全文获取类型
收费全文 | 2749篇 |
免费 | 150篇 |
国内免费 | 2篇 |
专业分类
2901篇 |
出版年
2022年 | 16篇 |
2021年 | 36篇 |
2020年 | 15篇 |
2019年 | 19篇 |
2018年 | 33篇 |
2017年 | 18篇 |
2016年 | 45篇 |
2015年 | 70篇 |
2014年 | 104篇 |
2013年 | 134篇 |
2012年 | 151篇 |
2011年 | 131篇 |
2010年 | 76篇 |
2009年 | 100篇 |
2008年 | 166篇 |
2007年 | 135篇 |
2006年 | 132篇 |
2005年 | 149篇 |
2004年 | 149篇 |
2003年 | 127篇 |
2002年 | 137篇 |
2001年 | 102篇 |
2000年 | 94篇 |
1999年 | 79篇 |
1998年 | 31篇 |
1997年 | 24篇 |
1996年 | 27篇 |
1995年 | 21篇 |
1994年 | 26篇 |
1993年 | 29篇 |
1992年 | 47篇 |
1991年 | 47篇 |
1990年 | 37篇 |
1989年 | 46篇 |
1988年 | 31篇 |
1987年 | 33篇 |
1986年 | 22篇 |
1985年 | 22篇 |
1984年 | 15篇 |
1983年 | 19篇 |
1982年 | 27篇 |
1981年 | 16篇 |
1979年 | 17篇 |
1978年 | 11篇 |
1974年 | 21篇 |
1971年 | 11篇 |
1969年 | 10篇 |
1968年 | 14篇 |
1967年 | 10篇 |
1966年 | 10篇 |
排序方式: 共有2901条查询结果,搜索用时 15 毫秒
41.
42.
Overexpression of genes of an extreme thermophile Thermus thermophilus, in Escherichia coli cells. 总被引:1,自引:1,他引:0 下载免费PDF全文
The 3-isopropylmalate dehydrogenase gene from an extreme thermophile, Thermus thermophilus, was not expressed in Escherichia coli unless a palindromic structure around the ribosome binding site was eliminated or a leader open reading frame was introduced into the upstream flanking region of the gene. This report suggests a way to increase the expression of this gene, with a high G+C content, in E. coli. 相似文献
43.
Sakamoto Atsushi; Ohsuga Hiroyuki; Wakaura Makoto; Mitsukawa Norihiro; Hibino Takashi; Masumura Takehiro; Sasaki Yukiko; Tanaka Kunisuke 《Plant & cell physiology》1993,34(6):965-968
A cDNA clone for copper/zinc-superoxide dismutase (Cu/Zn-SOD)was isolated from spinach (Spinacia oleracea L.) leaves. Itsnucleotide sequence showed that it codes for a precursor polypeptideof 222 amino acids, including the NH2-terminal 68-residue extensionwhich corresponds to a plastidic transit peptide. Northern hybridization,using plastidic and cytosolic Cu/Zn-SOD cDNAs as the probes,revealed that these two genes are differentially expressed inthe roots and leaves of spinach.
1Present address: Department of Biochemistry and Microbiology,Cook College, Rutgers University New Brunswick, NJ 08903-0231,U.S.A. 相似文献
44.
The ultrastructure of the opaque portion of the adductor muscle in the pecten Chlamys nobilis was investigated. The opaque portion was composed of smooth muscle cells that contained thin and thick filaments. The thick filaments were classified into two kinds, thinner and thicker, according to the statistical analysis of diameters. They were also classified as being shorter and longer, when isolated native filaments were examined. The thick filaments may consequently be classified into two kinds: thinner and shorter filaments, and thicker and longer ones. The thinner and shorter filaments were about 26.5 nm in diameter and 7.5 mum in length, and the thicker and longer ones were about 42.0 nm in diameter and 13.0 mum in length, respectively. A regular periodicity was apparent on the surface of the core after removal of myosin molecules from its surface. The periodicity seemed similar for the two kinds of thick filament. 相似文献
45.
Nitric Oxide Reversibly Suppresses Xanthine Oxidase Activity 总被引:10,自引:0,他引:10
Masami Fukahori Kohji Ichimori Hideyuki Ishida Hiroe Nakagawa Haruka Okino 《Free radical research》1994,21(4):203-212
The effects of nitric oxide (NO) on xanthine oxidase (XOD) activity and the site(s) of the redox center(s) affected were investigated. XOD activity was determined by superoxide (O2-) generation and uric acid formation. NO reversibly and dose-dependently suppressed XOD activity in both determination methods. The suppression interval also disclosed a dose-dependent prolongation. The suppression occurred irrespective of the presence or absence of xanthine; indicating that the reaction product of NO and O2-, peroxynitrite, is not responsible for the suppression. Application of synthesized peroxynitrite did not affect XOD activity up to 2 μM. Methylene blue, which is an electron acceptor from Fe/S center, prevented the NO-induced inactivation. The results indicate that NO suppresses XOD activity through reversible alteration of the flavin prosthetic site. 相似文献
46.
Masahiro Sato Norihiro Tada Reiko Iwase Egon Amann 《Molecular reproduction and development》1993,34(4):349-356
It is a well-known phenomenon that cultured mammalian cells that have been pricked in the presence of foreign DNA can be transformed. This micromanipulation ‘pricking’ technique was applied to mouse blastocysts to determine whether uptake of exogenous DNA would occur in the embryos. The middle region of the inner cell mass (ICM) was pricked three times in each blastocyst in a medium containing a linearized plasmid DNA. When the 60 treated blastocysts were transferred to the uterine horns of pseudopregnant females, 30 developing fetuses (50%) at the mid-gestation stage were obtained. Twenty-two of the 30 fetuses (73%) had less than 1 copy of the foreign DNA per diploid cell, as revealed by polymerase chain reaction (PCR)-Southern analysis, a sensitive technique combined with Southern blot processing of the PCR products. The 8 other fetuses were negative for the foreign DNA. When blastocysts were pricked in the presence of vector DNA coupling E. coli β-galactosidase (β-gal) gene to a mouse metallothionein-I (MT-I) promoter and assessed for β-gal activity histochemically after 1 and 5 days of culture in the presence of 1 μM CdCI2, at least 65% of the embryos exhibited β-gal activity mainly in the ICM region. These results indicate that mouse blastocysts can be transfected with a relatively high efficiency after pricking, and that the introduced gene expression occurs. This approach provides a means of mapping the regulatory elements of genes that are active in the mouse blastocyst ICM, and may be useful in investigating the fate of the ICM cells in an intact blastocyst by labeling them via pricking technique. © 1993 Wiley-Liss, Inc. 相似文献
47.
Sakamoto Norihiro; Takagi Toshihisa; Sakaki Yoshiyuki 《Bioinformatics (Oxford, England)》1993,9(4):427-434
We have developed ODS (Overlapping Oligonucleotide Databasefor Signal Sequence Search)the first relational databasethat integrates information on biological features into thesearch for signal sequences. In existing biological sequencedatabases, even relational ones, retrieving nucleotide sequencesbased on their biological features involves much labour andtime or even the development of a new program. GenBank sequencedata, including FEATURES records, are organized into three relationaltables in ODS. Nucleotide sequences are transformed into overlappingoligonucleotides in order to facilitate the signal sequencesearch rapidly without the need for specific alignment programs.This transformation leads to a one-to-one correspondence betweenthe nucleotide sequence and its biological feature. The signalsequence search by ODS is done in SQL queries and ODS obviatesthe need for molecular biologists to write computer programs.The application of ODS to searches of promoter regions revealedputative cis-acting elements and basic statistical analysesof occurrences of oligonucleotides showed interesting findingsconcerning the cg dinucleotide. 相似文献
48.
49.
M. Matsuda A. Kaneko M. Fukuyama T. Itoh M. Shingaki M. Inoue J.E. Moore P.G. Murphy Y. Ishida 《Journal of applied microbiology》1996,81(6):608-612
Two strains of urease-positive thermophilic Campylobacter (UPTC), CF89–12 and CF89–14, which were identified as UPTC by biochemical characterization, were found for the first time in river water in the Far East, namely, in Japan. The biochemical characteristics were identical to those of strains described previously by Bolton and colleagues. Furthermore, these two strains were positive for arylsulphatase. Consequently, it was demonstrated that UPTC may possibly be differentiated phenotypically from Campylobacter lari by the arylsulphatase test, as well as urease and nalidixic acid tests. Analysis by pulsed-field gel electrophoresis (PFGE) after digestion with Apa I, Sal I and Sma I, which were found to produce distributions of DNA fragments to be suitable for analysis of the genomic DNA from the thermophilic Campylobacter , respectively, demonstrated that these three restriction enzymes produced distributions of a relatively limited number of genomic DNA fragments and also demonstrated that the PFGE profiles obtained with the three restriction enzymes were indistinguishable between the two strains, respectively. The PFGE analysis and conventional fixed-field agarose gel electrophoresis suggested that the both genomes were approximately 1862 kb in length. Even though the two isolates of UPTC were isolated from water in different rivers in Japan, the results suggested that a single strain. as opposed to two distinct strains, was isolated. PFGE profiles after digestion with Sal I and Sma I, respectively, were also demonstrated to be distinctly different among strains isolated in Japan and previously in Europe. This is the first example of the isolation of UPTC from natural sources in countries other than those in Europe. 相似文献
50.