全文获取类型
收费全文 | 2487篇 |
免费 | 72篇 |
国内免费 | 15篇 |
专业分类
化学 | 2010篇 |
晶体学 | 39篇 |
力学 | 29篇 |
数学 | 122篇 |
物理学 | 374篇 |
出版年
2022年 | 11篇 |
2021年 | 19篇 |
2020年 | 34篇 |
2019年 | 31篇 |
2018年 | 25篇 |
2017年 | 11篇 |
2016年 | 54篇 |
2015年 | 48篇 |
2014年 | 44篇 |
2013年 | 107篇 |
2012年 | 87篇 |
2011年 | 143篇 |
2010年 | 75篇 |
2009年 | 66篇 |
2008年 | 130篇 |
2007年 | 133篇 |
2006年 | 132篇 |
2005年 | 124篇 |
2004年 | 132篇 |
2003年 | 118篇 |
2002年 | 130篇 |
2001年 | 69篇 |
2000年 | 47篇 |
1999年 | 40篇 |
1998年 | 34篇 |
1997年 | 30篇 |
1996年 | 39篇 |
1995年 | 21篇 |
1994年 | 26篇 |
1993年 | 33篇 |
1992年 | 24篇 |
1991年 | 29篇 |
1990年 | 26篇 |
1989年 | 19篇 |
1988年 | 24篇 |
1987年 | 29篇 |
1986年 | 17篇 |
1985年 | 51篇 |
1984年 | 43篇 |
1983年 | 27篇 |
1982年 | 34篇 |
1981年 | 41篇 |
1980年 | 31篇 |
1979年 | 32篇 |
1978年 | 20篇 |
1977年 | 16篇 |
1976年 | 17篇 |
1975年 | 20篇 |
1974年 | 15篇 |
1973年 | 13篇 |
排序方式: 共有2574条查询结果,搜索用时 62 毫秒
41.
A Kamizono N Inotsume K Miyamoto K Ueda T Miyakawa H Arimoto M Nakano 《Journal of chromatography. A》1991,567(1):113-120
A sensitive and selective method has been developed for the determination of sultopride and tiapride in serum using gas chromatography with a surface ionisation detector. No interfering peaks from endogenous substances were observed. The method showed good reproducibility and accuracy, and the standard curve was linear up to 2 micrograms/ml with a correlation coefficient of 0.999. This method is applicable to pharmacokinetic studies and therapeutic drug monitoring of sultopride and tiapride. 相似文献
42.
Toyohide Takeuchi Mototada Watanabe Tadashi Hamanaka Hiroki Haraguchi Daido Ishii 《Journal of separation science》1990,13(9):606-609
Capillary columns of 0.3-0.5 mm i.d. packed with 3- to 30-μm silica-based stationary phases for liquid chromatography were used for gas chromatographic separation of hydrocarbons. Column efficiencies were evaluated for various commercially available packing material. The best column efficiency was achieved with 5-μm octadecyl group bonded silica gel, the surface of which was coated with a poly (dimethylsiloxane) film. The 30-cm column produced 11,000 theoretical plates. 相似文献
43.
Synthesis and analgesic activity of novel heterocycles, [1]benzothiopyrano[3,4-b]pyrrole derivatives
M Hori T Kataoka H Shimizu E Imai N Iwata N Kawamura M Kurono K Nakano M Kido 《Chemical & pharmaceutical bulletin》1989,37(5):1282-1286
In order to develop analgesic compounds possessing a sulfur atom in the alicyclic ring, novel cis-fused heterocycles, [1]benzothiopyrano[3,4-b]pyrrole derivatives (II) were synthesized via a unique cyclization reaction starting from 4-(4-methoxyphenylthio)-2-butanone (1) or 6-methoxy-3,4-dihydro-2H-1-benzothiopyran-4-one (7). The analgesic effects of benzothiopyranopyrroles (16, 18) were measured by means of the writhing test. The phenolic derivative 18 completely inhibited the appearance of writhing at the dose of 50 mg/kg, but the methoxy derivative 16 had no analgesic effect. 相似文献
44.
I Kanamori S Nakano M Hurukawa Y Okumura C Higuchi M Yanase M Onogi 《Radioisotopes》1988,37(8):460-463
From the clinical use of RIA-gnost trypsin kit, the following results were obtained. 1. Standard curve showed a steep and good curve was shown. 2. Incubation: The condition for the first incubation was set at the room temperature for 10-24 hours and that for the second incubation at the room temperature for 3-5 hours. With these settings, satisfactory results were obtained. 3. Reproducibility and recovery: The C.V. of the reproducibility and the recovery were considered superior, and the values were below 10% and +/- 3%, respectively. 4. Correlation between trypsin and serum elestase-1: An excellent positive correlation (coefficient of correlation r = 0.889) was shown. 5. Serum trypsin concentration of normal and pancreatic diseases: The normal range was from 100 to 500 ng/ml. Acute pancreatitis rose obviously. Diabetes mellitus and chronic pancreatitis was below 500 ng/ml and the pancreatic cancer showed a tendency to scatter in the range of 50-1,250 ng/ml. The above results indicated that serum trypsin can be easily measured with high precision by using this method. Thus the method is considered useful for the diagnosis of pancreatic diseases. 相似文献
45.
Hiizu Iwamura Tadashi Sugawara Yuzo Kawada Kazuo Tori Ryonosuke Muneyuki Ryoji Noyori 《Tetrahedron letters》1979,20(36):3449-3452
Natural-abundance 17O NMR spectra have been measured for twenty one oxiranes. Their chemical shifts covering a 100 ppm range were interpreted in terms of the paramagnetic β- and diamagnetic γ-effects. In addition, through-space orbital interaction between the ethylenic π and the Walsh orbitals of the oxirane ring was suggested by a lowfield shift in norbornadiene -oxide. 相似文献
46.
Matsuo G Kawamura K Hori N Matsukura H Nakata T 《Journal of the American Chemical Society》2004,126(44):14374-14376
Brevetoxin-B (BTX-B), produced by the red tide organism, Gymnodium breve Davis, is the first member of marine polycyclic ethers to be structurally elucidated and one of the most potent neurotoxins. The structural feature is a trans-fused polycyclic ether ring system with 23 stereocenters. Its unique, complex structure and potent biological activity have attracted the attention of synthetic organic chemists. Total synthesis of BTX-B has been accomplished via the coupling of the ABCDEFG and IJK-ring segments, each ether ring of which was stereoselectively and efficiently constructed on the basis of SmI2-induced intramolecular cyclization, 6-endo-cyclization of hydroxy epoxide, ring-closing olefin metathesis, and SmI2-induced intramolecular Reformatsky-type reaction. Several kinds of double reactions at the left and right sides were efficiently used through the synthesis. 相似文献
47.
Tadashi Kawai Masako Komaki Tomokazu Iyoda 《Journal of molecular catalysis. A, Chemical》2002,190(1-2):45-53
Metathesis of 2-vinyl aromatic heterocycles such as furan, thiophene, pyrrole and pyridine in the presence of a molybdenum-based Schrock catalyst has been investigated from a synthetic point of view. The self-metathesis of 2-vinyl aromatic heterocycles was not successful. However, in cross-metathesis of thiophene, furan and styrene with 1-octene, the cross-metathesis product, heterodimer, was readily obtained selectively, together with only small amounts of the two corresponding self-metathesis products. The origin of the surprisingly high selectivity of heterodimer formation was elucidated through metallacyclobutane intermediate mechanism, observations of carbenes by in situ 1H NMR, and reaction products. 相似文献
48.
I Kanamori S Nakano F Tanaka M Hurukawa M Yanase Y Shinozuka C Higuchi Y Okumura 《Radioisotopes》1988,37(6):347-350
An IgE RIA kit (Sandwich method; Dainabott), is used to obtain the following results. (1) Standard curve: Since the range of reproduction rate show 3.16-7.07% (C.V.), the curve become steep. (2) Incubations under controlled situation: Both of the incubations are controlled at 15-30 degrees C for 2 h. (3) Reproducibility test: Coefficients of variation (C.V.) of intra-assay and inter-assay variation are 2.32-3.94% and 2.92-3.92% respectively. (4) Recovery test: A result of the recovery test range between 100.1-101.7%. (5) Dilution test: Multiple dilution effects are observed. (6) Average counts of the serum IgE for the controlled and diseased groups: The average counts of the serum IgE for the controlled group, atopic diseased group, allergic rhinitis group and allergic bronchial asthma are 144.9 +/- 183.2 IU/ml, 1,099.0 +/- 2,782.4 IU/ml, 1,150.9 +/- 2,063.3 IU/ml and 600.7 +/- 686.4 IU/ml respectively. The value of the diseased groups have tendency to show higher averages than the controlled group. Since the controlled and diseased groups show wide distributions of the serum IgE level, there is no significant difference of two variations. However the diseased groups have tendency to show higher ratio of the serum IgE level in blood than the controlled groups. These basic researches are quite meaningful, because they are able to apply for a supplemental diagnosis of the atopic and parasitic disease. 相似文献
49.
Kawasaki H Sasaki A Kawashima T Sasaki S Kakehashi R Yamashita I Fukada K Kato T Maeda H 《Langmuir : the ACS journal of surfaces and colloids》2005,21(13):5731-5737
Lyotropic phase behavior of the nonionic and the half-ionized oleyldimethylamine oxide (OlDMAO)/water systems was investigated using polarized light microscopy, small-angle X-ray diffraction, and differential scanning calorimetry. Nonionic OlDMAO formed isotropic micellar solution, nematic, hexagonal, cubic, and lamellar liquid crystalline phases as the surfactant concentration increased. In contrast, half-ionized OlDMAO (i.e., 1:1 mixture of the nonionic and the protonated species) had a greater tendency to form bilayer structures, and the phase diagram became quite similar to those of double-chained ionic surfactants rather than single-chained ones, despite the introduction of positive charges to the nonionic one. The preference of the bilayer structures in the half-ionized OlDMAO was interpreted in terms of the dimers stabilized by the hydrogen bond between the nonionic and protonated species. For alkyldimethylamine oxides with a saturated hydrocarbon chain (CnDMAO, chain length: n = 14, 16, and 18), the phase sequence of lyotropic liquid crystals was hardly affected by the protonation, but an elongation of the cylinders of the hexagonal phase was observed for the half-ionized C14DMAO. Consequently, it can be considered that the dominant bilayer formation of the half-ionized OlDMAO is attributed to the combined effect of the hydrogen-bonded dimer formation and the cis-double-bond configuration of the alkyl chain. 相似文献
50.
An introduction of nonlamellar-forming lipids into planar bilayers generates packing stress, which is important for the biological functions of plasma membranes and is a driving force for the lamellar-nonlamellar phase transition. We have investigated the phase behavior of a binary system consisting of egg yolk phosphatidylcholine and monoolein (MO) and the changes in the local orientation order of lipids in a lamellar-bicontinuous cubic phase transition. Small-angle X-ray scattering has revealed that the lamellar-bicontinuous cubic phase transition occurs at an MO molar fraction (X(MO)) between 0.6 and 0.7. These phases were dispersed to form liposomes and cubosomes to monitor the anisotropy of the incorporated fluorescence probe, in which Pluronic F127, used as a dispersion stabilizer of the cubic phase, has been proven not to alter the cubic structure and the location of the probes. Time-resolved fluorescence anisotropy measurements on these dispersions have revealed that the order parameter of the probe in the lamellar phase increases with increasing X(MO), and that it decreases during the transition to the cubic phase. This observation suggests that packing stress generated by the addition of the nonlamellar-forming lipid is released by the phase transition. 相似文献