全文获取类型
收费全文 | 4398篇 |
免费 | 336篇 |
国内免费 | 5篇 |
专业分类
4739篇 |
出版年
2022年 | 23篇 |
2021年 | 50篇 |
2020年 | 30篇 |
2019年 | 46篇 |
2018年 | 49篇 |
2017年 | 55篇 |
2016年 | 102篇 |
2015年 | 160篇 |
2014年 | 198篇 |
2013年 | 273篇 |
2012年 | 325篇 |
2011年 | 307篇 |
2010年 | 184篇 |
2009年 | 191篇 |
2008年 | 268篇 |
2007年 | 287篇 |
2006年 | 254篇 |
2005年 | 258篇 |
2004年 | 249篇 |
2003年 | 241篇 |
2002年 | 218篇 |
2001年 | 38篇 |
2000年 | 32篇 |
1999年 | 55篇 |
1998年 | 71篇 |
1997年 | 41篇 |
1996年 | 44篇 |
1995年 | 42篇 |
1994年 | 35篇 |
1993年 | 34篇 |
1992年 | 43篇 |
1991年 | 31篇 |
1990年 | 32篇 |
1989年 | 21篇 |
1988年 | 27篇 |
1987年 | 26篇 |
1986年 | 20篇 |
1985年 | 26篇 |
1984年 | 38篇 |
1983年 | 20篇 |
1982年 | 35篇 |
1981年 | 17篇 |
1980年 | 11篇 |
1979年 | 15篇 |
1978年 | 17篇 |
1977年 | 12篇 |
1976年 | 13篇 |
1975年 | 19篇 |
1974年 | 11篇 |
1969年 | 10篇 |
排序方式: 共有4739条查询结果,搜索用时 0 毫秒
11.
Gerd Joachim Dörrscheidt 《Biological cybernetics》1969,6(3):81-96
Summary From the communication engineers point of view the paper deals with networks consisting of linear filters and a special sort of controlled statistical pulse generators (SIG). The SIG responds to an analog signal with a sequence of Dirac impulses, where the probability for an output impulse at a given time depends on the instantaneous value of the input signal only. In connection with linear filters, however, systems can be realized in which the whole past of the input determines the statistical structure of the output. Therefore systems consisting of linear filters and SIGs (SIG networks) become interesting as models of biological systems, because in biological information processing transformations from analog signals into pulse trains occur very often. An example concerning the application of SIG systems in behavioural sciences will be discussed in a subsequent paper. In the present paper a theoretical analysis of the SIG and SIG networks is carried out by means of Statistical Communication Theory and Theory of Stochastic Processes. It is shown that under certain conditions very complex SIG networks can be treated with Correlation Theory. For one case not satisfying these conditions a solution on the base of Markoff processes is given.
Auszug aus einer von der Fakultät für Maschinenwesen und Elektrotechnik der Technischen Hochschule München genehmigten Dissertation.Herrn Prof. Dr.-Ing. H. Marko danke ich für das Interesse und die fördernde Kritik während des Entstehens der dieser Arbeit zugrundeliegenden Dissertation. Der Deutschen Forschungsgemeinschaft ist für die finanzielle Förderung der Untersuchungen zu danken. Die numerischen Berechnungen wurden auf der Rechenanlage TR4 des Leibniz-Rechenzentrums der Bayerischen Akademie der Wissenschaften durchgeführt. 相似文献
Auszug aus einer von der Fakultät für Maschinenwesen und Elektrotechnik der Technischen Hochschule München genehmigten Dissertation.Herrn Prof. Dr.-Ing. H. Marko danke ich für das Interesse und die fördernde Kritik während des Entstehens der dieser Arbeit zugrundeliegenden Dissertation. Der Deutschen Forschungsgemeinschaft ist für die finanzielle Förderung der Untersuchungen zu danken. Die numerischen Berechnungen wurden auf der Rechenanlage TR4 des Leibniz-Rechenzentrums der Bayerischen Akademie der Wissenschaften durchgeführt. 相似文献
12.
Joachim Messing 《Molecular biotechnology》1996,5(1):39-47
DNA sequence and expression analyses have greatly benefited from using M13 and pUC derived cloning vectors and their polycloning
sites. A chronology of the original concepts and experiments is reviewed. 相似文献
13.
Dieter Kreusch Johannes Lintig Joachim Schr?der 《Molecular & general genetics : MGG》1995,249(1):102-110
The occ and noc regions in octopine and nopaline Ti plasmids, respectively, are responsible for the catabolism of octopine and nopaline in Agrobacterium. The functions are activated in the presence of the opines by OccR and NocR, two related regulatory proteins, and the promoters contain common sequence motifs. We have investigated heterologous interactions between the regulators and the promoters. Previous experiments using all possible heterologous combinations of opines, regulators, and promoters in vivo had demonstrated that only the combination of nopalme, NocR, and the occ promoter led to limited promoter activation. We now show that OccR and NocR bind to the heterologous promoters in vitro and in vivo. The weak or non-existent promoter activation actually observed could be explained by the assumption that OccR and NocR use different activation mechanisms; we investigated protein-induced DNA bending because of reports that the two regulators differ in this respect. Analysis with a bending vector showed that both OccR and NocR induced a DNA bend that is relaxed in the presence of the respective opine. The data suggest that subtle differences in regulator/promoter interactions are responsible for the inactivity of the heterologous combinations. Investigations with a chimeric NocR/OccR protein indicated that it induced a DNA bend in both promoters. No opine-induced relaxation was detectable with the hybrid, and the inducible promoter was not activated. These findings suggest that bend relaxation may be an integral part of promoter activation. 相似文献
14.
A new, non-radioactive and cheap colorimetric method for determination of activity of sialyltransferases of various specifities using natural substrates based on 2-thiobarbituric acid assay is presented. The assay was tested with three different sialyltransferases (a-2,3 and a-2,6) and compared with the radioactive assay. 相似文献
15.
16.
A new approach for the reaction of Sepharose with cyanogen bromide is described, using triethylamine as a “cyano-transfer” reagent. An optimized procedure for activation at neutral pH was developed. This procedure requires only about 5% of the usual amount of cyanogen bromide. Activated resins are free of imidocarbonates and carbamates, containing only active cyanate esters. Extremely high coupling capacities (75 μmol ligand/g wet Sepharose 4B) can be obtained using this method. 相似文献
17.
18.
Thermal Denaturation of Native Striatal Tyrosine Hydroxylase: Increased Thermolability of the Phosphorylated Form of the Enzyme 总被引:5,自引:5,他引:0
Mitchell A. Lazar Roger J. W. Truscott Joachim D. Raese Jack D. Barchas 《Journal of neurochemistry》1981,36(2):677-682
Tyrosine hydroxylase was purified from bovine corpus striatum. The native enzyme had a half-life of 15 +/- 3 min at 50 degrees C. Phosphorylation of tyrosine hydroxylase with protein kinase purified from both corpus striatum and heart activated the enzyme, but activity was rapidly lost with additional preincubation of the enzyme at 30 degrees C. Thermal denaturation studies indicated that phosphorylated tyrosine hydroxylase had a half-life of 5 +/- 2 min at 50 degrees C 相似文献
19.
20.
A facile chemical synthesis of 1,2-dioleoyl and 1,2-dimyristoyl-sn-glycero-3-phospho-L-serine as well as the synthesis of several deuterated derivatives of phosphatidylserine (2 and 3 positions of serine and in the 3-glycerol position) are described. 360 MHz 1H NMR spectra of phosphatidylserine and the optical activity of various phosphatidylserine diastereomers were measured. 相似文献