全文获取类型
收费全文 | 2122篇 |
免费 | 101篇 |
国内免费 | 3篇 |
出版年
2023年 | 13篇 |
2022年 | 24篇 |
2021年 | 50篇 |
2020年 | 37篇 |
2019年 | 39篇 |
2018年 | 46篇 |
2017年 | 31篇 |
2016年 | 65篇 |
2015年 | 88篇 |
2014年 | 94篇 |
2013年 | 141篇 |
2012年 | 144篇 |
2011年 | 179篇 |
2010年 | 91篇 |
2009年 | 79篇 |
2008年 | 105篇 |
2007年 | 107篇 |
2006年 | 108篇 |
2005年 | 104篇 |
2004年 | 81篇 |
2003年 | 72篇 |
2002年 | 71篇 |
2001年 | 36篇 |
2000年 | 31篇 |
1999年 | 34篇 |
1998年 | 17篇 |
1997年 | 14篇 |
1996年 | 12篇 |
1995年 | 17篇 |
1994年 | 11篇 |
1993年 | 15篇 |
1992年 | 26篇 |
1991年 | 20篇 |
1990年 | 17篇 |
1989年 | 20篇 |
1988年 | 23篇 |
1987年 | 15篇 |
1986年 | 14篇 |
1985年 | 17篇 |
1984年 | 11篇 |
1983年 | 10篇 |
1982年 | 11篇 |
1981年 | 10篇 |
1980年 | 10篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1977年 | 8篇 |
1976年 | 6篇 |
1974年 | 9篇 |
1967年 | 5篇 |
排序方式: 共有2226条查询结果,搜索用时 15 毫秒
31.
S. Nair U. Prasada Rao J. Bennett M. Mohan 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1995,91(6-7):978-986
Forty-seven recombinant inbred (RI) lines derived from a cross between two indica rices, cv Phalguna and the Assam land race ARC 6650, were subjected to restriction fragment length polymorphism (RFLP) analysis using cloned probes defining 150 single-copy loci uniformly dispersed on the 12 chromosomes of rice. Of the probes tested, 47 detected polymorphism between the parents. Heterozygosity was calculated for each line and for each of the polymorphic loci. Average heterozygosity per line was 9.6% but was excessive (>20%) in the 5 lines that seemed to have undergone outcrossing immediately prior to harvest. Average heterozygosity detected by each probe across the 47 RI lines was 9.7%. The majority of probes revealed the low level of heterozygosity (<8%) expected for F5-F6 lines in a species showing about 5% outbreeding. On the other hand, 7 probes exhibited heterozygosity in excess of 15%, while with a eighth probe (RG2 from chromosome 11) heterozygosity varied according to the restriction enzyme employed, ranging from 2% with SaII to 72% with EcoRV. The presence of 34 recombination sites in a segment of the genome as short as 24 kb indicates a strong selection for recombination between two neighbouring loci, one required as homozygous for the Phalguna allele, and the other heterozygous. Since selection was principally for yield advantage over that of the high-yielding parent, Phalguna, one or both of these loci may be important for heterosis in this cross. The results also indicate that heterozygosity as measured by RFLP can depend on the particular restriction endonuclease employed. 相似文献
32.
The ability to withstand thermal stress in a laboratory population of the blowflyLucilia cuprina (measured as per cent adult survival following varying periods of exposure to elevated temperature up to a maximum of 48°C)
was in the order pupa > larva > adult. Pre-exposure to a mild heat shock (37°C) induced tolerance to temperatures which were
otherwise lethal. An analysis of heat shock-induced protein synthesis during development at similar elevated temperatures
presented patterns corresponding to the above observations on thermotolerance. The induced level of synthesis of major heat
shock proteins (viz., 79, 69, 28, 20 and 19 kDa) were greater in larval tissues than in most of the adult tissues except gonads.
The response varied between young (2 days) and old (30 days) adults in a tissue-specific manner. In general, heat shock protein
69 kDa was most abundant in all the tissues studied. Control as well as heat shocked Malpighian tubules of adults uniquely
showed two major [35S]methionine labelled bands corresponding to approximately 62 and 64 kDa. Immunoblots showed the 62 kDa protein to cross react
with an antibody againstHelioihis HSP60. Although the synthesis of the 62 kDa polypeptide was prominent only in Malpighian tubules of adult blowflies, nearly
equal levels of this HSP60 family polypeptide were present in all tissues (control as well heat shocked) except the larval
salivary glands. 相似文献
33.
The activity of the neutral, Mg2+-stimulated sphingomyelinase of cultured neuroblastoma cells (N1E-115) is enriched in the plasma membrane fraction and is reduced following treatment of intact or broken cells with trypsin, α-chymotrypsin, papain, and protease. Two protease-sensitive enzymes of the cell interior (lactate dehydrogenase and NADPH-cytochrome c reductase) are not affected by protease treatment of intact cells. These results indicate that the neutral, Mg2+-stimulated sphingomyelinase is oriented externally on the plasma membrane of the cultured neuroblastoma cell. 相似文献
34.
Uptake of Co2+ by three nickel-resistant strains (NiR1, NiR2, and NiR3) ofNeurospora crassa that differed in resistance to Co2+ has been studied. Uptake was linear with Co2+ concentration (up to 1 mM), with time (up to 6 h), and with pH between 3 and 6. Uptake rates were in the order NiR2>NiR1>NiR3. In all strains, there was gradual increase in Co2+ uptake between 10° and 28°C, with a much sharper increase between 28° and 40°C. Metabolic inhibitors decreased Co2+ uptake partially in all strains, except for KF in NiR3. About 50–80 g Co2+/100 mg dry weight was surface bound. Ni2+, Zn2+, and Mn2+ competed with Co2+, the effects being strain specific. Mg2+ inhibited Co2+ uptake in all strains with preformed mycelia. In NiR1 and NiR2 only with young mycelia (40 h old) was Mg2+ inhibitory to Co2+ uptake,during growth in the presence of Co2+. The results suggested the presence of two transport systems for Co2+ in NiR1 and NiR2, only one of which was sensitive to Mg2+; in contrast, NiR3 had a single system, which was sensitive to Mg2+. 相似文献
35.
Aqueous solutions of silver nitrate (10–100 g/plant) and cobalt chloride (125–500 g/plant), injected into the main stem of plants of the pistillate cv. 240 ofRicinus communis when the vegetative shoot apex was beginning to become reproductive, induced the formation of staminate (male) flowers with viable pollen in the normally strictly pistillate (female) terminal inflorescence, their number increasing with the dose of Ag+ and Co2+. No formation of bisexual flowers was noted. Female flowers pollinated with pollen from the induced male ones produced fruits and viable seeds. 相似文献
36.
A Singh K S Mohan S K Sethi D V Vadehra 《Acta microbiologica Academiae Scientiarum Hungaricae》1977,24(1):33-39
Neutralization of enterotoxins of Vibrio cholerae 569 B and Escherichia coli 10407 by antitoxins to V. cholerae 569 B, E. coli 334, 408-3 and 10407 was studies by intradermal inoculation test in the rabbit. Neutralization of V. cholerae enterotoxin by homologous as well as heterologous antisera of E. coli was observed, except that there was no neutralization of the enterotoxin by antiserum to E. coli 408-3 enterotoxin. Neutralization of E. coli enterotoxin to a varied extent by homologous as well as all heterologous antisera, including that of V. cholerae 569 B antitoxin, was also observed. 相似文献
37.
Copper toxicity has been studied in three nickel-resistant strains ofNeurospora crassa (NiR1, NiR2, and NiR3). NiR1 and NiR2, but not NiR3, were two-to threefold more sensitive than the parent wild strain (N. crassa EM 5297a) to Cu2+ on a normal N medium. On a nitrate N medium, Cu2+ was 16-fold more toxic to NiR3 because of reduced synthesis of nitrite reductase; NiR1 and NiR2 were only fivefold more sensitive to Cu2+, and nitrite reductase synthesis was unaffected. Mn2+ reversed Cu2+ toxicity on normal N medium only, in all strains. Fe3+ counteracted Cu2+ toxicity on nitrate N medium also. It was shown that Cu2+ affected Fe3+ utilization for nitrite reductase synthesis in NiR3 only and that in these Ni2+-resistant strains, Fe3+ antagonized effects of Cu2+, but not of other toxic metal ions. 相似文献
38.
Effects of cadmium salt on phosphomonoesterases activity and fertilizing ability of fowl spermatozoa. 总被引:6,自引:0,他引:6
Daily administration of cadmium salt for 25 days (2.5 mg per Kg body weight) in the male domestic fowl caused the end of treatment period. An increased incidences of concentration. Fertility dropped to zero at the end of the treatment period. Activity of acid and alkaline phosphomonoesterases were also drastically reduced by the end of treatment period. An increased incidences of morphological abnormalities of spermatozoa were noticed in the treated birds. After 46 days cessation of the treatment, full recovery of the above measures was found. These alterations suggest the reversible type of effect of cadmium chloride on the spermatozoa of male domestic fowl. 相似文献
39.
Each of 20 White Leghorn hens of 13 to 14 weeks were subjected to partial sinistral ovariectomy and sham-operations. In half of the hens from each group, the percentage of egg production and clutch size were noted until 50 weeks of age. The growing pattern of normal ovarian follicles was also recorded at 26 weeks of age in a rest half ofthe hens in the two groups. The percentage of egg production and the mean and variance of clutch size did not differ significantly (P / 0.05) between the partially ovariectomized and sham-operated groups. The growing yellow follicles (>8 mm) in the rapidly developing phase in these two groups did not vary, although the smaller follicles (4 to 8 mm in diameter) remained significantly (P / 0.01) more in the shamoperated control group than in the partially ovariectomized group. This observation indicates that smaller follicles (4 to 8 mm) developed in the larger (>8 mm) follicles more efficiently in partially ovariectomized hens than in the sham-operated (control) hens. In a second experiment, one group of hens had all the yellow follicles (>8 mm) removed, while a second group of hens was left untreated. On the 3rd and 6th day post treatment, the hens were examined for the presence of ovarian follicles. No significant (P / 0.05) difference in the growing pattern of subsequent follicles (2 to 4 or 4 to 8 mm) was detected due to treatment. These data demonstrate that the mechanisms that regulate follicular growth and atresia are adjust to maintain normal ovulation following partial ovariectomy. 相似文献
40.
It has been a generally held view that insulin does not significantly affect the incorporation of amino acids into liver protein. This interpretation was based on data obtained from studies using the branched chain amino acids, which are poorly metabolized by the hepatic tissue. The effect of insulin on 14CO2 formation and protein incorporation of several 1-14C-labeled or U-14C-labeled amino acids was studied in isolated rat hepatocytes and diaphragm pieces. It was shown that insulin enhanced 14CO2 formation and protein incorporation primarily of those carbons of amino acids which are metabolized through the mitochondrial Krebs cycle. Using aminooxyacetic acid (0.5 mM), a potent inhibitor of the transamination reaction, it was shown that there exists an "insulin-sensitive" pool of glutamate which is preferentially utilized for protein synthesis in the presence of insulin. The insulin effect on protein incorporation of 14C-labeled glutamate generated in the Krebs cycle was abolished in the presence of aminooxyacetic acid. We interpret these results to signify that mitochondrial transamination of alpha-ketoglutarate to glutamate is essential for insulin stimulation of 14C incorporation into hepatocyte protein. 相似文献