全文获取类型
收费全文 | 4684篇 |
免费 | 320篇 |
国内免费 | 6篇 |
出版年
2023年 | 19篇 |
2022年 | 34篇 |
2021年 | 96篇 |
2020年 | 40篇 |
2019年 | 65篇 |
2018年 | 68篇 |
2017年 | 56篇 |
2016年 | 86篇 |
2015年 | 184篇 |
2014年 | 206篇 |
2013年 | 288篇 |
2012年 | 333篇 |
2011年 | 330篇 |
2010年 | 207篇 |
2009年 | 197篇 |
2008年 | 245篇 |
2007年 | 288篇 |
2006年 | 255篇 |
2005年 | 228篇 |
2004年 | 241篇 |
2003年 | 203篇 |
2002年 | 180篇 |
2001年 | 79篇 |
2000年 | 77篇 |
1999年 | 65篇 |
1998年 | 38篇 |
1997年 | 40篇 |
1996年 | 31篇 |
1995年 | 38篇 |
1994年 | 31篇 |
1993年 | 23篇 |
1992年 | 57篇 |
1991年 | 43篇 |
1990年 | 57篇 |
1989年 | 33篇 |
1988年 | 44篇 |
1987年 | 37篇 |
1986年 | 29篇 |
1985年 | 26篇 |
1984年 | 30篇 |
1983年 | 31篇 |
1982年 | 41篇 |
1981年 | 31篇 |
1980年 | 32篇 |
1979年 | 35篇 |
1978年 | 21篇 |
1977年 | 14篇 |
1976年 | 21篇 |
1975年 | 16篇 |
1974年 | 23篇 |
排序方式: 共有5010条查询结果,搜索用时 15 毫秒
41.
Rogelio O. Arellano Fidel Ramón Amelia Rivera Guido A. Zampighi 《The Journal of membrane biology》1986,94(3):293-299
Summary The effect of pH was tested on the junction between crayfish lateral axons. By means of a glass capillary inserted into one of the axons, one side of the nunction was perfused with solutions of known pH while the junctional resistance,R
j, was monitored. Integrity of the gap junction was checked electron microscopically.R
j remained unchanged when the pH of the perfusate was lowered from 7.1 to 6.0. However, when the pH of the unperfused side of the junction was lowered by substituting acetate for chloride in the external solution,R
j rose, attesting to the integrity of the junction and its capacity to uncouple in the perfused state. We suggest that H+ does not affect the junctional channels directly, but acts through an intermediary which is inactivated or removed by the perfusion. 相似文献
42.
I Kiss L Aurell M Pozsgay P El?di 《Biochemical and biophysical research communications》1985,131(2):928-934
The hydrolysis of 35 tripeptidyl-p-nitroanilides was studied with human plasmin and the kinetic parameters were determined. The individual contribution of the various side chains to the kinetic parameters was calculated by regression analysis. Considering Km, substrates having Z-D-Ile-Phe-Lys as well as H-D-Ile-Phe-Lys sequences were found to be the best, while Bz-Ile-Leu-Lys and pGlu-Leu-Lys sequences are the best for kcat. The Km values of substrates protected at N-terminus are lower, their kcat values are higher than those of the unprotected ones with the same sequence. 相似文献
43.
Jozef Anné Patrick Verheyen Guido Volckaert Hendrik Eyssen 《Molecular & general genetics : MGG》1985,200(3):506-507
Summary A physical map of the actinophage VWB has been constructed using the restriction endonucleases BglII, ClaI, EcoRI, EcoRV, HindIII, KpnI and SphI. Phage VWB, genome size 47.3 kb, propagates on Streptomyces venezuelae, and it can also lysogenise this species. The three BglII-generated fragments of VWB DNA were cloned in pBR322, and subsequently mapped. In this manner the restriction map of the VWB phage genome was constructed.Abbreviations
dam
DNA adenine methylase activity
- kb
kilobase pairs
- ::
novel joint 相似文献
44.
A Verrillo A de Teresa C Martino G di Chiara 《Bollettino della Società italiana di biologia sperimentale》1985,61(2):183-188
Blood glucose, insulin and prolactin concentrations were determined before and after sulpiride injection (50 mg i.m.) in 20 non-insulin-dependent diabetic patients (10 with retinopathy and 10 without evidence of retinal damage) and 10 subjects with normal glucose tolerance. Prolactin response to sulpiride was significantly higher in diabetics than in controls (at 20 min., p less than 0.01; at 30 and 60 min., p less than 0.005; at 90 min., p less than 0.01; at 120 min., p less than 0.05). The sulpiride induced hyperprolactinemia did not influence blood glucose and plasma insulin levels in controls as well as in diabetic patients. Prolactin response to sulpiride was the same in diabetics with and in those without retinal changes. We conclude that acute hyperprolactinemia seems to have no influence on glucose homeostasis in normal and non insulin-dependent diabetic subjects. 相似文献
45.
C Toniolo G M Bonora A Bavoso E Benedetti B di Blasio V Pavone C Pedone 《Journal of biomolecular structure & dynamics》1985,3(3):585-598
The infrared absorption and 1H nuclear magnetic resonance analyses of chloroform solutions of the terminally-blocked segment corresponding to the 2-9 sequence of emerimicins III and IV, -(Aib)3-L-Val-Gly-L-Leu-(Aib)2-, are consistent with the presence of a 3(10)-helical structure of high thermal stability. The crystal structure of the octapeptide, obtained by X-ray diffraction indicates the formation of a right-handed 3(10)-helix, stabilized by six consecutive intramolecular N-H....O:C H-bonds, slightly distorted at the level of the L-Leu residue. 相似文献
46.
Stimulation of Phospholipase A2 and Secretion of Catecholamines from Brain Synaptosomes by Potassium and A23187 总被引:3,自引:3,他引:0
Abstract: Potassium depolarization of rat brain synaptosomes (containing incorporated l-acyl-2-[14C]arachidonyl-phosphatidylcholine) stimulated endogenous phospholipase A1 (EC 3.1.1.32) and A2 (EC 3.1.1.4), as determined by the formation of [14C]lysophosphatidylcholine, [14C]arachidonate, and [14C]prostaglandins, and also stimulated the secretion of [3H]catecholamines. The phospholipase A2 stimulation, dependent on calcium, was elicited in resting synaptosomes by A23187 and was demonstrated with incorporated 1-acyl-2-[l4C]oleoyl-phosphatidylcholine but not with incorporated [I4C]phosphatidylethanolamine or [l4C]phosphatidylserine. Inhibitors of phospholipase A2 [p-bromophenacylbromide (10 μM), trifluoperazine (3 μM), and quinacrine (3 μM) reduced the potassium-stimulated [3H]catecholamine release from synaptosomes to 78, 39. and 55%, respectively, of depolarized controls. The addition of lysophosphatidylcholine increased the release of [3H]norepinephrine to levels observed with potassium depolarization, whereas lysophosphatidylethanolamine, lysophosphatidylserine, and sodium dodecyl sulfate were much less effective. Potassium stimulation of synaptosomes increased the endogenous levels of free arachidonic acid and prostaglandins E2 and F2α. Indomethacin and aspirin decreased the amounts of prostaglandins formed, allowed the accumulation of free arachidonic acid, and diminished the potassium-stimulated release of [3H]dopamine. p-Bromophenacylbromide inhibited the formation of prostaglandin F2α. Addition of prostaglandin E2 inhibited, whereas prostaglandin F2α enhanced the release of [3H]norepinephrine. These results suggest that calcium influx induced by synaptosomal depolarization activates endogenous phospholipase A2, with subsequent formation of lysophosphatidylcholine and prostaglandins, both of which may modulate neurosecretion. 相似文献
47.
Evidence for two waves of induction of DNA enzymes in stimulated human lymphocytes 总被引:5,自引:3,他引:2
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)
Guido C. F. Pedrali Noy Leda Dalpra Antonia M. Pedrini Giovanni Ciarrocchi Elena Giulotto Fiorella Nuzzo Arturo Falaschi 《Nucleic acids research》1974,1(9):1183-1199
The stimulation of human lymphocytes with phytohaemoagglutinin induces the appearance or increase of several enzymes of DNA metabolism [Pedrini etal., Biochem. Biophys. Res. Comm., 47:1221(1972)]. With long times of stimulation, two phenomena are observed; an increase in the levels of DNA polymerase, of a DNase acting on single-stranded DNA, and of an endonuclease, occurring between the third and fourth day, in parallel with a wave of DNA synthesis;a second wave of increase of the same enzymes and of DNA ligase,occurring between the fifth and eight day when the DNA replication rate, as measured by thymidine-pulses, has decreased to values close to the background. 相似文献
48.
Summary In the Gasserian ganglion and testis of the rat the endothelium of the small blood vessels has a singular appearance due to the presence of a high number of microvillous processes. These arise from the luminal surface, either individually, or in small groups. The significance of this structure is not known. It is pointed out that these vessels are particularly sensitive to cadmium intoxication.This investigation was performed during a tenure by Dr. Gabbiani of a fellowship of the Medical Research Council of Canada and was supported by the National Institutes of Health (Grant No. 5R01 HE-08794-04) and the Ministère de la Santé du Québec (projet 604-7-635).The authors wish to thank Dr. S. M. Shea for his advice in the measurement of the villi. The technical assistance of Miss Virginia Gilmore and of Mr. Eduardo Garriga is gratefully acknowledged. 相似文献
49.
Summary Exponential phase cultures ofE. coli 15 T- cells growing on glucosemineral medium were supplemented with 2 mM l-cysteine-HCl. The optical density, acid soluble SH (AS-SH) as well as the DNA, RNA, and protein synthesis of the cultures were examined during this treatment and after return to normal growth conditions. Similarly, the survival of cells irradiated by a standard X-ray dose in cysteine-free buffer was measured.The development of radioresistance during the cysteine treatment as well as the loss of this acquired radioresistance after return to normal growth conditions could be divided into two phases: a) an instantaneous and b) a slow change of radioresistance. Phase a seems to be related to the changes occurring in the AS-SH content of the bacteria, while phase b is apparently dependent on the alterations in the synthesis of macromolecules.This work was partly presented at the 6th Annual Meeting of the European Society for Radiation Biology, Interlaken 1968. 相似文献
50.
Résumé Les Auteurs ont démontré que, en conditions histochimiques sur du matériel fixé au formol, les acides phosphotungstique et phosphomolybdique ont une double action: 1. une action oxydative à la charge des radicaux PAS-positifs (vic-glycols et éthyleniques) en milieu aqueux, et à la charge des radicaux aminiques en milieu anhydre; cette action entraine la transformation de ces radicaux en aldéhydes; 2. la formation d'une liaison chimique entre les aldéhydes et les molécules des acides phosphomolybdique et phosphotungstique. — La coloration du collagène, au contraire, n'est pas due ni aux radicaux aminiques ni vic-glycols et implique un mécanisme encore inconnu.
Observations about the specificity of staining of phosphotungstic and phosphomolybdic acid
Summary The authors demonstrated that phosphotungstic and phosphomolybdic acid applied to formol-fixed tissues explete two following actions: 1. An oxidative action on the PAS-positive radicals (double bonds, vic-glycols groups) if in water solution and on aminogroups if in anhydrous solution. This oxidation results in a production of aldehydic radicals 2. The formation of chemical bonds between the aldehydic new-formed groups and the molecules of phosphotungstic or phosphomolybdicacid.— However, the above mentioned mechanism of action is not applicable to the collagen staining for which a different explanation has to be supposed.相似文献