全文获取类型
收费全文 | 852篇 |
免费 | 22篇 |
国内免费 | 6篇 |
专业分类
化学 | 521篇 |
晶体学 | 25篇 |
力学 | 10篇 |
数学 | 153篇 |
物理学 | 171篇 |
出版年
2023年 | 9篇 |
2022年 | 16篇 |
2021年 | 10篇 |
2020年 | 15篇 |
2019年 | 8篇 |
2016年 | 14篇 |
2015年 | 15篇 |
2014年 | 19篇 |
2013年 | 46篇 |
2012年 | 36篇 |
2011年 | 48篇 |
2010年 | 19篇 |
2009年 | 20篇 |
2008年 | 45篇 |
2007年 | 46篇 |
2006年 | 39篇 |
2005年 | 43篇 |
2004年 | 41篇 |
2003年 | 26篇 |
2002年 | 49篇 |
2001年 | 10篇 |
2000年 | 13篇 |
1999年 | 9篇 |
1998年 | 10篇 |
1997年 | 6篇 |
1996年 | 9篇 |
1995年 | 5篇 |
1993年 | 7篇 |
1991年 | 5篇 |
1990年 | 6篇 |
1989年 | 5篇 |
1988年 | 14篇 |
1987年 | 7篇 |
1986年 | 9篇 |
1985年 | 12篇 |
1984年 | 13篇 |
1982年 | 14篇 |
1981年 | 12篇 |
1980年 | 10篇 |
1979年 | 9篇 |
1978年 | 15篇 |
1977年 | 11篇 |
1976年 | 10篇 |
1975年 | 11篇 |
1974年 | 8篇 |
1973年 | 5篇 |
1970年 | 5篇 |
1968年 | 6篇 |
1967年 | 7篇 |
1962年 | 4篇 |
排序方式: 共有880条查询结果,搜索用时 15 毫秒
91.
This work describes the performance of poly(methyl methacrylate) (PMMA) microfluidic DNA purification devices with embedded microfabricated posts, functionalized with chitosan. PMMA is attractive as a substrate for creating high surface area (SA) posts for DNA capture because X-ray lithography can be exploited for extremely reproducible fabrication of high SA structures. However, this advantage is offset by the delicate nature of the posts when attempting bonding to create a closed system, and by the challenge of functionalizing the PMMA surface with a group that invokes DNA binding. Methods are described for covalent functionalization of the post surfaces with chitosan that binds DNA in a pH-dependent manner, as well as for bonding methods that avoid damaging the underlying post structure. A number of geometric posts designs are explored, with the goal of identifying post structures that provide the requisite surface area without a concurrent rise in fluidic resistance that promotes device failure. Initial proof-of-principle is shown by recovery of prepurified human genomic DNA (hgDNA), with real-world utility illustrated by purifying hgDNA from whole blood and demonstrating it to be PCR-amplifiable. 相似文献
92.
Jerome P. Ferrance 《Electroanalysis》2011,23(12):2906-2914
Strings of single‐walled carbon nanotubes (SWCNT) were prepared using an aqueous dispersion of gellan gum wrapped nanotubes and crosslinked using Ca2+ ions. Various formulations were evaluated to determine the parameters for successful string formation; these included 8–12 % nanotube by weight, 60–70 % gellan gum, and 20–30 % KCl. Strings showed electrical conductivity when dried between ITO electrodes. Conductivity variations were observed and potential sources of the variation identified. Proteins were attached to the carbon nanotube strings with peroxidase enzymatic activity detected following horseradish peroxidase attachment. This work provides a basis for development of electronic biosensors based on these carbon nanotube strings. 相似文献
93.
We report the enantioselective synthesis of pseudolaric acid B (1a), a diterpene acid isolated from the bark of Pseudolarix kaempferi Gordon, which displays interesting antifungal, antifertility, and cytotoxic activity against multidrug resistant cell lines. Our synthesis utilizes a highly efficient metal-catalyzed [5 + 2] vinylcyclopropane-alkyne intramolecular cycloaddition to construct the polyhydroazulene core of the natural product. Elaboration to the tricyclic scaffold of the pseudolaric acids was completed with an intramolecular alkoxycarbonyl radical cyclization to form the quaternary center and a highly diastereoselective cerium acetylide addition to a methyl ketone for introduction of the acid side chain. 相似文献
94.
Kirill M. Skupov Pooja R. Marella Michel Simard Glenn P. A. Yap Nathan Allen David Conner Brian L. Goodall Jerome P. Claverie 《Macromolecular rapid communications》2007,28(20):2033-2038
The reaction of 2‐[bis(2‐methoxy‐phenyl)phosphanyl]‐4‐methyl‐benzenesulfonic acid (a) and 2‐[bis(2′,6′‐dimethoxybiphenyl‐2‐yl)phosphanyl]benzenesulfonic acid (b) with dimethyl(N,N,N′,N′‐tetramethylethylenediamine)‐palladium(II) (PdMe2(TMEDA)) leads to the formation of TMEDA bridged palladium based polymerization catalysts ( 1a and 1b ). Upon reaction with pyridine, two mononuclear catalysts are formed ( 2a and 2b ). These catalysts are able to homopolymerize ethylene and also copolymerize ethylene with acrylates or with norbornenes. With ligand b , high molecular weight polymers are formed in high yields, but higher comonomer incorporations are obtained with ligand a .
95.
Stéphanie Etienne C. Becker D. Ruch B. Grignard G. Cartigny C. Detrembleur C. Calberg R. Jerome 《Journal of Thermal Analysis and Calorimetry》2007,87(1):101-104
Silica nanoparticles of various sizes have
been incorporated by melt compounding in a poly(methyl methacrylate) (PMMA)
matrix to enhance its thermal and mechanical properties. In order to improve
nanoparticles dispersion, PMMA grafted particles have been prepared by atom
transfer radical polymerization (ATRP) from well-defined silica nanoparticles.
This strategy was expected to ensure compatibility between both components
of the PMMA nanocomposites. TEM analysis have been performed to evaluate the
nanosilica dispersion whereas modified and non-modified silica/PMMA nanocomposites
thermal stability and mechanical properties have been investigated by both
thermogravimetric and dynamical mechanical analysis. 相似文献
96.
Cyclic Hypervalent Iodine Reagents for Atom‐Transfer Reactions: Beyond Trifluoromethylation 下载免费PDF全文
Yifan Li Dr. Durga Prasad Hari Maria Victoria Vita Prof. Dr. Jerome Waser 《Angewandte Chemie (International ed. in English)》2016,55(14):4436-4454
Hypervalent iodine compounds are privileged reagents in organic synthesis because of their exceptional reactivity. Among these compounds, cyclic derivatives stand apart because of their enhanced stability. They have been widely used as oxidants, but their potential for functional‐group transfer has only begun to be investigated recently. The use of benziodoxol(on)es for trifluoromethylation (Togni's reagents) is already widely recognized, but other transformations have also attracted strong interest recently. In this Review, the development in the area since 2011 will be presented. After a short summary of synthetic methods to prepare benziodoxol(on)e reagents, their use to construct carbon–heteroatom and carbon–carbon bonds will be presented. In particular, the introduction of alkynes by using ethynylbenziodoxol(on)e (EBX) reagents has been highly successful. Breakthroughs in the introduction of alkoxy, azido, difluoromethyl, and cyano groups will also be described. 相似文献
97.
The aim of this work was to show usefulness of chemometric analysis in processing of the data describing production of drinking water in the Silesian region of Poland. Water samples have been collected within the period of 1 year and the quality of water was characterized by a number of physical, chemical and microbiological parameters. Principal component analysis (PCA) and STATIS (Structuration des Tableaux A Trois Indices de la Statistique) were employed to obtain the knowledge about the complete water treatment process. PCA makes it possible to uncover seasonal changes influencing the water treatment process. In particular, it was found out that the salt content, hardness and conductivity of water tend to obtain higher levels in winter rather than in summer, and the relatively lower acidity is also to be expected in winter. The sensory quality of water is considerably improved over the consecutive purification steps. Complementary information about the individual technological units of the process is gained with the STATIS approach. The obtained results show that the water produced by the two independent filtering branches of the water plant is of similar quality and the prescribed quality characteristics of drinking water are fulfilled. 相似文献
98.
Gao D McBean N Schultz JS Yan Y Mulchandani A Chen W 《Journal of the American Chemical Society》2006,128(3):676-677
A general method has been developed to immobilize antibodies onto an array surface by employing fusion proteins consisting of an elastin domain with tunable hydrophobic properties and an antibody-binding domain with high binding affinity and specificity for antibodies. Antibodies conjugated with the elastin fusion proteins can be directly printed on a self-assembled monolayer-modified glass slide in a functionally active orientation with a spatially defined pattern. An antibody array sensor for detection of tumor markers was fabricated to demonstrate the utility of the method. We expect that the method presented here could be a simple and universal platform to immobilize antibodies for the fabrication of a variety of antibody array sensors. 相似文献
99.
Chemical reactions and processes often involve chiral, yet racemic, cationic reagents, intermediates or products. To afford instead non racemic or enantiopure compounds, an asymmetric ion pairing of the cations with enantiopure anions can be considered--the counter ions behaving as asymmetric auxiliaries, ligands or reagents. Detailed herein is a short review of our approach towards gaining reliable and predictable control over stereoselective ion pairing phenomena through the synthesis and the use of novel configurationally stable hexacoordinated phosphate anions. 相似文献
100.
Karr AF Feng J Lin X Sanil AP Young SS Reiter JP 《Journal of computer-aided molecular design》2005,19(9-10):739-747
We present a method for performing statistically valid linear regressions on the union of distributed chemical databases that preserves confidentiality of those databases. The method employs secure multi-party computation to share local sufficient statistics necessary to compute least squares estimators of regression coefficients, error variances and other quantities of interest. We illustrate our method with an example containing four companies' rather different databases. 相似文献