全文获取类型
收费全文 | 2568篇 |
免费 | 203篇 |
国内免费 | 2篇 |
出版年
2021年 | 24篇 |
2019年 | 22篇 |
2018年 | 28篇 |
2017年 | 19篇 |
2016年 | 35篇 |
2015年 | 77篇 |
2014年 | 95篇 |
2013年 | 105篇 |
2012年 | 128篇 |
2011年 | 136篇 |
2010年 | 90篇 |
2009年 | 83篇 |
2008年 | 112篇 |
2007年 | 126篇 |
2006年 | 111篇 |
2005年 | 121篇 |
2004年 | 94篇 |
2003年 | 91篇 |
2002年 | 111篇 |
2001年 | 58篇 |
2000年 | 51篇 |
1999年 | 50篇 |
1998年 | 42篇 |
1997年 | 38篇 |
1996年 | 39篇 |
1995年 | 40篇 |
1994年 | 32篇 |
1993年 | 31篇 |
1992年 | 49篇 |
1991年 | 46篇 |
1990年 | 55篇 |
1989年 | 41篇 |
1988年 | 41篇 |
1987年 | 42篇 |
1986年 | 37篇 |
1985年 | 42篇 |
1984年 | 28篇 |
1983年 | 24篇 |
1982年 | 26篇 |
1981年 | 46篇 |
1980年 | 17篇 |
1979年 | 30篇 |
1978年 | 15篇 |
1975年 | 20篇 |
1974年 | 21篇 |
1972年 | 17篇 |
1971年 | 14篇 |
1970年 | 14篇 |
1969年 | 14篇 |
1968年 | 18篇 |
排序方式: 共有2773条查询结果,搜索用时 62 毫秒
41.
Interaction of azide with beef heart mitochondrial ATPase 总被引:1,自引:0,他引:1
This study examined the inhibition of azide as a probe of the magnesium regulation of beef heart mitochondrial ATPase (F1) catalysis. Azide elicited a slow hysteretic effect on both ATP and ITP hydrolysis of F1. This hysteretic effect was shown to be due to the consecutive binding of magnesium and azide, and to be independent of catalytic turnover. The azide binding site was also shown to be separate from the anion binding HCO3- site on F1. The results presented indicate that metal binding is important in the inhibition of the hydrolytic activity and regulation of F1. A model is presented which is consistent with the hysteretic inhibition of F1 by azide, in which there is a slow equilibration between free enzyme and the enzyme-magnesium-azide complex. 相似文献
42.
J. Jakupovic G. Schmeda-hirschmann A. Schuster C. Zdero F. Bohlmann R.M. King H. Robinson J. Pickardt 《Phytochemistry》1985,25(1):145-158
The investigation of nine Vernonia species afforded in addition to known sesquiterpenes 28 new ones. The structures were elucidated by high field 1H NMR spectroscopy and the configurations were determined by NOE difference spectroscopy and, in one case, by X-ray analysis. The results indicated that configurations of several previously reported sesquiterpene lactones have had to be revised. In addition to known types two new ones, the jalcaguaianolides and the vernojalcanolides, are described. Furthermore some unusual reaction products are presented which, in part, led to some natural occurring lactones. 相似文献
43.
Synthesis, transport and localization of a nuclear coded 22-kd heat-shock protein in the chloroplast membranes of peas and Chlamydomonas reinhardi 总被引:17,自引:5,他引:12
下载免费PDF全文
![点击此处可从《The EMBO journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The synthesis, transport and localization of a nuclear coded 22-kd heat-shock protein (HSP) in the chloroplast membranes was studied in pea plants and Chlamydomonas reinhardi. HSPs were detected in both systems by in vivo labeling and in vitro translation of poly(A)+RNA, using the wheat-germ and reticulocyte lysate systems. Heat-shock treatment of pea plants for 2 h at 42-45°C induces the expression of ˜10 nuclear coded proteins, among which several (18 kd, 19 kd, 22 kd) are predominant. A 22-kd protein is synthesized as a 26-kd precursor protein and is localized in a chloroplast membrane fraction in vivo. Following post-translational transport into intact chloroplasts in vitro of the 26-kd precursor, the protein is processed but the resulting 22-kd mature protein is localized in the chloroplast stroma. If, however, the in vitro transport is carried out with chloroplasts from heat-shocked plants, the 22-kd protein is preferentially transported to the chloroplast membrane fraction. In C. reinhardi the synthesis of poly(A)+RNAs coding for several HSPs is progressively and sequentially induced when raising the temperature for 1.5 h from 36°C to 42°C, while that of several preexisting RNAs is reduced. Various pre-existing poly(A)+RNAs endure in the cells at 42°C up to 5 h but are no longer translated in vivo, whereas some poly(A)−RNAs persist and are translated. As in pea, a poly(A)+RNA coded 22-kd HSP is localized in the chloroplast membranes in vivo, although it is translated as a 22-kd protein in vitro. The in vitro translated protein is not transported in isolated pea chloroplast which, however, processes and transports other nuclear coded chloroplast proteins of Chlamydomonas. The poly(A)+RNA coding for the 22-kd HSP appears after 1 h at 36°C. Its synthesis increases with the temperature of incubation up to 42°C, although it decreases after ˜2 h of heat treatment and the already synthesized RNA is rapidly degraded. The degradation is faster upon return of the cells to 26°C. None of the heat-induced proteins is identical to the light-inducible proteins of the chloroplast membranes. 相似文献
44.
DNA methylation of viruses infecting a eukaryotic Chlorella-like green alga. 总被引:15,自引:6,他引:9
下载免费PDF全文
![点击此处可从《Nucleic acids research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
J L Van Etten A M Schuster L Girton D E Burbank D Swinton S Hattman 《Nucleic acids research》1985,13(10):3471-3478
The genomic DNAs of the eukaryotic Chlorella-like green alga, strain NC64A, and eleven of its viruses all contain significant levels of 5-methyldeoxycytidine. In addition, the host DNA as well as six of the viral DNAs also contain N6-methyldeoxyadenosine. At least some of the methylated bases in the host reside in different base sequences than the methylated bases in the viruses as shown by differential susceptibility to restriction endonuclease enzymes. This suggests that the viruses encode for DNA methyltransferases with sequence specificities different from that of the host enzyme. 相似文献
45.
Gerhard Horstmann Renate Lüllmann-Rauch 《Virchows Archiv. B, Cell pathology including molecular pathology》1985,48(1):33-45
The purpose of this study was to examine whether the aortic and mitral valves of rats are involved in the mucopolysaccharidosis-like disorder induced by tilorone. Rats were treated with large doses of the drug for periods of 1-21 weeks. After chronic drug treatment the leaflets of both heart valves were thickened and opaque. In all treated animals the spongiosa layer of the stroma was crowded with vacuolated cells; the fibrosa layer was altered only after prolonged treatment. Ultrastructurally, the vacuolated cells of the spongiosa could be identified as histiocytes and fibroblasts, the former being the most susceptible cell type. The fibroblasts of the fibrosa represented the least sensitive cell type. The histochemical results showed that the clear cytoplasmic vacuoles in the spongiosa cells were due to lysosomal storage of polyanionic material with staining characteristics similar to cartilage matrix. After discontinuation of drug treatment the alterations persisted for several weeks. The present study shows that heart valves are involved in the mucopolysaccharidosis-like disorder induced by tilorone. The molecular pathomechanism of the disorder and the exact identification of the storage material must await further analysis. 相似文献
46.
Summary DNA haplotype constellations of the β-globin gene cluster have been analyzed in German families with hemoglobinopathies (Hb
Freiburg, Hb K?ln, Hb Presbyterian) and β-thalassemias. The polymorphis patterns obtained were compared to those found in
families from Greece, Italy, and Turkey affected by β-thalassemia syndromes. With the combined analysis of seven restriction
site polymorphisms a DNA-diagnostic prediction for additional offspring could be made with an overall frequency of 75% in
the four ethnic groups. 相似文献
47.
Jochen Zeil Renate Sandeman David Sandeman 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1985,157(5):607-617
Video recordings and single frame analysis were used to study the function of the second antennae of crayfish (Cherax destructor) as a sensory system in freely behaving animals. Walking crayfish move their antennae back and forth through horizontal angles of 100 degrees and more, relative to the body long axis. At rest, animals tend to hold their antennae at angular positions between 20 and 50 degrees. Movements of the two antennae are largely independent of each other. Before and during a turn of the body the ipsilateral antenna is moved into the direction of the turn. Solid objects are explored by repeatedly moving the antennae towards and across them. Both seeing and blinded crayfish can locate stationary objects following antennal contact. On antennal contact with a small novel object, a moving animal withdraws its antenna and attacks the object. When the antenna of a blinded crayfish is lightly touched with a brush the animal turns and attacks the point of stimulation. The direction taken and the distance covered during an attack can be correlated with: the angle at which the antenna is held at the moment of contact and the distance along the antennal flagellum at which the stimulus is applied. From behavioural evidence we conclude that crayfish use information about the angular position of their antennae and about the position of stimulated mechanoreceptors along the antennal flagellum to locate objects in their environment. We suggest ways in which an active tactile system-like the crayfish's antennae--could supply animals with information about the three-dimensional layout of their environment. 相似文献
48.
We studied whether intravenously administered inhibitors of leukotriene synthesis (diethylcarbamazine, DEC) or end-organ effect (FPL-55712) would change the distribution of regional pulmonary blood flow (rPBF) caused by left lower lobe (LLL) alveolar hypoxia in dogs. Both drugs failed to alter rPBF. In addition, the pressor response to whole-lung hypoxia was not blocked by an FPL-55712 infusion. On the other hand, nitroprusside, as a nonspecific vasodilator also administered intravenously, was able to partially reverse the effects of LLL hypoxia on rPBF. Thus our data do not support a role for leukotriene mediation of hypoxic pulmonary vasoconstriction in dogs. 相似文献
49.
50.
Neurospora crassa mutants deficient in asparagine synthetase 总被引:1,自引:0,他引:1
Neurospora crassa mutants deficient in asparagine synthetase were selected by using the procedure of inositol-less death. Complementation tests among the 100 mutants isolated suggested that their alterations were genetically allelic. Recombination analysis with strain S1007t, an asparagine auxotroph, indicated that the mutations were located near or within the asn gene on linkage group V. In vitro assays with a heterokaryon indicated that the mutation was dominant. Thermal instability of cell extracts from temperature-sensitive strains in an in vitro asparagine synthetase assay determined that the mutations were in the structural gene(s) for asparagine synthetase. 相似文献