全文获取类型
收费全文 | 2786篇 |
免费 | 63篇 |
国内免费 | 10篇 |
专业分类
化学 | 2084篇 |
晶体学 | 36篇 |
力学 | 33篇 |
数学 | 189篇 |
物理学 | 517篇 |
出版年
2022年 | 18篇 |
2021年 | 16篇 |
2020年 | 25篇 |
2019年 | 58篇 |
2018年 | 20篇 |
2017年 | 21篇 |
2016年 | 43篇 |
2015年 | 28篇 |
2014年 | 39篇 |
2013年 | 131篇 |
2012年 | 144篇 |
2011年 | 151篇 |
2010年 | 78篇 |
2009年 | 91篇 |
2008年 | 147篇 |
2007年 | 155篇 |
2006年 | 166篇 |
2005年 | 127篇 |
2004年 | 86篇 |
2003年 | 97篇 |
2002年 | 105篇 |
2001年 | 66篇 |
2000年 | 57篇 |
1999年 | 32篇 |
1998年 | 32篇 |
1997年 | 25篇 |
1996年 | 32篇 |
1995年 | 22篇 |
1994年 | 22篇 |
1993年 | 36篇 |
1992年 | 35篇 |
1991年 | 34篇 |
1990年 | 41篇 |
1989年 | 33篇 |
1988年 | 32篇 |
1987年 | 27篇 |
1986年 | 36篇 |
1985年 | 42篇 |
1984年 | 50篇 |
1983年 | 32篇 |
1982年 | 36篇 |
1981年 | 32篇 |
1980年 | 35篇 |
1979年 | 31篇 |
1978年 | 39篇 |
1977年 | 36篇 |
1976年 | 26篇 |
1975年 | 23篇 |
1974年 | 24篇 |
1973年 | 23篇 |
排序方式: 共有2859条查询结果,搜索用时 15 毫秒
21.
[reaction: see text] Several functionalized terminal allenes were prepared in moderate to excellent yield by a palladium-catalyzed reaction of chloroprene (2-chloro-1,3-butadiene) with soft nucleophiles. 相似文献
22.
N Shibata T Minouchi Y Hayashi H Shibata T Ono H Shimakawa 《Chemical & pharmaceutical bulletin》1989,37(7):1877-1880
The effects of temperature, hematocrit (Hct), lipid level in plasma and cyclosporin A (CyA) level in whole blood on the concentration of CyA in plasma measured by high-performance liquid chromatography were studied in vitro. With rise in blood storage temperature before cells were removed, the concentration of CyA in plasma was increased in the temperature range between 10 degrees C and 37 degrees C, but was decreased between 4 degrees C and 10 degrees C. With rise in Hct, the concentration of CyA in plasma was decreased, and it was more markedly decreased at the blood storage temperature of 4 degrees C than at 37 degrees C. A lipid supplementation study showed that the concentration of CyA in plasma was increased with rise in plasma triglyceride level and in plasma cholesterol level at the storage temperature of 4 degrees C but not at 37 degrees C. Studies of the effect of CyA concentration in blood on the CyA distribution in blood demonstrated that the cellular/plasma concentration (C/P) ratio at low levels (less than 200 micrograms/ml) of plasma CyA ranged from 4 to 10 and was about 2 times higher than that at higher concentrations at 4 degrees C, but the ratio was relatively constant at 37 degrees C. The saturation capacity of the cellular fraction for CyA showed considerable individual variations, but there was no difference between the capacities at 4 degrees C and 37 degrees C. The separation of plasma after equilibration at 37 degrees C made it possible to avoid the variations in the distribution of CyA in whole blood associated with changes in Hct, lipid level in plasma and CyA level in whole blood, and to obtain a measurement reflecting the physiologically significant concentration of CyA in plasma. 相似文献
23.
24.
The contribution of ionized and unionized species to the overall permeation of weak electrolytes through the skin was investigated to determine the effect of pH in the vehicle on the permeability of indomethacin (IDM), as a model drug, through hairless rat skin. The permeability of IDM through polydimethylsiloxane (silicone) and poly(2-hydroxyethyl methacrylate) (pHEMA) membranes which may reflect lipid and aqueous pathway, respectively, was also measured for comparison. As the pH in the vehicle increased, there was an exponential increase in the skin permeation rate of IDM. The permeation rate of IDM through the silicone membrane was constant independent of pH, whereas that through the pHEMA membrane increased with increasing pH, similar to the skin permeation. The permeability coefficients of ionized and unionized species through the skin estimated using the skin permeation rates and solubilities of IDM at various pHs were 1.50 x 10(-7) and 2.79 x 10(-5) cm/s, respectively. These results indicated that the permeation of ionized species greatly contributed to the total permeation of IDM at higher pH, and that the total permeation rate of IDM was determined by the permeation of unionized species at lower pH. These contributions depend on the pH and pKa values and the ratio of permeability coefficient of each species. It was also confirmed that the skin has at least two kinds of permeation pathways and these two species permeate through a different pathway. 相似文献
25.
Hiromu Hayashi 《Catalysis Surveys from Japan》1999,3(1):43-52
Additive telluromolybdates, MoO3·2TeO2 and MIIO·TeO2·MoO3 (MIITeMoO6; MII = Co, Mn, Zn), converted ethyl lactate selectively to pyruvate in a vaporphase fixedbed flow system at 250–300 °C. A synergy in activity was observed for binary TeO2–MoO3, and crystalline Te2MoO7 was suggested as the active species. The Rietveld analysis of powder XRD patterns of ternary CoTeMoO6 revealed the layer structure quite different from that of the reference Te2MoO7, but tellurium was again located adjacent to molybdenum linked through lattice oxygen. 相似文献
26.
Chiral β-dimethylaminoalkylphosphines were prepared starting with amino acids, (S)-alanine, (S)-phenylalanine, (R)-phenylglycine, (S)-valine, and (R)-tert-leucine. The chiral phosphines were found to be highly efficient ligands for a nickel catalyzed asymmetric Grignard cross-coupling reaction (38~94% optical yield). 相似文献
27.
Katsuki Kusakabe Kiyotaka IchikiJun-ichiro Hayashi Hideaki MaedaShigeharu Morooka 《Journal of membrane science》1996
Silica-polyimide microcomposite membranes were prepared on γ-alumina-coated α-alumina support tubes, and their gas permeation properties were evaluated with He, N2 and CO2. Smoothing of the substrate surface and hybridization of silica and polyamic acid were both effective to form defect-free thin composite membranes. The CO2 permeance of a membrane with a silica content of 68 wt% was one order of magnitude higher than that of a polyimide membrane having the same thickness. The permselectivity of CO2 to N2 was 30 at 30°C and 13 at 100°C. Contributions of the silica and polyimide phases to permeance of the composite membrane were analyzed with a two-phase permeation model. The effective thickness of the rate-controlling polyimide phase was less than one-tenth of the total thickness of the silica-polyimide membrane. 相似文献
28.
Y Hashimoto K Nakao N Hama M Mukoyama H Imura M Yasuhara R Hori 《Chemical & pharmaceutical bulletin》1992,40(6):1650-1652
The pharmacokinetics of rat brain natriuretic peptide (rBNP) was compared with that of alpha-rat atrial natriuretic peptide (alpha-rANP) in rats. After intravenous infusion in rats (600 pmol min-1kg-1 for 2 min), the disappearance of plasma rBNP was 4-fold slower than that of alpha-rANP. The estimated mean plasma clearance rates for rBNP and alpha-rANP were 45.9 ml min-1kg-1 and 74.4 ml min-1kg-1, respectively. The affinity of rBNP for the clearance receptor or degradation enzyme was considered to be lower than that of alpha-rANP. 相似文献
29.
[reaction: see text] A formal total synthesis of the sex attractant of male dried bean beetle, methyl (R,E)-(-)-tetradeca-2,4,5-trienoate, was achieved by a new efficient route utilizing the Pd-catalyzed asymmetric allene synthesis reaction. It was found that the atropisomeric biaryl bisphosphine (R)-segphos showed better enantioselectivity than (R)-binap in the Pd-catalyzed reaction for preparing alkyl-substituted axially chiral allenes. 相似文献
30.
Sadao Hayashi Toshihiro Hirai Sonoko Shimomichi Nobumasa Hojo 《Journal of polymer science. Part A, Polymer chemistry》1982,20(3):839-846
Polyiodide formed by complexation of poly(vinyl acetate) (PVAc) with iodine in the presence of iodide has been investigated by chemical analysis and resonance Raman spectrophotometry. When PVAc films were immersed in iodide-iodine aqueous solutions which had different ratios of iodide to iodine concentration [I?]/[I2], the complex films exhibited tremendous variations of swelling degree, despite the relatively small change in the amount of bound iodine. From a quantitative chemical analysis, the composition of polyiodide bound to PVAc was found to be 1.01 ± 0.035 in the molar ratio of iodide to iodine irrespective of the composition of the iodide-iodine aqueous solution ([I?]/[I2] = 2–500). The polyiodide formed in PVAc-iodine-iodide complex was therefore inferred to be (I3?)n. Resonance Raman spectra obtained on PVAc-iodine-iodide complexes were also identical to those of the benzamide-iodine complex, in which the polyiodide consists of (I3?)n, consistent with the result from chemical analysis. 相似文献