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排序方式: 共有671条查询结果,搜索用时 8 毫秒
71.
Yoshinao Kumagai Yuuki Enatsu Masanari Ishizuki Yuki Kubota Jumpei Tajima Toru Nagashima Hisashi Murakami Kazuya Takada Akinori Koukitu 《Journal of Crystal Growth》2010,312(18):2530-2536
Void formation at the interface between thick AlN layers and (0 0 0 1) sapphire substrates was investigated to form a predefined separation point of the thick AlN layers for the preparation of freestanding AlN substrates by hydride vapor phase epitaxy (HVPE). By heating 50–200 nm thick intermediate AlN layers above 1400 °C in a gas flow containing H2 and NH3, voids were formed beneath the AlN layers by the decomposition reaction of sapphire with hydrogen diffusing to the interface. The volume of the sapphire decomposed at the interface increased as the temperature and time of the heat treatment was increased and as the thickness of the AlN layer decreased. Thick AlN layers subsequently grown at 1450 °C after the formation of voids beneath the intermediate AlN layer with a thickness of 100 nm or above self-separated from the sapphire substrates during post-growth cooling with the aid of voids. The 79 μm thick freestanding AlN substrate obtained using a 200 nm thick intermediate AlN layer had a flat surface with no pits, high optical transparency at wavelengths above 208.1 nm, and a dislocation density of 1.5×108 cm−2. 相似文献
72.
73.
Junya Kobayashi Motoo Kinoshita Jun-ichi Kita Katsumi Yoshino 《International Journal of Infrared and Millimeter Waves》1996,17(7):1149-1163
Experimental infrared modulator elements have been fabricated utilizing the transient light scattering effect of ferroelectric liquid crystal with asymmetric waveform voltage drive. The new elements perform 80% modulation degrees at the 632.8nm. We have also achieved 30% modulation degrees in the 4 to 5µ m region where the strongest CO2 absorption bands exist. A new type of analyzer which monitors ambient air quality has been developed. This analyzer uses non-dispersive infrared absorption method and composes of a double-beam, a single detector and a pair of liquid crystal light modulator as the IR chopper. The detection has achieved 10ppm noise equivalent concentration. 相似文献
74.
Rui UmedaTakashi Nishimura Kenta KaibaToshimasa Tanaka Yuuki TakahashiYutaka Nishiyama 《Tetrahedron》2011,67(38):7217-7221
It was found that rhenium complex was an efficient catalyst for the acylative cleavage of C-O bond of ethers with acyl chlorides. When acyclic ethers were allowed to react with acyl chlorides in the presence of a catalytic amount of ReBr(CO)5, acylative cleavage of C-O bond of acyclic ethers smoothly proceeded to give the corresponding esters in moderate to good yields. Similarly, cyclic ethers were acylative cleaved by acyl chlorides to give the corresponding chloro substituted esters in good yields by the use of Re2O7 catalyst. 相似文献
75.
Ujiie K Kanayama N Asai K Kishimoto M Ohara Y Akashi Y Yamada K Hashimoto S Oda T Ohkohchi N Yanagihara H Kita E Yamaguchi M Fujii H Nagasaki Y 《Colloids and surfaces. B, Biointerfaces》2011,88(2):771-778
This paper describes the preparation of iron oxide nanoparticles, surface of which was coated with extremely high immobilization stability and relatively higher density of poly(ethylene glycol) (PEG), which are referred to as PEG protected iron oxide nanoparticles (PEG-PIONs). The PEG-PIONs were obtained through alkali coprecipitation of iron salts in the presence of the PEG-poly(4-vinylbenzylphosphonate) block copolymer (PEG-b-PVBP). In this system, PEG-b-PVBP served as a surface coating that was bound to the iron oxide surface via multipoint anchoring of the phosphonate groups in the PVBP segment of PEG-b-PVBP. The binding of PEG-b-PVBP onto the iron oxide nanoparticle surface and the subsequent formation of a PEG brush layer were proved by FT-IR, zeta potential, and thermogravimetric measurements. The surface PEG-chain density of the PEG-PIONs varied depending on the [PEG-b-PVBP]/[iron salts] feed-weight ratio in the coprecipitation reaction. PEG-PIONs prepared at an optimal feed-weight ratio in this study showed a high surface PEG-chain surface density (≈0.8 chainsnm(-2)) and small hydrodynamic diameter (<50 nm). Furthermore, these PEG-PIONs could be dispersed in phosphate-buffered saline (PBS) that contains 10% serum without any change in their hydrodynamic diameters over a period of one week, indicating that PEG-PIONs would provide high dispersion stability under in vivo physiological conditions as well as excellent anti-biofouling properties. In fact we have confirmed the prolong blood circulation time and facilitate tumor accumulation (more than 15% IDg(-1) tumor) of PEG-PIONs without the aid of any target ligand in mouse tumor models. The majority of the PEG-PIONs accumulated in the tumor by 96 h after administration, whereas those in normal tissues were smoothly eliminated by 96 h, proving the enhancement of tumor selectivity in the PEG-PION localization. The results obtained here strongly suggest that originally synthesized PEG-b-PVBP, having multipoint anchoring character by the phosphonate groups, is rational design for improvement in nanoparticle as in vivo application. Two major points, viz., extremely stable anchoring character and dense PEG chains tethered on the nanoparticle surface, worked simultaneously to become PEG-PIONs as an ideal biomedical devices intact for prolonged periods in harsh biological environments. 相似文献
76.
Stanis?aw Krompiec Mateusz Penkala Ewelina Kowalska Robert Penczek Piotr Bujak Witold Danikiewicz Grzegorz Spólnik Andrzej Kita Iwona Grudzka 《Monatshefte für Chemie / Chemical Monthly》2011,33(7):1241-1247
Abstract
Ru-catalyzed synthesis of mixed alkyl–alkyl acetals via addition of primary alcohols to allyl ethers has been extended to include long-chain and/or functionalized substrates. The catalytic systems for these reactions were generated from RuCl2(PPh3)3 and [RuCl2(1,5-COD)]x and phosphines [PPh3 or P(p-chlorophenyl)3] or SbPh3. Of particular importance is the almost quantitative elimination of transacetalization. The addition proceeds through allyl complexes, not via isomerization of allyl ethers––subsequent addition of ROH to vinyl ethers. 相似文献77.
Wada Y Harayama Y Kamimura D Yoshida M Shibata T Fujiwara K Morimoto K Fujioka H Kita Y 《Organic & biomolecular chemistry》2011,9(13):4959-4976
Various analogues of the marine alkaloids, discorhabdins, have been synthesized. The strategy contains spirocyclization with phenyliodine(III) bis(trifluoroacetate) (PIFA), oxidative fragmentation of the β-amino alcohols with the hypervalent iodine reagent C(6)F(5)I(OCOCF(3))(2), the detosylation and dehydrogenation reaction of the pyrroloiminoquinone unit in the presence of a catalytic amount of NaN(3) and the bridged ether synthesis with HBr-AcOH as the key reactions. All the synthesized compounds were evaluated by in vitro MTT assay for cytotoxic activity against the human colon cancer cell line HCT-116. Furthermore, the discorhabdin A oxa analogues were also evaluated against four kinds of tumor model cells, a human colon cancer cell line (WiDr), a human prostate cancer cell line (DU-145) and murine leukemia cell lines (P388 and L1210). For the identification of the target, discorhabdin A and the discorhabdin A oxa analogue were evaluated by an HCC panel assay. In the test, discorhabdins could have a novel mode of action with the tumor cells. 相似文献
78.
A silver-catalyzed carbomagnesiation of alkynes with alkyl halides and Grignard reagents afforded alkenyl Grignard reagents regioselectively, where the alkyl group of the alkyl halide, but not that of the Grignard reagent, was introduced into the alkyne. Application to δ-haloalkylacetylenes yielded cyclopentanes or a tetrahydrofuran containing an exo-methylene substituent via 5-exo-dig cyclization. 相似文献
79.
Tanaka H Zaima N Yamamoto N Suzuki M Mano Y Konno H Unno N Setou M 《Analytical and bioanalytical chemistry》2011,400(7):1873-1880
Arteriovenous fistulae (AVF) using vein grafts are frequently used for vascular access in hemodialysis. When superficial veins
are used as autogenous access grafts for hemodialysis, atherosclerotic-like tissue degeneration often causes stenosis and
obstruction. Although the differences between the pathology of degeneration in AVF and atherosclerosis (i.e., peripheral artery
occlusive disease (PAD)) are known, their underlying molecular mechanisms are not. We determined the characteristic abnormal
lipid metabolism of AVF. Oil red O staining clearly showed the accumulation of lipid molecules in AVF and PAD tissues. We
found that the staining pattern was different between AVF and PAD tissues. The media and adventitia of AVF and the intima
and media of PAD were intensely stained. Quantitative lipid analysis revealed that the amount of PL was significantly increased
in AVF and PAD. Next, we performed matrix-assisted laser desorption/ionization imaging mass spectroscopy and determined the
characteristic distribution of lysophosphatidylcholine (LPC) and phosphatidylcholine (PC) in AVF. The distribution patterns
of LPC (1-acyl 16:0) and PC (diacyl 16:0/20:4) were consistent with the Oil red O staining images, suggesting that metabolisms
related to LPC (1-acyl 16:0) and PC (diacyl 16:0/20:4) are altered in AVF. 相似文献
80.
Malicka E Sitko R Zawisza B Heimann J Kajewski D Kita A 《Analytical and bioanalytical chemistry》2011,399(9):3285-3292
The paper presents possibilities and difficulties in nondestructive analysis of small multielement single crystals performed
by means of X-ray spectrometry techniques: micro-X-ray fluorescence spectrometry (μ-XRF), energy-dispersive electron probe
microanalysis (ED-EPMA), and X-ray photoelectron spectroscopy (XPS). The capability of the X-ray spectroscopy techniques in
elemental analysis is demonstrated with the single crystals of selenide spinels of the general formula M
x
N
y
Cr
z
Se4 (M+2 and N+3 are, for example, Zn+2, V+3, Ga+3, Cd+2, In+3, and Sb+3). The results of the nondestructive analyses (μ-XRF, ED-EPMA, and XPS) are compared with those obtained by inductively coupled
plasma optical emission spectrometry (ICP-OES) and wavelength-dispersive X-ray spectrometry (WDXRF) following sample digestion.
The present study shows satisfactory agreement between the results of μ-XRF analysis performed using the standardless fundamental
parameter method and the results obtained with the WDXRF and ICP-OES analyses. If the measured single crystal is precisely
positioned, the difference between μ-XRF and wet analysis (WDXRF and ICP-OES) does not exceed 5% rel. The reliable results
of ED-EPMA can be obtained only if the measured area is sufficiently large, i.e., of 200 × 300 μm. Even if this condition
is fulfilled, the relative difference between the ED-EPMA and the wet analysis may reach 10% rel. In case of the XPS analysis,
the accuracy of results depends on the proper preparation of the sample surface. It should be free of contamination that can
be obtained by scraping in situ in ultrahigh vacuum. The ion etching, commonly used for cleaning the surface, leads to preferential
sputtering; therefore, the reliable results cannot be obtained. 相似文献