全文获取类型
收费全文 | 5674篇 |
免费 | 15篇 |
国内免费 | 9篇 |
专业分类
5698篇 |
出版年
2012年 | 197篇 |
2011年 | 358篇 |
2010年 | 154篇 |
2009年 | 16篇 |
2008年 | 320篇 |
2007年 | 428篇 |
2006年 | 458篇 |
2005年 | 434篇 |
2004年 | 460篇 |
2003年 | 492篇 |
2002年 | 475篇 |
2001年 | 308篇 |
2000年 | 515篇 |
1999年 | 286篇 |
1998年 | 39篇 |
1997年 | 18篇 |
1996年 | 11篇 |
1992年 | 27篇 |
1991年 | 30篇 |
1990年 | 31篇 |
1989年 | 37篇 |
1988年 | 39篇 |
1987年 | 24篇 |
1986年 | 25篇 |
1985年 | 24篇 |
1984年 | 19篇 |
1983年 | 16篇 |
1981年 | 10篇 |
1980年 | 11篇 |
1979年 | 15篇 |
1978年 | 16篇 |
1977年 | 11篇 |
1975年 | 25篇 |
1974年 | 18篇 |
1973年 | 11篇 |
1972年 | 19篇 |
1971年 | 18篇 |
1970年 | 11篇 |
1969年 | 12篇 |
1968年 | 11篇 |
1967年 | 15篇 |
1966年 | 10篇 |
1958年 | 23篇 |
1957年 | 26篇 |
1956年 | 26篇 |
1955年 | 22篇 |
1954年 | 22篇 |
1953年 | 13篇 |
1952年 | 13篇 |
1951年 | 10篇 |
排序方式: 共有5698条查询结果,搜索用时 15 毫秒
61.
Molecular genome analysis was for the first time carried out in the genus Stachys. RAPD analysis proved to be suitable for identifying the species-specific markers, studying the interspecific DNA polymorphism, and detecting the genetic changes that arise during in vitro culturing of Stachys sieboldii. In addition, RAPD was used for screening genetic variation in S. sieboldii regenerants obtained at various phytohormone concentrations. High cytokinin concentrations and multiple regeneration were shown to induce genetic changes detectable with RAPD patterns. High DNA polymorphism was demonstrated for two types of S. sieboldii callus cultures and for plants regenerated from a callus culture. 相似文献
62.
Il'inskaia ON Kolpakov AI Zelenikhin PV Kruglova ZF Choĭdash B Doroshenko EV Muliukin AL El'-Registan GI 《Mikrobiologiia》2002,71(2):194-199
The mutagenic activity of chemical analogues of microbial anabiosis autoinducers (the autoregulatory d1 factors of cell differentiation), which act to inhibit cell proliferation, to enhance cell tolerance, and to induce the transition of cells to anabiotic state, was studied using the Ames test. In the range of concentrations studied (0.1 to 100 micrograms/ml), alkyl-substituted hydroxybenzenes (AHBs) differing in hydrophobicity, i.e., methylresorcinol (C1-AHB) and hexylresorcinol (C6-AHB), as well as unsubstituted resorcinol, showed different growth-inhibiting and mutagenic effects. C6-AHB was found to inhibit the growth of Salmonella typhimurium TA100 and to induce its mutagenesis at a rate of 1.8 revertants/nmol. C1-AHB taken at low concentrations not only failed to inhibit bacterial growth but even stimulated it and exerted an antimutagenic effect. Unsubstituted resorcinol virtually did not influence bacterial growth and showed weak mutagenic activity. The growth-inhibiting effect of elevated C6-AHB concentrations correlated with the degree of the transition of the original phenotype producing S-type colonies to a phenotype producing R-type colonies. The role of AHB homologues, as microbial autoregulators with mutagenic activity, in the regulation and correlation of two processes (the phenotypic dissociation of microbial populations and the formation of resting microbial forms) is discussed. The accumulation of AHBs in senescent microbial cultures may induce adaptive mutations, change the expression of genes, and promote the development of minor cell subpopulations (phenotypes), thus providing for the adaptation of these cultures to varying environmental conditions. 相似文献
63.
64.
Korovkina EP Mikhaĭlov PP 《Radiatsionnaia biologiia, radioecologiia / Rossi?skaia akademiia nauk》2000,40(1):54-57
In experiments in mice, hamsters and dogs therapeutic radioprotective efficiency and toxicity of new water-soluble copolymer were studied. It was found that at intramuscular injection of the copolymer to dogs in a dose of 5 mg/kg 24 h after irradiation with a dose of 3.30 Gy (LD85/45) it showed pronounced therapeutic effect (68.1%). In mice and hamsters, the effect was less pronounced: 42-21% after irradiation with a dose of 8.0 Gy. The copolymer is low toxic substance and according to the State standards of Russian Federation belongs to the fourth class (harmless). 相似文献
65.
Deep-level diagnostic value of the rDNA-ITS region 总被引:14,自引:0,他引:14
The similarity of certain reported angiosperm rDNA internal transcribed
spacer (ITS) region sequences to those of green algae prompted our analysis
of the deep-level phylogenetic signal in the highly conserved but short
5.8S and hypervariable ITS2 sequences. We found that 5.8S sequences yield
phylogenetic trees similar to but less well supported than those generated
by a ca. 10-fold longer alignment from rDNA-18S sequences, as well as
independent evidence. We attribute this result to our finding that,
compared to 18S, the 5.8S has a higher proportion of sites subject to vary
and greater among-site substitution rate homogeneity. We also determined
that our phylogenetic results are not likely affected by intramolecular
compensatory mutation to maintain RNA secondary structure nor by evident
systematic biases in base composition. Despite historical homology, there
appears to be no ITS2 primary sequence similarity shared sufficient
similarity to cluster correctly on the basis of alignability. Our results
indicate that groups, however, share sufficient similarity to cluster
correctly on the basis of alignability. Our results indicate that ITS
region sequences can diagnose organismal origins and phylogenetic
relationships at many phylogenetic levels and provide a useful paradigm for
molecular evolutionary study.
相似文献
66.
Khegaĭ II 《Rossi?skii fiziologicheski? zhurnal imeni I.M. Sechenova / Rossi?skaia akademiia nauk》2001,87(7):960-964
The cortical actinin contents was found to be higher in the inner medulla of the rat kidney. Tropomyosin was distributed differently: it is lower in the cortex than in outer or inner medulla. The processes controlled by these proteins seem to be important for the vasopressin renal effects, and the irregular distribution of these proteins reflects participation of different renal areas in facultative water reabsorption. 相似文献
67.
Recognition of joy, anger, and fear by face expression in humans 总被引:1,自引:0,他引:1
Mikhaĭlova ES Nikitaeva ES Davydov DV 《Zhurnal vysshe? nervno? deiatelnosti imeni I P Pavlova》2001,51(4):443-451
Behavioral and neurophysiological characteristics of a visual recognition of emotions of joy, anger, and fear were studied in 9 young healthy men and 10 women. It was shown that these emotions were identified by subjects with different rate and accuracy; significant gender differences in recognition of anger and fear were found. Recording of visual evoked potentials (VEP) from the occipital (O1/2), medial temporal (T3/4), inferior temporal (T5/6), and frontal (F3/4) areas revealed differences (related with the type of emotion) in the latencies of P150, N180, P250, and N350 waves and in the amplitude of VEP components with the latencies longer than 250 ms. These differences were maximally expressed in T3/4 derivation. The subjects could be divided in two groups. The first group was characterized by increased VEP latencies and higher amplitudes of VEP components later than 250 ms in response to anger (in comparison with other types of emotions). These phenomena were observed in all the derivations but were most pronounced in T3/4. In the second group, only late P250 and N350 components had shorter latencies during recognition of fear. VEP amplitude variations related with the type of emotions were insignificant and were recorded in the occipital and frontal areas. The two groups of subjects also differed in psychoemotional personality characteristics. It is suggested that primary recognition of facial expression takes place in the temporal cortical areas. A possible correlation of electrophysiological indices of emotion recognition with personality traits is discussed. 相似文献
68.
Nurtdinov RN Neverov AD Mal'ko DB Kosmodem'ianskiĭ IA Ermakova EO Ramenskiĭ VE Mironov AA Gel'fand MS 《Biofizika》2006,51(4):589-592
EDAS, a database of alternatively spliced human genes, contains data on the alignment of proteins, mRNAs, and EST. It contains information on all exons and introns observed, as well as elementary alternatives formed from them. The database makes it possible to filter the output data by changing the cut-off threshold by the significance level. The database is accessible at http://www.gene-bee.msu.ru/edas/. 相似文献
69.
Pilinskaia MA Dybskiĭ SS Skaletskiĭ IuN Chumak VV Diagil' IS Liubarets TF Romanenko AE Bebeshko VG Bazyka DA 《T?Sitologii?a i genetika》2006,40(3):34-39
The results of proper investigations received under the cytogenetic examination of 225 persons (control groups, Chernobyl liquidators exposed to different radiation doses, oncogematology patients) had been summarized and analyzed. The conclusion concerning possibilities and limitations of FISH technique usage for retrospective biodosimetry of human radiation exposure has been presented. 相似文献
70.
Nine larvocysts of Echinococcus granulosus isolated from nine patients and one cyst derived from a naturally infested cattle have been examined. Genomic typing was carried out in order to identify strains of E. granulosus. All DNA samples were shown to have the same genotype, E. granulosus G1. 相似文献