全文获取类型
收费全文 | 824篇 |
免费 | 27篇 |
国内免费 | 2篇 |
专业分类
化学 | 649篇 |
晶体学 | 18篇 |
力学 | 17篇 |
数学 | 48篇 |
物理学 | 121篇 |
出版年
2022年 | 8篇 |
2021年 | 9篇 |
2020年 | 7篇 |
2019年 | 16篇 |
2018年 | 5篇 |
2017年 | 7篇 |
2016年 | 12篇 |
2015年 | 17篇 |
2014年 | 13篇 |
2013年 | 51篇 |
2012年 | 46篇 |
2011年 | 40篇 |
2010年 | 20篇 |
2009年 | 25篇 |
2008年 | 40篇 |
2007年 | 45篇 |
2006年 | 46篇 |
2005年 | 33篇 |
2004年 | 45篇 |
2003年 | 26篇 |
2002年 | 24篇 |
2001年 | 10篇 |
2000年 | 17篇 |
1999年 | 8篇 |
1998年 | 6篇 |
1997年 | 8篇 |
1996年 | 6篇 |
1995年 | 14篇 |
1993年 | 5篇 |
1992年 | 7篇 |
1991年 | 8篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 11篇 |
1984年 | 18篇 |
1983年 | 5篇 |
1982年 | 12篇 |
1981年 | 15篇 |
1980年 | 15篇 |
1979年 | 7篇 |
1978年 | 9篇 |
1977年 | 11篇 |
1976年 | 18篇 |
1975年 | 14篇 |
1974年 | 18篇 |
1973年 | 15篇 |
1968年 | 4篇 |
排序方式: 共有853条查询结果,搜索用时 15 毫秒
81.
Takahiro Takayama Toshiki Mochizuki Kenichiro Todoroki Jun Zhe Min Hajime Mizuno Koichi Inoue Hiroyasu Akatsu Ichiro Noge Toshimasa Toyo'oka 《Analytica chimica acta》2015
Chiral metabolites are found in a wide variety of living organisms and some of them are understood to be physiologically active compounds and biomarkers. However, the overall analysis of chiral metabolomics is quite difficult due to the high number of metabolites, the significant diversity in their physicochemical properties, and concentration range from metabolite-to-metabolite. To solve this difficulty, we developed a novel approach for chiral metabolomics fingerprinting and chiral metabolomics extraction, which is based on the labeling of a pair of enantiomers of chiral derivatization reagents (i.e., DMT-(S,R)-Pro-OSu and DMT-3(S,R)-Apy) and precursor ion scan chromatography of the derivatives. The multivariate statistics is also required for this strategy. The proposed procedures were evaluated by the detection of a diagnostic marker (i.e., d-lactic acid) using the saliva of diabetic patients. This method was used for the determination of biomarker candidates of chiral amines and carboxyls in Alzheimer's disease (AD) brain homogenates. As the results, l-phenylalanine (L-Phe) and l-lactic acid (L-LA) were identified as the decreased and increased biomarker candidates in the AD brain, respectively. Therefore, the proposed approach seems to be helpful for the determination of non-target chiral metabolomics possessing amines and carboxyls. 相似文献
82.
Ichiro Hisaki Shoichi Nakagawa Norimitsu Tohnai Mikiji Miyata 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2015,127(10):3051-3055
A C3‐symmetric π‐conjugated macrocycle combined with an appropriate hydrogen bonding module (phenylene triangle) allowed the construction of crystalline supramolecular frameworks with a cavity volume of up to 58 %. The frameworks were obtained through non‐interpenetrated stacking of a hexagonal sheet possessing three kinds of pores with different sizes and shapes. The activated porous material absorbed CO2 up to 96 cm3 g−1 at 195 K under 1 atm. 相似文献
83.
Nanocomposite materials consisting of an epoxy matrix and silicate clay particles have been processed and characterized mechanically.
The clay material used was a modified natural montmorillonite. The clay particles consisted of 1 nm thick layers with aspect
ratios in the range of 100–1000. The clay particles were mixed with acetone and sonicated, then mixed with the polymer, deaerated
and cured. The ultimate objective of processing was to produce a polymer/clay nanocomposite with separated (exfoliated) platelets,
dispersed as uniformly as possible. Samples were prepared with clay concentrations of up to 10 wt%. The process used resulted
in limited exfoliation but mostly intercalation, i.e., infusion of polymer between the silicate layers and increase of interlayer
spacing. The characteristics of the nanocomposite were assessed by transmission electron microscopy and x-ray diffraction.
Results from these observations show that the basal spacing of clay platelets increased from an initial pre-processing value
of 1.85 nm to 4.5 nm. Enhancement of mechanical properties was measured by tensile testing of coupons. Stiffness increases
of up to 50% over that of the unfilled epoxy were measured for clay concentrations of 5 wt%. Strength increases were also
measured for low clay concentrations and low strain rate loading. Micromechanics modeling of mechanical behavior is discussed
as a function of clay platelet dispersion. 相似文献
84.
Kanda M Sasamoto T Takeba K Hayashi H Kusano T Matsushima Y Nakajima T Kanai S Takano I 《Journal of AOAC International》2011,94(3):878-885
A new, rapid, and efficient method for determining the fumagillin residues in honey was developed. The samples extracted were analyzed using LC/MS/MS. Chromatographic separation of fumagillin was performed in gradient mode on a C8 column (100 x 2.0 mm, 5 microm) at 40 degrees C. The mobile phase consisted of a mixture of 2 mM ammonium formate-0.01% formic acid solution and methanol; the flow rate was set to 0.2 mL/min. Under these conditions, it was possible to measure fumagillin and its isomers as a single peak. The sample preparation procedure used is based on the QuEChERS (quick, easy, cheap, effective, rugged, and safe) method, which is fast (approximately 30 min) and uses less organic solvent. The fumagillin was extracted with acetonitrile containing 0.1% formic acid, then purified using a solid-phase extraction method with an Oasis mixed-mode weak anion-exchange cartridge. The overall recovery of fumagillin ranged from 88.1 to 99.4%; the intra- and interassay CVs were <4.5% and <4.9%, respectively. The LOQ was 0.1 microg/kg. LC/MS/MS coupled with the QuEChERS method showed strong potential as a method for determining fumagillin residues in honey. 相似文献
85.
The development of a new class of hydrazide type organocatalyst, (4R,5R)-1,3-bis(isopropylamino)-4,5-dihenylimidazolidin-2-one 2a, for enantioselective Diels-Alder reactions between cyclopentadiene and α,β-unsaturated aldehydes are presented. The new organocatalyst 2a promoted the reaction, affording Diels-Alder adducts in good yields with good levels of enantioselectivity. 相似文献
86.
Miyagawa T Nagai K Yamada A Sugihara Y Fukuda T Fukuda T Uchida R Tomoda H Omura S Nagamitsu T 《Organic letters》2011,13(5):1158-1161
The first total synthesis of citridone A has been achieved through regioselective intramolecular iodocyclization and regio- and stereoselective Pd(0)-catalyzed coupling as key reactions. 相似文献
87.
Harada T Nakagawa Y Ogura T Yamada Y Ohe T Miyagawa H 《Journal of chemical information and modeling》2011,51(2):296-305
Insect growth is regulated by the orchestrated event of ecdysteroids and their receptor proteins. Agonists/antagonists of ecdysteroid receptor are predicted to disrupt normal growth, providing good candidates of new insecticides. A database of over 2 million compounds was subjected to a shape-based virtual screening cascade to identify novel nonsteroidal hits similar to the known EcR ligand ponasterone A. Testing revealed micromolar hits against two strains of insect cells. Docking experiments against EcR were used to support the predicted binding mode of these ligands based on their overlay to ponasterone A. 相似文献
88.
Kobayashi M Kumagai S Zheng B Uraoka Y Douglas T Yamashita I 《Chemical communications (Cambridge, England)》2011,47(12):3475-3477
Cage-shaped proteins with an affinity for carbonaceous materials were constructed and used to assemble a nanostructure in which single-walled carbon nanotubes are surrounded by cobalt oxide nanoparticles with nanometre gaps. By changing the size of proteins and materials incorporated inside the cavity, similar structures with distinctively different properties can be fabricated. 相似文献
89.
Horie H Koyama I Kurahashi T Matsubara S 《Chemical communications (Cambridge, England)》2011,47(9):2658-2660
The linear codimerization of acrylates and alkynes to produce 1,3-dienes is successfully demonstrated using a nickel catalyst in association with 2-aminopyridine as an additive. 相似文献
90.
Ichiro Hayashi Mitsutoshi Kuroda 《Journal of the mechanics and physics of solids》2011,59(9):1731-1751
A series of systematic tensile and microbend tests were conducted on copper foil specimens with different thicknesses. The specimens were made of a copper foil having almost unidirectional crystal orientations that was considered to be nearly single-crystal. In order to investigate the effects of slip system interactions, two different crystal orientations relative to the tensile direction were considered in the tests: one is close to coplanar double-slip orientation, and the other is close to the ideal cube orientation (the tensile direction nearly coincides to [0 0 1]) that yields multi-planar multi-slip deformation. We extended the microbend test method to include the reversal of bending, and we attempted to divide the total amount of strain-hardening into isotropic and kinematic hardening components. In the tensile tests, no systematic tendency of size dependence was observed. In the microbend tests, size-dependent kinematic hardening behavior was observed for both the crystal orientations, while size dependence of isotropic hardening was observed only for the multi-planar multi-slip case. We introduce an extended crystal plasticity model that accounts for the effects of the geometrically necessary dislocations (GNDs), which correspond to the spatial gradients of crystallographic slips. Through numerical simulations performed using the model, the origin of the size-dependent behavior observed in the microbend tests is discussed. 相似文献