全文获取类型
收费全文 | 2505篇 |
免费 | 53篇 |
国内免费 | 3篇 |
专业分类
化学 | 1903篇 |
晶体学 | 23篇 |
力学 | 46篇 |
数学 | 105篇 |
物理学 | 484篇 |
出版年
2022年 | 11篇 |
2021年 | 16篇 |
2020年 | 14篇 |
2019年 | 23篇 |
2018年 | 22篇 |
2017年 | 19篇 |
2016年 | 29篇 |
2015年 | 27篇 |
2014年 | 34篇 |
2013年 | 101篇 |
2012年 | 115篇 |
2011年 | 128篇 |
2010年 | 72篇 |
2009年 | 77篇 |
2008年 | 128篇 |
2007年 | 135篇 |
2006年 | 158篇 |
2005年 | 141篇 |
2004年 | 133篇 |
2003年 | 118篇 |
2002年 | 95篇 |
2001年 | 62篇 |
2000年 | 62篇 |
1999年 | 41篇 |
1998年 | 35篇 |
1997年 | 47篇 |
1996年 | 36篇 |
1995年 | 31篇 |
1994年 | 28篇 |
1993年 | 32篇 |
1992年 | 47篇 |
1991年 | 26篇 |
1990年 | 24篇 |
1989年 | 20篇 |
1988年 | 39篇 |
1987年 | 32篇 |
1986年 | 33篇 |
1985年 | 49篇 |
1984年 | 41篇 |
1983年 | 17篇 |
1982年 | 28篇 |
1981年 | 25篇 |
1980年 | 20篇 |
1979年 | 33篇 |
1978年 | 20篇 |
1977年 | 18篇 |
1976年 | 12篇 |
1975年 | 18篇 |
1974年 | 20篇 |
1973年 | 13篇 |
排序方式: 共有2561条查询结果,搜索用时 31 毫秒
101.
102.
Hideki Omichi Jiro Okamoto 《Journal of polymer science. Part A, Polymer chemistry》1982,20(2):521-528
Methyl α,β,β-trifluoroacrylate (MTFA) was grafted onto polymer films with the multiple grafting technique initiated by α-rays: the yields were similar to those of the single-step grafting procedure with any irradiation dose. Grafted polymer obtained in the single-step experiments were distributed mainly near the film surface, whereas graft polymer from the multiple grafting experiments were distributed uniformly in the film at graft yields greater than 20%. The electric resistance of the hydrolyzed multiple graft polymer film in a 2N NaOH solution was much lower than that of one-step graft film at the same graft yield. 相似文献
103.
Ihori Y Yamashita Y Ishitani H Kobayashi S 《Journal of the American Chemical Society》2005,127(44):15528-15535
Catalytic enantioselective Mannich-type reactions of silicon enolates with aldimines were investigated using chiral zirconium catalysts prepared from Zr(O(t)Bu)(4), N-methylimidazole, and newly designed multidentate BINOL derivatives. These new multidentate BINOL ligands were designed on the basis of an assumed transition state structure of a chiral zirconium catalyst derived from two molecules of (R)-6,6'-Br(2)-BINOL. Not only tetradentate BINOL 4 but also tridentate BINOL derivatives were found to be effective, and high enantioselectivities were attained. In a structural study of the most effective zirconium complex prepared from tridentate ligand 6e, several NMR experiments and DFT calculations were carried out. Consequently, the structure of an active catalyst and plausible mechanism of asymmetric induction were elucidated. 相似文献
104.
Relative bone mineral content in the lumbar spine was measured by phantom B-MAs with the apparatus of computerized tomography in order to study the relationships between bone mineral content with age and parathyroid hormone in sera of randomized out- and in-patients and the hemodialysis patients. There exists a significant difference between male and female in the loss of bone mineral content of three groups. 相似文献
105.
F Oka H Sagawa K Yabe A Okuyama M Tachibana T Noge K Torizumi S Okamoto M Yasui T Tuda 《Radioisotopes》1988,37(10):572-575
The patients receiving maintenance hemodialysis were divided into two groups in the absence and the presence of bone pain and investigated the markers of bone pain in these patients. These results suggested that the duration of receiving hemodialysis, serum concentrations of alkaline phosphatase, osteocalcin and parathyroid hormone became to be the markers of bone pain. 相似文献
106.
Photophysical properties of porphyrin tapes 总被引:1,自引:0,他引:1
Cho HS Jeong DH Cho S Kim D Matsuzaki Y Tanaka K Tsuda A Osuka A 《Journal of the American Chemical Society》2002,124(49):14642-14654
The novel fused Zn(II)porphyrin arrays (Tn, porphyrin tapes) in which the porphyrin macrocycles are triply linked at meso-meso, beta-beta, beta-beta positions have been investigated by steady-state and time-resolved spectroscopic measurements along with theoretical MO calculations. The absorption spectra of the porphyrin tapes show a systematic downshift to the IR region as the number of porphyrin pigments increases in the arrays. The fused porphyrin arrays exhibit a rapid formation of the lowest excited states (for T2, approximately 500 fs) via fast internal conversion processes upon photoexcitation at 400 nm (Soret bands), which is much faster than the internal conversion process of approximately 1.2 ps observed for a monomeric Zn(II)porphyrin. The relaxation dynamics of the lowest excited states of the porphyrin tapes were accelerated from approximately 4.5 ps for the T2 dimer to approximately 0.3 ps for the T6 hexamer as the number of porphyrin units increases, being explained well by the energy gap law. The overall photophysical properties of the porphyrin tapes were observed to be in a sharp contrast to those of the orthogonal porphyrin arrays. The PPP-SCI calculated charge-transfer probability indicates that the lowest excited state of the porphyrin tapes (Tn) resembles a Wannier-type exciton closely, whereas the lowest excited state of the directly linked porphyrin arrays can be considered as a Frenkel-type exciton. Conclusively, these unique photophysical properties of the porphyrin tapes have aroused much interest in the fundamental photophysics of large flat organic molecules as well as in the possible applications as electric wires, IR sensors, and nonlinear optical materials. 相似文献
107.
Summary The retention and selectivity of flavonoids (baicalin, baicalein, wogonin, oroxylin A) inScutellariae radix have been studies by high-performance thin-layer chromatography on phenyldimethylethoxysilane-treated silica plates. The silica plates treated with phenyl groups were used for physical and chemical analysis. From elemental carbon analysis, the maximum number of bonded phenyl surface groups per gram was calculated to be 0.467×1021 (Oginal silica plate: Merck Art. 15109, Silica gel 100 F254). With methanol-1/15 M phosphate buffer (pH 6.2) mixtures as mobile phase, baicalin, baicalein, wogonin, and oroxylin A inScutellariae radix were separated. It has been shown that phenyl-treated plates are more suitable for selective separation of baicalin, baicalein, wogonin, and oroxylin A than octadecyl-treated plates. 相似文献
108.
N Teno K Wanaka Y Okada Y Tsuda U Okamoto A Hijikata-Okunomiya T Naito S Okamoto 《Chemical & pharmaceutical bulletin》1991,39(11):2930-2936
Specific plasma kallikrein inhibitors were designed and synthesized and their structure-activity relationship was studied. trans-4-Aminomethylcyclohexanecarbonyl (Tra)-lysyl-4-ethoxycarbonylanilide inhibited plasma kallikrein and plasmin with IC50 values of 23 and 210 microM, respectively, indicating that this compound is fairly specific to plasma kallikrein. Tra-arginyl-4-ethoxycarbonylanilide inhibited plasma kallikrein and plasmin with IC50 values of 16 and 480 microM, respectively. Tra-homoarginyl-4-carboxyanilide inhibited plasma kallikrein and plasmin with IC50 values of 14 microM and 1 mM, respectively. Finally, Tra-Arg(Mts)-4-acetylanilide (ACA) exhibited potent and selective inhibitory activity against plasma kallikrein (IC50 value for plasma kallikrein: 2 microM and for plasmin: 42 microM). 相似文献
109.
K Maruyama T Yuda A Okamoto C Ishikura S Kojima M Iwatsuru 《Chemical & pharmaceutical bulletin》1991,39(6):1620-1622
The effect in mice of the molecular weight of polyethyleneglycol on prolonging the circulation time of large unilamellar liposomes (LUVs) was examined using four different distearoyl N-(monomethoxy polyethyleneglycol succinyl) phosphatidylethanolamines (DSPE-PEGs). The molecular weights tested were 1000, 2000, 5000 and 12000. Incorporation of 6 mol% of DSPE-PEG in LUV composed of distearoylphosphatidylcholine (DSPC) / cholesterol (CH) (1:1 in molar ratio) increased the blood circulation half-life significantly more than those without DSPE-PEG derivatives. DSPE-PEGs with molecular weights of 1000 and 2000 prolonged the circulation time of liposomes more than other DSPE-PEGs with higher molecular weights, such as 5000 and 12000. Their effects are also higher than ganglioside GM1, a well described glycolipid with this effect. DSPC/CH LUV-incorporated DSPE-PEG with a molecular weight of 2000 displayed a high concentration in the blood, approximately 40% of the dose, 6 h after the injection. 相似文献
110.
The clinical significance of osteocalcin in sera of bone tumors were measured in sera of various kinds of bone tumors. The levels of osteocalcin were higher in bone tumors than those in normal subjects. Serum osteocalcin levels in hypercalcemic groups of bone metastasis and myeloma showed a remarkable increase in a parallelism with serum ALP and LDH levels. These results suggested to be directly or indirectly activated on osteoblast by bone tumors and to be synthesized osteocalcin in osteoblast. 相似文献