the gas phase under single collision condition at a collision energy of 11.8±0.3 kJ mol−1 exploiting the crossed molecular beams technique contemplated with electronic structure calculations. The reaction follows indirect scattering dynamics and is initiated through an initial barrierless insertion of the silicon atom into one of the four chemically equivalent germanium-hydrogen bonds forming a triplet collision complex (HSiGeH3; 3 i1 ). This intermediate underwent facile intersystem crossing (ISC) to the singlet surface (HSiGeH3; 1 i1 ). The latter isomerized via at least three hydrogen atom migrations involving exotic, hydrogen bridged reaction intermediates eventually leading to the H3SiGeH isomer i5 . This intermediate could undergo unimolecular decomposition yielding the dibridged butterfly-structured isomer 1 p1 (Si(μ-H2)Ge) plus molecular hydrogen through a tight exit transition state. Alternatively, up to two subsequent hydrogen shifts to i6 and i7 , followed by fragmentation of each of these intermediates, could also form 1 p1 (Si(μ-H2)Ge) along with molecular hydrogen. The overall non-adiabatic reaction dynamics provide evidence on the existence of exotic dinuclear hydrides of main group XIV elements, whose carbon analog structures do not exist. 相似文献