全文获取类型
收费全文 | 1858篇 |
免费 | 84篇 |
出版年
2021年 | 14篇 |
2020年 | 7篇 |
2019年 | 10篇 |
2018年 | 11篇 |
2017年 | 19篇 |
2016年 | 25篇 |
2015年 | 37篇 |
2014年 | 29篇 |
2013年 | 153篇 |
2012年 | 87篇 |
2011年 | 86篇 |
2010年 | 51篇 |
2009年 | 60篇 |
2008年 | 96篇 |
2007年 | 98篇 |
2006年 | 102篇 |
2005年 | 97篇 |
2004年 | 108篇 |
2003年 | 88篇 |
2002年 | 81篇 |
2001年 | 40篇 |
2000年 | 45篇 |
1999年 | 42篇 |
1998年 | 28篇 |
1997年 | 29篇 |
1996年 | 27篇 |
1995年 | 23篇 |
1994年 | 20篇 |
1993年 | 20篇 |
1992年 | 11篇 |
1991年 | 25篇 |
1990年 | 25篇 |
1989年 | 26篇 |
1988年 | 30篇 |
1987年 | 23篇 |
1986年 | 21篇 |
1985年 | 26篇 |
1984年 | 32篇 |
1983年 | 18篇 |
1982年 | 20篇 |
1981年 | 16篇 |
1980年 | 18篇 |
1979年 | 19篇 |
1978年 | 11篇 |
1977年 | 12篇 |
1976年 | 7篇 |
1975年 | 9篇 |
1974年 | 8篇 |
1973年 | 9篇 |
1968年 | 10篇 |
排序方式: 共有1942条查询结果,搜索用时 15 毫秒
81.
1. The properties of 3,5-di-tert-butyl-4-hydroxybenzylidenemalononitrile (SF 6847) were studied chemically and spectroscopically. Two molecular species of SF6847 were identified: the undissociated form (SFH; ?363, 10 mM?1) and the dissociated form (SF?; ?454, 35 mM?1). The pKa value of the molecule was determined to be 6.9.2. On the basis of these properties the interactions of SF6847 with liposomes and valinomycin · K+ were studied. The partition constants of SFH (Knp and SF? (K?p) to liposomes were determined separately; Knp was 56 mM?1 and was independent of the pH of the medium, whereas K?p dependend greatly on the pH, being 1.2 mM?1 at pH 7.0 and 2.9 mM?1 at pH 8.0. Using these values, the partition constant of total SF6847 (Kp) was calculated and found to be essentially the same as that calculated from the kinetics of proton uptake. It was concluded that the amount of SF? bound to liposomes is rate limiting for proton uptake.3. The effects of membrane potential on partition constants were studied. The K?p decreased greatly upon generation of a membrane potential negative inside the liposomes but increased upon generation of a membrane potential positive inside the liposomes.4. The interaction of SF6847 with valinomycin in aqueous solution and in liposomes was demonstrated only in the presence of potassium ion. Potassium ion could not be replaced by sodium ion. Evidence was obtained for the formation of the ternary complex valinomycin · K+ · SF? in liposomes and in hexane. It was concluded that SF? became more soluble in the liposomal membranes on formation of this ternary complex. All these results support our proposed mechanism for the proton uptake cycle (Yamaguchi, A. and Anraku, Y. (1978) Biochim. Biophys. Acta 501, 136–149). 相似文献
82.
M Ohashi T Taguchi S Ikegami 《Biochemical and biophysical research communications》1978,82(4):1084-1090
Aphidicolin, a tetracyclic diterpenoid, is known to be antiviral and to inhibit the incorporation of thymidine into DNA of cultured human embryonic lung cells. We examined effects of the compound on the activity of several DNA polymerases obtained from subcellular fractions of rat liver. Aphidicolin at a concentration of 15 μg/ml caused a 85% reduction in level of the activity of crude and partially purified DNA polymerases from the cytosol. However, aphidicolin even at a concentration of 75 μg/ml failed to affect the activity of crude and partially purified DNA polymerases from nuclear and mitochondrial fractions. 相似文献
83.
The specificity of sweet-potato beta-amylase in the vicinity of the phosphate ester groups was studied by determining the structures of the phosphorylated oligosaccharides (alpha-phosphodextrin and beta-limit-alpha-phosphodextrin) formed by its action on potato starch. The beta-limit-alpha-phosphodextrin was separated by chromatography on Dowex-1 (HCOO?) resin into three fractions that were distinguishable by the d.p. and by the ratio of d-glucose 6-phosphate residues to total organic phosphate. Each fraction contained linear molecules having one phosphate ester group that was not located at the reducing or non-reducing terminals. The smallest phosphodextrin was 62-phosphorylmaltotriose. It was deduced that beta-amylase hydrolysed (1→4)-α-d linkages from the non-reducing end until one or two d-glucosyl residues remained attached to the phosphorylated residue, depending on whether there was originally an odd or even number of glucosyl residues on the non-reducing side of the phosphorylated residue. 相似文献
84.
85.
Shiro Ohki Yoshimasa Nishigaki Katsuhiro Imaki Masayasu Kurono Fumio Hirata Toshio Hanyu Nobuhiko Nakazawa 《Prostaglandins & other lipid mediators》1976,12(2):181-186
Radioimmunoassay technique for measuring 5α,7α-dihydroxy-11-keto-tetranorprosta-1,16-dioic acid, the main urinary metabolite of PGF1α and PGF2α (PGF2α-MUM), was further improved.It was postulated based on some experimental data that the PGF2α-MUM exists in the urine mostly as dioic acid form, not as δ-lactone formThe daily excretion of PGF2α-MUM in men ranged from 14.43 μg to 36.14 μg and in women from 5.21 μg to 14.25 μg. 相似文献
86.
Keishi Abe Yoichi Otsuka Minoru Yasujima Satoru Ciba Masahide Seino Nobuo Irokawa Kaoru Yoshinaga Fumio Hirata Shiro Ohki Nobuhiko Nakazawa Toshio Hanyu 《Prostaglandins & other lipid mediators》1976,12(5):843-848
The excretion rates of main urinary metabolite of PG F2α were measured radioimmunologically in 4 healthy persons and in 13 essential hypertensives. The resting values were 9.3±0.73 in the former and 10.4±2.17 ng/min in the latter. There was no significant differences between them. The excretion of the metabolite decresed prominently after the administration of furosemide. The percent decrease was 57% in healthy persons and 70% in essential hypertension. The percent result supports that furosemide inhibit the catabolism of PG F2α. 相似文献
87.
Shiro Kobayashi 《Population Ecology》1976,17(2):243-254
Summary A mathematical model of the species-area relation is described for a group of limited species. This model is a modification
of that proposed earlier (Kobayashi, 1975), being assumed that the limited species are expected to occur in a habitat under consideration. The model equation
gives a sigmoid species-log area curve implying that few rare species are found in a group of species. The good agreement
between observation and this model is exemplified with the data of plant and arthropod communities. The implication of parameters
involved are examined in connection with those of the preceding model, and the underlying ecology of the model is discussed.
Contribution from the Laboratory of Applied Zoology, Yamagata University, No. 83. 相似文献
88.
Removal of the ganglion or severance of the nerve cords at the thorax in mature larvae of the swallowtail, Papilio xuthus, induced systemic distension of the body by swallowing excess air. Such a distension, however, was never induced by simultaneous extirpation of the brain, suboesophageal ganglion, or frontal ganglion, or by severance of the recurrent nerve. Removal of an abdominal ganglion induced distension of the posterior part of the body accompanied by shrinkage of the anterior part. The latter phenomenon appears to be induced by a different mechanism from that of systemic distension. 相似文献
89.
Light-induced charge separation in Photosystem I at low temperature is not influenced by vitamin K-1 总被引:2,自引:0,他引:2
The photoreduction of iron-sulfur centers was studied at low temperature in Photosystem I particles from spinach and the cyanobacterium Synechocystis 6803, which contain various amounts of vitamin K-1 (recently tentatively identified as the acceptor A1). The irreversible charge separation that was progressively induced at low temperature between P-700 and FA (or FB) by successive laser flashes was studied at 15 K. Its maximum amount after a large number of flashes was shown to be fairly independent of the number (0, 1 or 2) of vitamins K-1 per reaction center. Moreover, the first flash yield of this charge separation was diminished by only about 50% when vitamin K-1 was completely absent from the particles by comparison with particles containing one or two vitamin K-1 per reaction center. When FA and FB were prereduced, the iron-sulfur center FX was also reversibly photoreduced at 9 K in the absence of vitamin K-1. The implications of these results for the electron pathways of Photosystem I are discussed and it is proposed that a direct electron transfer from A0- to the iron-sulfur centers is highly efficient at low temperature. 相似文献
90.