全文获取类型
收费全文 | 6408篇 |
免费 | 208篇 |
国内免费 | 28篇 |
专业分类
化学 | 4497篇 |
晶体学 | 39篇 |
力学 | 177篇 |
数学 | 984篇 |
物理学 | 947篇 |
出版年
2024年 | 6篇 |
2023年 | 57篇 |
2022年 | 188篇 |
2021年 | 205篇 |
2020年 | 163篇 |
2019年 | 157篇 |
2018年 | 114篇 |
2017年 | 118篇 |
2016年 | 258篇 |
2015年 | 215篇 |
2014年 | 226篇 |
2013年 | 339篇 |
2012年 | 403篇 |
2011年 | 496篇 |
2010年 | 281篇 |
2009年 | 261篇 |
2008年 | 393篇 |
2007年 | 365篇 |
2006年 | 371篇 |
2005年 | 341篇 |
2004年 | 314篇 |
2003年 | 249篇 |
2002年 | 211篇 |
2001年 | 82篇 |
2000年 | 72篇 |
1999年 | 78篇 |
1998年 | 52篇 |
1997年 | 54篇 |
1996年 | 81篇 |
1995年 | 48篇 |
1994年 | 49篇 |
1993年 | 40篇 |
1992年 | 50篇 |
1991年 | 40篇 |
1990年 | 23篇 |
1989年 | 22篇 |
1988年 | 14篇 |
1987年 | 16篇 |
1986年 | 19篇 |
1985年 | 26篇 |
1984年 | 26篇 |
1983年 | 22篇 |
1982年 | 16篇 |
1981年 | 12篇 |
1980年 | 14篇 |
1979年 | 19篇 |
1977年 | 8篇 |
1976年 | 5篇 |
1975年 | 4篇 |
1906年 | 2篇 |
排序方式: 共有6644条查询结果,搜索用时 15 毫秒
181.
Katarína Hroboňová Andrea Spevak Ľubica Spišská Jozef Lehotay Jozef Čižmárik 《Chemical Papers》2013,67(5):477-483
The molecularly imprinted polymers (MIPs) were synthesised and the influence of the type of porogen, the nature of sample solvent, and the binding capacity of material were tested by high-performance liquid chromatography (HPLC). Umbelliferone was used as the template for imprint formation. Methacrylic acid was used as the monomer and acetonitrile, ethanol, and chloroform as porogen. Non-imprinted polymers (NIPs) were prepared by the same procedure. The highest value of the specific binding capacity (269 μg of umbelliferone per 100 mg of polymer) was obtained for polymers prepared in chloroform as porogen and methanol/water (φ r = 1: 1) as the sample solvent. The group-selective MIP was used as sorbent for the SPE pre-treatment of umbelliferone from plant extracts prior to HPLC analysis. Analysis of the spiked samples showed good recoveries (> 77 %). The limit of detection, limit of determination, and repeatability of the method were also calculated. 相似文献
182.
Multidimensional nano-HPLC coupled with tandem mass spectrometry for analyzing biotinylated proteins
Jens Sproß Sebastian Brauch Friedrich Mandel Moritz Wagner Stephan Buckenmaier Bernhard Westermann Andrea Sinz 《Analytical and bioanalytical chemistry》2013,405(7):2163-2173
Multidimensional high-performance liquid chromatography (HPLC) is a key method in shotgun proteomics approaches for analyzing highly complex protein mixtures by complementary chromatographic separation principles. Here, we describe an integrated 3D-nano-HPLC/nano-electrospray ionization quadrupole time-of-flight mass spectrometry system that allows an enzymatic digestion of proteins followed by an enrichment and subsequent separation of the created peptide mixtures. The online 3D-nano-HPLC system is composed of a monolithic trypsin reactor in the first dimension, a monolithic affinity column with immobilized monomeric avidin in the second dimension, and a reversed phase C18 HPLC-Chip in the third dimension that is coupled to a nano-ESI-Q-TOF mass spectrometer. The 3D-LC/MS setup is exemplified for the identification of biotinylated proteins from a simple protein mixture. Additionally, we describe an online 2D-nano-HPLC/nano-ESI-LTQ-Orbitrap-MS/MS setup for the enrichment, separation, and identification of cross-linked, biotinylated species from chemical cross-linking of cytochrome c and a calmodulin/peptide complex using a novel trifunctional cross-linker with two amine-reactive groups and a biotin label. Figure
Schematic representations of the online 3D-nano-HPLC/nano-ESI-Q-TOF-MS/MS setup; LP loading pump, NP nano-pump 相似文献
183.
Adriaan M. H. van der Veen Hugo Ent Annarita Baldan Valnei S. da Cunha Romeu J. Daroda Brian Lang Michele Schantz Manuela Ulberth-Buchgraber Andrea Held Ruth Hearn Richard J. C. Brown Paul J. Brewer 《Accreditation and quality assurance》2013,18(1):41-50
The main objective of the reference materials for biofuel specifications (BIOREMA) project is the development of two test materials (one bio-ethanol material and one biodiesel material) with well-established reference values. Of a series of three papers, this part describes the material preparation, homogeneity study, stability study, and characterisation of the bio-ethanol material. The test material thus obtained was used in an interlaboratory comparison (ILC) to assess current practices and comparability amongst laboratories providing bio-ethanol testing services. Only 13 participants provided data, resulting in a small dataset for evaluation. Further, it appeared that for a number of laboratories, there was not sufficient material for the determination of all requested parameters. In most cases, as far as the data permit, it can be concluded that the consensus values (based on participant’s results) are in good agreement with the reference or the BIOREMA values (obtained by NMIs participating in the project). For three parameters, namely ethanol content, water content, and density, there is good agreement between the reference and consensus values. For these parameters, the reproducibility standard deviation is close to, or even smaller than, the expanded uncertainty associated with the reference value. A number of parameters show very poor reproducibility, for example, pHe, electrolytic conductivity, and acidity. The same applies to sodium and copper content, which are very low and therefore challenging parameters to measure accurately. The results of the ILC underpin the need for certified reference materials and demonstrate the requirement for more robust quality control to improve the precision and trueness of the results from testing laboratories. 相似文献
184.
185.
Andrea Kühl Dietrich Bergner Hans-J. Ullrich Matthias Schlaubitz Peter Karduck 《Mikrochimica acta》1992,107(3-6):295-302
Parameters of the diffusion of N (up to 0.3 wt.%) in austenitic stainless steels (12 to 19 wt.% Cr, 12 to 16 wt.% Ni, up to 2 wt.% Mo) were determined within the temperature range of 1283–1573K. The small concentration gradients of N were successfully investigated using (1) mechanical serial sectioning technique in combination with either chemical N analysis or X-ray precision lattice parameter determination, and (2) measurements on microsections by means of either electron probe microanalysis or Kossel technique.The diffusion coefficients of N were found to be independent of its concentration. The alloying elements Cr and Mo reduce the N diffusivity in austenitic stainless steels which on the other hand is increased by Ni. 相似文献
186.
Reschiglian P Zattoni A Roda B Cinque L Melucci D Min BR Moon MH 《Journal of chromatography. A》2003,985(1-2):519-529
Interest in low-cost, analytical-scale, highly efficient and sensitive separation methods for cells, among which bacteria, is increasing. Particle separation in hollow-fiber flow field-flow fractionation (HF FlFFF) has been recently improved by the optimization of the HF FIFFF channel design. The intrinsic simplicity and low cost of this HF FlFFF channel allows for its disposable usage. which is particularly appealing for analytical bio-applications. Here, for the first time, we present a feasibility study on high-performance, hyperlayer HF FIFFF of micrometer-sized bacteria (Escherichia coli) and of different types of cells (human red blood cells, wine-making yeast from Saccharomyces cerevisiae). Fractionation performance is shown to be at least comparable to that obtained with conventional, flat-channel hyperlayer FIFFF of cells, at superior size-based selectivity and reduced analysis time. 相似文献
187.
Arturo ArduiniElisabetta Brindani Giovanna GiorgiAndrea Pochini Andrea Secchi 《Tetrahedron》2003,59(38):7587-7594
The synthesis of new hosts specifically designed for the recognition of neutral guests bearing donor-acceptor hydrogen bonding groups is described. These hosts are characterized by the presence of two distinct binding region in close proximity: the rigid π-donor cavity and the H-bond donor N-methylene-N′-phenylureido group inserted onto the upper rim of the calix[4]arene skeleton. The binding abilities of these receptors were investigated toward a series of neutral ditopic organic molecules in CDCl3 solution by 1H NMR spectroscopy. The results obtained show that rigidity of the calix[4]arene apolar cavity is the control element in determining efficiency. In fact, compared with the more rigid 2, host 10, where the rigidity of the cone structure is maintained by hydrogen bonding of the OH of the lower rim, a decrease of efficiency of almost one order of magnitude was observed. The cooperative effect of the two binding region of host 2 was verified with different classes of ditopic guests. Good efficiency in the recognition of urea derivatives and dimethylsulfoxide was achieved. 相似文献
188.
Emmanuel DardennesÁrpád Kovács-Kulyassa Andrea RenzettiJanos Sapi Jean-Yves Laronze 《Tetrahedron letters》2003,44(2):221-223
Chiral pyrano- and pyrrolidino-fused tryptamines were prepared by a diasteroselective trimolecular condensation between indole, Garner's aldehyde and Meldrum's acid, followed by selective functional group transformations. 相似文献
189.
Francesca CardonaEnrico Faggi Francesca LiguoriMartina Cacciarini Andrea Goti 《Tetrahedron letters》2003,44(11):2315-2318
Practical syntheses of nitrone 8 by two different approaches from sugars are reported. Its use as a versatile intermediate in highly selective 1,3-dipolar cycloaddition reactions constitutes the key step for novel total syntheses of hyacinthacine A2 (3) and 7-deoxycasuarine (20) by simple transformations of a common isoxazolidine adduct. 相似文献
190.
Andrea TrabocchiNicoletta Cini Gloria MenchiAntonio Guarna 《Tetrahedron letters》2003,44(17):3489-3492
A new constrained bicyclic α-amino acid proline-mimetic was developed. The synthesis was achieved starting from derivatives of the chiral pool, thus allowing to prepare analogues of either l- or d-proline by choosing appropriate stereoisomers of serine and α,β-isopropylidene-glycerol derivatives. The scaffolds were prepared as N-Fmoc-amino acid suitable for solid-phase peptide synthesis. 相似文献