全文获取类型
收费全文 | 2999篇 |
免费 | 126篇 |
国内免费 | 3篇 |
出版年
2022年 | 10篇 |
2021年 | 24篇 |
2020年 | 4篇 |
2019年 | 18篇 |
2018年 | 24篇 |
2017年 | 19篇 |
2016年 | 45篇 |
2015年 | 63篇 |
2014年 | 96篇 |
2013年 | 184篇 |
2012年 | 181篇 |
2011年 | 169篇 |
2010年 | 100篇 |
2009年 | 116篇 |
2008年 | 179篇 |
2007年 | 185篇 |
2006年 | 165篇 |
2005年 | 172篇 |
2004年 | 193篇 |
2003年 | 199篇 |
2002年 | 166篇 |
2001年 | 38篇 |
2000年 | 32篇 |
1999年 | 43篇 |
1998年 | 61篇 |
1997年 | 40篇 |
1996年 | 38篇 |
1995年 | 49篇 |
1994年 | 39篇 |
1993年 | 40篇 |
1992年 | 27篇 |
1991年 | 32篇 |
1990年 | 32篇 |
1989年 | 26篇 |
1988年 | 23篇 |
1987年 | 26篇 |
1986年 | 15篇 |
1985年 | 19篇 |
1984年 | 36篇 |
1983年 | 17篇 |
1982年 | 36篇 |
1981年 | 23篇 |
1980年 | 27篇 |
1979年 | 15篇 |
1978年 | 12篇 |
1977年 | 17篇 |
1976年 | 10篇 |
1975年 | 10篇 |
1973年 | 7篇 |
1971年 | 8篇 |
排序方式: 共有3128条查询结果,搜索用时 31 毫秒
61.
Summary The caudal spinal cord of Eigenmannia virescens is not enclosed in a neural canal of the vertebral column. In fact, a segmented vertebral column with neural and ventral arches is lacking and replaced by a non-segmented baton-like bony structure on which the free spinal cord is located. The baton consists of calcified bone tissue with bone cells. Individual differences exist as far as the length of the rod is concerned. The electromotor neurons of this caudal part of the spinal cord are histochemically acetylcholinesterase-positive. The electrocytes which surround this part of the spinal cord show strong enzymatic actitivity on the posterior innervated face. However, there is also activity on the non-innervated lateral and anterior faces. 相似文献
62.
63.
Yoshihide Yamasaki Osamu Shimamura Akira Kizu Masao Nakagawa Hamao Ijichi 《Life sciences》1982,31(5):471-478
The formaldehyde method was used to examine the interaction of PGE1 with morphine, β-endorphin and Met-enkephalin on rat mast cells by their effects on IgE-mediated 14C-serotonin release. PGE1 (2×10?8?2×10?5 M) caused a dose-related inhibition of the mediator release 1 min after an antigen challenge, and morphine (3×10?7?3×10?5 M) reversed this PGE1 effect dose-dependently and stereospecifically; naloxone (2×10?4 M) antagonized this action of morphine. β-Endorphin (3×10?7?10?5 M) and Met-enkephalin (3×10?6?10?4 M) mimicked this morphine action dose-dependently and were antagonized by naloxone (2×10?4 M). These results suggest that morphine and endorphins modulate immunological mediator release from rat mast cells through opioid receptors. 相似文献
64.
Summary Preadult viability and developmental time at four different temperatures, heat and cold resistances of adult flies, effects of acclimatization on heat resistance, and preferred temperature of adult flies were compared between two species of Drosophila, D. virilis and D. immigrans. Four Japanese local populations were surveyed for each species. As compared with immigrans, virilis was higher in its ability to tolerate both heat and cold stresses and was viable over a broader temperature range. On the other hand, immigrans revealed a superior ability to acclimatize and a rigid preference for gradually changing thermal environment. Differences between geographical populations are remarkable for heat tolerance in virilis and cold tolerance in immigrans. In conclusion, thermal adaptation of virilis seems to be based on the high tolerance to extreme temperatures and that of immigrans mainly on the behavioural preference for viable temperatures. 相似文献
65.
66.
Shigeru Itoh 《BBA》1979,548(3):596-607
Electrostatic characteristics of the membrane surface in the vicinity of P-700 were estimated by analyzing the salt and detergent effects on its reaction rate with ionic reagents using the Gouy-Chapman diffuse double layer theory in various preparations of chloroplasts.
Upon disruption of thylakoid membranes by sonic treatment or by treatment with digitonin, the reaction rate markedly increased, while the estimated surface charge density became smaller.
It was concluded that the membrane surface which determines the reaction rate between P-700 and the ionic reagents changed as the disruption of thylakoid structure. The outer thylakoid surface had more negative charges than the inner one.
Changes in the electrical potential profile across the thylakoid membrane during the illumination were also discussed from these results. 相似文献
67.
Ethylene production by axial and cotyledonary tissues excised from Xanthium pennsylvanicum Wallr. seeds was markedly (up to 5-fold) stimulated by the D-isomers of phenylalanine, valine, leucine, threonine, methionine and eithionine while the L-isomers caused no such effect. Responsiveness of these seed tissues to D-methionine appeared soon after the beginning of imbibition, reached a maximum after 6–12 and 12–24 h for the axial and cotyledonary tissues, respectively, and then decreased sharply. D-Phenylalanine and D-methionine also stimulated ethylene production in seed tissues of X. canadense Mill. and in cotyledonary segments from seeds of Helianthus annuus L., Cucurbita moschata Duch. and Vigna radiata (L.) Wilczek. The endogeneous ethylene production and the D-amino-acid-stimulated ethylene production by the seed segments was strongly inhibited by aminoethoxyvinyl glycine, a potent inhibitor of ethylene synthesis from L-methionine. 相似文献
68.
Shigeru Taketani Rikio Tokunaga 《Biochemical and biophysical research communications》1980,92(4):1343-1347
When rat liver mitochondria labeled with [59Fe]heme were incubated with microsomes in the presence of cytosol, about 16 % of the heme in mitochondria was transported to microsomes during a 1 hr-incubation period. In the absence of cytosol, little heme was transported. DEAE-Sephadex column chromatography of the cytosol partially purified by pH 5.1 treatment and ammonium sulfate precipitation (45–65%) revealed that there were at least two proteins with a releasing activity from mitochondria via heme transport. 相似文献
69.
Summary Comparative restriction cleavage analysis of the genomes of bacteriophage P7, of several recombinant phages between P7 and P1, and of bacteriophage P1 allowed to draw PstI, BglII, BamHI and HindIII cleavage maps of all genomes studied. The data obtained complement Yun and Vapnek's (1977) conclusions with regard to areas of major nonhomology based on electron microscopical heteroduplex analysis and they identify several additional minor differences between P1 and P7. The use of hybrid phage strains allowed to locate the genes for particular functions on the physical genome map.Abbreviations Cm
chloramphenicol
- Ap
ampicillin
- bp
base pairs
- kb
kilo-base pairs 相似文献
70.
Jean T. Walker Shigeru Iida Donald H. Walker Jr. 《Molecular & general genetics : MGG》1979,167(3):341-344
Summary Use of restriction endonucleases BglII, EcoRI, BamHI, and HindIII, has established that in small-headed (PIS) virions of coliphage P1, as a population, the entire genome found in big-headed (P1B) virions is represented. In addition, the origin and direction of DNA packaging are identical in P1S and P1B virions. 相似文献